Tuesday, February 28, 2023

Black Holes Are Not A Source Of Dark Energy

This recent claim picked up in the mass media struck me as dubious. A new preprint explains why.
The hypothesis that the mass of BHs increases with time according to the same law as the volume of the part of the Universe containing it and therefore the population of BHs is similar to dark energy in its action was recently proposed. We demonstrate the reasons why it cannot be accepted, even if all the assumptions on which this hypothesis is based are considered true.
S L Parnovsky, "Can black holes be a source of dark energy?" arXiv:2302.13333 (February 26, 2023).

Wednesday, February 22, 2023

Homo Erectus Held On Until 100,000 Years Ago In Indonesia

The three year old article quoted below speculates that some Southeast Asians may have a small amount of Homo Erectus ancestry. But I think that this is unlikely to have happened directly, due to the lack of overlap in human and Homo Erectus occupation and genetic differences too great to permit the birth of a hybrid individual (although it could be that modern humans dealt the death blow to relict Homo Erectus when they first encountered them en route to Australia and Papua New Guinea, which contrary to the Science article, happened closer to 70,000 years ago, perhaps shortly after the volcanic Toba eruption in Indonesia ca. 74,000 years ago).

But, it isn't inconceivable that an archaic Denisovan individual, a sister species to the Neanderthals and one source of archaic hominin admixture in modern humans, might have admixed with Homo Erectus, with whom they probably co-habited in Indonesia for thousands of years, leading to a small proportion of a modern human with Denisovan ancestry's Denisovan sourced DNA including Homo Erectus ancestry (perhaps about a percent of a percent, i.e. a few parts per 10,000). Indeed, there are some hints in Denisovan DNA of small amounts of admixture with H. erectus, although this is too small to be definitively identified separately in modern humans with Denisovan ancestry (which can be as high as about 5% of some aboriginal Australians and Papuans and Negritos from the Philippines today).

The time coincidence with the genetically estimated most recent common ancestor of Neanderthals and Denisovans, however, is a pretty close match to the time that H. erectus disappears in the archaeological record outside Indonesia, which also isn't that remote from the first appearance of modern humans. Therefore, it wouldn't be unreasonable to guess that modern humans, Neanderthals, and Denisovans were the cause of the extinction of H. erectus in their respective regions. 

If so, Denisovans may have been a very late arrival to the island of Java (i.e. ca. 100,000 years ago or later) and cohabited with them only briefly, which could explain the ability to H. erectus to persist there while going extinct everywhere else. It could also be the case that Denisovan's brought about the extinction of H. erectus in Indonesia tens of thousands of years before modern humans arrived on a path cleared by the Toba eruption.

H. floresiensis a.k.a. "hobbits" also co-habited in Indonesia with H. erectus and Denisovans (and possibly even modern humans), although it is unclear when they first appeared on the island of Flores. But, they were probably an even more basal (i.e. archaic) species of hominin than H. erectus such as H. habilis. So, they probably didn't directly admix genetically with Denisovans or modern humans due to their large genetic distance from them.
When seafaring modern humans ventured onto the island of Java some 40,000 years ago, they found a rainforest-covered land teeming with life—but they weren’t the first humans to call the island home. Their distant ancestor, Homo erectus, had traveled to Java when it was connected to the mainland via land bridges and lived there for approximately 1.5 million years. These people made their last stand on the island about 100,000 years ago, long after they had gone extinct elsewhere in the world, according a new study assigning reliable dates to previously found H. erectus fossils. 
. . . 
The newly dated fossils also bookend the existence of a remarkably long-lived human species, says Patrick Roberts, an archaeologist at the Max Planck Institute for the Science of Human History in Jena, Germany, who wasn’t involved with the study. 
. . .

