Wednesday, September 27, 2023

A New Anatolian Language, Called Kalasma, Is Discovered

Ancient Hittite records have revealed a previously unknown Anatolian language. It was probably spoken in or near the region indicated in red above. As the linked Language Log quotation of a press release from the researchers' institution explains:
An excavation in Turkey has brought to light an unknown Indo-European language. Professor Daniel Schwemer, an expert for the ancient near east from Würzburg, is involved in investigating the discovery.

The new language was discovered in the UNESCO World Heritage Site Boğazköy-Hattusha in north-central Turkey. This was once the capital of the Hittite Empire, one of the great powers of Western Asia during the Late Bronze Age (1650 to 1200 BC).

Excavations in Boğazköy-Hattusha have been going on for more than 100 years under the direction of the German Archaeological Institute. The site has been a UNESCO World Heritage Site since 1986; almost 30,000 clay tablets with cuneiform writing have been found there so far. These tablets, which were included in the UNESCO World Documentary Heritage in 2001, provide rich information about the history, society, economy and religious traditions of the Hittites and their neighbours.

Yearly archaeological campaigns led by current site director Professor Andreas Schachner of the Istanbul Department of the German Archaeological Institute continue to add to the cuneiform finds. Most of the texts are written in Hittite, the oldest attested Indo-European language and the dominant language at the site. Yet the excavations of this year yielded a surprise. Hidden in a cultic ritual text written in Hittite is a recitation in a hitherto unknown language.

Professor Daniel Schwemer, head of the Chair of Ancient Near Eastern Studies at Julius-Maximilians-Universität (JMU) Würzburg in Germany, is working on the cuneiform finds from the excavation. He reports that the Hittite ritual text refers to the new idiom as the language of the land of Kalašma. This is an area on the north-western edge of the Hittite heartland, probably in the area of present-day Bolu or Gerede.

The discovery of another language in the Boğazköy-Hattusha archives is not entirely unexpected, as Daniel Schwemer explains: "The Hittites were uniquely interested in recording rituals in foreign languages."

Such ritual texts, written by scribes of the Hittite king reflect various Anatolian, Syrian, and Mesopotamian traditions and linguistic milieus. The rituals provide valuable glimpses into the little known linguistic landscapes of Late Bronze Age Anatolia, where not just Hittite was spoken. Thus cuneiform texts from Boğazköy-Hattusha include passages in Luwian and Palaic, two other Anatolian-Indo-European languages closely related to Hittite, as well as Hattic, a non-Indo-European language. Now the language of Kalasma can be added to these.

Being written in a newly discovered language the Kalasmaic text is as yet largely incomprehensible. Daniel Schwemer’s colleague, Professor Elisabeth Rieken (Philipps-Universität Marburg), a specialist in ancient Anatolian languages, has confirmed that the idiom belongs to the family of Anatolian-Indo-European languages.

According to Rieken, despite its geographic proximity to the area where Palaic was spoken, the text seems to share more features with Luwian. How closely the language of Kalasma is related to the other Luwian dialects of Late Bronze Age Anatolia will be the subject of further investigation.
The Anatolian languages in the Indo-European language family are the least similar to other Indo-European language, which many linguists have interpreted as evidence of their deep time depth in the Indo-European language family. Some linguists have even suggested that the Indo-European languages have their origins in Anatolia and that their expansion from the Pontic Caspian steppe was a secondary migration. 

The linguists who take these positions are wrong. None of the other evidence is consistent with an old Indo-Anatolian languages hypothesis.

Instead, the Anatolian languages arrived in Anatolia from migrants ultimately derived from the Pontic Caspian steppe like Indo-European populations elsewhere. But they are relatively diverged from other Indo-European languages because the Copper Age Hattic society which the Hittites conquered and ultimately ruled, had far more staying power than the other societies were the Indo-European languages replaced Neolithic languages and Copper Age languages. The Hattic language survived as a liturgical language for many centuries after its speakers were conquered by the Hittites and it has far more substrate influence than other Neolithic substrate languages that Indo-European language experienced.

