Monday, May 31, 2021

Physics Anomalies Recapped

"Core Theory", which is to say the Standard Model of Particle Physics and General Relativity (with a cosmological constant), have only a few issues where there are serious tensions with the data or other fundamental problems.

1. GR and the SM are theoretically inconsistent.

First, the quantum mechanical, probabilistic Standard Model of Particle Physics has theoretical inconsistencies with the classical, deterministic theory that is General Relativity with a cosmological constant. 

Most likely, we need some sort of quantum gravity theory to solve this problem.

2. Dark matter phenomena don't have a widely accepted specific explanation that works in all circumstances.

Second, neither General Relativity as conventionally operationalized, nor any of the fundamental particles of the Standard Model, nor composite particles made of them, can explain the phenomena attributed to dark matter. 

All specific explanations of dark matter phenomena that have received intense examination from multiple independent investigators have serious flaws, and many potentially plausible explanations have not yet been seriously vetted.

(Note that "dark energy" in contrast, is satisfactorily explained by the cosmological constant of General Relativity which is part of exiting "Core Theory", although generalizing the cosmological constant to a quantum gravity theory is particularly challenging and there are challenges to this explanation.)

There are proposals (most notably this one) that potentially provide a road map to resolving these first two problems. 

But no proposal that could solve all of the dark sector phenomena issues have wide acceptance. In particular, the LambdaCDM cosmology, which is the so called "Standard Model of Cosmology" has many well know flaws that make it impossible to reconcile with all of the observational evidence.

Fortunately, physicists are devoting a great deal of effort on myriad experimental and theoretical fronts from particle accelerator experiments, to cosmic ray analysis, to gravitational wave detectors, to photon astronomy at every possible wavelength, to neutrino astronomy, to analytical studies, to many body simulations, to consider every possible explanation for dark matter and dark energy phenomena. 

Overwhelmingly, these experiments and analyses are ruling out possible explanations, and narrowing the parameter space of possible solutions within various leading paradigms. 

It isn't a very efficient process. Every week, many proposals that are already overwhelmingly disfavored by existing observational data and analysis are introduced unaware of what came before it in slightly different subfields of the collective scientific effort to understand dark matter and dark energy phenomena. But I am nonetheless encouraged that the firehose of new data will help to bring us closer to the truth eventually.

Many proposals (although none that I find very plausible) would require significant beyond the Standard Model physics with at least a new fundamental fermion or boson that constitutes dark matter and a new fundamental force mediated a massive carrier boson that governs the self-interactions (and possibly also ordinary matter interactions) of dark matter.

3. Are lepton universality violations real, and why or why not is this the case?

Third, lepton universality violations observed in a couple of kinds of B meson decays, in which different flavors of charged leptons (electrons, muons and taus) behave differently in ways not obviously due to their rest masses alone, seem to be inconsistent with the Standard Model.

This is really the only truly significant anomaly in high energy physics that could plausible give rise to new physics that is known today.

The fact that heavier charged leptons are more scarce than lighter ones is itself notable, and is suggestive of potential Standard Model solutions. So is the fact that experimental tests in a great many other contexts do no show lepton universality violations. In other words, I think that there is most probably something subtle wrong with how the Standard Model prediction is modeled that doesn't reflect something prosaic that the experimental measurements are seeing.

There are many very exotic explanations of this phenomena that have been proposed. But, I still expect that there are much better than even odds that a Standard Model explanation to it can be found. 

Also, even if new physics are required to explain it, these new physics, much like the new physics involved in inserting a CP violating phase into the CKM and PMNS matrixes when CP violation was seen experimentally in those processes, will probably be quite prosaic and won't introduce new kinds of exotic particles, like leptoquarks, nor will it fundamentally reshape the basic structure of the Standard Model. 

In the Standard Model, the interactions in which lepton universality violations arise are W boson mediated interactions that would probably be most parsimoniously explained by adding to the experimentally described properties of the W boson that already defies other rules, like CP conservation and conservation of quark flavor and lepton flavor, which are observed in all other processes.

Resolved Anomalies

Pretty much all other anomalies in modern physics (from the muon g-2 anomaly which is probably due to an incorrect calculation of the theoretical value by some groups with a correct calculation proposed in 2020, to the hypothetical X17 boson, to the 750 GeV anomaly, to sterile neutrinos in connection with the reactor antineutrino anomaly, to anomalies in very high energy cosmic ray decays, to the muonic proton radius puzzle, to the superluminal neutrinos that the Opera experiment thought that it saw, to the anomalous neutrinoless double beta decay observations of the Moscow experiments, to the XENON 1T anomalies) have good explanations due to experimental errors or flawed theoretical predictions that don't involve new physics. Some of the anomalous experimental results have been convincingly ruled out or discredited by multiple new experiments.

Remaining Tensions

The lepton universality violations and the tensions that have been resolved aren't the only experimental tensions in the Standard Model of Particle Physics. 

But others tensions that remain (like a lack of perfect unitarity in the CKM matrix, or the discrepancy in the lifetime of the neutron when measured in two different ways) are widely believed to be cases of experimental uncertainty and systemic error in experiments, rather than the result of "new physics."

Real Unsolved Questions

This doesn't mean that every single unsolved question in fundamental physics has been answered.