H. erectus arose in Africa about 1.9 million years ago. These toolmakers with relatively large brains migrated out of Africa and across Asia, crossing into Java by land bridges about 1.6 million years ago, when savanna-like open woodland covered much of the land. Later, sea levels rose, isolating these ancient Javans on an island. Meanwhile, in Africa and mainland Asia, H. erectus disappeared by about 500,000 years ago. 
. . . 
In 2008 and 2010, [the new study’s lead author, paleoanthropologist Russell] Ciochon’s team re-excavated the site, turning up 867 new fossils belonging to deer, wild cattle, and an extinct, elephantlike animal called a stegodon. Based on photographs and documents from the original excavation, they established that some of the newly found animal fossils came from the same rich bone bed as the H. erectus fossils. The researchers applied five types of radiometric dating, including a new method that provides both minimum and maximum dates, to those animal fossils and the sediments around them. The team concluded that the bones were buried between 117,000 and 108,000 years ago, the researchers report . . . in Nature.
From Science (reporting on a December 18, 2019 article in Nature).

Friday, February 17, 2023

Sabine Hossenfelder On "What's Going Wrong With Particle Physics?"

This video is a great, compact summary of the sociological problems with the particle physics field, essentially summing up the premises of her book Lost in Math, namely, that lots of the theories being pursued are either not really problems, or are solutions that are profoundly disfavored empirically but are still being doggedly pursued in ever more byzantine variations.

Married To A Model

This year's Valentine's Day poem from 4 gravitons:

Married to a Model

If you ever face a physics class distracted,
Rappers and footballers twinkling on their phones,
Then like an awkward youth pastor, interject,
“You know who else is married to a Model?”

Her name is Standard, you see,
Wife of fifty years to Old Man Physics,
Known for her beauty, charm, and strangeness too.
But Old Man Physics has a wandering eye,
and dreams of Models Beyond.

Let the old man bend your ear,
you’ll hear
a litany of Problems.

He’ll never understand her, so he starts.
Some matters she holds weighty, some feather-light
with nary rhyme or reason
(which he is owed, he’s sure).

She’s unnatural, he says,
(echoing Higgins et al.),
a set of rules he can’t predict.
(But with those rules, all else is possible.)

Some regularities she holds to fast, despite room for exception,
others breaks, like an ill-lucked bathroom mirror.

And then, he says, she’ll just blow up
(when taken to extremes),
while singing nonsense in the face of Gravity.

He’s been keeping a careful eye
and noticing anomalies
(and each time, confronting them,
finds an innocent explanation,
but no matter).

And he imagines others
with yet wilder curves
and more sensitive reactions
(and nonsense, of course,
that he’s lived fifty years without).

Old man physics talks,
that’s certain.
But beyond the talk,
beyond the phases and phrases,
(conscious uncoupling, non-empirical science),
he stays by her side.

He knows Truth, 
in this world,
is worth fighting for.

Genius In Action

I went to a conference which was totally about my specialization, and one Ph.D student gave his presentation, sounding very nervous. I could barely follow his talk, and thought I must have forgotten a lot of things, it seemed beyond my knowledge. 
At the any questions stage, someone stood up, and suggested one part was wrong, with an alternative explanation, which seemed convincing - lots of people nodding, as he said what would have happened if the student speaker had been right. 
Then instantly a second person stood up and said the first critic was right about the error, but his explanation was wrong, and explained why it was wrong and gave a second alternative explanation. Wow, criticizing an explanation and alternative explanation on a complex subject he had just heard 10 seconds ago. Lots of people nodding and ooing "oh yes." 
Then a third person stood up, gave his name and was immediately recognized as a Nobel prize winner, (who just happened to be in town visiting an friend), but not a specialist in the topics of the conference. He told the original presenter what their error was, then told the first critic what was really wrong with his alternative explanation, told the second critic that he was wrong in each alternative he had offered (including his wrong explanation of what was wrong) and then explained what was really really going on.

Silence. Every one sat going through what this not a specialist had said about everything, and slowly we all started nodding in agreement. We were all wiped out by how he could correct things outside of his own specialism and also how we all took so long to work out he was right. Genius is truly impressive when it swings into action.

From here (with minor spelling and punctuation edits and paragraph breaks added). 

Wednesday, February 15, 2023

The Únětice Culture

The biggest unsolved mystery related to the Únětice culture is its language and its possible role as the linguistic ancestor of later Western European linguistic developments. 

It might have spoken, for example, a language which is a common ancestor of Italic and Celtic languages (i.e. proto-Italo-Celtic).

