The History And Prehistory Of Human Disease

A new paper in Nature concludes from ancient DNA that while infectious diseases were common in humans since the hunter-gatherer era, that there was a real surge, not at the time of the Neolithic Revolution, but when steppe herders started to invade and conquerer farmers, and hunter-gatherers, possibly because they lived more closely with their animals and because the diseases that they carried helped facilitate their conquests. The New York Times also discusses the paper.

Infectious diseases have had devastating effects on human populations throughout history, but important questions about their origins and past dynamics remain. To create an archaeogenetic-based spatiotemporal map of human pathogens, we screened shotgun-sequencing data from 1,313 ancient humans covering 37,000 years of Eurasian history. We demonstrate the widespread presence of ancient bacterial, viral and parasite DNA, identifying 5,486 individual hits against 492 species from 136 genera. Among those hits, 3,384 involve known human pathogens, many of which had not previously been identified in ancient human remains. Grouping the ancient microbial species according to their likely reservoir and type of transmission, we find that most groups are identified throughout the entire sampling period. Zoonotic pathogens are only detected from around 6,500 years ago, peaking roughly 5,000 years ago, coinciding with the widespread domestication of livestock. Our findings provide direct evidence that this lifestyle change resulted in an increased infectious disease burden. They also indicate that the spread of these pathogens increased substantially during subsequent millennia, coinciding with the pastoralist migrations from the Eurasian Steppe

Martin Sikora, et al., "The spatiotemporal distribution of human pathogens in ancient Eurasia" Nature (July 9, 2025).

All the GUTs Worth Considering

A fairly short new paper (five pages plus seven pages of footnotes and an appendix) tries to list most or all of the possible Grand Unified Theories a.k.a. GUTs (i.e. theories the unify the three Lie groups of the Standard Model, but not gravity, into a single unified mathematical structure; unified theories that also include gravity are called Theories of Everything a.k.a. TOEs) that could include the Standard Model of Particle Physics, or an extension of it. 

There aren't all that many possibilities that are promising, and several decades of attempts to fit the Standard Model into one in a way that provides useful theoretical insight has not been very fruitful. While this line of inquiry isn't as troubled as supersymmetry (which is a dead man walking) or string theory (which is almost as troubled), it isn't very "hot" either.

Many potential GUTs, including the most minimal SU(5) GUT, would (1) imply violations of baryon number and/or lepton number conservation that aren't observed (e.g. proton decay, flavor changing neutral currents, and neutrinoless double beta decay), (2) lack some fundamental particles that are observed in the Standard Model, or (3) imply the existence of new fundamental particles beyond the Standard Model that haven't been observed (and in some cases, these particles have been ruled out to quite high energies). 

As a general rule, the bigger the Lie group of the unifying GUT, the more likely it is that it will imply far more new fundamental particles than there is any good reason to think that even a many particle dark sector should contain. Theoretical physicists prefer GUTs that imply as minimal an extension of the Standard Model as possible. Moreover, GUTs with certain kinds of new fundamental particles, such as those that imply more than three generations of fundamental Standard Model fermions, are strongly disfavored.

The experimental constraints on baryon number violating and lepton number violating processes (outside sphaleron interactions which are predicted in the Standard Model at extremely high energies but have not been observed) like proton decay, flavor changing neutral currents, and neutrinoless double beta decay are both very strict and very robust (i.e. they have been tested in multiple, independent ways). The exclusions of new fundamental particles are generally up to masses of several hundred to many thousands of GeVs, which is less strict, and the possibility of beyond the Standard Model fundamental particles is also strongly motivated (although not compelled) by the existence of dark matter phenomena. 

In the early days of GUT theories, a much sought after GUT property was that the three Standard Model forces unify at high enough energies in a manner that echos electroweak unification theory (which was one of the very attractive features of supersymmetry theory). But this has also been elusive. 

The Standard Model beta functions of the three Standard Model forces (electromagnetism, the weak force, and the strong force), which govern how the strength of these forces change with energy scale, extrapolated to arbitrarily high energy scales, based upon data all of the way up to the energy scales that can be reached by the Large Hadron Collider a.k.a. LHC (the highest energy scale high energy physics experiment every conducted), never unify. So, if a GUT the unifies the three Standard Model forces exists is some high energy scale, this must be due to new physics at energy scales above those that can be experimentally probed so far that is outside the domain of applicability of the Standard Model. 

Basically, given the energy scales that have already been reached by the LHC, energies at which the three Standard Model force could possibly unify haven't been present anywhere in the universe since some fraction of a second elapsed after the Big Bang. Of course, it is entirely possible that the three Standard Model forces simply don't unify at any energy scale that has ever existed or ever could exist.

Under a reasonable set of ab-initio assumptions, we define and chart the atlas of simple gauge theories with families of fermions whose masses are forbidden by gauge invariance. We propose a compass to navigate the atlas based on counting degrees of freedom. When searching for Grand-unification Theories with three matter generations, the free energy singles out the SU(5) Georgi-Glashow model as the minimal one, closely followed by SO(10) with spinorial matter. The atlas also defines the dryland of grand-unifiable gauge extensions of the standard model. We further provide examples relevant for gauge dual completions of the standard model as well as extensions by an additional SU(N) gauge symmetry.

Giacomo Cacciapaglia, Aldo Deandrea, Konstantinos Kollias, Francesco Sannino, "Grand-unification Theory Atlas: Standard Model and Beyond" arXiv:2507.06368 July 8, 2025).

The final paragraph of the conclusion of the main paper also enumerates some limitations on this paper serving as a truly comprehensive list of possibilities:

We have not considered yet scalar fields, as their mass cannot be prevented by any symmetry. Including spontaneous symmetry breaking of the gauge symmetry and generation of Yukawa couplings could imprint further constraints on the atlas, providing a phenomenological compass to navigate us towards the optimal high-energy theory. In our analysis, asymptotic freedom plays a crucial role in counting the degrees of freedom of each theory.

Non-Linear Cosmology Dynamics

Assuming the data has a Gaussian distribution (i.e. is distributed in a "normal" probability curve) is often reasonable, since this is what happens when data comes from independent simple percentage probability events. And, it is a convenient assumption when it works, because mathematically it is much easier to work with Gaussian distributions than most other probability distributions. But, sometimes reality is more complicated than that and this assumption isn't reasonable. 

The supernova data used to characterize dark energy phenomena isn't Gaussian. 

Trivially, this means that statistical uncertainty estimates based upon Gaussian distributions overestimate the statistical significance of observations in the fat tailed t-distribution. 