There are several properties of neutrinos that haven't been measured very accurately and we are still unclear if the rest mass of neutrinos arises in the same way that it does for other Standard Model fundamental particles. I very much doubt that see-saw models of neutrino mass that garner so many publications are right, but I don't have an explanation of my own that is a clearly superior alternative.

We are still quite fuzzy about what triggers the "collapse of the wave function" in quantum mechanics.

We still aren't clear regarding what axioms about the nature of physics are invalidated by the quantum phenomena known as "entanglement." We instead have a trio of assumptions (commonly called locality, causality, and reality), one of which must be false.

Similarly, the fact that the correct evaluation the path integral of the propagator of quantum electrodynamics requires the consideration of hypothetical photon paths that involve photons traveling at slightly more or less than the speed of light, contrary to special and general relativity, is a mystery that could be a clue to some deep insight into the nature of the universe. This is arguably the best hint that space-time itself may not be smooth and continuous in the true quantum gravity theory. The shut up and calculate school of physics doesn't really care. But I find it one of the most intriguing aspects of the established laws of physics.

We still don't know why the experimentally measured constants of the Standard Model take the values that they do, even though it seems to be due to some kind of deeper theory, rather than being random. I have ideas culled from the literature, and there are theoretical proposals that attempt to explain them. But honestly, this line of theoretical research in fundamental physics that is probably receiving too little attention.

Lepton universality violation and all of the real unsolved  questions above show strong signs of being answerable more or less entirely within the electroweak sector of the Standard Model, which is better understood and is possible to calculate more precisely with, and this is encouraging.

We have also probably devoted too little attention to the question of how plausible, minimalist quantum gravity theories impact the renormalization and beta functions of Standard Model experimentally measured constants at different momentum transfer scales. Any extrapolation of physics at the energies we've measured to the extreme high energies of the GUT scale or thereabouts that fails to take this into account must surely be incorrect, and quite modest tweaks to the Standard Model beta functions could significantly impact gauge force unification expectations, for example. In theory, this is a deterministic enterprise once the quantum gravity theory is well specified, so there is hope that is question could be solved in a single paper or two from a committed researcher.

We are still unclear about just what happened in the first moments after the Big Bang to give our modern universe the overall structure and global properties that is displays like the aggregate baryon number of the universe, the aggregate lepton number of the universe, the baryonic matter-antimatter asymmetry of the universe, and other large scale structure properties of the universe that we observe (e.g. properties often attributed to cosmological inflation). 

We also haven't characterized sphaleron processes in particle physics (the only Standard Model process that doesn't conserve lepton number and baryon number) very well. The answer is almost surely not, as almost every major paper on the subject suggests, either of the two CP violating processes in the Standard Model (W boson mediated changes in quark flavor and neutrino oscillation). 

I am highly skeptical the either cosmological inflation or beyond the Standard Model means of violating lepton number or baryon number are real. But I'm open to considering evidence to the contrary.

Finally, there are lots of complex processes (e.g. hadron structure, jet decays, and patron distribution functions), most of which involve quantum chromodynamics (QCD) strong force calculations that are hard to even approximate answer too accurately. These should, in theory, have an exact explanation in the Standard Model, and almost all physicists are confident that they do, but these questions are too difficult for us to currently calculate answers to with anything approaching the precision with which we can measure these complex processes experimentally. These questions will take centuries to fully master, if that ever happens.

But none of these other true unsolved problems in physics necessarily requires "new physics" beyond the Standard Model and general relativity to explain. It isn't impossible that they do, but there is no positive observational evidence, let alone unequivocal evidence, that this is the case.

Fake Unsolved Questions In Physics

Other so called "unsolved problems" in physics, like "the hierarchy problem", "naturalness", the "strong CP problem", baryogenesis, and leptogenesis, don't really deserve the name and are simply observationally unsupported presumptions about the laws of Nature that are false.

The Junk Heap Of Failed Theories

Despite the fact that we have very little apparent need for them, a huge amount of theoretical and experimental effort in fundamental physics is devoted to exploring one or more of a great many beyond the Standard Model theories.

The resolution of various particle physics anomalies is increasingly ruling out all or most of the parameter space of these theories, leaving them with little or no positive observational motivation.

These include supersymmetry, multiple Higgs doublet theories, myriad grand unified theories and theories of everything, technicolor, extra dimensions of space-time, leptoquarks, sterile neutrinos, string theory, and more.

Future Prospects

A resolution of dark matter phenomena without new particles and of lepton universality violations without new physics would wipe the field of almost all of the rest. I think that this could happen within my lifetime (at 50 years old) or at least, within my children's lifetime. We may not be in the promised land yet, but we can glimpse it in the distance from the mountain tops.

As I explained, above, this wouldn't be a true "end of science" as there would still be questions to be asked and complex phenomena to be understood. But we are very close, I think, to having a complete and accurate set of laws of nature and could get there soon.

When we get there, I suspect that the laws of physics will again look far simpler and more elegant, and will be easier to study as well, without having to master a host of hypothetical conjectures with a sophisticated and hard to master body of research associated with them, that do not pan out.

Three Experiments Contradict Reactor Anomaly Sterile Neutrino Hypothesis

Once again, experiments have ruled out a theory challenging the Standard Model of Particle Physics.

Several measurements of neutrino oscillation in connection with nuclear reactors suggested that there might be a fourth and/or fifth type of neutrino in addition to the three in the Standard Model (called the "Reactor Antineutrino Anomaly" in the paper below). 

