What Is Fundamental In Physics?

This is a question and my answer from the Physics Forums (officially written at the graduate school level, but dumbed down since the question indicates that the person asking isn't actually that sophisticated and knowledgable. The question is in a block quote, but my answer is not, for ease of reading.

Wiktorius I said:

TL;DR: Does physics establish that mass, particles, and fields are fundamental, or could they be emergent properties of a deeper physical structure?

Are mass, particles, and fields fundamental physical entities, or could they be observable consequences of a deeper physical structure? I am particularly interested in what experimental evidence allows us to distinguish between these possibilities.They aren't necessarily fundamental, but we have no real idea what kind of deeper physical structure could cause what we see and there are no experiments or observations that are likely to take place in the next few decades that can tell us.

Generally, going as deep as we possibly can, we think of particles in the context of an effective field theory as local excitations of fields.

But, most popular accounts, because it is more intuitive to understand, talk in terms of particles, with fermions corresponding to what we think of as matter in a colloquial sense, and bosons corresponding to "force fields" for the fundamental forces of the Standard Model.

Generally speaking, the mass of particles (both fundamental and composite) is not understood as fundamental. Massive Standard Model fundamental particles like electrons, muons, tau leptons, and quarks and W bosons and Z bosons and the Higgs boson (with the probable exception of the neutrinos whose mechanism for acquiring mass isn't well understood at this point) get their mass from their interactions with the Higgs field. Massive composite particles (like protons and neutrons) get their mass from a combination of the masses of the fundamental Standard Model particles that they are made up of (to a small extent) and from the energy of the gluon fields that bind them together (to a great extent). But the sometimes elusive concept of mass-energy is something that is fundamental and conserved.

There is no real consensus over whether gravity is something that arises from the exchange of massless spin-2 gravitons (which are bosons) in a way analogous to the way that electromagnetism arises from the exchange of massless spin-1 photons, or whether gravity is a property of space-time itself which is either classical and smooth, or as in the quantum gravity approach of loop quantum gravity, in which case space-time itself is discrete at some ultra-fine scale.

There is no consensus on this because we don't have any observational tools sufficiently powerful to distinguish between the hypotheses, and because while the math behind classical general relativity is hard, we haven't cracked the math behind quantum gravity theories of various kinds outside some very specific isolated cases in theories that don't hold true for all circumstances and have internal mathematical issues with them that make quantum gravity theories in the general case intractable.

We don't have any well accepted theories that explain why the couple dozen plus experimentally measured physical constants of the Standard Model plus general relativity have the values that they do, although electroweak theory does establish that a few of the Standard Model physical constants are not actually mathematically independent of each other, so the number of independent degrees of freedom in the experimentally measured physical constants of the Standard Model is a few less than the number of experimentally measured physical constants (e.g. the electromagnetic coupling constant, weak force coupling constant, W boson mass, and Z boson mass are related to each other by a formula which has fewer than four independent degrees of freedom).

There are some theories out there that go part of the way, providing a road map for possible ways to explain more of the experimentally measured physical constants of the Standard Model and general relativity. But while these are bit more than speculative, none of them are established in a settled way that can secure a scientific consensus or anything close to that. Moreover, as impressive as our scientific methods are, imprecision in measuring some of these experimentally measured physical constants limits the degree to which we can distinguish one explanation for their values from another. Many key physical constants are measured only to percent or part per thousand levels.

But the failure of scientists so far to find any meaningful deviations from the Standard Model in particle accelerator experiments and other terrestrial tests of it (like ultra-precise measurements of the anomalous magnetic moment of the muon) profoundly constrains any alternatives that would predict anything experimentally different from what the Standard Model predicts.

I can't recall ever meeting a physicist who thinks that there isn't some deeper theory that could explain why those physical constants have the values that they do. But most physicists, having seen the parade of physicists before them who have failed to find that deeper theory, are content to not go looking for it very seriously.

As a practical matter, even if you found the deeper theory that explained why most of those physical constants have the values that they do, it wouldn't necessary change much for most physicists, because we've already measured those physical constants to high precision in most of the cases where precise values are important to precise calculations. Having the deeper theory might allow you to assign more precise values to the physical constants whose values are hardest to measure, which would be a helpful thing on the margins as a practical matter and very personally satisfying, but that might be just about it.

Of course, if we knew why those physical constants had the values that they do, we would probably also rule out all sorts of beyond the Standard Model theories and models in a way that would be more satisfying than the way that we do now. But it wouldn't have many very practical consequences.

There are a variety of reasons why the most naively obvious alternative to the list of Standard Model particles being fundamental, which would be that they are composite particles of a smaller number of more fundamental particles (generically called preons), is unlikely to be an explanation. The reasons are a bit technical (e.g. the binding energy necessary for this to be the case is too great to be consistent with the hypothesis), but the consensus is that this is pretty much a dead end.

String theory, at first, seemed to be another path to a more fundamental explanation of the laws of nature than the Standard Model plus general relativity (which aren't themselves compatible with each other which implies that one or the other or both aren't truly fundamental) but this research agenda in the many decades since it was first introduced has turned out to be a quagmire that even many of its leading theorists don't claim is an accurate description of the world we actually live in, even though the things we learned along the way investigating it may have value.

So, while our core theories, the Standard Model and general relativity, probably aren't the most fundamental and complete explanations of the laws of nature that are possible, we really have no solid leads on alternatives.

Perhaps the most promising area where we might gain a better understanding is from astronomy where ill-understood concepts summarized as dark matter and dark energy might be better understood with more observational astronomy evidence. But we are far from reaching a consensus understanding of them, and are less confident about the baseline explanation of them called Lambda CDM (for cold dark matter) theory now than we have been since Lambda CDM was formulated.

The prospects for something more fundamental didn't always seem so bleak. In the late 1980s and early 1990s, a group of theories called "supersymmetry" and their gravitational extension, "supergravity" looked very promising. It would have explained many of the fundamental constants in an overall framework (although not all of them), it would have provided a path to unifying the Standard Model coupling constants at higher energies into a single force, it would have provided a candidate for dark matter particles that was sufficient to fit the astronomy and particle physics data available at the time, there was no evidence that the cosmological constant wasn't constant, it would have provided a bridge between the Standard Model and string theory, and a path to a workable theory of quantum gravity.

But bit by bit, that fell apart. Supersymmetry predicted particles with well defined properties, but when particle collider scientists looked for those predicted particles they weren't were they were assumed to be. Better data showed that the Standard Model coupling constants weren't on a path to converging at high energies. Better astronomy observations found that dark matter phenomena behaved differently than it would have if the supersymmetry candidates were what explained it. Better astronomy observations found that the cosmological constant might not be constant after all. The discovery that neutrinos had mass complicated the situation and the failure to detect neutrinoless beta decay complicated one of the most elegant explanations of neutrino mass that might fit better into the supersymmetry/string theory framework. The math necessary for string theory and quantum gravity turned out to be much more problematic than early researchers in these fields had hoped or expected at a very fundamental level. Strong experimentally confirmed anomalies that would deviate from the Standard Model to prove that supersymmetry was correct, instead failed to materialize. The experimental anomalies that seemed to potentially support supersymmetry went away as theoretical predictions and experimental measurements grew more precise.