It is hard to know definitively what language its people spoke, however, because the culture didn't have a written language. But, similarities and differences between artifacts at Únětice sites and in other archaeological cultures, and the genetics of people from the culture, could inform this debate. Genetically, according to Wikipedia at the link above:
Haak et al. 2015 examined the remains of 8 individuals of the Unetice culture buried in modern-day Germany c. 2200–1800 BC. The 3 samples of Y-DNA extracted belonged to Y-haplogroups I2a2I2c2 and I2, while the 8 samples of mtDNA extracted were determined to belong to haplogroup I3a (2 samples), U5a1W3a1U5b2a1bH4a1a1H3 and V. The examined Unetice individuals were found to be very closely related to peoples of the earlier Yamnaya cultureBell Beaker culture and Corded Ware culture. Their amount of steppe-related ancestry is comparable to that of some modern Europeans.

Allentoft et al. 2015 examined the remains of 7 individuals of the Unetice culture buried in modern-day Poland and Czech Republic from c. 2300–1800 BC. The 7 samples of mtDNA extracted were determined to belong to haplogroup U4U2e1f1H6a1bU5a1b1K1a4a1T2b and K1b1a. An additional male from the late Corded Ware culture or early Unetice culture in Łęki Małe, Poland of c. 2300–2000 BC was found to be a carrier of the paternal haplogroup R1b1a and the maternal haplogroup T2e. It was found that the people of the Corded Ware culture, Bell Beaker culture, Unetice culture and Nordic Bronze Age were genetically very similar to one another, and displayed a significant amount of genetic affinity with the Yamnaya culture.
The latest find about the culture, reported below, is also a useful reminder of how small scale even Bronze Age civilizations frequently were. It involves a settlement with the geographic size and population of a few urban residential city blocks, yet archaeologists see it as "a metallurgical centre and a stronghold of power" in that archaeological culture.
The Únětice culture, named for a type-site cemetery in the village of Únětice, was a Bronze Age culture that first emerged around 2300–1600 BC. The culture is distinguished by its characteristic metal objects, including ingot torcs, flat axes, flat triangular daggers, bracelets with spiral ends, disk- and paddle-headed pins, and curl rings, which are distributed over a wide area of Central Europe and beyond. One of the most important discoveries attributed to the Únětice Culture is the Nebra sky disc, found buried on the Mittelberg hill near Nebra in Germany. The Nebra sky disc is made from bronze and has a blue-green patina inlaid with gold symbols, that archaeologists have interpreted to represent the Sun or full moon, a lunar crescent, and the stars.

Archaeologists from the Adam Mickiewicz University have discovered a fortified Únětice Culture settlement, located near the town of Śmigiel, in the Kościan County of Poland. The settlement was situated on an island promontory, where 4,000-years-ago there was a lake on the edge of the Samica Kościańska valley, which today is a flowering meadow. The promontory was cut off from the mainland by a deep moat or ditch, with at least two rows of wooden palisades creating a fortified enclosure. The settlement occupied an area of 3.7 acres and supported a population of up to 100 people, which the researchers suggest was a metallurgical centre and a stronghold of power in the northern reaches of the Únětice Culture.

The results of the study, published in the “Journal of Archaeological Science: Reports” reveals that the settlement was discovered after a geoarchaeological analysis of the former lake which was formed when a glacier retreated around 18,000-years-ago. Based on core samples obtained by drilling, the lake started to shrink around 800 BC, eventually turning into a large bog at the turn of the era.
From here.

Tuesday, February 14, 2023

What Drives The Hubble Tension?

Stacy McGaugh suggests in his latest blog post that the Hubble tension is probably due to the estimate of Hubble's constant from the cosmic microwave background (CMB) which has gotten lower as greater precision measurements of it have been made, rather than from errors in recent time Hubble constant measurements as it is more common to suppose. 

He argues that observed early galaxy formation, which is contrary to the LambdaCDM model and thus not accounted for by it when calculating the early time Hubble constant from the CMB, is likely to be a big part of the discrepancy.