Non-trivially, this means that the underlying physics of dark matter phenomena are more mathematically complex than something like Newtonian gravity (often assumed for astronomy purposes as a reasonable approximation of general relativity) or a simple cosmological constant. Simple cosmology models don't match the data. 

This paper estimates dark energy parameters for more complex dark energy models that can fit the data.

Type Ia supernovae have provided fundamental observational data in the discovery of the late acceleration of the expansion of the Universe in cosmology. However, this analysis has relied on the assumption of a Gaussian distribution for the data, a hypothesis that can be challenged with the increasing volume and precision of available supernova data. 

In this work, we rigorously assess this Gaussianity hypothesis and analyze its impact on parameter estimation for dark energy cosmological models. We utilize the Pantheon+ dataset and perform a comprehensive statistical, analysis including the Lilliefors and Jarque-Bera tests, to assess the normality of both the data and model residuals. 

We find that the Gaussianity assumption is untenable and that the redshift distribution is more accurately described by a t-distribution, as indicated by the Kolmogorov Smirnov test. Parameters are estimated for a model incorporating a nonlinear cosmological interaction for the dark sector. The free parameters are estimated using multiple methods, and bootstrap confidence intervals are constructed for them.

Fabiola Arevalo, Luis Firinguetti, Marcos Peña, "On the Gaussian Assumption in the Estimation of Parameters for Dark Energy Models" arXiv:2507.05468 (July 7, 2025).

Steppe Ancestry In Italy

Blonde hair percentages, at a population statistics level, is a good proxy for Indo-European steppe ancestry levels (it's not as good as autosomal DNA, but the sample size and amount of fine grained geographic detail is much better). You'd need an estimate for the amount of steppe ancestry in Italians to calibrate this litmus test, however.

The first farmers of Europe had essentially 0% blonde hair, much like modern Sardinians, who are their closest genetic match. Blonde hair in Europe arrived more or less exclusively via steppe migration in late Neolithic to early Bronze Age from an ultimate homeland in the vicinity of modern Ukraine, although plenty of migration happened within Europe after this migration and not all steppe migrants had blonde hair. It is also possible to have very little steppe ancestry while still having the blonde hair gene. 

The chart shows the percentage of blond haired people in the regions shown on the map in (or near) Italy. Overall, about 8% of Italians are naturally blonde (another estimate suggests 15%). It suggests that Indo-European migration to Italy was largely north to south (with exceptions for urban centers) and reached southern Italy in far smaller proportions than northern Italy, although it is hard to know how much of the migration was modern, how much was medieval, how much was from the Roman era, and how much dates to pre-history.

Until the late 1870s, Italy was not a unified country, with Southern Europe belonging to the poorer Kingdom of the Two Sicilies with a more agricultural economy, and Northern Europe belonging to a number of smaller and more prosperous states with more mercantile economies, which could have impacted migration patterns by increasing migration from areas with more blonde people. 

From Reddit.

In the medieval era Northern Europeans, including the Normans and Vikings and Germanic tribes, had greater interactions with Northern Italy than with Southern Italy, as well. 

In the Roman era, migration to the Roman capital and its major cities from North Africa, Egypt, and the Levant might have diluted the percentage of people with steppe ancestry.

Shortly before the classical Roman era, there were a number of Greek colonies in Italy, which could be reflected in the purple regions on the map (about 4% of Greeks are naturally blonde), with some blurring out due to admixture with regions near former Greek colonies.

From Wikipedia.

A New Strong Force Coupling Constant Determination

The Particle Data Group value for the strong force coupling constant is 0.1180 ± 0.0009. This new determination, based upon earlier runs of LHC dijet data and lower energy HERA data, is consistent with the PDG value at the 0.1 sigma level. 

The strong force coupling constant is pervasively important in almost all high energy physics calculations, but it known much less precisely (with just one part per 131 parts precision) than most other Standard Model or fundamental physical constants. So, pinning this down more precisely is always big deal.

The beta function that describes how the strong force coupling constant runs with energy scale is an exact theoretical prediction of the Standard Model, with no experimental uncertainties. The conference presentation's confirmation that the strong force coupling constant runs with energy scale just as predicted in the Standard Model, over four orders of magnitude of energy scale, is arguably an even more important confirmation of the Standard Model, because there are fewer experimental confirmations of this in the literature.

In this talk we present a determination of the strong coupling constant αs and its energy-scale dependence based on a next-to-next-to-leading order (NNLO) QCD analysis of dijet production. 

Using the invariant mass of the dijet system to probe αs at different scales, we extract a value of αs(mZ) = 0.1178 ± 0.0022 from LHC dijet data. 

The combination of various LHC datasets significantly extends the precision and scale reach of the analysis, enabling the first determination of αs up to 7 TeV. By incorporating dijet cross sections from HERA, we further probe αs at smaller scales, covering a kinematic range of more than three orders of magnitude. Our results are in excellent agreement with QCD predictions based on the renormalization group equation, providing a stringent test of the running of the strong coupling across a wide energy range.

João Pires, "Precision determination of αs from Dijet Cross Sections in the Multi-TeV Range" arXiv:2507.01670 (July 2, 2025) (Contribution to the 2025 QCD session of the 59th Rencontres de Moriond).

A New Relativistic Generalization Of MOND (And More)

This six page article is just a conference paper summary of a much more involved modified gravity theory and its implications. The abstract is silent on how well it handles galaxy cluster physics, which deviate (in a quite systemic way) from simple toy-model MOND theories, or the Hubble tension.

We propose an alternative scalar-tensor theory based on the Khronon scalar field labeling a family of space-like three-dimensional hypersurfaces. This theory leads to modified Newtonian dynamics (MOND) at galactic scales for stationary systems, recovers GR plus a cosmological constant in the strong field regime, and is in agreement with the standard cosmological model and the observed cosmic microwave background anisotropies.

Luc Blanchet, Constantinos Skordis, "Khronon-Tensor theory reproducing MOND and the cosmological model" arXiv:2507.00912 (July 1, 2025) (Contribution to the 2025 Gravitation session of the 59th Rencontres de Moriond).

A fuller explanation of the theory can be found here.

Another lengthy paper by P. S. Bhupal Dev et al., examines the constraints dark matter-neutrino interactions which are very strict.