Supersymmetry isn't definitively ruled out yet, but any version of it that is discovered won't solve the problems that a large share of the physics community hoped and believed that it would in the late 1980s and early 1990s, before they had enough experimental data and mathematical understanding to realize that their beautiful solution to all of the unsolved problems in fundamental physics with a deeper theory wasn't going to hold together.

A generation or two later, we have bits and pieces of ideas - MOND, entropic gravity, axion-like ultralight dark matter particles, Koide's rule and extrapolations of it, multiple Higgs doublet theories, see saw theories of neutrino mass, and more. There are many more partial theories to explain one little thing that surfaced as an anomaly or possibility for a while that were later ruled out. But we have no real solid agenda for developing a deeper theory.

Who knows?

Maybe we're just a genius or three away from ending a period of non-consensus and confusion about a way forward and finding the deeper theories we need to explain the outstanding unsolved problems of fundamental physics. But I'm not that genius and there aren't a lot of good candidates among living physicists today for people who could be that genius.

POST SCRIPT (not in the original post):

It is notable that MOND and Koide's rule, two of the most successful enduring beyond the Standard Model theories, albeit both phenomenological only, both date to the early 1980s, before supersymmetry and string theory had become dominant trends in fundamental physics.

Neutrino physics

Neutrino mass was first discovered in 1998. This finding was replicated and confirmed in 2001. In 2015 Nobel prizes were awarded for the discovery that neutrinos are massive. Experimental determination of some of the parameters of neutrino oscillation (such as the CP violating phase) is still very crude and the absolute neutrino masses are still also not tightly established.

Supersymmetry and string theory advocates tend to strongly favor Majorana mass for neutrinos. The absolute masses of the neutrinos are still not known, only their mass differences. But there are strong hints from cosmology and from the magnitude of the mass differences, that neutrino masses are so small that we wouldn't expect to have observed definitive neutrinoless beta decay signals that would be proof of Majorana mass in neutrinos yet even if that was the source of neutrino mass. I personally find the hypothesis that neutrinos are their own antiparticles to be highly unlikely given that the main reason that they were hypothesized in the first place was to provide particle-antiparticle balance that conserves lepton number. There is a good chance that the bounds on absolute neutrino mass and the non-discovery of neutrinoless double beta decay will exclude a vanilla version of the Majorana mass hypothesis for neutrinos in my lifetime.

This said, I'm also not very impressed with see saw models, in which neutrinos have a Dirac mass arising from oscillations with one to three otherwise undetectable right handed neutrinos that are much more massive than their Standard Model active neutrino counterparts. 

The most plausible alternatives that I imagine, with only thin support from academic research, are that neutrinos either acquire their mass through a combination of their self-interactions via the weak force and their interactions with W bosons more generally, or acquire their mass through a second neutral scalar boson analogous to the Higgs boson.

More generally, I suspect that the role of the W boson in imparting mass to fundamental particles is underrated relative to the rule of the Higgs boson in doing so.

Higgs physics

The Higgs boson was discovered in 2012, although it was predicted about forty years earlier and efforts continue at the Large Hadron Collider (LHC), and in reanalysis of Tevatron collider data, to confirm that its properties are actually fully consistent with the Standard Model Higgs boson predicted in the early 1970s (so far no experimental data disproves this hypothesis and the extent to which it could deviate from that hypothesis is heavily constrained by the data that we do have). The measured mass of the Higgs boson according to the Particle Data Group, which is 125.11  ± 0.11 GeV/c², significantly constrains that parameter space of many supersymmetry (a.k.a. SUSY) theories.

One largely back burner issue is that a global electroweak fit would favor a Higgs boson mass of 90 + 21 -18 GeV/c², which is consistent at the two sigma level with the measured Higgs boson mass, but has a best fit value 1.7 sigma below the measured value which is still a bit puzzling.

There are exclusions of additional Higgs bosons (neutral, charged) proposed by some beyond the Standard Model theories, which the Particle Data Group also underplays, but which are indeed not quite as insurmountable as the exclusions for supersymmetric particles.

Supersymmetry

While supersymmetry papers are still being published, this line of beyond the Standard Model physics inquiry has greatly fallen out of favor from its heyday. A large share of physicists expected it to be discovered at the LHC but that didn't happen.

The Particle Data Group has a full page of supersymmetry exclusions from experiments, which in my humble opinion is too conservative. But it is a difficult set of experimental data points to present because many of the exclusions of model dependent. The three linked review articles on that page, however, are helpful.

The main reasons that supersymmetric particles are disfavored as dark matter candidates (called WIMPs) now are that: 

(1) direct dark matter detection experiments (such as Lux-Zepplin which detected a single first candidate for a direct dark matter detection signal earlier this month mostly like with a mass of about 1 TeV/c² which is six times the top quark mass and four times the mass of a uranium atom) imply a far smaller cross-section of interaction that the cross-section of interaction predicted by supersymmetry theories;

(2) galaxy dynamics (particularly the core-cusp problem) disfavor a dark matter candidate in the 1 TeV/c² or more mass range (even though plenty of preprints hypothesizing that the LZ candidate is a WIMP are out there) and really favor dark matter particle candidates in the 10 keV/c² or less mass range; and

(3) particle collider bounds on the minimum mass of supersymmetric particles that could plausibly be dark matter candidates are generally in the hundreds of GeV/c² or more range.

The consistency of the experimentally measured value of the anomalous magnetic moment of the muon (muon g-2) and the Standard Model predicted value of that quantity, strongly disfavors the existence of supersymmetry below very high energies. 

Cracking Linear Elamite

Four years ago, French archaeologist François Desset reportedly cracked the 4,000 year old Linear Elamite script, "[m]ade up of 77 signs – diamonds, curves, and other geometric patterns – the writing system comes from the Bronze Age civilisation of Elam" in Southwest Iran that collapsed long ago. The script was rediscovered in 1903, but has eluded decipherment until now. 

Elam is shown in red.

The Elamite language has partially been known long before this breakthrough from inscriptions of the language made in an Elamite cuneiform script, which was adapted from Akkadian cuneiform. This language was still spoken in the first century CE, and probably went extinct around the eleventh century CE. Most linguists consider it to be a language isolate (and in my review of this literature, I have not found that Elamo-Dravidian hypothesis to be a credible one).

Elamite is regarded by the vast majority of linguists as a language isolate,[31][32] as it has no demonstrable relationship to the neighbouring Semitic languages, Indo-European languages, or to Sumerian, despite having adopted the Sumerian-Akkadian cuneiform script.