Friday, February 10, 2023

Blogroll Purge

Many of the "notable links" in the sidebar are dead or go to defunct blogs. I am purging them from the sidebar, but saving the names of the linked sites and the links that aren't dead for dormant blogs here for future reference to access the existing posts at those links, and also, in case the links are restored or the blogs are revived. I've also resorted the sidebar links alphabetically. The links removed were:

Tuesday, February 7, 2023

A New Top Quark Mass Measurement

The latest top quark mass measurement at the Large Hadron Collider (LHC) is on the low side relative to previous measurements and the global average (which is 172.69 ± 0.30 from direct measurements), and is fairly precise despite using a fairly complex set of decay products to measure it. 

The new measurement is 1.93 sigma from the global average, so the new measurement is just barely consistent with the global average. In contrast, many other recent LHC measurements of the top quark mass have been high (almost two sigma high in at least one case) relative to the global average.
The mass of the top quark is measured in 36.3 fb−1 of LHC proton-proton collision data collected with the CMS detector at s√ = 13 TeV. The measurement uses a sample of top quark pair candidate events containing one isolated electron or muon and at least four jets in the final state. For each event, the mass is reconstructed from a kinematic fit of the decay products to a top quark pair hypothesis. A profile likelihood method is applied using up to five observables to extract the top quark mass. The top quark mass is measured to be 171.77 ± 0.37 GeV. This approach significantly improves the precision over previous measurements.
CMS Collaboration, "Measurement of the top quark mass using a profile likelihood approach with the lepton+jets final states in proton-proton collisions at s√ = 13 TeV" arXiv:2302.01967 (February 3, 2023).

Monday, February 6, 2023

Dark Matter Still Has Nothing On MOND In The Milky Way

The more complex dark matter particle mass models of the Milky Way, perform not better in describing what we see with other telescopes than the far simply MOND model when it comes to the Milky Way's rotation curve.
We use data from the Gaia DR3 dataset to estimate the mass of the Milky Way (MW) by analyzing the rotation curve in the range of distances 5 kpc to 28 kpc. 
We consider three mass models: the first model adds a spherical dark matter (DM) halo, following the Navarro-Frenk-White (NFW) profile, to the known stellar components. The second model assumes that DM is confined to the Galactic disk, following the idea that the observed density of gas in the Galaxy is related to the presence of more massive DM disk (DMD), similar to the observed correlation between DM and gas in other galaxies. The third model only uses the known stellar mass components and is based on the Modified Newton Dynamics (MOND) theory. 
Our results indicate that the DMD model is comparable in accuracy to the NFW and MOND models and fits the data better at large radii where the rotation curve declines but has the largest errors. For the NFW model we obtain a virial mass M(vir)=(6.5±0.3)×10^11M⊙ with concentration parameter c=14.5, that is lower than what is typically reported. In the DMD case we find that the MW mass is M(d)=(1.6±0.5)×10^11M⊙ with a disk's characteristic radius of Rd=17 kpc.
Francesco Sylos Labini, et al., "Mass models of the Milky Way and estimation of its mass from the GAIA DR3 data-set" arXiv:2302.01379 (February 2, 2023) (accepted for publication in The Astrophysical Journal).

Friday, February 3, 2023

Physics Needs Better Literature Reviews

One of my favorite physicists, Stacy McGaugh, reacting to a tweet expressing the same opinion by another of my favorite physicists, Sabine Hossenfelder, bemoans a cultural and institutional problem with the fundamental physics community that I agree is a serious one. 

What is it?

Physicists routinely publish papers that fail to review the literature sufficiently to identify the fact that previous published work already rules out, disproves, or contradicts the hypotheses that they are advancing in their papers.

It is a standard and almost universal practice that pretty much every thesis, dissertation, and published physics paper (other than a very short letter preliminarily reporting a very narrow measurement or result before a full length analysis of the results can be published) contains some review of the literature that brings the reader to the point of scientific knowledge where the matters being addressed by the authors in the new thesis, dissertation, or paper begins.

But, in many cases, this literature review is half-hearted and perfunctory, and misses key prior work relevant to the new paper.