Also, the Hattic substrate language was itself greatly diverged from substrate languages descended from Western Anatolian Neolithic languages found in Europe (Basque is probably the sole living language descendant of this family of languages), whose more limited influence on the Indo-European languages of the people who conquered them was similar because the substrate languages had a common origin about two to three thousand years earlier. The early metal age Hattic people's language replaced the Neolithic languages of Anatolia when then migrated to this area from the highlands to its east.
Based on toponyms and personal names, however, it may have been related to the otherwise-unattested Kaskian language. Certain similarities between Hattic and both Abkhazo-Adyghean and Kartvelian languages have led to proposals by some scholars about the possibility of a linguistic bloc from central Anatolia to the Caucasus.

It seems likely that Minoan was also part of a linguistic macro-family that included Hattic, other Caucasian language families, and possibly other now extinct ergative languages of the region. 

Archaeological evidence, early historical written records from a Mesopotamian trading outpost at the south central fringe of Anatolia, and genetic evidence all support a late arrival of Anatolian languages to Anatolia (ca. 2000 BCE), followed by an adoption of the Anatolian languages there through language shift due to elite dominance of Hittite and other Anatolian language speakers, in part, due to their early superiority in metallurgy. They didn't leave much of a demic impact on the population of Anatolia, in stark contrast to the large scale male dominated demic near replacement seen in other areas where Indo-Europeans conquered territories whose Neolithic civilizations had collapsed due to serious climate events and soil exhaustion from their primitive agricultural methods.

The attested Indo-European language that was probably closest to proto-Indo-European (i.e.  the most basal attested Indo-European language) is Tocharian, which was spoken in the Tarim Basin for centuries by phenotypically and genetically West Eurasian peoples.

Proto-Indo-European languages probably originate in the Sredny Stog culture (ca. 4500 BCE to 3500 BCE), possibly fusing, on a more or less equal basis early herder languages of the Pontic Caspian steppe based upon Eastern hunter-gatherer languages of the region (possibly with some borrowing from Caucasian hunter-gather languages from whom they may have acquired some wives in a contact zone near the northern slope of the Caucasian mountains), with early Neolithic farmers on the frontier of farming at the time speaking a language derived from a Western Anatolian Neolithic language. The Khvalynsk culture of Western steppe herders (in the middle Volga region) and the Neolithic first farmers from the Cucuteni-Trypillia culture (centered in modern day Moldova and Western Ukraine) probably both contributed to the hybrid Sredny Stog culture that emerged in their contact zone. The nearby and roughly contemporaneous Cernavodă culture may have been another of the very earliest linguistically Indo-European societies. There are strong hints that the Sredny Stog culture was either the first to have domesticated the horse, or was one of the first cultures to have domesticated horses which were domesticated nearby.

Wednesday, September 20, 2023

More On Wide Binary Stars

This somewhat mixed result is the latest episode in the wide binary star dynamics debate. It shows strong signs of non-Newtonian behavior, although not necessarily MOND-like. This is important because dark matter particle models shouldn't produce non-Newtonian dynamics in wide binary stars.
It is found that Gaia DR3 binary stars selected with stringent requirements on astrometric measurements and radial velocities naturally satisfy Newtonian dynamics without hidden close companions when projected separation s>2 kau, showing that pure binaries can be selected. It is then found that pure binaries selected with the same criteria show a systematic deviation from the Newtonian expectation when s<2 kau. 
When both proper motions and parallaxes are required to have precision better than 0.003 and radial velocities better than 0.2, I obtain 1558 statistically pure binaries within a 'clean' G-band absolute magnitude range. From this sample, I obtain an observed to Newtonian predicted kinematic acceleration ratio of γ(g)=g(obs)/g(pred)=1.43+0.23−0.19 for acceleration <10^−10 m s^−2, in excellent agreement with a recent finding 1.43±0.06 for a much larger general sample with the amount of hidden close companions self-calibrated. I also investigate the radial profile of stacked sky-projected relative velocities without a deprojection to the 3D space. The observed profile matches the Newtonian predicted profile for s<2 kau without any free parameters but shows a clear deviation at a larger separation with a significance of 4.6σ. The projected velocity boost factor for s>8 kau is measured to be γ(v(p))=1.18±0.06 matching γ(g)‾‾√. 
Finally, for a small sample of 23 binaries with exceptionally precise radial velocities (precision <0.0043) the directly measured relative velocities in the 3D space also show a boost at larger separations. These results robustly confirm the recently reported gravitational anomaly at low acceleration for a general sample.
Kyu-Hyun Chae, "Robust Evidence for the Breakdown of Standard Gravity at Low Acceleration from Statistically Pure Binaries Free of Hidden Companions" arXiv:2309.10404 (September 19, 2023) (submitted to ApJ (this new work complements the paper ApJ, 952, 128 (arXiv:2305.04613) in an important way).