An Elamo-Dravidian family connecting Elamite with the Brahui language of Pakistan and Dravidian languages of India was suggested in 1967 by Igor M. Diakonoff[33] and later, in 1974, defended by David McAlpin and others.[34][35] In 2012, Southworth proposed that Elamite forms the "Zagrosian family" along with Brahui and, further down the cladogram, the remaining Dravidian languages; this family would have originated in Southwest Asia (southern Iran) and was widely distributed in South Asia and parts of eastern West Asia before the Indo-Aryan migration.[36] Recent discoveries regarding early population migration based on ancient DNA analysis have revived interest in the possible connection between proto-Elamite and proto-Dravidian.[37][38][39][40] A critical reassessment of the Elamo-Dravidian hypothesis has been published by Filippo Pedron in 2023.[41]

Václav Blažek proposed a relation with the Semitic languages.[42]

In 2002 George Starostin published a lexicostatistic analysis finding Elamite to be approximately equidistant from Nostratic and Semitic.[43]

None of these ideas have been accepted by mainstream historical linguists.[31]

Desset accomplished this primarily by using proper names to decode the meaning of those signs and applying that method to ten new Linear Elamite texts inscribed on vases, according an April 28, 2026 story from France 24. This story of breakthrough is also reported in National Geographic, January 2026, pp. 110-131, entitled, "Decoding the Lost Scripts of the Ancient World", by Joshua Hammer. Hat top to Language Log. The Smithsonian magazine also has a recent article on the topic. It isn't entirely clear to me why this development is making headlines now, four years after the leading article on the topic was published (which I blogged at the time, see also an earlier post on a related topic).

Wikipedia (at the link above) explains that:

In 2022, Desset et al. (2022) argued that Linear Elamite is an alpha-syllabary, which would make it the oldest known purely phonographic writing system.[5] However, they admit that some logograms may have been used, although only rarely and not systematically, arguing that Elamite scribes rejected logographic writing in the 3rd millennium BCE.[30] Other researchers, such as the linguist Michael Mäder, dispute this, arguing that only around 70 percent of Linear Elamite characters are likely to be purely phonographic and that the remainder are logograms, as evidenced by mathematical analyses of Linear Elamite inscriptions.[3][31]

His 2022 article is the capstone of the project. Its abstract states:

Linear Elamite writing was used in southern Iran in the late 3rd/early 2nd millennium BCE (ca. 2300–1880 BCE). First discovered during the French excavations at Susa from 1903 onwards, it has so far resisted decipherment. The publication of eight inscribed silver beakers in 2018 provided the materials and the starting point for a new attempt; its results are presented in this paper. A full description and analysis of Linear Elamite of writing, employed for recording the Elamite language, is given here for the first time, together with a discussion of Elamite phonology and the biscriptualism that characterizes this language in its earliest documented phase.

Desset's main publications on the subject are as follows: 

Desset, François (2018a). "Linear Elamite Writing". In Álvarez-Mon, Javier; Basello, Gian Pietro; Wicks, Yasmina (eds.). The Elamite World. Abingdon, Oxon: Routledge. pp. 397–415. ISBN 978-1-315-65803-2.

Desset, François (2018b). "Nine Linear Elamite Texts Inscribed on Silver "Gunagi" Vessels (X, Y, Z, F', H', I', J', K' and L'): New Data on Linear Elamite Writing and the History of the Sukkalmaḫ Dynasty". Iran. 56 (2): 105–143. doi:10.1080/05786967.2018.1471861. S2CID 193057655.

Desset, François (2020a). "Breaking the Code: The Decipherment of Linear Elamite, a Forgotten Writing System of Ancient Iran (3rd Millenium BC)". Canal-U.

Desset, François (2020b). A New History of Writing on The Iranian Plateau – via YouTube.

Desset, François (1 September 2021). "On The Decipherment of Linear Elamite Writing". The Postil (Interview). Interviewed by Robert M. Kerr.

Desset, François; Tabibzadeh, Kambiz; Kervran, Matthieu; Basello, Gian Pietro; Marchesi, Gianni (2022). "The Decipherment of Linear Elamite Writing". Zeitschrift für Assyriologie und vorderasiatische Archäologie. 112 (1): 11–60. doi:10.1515/za-2022-0003. ISSN 0084-5299. S2CID 250118314.

A Notable Life In Quantum Physics

Chien-Shiung Wu was one of the pioneers of quantum mechanics and high energy physics, and was a female Chinese physicists in an era where women still made up only a tiny percentage of scientists in the field. 

If something remembers you with a speech like this, one hundred and ten years after you were born, when you have long passed away, then you did something right in life.

In 1950, Chien-Shiung Wu and her student published a coincidence experiment on entangled photon pairs that were created in electron-positron annihilation. This experiment precisely verified the prediction of quantum electrodynamics. 

Additionally, it was also the first instance of a precisely controlled quantum entangled state of spatially separated particles, although Wu did not know about this at the time. 

In 1956, Wu initiated and led the so-called Wu experiment, which discovered parity nonconservation, becoming one of the greatest experiments of the 20th century. 

As Chen Ning Yang said, Wu's experiments were well known for their precision and accuracy. Experimental precision and accuracy manifested Wu's scientific spirit, which we investigate here in some detail. 

Yu Shi, "Scientific Spirit of Chien-Shiung Wu: From Quantum Entanglement to Parity Nonconservation" arXiv:2504.16978 (May 31, 2022) (This paper is the translated transcript of the speech the author made at the International Symposium Commemorating the 110th Anniversary of the Birth of Chien-Shiung Wu, on May 31, 2022 in Chinese. The above abstract is the translation of the original abstract of the speech.)

She earned her undergraduate degree in physics (which had a thesis requirement at the time) in China in 1934, prior to the Maoist Revolution, and earned a PhD working under a professor only three years older than her who had studied under Madame Curie, and under the first female PhD in Physics in China, who earned that degree at the University of Michigan (where I also earned my graduate degree). Wu earned her PhD at the University of California at Berkley in 1940 (thirty years before my father earned his PhD at Stanford).

Wu was admitted by the University of Michigan to study at her own expense, and was financially supported by her uncle. On her way to Michigan, Wu visited Berkeley, where she was so impressed, especially by Ernest O. Lawrence’s cyclotron, that she wanted to stay in Berkeley. The cyclotron had been invented by Lawrence, so it was an ideal place for studying physics. Another important factor that influenced Wu’s decision was that she cared a lot about gender equality, and there was gender discrimination at the University of Michigan. In addition, there were a lot of Chinese students at the University of Michigan at the time, and Wu didn’t want her socializing be dominated by fellow Chinese students. So she stayed in Berkeley. Her decision reflected her devotion to physics as a woman.

She then taught at Smith (from which my sister-in-law graduated), and then Princeton, and then she worked at Columbia University as part of the Manhattan Project. 

She was highly productive (publishing more than fifty papers in the early 1950s when a huge share of U.S. women were homemakers in the Baby Boom), and her early post-war research agenda involved the verification of Fermi’s theory of β decay.

Chien-Shiung Wu served as the President of the American Physical Society from 1975 to 1976.

James W. Cronin, who won the 1980 Nobel Prize for his discovery of charge conjugation-parity (CP) nonconservation, once said, “The great discovery of Chien-Shiung Wu started the golden age of particle physics.” 

She continued to publish through at least 1980, and died in February of 1997. The author of the paper had met her.

John Hawks On Scientific Consensus

John Hawks, an anthropologist who specializes in archaic hominins, considers at his blog what the term "scientific consensus" means in reaction to an article in the peer reviewed scientific journal Science. He begins as follows:

In an editorial in this week's Science, the journal's editor Holden Thorp develops an argument that the notion of “scientific consensus” has confused public discussion of science. In Thorp's view, the public misunderstands “consensus” as something like the result of an opinion poll. He cites the communication researcher Kathleen Hall Jamieson, who observes that arguments invoking “consensus” are easy for opponents to discredit merely by finding some scientists who disagree.

