The Uto-Aztecian peoples of the Great Basin at the time of first contact with Europeans (in Western Colorado, the Utes) arrived in the Great Basin and one of three separate Uto-Aztecian peoples with distinct language from Eastern California Valleys in a fairly rapid migration around 1000 CE, which is about the same time as the Na-Dene migration from the Pacific Northwest to the American Southwest.
They replaced the Fremont people who had an ethnic affinity with the modern Hopi Indians (see also here and here).
A combination of linguistic evidence, ethnography, oral histories, genetic evidence (which shows the discontinuity between earlier remains and modern Native American populations in the region), and the archaelogical evidence seem to support this account.
The best guess at the reason for the shift is that the big game oriented hunting of the Fremont lost effectiveness as a way to make a living there relative to the smaller animal and seed based subsistence of the Uto-Aztecians. Climate, of course, is also always a serious suspect in this kind of transition, particularly since it involved three parallel migrations of Uto-Aztecians and another parallel Na-Dene migration (probably actually more than one of these migrations as well) rather than just a single migrating group - disfavoring "great men of history" or "single decisive event" type explanations.
A key take away point is that the notion that North American prehistory was relatively static is increasingly being discredited as we learn more. The relatively recent mass folk migrations so familar from old school European history and from other Old World prehistory reconstructions with linguistics and archaeology also characterize North American prehistory. We are starting to be able to fill in some of the big waves of migration and replacement, large scale archaeolgical cultures that rose and fell with hints at the causes, and links between successive prehistoric cultures in the New World as well as the old. In short, North American prehistory is starting to look more like a historical account and less like a vague prologe to the eras we understand from historical records.
Tuesday, April 2, 2013
Jewish v. Catholic v. Orthodox Calendars
Sasha Volokh has a nice discussion of the differences between the Roman Catholic and Orthodox calendars and Easter calculations (which arose from the need to fit Easter to the Roman calendar, and the Roman Catholic embrace of calendar reforms to match the seasons which were not adopted by Orthodox Christians).
Along the way, she also reminds us where the A.D. v. B.C. system of numbering years (which I customarily write C.E. for current era, or B.C.E. for before current era, to strip the meaning of the original abbreviations which in latin mean "year of our Lord" and "before Christ").
Part 1: Orthodox Easter, what's up with that?
Calendars, Religion and Agriculture.
These calendars and their history are particularly interesting because they represent a convergence of astronomy (which the Roman Catholic church has long invested resources to study because of its relevance of the calendar), mathematics (which has generally been less secular than empirical science), and religion.
Most have had religious affiliations, with some rare exceptions like the short lived French Republican Calendar which was intentionally a secular departure from the Roman Catholic Georgian calendar on the theory that the Roman Catholic Church was deeply intertwined with the French monarchy that the French Revolution deposed. As Wikipedia explains, it was "used by the French government for about 12 years from late 1793 to 1805, and for 18 days by the Paris Commune in 1871. The new system was designed in part to remove all religious and royalist influences from the calendar, and was part of a larger attempt at decimalisation in France." The effort to shed the quasi-base twelve/base sixty Sumerian time keeping system failed more quickly:
Calendars and Ancient Cultures
Many independent Neolithic cultures have apparently developed its own rather sophisticated calendar as this is necessary for optimum agricultural production. The Roman solar calendar is adapted from 365 day solar calendar developed by the Egyptians, probably based on an earlier or at least influenced by a parallel lunisolar Sumerian calendar with twelve months of thirty days and some extra-calendary days.
There is a lunisolar Chinese calendar that is still in use for ceremonial and holiday purposes in areas formerly in the Chinese sphere of influence (i.e. China, Japan, Korea, Tibet, all of much of Southeast Asia, Mongolia and the homeland of the Turkish peoples).
There was a Mayan calendar that has been reconstructed that died when the Conquistadors crushed the Aztec Empire in the 1500s.
There are a related mix of lunisolar Hindu calendars.
There have been a number of African calendars. There was a pre-Islamic, Julian calendar derived Berber calendar. Timbuktu in its heyday also made use of the Julian calendar. There is evidence of African megalithic era calendars in addition to the Egyptian one and there are other traditional African calendars.
I don't know if the Papuans had indigeneous calendars, which may have been less important for tropical agriculture. However, my ignorance of the ancient traditional calendar practices of non-Western civilizations that have since adopted the Western calendar doesn't mean that they didn't exist.
To my knowledge, there is no evidence that any pre-agricultural society developed sophisticated and precise calendars of these kind. The literary trope is that they kept track of the passing of lunar months without naming them, knew the seasons (probably with more internal definition than the modern four seasons) and counted years but didn't necessarily have a system for numbering them over long periods of time (perhaps using reginal systems based on the reign of chiefs whose names were recalled in oral histories). I don't know how accurate that is, but the lack of a system of writing would cetainly be detrimental to maintaining a formal calendar or keeping track of dates in the modern fashion, and some of this trope may be derived from actual interactions with Native Americans who were hunters and gathers or pastoralists, so I won't discount it out of hand either.
Other Calendars
The Islamic Calendar
Thus, the Islamic calendar is closer to the lunar Hebrew calendar than to the Gregorian calendar that is the dominant one worldwide.
The Hebrew Calendar
Along the way, she also reminds us where the A.D. v. B.C. system of numbering years (which I customarily write C.E. for current era, or B.C.E. for before current era, to strip the meaning of the original abbreviations which in latin mean "year of our Lord" and "before Christ").
Part 1: Orthodox Easter, what's up with that?
Easter is this Sunday, March 31. But Orthodox Easter, celebrated by most branches of the Eastern Orthodox Church (including the Russian Orthodox Church) and some Oriental Orthodox churches, is May 5 this year, a full five weeks after Easter as celebrated by Western Christian churches. . . . The five-week difference has happened recently in 2002, 2005, and 2008. But in 2001, 2004, 2007, 2010, and 2011, Western and Orthodox Easter fell on the same day. And in 2000, 2003, 2006, 2009, and 2012, Orthodox Easter was one week after Western Easter. What’s up with that? . . .
The Julian calendar, introduced in 45 BC, is easy: the year is 365 days long, except that we have a leap year every four years. After some confusion caused by off-by-one errors, apparently the proper sequence of leap years was reestablished by AD 4 or AD 8. . . . [The prior calendar has just 365 days which was worse.] Trouble is, the year isn’t quite 365.25 days long; the tropical year, which is the most relevant one for seasonal purposes, is more like 365.24219 days. . . after 400 Julian years, you’ll be 3.124 days off. . . . The Gregorian calendar fixes this problem by removing 3 days every 400 years. . . . remove the leap days in 2100, 2200, and 2300. So of the century years, the only ones that remain leap years are 1600, 2000, 2400, etc., the ones divisible by 400. Now the average year length is 365.2425, which is off from 365.24219 by 0.00031 days, so the years are still too long, but by a much smaller margin, so the date of the solstice will creep earlier and earlier much more slowly (by, on average, a day every 3226 years). . .Part 2: Orthodox Easter, what's up with that?
[B]ut how do you actually get it adopted? The Gregorian reform was proposed by Pope Gregory XIII, and Catholic countries mostly adopted it in or shortly after 1582. By then, the error was 10 days; to prevent the backward creep of the date of astronomical phenomena, it was necessary to move the calendar date forward in one swell foop. The first places to adopt were Spain, Portugal, the Polish-Lithuanian Commonwealth, and most of Italy; there, September 4, 1582 was immediately followed by September 15, 1582. France adopted the calendar later in 1582, and other places adopted in 1583. The Protestant countries mostly adopted the new calendar over the course of the 18th century; England did it in 1752, by which time the error was 11 days.
The Orthodox countries of Eastern Europe lagged behind, though, and by 1918, the error was 13 days. In 1918, the new Soviet government adopted the Gregorian calendar; January 31, 1918 was followed by February 14, 1918. But the Russian Orthodox church didn’t change calendars, and, as the other Orthodox countries adopted the new calendar in the 1910s and 1920s, neither did their churches. (Some churches have adopted the Revised Julian calendar or Milankovic calendar, which is different than the Gregorian calendar, but is temporarily aligned with it.) So most Orthodox churches continue to follow the old calendar. Since 2000 was a leap year for both the Julian and Gregorian calendars, the error continues to be 13 days, and will continue to be 13 days until 2100. Thus, the date that the Orthodox churches consider to be December 25 is what we call January 7.
Easter Sunday is the day when Jesus Christ rose from the dead, and the Gospels say that happened when he came to Jerusalem to celebrate Passover. So in principle, you could think that Easter happens at Passover — more precisely, on 14 Nisan, the day before Passover starts on 15 Nisan. . . . Now the Jewish calendar is a complicated thing, but the bottom line is that 15 Nisan is always on a full moon after the spring equinox. How do they guarantee that this happens? Intercalation, that’s how. Because Jewish months are lunar, the folks in charge of the calendar stick in a whole nother month, called Adar II, before Nisan just to ensure that Passover is on a full moon after the equinox.
So why not tie Easter to Passover and celebrate it whenever 14 Nisan would fall in the Jewish calendar? The Christians who believed you should do this were called Quartodecimans, or “fourteeners” if you will. Various Christian communities followed the “14 Nisan” rule and just asked their local Jews when Passover started, but after controversies in the second and third centuries, Christians ended up settling the matter at the Council of Nicaea in 325.
The Nicene rule separated the Christian computation method from the Jewish one. In the first place, there was a concern over being in spring: though these days, 15 Nisan is always a full moon after the spring equinox, sometimes Easter ended up being celebrated before the equinox, apparently, said the bishop of Alexandria, “through negligence and error” on the part of the Jewish calendrical authorities. (It’s not necessarily negligence and error, because you could also choose to date the start of spring, as some Jews did, as the time the barley ripens. If you did that, Passover could sometimes fall before the equinox.)
In the second place . . . apparently, not all Jewish communities at the time calculated their months in exactly the same way. This might actually be the same concern, if some communities used the equinox and others used the barley, or if barley ripened at different times in different places.
In the third place, reported Emperor Constantine: “It was . . . declared improper to follow the custom of the Jews in the celebration of this holy festival, because, their hands having been stained with crime, the minds of these wretched men are necessarily blinded.” . . .
Christian churches . . . figure out the full moon after the spring equinox — but also add on an extra rule, which is that Easter should fall on a Sunday. So that’s where we get the rule that Easter is the Sunday after the full moon after the spring equinox. (In principle, that still means that Western Easter should fall within Passover, but since Hillel II’s reforms in the 4th century, the Jewish calculations for Nisan are based on a formula and not on astronomy — see Gauss’s formula for the date of Pesach. Thus, in 2008, Western Easter fell on March 23, while Passover didn’t start until April 20.) . . .
For purposes of calculating Easter, [Roman Catholics and Orthodox Christians] use March 21 instead of the true date of the equinox, which could be March 19 or March 20. (The complexities behind “full moon” will be in a later post.) . . .March 21 is considered to fall on a different day depending on your calendar, and March 21 in the Julian calendar is what we in the West would call April 3.Part 3: Orthdox Easter, what's up with that?
[A]n “ecclesiastical full moon,” . . . is defined as being 14 days after the “ecclesiastical new moon,” which is different than the actual new moon. Why do this? Well, you want to be able to figure out when Easter falls ahead of time rather than when you actually observe a new moon, so you want to be able to have tables to predict the new moon. Hopefully the tables correspond with astronomical reality, but the Council of Nicaea also thought it was important that all Christians celebrate Easter on the same date, and people in different places in the world might observe a new moon on slightly different days. So, in practice, we determine the ecclesiastical new moon by means of tables, and different tables (with different accuracies) are responsible for disagreements in calculating the date of Easter. . . . there’s a big section on how to do the actual calculations in the Wikipedia article on the Computus. Consider a lunar month of 29.5 days. We could define a lunar year as consisting of 12 lunar months, with lengths alternating between 29 and 30 days. That gives us a year of 29.5 x 12 = 354 days. That’s 11 days shorter than a solar (non-leap) year. . . . [the] lunar month . . . [is] actually 29.53059 days. All this gets us a table predicting when ecclesiastical full moons (i.e., 14 days after ecclesiastical new moons) fall. This works for most years. But comparing this Easter table with an actual table of full moons, we see that, for the period 2005-2013, it’s off in 2008 (Mar. 22 vs. Mar. 21), 2009 (Apr. 10 vs. Apr. 9), 2010 (Mar. 30 vs. Mar. 29), and 2012 (Apr. 7 vs. Apr. 6).
This particular Easter table is based on the Metonic cycle, named after Meton of Athens, who figured it out in the 5th century BC. This method is still how they figure out when to intercalate months in the Jewish (lunar) calendar. The monk Dionysius Exiguus published an adaptation of Metonic cycles into the Julian calendar in 525 (along the way he invented the practice of counting years [incorrectly] from the birth of Christ). His tables replaced earlier (less accurate) tables, for instance by Victorius of Aquitaine. It took a while for the Dionysian tables to replace the Victorian tables everywhere, and this difference is responsible for the differences in Easter calculation between the Irish church and the Roman church that were resolved at the Synod of Whitby in Northumbria in 664.
How do the Orthodox do it? They just use the Metonic cycle without any corrections, which departs from the full moon by more than three days every millennium. . . . You can see the results in Table 1 on this website, showing the differences between Western and Orthodox Easter. From 1583 to the 2000s, the differences are 0, 1, 4, or 5 weeks. After 2100, the four-week difference drops out, and we only have differences of 0, 1, or 5 weeks. By the 2400s, the differences will be 0, 1, 5, or 6 weeks. By the 2700s, the two Easters will never overlap, and we’ll have differences of 1, 2, 5, or 6 weeks.There was also an April Fool's Day fake post.
Calendars, Religion and Agriculture.
These calendars and their history are particularly interesting because they represent a convergence of astronomy (which the Roman Catholic church has long invested resources to study because of its relevance of the calendar), mathematics (which has generally been less secular than empirical science), and religion.