Tuesday, September 19, 2023

CP Violation In The Standard Model Quantified And More

There are two components of the Standard Model of Particle Physics that violate charge parity (CP) conversation, which is to say that the laws of physics are asymmetric between interactions going forward in time and interactions going backward in time. One is the CP violation parameter of the four parameter CKM matrix, which is called beta (β), and applies to W boson mediated changes in quark flavor. The other is the CP violation parameter of the PMNS matrix which governs neutrino flavor oscillations, which has been measured only crudely but is very likely to be non-zero given current measurements to date.

A new measurement of the CKM matrix CP violation parameter using the decays of electromagnetically neutral B mesons has been made by the LHCb experiment  at the Large Hadron Collider (LHC). This is "the most precise single measurement of the CKM angle β to date and is more precise than the current world average." The status quo leading up to this new measurement was as follows:

Measurements of CP violation in neutral meson decays to charmonium final states have thus resulted in a high degree of precision for the angle β of the CKM matrix: sin(2β) = 0.699 ± 0.017. The first observation of CP violation in the B-meson system was reported in the B0→J/ψK0 S channel by the BaBar andBelle collaborations. The measurement of the CP-violation parameters in (2β) has been updated several times by these experiments, and more recently by the LHCb andBelleII collaborations.

The new paper, regrettably, doesn't actually report its measured value of β but does provide a formula to convert a parameter that it does measure to β. Assuming no beyond the Standard Model physics:
The parameter S can be related to the CKM angle β as S = sin(2β+∆ϕd+ . . . ). . . . Contributions from penguin topologies to the decay amplitude that cause an additional phase shift ∆ϕd are CKM suppressed, hence deviations of S from sin(2β) are expected to be small in the Standard Model.

The bottom line value, simultaneously fitting data from three different decay modes for S is S = 0.717 ± 0.013(stat) ± 0.008(syst).

Another new paper recaps the latest and greatest measurements of the masses of the five hadronizing Standard Model quarks and the strong force coupling constant:

Monday, September 18, 2023

When And Why Was The Sahara Green?

We've made lots of progress in understanding African Paleoclimates. 

The two images above are from the paper cited below. The image below is from Wikipedia (see also a list of notable climate events here and here).

There is widespread evidence that the Sahara was periodically vegetated in the past, with the proliferation of rivers, lakes and water-dependent animals such as hippos, before it became what is now desert. These North African Humid Periods may have been crucial in providing vegetated corridors out of Africa, allowing the dispersal of various species, including early humans, around the world.

The so-called ‘greenings’ are thought to have been driven by changes in Earth’s orbital conditions, specifically Earth’s orbital precession. Precession refers to how Earth wobbles on its axis, which influences seasonality (i.e. the seasonal contrast) over an approximate 21,000-year cycle. These changes in precession determine the amount of energy received by the Earth in different seasons, which in turn controls the strength of the African Monsoon and the spread of vegetation across this vast region.

A major barrier to understanding these events is that the majority of climate models have been unable to simulate the amplitude of these humid periods, so the specific mechanisms driving them have remained uncertain.