The extra one or two neutrinos would oscillate with the three "active" neutrinos, but which are "sterile" in the sense that they like interactions via the weak force that active neutrinos are charged under. (All neutrinos lack electromagnetic charge and strong force color charge, and all particles interact via gravity, which is the fourth "Core Theory" force. It is unclear if neutrinos interact directly with the Higgs field as the other Standard Model particles with non-zero rest mass do.) As the introduction to the paper below explains:

The Reactor Antineutrino Anomaly (RAA) appeared in 2011, following a revision of the predicted neutrino fluxes for the main isotopes in nuclear fuel (235U, 238U, 239Pu, 241Pu). The upward reevaluation of predicted fluxes resulted in a data-to-prediction deficit of about 5%. 
One hypothesis to explain this deficit consists in oscillations to a sterile neutrino state, since sterile neutrinos are not observable in detectors. . . .
Based on data available at the time, the RAA best-fit parameters are of the order of sin^2(2θ(new)) ∼ 0.1 and ∆m(new)^2 ∼ 2 eV^2. 
Notably, this mass splitting translates into an oscillation length from 2 to 10 meters (depending on the neutrino energy), which is the typical length on which oscillations would develop. 
Therefore, a new generation of neutrino detectors were designed to study such oscillations, combining two key requirements: (i) a distance from detector to reactor core of about 10 m, to be able to probe the RAA hypothesis; (ii) a segmented detector covering several baselines over ∼ 2 m, so that oscillations could develop inside the detector and be seen by comparing spectra from the detector’s subparts. Experiments operating such detectors are, for instance, Stereo, PROSPECT and DANSS.

It is fair to say that a new round of experiments have ruled out the sterile neutrino hypothesis that the anomaly generated, consistent with the weak force carrier boson decay and cosmology evidence, both of which strongly disfavor this possibility. 

A conference paper from the Moriond 2021 conference reviewing the results of three experiments designed to test the sterile neutrino hypothesis shows that all three experiments strongly disfavor a sterile neutrino explanation of the Reactor Antineutrino Anomaly. Specifically, the paper notes that:

The best-fit point of the RAA is strongly excluded: at > 99% C.L. by Stereo, at > 95% C.L. by PROSPECT, and at > 5σ by DANSS. A large portion of the RAA 95% C.L. region is excluded as well. The only remaining region of the parameter space still unrejected corresponds to ∆m^2 > 5 eV^2 where experiments at O(10 m) have little sensitivity.

This is illustrated with the following trio of charts:

The conclusion of the paper explains that an alternative hypothesis, which is that the model used to predict the number of antineutrinos produced by commercial nuclear reactors with a mix of fuels was flawed because it overestimated the number of antineutrinos produced by the uranium-235 component of the fuel mix, is a more likely cause of the anomaly.

Since the emergence of the RAA, an intense experimental effort has developped around very short-baseline reactor neutrino detectors, in order to search for active-to-sterile oscillations. A decade later, the best-fit parameters and a large portion of the allowed region in parameter space are ruled out by Stereo, PROSPECT or DANSS. With these segmented detectors, model-independent analyses have been performed by comparing the antineutrino spectra from several baselines, and no sign of oscillations have been found. 
Another explanation is then required to understand the data-to-prediction deficit of about 5%, which first suggested the hypothesis of a sterile neutrino. 
The contributions of 235U and 239Pu to this deficit have been separated by the Daya Bay collaboration and favor that the deficit is mostly carried by 235U. The 235U deficit is measured at (7.8±2.7)%. The measurement by Stereo on a pure 235U flux yields a compatible deficit of (5.2±2.4)%, with a pure-235U world average now at (5.0±1.3)%. 
Finally, a recent repetition by Kopeikin et al. of the measurement of 235U and 239Pu β spectra, used as inputs for the Huber-Mueller model [ed. used to determine the predicted number of neutrino events], indicates that the ratio of 235U/239Pu fluxes may have been overestimated by 5.4%. The global picture . . . suggests that the 239Pu normalization may be correct, and the 235U normalization overestimated in the HM model by 5-6%.

The paper also discuses the "5 MeV bump" excess of events at that energy at experiments running at commercial reactors (Daya Bay, RENO, Double Chooz) that is observed. 

But this doesn't necessarily suggest fundamental new physics surrounding neutrinos as opposed to a lack of a full understanding of the details of a complex set of reactions in a mixed fuel commercial nuclear reactor similar to the one that produced the Reactor Antineutrino Anomaly. The data, collectively, concerning the 5 MeV bump is inconclusive at this time.

The paper and its abstract are as follows:
Reactor neutrinos have been an intense field of investigation for the last decade. Two anomalies are discussed in this document. First, a status of the sterile neutrino searches by STEREO, PROSPECT and DANSS is presented. The best-fit parameters of active-to-sterile oscillations from the Reactor Antineutrino Anomaly are strongly rejected by these experiments. 
Second, the analyses of the shape anomaly ("5 MeV bump") by STEREO and PROSPECT, both using a virtually pure-235U neutrino flux, are detailed. Results show a significant excess of events at 5-6 MeV and indicate that the bump observed at commercial reactors is not specific to a particular isotope but rather shared among U and Pu.
Matthieu Licciardi "Results of STEREO and PROSPECT, and status of sterile neutrino searches" (May 28, 2021) (Contribution to the 2021 EW session of the 55th Rencontres de Moriond).