Most have had religious affiliations, with some rare exceptions like the short lived French Republican Calendar which was intentionally a secular departure from the Roman Catholic Georgian calendar on the theory that the Roman Catholic Church was deeply intertwined with the French monarchy that the French Revolution deposed. As Wikipedia explains, it was "used by the French government for about 12 years from late 1793 to 1805, and for 18 days by the Paris Commune in 1871. The new system was designed in part to remove all religious and royalist influences from the calendar, and was part of a larger attempt at decimalisation in France." The effort to shed the quasi-base twelve/base sixty Sumerian time keeping system failed more quickly:
Each day in the Republican Calendar was divided into ten hours, each hour into 100 decimal minutes, and each decimal minute into 100 decimal seconds. Thus an hour was 144 conventional minutes (more than twice as long as a conventional hour), a minute was 86.4 conventional seconds (44% longer than a conventional minute), and a second was 0.864 conventional seconds (13.6% shorter than a conventional second). Clocks were manufactured to display this decimal time, but it did not catch on. Mandatory use of decimal time was officially suspended 7 April 1795, although some cities continued to use decimal time as late as 1801.Also, for all of its archacism, the Papal Observatory was actually instrumental in the Roman Catholic doctrinal acceptance of the Big Bang, which, while not literally the account(s) given in the Torah's Book of Genesis, does at least provide a scientific basis for stating that the world has a beginning and was in a sense "created" at a particular moment in time, contrary to pre-Big Bang scientific cosmology which had assumed an eternal and unchanging universe for the most part. This is a big part of the reason that there are so few Young Earth Creationists in Europe. Galileo, who was famous punished by the Roman Catholic church for spreading his astronomy discoveries was a target only because the Roman Catholic church had cared about the calendar and astronomy and developed offical views on it in the first place.
Calendars and Ancient Cultures
Many independent Neolithic cultures have apparently developed its own rather sophisticated calendar as this is necessary for optimum agricultural production. The Roman solar calendar is adapted from 365 day solar calendar developed by the Egyptians, probably based on an earlier or at least influenced by a parallel lunisolar Sumerian calendar with twelve months of thirty days and some extra-calendary days.
There is a lunisolar Chinese calendar that is still in use for ceremonial and holiday purposes in areas formerly in the Chinese sphere of influence (i.e. China, Japan, Korea, Tibet, all of much of Southeast Asia, Mongolia and the homeland of the Turkish peoples).
There was a Mayan calendar that has been reconstructed that died when the Conquistadors crushed the Aztec Empire in the 1500s.
There are a related mix of lunisolar Hindu calendars.
There have been a number of African calendars. There was a pre-Islamic, Julian calendar derived Berber calendar. Timbuktu in its heyday also made use of the Julian calendar. There is evidence of African megalithic era calendars in addition to the Egyptian one and there are other traditional African calendars.
[The] Namoratunga a group of megaliths, dated 300 BCE, was used by Cushitic speaking people as an alignment with star systems tuned to a lunar calendar of 354 days. . . . Great Zimbabwe could have been an astronomical observatory . . . In southern Zimbabwe the shadow of the Moon appears between 0610 and 0620 near the site. Megaliths east of the Great Enclosure align with the Moon, the Sun, and stars during important astronomical events of the year. One Megalith could be an eclipse predictor. The conical structure aligns with a supernova in the Vela, 700–800 years ago.
Three types of calendars can be found in Africa: 1. Lunar 2. Solar 3. Stellar. Most African calendar are a combination of the three. African Calendars: Akan Calendar, Egyptian calendar, Berber calendar, Ethiopian Calendar, Igbo calendar, Yoruba Calendar, Shona calendar, Swahili calendar, Xhosa calendar, Borana calendar, Luba calendarI'm haven't researched traditional African calendars to know the era of their origins and influences.
I don't know if the Papuans had indigeneous calendars, which may have been less important for tropical agriculture. However, my ignorance of the ancient traditional calendar practices of non-Western civilizations that have since adopted the Western calendar doesn't mean that they didn't exist.
To my knowledge, there is no evidence that any pre-agricultural society developed sophisticated and precise calendars of these kind. The literary trope is that they kept track of the passing of lunar months without naming them, knew the seasons (probably with more internal definition than the modern four seasons) and counted years but didn't necessarily have a system for numbering them over long periods of time (perhaps using reginal systems based on the reign of chiefs whose names were recalled in oral histories). I don't know how accurate that is, but the lack of a system of writing would cetainly be detrimental to maintaining a formal calendar or keeping track of dates in the modern fashion, and some of this trope may be derived from actual interactions with Native Americans who were hunters and gathers or pastoralists, so I won't discount it out of hand either.
Other Calendars
The Islamic Calendar
The Islamic calendar, Muslim calendar or Hijri calendar (AH) is a lunar calendar consisting of 12 months in a year of 354 or 355 days. Being a purely lunar calendar, it is not synchronized with the seasons. With an annual drift of 10 or 11 days, the seasonal relation repeats about every 33 Islamic years (every 32 solar years). It is used to date events in many Muslim countries (concurrently with the Gregorian calendar), and used by Muslims everywhere to determine the proper days on which to observe the annual fast (see Ramadan), to attend Hajj, and to celebrate other Islamic holidays and festivals. The first year was the Islamic year beginning in AD 622 during which the emigration of Muhammad from Mecca to Medina, known as the Hijra, occurred. Each numbered year is designated either H for Hijra or AH for the Latin anno Hegirae (in the year of the Hijra), hence, Muslims typically call their calendar the Hijri calendar. The current Islamic year is 1434 AH. In the Gregorian calendar 1434 AH runs from approximately 14 November 2012 (evening) to 4 November 2013 (evening).
Thus, the Islamic calendar is closer to the lunar Hebrew calendar than to the Gregorian calendar that is the dominant one worldwide.
The Hebrew Calendar
[U]ntil the Tannaitic period (approximately 10–220 CE) the months were set by observation of a new crescent moon, with an additional month added every two or three years to correct for the difference between twelve lunar months and the solar year and, therefore, to keep Passover in the spring. The addition of the extra month was also based on observation of natural events: specifically, the ripening of the barley crop; the age of the kids, lambs, and doves; the ripeness of the fruit trees; and the relation of the date to the tekufah (seasons). Through the Amoraic period (200–500 CE) and into the Geonic period, this system was displaced by mathematical rules. The principles and rules appear to have been settled by the time Maimonides compiled the Mishneh Torah in the 12th century. . . . The Hebrew calendar era used at present is the Anno Mundi epoch (Latin for "in the year of the world"; Hebrew: לבריאת העולם, "from the creation of the world") . . . the words or abbreviation (A.M. or AM) for the era should properly precede the date rather than follow it, although this is no longer always followed. . . . AM 5772 began at sunset on 28 September 2011 and ended on 16 September 2012. AM 5773 began at sunset on 16 September 2012 and will end on 4 September 2013.Despite the fact that the Hebrew calendar is implicitly based on a Young Earth Creationist theology, few Jews in Israel and the United States (which is where the majority of Jews live), are Young Earth Creationists.
Back To Ancient History
The burst of early spring physics conferences seem to be past and so it is time to think about the deep past and population genetics again.
* John Hawks have flagged a number of interesting articles. One study, linking population size and technological complexity in Oceania at first contact with European sailors reaches a facinating conclusion:
There are creoles whose formation process is well documented, and short of creoles punctuated language evolution via intense language contact. There are instances of isolated communities of deaf people developing their own personal sign languages from scratch. There is a growing literature discussing how societies and subcultures that split off (e.g. the differentiation of the Romance languages, revolutionary Americans, gang members, mother-in-law languages and "women's languages", Urdu v. Hindi) deliberately differentiate themselves linguistically as a means of distinguishing between insiders and outsiders and developing cultural identity. There are lots of data points on what drives language shift, which language formation requires, but language formation also requires more.
There are purposefully constructed languages or linguistic constructs (e.g. pig latin) although very few of them seem to catch on. They are like third parties in a two party biased first past the post single member district electoral system. The viable ones form out of schism in existing ones or are driven by nationalism (e.g. reconstructed modern Hebrew), not to advance intellectually compelling ideas.
I think that the extent to which language formation and change is punctuated rather than evolutionary is greatly underestimated. But, I'm curious in particular about how more tightly integrated features of a language like phonetics and grammer change relative to less core features like non-core lexical change. For example, feminism has made some pretty significant changes in these kinds of features recently in English.
In particular, I'm curious about what circumstances might lead to the formation of a new viable language in the modern era.
* John Hawks have flagged a number of interesting articles. One study, linking population size and technological complexity in Oceania at first contact with European sailors reaches a facinating conclusion:
Much human adaptation depends on the gradual accumulation of culturally transmitted knowledge and technology. Recent models of this process predict that large, well-connected populations will have more diverse and complex tool kits than small, isolated populations. While several examples of the loss of technology in small populations are consistent with this prediction, it found no support in two systematic quantitative tests. Both studies were based on data from continental populations in which contact rates were not available, and therefore these studies do not provide a test of the models. Here, we show that in Oceania, around the time of early European contact, islands with small populations had less complicated marine foraging technology. This finding suggests that explanations of existing cultural variation based on optimality models alone are incomplete because demography plays an important role in generating cumulative cultural adaptation. It also indicates that hominin populations with similar cognitive abilities may leave very different archaeological records, a conclusion that has important implications for our understanding of the origin of anatomically modern humans and their evolved psychology.* On the methodology front, someone has found a way to turn W.E.I.R.D. samples into a feature rather than a bug when doing genomics:
Although much is known about college students as a special sample in terms of their behavioral traits such as intelligence and academic motivation, no studies have examined whether college students represent a “biased” sample in terms of their genotype frequencies. The present study investigated this issue by examining the Hardy–Weinberg equilibrium of genotype frequencies of 284 SNPs covering major neurotransmitter genes in a sample of 478 Chinese college students, comparing these frequencies with those of a community sample (the 1000 Genomes dataset), and examining behavioral correlates of the SNPs in Hardy–Weinberg disequilibrium. Results showed that 24 loci showed Hardy–Weinberg disequilibrium among college students, but only two of these were in disequilibrium in the 1000 Genomes sample. These loci were found to be associated with mathematical abilities, executive functions, motivation, and adjustment-related behaviors such as alcohol use and emotion recognition. Generally, genotypes overrepresented in the college sample showed better performance and adjustment than under-represented or non-biased genotypes. This study illustrates a new approach to studying genetic correlates of traits associated with a socially-selected group—college students—and presents the first evidence of genetic stratification in terms of education attainment.* On the "to do" list, one of the projects at the top of list is to look into the circumstances that lead to language formation, which may or may not be distinct from "ordinary" language evolution. A number of examples and leads to research come to mind to get at it, but full fledged language formation is very rare and mostly prehistoric with the exception of certain creoles and a couple of other outliers.
There are creoles whose formation process is well documented, and short of creoles punctuated language evolution via intense language contact. There are instances of isolated communities of deaf people developing their own personal sign languages from scratch. There is a growing literature discussing how societies and subcultures that split off (e.g. the differentiation of the Romance languages, revolutionary Americans, gang members, mother-in-law languages and "women's languages", Urdu v. Hindi) deliberately differentiate themselves linguistically as a means of distinguishing between insiders and outsiders and developing cultural identity. There are lots of data points on what drives language shift, which language formation requires, but language formation also requires more.
There are purposefully constructed languages or linguistic constructs (e.g. pig latin) although very few of them seem to catch on. They are like third parties in a two party biased first past the post single member district electoral system. The viable ones form out of schism in existing ones or are driven by nationalism (e.g. reconstructed modern Hebrew), not to advance intellectually compelling ideas.
I think that the extent to which language formation and change is punctuated rather than evolutionary is greatly underestimated. But, I'm curious in particular about how more tightly integrated features of a language like phonetics and grammer change relative to less core features like non-core lexical change. For example, feminism has made some pretty significant changes in these kinds of features recently in English.
In particular, I'm curious about what circumstances might lead to the formation of a new viable language in the modern era.
Monday, April 1, 2013
MOND From Ultra-Fast Outflows of Black Holes
Modified gravity theory (MOND) supposes that at a critical amount of gravitational accelleration (a-zero), that the force of gravity starts to decline by a factor of 1/r, rather than 1/r^2. This holds true for galaxies of all sizes, but not for galactic clusters, where it is an underestimate.
Is there a way that this empirical relationship could come about without exotic forms of matter or alterning Einstein's laws of general relativity?
I think that there is, with the help of a phenomena called "ultra-fast outflows" (aka black hole barf) which puts matter just were inferred dark matter distributions need it to go. This post explains that conjecture.
In this view, the large scale structure of a galaxy is largely driven by the properties of its central black holes which is largely one dimensional (see for example, some references here). The radius of a black hole's event horizon is approximately 2.95 times it mass in units of the mass of Earth's sun, adjusted by a factor of up to two for angular momentum (which varies considerably between black holes) and electromagnetic charge (which in practice is almost always almost electrically neutral like the stars that collapse to form them). Black holes of the same mass and angular momentum and charge are for all practical purposes identical, so it makes sense that they galaxies that they would attract to surround them would also be similar (and why we only start seeing certain phenomena associate with black holes at the galactic level).
The "mass of a galaxy's central black hole and the velocity of stars in a vast, roughly spherical structure known as its bulge" are closely related. So is the structure of the galaxy. Elliptical galaxies almost always have black holes in one size range, while spiral galaxies almost always have black holes in another size range. Every type of galaxy has a particular sized black hole associated with it and galaxies of all kinds tend to have some disk of rotation.
If galactic structure is a function of black hole size, that might not be the only thing that is a function of its size.
Now, an axis of relativistic matter perpendicular to a spinning disk of matter can get very long relative to the galactic disk travelling at 14%-50% of the speed of light, or the speed of light itself in the case of X-rays over billions of years, with nothing else in the way but the tug of the galaxy's own gravity. The Milky Way galaxy, for example, has a radius of about 50,000 to 60,000 light years, a blink of an eye for a body with 13.2 billion year old stars in it.