Thorp notes that what scientists mean by “consensus” is much deeper than a popularity contest. He describes it as “a process in which evidence from independent lines of inquiry leads collectively toward the same conclusion.” Leaning into this idea, Thorp argues that policymakers should stop talking about “scientific consensus” and instead use a different term: “convergence of evidence”.

It would be a big move for a magazine representing the entire breadth of American science to reject the idea of scientific consensus.

For the last twenty years the idea of “scientific consensus” has been widely adopted by scientific organizations and policymakers, especially applied to politically contentious topics such as climate change, vaccine hesitancy, and COVID-19 response. Many organizations shifted their policy advocacy by issuing statements reflecting the consensus of their members. Science itself helped launch this era with the publication of Naomi Oreskes' 2004 article, “The Scientific Consensus on Climate Change”. This article recounted the number of organizations representing scientists that had issued statements or policy documents about the evidence for human-induced climate change.

The purpose of such statements was to counter public perceptions that there might be significant scientific disagreement about climate change.

There use of the term has grown steadily since the late 1960s (image from the linked blog entry):

Another chart in the blog post notes that use of the term "convergence of evidence" peaked in the 1950s and that "scientific consensus" overtook it in frequency of use around 1985.

Hawks argues that there is also a place for the concept of a consilience of evidence:

The idea was formulated by the nineteenth-century philosopher William Whewell, who also coined the word scientist. Whewell wanted to understand how observations give rise to theories. His idea was that the induction of a hypothesis or theory from observations requires another step, a step in which evidence developed by other means of observation must also show consistency with the same theory or hypothesis. He used the term “consilience” for this matching of evidence of different kinds.

Michael Ruse noted Charles Darwin's work as a hallmark of the consilience approach. Darwin brought together evidence from entirely different fields of inquiry: animal and plant breeding, geology, natural history, biogeography, sociology, and many others. He had a remarkable ability to answer questions in one field by examining data in another field entirely. The ability to bring together observations that seem disconnected from each other, explain all of them with one unifying explanation is a powerful mode of scientific thinking.

Consilience of evidence also helps to answer criticism that scientists are closing off debate by excluding ideas that do not fit within their disciplinary boundaries. Where “convergence of evidence” may seem inward-facing, confined to a single research tradition, consilience is explicitly outward-reaching. It requires translation and integration across disciplinary boundaries and sometimes even across different ways of knowing.

I'm skeptical of both the "convergence of evidence" question, which has many of the same problems, and the "consilience of evidence" phrase, which is just beyond the vocabulary of most of the people for whom the rhetoric in which the term might be used is directed.

But the deeper and ultimate question is how to draw the line between what is settled and accepted science, to which any legitimate future challenge has not yet manifested, and scientific ideas which remain the subject of controversy among scientists. 

On one hand, one doesn't really want to adopt the standard of a "hecklers veto" which suggests that a crackpot with weak methodology or methods that cause other scientists inclined to be sympathetic to not take the crackpot seriously, is sufficient to upset a scientific consensus. But on the other hand, one doesn't want to leave the misimpression that scientific truth is a popularity contest or a matter of democratic decision-making, or that the authority and prestige of individual scientists holding a scientific opinion is more important than the evidence and reasoning supporting their opinions. 

When there are two well-reasoned theories advanced by people who are behaving like genuine scientists that are each supported by evidence that doesn't conclusively disprove the alternative, there is no scientific consensus on which one is correct (although there are still many crackpot theories that are definitively rejected by the scientific consensus even at times where there is not a scientific consensus around more than one disputed possible scientific truth to explain the world).

Making these distinctions at a vague, common sense level, in actual real world cases, usually isn't that hard. But putting into words a rule that puts some cases on one side of the line, and other cases on the other side of the line, can be challenging.

Progress On The Harappan Script

Dr. Srini Kalyanaraman has been doing some painstaking work and making slow but steady incremental progress in making sense of the Harappan script. 

Like the Vinca script and the earliest Minoan writing, it is probably more of a collection of brands, logos, and ideograms than a full script for the Harappan language that could be used for any purpose. The Harappan language was the language of a people who called themselves Meluhha, according to the records of ancient Sumerians who traded with them and had a trade colony of Harappans in the Middle Bronze Age.

 

I get regular updates on his new papers, because I was apparently cited once in one of his papers, from a firm called Academia. But there are lots of them, and I haven't had time to follow them closely, paper by paper. In the indefinite "someday" future, when I have the time to do so, I aspire to download and review them all and write a post or two about them.

The Hubble Tension Considered

When Did We Learn That The Universe Is Expanding?

There is no reasonable doubt that the size of the observable universe has expanded over the last 13.8 billion years or so from time when it was dramatically smaller than it is today called the Big Bang.

Why this happened and the details of the very first moments of it are still the subject of ongoing research, but there is near universal consensus about the broad outlines of this process from Big Bang nucleosynthesis (end about 15 minutes after the Big Bang in a conventional cosmological chronology) to the present.

A 1924 paper by Carl Wirtz, which was one of the earliest to note the astronomy observations now explained with the expansion of the universe and to reach the conclusion that the universe was expanding has been made more widely available in an English translation on the 100th anniversary of its publication. 

Better know cosmologist Edwin Hubble, who read Wirtz's work, reached the same conclusion from the data and improved upon it by proposing "Hubble's Law" which quantified and characterized this expansion with what has come to be known as Hubble's Constant, in 1929.

Quantifying and characterizing any changes in the rate at which the universe has expanded has proven to be a more challenging problem which we are still wrestling with a century later.

General relativity with a cosmological constant is an idea that had been proposed only a few years earlier when Wirtz and Hubble made their early ground breaking conclusions that astronomy observations supported an expanding universe.

Once Hubble's Law was proposed, the race was on to measure Hubble's constant, sometimes producing conflicting results. Some of the early estimates of it (in (km/s)/Mpc units), one of which predated the formal publication of Hubble's law, were as follows (often with significant uncertainties or no estimated uncertainties):

1927  625

1929  500

1956  180

1958    75

early 1970s 55

mid-1970s 100

late 1970s to 1994 50-90

The best fit values for estimates made since 1994 have ranged from 69.8 to 76.9, and the uncertainties in those estimates has more or less steadily fallen to as little as 0.42 for CMB based indirect early time estimates and as little as 1.0 for some late time direct measurements.

Notably, it took less than 30 years from the publication of Hubble's law to get measurements of the value of Hubble's constant that were reasonably close to the modern measured value.

Previous discrepancies between measurements of the Hubble constant which is functionally related to the cosmological constant of general relativity, have had discrepancies and tensions (much bigger in magnitude than the current "Hubble tension") before, but those were always resolved by reducing sources of measurement uncertainty in the differing values of the Hubble constant from different kinds of observations.

The LambaCDM "Standard Model of Cosmology" assumes that this expansion is explained by general relativity with a cosmological constant. The source of  this phenomena due to this cosmological constant in the LambdaCDM model is often called "dark energy."

The Hubble Tension

The simple explanation of this expansion with a constant cosmological constant in general relativity (which by the way, facially, at least, is a gravitational modification and not a new substance or separate force), which leads to a constant value of the Hubble constant, however, has broken down in the last few years. 