We present a comprehensive analysis of the interactions of neutrinos with the dark sector within the simplified model framework. We first derive the exact analytic formulas for the differential scattering cross sections of neutrinos with scalar, fermion, and vector dark matter (DM) for light dark sector models with mediators of different types. We then implement the full catalog of constraints on the parameter space of the neutrino-DM and neutrino-mediator couplings and masses, including cosmological and astrophysical bounds coming from Big Bang Nucleosynthesis, Cosmic Microwave Background, DM and neutrino self-interactions, DM collisional damping, and astrophysical neutrino sources, as well as laboratory constraints from 3-body meson decays and invisible Z decays. 

We find that most of the benchmarks in the DM mass-coupling plane adopted in previous studies to get an observable neutrino-DM interaction effect are actually ruled out by a combination of the above-mentioned constraints, especially the laboratory ones which are robust against astrophysical uncertainties and independent of the cosmological history. 

To illustrate the consequences of our new results, we take the galactic supernova neutrinos in the MeV energy range as a concrete example and highlight the difficulties in finding any observable effect of neutrino-DM interactions. 

Finally, we identify new benchmark points potentially promising for future observational prospects of the attenuation of the galactic supernova neutrino flux and comment on their implications for the detection prospects in future large-volume neutrino experiments such as JUNO, Hyper-K, and DUNE. We also comment on the ultraviolet-embedding of the effective neutrino-DM couplings.

Razib Khan on Denisovans

Razib Khan does a good job of summing up some of the things that we've learned in recent years about Denisovans, an archaic hominin clade.

[I]n June 2025, Chinese paleogeneticist Qiaomei Fu published data finally connecting specific fossil remains to Denisovans, utilizing both mtDNA and protein sequencing methods. And so now we know that Denisovans and Homo longi, are one and the same. A rather well preserved fossil from Harbin, China, a nearly complete skull, first identified as a new species in a 2021 publication, and colloquially dubbed Dragon Man, turns out to have DNA that we can now see neatly matches the sequences extracted from Denisova cave. For fifteen years, the label Denisovan only applied in a genomic context. No longer. Denisovan physical remains were in fact in plain sight all along.

This is not entirely a surprise. Some geneticists and paleoanthropologists have long assumed that many among the wealth of the fossils languishing yet to be identified, catalogued or named in East Asian collections today were Denisovans (I said as much in a podcast with Vagheesh Narasimhan of UT Austin, when H. longi was announced four years ago). Also, since 2010, we have established that Denisovans are the ancestors of more than Papuans and other Australasians. The Negrito peoples of the Philippines have a substantial contribution from Denisovans, the same as their Papuan neighbors from New Guinea to the south. But when you set aside their majority Austronesian ancestry (a much more recent overlay), it appears their forager ancestors (today some 35% of their ancestry) carried even more Denisovan ancestry than Papuans, on the order of 7-8%. It is also clear that low, but detectable, levels of Denisovan ancestry appear today in populations across South, East and Southeast Asia, at fractions of 0.1-0.3%.

 

Partial skull of Homo longi, AKA a Denisovan

The attested presence of Denisovan ancestry across a vast triangle stretching from Pakistan to Japan to Australia argues that they were present across vast territories. Deeper analysis of the Denisovan fragments in the genomes of Asians, Melanesians and Australians suggest at minimum two admixture events with two very distinct Denisovan populations. One population is clearly related to the genomes we have from Denisova cave. These northern Denisovans mixed with the ancestors of modern East Asians. But the Denisovan ancestry in South and Southeast Asians, as well as in Melanesians and Australians, is clearly from a population with a distinct ancestry; likely one that split off from the northern subspecies as long as more than 350,000 years ago. And the plot thickens, because tentative evidence gleaned from comparing the segments carried by these populations with southern Denisovan ancestry suggests distinct admixtures here as well; one in South Asians, another in Southeast Asians (a common one with Melanesians and Australians), and perhaps even one or two further ones in the outer reaches of prehistoric Sundaland and Sahul.

Are Oxygen Levels Related To Earth's Magnetic Field?

The strength of Earth’s magnetic field seems to rise and fall in line with the abundance of oxygen in the planet’s atmosphere, a study of geological records spanning the past half a billion years has found.

From the journal Nature. 

Among other things, the overall oxygen levels in the atmosphere impacts how large animals get, with more oxygen favoring larger animals.

It isn't clear what causes drive the correlation, although there probably is a cause.

Criticism Of Numerical Approaches To Indo-European Language Phylogeny

I've long been critical of Gray & Atkinson and the New Zealand school's efforts to do computational linguistics for the Indo-European languages, and specifically questioned Heggarty (2023) when it was released. A big factor in that is mishandling the importance of language contact, which can vary depending upon the relative dominance of the languages in contact and the nature of the words, phonetic values, and grammatical structures involved.

In this paper, we present a brief critical analysis of the data, methodology, and results of the most recent publication on the computational phylogeny of the Indo-European family (Heggarty et al. 2023), comparing them to previous efforts in this area carried out by (roughly) the same team of scholars (informally designated as the “New Zealand school”), as well as concurrent research by scholars belonging to the “Moscow school” of historical linguistics. 

We show that the general quality of the lexical data used as the basis for classification has significantly improved from earlier studies, reflecting a more careful curation process on the part of qualified historical linguists involved in the project; however, there remain serious issues when it comes to marking cognation between different characters, such as failure (in many cases) to distinguish between true cognacy and areal diffusion and the inability to take into account the influence of the so-called derivational drift (independent morphological formations from the same root in languages belonging to different branches). 

Considering that both the topological features of the resulting consensus tree and the established datings contradict historical evidence in several major aspects, these shortcomings may partially be responsible for the results. Our principal conclusion is that the correlation between the number of included languages and the size of the list may simply be insufficient for a guaranteed robust topology; either the list should be drastically expanded (not a realistic option for various practical reasons) or the number of compared taxa be reduced, possibly by means of using intermediate reconstructions for ancestral stages instead of multiple languages (the principle advocated by the Moscow school).

Alexei S. Kassian and George Starostin, "Do 'language trees with sampled ancestors' really support a 'hybrid model' for the origin of Indo-European? Thoughts on the most recent attempt at yet another IE phylogeny". 12 (682) Humanities and Social Sciences Communications (May 16, 2025).

From the body text:

Discussion and conclusions

In the previous sections, we have to tried to identify several factors that might have been responsible for the dubious topological and chronological results of Heggarty et al. 2023 experiment, not likely to be accepted by the majority of “mainstream” Indo-European linguists. Unfortunately, it is hard to give a definite answer without extensive tests, since, in many respects, the machine-processed Bayesian analysis remains a “black box”. We did, however, conclude at least that this time around, errors in input data are not a key shortcoming of the study (as was highly likely for such previous IE classifications as published by Gray and Atkinson, 2003; Bouckaert et al. 2012), although failure to identify a certain number of non-transparent areal borrowings and/or to distinguish between innovations shared through common ancestry and those arising independently of one another across different lineages (linguistic homoplasy) may have contributed to the skewed topography.