A very long axis of matter relative to the galactic disk through is focus at the black hole creates an acceleration of point masses in the galactic disk in the form of GM/r (where G is the gravitational constant, M is the mass of the axis, and r is the distance from the black hole of the object in the galactic disk). The black hole itself and the central bulge, meanwhile, will exert a force like a point mass in the form GM/r^2.
To replicate the MOND modification to gravity, where gravity starts acting like a 1/r force (just like the magnetic field from a long wire) instead of a 1/r^2 force of a point source, where the transition takes place at a fixed acceleration a-zero in all galaxies (with a-zero being approximately 1.2*10^-10 ms^-2), the gravitational mass of the material spewed by the central black hole of every galaxy (in the last five million years or so) must be approximately proportional to (but multiple orders of magnitude smaller than) the square root of the central bulge's mass for almost all galaxies. In particular, it must be equal to the square root of a-zero times the square root of the central bulge's mass times a constant with units of length to assure that the formula is dimensionally consistent. Also note that for these purposes, relativistic momentum in the particles and the energy in the X-rays count as mass.
If this relationship holds true, the ordinary X-rays, and ordinary Standard Model matter in the particle flows and ultra-fast outflows from a black hole (mostly non-luminous) over thirteen billion years or so. Actually, any lengthy of time much longer than the radius of the galaxy in light years, perhaps by a factor of fifty or a hundred, so more like 5 million years or more for a Milky Way sized galaxy (about 0.2% of its age), will have almost the same effect since the far edges of the axis mass don't influence the outcome by too much. For example, the mass of the Milky Way galaxy is about 10^12 solar masses. So, the axial mass would need to be 10^6 solar masses, times 10^-5 (i.e. 10 solar masses), times a constant to fix the proper unit conversions between solar masses and the square root of a-zero as express in meters per second squared. In a galaxy that is spewing out a bit more than one solar mass a year into its axis for many millions of years, the order of magnitude may be about right even if the unit conversion factor is quite large (say in the hundreds of thousands).
The inapplicability of the MOND law in galactic clusters, which unlike ordinary galaxies, aren't structured around a single black hole, also immediately makes sense if this explains dark matter. But, balancing the ledgers in these systems, if you don't need exotic dark matter for the rest of the galaxies, isn't hard. As previously explained in two sets of quotes from people more expert than I which I merge below from this post:
Ultra-fast outflows may be just the thing to explain where some more of the missing baryons have gone - into the axis.
Note also, that since we are only concerned about dark matter-MOND effects very close to the outer rim of the galactic disk and beyond in that plane where we can observe them, rather than spherically, not nearly as much dim axial matter is require to generate the observed effects.
Also, this dim axial matter, rather than being an exotic relic of the early universe that must be explained with some new kind of baryongenesis or the equivalent has a know, recent and dynamic origin.
The MOND effect could also partially be due to the effects in general relativity, but not in Newtonian gravity, of the rotation of the galactic plane itself, an angular momentum that gravitates in general relativity but not in Newtonian gravity. This too should have a 1/r effect, and while it is slight, becomes signficant relative to the point source-like central bulge gravitational effect that falls of like 1/r^2 in the outer fringe of the galaxy that would be added to the axial matter effects.
As in other posts with this tag, the ideas contained in this post are my personal conjectures based on back of napkin class estimates, which while not coming from nowhere, also do not necessarily have any wide currency in the scientific community.
Also, as a footnote it is worth noting that any model of non-collisionless dark matter with particles that weigh less than 45 GeV and does not have electromagnetically charged dark matter particles, just like MOND, requires a new force law of some kind to apply to self-interactions in the dark sector. We know that such particles can't interact via the weak force or they would have been detected in W and Z boson decays.
Is there a way that this empirical relationship could come about without exotic forms of matter or alterning Einstein's laws of general relativity?
I think that there is, with the help of a phenomena called "ultra-fast outflows" (aka black hole barf) which puts matter just were inferred dark matter distributions need it to go. This post explains that conjecture.
In this view, the large scale structure of a galaxy is largely driven by the properties of its central black holes which is largely one dimensional (see for example, some references here). The radius of a black hole's event horizon is approximately 2.95 times it mass in units of the mass of Earth's sun, adjusted by a factor of up to two for angular momentum (which varies considerably between black holes) and electromagnetic charge (which in practice is almost always almost electrically neutral like the stars that collapse to form them). Black holes of the same mass and angular momentum and charge are for all practical purposes identical, so it makes sense that they galaxies that they would attract to surround them would also be similar (and why we only start seeing certain phenomena associate with black holes at the galactic level).
The "mass of a galaxy's central black hole and the velocity of stars in a vast, roughly spherical structure known as its bulge" are closely related. So is the structure of the galaxy. Elliptical galaxies almost always have black holes in one size range, while spiral galaxies almost always have black holes in another size range. Every type of galaxy has a particular sized black hole associated with it and galaxies of all kinds tend to have some disk of rotation.
If galactic structure is a function of black hole size, that might not be the only thing that is a function of its size.
Active black holes acquire their power by gradually accreting -- or "feeding" on -- million-degree gas stored in a vast surrounding disk. This hot disk lies within a corona of energetic particles, and while both are strong X-ray sources, this emission cannot account for galaxy-wide properties. Near the inner edge of the disk, a fraction of the matter orbiting a black hole often is redirected into an outward particle jet. Although these jets can hurl matter at half the speed of light, computer simulations show that they remain narrow and deposit most of their energy far beyond the galaxy's star-forming regions. . . .
At the centers of some active galaxies, X-ray observations at wavelengths corresponding to those of fluorescent iron show that this radiation is being absorbed. This means that clouds of cooler gas must lie in front of the X-ray source. What's more, these absorbed spectral lines are displaced from their normal positions to shorter wavelengths -- that is, blueshifted, which indicates that the clouds are moving toward us.
In two previously published studies, [Francesco] Tombesi and his colleagues showed that these clouds represented a distinct type of outflow. In the latest study, which appears in the Feb. 27 issue of Monthly Notices of the Royal Astronomical Society, the researchers targeted 42 nearby active galaxies using the European Space Agency's XMM-Newton satellite to hone in on the location and properties of these so-called "ultra-fast outflows" -- or UFOs, for short. The galaxies, which were selected from the All-Sky Slew Survey Catalog produced by NASA's Rossi X-ray Timing Explorer satellite, were all located less than 1.3 billion light-years away.
The outflows turned up in 40 percent of the sample, which suggests that they're common features of black-hole-powered galaxies. On average, the distance between the clouds and the central black hole is less than one-tenth of a light-year. Their average velocity is about 14 percent the speed of light, or about 94 million mph, and the team estimates that the amount of matter required to sustain the outflow is close to one solar mass per year -- comparable to the accretion rate of these black holes.
"Although slower than particle jets, UFOs possess much faster speeds than other types of galactic outflows, which makes them much more powerful," Tombesi explained. "They have the potential to play a major role in transmitting feedback effects from a black hole into the galaxy at large."
By removing mass that would otherwise fall into a supermassive black hole, ultra-fast outflows may put the brakes on its growth. At the same time, UFOs may strip gas from star-forming regions in the galaxy's bulge, slowing or even shutting down star formation there by sweeping away the gas clouds that represent the raw material for new stars. Such a scenario would naturally explain the observed connection between an active galaxy's black hole and its bulge stars.
Tombesi and his team anticipate significant improvement in understanding the role of ultra-fast outflows with the launch of the Japan-led Astro-H X-ray telescope, currently scheduled for 2014. In the meantime, he intends to focus on determining the detailed physical mechanisms that give rise to UFOs, an important element in understanding the bigger picture of how active galaxies form, develop and grow.So, black holes, rather than merely absorbing everything that comes their way are constantly spewing X-rays, particles and ultra-fast outflows at relativistic speeds away from the central black hole, more of less on the axis perpendicular to the galaxy's plane of rotation.
Now, an axis of relativistic matter perpendicular to a spinning disk of matter can get very long relative to the galactic disk travelling at 14%-50% of the speed of light, or the speed of light itself in the case of X-rays over billions of years, with nothing else in the way but the tug of the galaxy's own gravity. The Milky Way galaxy, for example, has a radius of about 50,000 to 60,000 light years, a blink of an eye for a body with 13.2 billion year old stars in it.
A very long axis of matter relative to the galactic disk through is focus at the black hole creates an acceleration of point masses in the galactic disk in the form of GM/r (where G is the gravitational constant, M is the mass of the axis, and r is the distance from the black hole of the object in the galactic disk). The black hole itself and the central bulge, meanwhile, will exert a force like a point mass in the form GM/r^2.
To replicate the MOND modification to gravity, where gravity starts acting like a 1/r force (just like the magnetic field from a long wire) instead of a 1/r^2 force of a point source, where the transition takes place at a fixed acceleration a-zero in all galaxies (with a-zero being approximately 1.2*10^-10 ms^-2), the gravitational mass of the material spewed by the central black hole of every galaxy (in the last five million years or so) must be approximately proportional to (but multiple orders of magnitude smaller than) the square root of the central bulge's mass for almost all galaxies. In particular, it must be equal to the square root of a-zero times the square root of the central bulge's mass times a constant with units of length to assure that the formula is dimensionally consistent. Also note that for these purposes, relativistic momentum in the particles and the energy in the X-rays count as mass.
If this relationship holds true, the ordinary X-rays, and ordinary Standard Model matter in the particle flows and ultra-fast outflows from a black hole (mostly non-luminous) over thirteen billion years or so. Actually, any lengthy of time much longer than the radius of the galaxy in light years, perhaps by a factor of fifty or a hundred, so more like 5 million years or more for a Milky Way sized galaxy (about 0.2% of its age), will have almost the same effect since the far edges of the axis mass don't influence the outcome by too much. For example, the mass of the Milky Way galaxy is about 10^12 solar masses. So, the axial mass would need to be 10^6 solar masses, times 10^-5 (i.e. 10 solar masses), times a constant to fix the proper unit conversions between solar masses and the square root of a-zero as express in meters per second squared. In a galaxy that is spewing out a bit more than one solar mass a year into its axis for many millions of years, the order of magnitude may be about right even if the unit conversion factor is quite large (say in the hundreds of thousands).
The inapplicability of the MOND law in galactic clusters, which unlike ordinary galaxies, aren't structured around a single black hole, also immediately makes sense if this explains dark matter. But, balancing the ledgers in these systems, if you don't need exotic dark matter for the rest of the galaxies, isn't hard. As previously explained in two sets of quotes from people more expert than I which I merge below from this post:
Clusters you certainly could fit just with baryons. They’re rare systems. If that is the only place we need dark baryons, then do the integrals. You can satisfy the residual mass discrepancy in clusters in MOND without making much dent in the BBN missing baryon budget.
Do I *like* such a solution? Certainly not. Neither do I like that fact that clusters are the only systems that come close to having the right baryon content in LCDM. Why are galaxies missing more than half of their baryons? Dwarfs > 90%? . . .
90% of all cosmic baryons are presently undetected, right? Only a fraction of the baryonic matter we see directly is in clusters (O(a few percent), let’s say 10%) So why can’t a small fraction, say O(2%), of all the cosmic dark baryons be in the form of e.g. jupiters in the central parts of clusters? They and stars would then dominate the cluster mass and be dissipationless —> no problem with the bullet cluster in MOND. . . . In [Sander's paper] http://arxiv.org/abs/astro-ph/0703590 he states about cluster dark matter in MOND: “For example, there are more than enough undetected baryons to make up the missing dark component; they need only be present in some non-dissipative form which is difficult to observe.”Conveniently, for example, new observations have discovered a high abundance of low luminosity starts in galactic clusters relative to regular galaxies, explaining some of their seemingly dark matter. Likewise, estimates of the amount of atomic hydrogen have been underestimates as have estimates of the amount of dim matter in elliptical galaxies.
Ultra-fast outflows may be just the thing to explain where some more of the missing baryons have gone - into the axis.
Note also, that since we are only concerned about dark matter-MOND effects very close to the outer rim of the galactic disk and beyond in that plane where we can observe them, rather than spherically, not nearly as much dim axial matter is require to generate the observed effects.
Also, this dim axial matter, rather than being an exotic relic of the early universe that must be explained with some new kind of baryongenesis or the equivalent has a know, recent and dynamic origin.
The MOND effect could also partially be due to the effects in general relativity, but not in Newtonian gravity, of the rotation of the galactic plane itself, an angular momentum that gravitates in general relativity but not in Newtonian gravity. This too should have a 1/r effect, and while it is slight, becomes signficant relative to the point source-like central bulge gravitational effect that falls of like 1/r^2 in the outer fringe of the galaxy that would be added to the axial matter effects.
As in other posts with this tag, the ideas contained in this post are my personal conjectures based on back of napkin class estimates, which while not coming from nowhere, also do not necessarily have any wide currency in the scientific community.
Also, as a footnote it is worth noting that any model of non-collisionless dark matter with particles that weigh less than 45 GeV and does not have electromagnetically charged dark matter particles, just like MOND, requires a new force law of some kind to apply to self-interactions in the dark sector. We know that such particles can't interact via the weak force or they would have been detected in W and Z boson decays.
Standard Model Unstoppable
A March 30, 2013 post at Resonnances sums up the myriad way that previous hints of beyond the Standard Model of Particle Physics have been crushed by recent data showing the previous results to be statistical flukes or by reanalysis of old data hinting at BSM physics which has been found to be flawed (e.g. a coding error at Tevatron).
In addition to discoveries I've discussed at length previously, the new data and analysis have essentially eliminated hints of:
* CP violation in D meson decay at 10x to 100x the expected value;
* Evidence hinting at a 145 GeV particle seen at Tevatron (this was the coding error);
* Tightened experimental limitations from "the MEG experiment which searches μ → e γ decays. The standard model predicts this decay should be too rare to be observable (a tiny branching fraction is induced via the neutrino mixing). On the other hand, it is straightforward to produce a large branching fraction in models with new sources of lepton flavor violation, including supersymmetric and composite Higgs models. The latest MEG update sets the limit on the branching fraction at 5.7x10^‐13 at 90% CL, which represents a factor of 4 improvement of the previous limit."