This study deployed a recently-developed climate model to simulate the North African Humid periods to greatly advance understanding of their driving mechanisms.

The results confirm the North African Humid Periods occurred every 21,000 years and were determined by changes in Earth’s orbital precession. This caused warmer summers in the Northern Hemisphere, which intensified the strength of the West African Monsoon system and increased Saharan precipitation, resulting in the spread of savannah-type vegetation across the desert.

The findings also show the humid periods did not occur during the ice ages, when there were large glacial ice sheets covering much of the high latitudes. This is because these vast ice sheets cooled the atmosphere and suppressed the tendency for the African monsoon system to expand. This highlights a major teleconnection between these distant regions, which may have restricted the dispersal of species, including humans, out of Africa during the glacial periods of the last 800,000 years.

From a Science Daily press release

The paper and its abstract are as follows:

The Sahara region has experienced periodic wet periods over the Quaternary and beyond. These North African Humid Periods (NAHPs) are astronomically paced by precession which controls the intensity of the African monsoon system. However, most climate models cannot reconcile the magnitude of these events and so the driving mechanisms remain poorly constrained. Here, we utilise a recently developed version of the HadCM3B coupled climate model that simulates 20 NAHPs over the past 800 kyr which have good agreement with NAHPs identified in proxy data
Our results show that precession determines NAHP pacing, but we identify that their amplitude is strongly linked to eccentricity via its control over ice sheet extent. During glacial periods, enhanced ice-albedo driven cooling suppresses NAHP amplitude at precession minima, when humid conditions would otherwise be expected
This highlights the importance of both precession and eccentricity, and the role of high latitude processes in determining the timing and amplitude of the NAHPs. This may have implications for the out of Africa dispersal of plants and animals throughout the Quaternary.
Edward Armstrong, Miikka Tallavaara, Peter O. Hopcroft, Paul J. Valdes, "North African humid periods over the past 800,000 years." 14(1) Nature Communications (2023) (open access) DOI: 10.1038/s41467-023-41219-4

Monday, September 11, 2023

The Evolutionary Biology Of The Uncanny Valley

The obvious candidates giving rise to an evolutionary biology source for the uncanny valley effect in reality would be other archaic hominin species like Neanderthals, Denisovans, Homo erectus, and Homo floresiensis (a.k.a. "Hobbits"). And, this reaction may have evolved at the time of our pre-modern human ancestors because there were many species of the genus Homo in existence at that time, some of whom would have interacted with each other in Africa.

Less obviously, it could be something the developed to recognize when other people were suffering from diseases, physical and/or mental, or to trigger you not to trust what you see when you are under the influence of a hallucinogen.

It could also be a side effect our cognitive abilities developed for recognizing and evaluating other people, e.g., distinguishing people from another race or region, whose mechanism produces weird results when you are at the fringe of its domain of applicability.

Wikipedia notes at least nine theories to explain the psychological quirk, none of which is really dominant explanations in the academic community. They are:
Mate selection: Automatic, stimulus-driven appraisals of uncanny stimuli elicit aversion by activating an evolved cognitive mechanism for the avoidance of selecting mates with low fertility, poor hormonal health, or ineffective immune systems based on visible features of the face and body that are predictive of those traits.

Mortality salience: Viewing an "uncanny" robot elicits an innate fear of death and culturally supported defenses for coping with death's inevitability.... [P]artially disassembled on subconscious fears of reduction, replacement, and annihilation: (1) A mechanism with a human façade and a mechanical interior plays on our subconscious fear that we are all just soulless machines. (2) Androids in various states of mutilation, decapitation, or disassembly are reminiscent of a battlefield after a conflict and, as such, serve as a reminder of our mortality. (3) Since most androids are copies of actual people, they are doppelgängers and may elicit a fear of being replaced, on the job, in a relationship, and so on. (4) The jerkiness of an android's movements could be unsettling because it elicits a fear of losing bodily control.