For example, one of my pet peeves is when a paper says that their proposal is "well motivated" by concepts developed decades earlier that have later been found to be deeply flawed.

This isn't a "mortal sin". The physics literature is vast and it grows every week. Not everyone in the discipline can devote the time that I do to reading every abstract in a whole range of related fundamental physics categories every day when it comes out on arXiv. And, there are multiple ways of looking at a problem that can make identifying relevant papers challenging (the same issue comes up in doing patent and trademark searches, or searching for precedents related to a legal issue).

But, if you are going to be advancing a new hypothesis in this field, you really should do a proper literature review (and more generally, you should really know the literature relevant to your work from multiple perspectives) before advancing theories that are contradicted by other observational evidence or theoretical considerations that you don't mention or engage with in your paper.

You don't have to agree with everything else that has ever been published. Sometimes previously published papers are incorrect and you are right. But when that happens, rather than ignoring what previously published papers have to say, you really should engage with prior contradictory papers and explain why you think that their observations or analysis is flawed or inapplicable, and thus doesn't actually contradict your work.

You don't necessarily have to spell out the contradictions or flaws of the prior work in full in every new paper in a series of papers developing an idea. It is sufficient to do it once in your first paper identifying what you believe is a flaw in prior work and then to cite that that discussion, incorporating it by reference and with a brief mention, in later papers. But that is very different from ignoring contradictory prior work entirely.

If the authors of physics papers did more diligent and comprehensive literature reviews (and peer reviewers did a better job of insisting on better quality reviews of the literature which would catch both many innocent omissions and many cases where prior contradictory work is willfully ignored), the quality of the papers that did get published would be greater. This is because a lot of speculative garbage papers that ignore known insurmountable obstacles to their work would be dropped before they were presented.

Mirror Cosmology Recapped

Here is a recap, all in one place, of work on mirror cosmology with an anti-matter universe before the Big Bang that is a mirror of our own and our own matter dominated universe that I've previously blogged, stripped of (probably wrong) speculations about dark matter and right handed neutrinos:

We argue that the Big Bang can be understood as a type of mirror. We show how reflecting boundary conditions for spinors and higher spin fields are fixed by local Lorentz and gauge symmetry, and how a temporal mirror (like the Bang) differs from a spatial mirror (like the AdS boundary), providing a possible explanation for the observed pattern of left- and right-handed fermions. By regarding the Standard Model as the limit of a minimal left-right symmetric theory, we obtain a new, cosmological solution of the strong CP problem, without an axion.
Latham Boyle, Martin Teuscher, Neil Turok, "The Big Bang as a Mirror: a Solution of the Strong CP Problem" arXiv:2208.10396 (August 22, 2022). The body text states:
In a series of recent papers, we have argued that the Big Bang can be described as a mirror separating two sheets of spacetime. Let us briefly recap some of the observational and theoretical motivations for this idea.

Observations indicate that the early Universe was strikingly simple: a fraction of a second after the Big Bang, the Universe was radiation-dominated, almost perfectly homogeneous, isotropic, and spatially flat; with tiny (around 10^−5) deviations from perfect symmetry also taking a highly economical form: random, statistically gaussian, nearly scale-invariant, adiabatic, growing mode density perturbations. Although we cannot see all the way back to the bang, we have this essential observational hint: the further back we look (all the way back to a fraction of a second), the simpler and more regular the Universe gets. This is the central clue in early Universe cosmology: the question is what it is trying to tell us.

In the standard (inflationary) theory of the early Universe one regards this observed trend as illusory: one imagines that, if one could look back even further, one would find a messy, disordered state, requiring a period of inflation to transform it into the cosmos we observe.

An alternative approach is to take the fundamental clue at face value and imagine that, as we follow it back to the bang, the Universe really does approach the ultra-simple radiation-dominated state described above (as all observations so far seem to indicate).

Then, although we have a singularity in our past, it is extremely special. Denoting the conformal time by τ , the scale factor a(τ) is ∝ τ at small τ so the metric g^(µν) ∼ a(τ)^(2ηµν) has an analytic, conformal zero through which it may be extended to a “mirror-reflected” universe at negative τ.