* SUSY stops (the bosonic partner of the top quark) must be at least 700 GeV and gluinos (fermionic partners of gluons) must be at least 1.3 TeV, with some basic assumptions in both cases. Of course, no experimental data points to their existence at all.
The six parameter lamda CDM model of cosmology is likewise strongly affirmed by the Planck cosmic microwave background radiation (CMB) measurements. Among other things, the data support a treatment of dark energy as nothing more or less than the cosmological constant first proposed in 1916 by Einstein. The last data point from Planck will be in within a year or so.
The outstanding measurements to be made to complete Standard Model neutrino physics (the mixing angles, mass hiearchy, absolute masses, Dirac v. Majorana character and CP violating phase) are the focus of enough experimental work that they could be determined by the time my children are old enough to be in graduate school.
Arguably the difference in measurements between the size of protons in muonic hydrogen and ordinary hydrogen, and the anomalous muon magnetic dipole moment are up in the air, but this could also be a result of an underestimated systemic error in either the theoretical calculation, the experimental measurement, or both. The former is in theory a 4.4 to 4.6 sigma effect (the value values differ by about 0.02 fm, which is about 2.5% of the mean value of the ordinary hydrogen and muonic hydrogen values). The 3.4 sigma discrepancy in the latter still matches the theoretical value to about nine significant digits. There is good reason to suspect that the tensions between the measurements in both cases will resolve with more precise measurements.
What's left? All that is left(or will be left in a few years) is:
1. WSM (within the Standard Model) theorizing about why it is the way that it is in nature from deeper principles;
2. Theoretical inconsistencies between General Relativity and the Standard Model, but none are within the capacity of empirical observations to resolve them a determine what kind of quantum gravity theory must be correct; and
3. Dark matter, which is pretty much the only game left in town for experimentally supported BSM physics that we know must exist and there are no solutions for it.
Dark Matter Recapped
There are indisputably large dark matter effects that are observed phenomologically, whatever their actual cause. It accounts for 26.8% of the aggregate mass-energy equivalent of the universe in CBM data from Planck in the lamda CDM model (about 83% of mass-energy not attributable to the fully understood cosmological constant that gives rise to the dark energy value). We see it in almost every galactric rotation curve and the kinematics of galactric clusters. We see it in gravitational lensing data. We see it when galaxies collide. But, no candidate dark matter particle has been identified and direct dark matter searches are at best inconclusive and at worst rule out the favorite candidates for it. We have no consensus model of dark matter that can fit all of the data.
Hot dark matter and cold dark matter seem to be inconsistent with observed galactric structure (predicting too little and too much structure respectively). Hot dark matter also is disfavored by the Planck data and can't be massive enough to explain all dark matter. No consensus dark matter theory reproduces the observed data's tight structure which empirical relationships like the Tully-Fisher law and the empirical success of a one parameter MOND theory at the galactric level show exists and must be reproduced by an empirically valid dark matter theory.
Simple MOND theories have to be generalized to be relativistic and aren't an easy fit with galactric cluster data even though they are a good and parsimonious fit to the galactric scale data. They also don't work well with a possible dark matter filament observation.
In short, if there is a particle that fits the dark matter paradigm, it seems as if it is a fit for some variant on a singlet sterile neutrino warm dark matter particle with a particle mass of 1.6 keV to 2.2 keV with tight constraints on its non-gravitational self-interactions, if any, via a light or massless dark sector boson that would allow for heat exchange through dark matter collisions within dark matter halos. This is a much tighter parameter space than we had even a couple of years ago. Indeed, there is considerable tension in these estimates and it isn't certain that a single set of values can accomodate the entire parameter space.
We are in a delicate balance between a very precisely described single kind of warm dark matter particle with a possible self-interaction force, and a world in which all dark matter models are inconsistent with the evidence. For example, overly simple warm dark matter models may be inconsistent with the dwarf galaxy formation that we observe (accord here and here and here). So some sort of self-interaction may be necessary even in warm dark matter models to fit the data.
Since the total amount of dark matter, for example, in the Milky Way, can be fairly easily estimated as can the profile of the dark matter halo, localized dark matter particle per cubic space estimates can be made fairly accurately providing a small target for direct dark matter detection experiments.
In addition to discoveries I've discussed at length previously, the new data and analysis have essentially eliminated hints of:
* CP violation in D meson decay at 10x to 100x the expected value;
* Evidence hinting at a 145 GeV particle seen at Tevatron (this was the coding error);
* Tightened experimental limitations from "the MEG experiment which searches μ → e γ decays. The standard model predicts this decay should be too rare to be observable (a tiny branching fraction is induced via the neutrino mixing). On the other hand, it is straightforward to produce a large branching fraction in models with new sources of lepton flavor violation, including supersymmetric and composite Higgs models. The latest MEG update sets the limit on the branching fraction at 5.7x10^‐13 at 90% CL, which represents a factor of 4 improvement of the previous limit."
* SUSY stops (the bosonic partner of the top quark) must be at least 700 GeV and gluinos (fermionic partners of gluons) must be at least 1.3 TeV, with some basic assumptions in both cases. Of course, no experimental data points to their existence at all.
The six parameter lamda CDM model of cosmology is likewise strongly affirmed by the Planck cosmic microwave background radiation (CMB) measurements. Among other things, the data support a treatment of dark energy as nothing more or less than the cosmological constant first proposed in 1916 by Einstein. The last data point from Planck will be in within a year or so.
The outstanding measurements to be made to complete Standard Model neutrino physics (the mixing angles, mass hiearchy, absolute masses, Dirac v. Majorana character and CP violating phase) are the focus of enough experimental work that they could be determined by the time my children are old enough to be in graduate school.
Arguably the difference in measurements between the size of protons in muonic hydrogen and ordinary hydrogen, and the anomalous muon magnetic dipole moment are up in the air, but this could also be a result of an underestimated systemic error in either the theoretical calculation, the experimental measurement, or both. The former is in theory a 4.4 to 4.6 sigma effect (the value values differ by about 0.02 fm, which is about 2.5% of the mean value of the ordinary hydrogen and muonic hydrogen values). The 3.4 sigma discrepancy in the latter still matches the theoretical value to about nine significant digits. There is good reason to suspect that the tensions between the measurements in both cases will resolve with more precise measurements.
What's left? All that is left(or will be left in a few years) is:
1. WSM (within the Standard Model) theorizing about why it is the way that it is in nature from deeper principles;
2. Theoretical inconsistencies between General Relativity and the Standard Model, but none are within the capacity of empirical observations to resolve them a determine what kind of quantum gravity theory must be correct; and
3. Dark matter, which is pretty much the only game left in town for experimentally supported BSM physics that we know must exist and there are no solutions for it.
Dark Matter Recapped
There are indisputably large dark matter effects that are observed phenomologically, whatever their actual cause. It accounts for 26.8% of the aggregate mass-energy equivalent of the universe in CBM data from Planck in the lamda CDM model (about 83% of mass-energy not attributable to the fully understood cosmological constant that gives rise to the dark energy value). We see it in almost every galactric rotation curve and the kinematics of galactric clusters. We see it in gravitational lensing data. We see it when galaxies collide. But, no candidate dark matter particle has been identified and direct dark matter searches are at best inconclusive and at worst rule out the favorite candidates for it. We have no consensus model of dark matter that can fit all of the data.
Hot dark matter and cold dark matter seem to be inconsistent with observed galactric structure (predicting too little and too much structure respectively). Hot dark matter also is disfavored by the Planck data and can't be massive enough to explain all dark matter. No consensus dark matter theory reproduces the observed data's tight structure which empirical relationships like the Tully-Fisher law and the empirical success of a one parameter MOND theory at the galactric level show exists and must be reproduced by an empirically valid dark matter theory.
Several discrepancies between the predictions of the particle cold dark matter paradigm and observations of galaxies and their clustering have arisen:
The cuspy halo problem: cold particle dark matter predicts that the density distribution of DM halos be much more peaked than what is observed in galaxies by investigating their rotation curve.
The missing satellites problem: cold particle dark matter predicts larger numbers of small dwarf galaxies (about one thousandth the mass of the Milky Way) than are observed.
Warm dark matter refers to particles with a free-streaming length comparable to the size of a region which subsequently evolved into a dwarf galaxy. This leads to predictions which are very similar to cold dark matter on large scales, including the CMB, galaxy clustering and large galaxy rotation curves, but with less small-scale density perturbations. This reduces the predicted abundance of dwarf galaxies and may lead to lower density of dark matter in the central parts of large galaxies; some researchers consider this may be a better fit to observations.Warm dark matter and/or self-interactions of dark matter might explain it. But simple warm dark matter models while solving the missing satellites problem don't solve the cuspy halo problem, so both a light particle and self-interaction of some type may be necessary to fit the dark matter particle paradigm to the evidence if it can be fit at all. An example of recent efforts to resolve the outstanding issues with dark matter theories can be found at:
Beyond Collisionless Dark Matter: Particle Physics Dynamics for Dark Matter Halo Structure Authors:Sean Tulin, Hai-Bo Yu, Kathryn M. Zurek (Submitted on 15 Feb 2013)
Abstract: Dark matter (DM) self-interactions have important implications for the formation and evolution of structure, from dwarf galaxies to clusters of galaxies. We study the dynamics of self-interacting DM via a light mediator, focusing on the quantum resonant regime where the scattering cross section has a non-trivial velocity dependence. While there are long-standing indications that observations of small scale structure in the Universe are not in accord with the predictions of collisionless DM, theoretical study and simulations of DM self-interactions have focused on parameter regimes with simple analytic solutions for the scattering cross section, with constant or classical velocity (and no angular) dependence. We devise a method that allows us to explore the velocity and angular dependence of self-scattering more broadly, in the strongly-coupled resonant and classical regimes where many partial modes are necessary for the achieving the result. We map out the entire parameter space of DM self-interactions --- and implications for structure observations --- as a function of the coupling and the DM and mediator masses. We derive a new analytic formula for describing resonant s-wave scattering. Finally, we show that DM self-interactions can be correlated with observations of Sommerfeld enhancements in DM annihilation through indirect detection experiments. . . .Recent research constrains warm dark matter models to have masses approximately in the range of 1-2 keV and also tightly bounds their possible self-interactions. The observed Tully-Fisher relation is inconsistent with lighter warm dark matter particles. Observations of the Andromeda Galaxy suggest an upper limit on warm dark matter particle sizes of about 2.2 keV. Long gamma ray burst data imposes similar constraints placing a floor value of about 1.6-1.8 keV for combined limits from the various sources of 1.6-2.2 keV. Warm dark matter particle masses are in a mass range that is inconsistent with any weakly or electromagnetically interacting particle that a W or Z boson can decay into or couple with as we know from precision electroweak observations. It also couldn't interact via the strong force. So we have no Standard Model mechanism for creating it. As Wikipedia explains:
As is well known, the collisionless cold DM (CCDM) paradigm has been highly successful in accounting for large scale structure of the Universe. However, it is far from clear that this paradigm can also successfully explain the small scale structure of the Universe. Precision observations of dwarf galaxies show DM distributions with cores, in contrast to cusps predicted by CCDM simulations. It has also been shown that the most massive subhalos in CCDM simulations of Miky Way (MW) size halos are too dense to host the observed brightest satellites of the MW. Lastly, chemo-dynamic measurements in at least two MW dwarf galaxies show that the slopes of the DM density profiles are shallower than predicted by CCDM simulations. These small scale anomalies, taken at face value, may indicate that other interactions besides gravity play a role in structure formation.
A challenge for [the warm dark matter] model is that there are no very well-motivated particle physics candidates with the required mass ~ 300 eV to 3000 eV. There have been no particles discovered so far that can be categorized as warm dark matter. There is a postulated candidate for the warm dark matter category, which is the sterile neutrino: a heavier, slower form of neutrino which does not even interact through the Weak force unlike regular neutrinos. Interestingly, some modified gravity theories, such as Scalar-tensor-vector gravity, also require that a warm dark matter exist to make their equations work out.Small scale structure rules out a mix of warm and dark matter. Only the pure warm dark matter models fit those constraints. Other studies disfavor models with two kinds of warm dark matter of different masses.
Simple MOND theories have to be generalized to be relativistic and aren't an easy fit with galactric cluster data even though they are a good and parsimonious fit to the galactric scale data. They also don't work well with a possible dark matter filament observation.
In short, if there is a particle that fits the dark matter paradigm, it seems as if it is a fit for some variant on a singlet sterile neutrino warm dark matter particle with a particle mass of 1.6 keV to 2.2 keV with tight constraints on its non-gravitational self-interactions, if any, via a light or massless dark sector boson that would allow for heat exchange through dark matter collisions within dark matter halos. This is a much tighter parameter space than we had even a couple of years ago. Indeed, there is considerable tension in these estimates and it isn't certain that a single set of values can accomodate the entire parameter space.
We are in a delicate balance between a very precisely described single kind of warm dark matter particle with a possible self-interaction force, and a world in which all dark matter models are inconsistent with the evidence. For example, overly simple warm dark matter models may be inconsistent with the dwarf galaxy formation that we observe (accord here and here and here). So some sort of self-interaction may be necessary even in warm dark matter models to fit the data.
Since the total amount of dark matter, for example, in the Milky Way, can be fairly easily estimated as can the profile of the dark matter halo, localized dark matter particle per cubic space estimates can be made fairly accurately providing a small target for direct dark matter detection experiments.
Thursday, March 28, 2013
Cosmic accounting and neutrino mass
What is the universe made of?
A very large part of the mass-energy of the universe according to the six parameter lambda CDM model that predicts the patterns of cosmic microwave background radiation which we observe at about 2.7 degrees Kelvin, is attributable to "dark energy" and "dark matter", and a tiny little bit in principle (which the model disregards) is attributable to ambiant radiation. The rest is "ordinary" matter of the kind described by the Standard Model of Particle Physics which is the subject of this post.