Pathogen avoidance: Uncanny stimuli may activate a cognitive mechanism that originally evolved to motivate the avoidance of potential sources of pathogens by eliciting a disgust response. "The more human an organism looks, the stronger the aversion to its defects, because (1) defects indicate disease, (2) more human-looking organisms are more closely related to human beings genetically, and (3) the probability of contracting disease-causing bacteria, viruses, and other parasites increases with genetic similarity." The visual anomalies of androids, robots, and other animated human characters cause reactions of alarm and revulsion, similar to corpses and visibly diseased individuals.

Sorites paradoxes: Stimuli with human and nonhuman traits undermine our sense of human identity by linking qualitatively different categories, human and nonhuman, by a quantitative metric: degree of human likeness.

Violation of human norms: If an entity looks sufficiently nonhuman, its human characteristics are noticeable, generating empathy. However, if the entity looks almost human, it elicits our model of a human other and its detailed normative expectations. The nonhuman characteristics are noticeable, giving the human viewer a sense of strangeness. In other words, a robot stuck inside the uncanny valley is no longer judged by the standards of a robot doing a passable job at pretending to be human, but is instead judged by the standards of a human doing a terrible job at acting like a normal person. This has been linked to perceptual uncertainty and the theory of predictive coding.

Conflicting perceptual cues: The negative effect associated with uncanny stimuli is produced by the activation of conflicting cognitive representations. Perceptual tension occurs when an individual perceives conflicting cues to category membership, such as when a humanoid figure moves like a robot, or has other visible robot features. This cognitive conflict is experienced as psychological discomfort (i.e., "eeriness"), much like the discomfort that is experienced with cognitive dissonance. Several studies support this possibility. Mathur and Reichling found that the time subjects took to gauge a robot face's human- or mechanical-resemblance peaked for faces deepest in the uncanny valley, suggesting that perceptually classifying these faces as "human" or "robot" posed a greater cognitive challenge. However, they found that while perceptual confusion coincided with the uncanny valley, it did not mediate the effect of the uncanny valley on subjects' social and emotional reactions—suggesting that perceptual confusion may not be the mechanism behind the uncanny valley effect. Burleigh and colleagues demonstrated that faces at the midpoint between human and non-human stimuli produced a level of reported eeriness that diverged from an otherwise linear model relating human-likeness to affect. Yamada et al. found that cognitive difficulty was associated with negative affect at the midpoint of a morphed continuum (e.g., a series of stimuli morphing between a cartoon dog and a real dog). Ferrey et al. demonstrated that the midpoint between images on a continuum anchored by two stimulus categories produced a maximum of negative affect, and found this with both human and non-human entities. Schoenherr and Burleigh provide examples from history and culture that evidence an aversion to hybrid entities, such as the aversion to genetically modified organisms ("Frankenfoods"). Finally, Moore developed a Bayesian mathematical model that provides a quantitative account of perceptual conflict. There has been some debate as to the precise mechanisms that are responsible. It has been argued that the effect is driven by categorization difficulty, configural processing, perceptual mismatch, frequency-based sensitization, and inhibitory devaluation. 
Threat to humans' distinctiveness and identity: Negative reactions toward very humanlike robots can be related to the challenge that this kind of robot leads to the categorical human – non-human distinction. Kaplan stated that these new machines challenge human uniqueness, pushing for a redefinition of humanness. Ferrari, Paladino and Jetten found that the increase of anthropomorphic appearance of a robot leads to an enhancement of threat to the human distinctiveness and identity. The more a robot resembles a real person, the more it represents a challenge to our social identity as human beings.

Religious definition of human identity: The existence of artificial but humanlike entities is viewed by some as a threat to the concept of human identity. An example can be found in the theoretical framework of psychiatrist Irvin Yalom. Yalom explains that humans construct psychological defenses to avoid existential anxiety stemming from death. One of these defenses is 'specialness', the irrational belief that aging and death as central premises of life apply to all others but oneself. The experience of the very humanlike "living" robot can be so rich and compelling that it challenges humans' notions of "specialness" and existential defenses, eliciting existential anxiety. In folklore, the creation of human-like, but soulless, beings is often shown to be unwise, as with the golem in Judaism, whose absence of human empathy and spirit can lead to disaster, however good the intentions of its creator.