One additional hypothesis is that the number of characters (170 Swadesh concepts) is simply too low for the given number of taxa (161 lects). From the combinatorial and statistical point of view, it is a trivial consideration that more taxa require more characters for robust classification (see Rama and Wichmann, 2018 for attempts at estimation of optimal dataset size for reliable classification of language taxa). Previous IE classifications by Gray, Atkinson et al. involved fewer taxa and more characters (see Table 1 for the comparison).

Table 1 suggests that the approach maintained and expanded upon in Heggarty et al. 2023 project can actually be a dead-end in classifying large and diversified language families. In general, the more languages are involved in the procedure, the more characters (Swadesh concepts) are required to make the classification sufficiently robust. Such a task, in turn, requires a huge number of man-hours for wordlist compilation and is inevitably accompanied by various errors, partly due to poor lexicographic sources for some languages, and partly due to the human factor. Likewise, expanding the list of concepts would lead us to less and less stable concepts with vague semantic definitions.

Instead of such an “expansionist” approach, a “reductionist” perspective, such as the one adopted by Kassian, Zhivlov et al. (2021), may be preferable, which places more emphasis on preliminary elimination of the noise factor rather than its increase by manually producing intermediate ancestral state reconstructions (produced by means of a transparent and relatively objective procedure). Unfortunately, use of linguistic reconstructions as characters for modern phylogenetic classifications still seems to be frowned upon by many, if not most, scholars involved in such research — in our opinion, an unwarranted bias that hinders progress in this area.

Overall one could say that Heggarty et al. (2023) at the same time represents an important step forward (in its clearly improved attitude to selection and curation of input data) and, unfortunately, a surprising step back in that the resulting IE tree, in many respects, is even less plausible and less likely to find acceptance in mainstream historical linguistics than the trees previously published by Gray & Atkinson (2003) and by Bouckaert et al. (2012). 

Consequently, the paper enhances the already serious risk of discrediting the very idea of the usefulness of formal mathematical methods for the genealogical classification of languages; it is highly likely, for instance, that a “classically trained” historical linguist, knowledgeable in both the diachronic aspects of Indo-European languages and such adjacent disciplines as general history and archaeology, but not particularly well versed in computational methods of classification, will walk away from the paper in question with the overall impression that even the best possible linguistic data may yield radically different results depending on all sorts of “tampering” with the complex parameters of the selected methods — and that the authors have intentionally chosen that particular set of parameters which better suits their already existing pre-conceptions of the history and chronology of the spread of Indo-European languages. 

While we are not necessarily implying that this criticism is true, it at least seems obvious that in a situation of conflict between “classic” and “computational” models of historical linguistics, assuming that the results of the latter automatically override those of the former would be a pseudo-scientific approach; instead, such conflicts should be analyzed and resolved with much more diligence and much deeper analysis than the one presented in Heggarty et al. 2023 study.

Hadron Molecules v. True Composite States

Any time that you have four to six quarks in some sort of bound state, the question that is presented is whether it is a true tetra-, penta-, or hexaquark, or whether it is a hadron molecule with the same valence quarks.

In a true tetra-, penta-, or hexaquark, the valence quarks are bound direct to each other by gluons. In a hadron molecule, mesons or baryons are bound to each other either by something analogous to the nuclear binding force (carried by mesons in atomic nuclei, mostly, but not entirely, pions) or electromagnetically (as in an ordinary molecule made up of atoms bound electromagnetically).

A new preprint looks at four pentaquark states with a valence charm quark and finds that all of them are hadron molecules rather than true pentaquarks.

Theories To Explain The Fundamental Fermion Masses

A new review paper which will be a chapter in an Encyclopedia of Particle Physics summarizes various theories that have been advanced to explain the fundamental fermion masses in the Standard Model, and while it isn't complete, its table of contents is a nice summary of some of the leading approaches.

2 Fermion masses and mixing angles 

2.1 The Standard Model 

2.2 Neutrino masses 

Majorana neutrino masses

The seesaw mechanism

Type-I seesaw

Type-III seesaw

Type-II seesaw

Dirac neutrino mass

2.3 The data 

3 In search of an organizing principle 

4 Grand Unified Theories 

4.1 SU(5) GUTs 

4.2 SU(10) GUTs 

5 Fermion masses from quantum corrections 

5.1 Radiative fermion masses 

5.2 Infrared fixed points 

6 CompositeFermions 

6.1 Massless composite fermions 

6.2 Partial compositeness 

7 Flavor Symmetries 

7.1 The Froggatt-Nielsen Model 

7.2 Variants and alternatives 

8 Fermion masses in String Theory 

8.1 Aiming at the SM from strings 

8.2 Eclectic flavor symmetries from heterotic orbifolds 

8.3 Flavor in models with D-branes 

8.4 Metaplectic flavor symmetries from magnetized branes

The LP & C relationship, and the kind of dynamical balancing rules that I favor don't get a mention, although they come closest to the quantum corrections approach. 

Missing Baryon Problem Solved

Connor et al. assess that about 3/4 of all baryons are in the intergalactic medium (IGM), give or take 10% – the side bars illustrate the range of uncertainty. Many of the remaining baryons are in other forms of space plasma associated with but not in galaxies: the intracluster medium (ICM) of rich clusters, the intragroup medium (IGroupM) of smaller groups, and the circumgalactic medium (CGM) associated with individual galaxies. All the stars in all the galaxies add up to less than 10%, and the cold (non-ionized) atomic and molecular gas in galaxies comprise about 1% of the baryons.

For a long time at least half to a third of the ordinary atoms that other observations and Big Bang Nucleosynthesis predicted exist hadn't been found. (And, to be clear, this "missing baryon problem" was separate and distinct from the "dark matter" problem.)

Now, they are all accounted for. The missing ones were in the intergalactic medium (i.e. in the deep space between galaxies at a density of about one hydrogen atom per cubic meter). 

Stacy McGaugh at his blog Triton Station explains how this happened. The money chart is above.

Conformal Cosmology

An interesting GR based response to dark matter and dark energy that makes one subtle adjustment to the standard analysis. I'll have to give it a more careful read before saying more about it.

This paper is published in a peer reviewed journal (although not a high profile one) and the author has seven prior peer reviewed journal publications since 2016, one with Pavel Kroupa, a leading astronomer in the MOND literature, as a co-author. So, this is not the work of a crackpot non-astronomer.