The best evidence we have available to us suggests that the universe, at a very fine grained level, is almost perfectly electromagnetically neutral. Since conservation of net charge is maintained in all interactions, this has always been true going back as far as the laws of physics hold.
The best evidence we have available also suggests that protons, neutrons and electrons make up virtually all of the ordinary matter in the universe (i.e. other than dark matter and dark energy), with only an infinitessimal share of it at any one time consisting of mesons, hadrons other than protons and neutrons, muons and taus, all of which are extremely unstable.
Thus, there is almost exactly one electron for every proton in the universe.
Each proton is made up of two up quarks and one down quark. It is possible to estimate the number of neutrons relative to the number of protons as well. About 90% of all known (non-dark matter) atoms are protium (H-1), with proton and electron but no neutron, and over 98% of the remainder is helium-4, with two protons, two neutrons, and two electrons. In general, for heavier atoms, there are far more protons than neutrons in the naturally occuring isotypes in the proportions in which they appear in nature. So, the ratio of protons to neutrons is probably between 19-1 and 20-1.
Thus, about 65% of the quarks in the universe are up quarks, about 35% of the quarks in the universe are down quarks, a tiny fraction of a percent of the quarks in the universe at any given moment are strange, charm, bottom or top quarks, and any even smaller fraction of a fraction of a percent of quarks in the universe at any given time are antiquarks.
In the Standard Model, baryon number, which is the number of quarks minus the number of antiquarks, divided by three, is perectly conserved. Likewise, lepton number which is the number of leptons (i.e. electrons, muons, taus and neutrinos) minus the number of antileptons, is likewise perfectly conserved.
How are neutrinos created?
Neutrinos can be created in two known ways.
A neutrino-antineutrino pair can be created from the decay of a Z boson. A Z boson is a heavy electromagnetically neutral weak force boson that couples proportionally to the weak force coupling constant and a particle's weak isospin, to all massive fundamental particles in the Standard Model a bit like a heavy photon.
Far more commonly, neutrinos are created when a W boson decays to a charge lepton and a neutrino or antineutrino. When the W+ boson decays, it often decays to a positron and electron neutrino, to an antimuon and muon neutrino, or to an antitau and tau neutrino. In the more common situation, the decay of a W- boson emitted in connection with nuclear beta decay, the W- boson decays to an electron and electron antineutrino, to a muon and a muon antineutrino, or to a tau and a tau antineutrino.
Of course, when a muon or tau are produced, they decay with a high probability to a neutrino and a W+ boson, which in turn decays to another neutrino and a charged antilepton, which in turn annihilates with charged lepton or decays further, often into two antineutrinos and a charged lepton.
The beta decay channel is by far the most common means by which neutrinos are created. It is fair to assume that there is one antineutrino in existence for every electron (and for each muon and tau) in existence, in addition to an additional antineutrino for every ordinary neutrino in existence that does not have a positron, antimuon or antitau counterpart.
Thus, the vast majority of neutrinos are actually antineutrinos. Likewise, the vast majority of antimatter particles in the universe are antineutrinos.
The mass proportions of ordinary matter in the universe
Protons and neutrons each have masses about 2000 times that of the electron. So about 99.997% of the non-dark matter in the universe is made up of protons and neutrons (and less than 1% of that is attributable to the rest mass of the quarks in those hadrons - the rest arises dynamically from the strong nuclear force exchange of gluons between them which is mostly localized in the central 1/3rd of a proton or neutron's diameter).
Almost all of the rest of the non-dark matter in the universe comes from electrons. Electrons, in turn have masses of about 1,000,000 to 1,000,000,000 times that of the three known kinds of neutrinos and antineutrinos. Thus, anti-matter makes up something on the order of between one part in two billion and one part in two trillion of the non-dark matter, non-dark energy in the universe by weight, although it is hard to know how many neutrino-antineutrino pairs have been created through sequences of W+ boson decays or Z boson decays and not annihilated each other. This gross asymmetry of matter and antimatter in the universe is one of the great unsolved questions of physics.
Quarks and charged leptons have a powerful tendency to rapidly decay to the first generation versions of these particles (up quarks, down quarks, and electrons). But, once you have an antineutrino of a particular type, it oscillates between the three different kinds of antineutrinos and the parameters of those oscillations are just on the brink of being determined. So, we don't know very accurately what proportions of the different antineutrino types are in the universe.
A few personal conjectures on neutrino mass and matter-antimatter asymmetry
One of the other great unsolved questions in physics is why neutrinos are so much less massive than all of the other Standard Model fermions.
My intuition is that the answer to this question has a deep connection to the matter-antimatter asymmetry in the universe and probably also to the fact that the up quark is stable and the down quark is not unless found neutrons confined in an atomic nuclei.
Since neutrons decay into protons, this decay must be balanced by a negatively charged leptons and in order to conserve lepton number and electromagnetic charge, an electromagnetically neutral antilepton. If neutrons decayed into protons, it would take a charged antilepton and an electromagnetically neutral lepton to balance the books.
One of the reasons I doubt that neutrinos are their own antiparticles and have Majorana mass is that their essential function in beta decay is to be antileptons that can balance lepton number. If a neutrino and an antineutrino were the same thing, this wouldn't work. Their intrinsic antimatter character is critical to the role that antineutrinos play in particle physics.
One way to describe an antiparticle is as an ordinary particle going backward in time.
One way to interpret an annihilation event when a charged particle and charged antiparticle come into contact, and give rise to a photon with energy equal to their combined mass-energy, is that a single particle moving forward in time is knocked backward in time by the incredibly powerful punch of a superenergetic photon. In this interpretation, the amount of energy necessary to make a particle moving forward in time reverse direction is equal to two times its rest mass time the speed of light squared, plus an adjustment for its momentum. The energy released in a matter-antimatter annihilation is many orders of magnitude greater than the energy released in a nuclear fusion reaction involving the same mass of reactants.
If you apply the intuition of this interpretation to W- boson decay, you would reason heuristically that a W- boson wants to decay into two particles of roughly equal mass energy. On one side of the balance is the mass-energy necessary to create an electron. On the other side of the balance is the mass-energy necessary to create a neutrino and then convert it from a particle into the antiparticle that is necessary to keep the interaction's lepton number balanced. The feat of creating even a tiny amount of antimatter counterbalances the much easier act of creating of ordinary matter in the form of an electron on the other side of the balance.
The neutrinos then seek a hiearchy of masses between the three generations of neutrinos in a manner similar to that of charged leptons and quarks - but the need to cross the matter-antimatter barrier profoundly suppresses the amount of mass transmitted from charged leptons to antineutrinos via W boson exchange relative to the parallel process for quarks (outlined as a conjecture here). Effectively, because of this matter-antimatter barrier, neutrinos are only receiving mass contributions from other neutrinos, and charged leptons are receiving contributions only from other charged leptons, unlike up-like quarks which receive contributions from all of the other down-like quarks they can interact with, and down-like quarks which receive contributions from all of the other up-like quarks they can interact with.
I also suspect that the matter-antimatter imbalance in the universe has been with us since not long at all after the Big Bang, probably at the very least by the end of the inflationary era. Our matter dominanted universe is an arrow of time. I suspect, but can't prove that there is another universe that exists in the time before the Big Bang, in which causality run in the other direction and what we call antimatter is just as predominant as what we call ordinary matter is in our universe. Our universe is rushing away from the Big Bang in one direction in time, and the other universe is rushing away from the Big Bang in the other direction in time. At the "time zero" boundary within the Big Bang, pure energy condenses into matter-antimatter particle pairs with the matter particles ending up on our side of t=0 and the antimatter particles undering up on their side of t=0, because the fundamental essence of matter is that it moves forward in time (as we reckon it) and the fundamental essence of antimatter is that it moves backward in time.
Once you start with a matter dominated universe, annhilation of stray particles of charged antimatter, and ordinary W boson and Z boson decays perpetuate a matter dominated universe with the sole residual exception being about one part per two billion to two trillion of the mass-energy of the universe in the form of antineutrinos.
The questions aren't answered by the Standard Model itself. They may not even be answerable questions except to the extent that the observed masses of particles and their frequencies coincide, or do not coincide, with a more rigorous version of these heuristic ideas, or to the extent that this kind of thinking also fosters a train of thought that leads to other conclusions that are somehow more rigorously testable.
But, the notion that focusing on the antimatter character of most neutrinos in accounting for their tiny mass, rather than on their lack of electromagnetic charge, may be a useful exercise.
An alternative, although not entirely independent heuristic, could also play a role. The constant process of alternating between left parity and right parity modes while retaining the same character on the particle-antiparticle dimension, possibly due to the Higgs field, may be an important process in the generation of the rest masses of the fundamental particles. Since neutrinos can only change between a left parity and right parity mode by simultaneously changing from a particle to an antiparticle mode, which poses a much greater barrier to that transition, their masses are suppressed.
A very large part of the mass-energy of the universe according to the six parameter lambda CDM model that predicts the patterns of cosmic microwave background radiation which we observe at about 2.7 degrees Kelvin, is attributable to "dark energy" and "dark matter", and a tiny little bit in principle (which the model disregards) is attributable to ambiant radiation. The rest is "ordinary" matter of the kind described by the Standard Model of Particle Physics which is the subject of this post.
The best evidence we have available to us suggests that the universe, at a very fine grained level, is almost perfectly electromagnetically neutral. Since conservation of net charge is maintained in all interactions, this has always been true going back as far as the laws of physics hold.
The best evidence we have available also suggests that protons, neutrons and electrons make up virtually all of the ordinary matter in the universe (i.e. other than dark matter and dark energy), with only an infinitessimal share of it at any one time consisting of mesons, hadrons other than protons and neutrons, muons and taus, all of which are extremely unstable.
Thus, there is almost exactly one electron for every proton in the universe.
Each proton is made up of two up quarks and one down quark. It is possible to estimate the number of neutrons relative to the number of protons as well. About 90% of all known (non-dark matter) atoms are protium (H-1), with proton and electron but no neutron, and over 98% of the remainder is helium-4, with two protons, two neutrons, and two electrons. In general, for heavier atoms, there are far more protons than neutrons in the naturally occuring isotypes in the proportions in which they appear in nature. So, the ratio of protons to neutrons is probably between 19-1 and 20-1.
Thus, about 65% of the quarks in the universe are up quarks, about 35% of the quarks in the universe are down quarks, a tiny fraction of a percent of the quarks in the universe at any given moment are strange, charm, bottom or top quarks, and any even smaller fraction of a fraction of a percent of quarks in the universe at any given time are antiquarks.
In the Standard Model, baryon number, which is the number of quarks minus the number of antiquarks, divided by three, is perectly conserved. Likewise, lepton number which is the number of leptons (i.e. electrons, muons, taus and neutrinos) minus the number of antileptons, is likewise perfectly conserved.
How are neutrinos created?
Neutrinos can be created in two known ways.
A neutrino-antineutrino pair can be created from the decay of a Z boson. A Z boson is a heavy electromagnetically neutral weak force boson that couples proportionally to the weak force coupling constant and a particle's weak isospin, to all massive fundamental particles in the Standard Model a bit like a heavy photon.
Far more commonly, neutrinos are created when a W boson decays to a charge lepton and a neutrino or antineutrino. When the W+ boson decays, it often decays to a positron and electron neutrino, to an antimuon and muon neutrino, or to an antitau and tau neutrino. In the more common situation, the decay of a W- boson emitted in connection with nuclear beta decay, the W- boson decays to an electron and electron antineutrino, to a muon and a muon antineutrino, or to a tau and a tau antineutrino.
Of course, when a muon or tau are produced, they decay with a high probability to a neutrino and a W+ boson, which in turn decays to another neutrino and a charged antilepton, which in turn annihilates with charged lepton or decays further, often into two antineutrinos and a charged lepton.
The beta decay channel is by far the most common means by which neutrinos are created. It is fair to assume that there is one antineutrino in existence for every electron (and for each muon and tau) in existence, in addition to an additional antineutrino for every ordinary neutrino in existence that does not have a positron, antimuon or antitau counterpart.
Thus, the vast majority of neutrinos are actually antineutrinos. Likewise, the vast majority of antimatter particles in the universe are antineutrinos.
The mass proportions of ordinary matter in the universe
Protons and neutrons each have masses about 2000 times that of the electron. So about 99.997% of the non-dark matter in the universe is made up of protons and neutrons (and less than 1% of that is attributable to the rest mass of the quarks in those hadrons - the rest arises dynamically from the strong nuclear force exchange of gluons between them which is mostly localized in the central 1/3rd of a proton or neutron's diameter).
Almost all of the rest of the non-dark matter in the universe comes from electrons. Electrons, in turn have masses of about 1,000,000 to 1,000,000,000 times that of the three known kinds of neutrinos and antineutrinos. Thus, anti-matter makes up something on the order of between one part in two billion and one part in two trillion of the non-dark matter, non-dark energy in the universe by weight, although it is hard to know how many neutrino-antineutrino pairs have been created through sequences of W+ boson decays or Z boson decays and not annihilated each other. This gross asymmetry of matter and antimatter in the universe is one of the great unsolved questions of physics.
Quarks and charged leptons have a powerful tendency to rapidly decay to the first generation versions of these particles (up quarks, down quarks, and electrons). But, once you have an antineutrino of a particular type, it oscillates between the three different kinds of antineutrinos and the parameters of those oscillations are just on the brink of being determined. So, we don't know very accurately what proportions of the different antineutrino types are in the universe.
A few personal conjectures on neutrino mass and matter-antimatter asymmetry
One of the other great unsolved questions in physics is why neutrinos are so much less massive than all of the other Standard Model fermions.
My intuition is that the answer to this question has a deep connection to the matter-antimatter asymmetry in the universe and probably also to the fact that the up quark is stable and the down quark is not unless found neutrons confined in an atomic nuclei.