Uncanny valley of the mind or AI: Due to rapid advancements in the areas of artificial intelligence and affective computing, cognitive scientists have also suggested the possibility of an "uncanny valley of mind". Accordingly, people might experience strong feelings of aversion if they encounter highly advanced, emotion-sensitive technology. Among the possible explanations for this phenomenon, both a perceived loss of human uniqueness and expectations of immediate physical harm are discussed by contemporary research.

What Does A Theoretical Physicist's Office Look Like?


The Imjin Wars In Korea

Incredibly destructive wars are nothing new.
[T]he most significant destruction on the Korean Peninsula was wrought by the Japanese invasions of the late sixteenth century. Nearly two million Koreans, a staggering 20 percent of the population, perished during the Imjin Wars, Toyotomi Hideyoshi’s campaigns of 1592-1598 to subjugate the Korean Peninsula. Hideyoshi’s object was the conquest of Ming China (1368-1644) but the result was to turn Korea into a ruined land.

Friday, September 8, 2023

Strengthening Evidence Of Another Predicted Higgs Boson Decay Channel

This is now reasonably strong (3.4 sigma) evidence from the LHC of Higgs boson decays to a Z boson and a photon at a rate consistent with the Standard Model predicted branching fraction for decays of this kind.

This was first hinted at in April of 2022, and this report reiterates results announced in May of this year. 
The first evidence for the Higgs boson decay to a Z boson and a photon is presented, with a statistical significance of 3.4 standard deviations. The result is derived from a combined analysis of the searches performed by the ATLAS and CMS Collaborations with proton-proton collision data sets collected at the CERN Large Hadron Collider (LHC) from 2015 to 2018. These correspond to integrated luminosities of around 140 fb−1 for each experiment, at a center-of-mass energy of 13 TeV. The measured signal yield is 2.2±0.7 times the Standard Model prediction, and agrees with the theoretical expectation within 1.9 standard deviations.
ATLAS, CMS Collaborations, "Evidence for the Higgs boson decay to a Z boson and a photon at the LHC" arXiv:2309.03501 (September 7, 2023).

Thursday, September 7, 2023

Evidence Of Warm Dark Matter Annihilation Undermined

A new study fails to replicate the findings of five out of six papers that claim to have seen a 3.5 keV radiation line which arguably is the footprint of dark matter annihilation, using the same underlying data. 

The new study, with multiple authors, argues that the backgrounds were not correctly modeled and also identifies other methodological flaws in those papers. This greatly weakens on line of evidence in support of particle dark matter that can annihilate into ordinary matter or photons through collisions with other dark matter particles, which if the data were more solid would support a popular version of a warm dark matter particle model.

At least at face value, this is a rather stunning refutation of the work of the authors of the previous papers.

The 3.5 keV line is a purported emission line observed in galaxies, galaxy clusters, and the Milky Way whose origin is inconsistent with known atomic transitions and has previously been suggested to arise from dark matter decay. We systematically re-examine the bulk of the evidence for the 3.5 keV line, attempting to reproduce six previous analyses that found evidence for the line. Surprisingly, we only reproduce one of the analyses; in the other five we find no significant evidence for a 3.5 keV line when following the described analysis procedures on the original data sets. For example, previous results claimed 4σ

evidence for a 3.5 keV line from the Perseus cluster; we dispute this claim, finding no evidence for a 3.5 keV line. We find evidence for background mismodeling in multiple analyses. We show that analyzing these data in narrower energy windows diminishes the effects of mismodeling but returns no evidence for a 3.5 keV line. We conclude that there is little robust evidence for the existence of the 3.5 keV line. Some of the discrepancy of our results from those of the original works may be due to the earlier reliance on local optimizers, which we demonstrate can lead to incorrect results. For ease of reproducibility, all code and data are publicly available.  
Christopher Dessert, Joshua W. Foster, Yujin Park, Benjamin R. Safdi, "Was There a 3.5 keV Line?" arXiv:2309.03254 (September 6, 2023).