Friday, May 28, 2021

Indo-European Germs

One of the most influential books that got me started thinking about prehistory was "Guns, Germs and Steel" by Jared Diamond.

The germs trope has resurfaced again, in a place that makes sense, but adds new insight to the historical process by which Europe, South Asia and West Asia came into their current forms.

In a podcast between Razib Khan and Dr. Kristian Kristiansen, it comes out that early Indo-Europeans brought the plague to Europe, and they discuss the role it may have played in the collapse of “Old Europe.”

Thursday, May 27, 2021

New Data Confirms Low Sum Of Neutrino Masses

New Cosmology Bounds On Neutrino Mass

The Dark Energy Survey (DES) has confirmed that the sum of the three neutrino masses in a lambdaCDM model should be less than 130 meV/c^2 with 95% confidence, using the combined results of DES Year 3, Planck, and other low redshift datasets, all of which are consistent with each other. 

There will probably be no major adjustments in these bounds before the year 2026.

A January 2021 article explains the methodology involved to set this bound. The pre-DES bound from "the latest 2018 Planck data, in conjunction with measurements of the baryon acoustic oscillations (BAO) from the Baryon Oscillation Spectroscopic Survey (BOSS)" was 120 meV/c^2 at 95% C.L. 

Direct Measurements Of Neutrino Mass

The tightest directly measured bound on the mass of the electron anti-neutrino (which should be the same as the electron neutrino) is that it is less than 800 meV/c^2 with 90% confidence. This limit from the KATRIN experiment is expected to ultimately be reduced to 200 meV/c^2 with 90% confidence when the experiment has run its course and collected all of the data it plans to collect.

Limits on Neutrino Masses From Neutrino Mixing

The differences between the three neutrino mass eigenstates is known with much greater precision from neutrino mixing data, although the observational data only mildly favor the "normal" ordering of neutrino masses seen in the charged leptons and quarks, over an "inverse" ordering of neutrino masses.

The square of the difference between the first and second neutrino mass is 75.3 ± 1.8 meV^2/c^4 (i.e. about 8.7 meV/c^2, and at least 8.5 meV/c^2 at two sigma).

The square of the difference between the second and third neutrino mass is 2453 ± 34.2 meV^2/c^4 if there is a a normal ordering (i.e. about 49.5 meV/c^2 and at least 48.8 meV/c^2 at two sigma), or -2546 + 34 - 40 meV^2/c^4 in an inverse ordering.

So, if the lightest neutrino mass is negligibly greater than zero, then the sum of the three neutrino masses is at two sigma (roughly 95% confidence interval) not less than 57.3 meV/c^2.

Limits on Neutrino Majorana Mass From Neutrinoless Double Beta Decay

Neutrinoless double beta decay has not been observed. If neutrinos have Dirac mass, it never occurs. If neutrinos have Majorana mass, the non-detection of neutrinoless double beta decay places an upper bound on the Majorana mass of neutrinos at 180 meV/c^2 as a 90% confidence interval.

Like the direct mass detection bound from KATRIN, this bound is not competitive with the upper bounds on neutrino mass from cosmology observations and neutrino mixing.

The Combined Limits On Neutrino Masses

The neutrino mixing and cosmology bounds constrain the sum of the three neutrino masses in a normal ordering to be between 57.3 meV/c^2 and 130 meV/c^2, with about 90% of the possible variation within that range being a function of the lightest neutrino mass eigenstate, which must be less than 24.3 meV/c^2, with a value at the low end of this range favored. Uncertainty in mass differences from neutrino mixing accounts for about only 2.2 meV/c^2 of the possible variation within this range.

There are good theoretical arguments, none of which are established definitively, however, for the lightest neutrino mass to be non-zero, even if it is arbitrarily small. This is because particles with zero mass have qualitatively different properties than particles with non-zero mass, because all other fermions have non-zero rest mass, and because all other particles that interact via the weak force have non-zero rest mass. Also, all other particles which experience CP violation have non-zero rest mass, and there is strong evidence that neutrino oscillation has a non-zero CP violating phase. CP violation (which is equivalent to time reversal asymmetry) makes less theoretical sense in the case of a particle with zero rest mass, because particles with zero rest mass do not experience the passage of time in their own reference frame.

In an inverse neutrino mass hierarchy the sum of the three neutrino masses must be at least 96 meV/c^2 at two sigma, which is quite close to the 130 meV/c^2 upper bound from the combined cosmology data.

The direct measurement of electron anti-neutrino mass is not competitive with these boundaries but is also not inconsistent with them. This is also true of the bound on the Majorana mass of neutrinos from neutrinoless double beta decay detection experiments. 

The cosmology constraint on the lightest neutrino mass is 33 times stronger than the direct measurement constraint, and could be as little as 8 times stronger when the KATRIN experiment is complete. It is about 7.5 times stronger than the bound imposed by the non-detection of neutrinoless double beta decay in a scenario in which neutrinos have exclusively Majorana mass.

The Number of Neutrino Types

Data from W and Z boson decays likewise tightly constrain the number of active neutrinos with masses of less than 45,000,000,000,000 meV/c^2 to exactly three.

Cosmology data also strongly supports the hypothesis that there are exactly three generations of neutrinos (with no sterile neutrinos having a mass of 1,000,000,000 meV/c^2 or less) (also here). A far heavier sterile neutrino, however, would not be discernible as a neutrino from cosmology data and instead would look like a type of dark matter particle.