Since neutrons decay into protons, this decay must be balanced by a negatively charged leptons and in order to conserve lepton number and electromagnetic charge, an electromagnetically neutral antilepton. If neutrons decayed into protons, it would take a charged antilepton and an electromagnetically neutral lepton to balance the books.
One of the reasons I doubt that neutrinos are their own antiparticles and have Majorana mass is that their essential function in beta decay is to be antileptons that can balance lepton number. If a neutrino and an antineutrino were the same thing, this wouldn't work. Their intrinsic antimatter character is critical to the role that antineutrinos play in particle physics.
One way to describe an antiparticle is as an ordinary particle going backward in time.
One way to interpret an annihilation event when a charged particle and charged antiparticle come into contact, and give rise to a photon with energy equal to their combined mass-energy, is that a single particle moving forward in time is knocked backward in time by the incredibly powerful punch of a superenergetic photon. In this interpretation, the amount of energy necessary to make a particle moving forward in time reverse direction is equal to two times its rest mass time the speed of light squared, plus an adjustment for its momentum. The energy released in a matter-antimatter annihilation is many orders of magnitude greater than the energy released in a nuclear fusion reaction involving the same mass of reactants.
If you apply the intuition of this interpretation to W- boson decay, you would reason heuristically that a W- boson wants to decay into two particles of roughly equal mass energy. On one side of the balance is the mass-energy necessary to create an electron. On the other side of the balance is the mass-energy necessary to create a neutrino and then convert it from a particle into the antiparticle that is necessary to keep the interaction's lepton number balanced. The feat of creating even a tiny amount of antimatter counterbalances the much easier act of creating of ordinary matter in the form of an electron on the other side of the balance.
The neutrinos then seek a hiearchy of masses between the three generations of neutrinos in a manner similar to that of charged leptons and quarks - but the need to cross the matter-antimatter barrier profoundly suppresses the amount of mass transmitted from charged leptons to antineutrinos via W boson exchange relative to the parallel process for quarks (outlined as a conjecture here). Effectively, because of this matter-antimatter barrier, neutrinos are only receiving mass contributions from other neutrinos, and charged leptons are receiving contributions only from other charged leptons, unlike up-like quarks which receive contributions from all of the other down-like quarks they can interact with, and down-like quarks which receive contributions from all of the other up-like quarks they can interact with.
I also suspect that the matter-antimatter imbalance in the universe has been with us since not long at all after the Big Bang, probably at the very least by the end of the inflationary era. Our matter dominanted universe is an arrow of time. I suspect, but can't prove that there is another universe that exists in the time before the Big Bang, in which causality run in the other direction and what we call antimatter is just as predominant as what we call ordinary matter is in our universe. Our universe is rushing away from the Big Bang in one direction in time, and the other universe is rushing away from the Big Bang in the other direction in time. At the "time zero" boundary within the Big Bang, pure energy condenses into matter-antimatter particle pairs with the matter particles ending up on our side of t=0 and the antimatter particles undering up on their side of t=0, because the fundamental essence of matter is that it moves forward in time (as we reckon it) and the fundamental essence of antimatter is that it moves backward in time.
Once you start with a matter dominated universe, annhilation of stray particles of charged antimatter, and ordinary W boson and Z boson decays perpetuate a matter dominated universe with the sole residual exception being about one part per two billion to two trillion of the mass-energy of the universe in the form of antineutrinos.
The questions aren't answered by the Standard Model itself. They may not even be answerable questions except to the extent that the observed masses of particles and their frequencies coincide, or do not coincide, with a more rigorous version of these heuristic ideas, or to the extent that this kind of thinking also fosters a train of thought that leads to other conclusions that are somehow more rigorously testable.
But, the notion that focusing on the antimatter character of most neutrinos in accounting for their tiny mass, rather than on their lack of electromagnetic charge, may be a useful exercise.
An alternative, although not entirely independent heuristic, could also play a role. The constant process of alternating between left parity and right parity modes while retaining the same character on the particle-antiparticle dimension, possibly due to the Higgs field, may be an important process in the generation of the rest masses of the fundamental particles. Since neutrinos can only change between a left parity and right parity mode by simultaneously changing from a particle to an antiparticle mode, which poses a much greater barrier to that transition, their masses are suppressed.
Wednesday, March 27, 2013
Strassler On Talking About Science
I think it very important for scientific experts to be clear, when they speak in public, about what is known and well-established, what is plausible and widely believed but still needs experimental checks, and what is largely speculative and could very well be false. (For example: The Higgs particle and field are nearly established; inflation is increasingly plausible; any connection between them is speculative.) . . .
Just as we widely agree the Higgs particle must have zero spin, and that the inflaton is quite likely to have zero spin, I’d like to see a consensus emerge that public communication of particle physics, string theory and cosmology should also have zero spin. Too bad that’s still a rather speculative idea.From Matt Strassler's blog.
His point is well taken. I'd would draw the lines between some of the categories he identifies in moderately different places than he does, but his framework is a sound one.
I would suggest, however, that in many cases there are two or three competing positions which are plausible and widely believed by a subset of the scientific community which are not "largely speculative", and that in those cases (e.g. SUSY, MOND and loop quantum gravity), it would be helpful to acknowledge that there are competing theories and to explain their relative levels of acceptance.
Often there will be a majority or plurality position, and one or more minority views held by significant numbers of respectable mainstream scientists, which have not been resolved and may be impossible to resolve for extended periods of time due to a limited experimental data. In these cases, all off the competing theories generally produce very similar predicted phenomenological outcomes within the range of experimental data whose accuracy is not seriously subject to question. indeed, sometimes these differing positions arise from disputes over the validity of alternative experimental methods.
Likewise, it is often important to distinguish between largely speculative ideas that are professionally respectable ideas, even if they are not widely believed by any subset of the scientific community at this point, and "crackpot" ideas that are starkly contradicted by widely accepted empirical evidence and are contrary to widely accepted physical laws, or are internally flawed in deep ways (e.g. they are not mathematically or dimensionally consistent).
This is particularly important in the area of fundamental physics, where the proportion of all published work of professional physicists that is largely speculative is much larger than in many other academic disciplines.
A huge share of the published work in theoretical physics analyze toy models of possible laws of nature that are largely speculative or even known to be contrary to empirical evidence, but are not "crackpot" ideas. They are published with an eye towards understanding the implications of that class of mathematical models to see if they could possibly be made to correspond to empirical evidence if further developed, and to determine what implictations the "new physics" in those models beyond the Standard Model and general relativity might show. These papers are intermediate steps in the massive undertaking of looking for a final and complete set of the laws of nature and are driven by the known imperfections, at least from a point of view of a comprehensive and rigorous set of laws of nature, with the status quo. But, for the most part, they don't even pretend to be plausible and widely believed evidence based inferrences about the way that the world already is right now.
A person not familiar with this state of the published and peer reviewed literature in theoretical physics could easily be led astray into thinking that largely speculative ideas have more importance than they actually do, because these kinds of published and peer reviewed papers setting forth largely speculative ideas are far more rare in many other academic disciplines.
I'd also note that it is often the case that we know with a great deal of confidence that some scientific proposition is X or Y, but don't know which one is correct. The range of possibilities may be "known and well established", but statements about which of the possibilities is actually right may be "largely speculative."
Monday, March 25, 2013
The Lamda CDM Model Says Little About CDM
Cosmic microwave background radiation studies, culminating in an as good as it gets (i.e. inherent theoretical limits on measurement are dominant relative to experimental imprecision), one time measurement by Planck satellite which released all of its data except the polarization data last week, produces results that are fitted to the "Standard Model of Cosmology" called the six parameter lambda CDM model, with a few additional parameters considered.
One often overlooked, but absolutely key point to understand about the lambda CDM model is that it doesn't really meaningfully specify much about the CDM part. It establishes that there must be a certain amount of very generally described non-hot dark matter, but very little more.
One often overlooked, but absolutely key point to understand about the lambda CDM model is that it doesn't really meaningfully specify much about the CDM part. It establishes that there must be a certain amount of very generally described non-hot dark matter, but very little more.
Thursday, March 21, 2013
Precision Cosmic Background Radiation Results In
The Planck satellite team has released the most detailed ever data on cosmic background radiation in the universe which tells us a great deal about the basic parameters of cosmology (more papers here).
The new data shrink the estimated proportion of dark energy relative to matter (i.e. it has a best fit value for the cosmological constant that is a bit smaller).
Taken together with other data, the results strongly favors a cosmology with just three generations of neutrinos with a sum of the three respective mass eigenvalues of between 0.06 and 0.23 eV of mass with the best fit at the bottom of that range. A sterile neutrino of the kind suggested by the reactor anomalies at two Earth bound neutrino experiments (LSND and MiniBooNE) is not a good fit and if there was one would have to have less than 0.5 eV of mass which is considerably smaller than the estimate from reactor anomalies observed to date and other data of 1.3 eV or so. In a nutshell, the Standard Model triumphs once again. See posts on the state of these measurements pre-Planck here and here based on the 9 year WMAP data.
It is also important to note that the cold dark matter in the lambda CDM model doesn't say very much about the nature of the dark matter component of the model at all. It does not specify some specific dark matter model.
Analysis of the possibility of a sterile neutrino by the Planck team is not a good fit and imposes a mass limit of about 0.5 eV on the sterile neutrino species is is considerably less than the mass suggested by reactor anomaly data.
UPDATE: I posted the following as a comment at the Not Even Wrong Blog without links.
The result I read in paper sixteen was Neff=3.30 +/- 0.27 v. Neff 3.046 for the three Standard Model neutrinos. So, their result is a little less than one sigma from the Standard Model value. A four neutrino model would have an Neff of a bit more than 4.05, which is about three sigma from the measured value which is roughly a 99% exclusion and is a confirmation of the Standard Model.
Planck also combines data from multiple sources puts a cap on the sum of three neutrino masses in a three Standard Model neutrino scenario of 0.24 eV (at 95% CI) with a best fit value of 0.06 eV. The floor from non-astronomy experiments is 0.06 eV in a normal neutrino mass hierachy (based on the difference between mass one and mass two, and between mass two and mass three which are both known to about two significant digits) and 0.1 eV in an inverted neutrino mass hierachy. In a normal neutrino mass hierarchy, this puts the mass of the electron neutrino at between 0 and 0.06 eV, with the low end preferred (I personally expect that an electron neutrino is significantly less than the mass difference between the first and second neutrino type of about 0.006 eV).
Note that a particle that is in the hundreds or thousands of eVs would not count towards Neff because it is not light enough to be relativistic at 380,000 years after the Big Bang. So, it really only rules out a light sterile neutrino, rather than a heavy one. The LSND and MiniBooNE reactor anomalies have hinted at a possible fourth generation sterile-ish neutrino of about 1.3 eV +/- about 30%, so the Planck people did a study on the sum of mass limits if there were a disfavored four and not just three relativistic species and came up with a cap on sterile neutrino mass in that scenario of about 0.5 eV +/- 0.1 eV, which is about 2.5 sigma away from the value of the LSND/MiniBooNE anomaly estimates considering the combined uncertainties.
LEP ruled out a fourth species of fertile neutrino of under 45 GeV, and I wouldn’t be going out on a limb to say without actually doing the calculations that a fertile neutrino of 45 GeV to 63 GeV, if it existed, would have wildly thrown off all of the Higgs boson decay cross-sections observed (since a decay to a 45 GeV to 63 GeV neutrino-antineutrino pair from a 125.7 GeV Higgs boson would have been a strongly favored decay path if it existed) and is in fact therefore excluded by the lastest round of LHC data.
The LEP data already excluded fertile neutrinos in the 6 GeV to 20 GeV mass range where there are contradictory direct dark matter detection experiment results at different experiments.
But, a particle that we would normally call a sterile neutrino for other purposes in the Warm Dark Matter mass range of KeV or the Cold Dark Matter mass range of GeV to hundreds of GeV, or anything in between (including any of the possible direct dark matter detection signals or anything that would generate the Fermi line at 130 GeV), would not be a relativistic particle within the meaning of Neff which only counts particles that would move at relativistic speed given their masses at the relevant time.
ADDITONAL UPDATE: The mass difference of neutrino mass one and neutrino mass two is about 0.009 (usually reported squared at about 7.5 * 10^-5 eV) are about 0.5 (usually reported squared at about 2.5 * 10^-3 eV) for a combined 0.509. If the neutrino mass hierarchy is broadly similar to that of the quarks and the charged leptons (it is impossible to fit the values already known to a perfect Koide triple), one would expect an electron neutrino mass on the order of 0.001 eV (i.e. 1 meV) or less.
Planck is the beginning and to a great extent the end of cosmic background radiation physics.
Also, the precision of the Planck data is so much better than anything that has come before it, including the previously state of the art 9-year WMAP data released earlier this year, that you can basically ignore any pre-Planck data on cosmic background radiation in any respect that Planck data addresses the subject. If you use the Particle Data Group approach of computing global averages with weights inversely proportional to margin of error, the relative weights are perhaps 9-1 or more.
Realistically, Planck and successor cosmic background radiation experiments may be the only way to experimentally probe this truly high energy physics regime of the early universe for decades and possible ever. There are good theoretical reasons why we can't directly observe anything older (e.g. star formation happened after the cosmic background radiation arose, so there was nothing to make coherent light emitting objects). And, almost nothing in the current universe or any experiment we could create has higher energies than the pre-cosmic background radiation universe we are probing with this data.
Planck is measuring the entire universe-wide cosmic background radiation data set of one. We can't measure some other universe's cosmic background radiation outside of computer simulations and there is no reason that the cosmic background radiation that is observable from our solar system or anywhere nearby we can send a space probe should change noticably in my lifetime or the lifetime of my children or grandchildren. Future experiments can be more precise, but we understand electromagnetism almost perfectly and know all of the properties of cosmic backgrond radiation that it is even theoretically possible to measure and have measured almost all of them already (or are on the verge of doing so in the next few years) at Planck. Details can be refined, but the big picture won't change. Really:
I'll have to leave for a future post an in depth analysis of the constraints that the Planck findings place on cosmology apart from dark energy proportions, dark matter amounts, and neutrino generations and masses, but I'll discuss a few briefly in this post. There are several really interesting things going on there.