Increasingly powerful space telescopes have shown a tension between the high precision determination of the Hubble constant inferred from the Planck cosmic microwave background (CMB) observations early in the universe's history, and late universe measurements of the Hubble constant.

[M]easurements from the Planck mission published in 2018 indicate a lower value of 67.66 ± 0.42 (km/s)/Mpc, although, even more recently, in March 2019, a higher value of 74.03 ± 1.42 (km/s)/Mpc has been determined using an improved procedure involving the Hubble Space Telescope. The two measurements disagree at the 4.4σ level, beyond a plausible level of chance. The resolution to this disagreement is an ongoing area of active research.

The chart below from the same link summarizes some of these recent measurements. 

New late time measurements in the last few years from sources including the James Webb Space Telescope and DESI, since the chart below was made, with one or two exceptions (such as a July 2023 estimate based upon astronomy observations of kilonova that produced a late time value of Hubble's constant of 67.0 ± 3.6) that can't cancel out independent late time measurements to the contrary, have generally strengthened the evidence that the Hubble tension is real and not just a product of observational uncertainty.

Even in the face of the Hubble tension, Hubble's Law is still a good first approximation description of the rate at which the universe is expanding. The difference in the measured values of Hubble's constant, in measurements of its value from times that are up to about 13 billion years apart, is less than 10%. 

This is still highly statistically significant (more than 5 sigma), because the relative uncertainty in the difference between the most precise measurements is less than 2%. But in plenty of astronomy contexts, a field not generally known for its high precision by physics standards, 10% precision is still excellent.

But from a fundamental laws of physics and cosmology perspective, if these results are confirmed, the consequences are profound. 

Any changes to Hubble's constant over time demand that the simple cosmological constant explanation of these observations be discarded, effectively rewriting a part of the equations of general relativity with deep cosmological implications, in favor of a new theory.

Possible Resolutions Of The Hubble Tension

Time will tell how the Hubble tension is resolved.

There are basically three possible resolutions to the Hubble tension (more than one of which could each provide a partial explanation).

1. Indirect Early Universe Estimates Are Wrong. The CMB based determination of Hubble's constant in the early universe (about 380 million years after the Big Bang according to the LambdaCDM model) is flawed somehow, in a way that underestimates the value of the Hubble constant in the early universe. 

McGaugh, for example, has suggested that this is a plausible full or partial explanation.

For example, maybe the Planck collaboration omitted one or more theoretically relevant components of the formula for converting CMB observations to a Hubble constant value that were reasonably believed to be negligible (indeed, it almost certainly did so). But it could be that one or more of the components omitted from the Planck collaboration's calculated value of Hubble's constant from the CMB data actually increase the calculated value by something on the order of 9% because some little known factor makes the component(s) omitted have a value much higher than one would naively expect.

Also, since the indirect determination of the value of Hubble's constant from CMB measurements is model dependent, any flaw in the model used could cause its determination of Hubble's constant to be inaccurate.

An indirect CMB based determination of Hubble's constant is implicitly making a LamdaCDM model dependent determination of how much the universe had expanded since the Big Bang at the time that the CMB arose. If the LambdaCDM model's indirect calculation of Hubble's constant predicts that the CMB arose later than it actually did, then its indirect determination of the value of Hubble's constant would also be too low, and a high early time value of Hubble's constant would resolve the problem.

This is a plausible possibility because the James Webb Space Telescope has confirmed that the "impossible early galaxies problem" is real, implying that there is definitely some significant flaw (of not too far from the right magnitude and in the right direction) in the LambdaCDM models description of the early universe, although the exactly how much earlier than expected galaxies arose in the early universe (which is a mix of cutting edge astronomy, statistical analysis, and LambdaCDM modeling) hasn't been pinned down with all much precision yet.

The impossible early galaxy problem is that galaxies form significantly earlier after Big Bang than the LambdaCDM model predicts that they should. The galaxies seen by the JWST at about redshift z=6 (about 1.1 billion years after the Big Bang) are predicted in the LambdaCDM model to apear at about redshift z=4 (about 1.7 billion years after the Big Bang).

If the CMB arose more swiftly after the Big Bang than the LambdaCDM model predicts it did but the amount by which the universe had expanded at that point was about the same, in much the same way that galaxy formation actually occurred earlier than the LambdaCDM model predicted that it would, then that could fully or partially resolve the Hubble tension.

The relationship between Hubble's constant and the amount of expansion in the universe at any given point in time is non-linear (it's basically exponential). So, figuring out how much of a roughly 55% discrepancy at 1.1 billion years after the Big Bang in galaxy formation time translates into in Hubble constant terms, at about 380 million years after the Big Bang, is more involved than I have time to work out today, even though it is really only an advanced pre-calculus problem once you have the equations set up correctly. But my mathematical intuition is solid enough to suspect that the effect isn't too far from the 9% target to within the uncertainties in the relevant measurements.

2. Late Time Direct Measurements Share A Systemic Error. The multiple different, basically independent, methods of measuring Hubble's constant in the late universe are flawed in a way that causes them to overestimate Hubble's constant in roughly the same amount.

The problem is that since several different methods have been used and reach similar higher values for Hubble's constant in the late universe, so the issue can't be one that is particular to only a single method of determining Hubble's constant.

For example, one explanation that has been explored is that the little corner of the universe around the Milky Way from the perspective of solar system observers has some local dynamics, or has local distortions that impact light at the relevant wavelengths reaching us in the solar system (e.g. due to localized gravitational lensing or local distributions of interstellar gas and dust) that has nothing to do with the expansion of the universe, but is indistinguishable, by the most precise existing methods used to measure Hubble's constant in the late time universe, from an increase in Hubble's constant of about 6.4 (km/s)/Mpc. 

I've bookmarked a number of papers exploring this hypothesis but haven't had the time to analyze them as a group or compile them in a blog post.

3. Hubble's Constant Isn't Constant. The third possibility is that Hubble's constant genuinely isn't constant and the rate of the expansion of the universe attributed to a cosmological constant in the equations of General Relativity is mistaken. Thus, new physics are necessary to explain these observations.

This is, of course, the most exciting possible answer. But I'll save consideration of some of these alternative theories to a cosmological constant for another post (and I won't address them in the comments to this post either). 

Suffice it to say that there are many proposals for alternatives that could resolve the Hubble tension out there in the literature.

The Voynich Manuscript Is Not A Hoax

Image via Wikipedia

A post at Language Log explains how multispectral imaging from ten years ago (which was just recently released due to the efforts of a determined blogger) reveal that the Voynich Manuscript, an illustrated vaguely alchemical and astrological handwritten tome in an indecipherable code, probably written around 1425 CE, is not a hoax or fake. 

Claimed efforts to decipher it have likewise flopped.

Remains Of 1181 CE Supernova Found

Chinese astronomers without telescopes saw a "guest star" as bright as Saturn in the year 1181 CE for about six months, which is now understood to have been a supernova. 

The remnants of it, and the particular type of supernova it was, a Type 1ax formed when two white dwarfs make an incomplete merger, have now been determined.

Atri's Eclipse

This paper on ancient astronomy is relevant to dating the Rig Veda itself, and by association, the timing of the Indo-Aryan migration to India. 