Neutrino mixing data less definitively rule out the possibility of one or two additional neutrinos that oscillate, but do not interact via the electromagnetic, weak or strong forces, although the neutrino mixing data still favors the default three neutrino hypothesis over the one and two sterile neutrino alternatives (see also here).

Wednesday, May 26, 2021

Systemic Measurement Error Probably Explains The Hubble Tension


The Hubble constant quantifies the rate at which the universe is expanding. 

One of the big unresolved problems in cosmology is the discrepancy between the value of the Hubble constant as estimated from the cosmic microwave background (CMB) and related whole sky observations of the earliest moments of the universe (most precisely measured by the Planck collaboration), and the estimated value of the Hubble constant measured from observations of much younger stars that are closer to us in time and space.  

This discrepancy could be because the value of the "constant" has actually changed over time (an assumption that calls for "New Physics"), or it could be due to errors in one of the measurements (most likely the measurement of younger stars which has a far larger margin of error).

As the authors of a new pre-print (cited below with its abstract) explain:

As is well known, there is a tension between the value of the Hubble constant as inferred from small and large distance measurements, most significantly between the values inferred from Type Ia supernova (SNIa) distances to redshifts z ∼ 0.1 calibrated by Cepheid observations, as measured by the SH0ES team, and the distance to the cosmic microwave background (CMB) decoupling surface at z ∼ 1090, as measured by the Planck satellite. The former yields H(0) = 73.2 ± 1.3 (in units of km/s/Mpc used from now on) (Riess et al. 2021) and the latter H(0) = 67.4±0.5 (Aghanim et al. 2020); a 4.1 σ tension. 

The tension between other measurements is not as significant.

The chart below from the pre-print compares the SH0ES and Planck results that are in such strong tension with each other, with four other leading measurements of the Hubble constant made using three other measurement methods (gravitational waves, tip of red giant branch calibration, and gravitational lensing). 

"Z" in astronomy, used on the Y-axis in the chart above, refers to how far the light has traveled, in terms of the observed redshift of the light, rather than years, with a larger value of Z being older. The chart below, from this Wikipedia link, converts "z" to billions of years in the past, in red, which has an asymptote at the Big Bang about 13.8 billion years ago. Z values more than 10 are all similar in absolute age but get increasingly close to the Big Bang. The cosmic microwave background has a redshift of z = 1089, corresponding to an age of approximately 379,000 years after the Big Bang; z = 1 is about 7 billion years ago and z = 0.1 is about 1 billion years ago (with the last two figures based upon eyeballing the chart).

The New Paper

The new pre-print argues that the problem is a systemic error in how the Hubble constant is determined from the measurements of younger stars. It argues that the analysis that produces the discrepancy does so because it makes the unjustified assumption that all Cepheid variable stars of the same brightness are exactly the same color. It argues that this assumption is flawed because the light from those stars is distorted en route to Earth by factors such as interstellar dust. 

If the assumption that the colors are exactly the same apart from red shift is true, the red shift of those stars can be determined with the precision needed to accurately estimate the Hubble constant. But, if the colors are distorted as light travels to Earth, determining redshift from the light from Cepheids is not nearly as precise as this method has been claimed to be. 

The pre-print offers a very plausible resolution of the discrepancy. If correct, it would also kill a legion of rather far fetched revisions of the laws of Nature proposed to explain the discrepancy.

The paper and its abstract are as follows:

Motivated by the large observed diversity in the properties of extra-galactic extinction by dust, we re-analyse the Cepheid calibration used to infer the local value of the Hubble constant, H(0), from Type Ia supernovae. 
Unlike the SH0ES team, we do not enforce a universal color-luminosity relation to correct the near-IR Cepheid magnitudes. Instead, we focus on a data driven method, where the measured colors of the Cepheids are used to derive a color-luminosity relation for each galaxy individually. 
We present two different analyses, one based on Wesenheit magnitudes, a common practice in the field that attempts to combine corrections from both extinction and variations in intrinsic colors, resulting in H(0)=66.9±2.5 km/s/Mpc, in agreement with the Planck value. 
In the second approach, we calibrate using color excesses with respect to derived average intrinsic colors, yielding H(0)=71.8±1.6 km/s/Mpc, a 2.7σ tension with the value inferred from the cosmic microwave background. 
Hence, we argue that systematic uncertainties related to the choice of Cepheid color-luminosity calibration method currently inhibits us from measuring H(0) to the precision required to claim a substantial tension with Planck data.
Edvard Mortsell, Ariel Goobar, Joel Johansson, Suhail Dhawan, "The Hubble Tension Bites the Dust: Sensitivity of the Hubble Constant Determination to Cepheid Color Calibration" arXiv (May 24, 2021).

Friday, May 21, 2021

A Gobekli Tepe Conjecture

Gobekli Tepe is a decorative megalithic monument in what is now Turkey build about three thousand years before the Fertile Crescent Neolithic revolution facilitated sedentary lifestyles and vastly increased population densities (by a factor of perhaps 100) though the domestication of plants and animals for food and other useful purposes. It is the only pre-Neolithic structure of its kind in the world. My attention now is prompted by a recent article about it that asks more generally, if there were pre-Neolithic civilizations that were more than just wandering bands of hunter-gatherers.

The article prompts two responses.