[W]e point out that, by taking seriously the symmetries and complex analytic properties of this extended two-sheeted spacetime, we are led to elegant and testable new explanations for many of the observed features of our Universe including: . . . (ii) the absence of primordial gravitational waves, vorticity, or decaying mode density perturbations; (iii) the thermodynamic arrow of time (i.e. the fact that entropy increases away from the bang); and (iv) the homogeneity, isotropy and flatness of the Universe, among others.

In a forthcoming paper, we show that, with our new mechanism for ensuring conformal symmetry at the bang, this picture can also explain the observed primordial density perturbations.

In this Letter, we show that: (i) there is a crucial distinction, for spinors, between spatial and temporal mirrors; (ii) the reflecting boundary conditions (b.c.’s) at the bang for spinors and higher spin fields are fixed by local Lorentz invariance and gauge invariance; (iii) they explain an observed pattern in the Standard Model (SM) relating left- and right-handed spinors; and (iv) they provide a new solution of the strong CP problem. . . .

In this paper, we have seen how the requirement that the Big Bang is a surface of quantum CT symmetry yields a new solution to the strong CP problem. It also gives rise to classical solutions that are symmetric under time reversal, and satisfy appropriate reflecting boundary conditions at the bang.

The classical solutions we describe are stationary points of the action and are analytic in the conformal time τ. Hence they are natural saddle points to a path integral over fields and four-geometries. The full quantum theory is presumably based on a path integral between boundary conditions at future and past infinity that are related by CT-symmetry. The cosmologically relevant classical saddles inherit their analytic, time-reversal symmetry from this path integral, although the individual paths are not required to be time-symmetric in the same sense (and, moreover may, in general, be highly jagged and non-analytic).

We will describe in more detail the quantum CT-symmetric ensemble which implements (12), including the question of whether all of the analytic saddles are necessarily time-symmetric, and the calculation of the associated gravitational entanglement entropy, elsewhere.
Another paper discusses one of the earlier papers by the authors above and elaborates on the foundation of their work:
In a recent work, Turok, Boyle and Finn hypothesized a model of universe that does not violate the CPT-symmetry as alternative for inflation. With this approach they described the birth of the Universe from a pair of universes, one the CPT image of the other, living in pre- and post-big bang epochs. The CPT-invariance strictly constrains the vacuum states of the quantized fields, with notable consequences on the cosmological scenarios.

Here we examine the validity of this proposal by adopting the point of view of archaic cosmology, based on de Sitter projective relativity, with an event-based reading of quantum mechanics, which is a consequence of the relationship between the universal information reservoir of the archaic universe and its out-of-equilibrium state through quantum jumps. In this scenario, the big bang is caused by the instability of the original (pre)vacuum with respect to the nucleation of micro-events that represent the actual creation of particles.

Finally, we compare our results with those by Turok et al., including the analytic continuation across the big bang investigated by Volovik and show that many aspects of these cosmological scenarios find a clear physical interpretation by using our approach. Moreover, in the archaic universe framework we do not have to assume a priori the CPT-invariance like in the other models of universe, it is instead a necessary consequence of the archaic vacuum structure and the nucleation process, divided into two specular universes.
Ignazio Licata, Davide Fiscaletti, Leonardo Chiatti, Fabrizio Tamburini, "CPT Symmetry in Projective de Sitter Universes" arXiv:2002.07550 (February 18, 2020).
The universe before the Big Bang is the CPT reflection of the universe after the bang, so that the state of the universe does not spontaneously violate CPT. The universe before the bang and the universe after the bang may be viewed as a universe/anti-universe pair, created from nothing. The early universe is radiation dominated and inflationary energy is not required. We show how CPT selects a preferred vacuum state for quantum fields on such a cosmological spacetime. This, in turn, leads to a new view of the cosmological matter/anti-matter asymmetry[.]
Latham Boyle, Kieran Finn, Neil Turok, "The Big Bang, CPT, and neutrino dark matter" arXiv:1803.08930 (March 23, 2018).