The dates that are proposed are very early compared to estimates of the timing of the Rig Veda from other sources, which could reflect an oral tradition from either the pre-existing Indo-Iranian (which is associated with the the early Andronovo culture of ca. 2000 BCE) or Harappan cultures. 

It could reflect misanalysis by the authors of the "legendary history" described in the Rig Veda, which could correspond to knowledge of the existence of solar ellipses and a fictional invention with religiously or symbolically important dates (at a time when nobody could confirm the account), and not to a particular actual solar ellipse in India with the timing relative to the equinoxes described.

The earliest written reference in Indian astronomy to a total solar eclipse is in the Rig Veda where Rishi Atri is said to have demolished the asura Swarbhanu to liberate the Sun from a total solar eclipse. 

The Rig Veda describes the occurrence of the eclipse, how the Sun suddenly disappeared in the daytime under the spell of the Asura. The people and gods were scared but the Great Sage Atri saved the Sun and restored his full glory. While discussing the eclipse, Tilak refers to the eclipse as having occurred when the Vernal Equinox was in Orion and three days before the Autumnal Equinox. 

Based on these data, we identify Atris eclipse as the one that occurred on 22 October 4202 BC or on 19 October 3811 BC.

Mayank Vahia, Misturu Soma, "An examination of "Atri's Eclipse" as described in the Rig Veda" arXiv:2407.19733 (July 29, 2024). This is a post-print of 26 (2) Journal of Astronomical History and Heritage 405-410 (2023).

The introduction in the body text notes that:

The Rig Veda is one of the oldest known documents. It dates from 1500 BC, when its contents were assimilated and formalised on the basis of traditions of different schools of thought. It was essentially a summary of various religious ideas and philosophies, as well as their image of the world and its working as understood at that time. It comprises a set of 10 books associated with 10 different groups of priests who assimilated different aspects of the prevailing belief systems (see Dalal, 2014; Donigar, 1984). The writing style in the Rig Veda is highly poetic and abstract, and sometimes it is difficult to understand. It also requires some experience in order to interpret it.

While the Rig Veda dates from 1500 BC, there is a significant amount of evidence that it incorporates memories of events that were much further back in time. For example, it discusses events when the Vernal Equinox was in Orion, which occurred around 4500 BC, while the final reference to the Vernal Equinox in the Rig Veda relates to its being in the Pleiades, which happened in 2230 BC.

There are various other astronomical references in the Rig Veda, and one of these refers to a solar eclipse, which is the subject of this paper.

For the sake of argument, assuming that the Rig Veda is indeed referring to real historical events when it talks about where the equinoxes are (and that the means of determining which constellation is associated with an equinox), it could also help determine which part of of the hybrid culture that produced Hinduism in India, i.e. the Indo-Iranian tradition or the Harappan tradition, is the predominant source for the Rig Veda.

The dates suggested for Atri's Eclipse coincide roughly with the time at which the Proto-Indo-European language emerged. But this seems like a better fit to more sedentary and agricultural early Indus Valley civilization (the strict sense IVC dates to 3300 BCE, but agricultural societies in continuity with it were present there from 6500 BCE), which would have been expected to have better astronomy in that time frame. The more pastoral initial Proto-Indo-European society would be expected to have less advanced astronomy at that time. So, the Rig Veda could recount Harappan oral traditions (it had some writing, but the Harappan script was probably not a full written language) translated from the Harappan language into Sanskrit.

Another hint could be derived from comparing the Avesta, in the Avestan language, with the Rig Veda, written in Sanskrit. Where something is present in both, like the drug soma, it is likely to derive from a shared Indo-Iranian tradition. Where  something is only found in the Rig Veda with no parallel in the Avesta it is more likely to have Harappan origins. But, the Avesta was compiled much later than the Rig Veda so a great deal of the Indo-Iranian tradition might have been lost or deliberately omitted by Zoroaster (who by tradition is its author) at that point in the 500s BCE. The oldest part of the Avesta, the 17 hymns called the Gathas written in Old Avestan comprise only about 6,000 words in 238 stanzas and have linguistic and cultural similarities to the Rig Veda, which has 1,028 hymns with 10,600 verses.

The Rig Veda and the historic religion of the Indo-Europeans were both polytheistic, while Zoroastrianism is usually characterized as dualistic. We know, however, that significant parts of what became the Hindu religious tradition deviated for the common Indo-European source of the religious traditions of the Norse, the Greeks, and the Romans, for example, and also have no source in Egyptian mythology. These deviations are plausibly attributed to Harappan sources.

The Wikipedia article on the Rig Veda is suggestive of a more Indo-Iranian than Harappan society, and states that:

The Rigveda offers no direct evidence of social or political systems in the Vedic era, whether ordinary or elite. Only hints such as cattle raising and horse racing are discernible, and the text offers very general ideas about the ancient Indian society. There is no evidence, state Jamison and Brereton, of any elaborate, pervasive or structured caste system. Social stratification seems embryonic, then and later a social ideal rather than a social reality.  

The society was semi-nomadic and pastoral with evidence of agriculture since hymns mention plow and celebrate agricultural divinities. There was division of labor and a complementary relationship between kings and poet-priests but no discussion of a relative status of social classes.  

Women in the Rigveda appear disproportionately as speakers in dialogue hymns, both as mythical or divine Indrani, Apsaras Urvasi, or Yami, as well as Apāla Ātreyī (RV 8.91), Godhā (RV 10.134.6), Ghoṣā Kākṣīvatī (RV 10.39.40), Romaśā (RV 1.126.7), Lopāmudrā (RV 1.179.1–2), Viśvavārā Ātreyī (RV 5.28), Śacī Paulomī (RV 10.159), Śaśvatī Āṅgirasī (RV 8.1.34). The women of the Rigveda are quite outspoken and appear more sexually confident than men, in the text. Elaborate and aesthetic hymns on wedding suggest rites of passage had developed during the Rigvedic period. There is little evidence of dowry and no evidence of sati in it or related Vedic texts.

The Rigvedic hymns mention rice and porridge, in hymns such as 8.83, 8.70, 8.77 and 1.61 in some versions of the text; however, there is no discussion of rice cultivation.  

The term áyas (metal) occurs in the Rigveda, but it is unclear which metal it was. Iron is not mentioned in Rigveda, something scholars have used to help date Rigveda to have been composed before 1000 BCE. Hymn 5.63 mentions "metal cloaked in gold", suggesting that metalworking had progressed in the Vedic culture.

Some of the names of gods and goddesses found in the Rigveda are found amongst other belief systems based on Proto-Indo-European religion, while most of the words used share common roots with words from other Indo-European languages. However, about 300 words in the Rigveda are neither Indo-Aryan nor Indo-European, states the Sanskrit and Vedic literature scholar Frits Staal. Of these 300, many – such as kapardin, kumara, kumari, kikata – come from Munda or proto-Munda languages found in the eastern and northeastern (Assamese) region of India, with roots in Austroasiatic languages. The others in the list of 300 – such as mleccha and nir – have Dravidian roots found in the southern region of India, or are of Tibeto-Burman origins. A few non-Indo-European words in the Rigveda – such as for camel, mustard and donkey – belong to a possibly lost Central Asian language. The linguistic sharing provides clear indications, states Michael Witzel, that the people who spoke Rigvedic Sanskrit already knew and interacted with Munda and Dravidian speakers.