First, that fishing based communities were the most advanced in the pre-Neolithic world, because they could advance in technology with the sedentary lifestyle this made possible in a way that wasn't possible for nomadic terrestrial hunter-gatherers. 

There is no doubt that prior to the domestication of plants and animals, that communities with fishing based food production, in part, because it could be sedentary were the most “civilized”. There were relatively “advanced” fishing based civilizations. in Pacific Northwest, on the coast of the eastern Baltic Sea, or the Jomon, or the Calusa of Southwest Florida that fit this description. For example, the earliest inventors of pottery, the Jomon of Japan and the fishing villages of coastal China fit this description.

But, second, while fishing based economies explain many of the particular advanced pre-Neolithic civilization, this doesn’t explain the singular wonder of Gobekli Tepe in the highlands of Anatolia. 

There is also rather convincing suggestive evidence (also here) from what it depicted in the carvings there, that Gobekli Tepe, at least in its final incarnation and design, memorializes an extraterrestrial impact event that gave rise to the Younger Dryas climate event (also, regarding the ET impact theory, here and here and here and here).

Now, it is true that the scale of terrestrial hunter-gather communities are usually underestimated, because pre-Neolithic terrestrial hunter-gather communities would have thrived and dominated the very most prime territory.

In contrast, the post-Neolithic Holocene era is a long secular trend of terrestrial hunter-gatherers being evicted by farmers and herders from more desirable territory to places that are of no use to farmers and marginal even for herders, like the Kalahari desert, the depths of the Congo and Amazon jungles, and the Arctic and sub-Arctic tundra and northern coasts. 

Marginal environments can only support smaller, more marginal communities of people, since hunting and gathering generates fewer calories were acre/hectare of land, and since crossing a desert or tundra by foot takes about the same amount of time as crossing a verdant meadow or game rich river basins by foot. Travel by foot set a boundary on how far away from each other people in the same community in a meaningful sense could be from each other that was the same for all terrestrial hunter-gatherers. 

But, the more fruitful the land, the more people that more or less fixed size geographic region could be. And, even places that were not truly primarily fish based food production communities may have supplemented their diets with some coastal shellfish gathering or a minor but significant contribution from riverine fish and freshwater animals (like eels, frogs, turtles and crayfish) that provided an additional food source that again increased the carrying capacity of already prime territory. There is also evidence in Natufian archaeology of proto-farming in the pre-Neolithic Near East, where desirable wild types of plants in a particular place where they were already present were encouraged to grow and tended.

So, while modern hunter-gather communities may live in bands of dozens or hundreds of people, pre-Neolithic hunter-gatherer communities might very well have included thousands or tens of thousands people in the most prime territories. These communities would have had been far less concentrated in any one place than even the most primitive Neolithic farming communities, but it doesn’t seem at all implausible that there could have been seasonal hot spots on some sort of regular circuit in the community’s territory as multiple bands of people flocked to wild berry groves when they were in season, to fish runs in rivers at spawning times, to water holes in dry seasons, to migration routes of particular animals at the appropriate times. So, even if a large community of say 10,000 people who were a walkable distance from each other was broken up into 100 primary bands of 100 people each, there might be groups of several thousand in the hottest spots several times a year in places where food was especially abundant.

Another strongly suggestive bit of evidence that communities had significant and meaningful organization above the level of the nomadic band of terrestrial hunter-gatherers is that the measurement of the genetic distinctiveness of Levantine hunter-gatherers (Natufians) from Caucasian/Iranian hunter-gatherers, was as great as that between Europeans and East Asians in modern times, despite the fact that they had geographically adjacent territories. You can’t get that kind of genetic population structure between geographically adjacent populations without either truly insurmountable geographic barriers (and there were mountains and arid areas to serve as barriers that helped divide the communities, but not that insurmountable) or strong socially enforced endogamy norms and linguistic and political identity differences. The lowland Levantine Natufians and the West Asian highland Caucasian hunter gathers (CHG) were clearly not friends, probably didn’t have much occasion to even engage in trade with each other, and genetics indicate, didn’t engage in bride exchange with each other. In political science terms, these genetic signs tell us that “nations” of co-ethnics with a shared identity far preceded governmental organizations called “states”.

Gobekli Tepe is still a puzzle, however, even if some pre-Neolithic hunter-gatherer communities were much larger and more prosperous than modern ones. It may have been in one of the most prime territory in the world at the time, at true Eden, making its community particular large and affording that community more excess resources of time and food than most. But it was surely not the only such place.

But there is just nothing else, anywhere in the world, including in communities with fishing based food production, in the pre-Neolithic world, of this scale and sophistication. There was stone working, mostly for tools, and there was cave art and there were decorative personal effects, but it really was something new under the Sun, never before seen in human history.

Why then, about 13000 BP? 

Why there, right at the epicenter of the Fertile Crescent Neolithic Revolution’s emergence three thousand years later? 

This wasn’t a community based upon food production by fishing. Analysis of the trash left behind at the site by its builders shows that a big share of their food consumption at the time it was built was wild terrestrial game, and it doesn't seem to have a long term Mesolithic permanent residential village or city associated it.

But, one hypothesis could explain its uniqueness is that this was a site of mixed seasonal proto-farming and terrestrial hunter-gatherer food production pre-Younger Dryas, on the cusp of being the first community in the world to start a first neolithic revolution. 