* First, the new Planck data provide much more meaningful experimental constraints on theories of "inflation" shortly after the Big Bang, which after dark matter, is probably the second biggest set of experimental data screaming out for new physics.
Because inflation takes place in the extremely high energy extremely early universe (when it was smaller than one meter and only a tiny fraction of a second old) is hard to make inferrences about in the context of experiments like the LHC and observable astronomy which are many orders of magnitude below the energy densities present in the proposed inflationary era, so "new physics" in this area outside the range of our experience or likely future is far less consequential than dark matter which affects the world we see today. But, "new physics" is still a big deal and may be important to the structure of a "Theory of Everything" or a quantum gravity theory (e.g. string theory vacua), at the very least by ruling out theories that have high energy behavior inconsistent with the experimental boundaries of inflation scenarios.
A lot of inflation theories that have been viable candidates, receiving serious discussion almost ever since the need for inflation in a cosmology theory was discovered in the 1970s (around the same time that the Standard Model was formulated), have been ruled out by the latest round of Planck data. Planck strongly disfavors power law inflation, the simplest hybrid inflationary models, simple monomial models with n > 2, single fast roll inflation scenarios, multiple stage inflation scenarios, inflation scenarios with flat or concave potentials, dynamical dark energy, time variations of the fine structure constant are all strongly disfavored. Any theory that would create non-Gaussian statistics of the CMB anisotropies, non-flat universes, tensor modes, or statistically discernable deviations from isotropy at L >50 are ruled out.
If your theory was phenomenologically distinct from "single slow roll inflation scenarios with convex potential" in any non-subtle way, you were wrong, thanks for playing.
I will need to read more to fully understand these implications myself, but more inflation theories have died today than on any previous day in history and than will on any day to come in the future (since there are fewer inflation theories left than the number of inflation theories killed today). A book length catalog (300 pages) of the pre-March 21 ranks of inflation theories is available at arxiv. What is inflation?
* Second, the lack of scale invariance in the power law of cosmic background radiation has been confirmed parameterized at a value of about 0.96 with 1.00 being a pure scale invariant power law. The lamda CDM model has a parameter to describe this deviation, but no mechanism to make it happen. This is a prediction of many inflation models.
* Third, something weird seems to be going on between L's 20 and 30. This is the only material respect in which the Planck data deviate from the lamda CDM model. Intuitively, it seems very plausible that the source of the L's 20 to 30 deviation and the source of the lack of scale invariance could be the same. Some small second order effect not captured by the six parameter lamda CDM model appears to be involved here.
For example, both the lack of scale invariance and the weirdness from L's 20 to 30 are both plausible consequences of the place on the spectrum from hot dark matter to cold dark matter than a dark matter particle resides.
Roughly speaking, in simple single dark matter particle models, the mass of the particle (or the dominant particle if there are multiple kinds but one has a predominant impact on phenomenology in the way the first generation fermions that form protons, neutrons and atoms in the Standard Model do) governs where deviations in large scale structure related to scale arise. Hot dark matter has almost no large scale structure. Warm dark matter gives rise to roughly the amount of large scale structure we observe. Cold dark matter gives rise to more dwarf galaxies and large scale structure that is more finely grained than we observe.
All of this, of course, is model dependent and the generalizations are based on a simple, almost completely non-interacting dark sector with just one kind of particle and no significant new forces from those know to use already. A single instance of inflation alone is enough to get the observed scale invariance in a lamda CDM model, but doesn't explain the L's 20 to 30 anomaly, which could have an entirely different source (or simply be random variation that is improbable but has no deeper cause, or experimental error).
Some persepective on this anomaly from this blog:
* Fourth, the fact that space-time is "flat" to a precision of 0.1% is remarkable given that we conceive of general relativity as a warping of space-time. Overwhelmingly, this warping of space-time due to gravity is local rather than global.
What drives the conclusions about inflation?
The preference for a simple model is driven by several factors:
(1) The data is a good fit to a simple power law with a not quite scale invariant exponent of about 0.96 rather than 1.0 (with a five sigma difference from a 1.0 value) that shows no statistically significant tendency to change over time (i.e. the best fit value for the running of the spectral index is about 1.5 sigma from zero at -0.0134 +/- 0.0090).
(2) The best fit value for a tensor contribution has its best fit at or nearly at zero. The absence of any indication of a tensor mode in the inflaton as opposed to a mere scalar inflaton seems to be another important factor that is driving the exclusion of other models. "In a model admitting tensor fluctuations, the 95% CL bound on the tensor-to-scalar ratio is r0.002 < 0.12 (< 0.11) using Planck+WP (plus high-L`). This bound on r implies an upper limit for the inflation energy scale of 1.9*10^16 GeV . . . at 95% CL." (3) The best fit values of inflation scenarios are likewise almost maximally concave (i.e. potential drops more in the early part of a decline in inflaton potential than later on). The Planck report concludes by noting that: "The simplest inflationary models have passed an exacting test with the Planck data. The full mission data including Planck’s polarization measurements will help answer further fundamental questions, including the possibilities for nonsmooth power spectra, the energy scale of inflation, and extensions to more complex models."
Evidence for a GUT?
The coincidence of the Planck upper limits on inflation energy scale with the completely independently derived grand unification scale based upon the running of the Standard Model (or SUSY) coupling constants is impressive. Even if SUSY is not the way the coupling constants converge, the notion of a grand unification at inflation energies by some means (perhaps by considering quantum gravity theories) is aesthetically very tempting.
Mostly Off Topic Other Items Of Interest:
More On Why We Don't Need SUSY
Woit has an interesting post on a talk by LHC physicist Joe Lyyken on why the "hierachy problem" that SUSY seeks to solve isn't actually a problem with anything but how theoretical physicists are thinking about the issue.
Dark Matter and MOND
* Somewhat off topic, in January of this year, an interesting new MOND paper by MOND inventor Milgrom and two co-authors was published (arguing that much of the dark matter effects are due to a modification of the law of gravity rather than dark matter particles) setting forth a MOND cosmology.
* The dominant unresolved question in physics remains the need to understand dark matter phenomena. As I've said before, and as Planck confirms once again, a simple cosmological constant completely explains dark energy within the context of the same theory of General Relativity that we've had for a century now - dark energy, rather than being mysterious, is a solved problem.
General relativity does not explain dark matter phenomena which are operationally defined as deviations from the predictions of general relativity that are observed by astronomers that don't relate to "inflation" in cosmology. The Standard Model provides no dark matter candidates and the LHC is foreclosing more of them. The lamda CDM model separately accounts for mass from baryons, neutrinos, radiation and effective mass-energy from the cosmological constant and has dark matter left over, but this six parameter fit to cosmic background radiation data collected as WMAP and Planck, for example, does very little to specify the nature of the dark matter component. Direct dark matter searches that have shown any dark matter signals contradict each other and are condicted by searches that have come up empty in roughly the 10 GeV to 100 GeV range for all but the very lowest cross-sections of interaction (well below that of neutrinos).
Simulations have shown that WIMPS or other simple Cold Dark Matter scenarios produce more dwaft galaxies than we observe and none of the Cold Dark Matter models can rival MOND in closely approximating almost all galaxy level dark matter effects in a predictive manner with just a single experimentally measured constant. The cuspy dark matter halos predicted by Cold Dark Matter models are likewise contrary to what we observe, which is inferred halo distributions of dark matter that look more like rugby balls with their long axis passing through a galaxy's central black hole and poking up out from the plane of the galaxy's rotation.
The new data shrink the estimated proportion of dark energy relative to matter (i.e. it has a best fit value for the cosmological constant that is a bit smaller).
Taken together with other data, the results strongly favors a cosmology with just three generations of neutrinos with a sum of the three respective mass eigenvalues of between 0.06 and 0.23 eV of mass with the best fit at the bottom of that range. A sterile neutrino of the kind suggested by the reactor anomalies at two Earth bound neutrino experiments (LSND and MiniBooNE) is not a good fit and if there was one would have to have less than 0.5 eV of mass which is considerably smaller than the estimate from reactor anomalies observed to date and other data of 1.3 eV or so. In a nutshell, the Standard Model triumphs once again. See posts on the state of these measurements pre-Planck here and here based on the 9 year WMAP data.
It is also important to note that the cold dark matter in the lambda CDM model doesn't say very much about the nature of the dark matter component of the model at all. It does not specify some specific dark matter model.
Scientific results include robust support for the standard, six parameter lambda CDM model of cosmology and improved measurements for the parameters that define this model, including a highly significant deviation from scale invariance of the primordial power spectrum. The values for some of these parameters and others derived from them are significantly different from those previously determined. Several large scale anomalies in the CMB temperature distribution detected earlier by WMAP are confirmed with higher confidence. Planck sets new limits on the number and mass of neutrinos, and has measured gravitational lensing of CMB anisotropies at 25 sigma. Planck finds no evidence for non-Gaussian statistics of the CMB anisotropies. There is some tension between Planck and WMAP results; this is evident in the power spectrum and results for some of the cosmology parameters. In general, Planck results agree well with results from the measurements of baryon acoustic oscillations.The cosmological parameters paper is probably the most interesting in terms of providing concrete results. With regard to neutrinos it finds that "Using BAO and CMB data, we find Neff = 3.30 0 +/- 0.27 for the effective number of relativistic degrees of freedom, and an upper limit of 0.23 eV for the sum of neutrino masses. Our results are in excellent agreement with big bang nucleosynthesis and the standard value of Neff = 3.046. . . . Since the sum of neutrino masses must be greater than approximately 0.06 eV in the normal hierarchy scenario and 0.1 eV in the degenerate hierarchy (Gonzalez-Garcia et al. 2012), the allowed neutrino mass window is already quite tight and could be closed further by current or forthcoming observations (Jimenez et al. 2010; Lesgourgues et al. 2013)." The best fit value for the sum of neutrino masses in the Planck data is 0.06 eV, but the data are not terribly precise.
We find no evidence for extra relativistic species, beyond the three species of (almost) massless neutrinos and photons. The main effect of massive neutrinos is a suppression of clustering on scales larger than the horizon size at the non-relativisitic transition. . . . Using Planck data in combination with polarization measured by WMAP and high-L` anisotropies from ACT and SPT allows for a constraint on the sum of the neutrino species masses of < 0.66 eV (95% CL) based on the [Planck+WP+highL] model. Curiously, this constraint is weakened by the addition of the lensing likelihood the sum of the neutrino species masses of < 0.85 eV (95% CL), reflecting mild tensions between the measured lensing and temperature power spectra, with the former preferring larger neutrino masses than the latter. Possible origins of this tension are explored further in Planck Collaboration XVI (2013). . . . The signal-to-noise on the lensing measurement will improve with the full mission data, including polarization, and it will be interesting to see how this story develops.
– using a likelihood approach that combines Planck CMB and lensing data, CMB data from ACT and SPT at high L`s, and WMAP polarized CMB data at low L`s, we have estimated the values of a “vanilla” 6-parameter lambda CDM model with the highest accuracy ever. These estimates are highly robust, as demonstrated by the use of multiple methods based both on likelihood and on component-separated maps.
– The parameters of the Planck best-fit 6-parameter lambda CDM are significantly different than previously estimated. In particular, with respect to pre-Planck values, we find a weaker cosmological constant (by 2 %), more baryons (by 3 %), and more cold dark matter (by 5 %). The spectral index of primordial fluctuations is firmly established to be below unity, even when extending the CDM model to more parameters.
– we find no significant improvements to the best-fit model when extending the set of parameters beyond 6, implying no need for new physics to explain the Planck measurements.
– The Planck best-fit model is in excellent agreement with the most current BAO data. However, it requires a Hubble constant that is significantly lower ( 67 km s^-1 Mpc^-1) than expected from traditional measurement techniques, raising the possibility of systematic effects in the latter.
– An exploration of parameter space beyond the basic set leads to: (a) firmly establishing the effective number of relativistic species (neutrinos) at 3; (b) constraining the flatness of space-time to a level of 0.1%; (c) setting significantly improved constraints on the total mass of neutrinos, the abundance of primordial Helium, and the running of the spectral index of the power spectrum.
– we find no evidence at the current level of analysis for tensor modes, nor for a dynamical form of dark energy, nor for time variations of the fine structure constant. . . .
– we find important support for single-field slow-roll inflation via our constraints on running of the spectral index, curvature and fNL.
– The Planck data squeezes the region of the allowed standard inflationary models, preferring a concave potential: power law inflation, the simplest hybrid inflationary models, and simple monomial models with n > 2, do not provide a good fit to the data.
– we find no evidence for statistical deviations from isotropy at L >50, to very high precision.
– we do find evidence for deviations from isotropy at low L`s. In particular, we find a coherent deficit of power with respect to our best-fit lambda CDMmodel at L`s between 20 and 30.
– We confirm the existence of the so-called WMAP anomalies.
Analysis of the possibility of a sterile neutrino by the Planck team is not a good fit and imposes a mass limit of about 0.5 eV on the sterile neutrino species is is considerably less than the mass suggested by reactor anomaly data.
UPDATE: I posted the following as a comment at the Not Even Wrong Blog without links.
The result I read in paper sixteen was Neff=3.30 +/- 0.27 v. Neff 3.046 for the three Standard Model neutrinos. So, their result is a little less than one sigma from the Standard Model value. A four neutrino model would have an Neff of a bit more than 4.05, which is about three sigma from the measured value which is roughly a 99% exclusion and is a confirmation of the Standard Model.
Planck also combines data from multiple sources puts a cap on the sum of three neutrino masses in a three Standard Model neutrino scenario of 0.24 eV (at 95% CI) with a best fit value of 0.06 eV. The floor from non-astronomy experiments is 0.06 eV in a normal neutrino mass hierachy (based on the difference between mass one and mass two, and between mass two and mass three which are both known to about two significant digits) and 0.1 eV in an inverted neutrino mass hierachy. In a normal neutrino mass hierarchy, this puts the mass of the electron neutrino at between 0 and 0.06 eV, with the low end preferred (I personally expect that an electron neutrino is significantly less than the mass difference between the first and second neutrino type of about 0.006 eV).