The cosmic time dilation observed in Type Ia supernova light curves suggests that the passage of cosmic time varies throughout the evolution of the Universe. This observation implies that the rate of proper time is not constant, as assumed in the standard FLRW metric, but instead is time-dependent. Consequently, the commonly used FLRW metric should be replaced by a more general framework, known as the Conformal Cosmology (CC) metric, to properly account for cosmic time dilation. 

The CC metric incorporates both spatial expansion and time dilation during cosmic evolution. As a result, it is necessary to distinguish between comoving and proper (physical) time, similar to the distinction made between comoving and proper distances. In addition to successfully explaining cosmic time dilation, the CC metric offers several further advantages: (1) it preserves Lorentz invariance, (2) it maintains the form of Maxwell's equations as in Minkowski space-time, (3) it eliminates the need for dark matter and dark energy in the Friedmann equations, and (4) it successfully predicts the expansion and morphology of spiral galaxies in agreement with observations.

Vaclav Vavrycuk, "Time dilation observed in Type Ia supernova light curves and its cosmological consequences" arXiv:2506.19099 (June 23, 2025) (published in 13 Galaxies 55 (2025)).

Kroupa has also published a new cosmology paper (although I'm not optimistic about this MOND plus sterile neutrinos in clusters approach).

The νHDM is the only cosmological model based on Milgromian Dynamics (MOND) with available structure formation simulations. While MOND accounts for galaxies, with a priori predictions for spirals and ellipticals, a light sterile neutrino of 11 eV can assist in recovering scaling relations on the galaxy-cluster scales. In order to perform MONDian cosmological simulations in this theoretical approach, initial conditions derived from a fit to the angular power spectrum of Cosmic Microwave Background (CMB) fluctuations are required. 

In this work, we employ CosmoSIS to perform a Bayesian study of the νHDM model. Using the best-fit values of the posterior, the CMB power spectrum is reevaluated. The excess of power in the transfer function implies a distinct evolution scenario, which can be used further as an input for a set of hydro-dynamical calculations. The resulting values H0 ≈ 56 km/s/Mpc and Ωm0≈0.5 are far from agreement with respect to the best fit ones in the canonical Cold Dark Matter model, but may be significant in MONDian cosmology. The assumed Planck CMB initial conditions are only valid for the ΛCDM cosmology. This work constitutes a first step in an iterative procedure needed to disentangle the model dependence of the derived initial density and velocity fields.

Nick Samaras, Sebastian Grandis, Pavel Kroupa, "On the initial conditions of the νHDM cosmological model" arXiv:2506.19196 (June 23, 2025) (accepted for publication in MNRAS).

Muon g-2 Limits On BSM Physics

A new preprint explores how the lack of a muon g-2 anomaly constrains beyond the Standard Model particle physics models. The new constraints are strict but aren't easily summarized in a few words. Another paper looks at the impact on supersymmetry theories.

Homo Longi Were Denisovans

The archaic hominin skull from China provisionally classified as a member of the species Homo Longi has been linked to Denisovan DNA and proteins. This also makes it possible to know what a Denisovan looked like as shown in the image below.

The connection has been suspected, but not proven, for some time.

Population Replacement In The Columbian Highlands

In Europe, the first farmers of Europe, derived from Western Anatolian farmers, largely replaced Europe's original hunter-gatherers (who actually show continuity between the periods before and immediately after the Last Glacial Maximum), and in turn, received very substantial genetic admixture from late Copper Age/early Bronze Age Indo-Europeans from more or less where Ukraine is today. This diluted both first farmer ancestry, and the already highly diluted European hunter-gather ancestry that was admixed into those first farmer populations. In some places, like Britain, the population replacement of first farmers by Indo-Europeans was nearly complete.

Something similar apparently happened in East and Southeast Asia.

A new study established that the Americas did not break from this pattern, with some of its early agriculturists replacing pre-existing hunter-gatherer populations in a similarly genocidal pattern. If anything, this replacement was even more complete.

Sometime between 4000 BCE and 0 CE, in the Columbian highlands, probably coinciding with a new archaeological culture whose artifacts appear around 1000 BCE to 800 BCE, a millennium after maize cultivation began around 1800 BCE (but possibly before the full blown ceramic culture emerged), a clade of indigenous South American hunter-gatherers (with ancestry dating back to the initial wave of human settlement of South America) were replaced by a different group of indigenous South Americans.

The 1800 BCE date is from A. Gómez, et al., "A Holocene pollen record of vegetation change and human impact from Pantano de Vargas, an intra-Andean basin of Duitama, Colombia." 145 Rev. Palaeobot. Palynol. 143–157 (2007) (full paper available here), and really only definitively points to deforestation and Amaranth cultivation at that point in the highlands of Columbia.

From Wikipedia.

The population that replaced them, which is genetically linked to the speakers of Chibchan languages and probably originated in Central America, has remained the dominant population of the region in genetic continuity with their ancestors since this population replacement occurred, although later populations admixed with them and brought new languages in some parts of the region. 

There is no evidence that anyone from the pre-agricultural, pre-ceramic culture that was replaced in the Columbian highlands survived, or even significantly admixed with surviving populations.

The new agriculturalist culture did not really come into its own archaeologically until 1000 BCE to 800 BCE, so we can't know for sure if the replacement took place suddenly (although the lack of admixture between the new and old populations suggests that it did) or more gradually, or how long after maize cultivation, a thousand years earlier than this culture's pots appeared, the population replacement happened. 

Conservatively, it happened in some short time period between 1800 BCE and 800 BCE (about 3,000 to 4,000 years after it happened in Europe). Realistically, it probably happened on the later side of that time range when other components of the emerging farmer culture, like pottery and possibly other key domesticated plants and/or animals, joined with improved maize cultivation to give rise to a technologically dominant new culture.

The introduction and discussion sections of a new study released May 28, 2025 in the journal Scientific Advances by Kim-Louise Krettek, et al., explain that:

Genetic studies on ancient and present-day Indigenous populations have substantially contributed to the understanding of the settlement of the Americas. Those studies revealed that the population ancestral to non-Arctic Native Americans derives from a genetic admixture between ancient East Asian and Siberian groups somewhere in North-East Asia before 20,000 years before the present (yr B.P.). Around 16,000 yr B.P., after its arrival in North America, this genetic ancestry split into two lineages known as northern Native American and southern Native American. While northern Native American ancestry is largely confined to ancient and current populations of North America, the southern Native American lineage expanded further south and constitutes the main ancestry component of ancient and present-day Indigenous South Americans. 