This prospect fizzled, however, and other potential independent neolithic revolutions failed to launch as they would three thousand years later, because the Younger Dryas event set that development in human progress back several thousand years due to climate conditions it created that were unfavorable to domestication of plants and animals.

Perhaps construction of Gobekli Tepe had begun prior to the Younger Dryas as what would have been the world’s first Neolithic megalithic structure (something that early Neolithic communities worldwide seem to independently create for astronomy purposes). But, when the Younger Dryas hit, it ended up being something that was pushed to completion anyway as a memorial to what might have been until changing climate conditions crushed the incipient neolithic breakthrough. Lots of powerful people in their community would have still had fresh visions of what was about to emerge with a Neolithic revolution that they were about to usher in, and they were literally praying that this kind of monument could recapture the civilized greatness that was slipping away from them inexorably due to the Younger Dryas. Since their proto-farming efforts collapsed, they have have made this herculean construction effort instead with periodic seasonal gathering coinciding with game migrations or abundant amounts of wild food plants to harvest in this location to achieve this, when societies that hadn't glimpsed the possibility of a neolithic revolution wouldn't have tried or bothered.

This is just speculation, of course, but it is a reasonable inference from what we know that could explain all of the available facts. 

Most other explanations about early Mesolithic civilization either fail to explain why there wasn’t something comparable to Gobekli Tepe anywhere else in the world in the pre-Neolithic era, or why Gobekli Tepe didn’t emerge in a fishing based community. If other explanations were right, we would have expected to see many such structures in the world, and we don’t. But, a first  neolithic revolution in the world (whose timing is explained by the fact that climate was first the LGM ice age, and then extremely variable on very short time scales until not long before the Younger Dryas) that was aborted suddenly by an extraterrestrial impact causing the Younger Dryas, that is arguably depicted in its engravings, does explain why this site is unique (with a location for a first in the same place where the actual first Neolithic occurred), and also explains why it happened in this one place and was then not repeated for another three thousand years.

Thursday, May 20, 2021

The Domestication Of The Opium Poppy

The opium poppy was not part of the Fertile Crescent Neolithic package of domesticated crops, but was added soon afterwards. 

[T]he opium poppy (Papaver somniferum L.) was domesticated in the western Mediterranean, where its presumed progenitor Papaver somniferum subsp. setigerum (DC.) Arcang is native and still grows wild today.

Using a new method of analysis, researchers from the universities of Basel and Montpellier have now been able to strengthen the hypothesis that prehistoric farmers living in pile dwellings around the Alps began to cultivate and use the opium poppy on a large scale from about 5500 BCE. By doing so, they contributed to its domestication, as the team reports in the journal Scientific Reports.

From this press release about  Ana Jesus, et al., "A morphometric approach to track opium poppy domestication." 11(1) Scientific Reports (2021) DOI: 10.1038/s41598-021-88964-4.

Wednesday, May 19, 2021

Data Points Regarding Bell Beaker Origins

Razib Khan notes that the Yamnaya (or at least the Eastern Yamnaya for whom we have ancient Y-DNA samples, it is plausible that Western Yamnaya might have a clad of Y-DNA R1b closer to the Bell Beaker Indo-Europeans) cannot be the directly ancestral population to either the Corded Ware culture, or the people with steppe ancestry within the Bell Beaker culture, the two main archaeological cultures that brought the Indo-European languages to Europe. 

Instead, when the Yamnaya culture collapsed, Y-DNA suggests that some of its men (at least in the East) fled to Central Asia, and a minority were integrated into Indo-Iranian society. Most of their men were probably slaughtered or died from other conditions that precipitated their collapse and replacement.

"Matt" commenting at the same post, provides a link to a March 2021 talk by David W. Anthony (author of "The Horse, Wheel, and Language") comparing various autosomal ancient DNA samples in a PCA chart which Matt extracted from the presentation and annotated. Matt carefully provides a chart with and without his contributions to clearly attribute with comments are his, but I will include only the one he has marked up below.

This chart, labels notwithstanding, doesn't have any true Bell Beaker individuals shown, only members of the Unetice culture (a probably Indo-European culture ca. 2300 BCE to 1800 BCE in Central Europe including Southern and Central Germany, Austria, Czechia, Slovakia, parts of Poland, and Western Ukraine whose link to Corded Ware or Bell Beaker culture is unclear), and the Corded Ware culture. 

But the chart does suggest that Yamnaya people from Moldova, Hungary and Bulgaria (and less clearly culturally identified people from copper age Bulgaria and from Romania), who show an admixture pull towards the Neolithic farmer cultures of the Central and Eastern Europe, are a close genetic match for the subsequent Corded Ware culture and Unetice culture people. 

And, while the respective cultures were very distinct in Y-DNA (three of the ancient Unetice Y-DNA samples are I2 while one is R1b, those Y-DNA haplogroups plus a predominance of R1a are found in Corded Ware, and Bell Beaker is predominantly R1b), the autosomal DNA of steppe migrants to Europe was quite similar.

Thus, if you are looking for a launching point for the Bell Beaker culture, Southeast and Central Europe is a very plausible place to look.

Also, the original Bell Beaker culture in Iberia, according to ancient DNA, was probably not a product of steppe people. Instead, as it expanded out of Iberia, this culture was adopted by steppe migrants in Western Europe via central Europe, perhaps, in part, adopting some of the culture of their local wives.