Witzel, however, was late to recognize that there was a distinct Harappan language which was neither Munda nor Dravidian.

As an aside, the Harappans did trade with the Sumerians who had a full written language and not just a set of symbols like the Harappan and Vinca scripts. Neither the Sumerian written language, nor the entire concept of it, however, seems to have been borrowed by the Harappans. Perhaps this was because Sumerian writing was largely confined to a small class of priest-clerks and perhaps some aristocrats, and perhaps because Sumerian-Harappan trade was thin and the Harappan maritime merchants may not have been all that influential in Harappan society. The Harappan script seems to have been used largely by merchants.

Minotaur Labyrinth May Be Been Discovered In Crete.

A 4,000-year-old circular structure resembling Minoan tomb architecture was unearthed near Kastelli, Crete, suggesting it could be the legendary labyrinth of King Minos.

From the Jerusalem Post.

The Past, Present, And Future Of Modern Physics

The Past

Modern physics started a little more than a century ago in the early 1900s. 

The state of physics immediately before that point is still taught in universities as a classical approximation of more fundamental physical laws found in modern physics which is often called "classical physics."

Classical physics consists of Newtonian mechanics and Newtonian gravity and calculus, dating to the late 1600s, Maxwell's equations of electromagnetism and classical optics, the laws of thermodynamics and their derivation from statistical mechanics, fluid mechanics, and the proton-neutron-electron model of the atom exemplified in the Periodic Table of the Elements.

Modern physics starts with a scientific understanding of radioactive decay, special relativity, general relativity, and quantum mechanics, which was developed between about 1896 and 1930. It also includes nuclear physics and neutrino physics, that begin in earnest in the 1930s, the Standard Model of Particle Physics and hadron physics that were formulated in the modern sense in the early 1970s, with the three generations of fermions established by 1975. Various beyond the Standard Model extensions of that model mostly date to the 1980s or later, even though the first hints of some of them were considered earlier. The penultimate Standard Model particle to be experimentally confirmed was the top quark in 1994. The fact that neutrinos were massive and oscillate was confirmed by 1998. All particles predicted by the Standard Model of Particle Physics were discovered by 2012 when the Higgs boson was discovered. Subsequent research has confirmed that the particle discovered is a good match to the Standard Model Higgs boson.

Some of the notable developments in Standard Model physics since 2012 have been the experimental exclusion of many extensions of the Standard Model over ever increasing ranges of energies and parameter spaces, the discovery of many hadrons predicted in the Standard Model including tetraquarks and pentaquark together with measurements of their properties, progress in calculating parton distribution functions from first principles, and refinement of our measurements of the couple dozen experimentally determined physical constants of the Standard Model.

Modern physics also includes modern astrophysics and cosmology including the Big Bang Theory and the concept of black holes which coincided with general relativity, dark matter phenomena first observed and neutron stars were first proposed in the 1930s, neutron stars were first observed in the 1967 and the first observation of a black hole was in 1971, cosmological inflation hypotheses date to 1980, the possibility of dark energy phenomena was part of general relativity but it wasn't confirmed until 1998, the LambdaCDM model of cosmology was proposed in the mid-1990s and became the paradigm when dark energy was observationally confirmed in 1998. Quantum gravity hypotheses and hypotheses to explain baryogenesis and leptogenesis have seen serious development mostly since 1980 although early hypotheses along these lines have been around since the inception of modern physics.

The Present

As of 2024, modern physics is dominated by the "core theories" of special relativity, general relativity, and the Standard Model of Particle Physics, none of which have been clearly contradicted by observational evidence after more than a century of looking in the case of relativity and half a century of the Standard Model which has been refined since its original scheme only to expand it to exactly three generation of fermions and to attempt to integrate massive neutrinos and neutrinos oscillation.

On one hand, there are many areas of wide consensus in modern physics. Special relativity has been exhaustively confirmed experimentally and observationally. The predictions of General Relativity including the Big Bang, black holes, strong field behavior in contexts like the dynamics of massive binary systems and compact objects, and its predictions like the precession of Mercury and frame dragging in the solar system context have been observationally confirmed to high precision. Half a century of high energy physics experiments and cosmic ray and neutron star observations have never definitively contradicted the Standard Model (apart from expanding it to exactly three generation of fermions and adding massive neutrinos) and have made myriad predictions to exquisite precision.

There are a variety of open questions and matters of ongoing investigation in modern physics, however.

Two important phenomena predicted by the Standard Model: sphaleron interactions and glue balls (i.e. hadrons made entirely of gluons), have not yet been observed. We still don't know the absolute masses of the neutrino mass eigenstates or even if they have a "normal" or "inverted" mass hierarchy, the quadrant of one of the neutrino mass oscillation parameters, more than the vaguest estimate of the CP violating phase among the potential seven experimentally observed neutrino related physical constants, or the mechanism by which neutrino mass arises. We've seen patterns in the experimentally measured parameters of the Standard Model but have no solid theory to explain their values. While we can predict the "spectrum" of pseudoscalar and vector mesons and of three quark baryons with their properties for the most part, we are still struggling to explain the observed spectrum of scalar and axial vector mesons, we are in the early stage of working out the spectrum of possible four and five quark hadrons including both true four and five quark bound systems and "hadron molecules". And we can't even really predict, a priori, why the exact handful of light pseudoscalar and vector mesons are blends of valence quark combinations rather than individual particles although we can explain their structures with post-dictions. While in principle parton distribution functions can be calculated from first principles in the Standard Model, we've only managed to actually do that, somewhat crudely and in only a few special cases, in the last few years.

Investigation of just what triggers wave function collapse, how quantum entanglement works, the extent to which virtual particles and quantum tunneling must obey special and general relativity, and the correct "interpretation" of quantum mechanics is ongoing. At an engineering level, we are in the very early days of developing quantum computers.

We have a good working model of the residual strong force that binds nucleons in an atom, but have not derived all of nuclear physics or even the residual strong force, from the first principles of quantum chromodynamics (QCD), the Standard Model theory of the strong force. While we understand the principles behind sustainable nuclear fusion power generation, we don't have the engineering realization of it quite worked out. We have mapped out the periodic table of the elements and isotopes all of the way to quite ephemeral elements and isotopes that are only created synthetically, but we can't confidently predict whether or not there are as yet undiscovered elements that are in an island of stability. We are on the brink of mastering condensed matter physics issues like how to create high temperature superconductors and the structure and equation of state of neutron stars.

The search for deviations from the Standard Model in high energy physics has been relentless, particularly since 1994, when all Standard Model particles except the top quark had been discovered. Mostly this has been a tale of crushed dreams. Experiments have largely ruled out huge portions of the parameter space of supersymmetry, multiple Higgs doublet theories, technicolor, leptoquarks, preon theories, fourth or greater generation fermion theories, all manner of grand unified theories of particle physics, proton decay, neutron-antineutron oscillation, flavor changing neutral currents at the tree level, neutrinoless double beta decay or other affirmative evidence for Majorana neutrinos, lepton flavor violation, lepton unitarity violations, non-standard neutrino interactions, and sterile neutrinos. No dark matter candidates have been observed experimentally. We've even observationally ruled out changes in many of its fundamental constants for a period looking back of many billions of years.