Near Hominin Extinction About 870,000 Years Ago?

I have no doubt that there was a serious bottleneck in hominin populations at roughly the time claimed. But effective population size is a tricky statistic that is further from what people think it means than most people realize, so don't take the absolute magnitude of the bottleneck, or the naive assumptions about the census population of these archaic hominins at this time, too literally. As the New York Times explains:
[O]utside experts said they were skeptical of the novel statistical methods that the researchers used for the study. “It is a bit like inferring the size of a stone that falls into the middle of the large lake from only the ripples that arrive at the shore some minutes later,” said Stephan Schiffels, a population geneticist at Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.

The researchers also put too much faith in a model that assumes a single universal mutation rate for genetic evolution, when there is good research to suggest that some parts of the genome evolve at faster rates than other parts of the genome. On the scale of several tens of thousands of generations, those fine points could become important.

Modern humans evolved around 300,000 years ago, and the speciation event that the authors suggests might coincide with this population bottleneck would have given rise to the common ancestor of modern humans, Neanderthals, and Denisovans.

The circumstances driving this 117,000 year period in which hominins may have come close to extinction aren't entirely clear. The editor's summary states:
The model detected a reduction in the population size of our ancestors from about 100,000 to about 1000 individuals, which persisted for about 100,000 years. The decline appears to have coincided with both major climate change and subsequent speciation events.
The paper and its abstract are as follows:
Population size history is essential for studying human evolution. However, ancient population size history during the Pleistocene is notoriously difficult to unravel. 
In this study, we developed a fast infinitesimal time coalescent process (FitCoal) to circumvent this difficulty and calculated the composite likelihood for present-day human genomic sequences of 3154 individuals. 
Results showed that human ancestors went through a severe population bottleneck with about 1280 breeding individuals between around 930,000 and 813,000 years ago. The bottleneck lasted for about 117,000 years and brought human ancestors close to extinction. 
This bottleneck is congruent with a substantial chronological gap in the available African and Eurasian fossil record. Our results provide new insights into our ancestry and suggest a coincident speciation event.

One very basic methodological issue with the speculation that hominins went nearly extinct around 870,000 years ago made by this study, for example, is that genetic information from currently living modern humans showing a population bottleneck only tells us about our direct ancestors. 

As of 870,000 years ago, there was at least one species of the genus Homo, Homo erectus which had already dispersed from Africa to Eurasia. There is good reason to believe that there may have actually been more than one at that point, because the most plausible characterization of Homo floresiensis on the island of Flores in Indonesia and similar archaic hominins in the Philippines, is that this is a more archaic hominin species than Homo erectus.

Therefore, it is possible that these archaic hominin species suffered less severe bottleneck effects somewhere in Eurasia or Oceania that was outside of Africa, which subsequent events, such as the expansion of modern humans, Neanderthals, and Denisovans into Eurasia or later climate catastrophes, or a combination of causes, led to the complete extinction of them at some later time, even though these archaic hominins had weathered the circumstances of 870,000 years ago better than our direct ancestors did.

One can imagine a narrative, for example, in which Homo erectus in Southeast Asia wasn't hit nearly so hard as African Homo erectus around 870,000 years ago, but then was driven to extinction there by the one two punch of the Toba eruption and modern human expansion into Southeast Asia in the wake of that eruption around 70,000 years ago. But, if hominins had gone extinct in Africa, the second prong of this one two punch would have never wiped out Southeast Asian Homo erectus and events might have played out differently. Southeast Asian Homo erectus might have back migrated to Africa 120,000 year or so after Africa experienced the conditions that drove hominins to near extinctions, when those conditions abated.