Note that a particle that is in the hundreds or thousands of eVs would not count towards Neff because it is not light enough to be relativistic at 380,000 years after the Big Bang. So, it really only rules out a light sterile neutrino, rather than a heavy one. The LSND and MiniBooNE reactor anomalies have hinted at a possible fourth generation sterile-ish neutrino of about 1.3 eV +/- about 30%, so the Planck people did a study on the sum of mass limits if there were a disfavored four and not just three relativistic species and came up with a cap on sterile neutrino mass in that scenario of about 0.5 eV +/- 0.1 eV, which is about 2.5 sigma away from the value of the LSND/MiniBooNE anomaly estimates considering the combined uncertainties.
LEP ruled out a fourth species of fertile neutrino of under 45 GeV, and I wouldn’t be going out on a limb to say without actually doing the calculations that a fertile neutrino of 45 GeV to 63 GeV, if it existed, would have wildly thrown off all of the Higgs boson decay cross-sections observed (since a decay to a 45 GeV to 63 GeV neutrino-antineutrino pair from a 125.7 GeV Higgs boson would have been a strongly favored decay path if it existed) and is in fact therefore excluded by the lastest round of LHC data.
The LEP data already excluded fertile neutrinos in the 6 GeV to 20 GeV mass range where there are contradictory direct dark matter detection experiment results at different experiments.
But, a particle that we would normally call a sterile neutrino for other purposes in the Warm Dark Matter mass range of KeV or the Cold Dark Matter mass range of GeV to hundreds of GeV, or anything in between (including any of the possible direct dark matter detection signals or anything that would generate the Fermi line at 130 GeV), would not be a relativistic particle within the meaning of Neff which only counts particles that would move at relativistic speed given their masses at the relevant time.
ADDITONAL UPDATE: The mass difference of neutrino mass one and neutrino mass two is about 0.009 (usually reported squared at about 7.5 * 10^-5 eV) are about 0.5 (usually reported squared at about 2.5 * 10^-3 eV) for a combined 0.509. If the neutrino mass hierarchy is broadly similar to that of the quarks and the charged leptons (it is impossible to fit the values already known to a perfect Koide triple), one would expect an electron neutrino mass on the order of 0.001 eV (i.e. 1 meV) or less.
Planck is the beginning and to a great extent the end of cosmic background radiation physics.
Also, the precision of the Planck data is so much better than anything that has come before it, including the previously state of the art 9-year WMAP data released earlier this year, that you can basically ignore any pre-Planck data on cosmic background radiation in any respect that Planck data addresses the subject. If you use the Particle Data Group approach of computing global averages with weights inversely proportional to margin of error, the relative weights are perhaps 9-1 or more.
Realistically, Planck and successor cosmic background radiation experiments may be the only way to experimentally probe this truly high energy physics regime of the early universe for decades and possible ever. There are good theoretical reasons why we can't directly observe anything older (e.g. star formation happened after the cosmic background radiation arose, so there was nothing to make coherent light emitting objects). And, almost nothing in the current universe or any experiment we could create has higher energies than the pre-cosmic background radiation universe we are probing with this data.
Planck is measuring the entire universe-wide cosmic background radiation data set of one. We can't measure some other universe's cosmic background radiation outside of computer simulations and there is no reason that the cosmic background radiation that is observable from our solar system or anywhere nearby we can send a space probe should change noticably in my lifetime or the lifetime of my children or grandchildren. Future experiments can be more precise, but we understand electromagnetism almost perfectly and know all of the properties of cosmic backgrond radiation that it is even theoretically possible to measure and have measured almost all of them already (or are on the verge of doing so in the next few years) at Planck. Details can be refined, but the big picture won't change. Really:
In the early 1990s, the COBE satellite gave us the first precision, all-sky map of the cosmic microwave background, down to a resolution of about 7 degrees. About a decade ago, WMAP managed to get that down to about half-a-degree resolution. But Planck? Planck is so sensitive that the limits to what it can see aren’t set by instruments, but by the fundamental astrophysics of the Universe itself! In other words, it will be impossible to ever take better pictures of this stage of the Universe than Planck has already taken.Inflation and Cosmology Findings
I'll have to leave for a future post an in depth analysis of the constraints that the Planck findings place on cosmology apart from dark energy proportions, dark matter amounts, and neutrino generations and masses, but I'll discuss a few briefly in this post. There are several really interesting things going on there.
* First, the new Planck data provide much more meaningful experimental constraints on theories of "inflation" shortly after the Big Bang, which after dark matter, is probably the second biggest set of experimental data screaming out for new physics.
Because inflation takes place in the extremely high energy extremely early universe (when it was smaller than one meter and only a tiny fraction of a second old) is hard to make inferrences about in the context of experiments like the LHC and observable astronomy which are many orders of magnitude below the energy densities present in the proposed inflationary era, so "new physics" in this area outside the range of our experience or likely future is far less consequential than dark matter which affects the world we see today. But, "new physics" is still a big deal and may be important to the structure of a "Theory of Everything" or a quantum gravity theory (e.g. string theory vacua), at the very least by ruling out theories that have high energy behavior inconsistent with the experimental boundaries of inflation scenarios.
A lot of inflation theories that have been viable candidates, receiving serious discussion almost ever since the need for inflation in a cosmology theory was discovered in the 1970s (around the same time that the Standard Model was formulated), have been ruled out by the latest round of Planck data. Planck strongly disfavors power law inflation, the simplest hybrid inflationary models, simple monomial models with n > 2, single fast roll inflation scenarios, multiple stage inflation scenarios, inflation scenarios with flat or concave potentials, dynamical dark energy, time variations of the fine structure constant are all strongly disfavored. Any theory that would create non-Gaussian statistics of the CMB anisotropies, non-flat universes, tensor modes, or statistically discernable deviations from isotropy at L >50 are ruled out.
If your theory was phenomenologically distinct from "single slow roll inflation scenarios with convex potential" in any non-subtle way, you were wrong, thanks for playing.
I will need to read more to fully understand these implications myself, but more inflation theories have died today than on any previous day in history and than will on any day to come in the future (since there are fewer inflation theories left than the number of inflation theories killed today). A book length catalog (300 pages) of the pre-March 21 ranks of inflation theories is available at arxiv. What is inflation?
Dark energy is broadly similar to inflation, and is thought to be causing the expansion of the present-day universe to accelerate. However, the energy scale of dark energy is much lower, 10−12 GeV, roughly 27 orders of magnitude less than the scale of inflation.Basically, inflation this involves a scalar field called the inflaton that is dissipated in the inflation process.
According to inflation theory, the inflaton field provided the mechanism to drive a period of rapid expansion from 10−35 to 10−34 seconds after the initial expansion that formed the universe.
The inflaton field's lowest energy state may or may not be a zero energy state. This depends on the chosen potential energy density of the field. Prior to the expansion period, the inflaton field was at a higher-energy state. Random quantum fluctuations triggered a phase transition whereby the inflaton field released its potential energy as matter and radiation as it settled to its lowest-energy state. This action generated a repulsive force that drove the portion of the universe that is observable to us today to expand from approximately 10−50 metres in radius at 10−35 seconds to almost 1 metre in radius at 10−34 seconds.
Inflaton conforms to the convention for field names, and joins such terms as photon and gluon. The process is "inflation"; the particle is the "inflaton".
* Second, the lack of scale invariance in the power law of cosmic background radiation has been confirmed parameterized at a value of about 0.96 with 1.00 being a pure scale invariant power law. The lamda CDM model has a parameter to describe this deviation, but no mechanism to make it happen. This is a prediction of many inflation models.
* Third, something weird seems to be going on between L's 20 and 30. This is the only material respect in which the Planck data deviate from the lamda CDM model. Intuitively, it seems very plausible that the source of the L's 20 to 30 deviation and the source of the lack of scale invariance could be the same. Some small second order effect not captured by the six parameter lamda CDM model appears to be involved here.
For example, both the lack of scale invariance and the weirdness from L's 20 to 30 are both plausible consequences of the place on the spectrum from hot dark matter to cold dark matter than a dark matter particle resides.
Roughly speaking, in simple single dark matter particle models, the mass of the particle (or the dominant particle if there are multiple kinds but one has a predominant impact on phenomenology in the way the first generation fermions that form protons, neutrons and atoms in the Standard Model do) governs where deviations in large scale structure related to scale arise. Hot dark matter has almost no large scale structure. Warm dark matter gives rise to roughly the amount of large scale structure we observe. Cold dark matter gives rise to more dwarf galaxies and large scale structure that is more finely grained than we observe.
All of this, of course, is model dependent and the generalizations are based on a simple, almost completely non-interacting dark sector with just one kind of particle and no significant new forces from those know to use already. A single instance of inflation alone is enough to get the observed scale invariance in a lamda CDM model, but doesn't explain the L's 20 to 30 anomaly, which could have an entirely different source (or simply be random variation that is improbable but has no deeper cause, or experimental error).
Some persepective on this anomaly from this blog:
Planck sees the same large scale anomalies as WMAP, thus confirming that they are real rather than artifacts of some systematic error or foreground contamination (I believe Planck even account for possible contamination from our own solar system, which WMAP didn't do). These anomalies include not enough power on large angular scales (ℓ≤30 ), an asymmetry between the power in two hemispheres, a colder-than-expected large cold spot, and so on.
The problem with these anomalies is that they lie in the grey zone between being not particularly unusual and being definitely something to worry about. Roughly speaking, they're unlikely at around a 1% level. This means that how seriously you take them depends a lot on your personal prejudices priors. One school of thought – let's call it the "North American school" – tends to downplay the importance of anomalies and question the robustness of the statistical methods by which they were analysed. The other – shall we say "European" – school tends instead to play them up a bit: to highlight the differences with theory and to stress the importance of further investigation. Neither approach is wrong, because as I said this is a grey area. But the Planck team, for what it's worth, seem to be in the "European" camp.
* Fourth, the fact that space-time is "flat" to a precision of 0.1% is remarkable given that we conceive of general relativity as a warping of space-time. Overwhelmingly, this warping of space-time due to gravity is local rather than global.
What drives the conclusions about inflation?
The preference for a simple model is driven by several factors:
(1) The data is a good fit to a simple power law with a not quite scale invariant exponent of about 0.96 rather than 1.0 (with a five sigma difference from a 1.0 value) that shows no statistically significant tendency to change over time (i.e. the best fit value for the running of the spectral index is about 1.5 sigma from zero at -0.0134 +/- 0.0090).
(2) The best fit value for a tensor contribution has its best fit at or nearly at zero. The absence of any indication of a tensor mode in the inflaton as opposed to a mere scalar inflaton seems to be another important factor that is driving the exclusion of other models. "In a model admitting tensor fluctuations, the 95% CL bound on the tensor-to-scalar ratio is r0.002 < 0.12 (< 0.11) using Planck+WP (plus high-L`). This bound on r implies an upper limit for the inflation energy scale of 1.9*10^16 GeV . . . at 95% CL." (3) The best fit values of inflation scenarios are likewise almost maximally concave (i.e. potential drops more in the early part of a decline in inflaton potential than later on). The Planck report concludes by noting that: "The simplest inflationary models have passed an exacting test with the Planck data. The full mission data including Planck’s polarization measurements will help answer further fundamental questions, including the possibilities for nonsmooth power spectra, the energy scale of inflation, and extensions to more complex models."
Evidence for a GUT?
The coincidence of the Planck upper limits on inflation energy scale with the completely independently derived grand unification scale based upon the running of the Standard Model (or SUSY) coupling constants is impressive. Even if SUSY is not the way the coupling constants converge, the notion of a grand unification at inflation energies by some means (perhaps by considering quantum gravity theories) is aesthetically very tempting.
Mostly Off Topic Other Items Of Interest:
More On Why We Don't Need SUSY
Woit has an interesting post on a talk by LHC physicist Joe Lyyken on why the "hierachy problem" that SUSY seeks to solve isn't actually a problem with anything but how theoretical physicists are thinking about the issue.
Dark Matter and MOND
* Somewhat off topic, in January of this year, an interesting new MOND paper by MOND inventor Milgrom and two co-authors was published (arguing that much of the dark matter effects are due to a modification of the law of gravity rather than dark matter particles) setting forth a MOND cosmology.
* The dominant unresolved question in physics remains the need to understand dark matter phenomena. As I've said before, and as Planck confirms once again, a simple cosmological constant completely explains dark energy within the context of the same theory of General Relativity that we've had for a century now - dark energy, rather than being mysterious, is a solved problem.
General relativity does not explain dark matter phenomena which are operationally defined as deviations from the predictions of general relativity that are observed by astronomers that don't relate to "inflation" in cosmology. The Standard Model provides no dark matter candidates and the LHC is foreclosing more of them. The lamda CDM model separately accounts for mass from baryons, neutrinos, radiation and effective mass-energy from the cosmological constant and has dark matter left over, but this six parameter fit to cosmic background radiation data collected as WMAP and Planck, for example, does very little to specify the nature of the dark matter component. Direct dark matter searches that have shown any dark matter signals contradict each other and are condicted by searches that have come up empty in roughly the 10 GeV to 100 GeV range for all but the very lowest cross-sections of interaction (well below that of neutrinos).
Simulations have shown that WIMPS or other simple Cold Dark Matter scenarios produce more dwaft galaxies than we observe and none of the Cold Dark Matter models can rival MOND in closely approximating almost all galaxy level dark matter effects in a predictive manner with just a single experimentally measured constant. The cuspy dark matter halos predicted by Cold Dark Matter models are likewise contrary to what we observe, which is inferred halo distributions of dark matter that look more like rugby balls with their long axis passing through a galaxy's central black hole and poking up out from the plane of the galaxy's rotation.
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