The map below from Wikipedia places several of the cultures. The Neolithic farmer Globular Amphora culture (ca. 3400 BCE to 2800 BCE), immediately preceded the Corded Ware culture.

This map from Wikipedia places the Neolithic farmer Tripolye culture (ca. 5500 BCE to 2750 BCE) to the South of the Globular Amphora culture.

Thursday, May 13, 2021

Hiatus Notice

My day job includes tax law. The tax deadline this year is May 17, 2021. You won't be hearing from me until that deadline has passed and then I've had a chance to decompress and resolve backlogs in other work after that. 

Possibly, I may not be able to blog until mid-June, due to some exciting developments as my young adult children are growing up, that call for my full attention.

Tuesday, May 4, 2021

Greek Ancient DNA Fleshes Out The Historical Linguistics Narrative

Razib Khan and Bernard have posts on a new paper with Greek ancient DNA. Razib's summary hits the nail on the head:

1) the main pulse of Indo-Europeans, the proto-Greeks, arrived ~2300 BCE to “mainland Greece” (i.e., the north). This notwithstanding other earlier contacts noted in the text between the Pontic steppe and the Balkans

2) The Minoans and other peoples of the Aegean did not have this ancestry. This is not surprising. But, this works seems to confirm a likely pulse of ancestry into the Aegean ~4000 BCE with roots in eastern Anatolia and/or the Caucasus. This is a minority component, but seems correlated with the arrival of Y chromosomal group haplogroup J2, and has been detected as far west as Sicily.

3) The above component is related to the contributor to about half the ancestry among the Yamnaya samples. But, the Yamnaya samples themselves are about half “Eastern Hunter-Gatherer” (EHG), which itself can be decomposed as 25% “Western Hunter-Gatherer” (WHG) and 75% “Ancient North Eurasian” (ANE). This EHG component was lacking entirely in the Minoans of the Bronze Age and is lacking in modern Cypriots (who are mostly ethnically Greek). In contrast, the EHG component begins to increase in the Balkans during the late Neolithic.

4) There seems to have been a further dilution of the steppe component among the Bronze Age Greeks as they moved from the north to the south. The largest component of Greek ancestry then, and now, remains “Early European Farmer” (EFF), related to and descended from “Anatolian Farmer” (AF).

5) Modern Greek samples have more steppe than late Bronze Age samples (Mycenaeans). I am confident this is due to early medieval Slav tribes, who moved as far south as the Peloponnese in large numbers. I’ve looked at a fair number of Greek samples, and some of them have way less steppe ancestry than others, with the latter matching those labeled “northern Greek” by the Estonian Biocentre dataset. I think many of these former are likely island Greeks from the Aegean or Greeks who descend from early 20th century migrants from Anatolia.

So, basically, you have a four wave model:

1. Anatolian Neolithic migrants.

2. Copper Age/Early Bronze Age migrants from West Asian highlands.

3. Indo-Europeans from North to South and petering out as they move south.

4. Medieval Slavs (who are Indo-European) also on a North to South cline. 

Davidski at Eurogenes confirms the likelihood that there was a wave of Slavic migration to Greece along these lines but is more skeptical that we have good enough data to make strong conclusions about the overall population history.

The West Asian highlands wave largely didn't make it into Europe (apart from Sicily, a few other places in Italy, Malta, European Turkey, and Greece).

The presence of this substrate in the places where the Anatolian languages emerged, and its absence elsewhere, is, in my humble opinion, what makes the Anatolian Indo-European languages (most famously Hittite) so divergent, despite the fact that it is really contemporaneous with Mycenaean Greek, Sanskrit, Avestian Persian, Tocharian, and other European Indo-European macro-language families.

This West Asian highlands wave also tends to support my hypothesis that there is a macro-language family associated with it that includes Minoan, Hattic, Hurrian, Kassite, and probably some of the Caucasian languages, in addition to providing an Anatolian Indo-European language substrate. 

I'd also guess that at a time depth too great to construct using standard linguistic methods, that all or most of the Caucasian languages, Sumerian, and Elamite are also part of this macro-language family, for which ergative grammar is probably a good litmus test. 

This data and Razib's analysis also suggest the possibility of using Y-DNA J2 as a possible tracer of this language family's range in cases where subsequent languages acquired by language shift can't be ruled out, and to narrow down which Caucasian languages were mostly likely associated with this wave (most likely the Northeast Caucasian languages like Chechen and Ingush, where Y-DNA J2 present in a majority of men who speak those languages).

Map via Wikipedia

If Y-DNA J2 is a reliable tracer of this wave, then it also suggests that Basque and the extinct Vasconic languages are probably not associated with it. See, e.g., here. This thus favors the alternative hypothesis that Basque is derived from the language of the first farmers of Iberia, probably derived from the languages of West Anatolian early Neolithic farmers, rather than languages related to, for example, Minoan, Hattic and Hurrian.

Map via Wikipedia

Map via Eupedia

Indeed, quite likely, both the Western Anatolian language family of the Neolithic first farmers, and the West Asian highlands language of the early metal age were remote cousins within this macro-language family, with Y-DNA G (associated with the first wave Anatolian farmers), J1 and J2 tracing deep historic outlines of some of its main branches (with J1 eventually undergoing language shift or language evolution to Afro-Asiatic languages like Arabic, Coptic, Berber and the Ethiopian languages).

Further Reading