Southern Native American ancestry diversified within North America into at least three sublineages, i.e., one related to the Clovis-associated Anzick-1 individual from western Montana (USA), one found in ancient California Channel Islands individuals and the last one representing the main ancestry source of modern-day Central and South Americans.  

Each of these sublineages provided a wave of ancestry into the gene pool of ancient South Americans. Individuals from Chile and Brazil dating back to around 12,000 and 10,000 yr B.P., respectively, were more genetically related to the Anzick-1 genome than individuals from the eastern Southern American coast, Southern Cone and the Andes from 10,000 yr B.P. onward. In addition, the California Channel Islands ancestry was found in the Central Andes by 4200 yr B.P. and became widespread in the region thereafter. However, the exact timing of these population movements into the southern subcontinent remains largely unsolved to date. 

The Isthmo-Colombian area, stretching from the coast of Honduras to the northern Colombian Andes, is critical to understanding the peopling of the Americas. Besides being the land bridge between North and South America, it is at the center of the three major cultural regions of Mesoamerica, Amazonia, and the Andes. At the time of European contact, the region was inhabited by a complex mosaic of human populations, mainly speakers of Chibchan, Chocoan, Carib, and Arawakan languages. 

Among those populations, those who were speakers of Chibchan languages were the most widespread in the region in terms of demography, cultural diversity, and territorial distribution. Chibchan is a language family with multiple, highly distinct branches, many of which are still spoken today in different regions of the Isthmo-Colombian area. The homeland and antiquity of the Proto-Chibchan language and the ancestor of all Chibchan languages remain subjects of debate. High intrafamily variation in terms of lexicon and grammar suggests that the language family is ancient and began diversifying several thousand years ago. The locus of that incipient diversification, however, is still uncertain. Most scholars believe that this protolanguage began to diversify in Lower Central America, where the largest number of these languages is spoken today. However, some evidence suggests that Proto-Chibchan might have originated in South America and then diversified in Central America at a much later date. 

Genetic studies of ancient and present-day Isthmo-Colombian Indigenous populations revealed a distinctive ancestry component primarily associated with speakers of Chibchan languages. However, whereas mitochondrial DNA (mtDNA) studies suggested a migration of Chibchan-related ancestry from Central America into Colombia and Venezuela, genome-wide studies favored an opposite, south-to-north population movement. According to the latter model, speakers of Chibchan languages from Central America are not direct descendants of the first settlers in the region but, instead, derive from a more recent back migration from South to Central America. 

The southernmost region of the Isthmo-Colombian area is the Altiplano Cundiboyacense (hereafter Altiplano). This plateau with an average altitude of 2600 m in the Eastern Cordillera of the Colombian Andes was inhabited by ancient hunter-gatherer groups from the Late Pleistocene. During the Early and Middle Holocene phases of the Preceramic period (~11,500 to 4000 yr B.P.), populations on the Altiplano underwent multiple cultural transformations, most notably increased sedentism and a transition from a hunter-gatherer subsistence to the introduction of horticultural practices and forest management. However, it was not until the early Late Holocene, ~3800 yr B.P., that the first clear evidence of maize cultivation appeared. 

During the subsequent Formative period (~3000 to 1000 yr B.P.), a distinct type of pottery emerged on the Altiplano that is referred to as the Herrera ceramic complex, also known in the literature as the Herrera period (2800 to 1200 yr B.P.). It is still highly debated whether Herrera-associated groups on the Altiplano derived from an in situ development of local hunter-gatherers or were a consequence of population dispersals into the region. 

Around 1200 yr B.P., a cultural phase, known as the Muisca period, began on the Altiplano and lasted until the imposition of the Hispanic Colonial regime in the mid-16th century. Most available evidence is suggestive of population continuity with the preceding Herrera period. The Muisca period is characterized by a relatively continuous process of demographic growth, development of agriculture and trade, and social and political complexification. These factors played a considerable role in shaping the Muisca culture and gave rise to the Chibchan-speaking population that dominated the Altiplano until European colonization. 

While several studies have reported mtDNA data from ancient Colombian individuals, genome-wide data from this region are still entirely lacking to date. In this study, we generated mtDNA and genome-wide data of 21 ancient individuals from two areas of the Altiplano (Bogotá plateau and Los Curos). Our data, spanning a time transect between around 6000 and 500 yr B.P., provide an opportunity to explore several key questions: 

(i) Which southern Native American genetic ancestry do Preceramic individuals from the Altiplano derive from? 

(ii) Were the cultural transformations associated with the Herrera and Muisca periods accompanied by migrations and demographic changes? 

(iii) How is the genetic ancestry observed in speakers of Chibchan languages related to that of ancient individuals from the Altiplano? 

(iv) What are the genetic relationships between the generated ancient genomes and the existing genomic data of present-day Indigenous communities from Colombia and neighboring regions?

In this study, we generated genome-wide data from 21 individuals spanning a time transect of almost 6000 years from the Altiplano, which represents the southern edge of the Isthmo-Colombian area. Our findings contribute to a better understanding of the population history of this area, a key region in the peopling process of South America. We show that the hunter-gatherer population from the Altiplano dated to around 6000 yr B.P. lack the genetic ancestry related to the Clovis-associated Anzick-1 genome and to ancient California Channel Island individuals, suggesting their affiliation to the southern Native American lineage that became the primary source of ancestry of South Americans by 9000 yr B.P. 

However, unlike ancient genomes from the Andes and the Southern Cone that are associated with the same wave of ancestry, the analyzed Preceramic individuals from Colombia do not share distinct affinity with any ancient or modern-day population from Central and South America studied to date. Colombia_Checua_6000BP can thus be modeled as a previously undescribed distinct lineage deriving from the radiation event that gave rise to multiple populations across South America during its initial settlement. 

The cultural transition between the Preceramic and Herrera periods is associated with a seemingly complete replacement of the local genetic profile. This challenges the model where local hunter-gatherers developed in situ as suggested by morphometric studies and an ancient mtDNA time transect. Instead, our study provides evidence for a major genetic turnover on the Altiplano occurring after 6000 yr B.P. but before 2000 yr B.P. Since the mechanisms and precise temporal scale of this replacement event remain uncertain, we cannot directly associate it with the emergence of maize cultivation ~3800 yr B.P. However, our data do support the archaeological hypothesis that the introduction of pottery associated with the Herrera ceramic complex was mediated through population dispersals. 