Further New York Times discussion of the new study (at the same link) notes that:
After decades of fossil hunting, the record of ancient human relatives remains relatively scarce in Africa in the period between 950,000 and 650,000 years ago. The new study offers a potential explanation: there just weren’t enough people to leave behind many remains, Dr. Hu said.

Brenna Henn, a geneticist at the University of California, Davis, who was not involved in the new study, said that a bottleneck was “one plausible interpretation.” But today’s genetic diversity might have been produced by a different evolutionary history, she added.

For example, humans might have diverged into separate populations then come together again. “It would be more powerful to test alternative models,” Dr. Henn said. 
Dr. Hu and his colleagues propose that a global climate shift produced the population crash 930,000 years ago. They point to geological evidence that the planet became colder and drier right around the time of their proposed bottleneck. Those conditions may have made it harder for our human ancestors to find food. 
But Nick Ashton, an archaeologist at the British Museum, noted that a number of remains of ancient human relatives dating to the time of the bottleneck have been found outside Africa. 
If a worldwide disaster caused the human population in Africa to collapse, he said, then it should have made human relatives rarer elsewhere in the world. 
“The number of sites in Africa and Eurasia that date to this period suggests that it only affected a limited population, who may have been ancestors of modern humans,” he said. 

Wednesday, September 6, 2023

Fifth Forces And The Hubble Tension

Gravity modification theories seem to more easily solve the Hubble tension than alternative theories.
Fifth forces are ubiquitous in modified theories of gravity. In this paper, we analyze their effect on the Cepheid-calibrated cosmic distance ladder, specifically with respect to the inferred value of the Hubble constant (H0). We consider a variety of effective models where the strength, or amount of screening, of the fifth force is estimated using proxy fields related to the large-scale structure of the Universe. For all models considered, the local distance ladder and the Planck value for H0 agrees with a probability ≳20%, relieving the tension compared to the concordance model with data being excluded at 99% confidence. The alleviated discrepancy comes partially at the cost of an increased tension between distance estimates from Cepheids and the tip of the red-giant branch (TRGB). Demanding also that the consistency between Cepheid and TRGB distance estimates is not impaired, some fifth force models can still accommodate the data with a probability ≳20%. This provides incentive for more detailed investigations of fundamental theories on which the effective models are based, and their effect on the Hubble tension.
Marcus Högås, Edvard Mörtsell, "The Hubble tension and fifth forces: a cosmic screenplay" arXiv:2309.01744 (September 4, 2023).

Friday, September 1, 2023

The Hubble Tension Is Hard To Resolve

The simplest solutions to the disparities in measurements of the Hubble constant at early and late times in the history of the universe probably won't work.
The Hubble tension has now grown to a level of significance which can no longer be ignored and calls for a solution which, despite a huge number of attempts, has so far eluded us. Significant efforts in the literature have focused on early-time modifications of ΛCDM, introducing new physics operating prior to recombination and reducing the sound horizon. 
In this opinion paper I argue that early-time new physics alone will always fall short of fully solving the Hubble tension. I base my arguments on seven independent hints, related to 1) the ages of the oldest astrophysical objects, 2) considerations on the sound horizon-Hubble constant degeneracy directions in cosmological data, 3) the important role of cosmic chronometers, 4) a number of ``descending trends'' observed in a wide variety of low-redshift datasets, 5) the early integrated Sachs-Wolfe effect as an early-time consistency test of ΛCDM, 6) early-Universe physics insensitive and uncalibrated cosmic standard constraints on the matter density, and finally 7) equality wavenumber-based constraints on the Hubble constant from galaxy power spectrum measurements. 
I argue that a promising way forward should ultimately involve a combination of early- and late-time (but non-local -- in a cosmological sense, i.e. at high redshift) new physics, as well as local (i.e. at z∼0) new physics, and I conclude by providing reflections with regards to potentially interesting models which may also help with the S8 tension.
Sunny Vagnozzi, "Seven hints that early-time new physics alone is not sufficient to solve the Hubble tension" arXiv:2308.16628 (August 31, 2023) (accepted for publication in Universe).