Some of their key earlier papers by some of these authors (which I haven't yet read and don't necessarily endorse) are: "Gravitational entropy and the flatness, homogeneity and isotropy puzzles" arXiv:2201.07279, "Two-Sheeted Universe, Analyticity and the Arrow of Time" arXiv:2109.06204, and "CPT-Symmetric Universe" arXiv:1803.08928. 
In the multiverse, the universes can be created in entangled pairs with spacetimes that are both expanding in terms of the time variables experienced by internal observers in their particle physics experiments. The time variables of the two universes are related by an antipodal-like symmetry that might explain why there is no antimatter in our universe: at the origin, antimatter is created, by definition and for any observer, in the observer's partner universe. The Euclidean region of the spacetime that separates the two universes acts as a quantum barrier that prevents matter-antimatter from collapse.
Salvador J. Robles-Perez, "Restoration of matter-antimatter symmetry in the multiverse" arXiv:1706.06304 (June 20, 2017).

In physical cosmology, cosmic inflation, cosmological inflation, or just inflation, is a theory of exponential expansion of space in the early universe. The inflationary epoch lasted from 10^−36 seconds after the conjectured Big Bang singularity to some time between 10^−33 and 10^−32 seconds after the singularity. Following the inflationary period, the universe continued to expand, but at a slower rate. The acceleration of this expansion due to dark energy began after the universe was already over 7.7 billion years old (5.4 billion years ago). . . . It was developed further in the early 1980s. It explains the origin of the large-scale structure of the cosmos. Quantum fluctuations in the microscopic inflationary region, magnified to cosmic size, become the seeds for the growth of structure in the Universe. Many physicists also believe that inflation explains why the universe appears to be the same in all directions (isotropic), why the cosmic microwave background radiation is distributed evenly, why the universe is flat, and why no magnetic monopoles have been observed.
Magnetic monopoles are already a non-existent problem so in this respect, cosmological inflation is merely ruling out a rubbish theory with no observational support.

Thursday, February 2, 2023

Galaxies Ten Billion Years Ago Look A Lot Like Galaxies Today

The LambdaCDM model expects galaxies to take longer to appear when they do and to evolve significantly over time scales of billions of years. But, the latest observations of galaxies as much as 10 billion years old suggest that galaxies then had basically the same dynamics that they do now
We study the dynamics of cold molecular gas in two main-sequence galaxies at cosmic noon (zC-488879 at z≃1.47 and zC-400569 at z≃2.24) using new high-resolution ALMA observations of multiple 12CO transitions. For zC-400569 we also re-analyze high-quality Hα data from the SINS/zC-SINF survey. 
We find that (1) Both galaxies have regularly rotating CO disks and their rotation curves are flat out to ∼8 kpc contrary to previous results pointing to outer declines in the rotation speed Vrot; (2) The intrinsic velocity dispersions are low (σCO≲15 km/s for CO and σHα≲37 km/s for Hα) and imply Vrot/σCO≳17−22 yielding no significant pressure support; (3) Mass models using HST images display a severe disk-halo degeneracy: models with inner baryon dominance and models with "cuspy" dark matter halos can fit the rotation curves equally well due to the uncertainties on stellar and gas masses; (4) Milgromian dynamics (MOND) can successfully fit the rotation curves with the same acceleration scale a0 measured at z≃0. 
The question of the amount and distribution of dark matter in high-z galaxies remains unsettled due to the limited spatial extent of the available kinematic data; we discuss the suitability of various emission lines to trace extended rotation curves at high z. Nevertheless, the properties of these two high-z galaxies (high Vrot/σV ratios, inner rotation curve shapes, bulge-to-total mass ratios) are remarkably similar to those of massive spirals at z≃0, suggesting weak dynamical evolution over more than 10 Gyr of the Universe's lifetime.
Federico Lelli, Zhi-Yu Zhang, Thomas G. Bisbas, Lingrui Lin, Padelis Papadopoulos, James M. Schombert, Enrico Di Teodoro, Antonino Marasco, Stacy S. McGaugh, "Cold gas disks in main-sequence galaxies at cosmic noon: Low turbulence, flat rotation curves, and disk-halo degeneracy" arXiv:2302.00030 (January 31, 2023) (Accepted for publication in Astronomy and Astrophysics).