Our results show that the incoming genetic ancestry on the Altiplano is related to ancient and present-day populations speaking Chibchan languages from Central America. This can be explained most parsimoniously by Chibchan-related migrations from Lower Central America to South America, rather than back-migration to the isthmus. 

A separate study found evidence for a previously unknown south-to-north expansion of Chibchan-related ancestry from Lower Central America into the Mayan territories of Belize by 5600 yr B.P. Therefore, rather than modeling Central American populations associated with Chibchan languages as deriving from a mixture between North and South American ancestries, these results are consistent with an origin of Chibchan-related ancestries in Lower Central America, followed by bidirectional gene flow toward both Meso- and South America. This model of an original “Chibchan homeland” in Central America is supported not only by mtDNA studies on present-day populations who speak Chibchan languages but also from linguistic observations, indicating that the isthmus region exhibits the highest diversity within this language family. 

From an archaeological perspective, the Chibchan-related ancestry is first identified in 2000-year-old individuals associated with Herrera ceramics. In addition, previously sequenced Ceramic-associated individuals from Venezuela dated to 2400 yr B.P. also showed a high affinity to Central American populations speaking Chibchan languages. Despite the similar ancestry pattern and temporal frame, the two populations do not appear to form a simple sister group. This could be in line with linguistic evidence that suggests multiple, distinct Chibchan language expansions into South America, but additional studies will be necessary to further clarify this issue. 

After the arrival of the Chibchan-related ancestry, which completely reshaped the genetic landscape of the region, we find evidence of a long period of genetic continuity in the genetic profile of the local populations for over 1500 years (from at least 2000 to 500 yr B.P.). The stability in genetic ancestry encompasses the end of the Herrera period and the beginning of the Muisca period. This points to a scenario in which populations speaking languages from the Chibchan lineage would have settled the Altiplano before the emergence of traits normally associated with the Muisca culture, and it shows that this cultural transition took place without a substantial migration from regions with a distinct genetic ancestry composition. In addition, such a genetic continuity extends through different cultural phases within the Muisca period and persists until the Spanish colonization. Colonial linguistic documentation established that Muisca people spoke a now extinct Chibchan language. Our findings not only confirm their genetic link with speakers of Chibchan languages from Central America but also suggest that ancestral Chibchan languages, possibly basal to the Magdalenic branch that gave rise to the documented Muisca language, might have already been spoken on the Altiplano during the pre-Muisca Herrera period. 

While the representation of Indigenous populations in our dataset is certainly not exhaustive, the observed spatial pattern in the genetic affinity of post-2000 yr B.P. ancient Colombians with present-day Indigenous populations raises questions regarding the uneven distribution of populations speaking Chibchan languages across the Isthmo-Colombian area at the time of the Hispanic colonization, also referred to as a Chibchan “archipelago”. 

One possible explanation is that this distribution resulted from separate dispersals from Central America to different locations of northern South America rather than a single expansion wave, as suggested by the internal branching pattern of the Chibchan language family. However, it is also possible that the initial spread was more widespread and got later fragmented by post-Chibchan migration and admixture events. The observation that Chibchan-affiliated populations from northern Colombia have a significantly reduced genetic affinity to post-2000–yr B.P. ancient Colombians than to Lower Central Americans supports the role of population admixture in shaping the genetic diversity of northern South America.

Also, while the earlier South American hunter-gatherer clade that went extinct probably dated to the founding wave of the modern humans in South America, they did not have notable Australasian or Melanesian ancestry, disfavoring the existence of a dramatically genetically distinct founding population of the Americas that preceded the main founding wave of modern humans and has Australasian or Melanesian genetic affinities that ancient.

Chinese Script v. English Statistics

The average number of strokes in a Chinese character is roughly 12.

The average number of strokes in a letter of the English alphabet is 1.9.

The average number of syllables in an English word is 1.66 (and 5 letters).

The average number of syllables in a Chinese word is roughly 2 (and 24 strokes).

The average number of words in an English sentence is 15-20.

The average number of words in a Chinese sentence is 25 (ballpark figure; see here)

Chinese has more than 100,000 characters.

English has 26 letters.

Total number of English words; over 600,000 (Oxford English Dictionary)

Total number of Chinese words: a little over 370,000 (Hànyǔ dà cídiǎn 漢語大詞典 [Unabridged dictionary of Sinitic])

From Language Log.

Quantum Gravity Can't Violate CPT

The reasoning in this article is sound and means that quantum gravity should preserve Charge-Parity-Time (CPT) symmetry, not just in an emergent low energy approximation, but at all energy scales.

CPT symmetry is at the heart of the Standard Model of particle physics and experimentally very well tested, but expected to be broken in some approaches to quantum gravity. It thus becomes pertinent to explore which of the two alternatives is realized: (i) CPT symmetry is emergent, so that it is restored in the low-energy theory, even if it is broken beyond the Planck scale, (ii) CPT symmetry cannot be emergent and must be fundamental, so that any approach to quantum gravity, in which CPT is broken, is ruled out. 

We explore this by calculating the Renormalization Group flow of CPT violating interactions under the impact of quantum fluctuations of the metric. We find that CPT symmetry cannot be emergent and conclude that quantum-gravity approaches must avoid the breaking of CPT symmetry. 

As a specific example, we discover that in asymptotically safe quantum gravity CPT symmetry remains intact, if it is imposed as a fundamental symmetry, but it is badly broken at low energies if a tiny amount of CPT violation is present in the transplanckian regime.

Astrid Eichhorn, Marc Schiffer, "No dynamical CPT symmetry restoration in quantum gravity" arXiv:2506.12001 (June 13, 2025).

Ancient UP Agriculture

Drone based LIDAR has made a major new find in North America:

A new study has found that a thickly forested sliver of Michigan’s Upper Peninsula is the most complete ancient agricultural location in the eastern United States. The Sixty Islands archaeological site is recognized as the ancestral home of the Menominee Nation. Known to the members of the tribe as Anaem Omot (Dog’s Belly), the area is a destination of pilgrimage, where remains of the settlement date to as far back as 8,000 B.C.

Located along a two-mile stretch of the Menominee River, Sixty Islands is defined by its cold temperatures, poor soil quality and short growing season. Although the land has long been considered unsuitable for farming, an academic paper published on Thursday in the journal Science revealed that the Menominee’s forbears cultivated vast fields of corn and potentially other crops there.

From the New York Times.

I'll update if time permits after reading the full paper.

The Latest Neutrino Mixing Data

The work to measure the mixing properties of neutrinos continues. A normal mass ordering and near maximal CP violation continues to be preferred.

T2K has made improved measurements of three-flavor neutrino mixing with 19.7(16.3) × 10^20 protons on target in (anti-)neutrino-enhanced beam modes. A new sample of muon-neutrino events with tagged pions has been added at the far detector, increasing the neutrino-enhanced muon-neutrino sample size by 42.5%. In addition, new samples have been added at the near detector, and significant improvements have been made to the flux and neutrino interaction modeling. T2K data continues to prefer the normal mass ordering and upper octant of sin^2θ(23) with a near-maximal value of the charge-parity violating phase with best-fit values in the normal ordering of δCP=−2.18+1.22−0.47, sin^2θ(23)=0.559+0.018−0.078 and Δm(23)^2=(+2.506+0.039−0.052)×10^−3 eV^2.

The T2K Collaboration, "Results from the T2K experiment on neutrino mixing including a new far detector μ-like sample" arXiv:2506.05889 (June 6, 2025).

The preference for the upper quadrant was about 2.3 sigma, and the preference for a normal ordering was about 2.7 sigma. With regard to CP-violation:

The data preferred values of δCP close to −π/2 radians, excluding values around +π/2 radians at >3σ, and excluding the CP-conserving values of 0 and π at 90% confidence. However [with further analysis] . . . the result to no longer exclude δCP = π at 90% confidence. The result was statistically limited and can be expected to improve as more data is accumulated.

New World Y1K Demographic Trends

Viewing event 350 years apart as part of the same trend is further in the direction of lumping than I'm comfortable with, but it is good to have a perspective on the pre-Columbian Americas that isn't static, with the implicit assumption that it was always the way it was when Europeans first encountered it.

[A] team led by archaeologist Robert Kelly of the University of Wyoming has studied this period using a previously assembled database of some 100,000 radiocarbon dates from across the United States. (See “Save the Dates.”) They used the dates to track population movements and demographic decline during this turbulent era, which was marked by drought, warfare, and disease. “We knew in a piecemeal fashion that these conditions drove demographic changes in different regions,” says Kelly. “But the radiocarbon data gives us a powerful new tool to understand population decline across the continent.”

After dividing the United States into 18 watersheds, the team analyzed the frequency of radiocarbon dates in each region and demonstrated that a cascading demographic collapse began in the central Rockies around a.d. 800 and later accelerated in multiple regions of central North America after 1150. The team’s analysis shows that the population of watersheds in California, the Pacific Northwest, the Great Lakes, and New England actually grew during the same period. This was likely because groups made their way from regions stricken by drought and warfare toward the coasts. Nonetheless, the radiocarbon data suggests that the overall Native American population declined by at least 30 percent from its peak before 1150.

From Archaeology Magazine.

The Latest Wide Binary Paper Shows Newtonian Behavior

The Wide Binary analysis debate continues. This paper doesn't see MOND-like behavior in wide binaries.

Of the 44 pairs observed with HARPS, 27% show sign of multiplicity or are not suitable for the test, and 32 bona-fide WBs survive our selection. Their projected separation s is up to 14 kAU, or 0.06 parsec. We determine distances, eccentricities and position angles to reproduce the velocity differences according to Newton's law, finding reasonable solutions for all WBs but one, and with some systems possibly too near pericenter and/or at too high inclination. Our (limited) number of WBs does not show obvious trends with separation or acceleration and is consistent with Newtonian dynamics. We are collecting a larger sample of this kind to robustly assess these results.

From R. Saglia (2025).

Conformal Gravity As A Dark Matter Alternative

One proposed modification of General Relativity that has been proposed to explain dark matter phenomena is Conformal Gravity, which basically preserves angles in transformations adding an additional symmetry to GR.

A new paper suggests that Conformal Gravity fails in elliptical galaxies.

As an alternative gravitational theory to General Relativity (GR), the Conformal Gravity (CG) has recently been successfully verified by observations of Type Ia supernovae (SN Ia) and the rotation curves of spiral galaxies. 

The observations of galaxies only pertain to the non-relativistic form of gravity. In this context, within the framework of the Newtonian theory of gravity (the non-relativistic form of GR), dark matter is postulated to account for the observations. On the other hand, the non-relativistic form of CG predicts an additional potential: besides the Newtonian potential, there is a so-called linear potential term, characterized by the parameter γ∗, as an alternative to dark matter in Newtonian gravity. 

To test CG in its non-relativistic form, much work has been done by fitting the predictions to the observations of circular velocity (rotation curves) for spiral galaxies. 

In this paper, we test CG with the observations from elliptical galaxies. Instead of the circular velocities for spiral galaxies, we use the velocity dispersion for elliptical galaxies. By replacing the Newtonian potential with that predicted by non-relativistic form of CG in Hamiltonian, we directly extend the Jeans equation derived in Newtonian theory to that for CG. By comparing the results derived from the ellipticals with that from spirals, we find that the extra potential predicted by CG is not sufficient to account for the observations of ellipticals. Furthermore, we discover a strong correlation between γ∗ and the stellar mass M∗ in dwarf spheroidal galaxies. This finding implies that the variation in γ∗ violates a fundamental prediction of Conformal Gravity (CG), which posits that γ∗ should be a universal constant.

Li-Xue Yue, Da-Ming Chen, "Test of conformal gravity as an alternative to dark matter from the observations of elliptical galaxies" arXiv:2506.03955 (June 4, 2025).

The Missing Baryons Are Probably In Deep Space

The missing baryon problem is that we can't find where all of the ordinary matter that should exist is located. New studies such as this one strongly suggest that it is mostly spread diffusely between galaxies.

Fast radio bursts (FRBs) are emerging as powerful cosmological probes for constraining the baryon fraction in the intergalactic medium (IGM), offering a promising avenue to address the missing baryon problem. In this paper, we analyze constraints on the IGM baryon fraction (fIGM) using 92 localized FRBs, incorporating a corrected probability distribution function for the IGM dispersion measure within three different cosmological models. We find that variations in the underlying cosmological model have a negligible impact on the inferred values of fIGM. While the NE2001 Galactic electron density model yields slightly higher fIGM values compared to the YMW16 model, the results are consistent within the 1σ confidence level. Additionally, there is no statistically significant evidence for redshift evolution in fIGM. Our analysis constrains fIGM to the range 0.8∼0.9, providing strong support for the idea in which the majority of the missing baryons reside in the diffuse IGM.

Yang Liu, Yuchen Zhang, Hongwei Yu, Puxun Wu, "Constraining the Baryon Fraction in the Intergalactic Medium with 92 localized Fast Radio Bursts" arXiv:2506.03536 (June 4, 2025).