There have been some statistically significant, but tiny, discrepancies between the experimentally measured value of the anomalous magnetic moment of the muon and the value predicted by the Standard Model, although this increasingly looks like it is a function of erroneous calculations of the predicted value rather than evidence of new physics. While most experimental anomalies suggesting new particles have been ruled out there have been some very weak experimental hints of a 17 MeV particle (X17) whose alleged experimental hints may have other explanations, and an electromagnetically neutral second scalar Higgs boson at about 95 GeV, neither of which have been fully ruled out, but neither of which is likely to amount to anything, and their have been weak experimental hints, that are to some extent mutually inconsistent between different experiments of one or two possible "sterile neutrinos" (which could also be a dark matter candidate). The anomalous magnetic moment of the electron measured experimentally isn't a perfect fit to its theoretically predicted value although it is very close. The experimentally measured couplings of the Standard Model Higgs boson aren't a perfect fit to the theoretical predictions although they are reasonably close to within experimental uncertainties. While early hints of lepton universality violations were ruled out when the experimental data improved, there are still some minor lepton flavor ratio anomalies out there. Still, there is every reason to think that these anomalies won't last and that the particle content of the Standard Model is complete with the possible exceptions of one or more particles involved in the mechanism that generates neutrino masses, a massless or nearly massless graviton, and one or more dark matter candidates with properties that make them almost impossible to detect in a particle collider.

Thus, while there are a few details and implementations left to work out, the Standard Model, high energy physics, and nuclear physics are close to being complete and we don't expect any new discoveries in this area to identify anything deeply wrong with what we know now, even though if we are really lucky, more research and greater precision might grant us a deeper understanding of why the Standard Model has the properties that it does.

The situation in astrophysics and cosmology is much less settled, and while the handful of particle colliders on the planet provide us with a trickle of new high energy physics data in some very narrow extensions of existing high energy physics parameter space, a host of new "telescopes" in the broad sense of the term is providing torrents of new astronomy observations that our existing modern physics theories struggle to explain. The leading paradigm in astrophysics and cosmology, the LambdaCDM "Standard Model of Cosmology" is a dead man walking, mostly for lack of a consensus on what to replace it with.

"Telescopes" aren't just visual light telescopes on the surface of the Earth anymore, and even those are vastly improved. Modern "telescopes" see the entire range of the electromagnetic spectrum from ultra-low frequency radio waves to ultra-high energy gamma waves, not just from Earth but also based in space, with extreme resolutions. We have neutrino "telescopes". We have "cosmic ray detectors" which observe non-photon particles that rain down on Earth from space. We have gravitational wave "telescopes" that have made many important discoveries, including the observation of many intermediate size black holes. In some cases we can do "multi-messenger astronomy" which combined signals from multiple kinds of telescopes that come from a single event (something that has places strong bounds on both the speed of neutrinos and the speed of gravitational waves, which have both been as predicted by special and general relativity).

We have overwhelming observational evidence of dark matter phenomena. But we have no dark matter particle candidate and no gravity based explanation for dark matter phenomena that fits all of the data and has secured wide acceptance, although we have an ever filling cemetery of ruled out explanations for dark matter, like MACHOs, primordial black holes, supersymmetric WIMPs, and cold dark matter particles that form NFW halos. Attempts to explain dark matter through the gravitomagnetic effects of general relativity in galaxies have also failed. And there are dozens of distinct types of observations contrary to the predictions of LambdaCDM. Fairly sophisticated comparisons of predictions with observations strong disfavor warm dark matter candidates and thermal relic GeV mass scale self-interacting dark matter candidates. QCD axions and QCD bound exotic hadrons are also largely ruled out. Toy model MOND can't be the exclusive explanation for dark matter phenomena, and neither can some of its relativistic generalizations like TeVeS, although MOND is a very simple theory that explains almost all dark matter phenomena observed up to the galaxy scale with a single new parameter and has with some mild generalizations explained the cosmic radio background (CMB) observations and the impossible early galaxies problem. But while MOND may be on the right track it doesn't quite get many features of galaxy clusters right (although a similar scaling law can work there) and has trouble with some out of disk plane feature of spiral galaxies. The data on wide binaries, which would distinguish between a variety of dark matter particle and gravitational based theories to explain dark matter phenomena are current inconclusive and have received contradictory interpretation. A variety of gravitational explanations of dark matter phenomena are promising, however, as are dark matter particle theories with extreme low mass dark matter candidates like axion-like particles which have wave-like properties.

We have inconsistent measurements of the Hubble constant which is one of two observations that contribute to our estimate of the amount of dark energy in a simple LambdaCDM model where dark energy is simply a specific constant value of the cosmological constant suggesting that the cosmological constant, lambda, may not actually be constant.

The allowed parameter space for cosmological inflation continues to narrow with the non-detection of primordial gravitational waves at ever greater precisions. There are strong, but not conclusive suggestions that the universe may be anisotropic and inhomogeneous even at the largest scales, contrary to the prevailing cosmology paradigm.

There are no widely accepted satisfactory answer to the question of baryogenesis and leptogenesis, although improvements in the precision and energy scale reach of the Standard Model and improved astronomy observations increasingly push any meaningful baryogenesis and leptogenesis closer to the Big Bang, with any significant changes in the aggregate baryon number and lepton number of the universe pretty much pushed to the first microsecond after the Big Bang at this point.

None of the unknowns in astrophysics and cosmology have any real practical engineering implications. But the Overton window of possibilities that are being seriously investigated in these fields is vastly broader than in high energy physics or quantum mechanics.

The Future

The good news is that the torrent of astronomy data that is pouring in from many independent research groups is providing us with the data we need to more definitively rule out or confirm various competing hypotheses in astrophysics and cosmology. We have a lot of shiny new tools both in the form in many different kinds of vastly improved "telescopes" and in the form of profoundly improved computational power and artificial intelligence tools to analyze this vast amount of new data to allow us to have scientific advances in these fields which are not just driven by observations and not group think or the sociology of the discipline, even though it may take the deaths of a generation or two of astrophysicists for the field to fully free itself from outdated ideas that are no longer supported by the data.

Even if we don't reach a consensus around a new observationally supported and theoretically consistent paradigm in my lifetime of two or three more decades, I am very hopeful that we will do so within the lives of my children and of my grandchildren to be.

I have strong suspicions about what the new paradigm will look like.

Dark matter phenomena will be explained most likely by a gravitational explanation with strong similarities to work of Alexandre Deur, whether or not his precise attempt to derive his conclusions from non-perturbative general relativity effects holds up. The consensus will also probably likely be that quantum gravity does exist, although it may take quite a while to prove that with observations.

Also, like Deur, and unlike the vast majority of other explanations, I think that the ultimate explanation for dark energy phenomena will conserve mass-energy both globally and locally and will not be a true physical constant. The cosmological constant of general relativity will probably ultimately be abandoned even though it is a reasonable first order approximation of what we observe. This will also mean that the aggregate mass-energy of the universe at any given time will be finite and conserved; it will be a non-zero boundary condition at t=0 of the Big Bang.

Thus, I suspect that a century from now, the consensus will be that there are no dark matter particles and there is no dark energy substances, and that these were just products of theoretical misconceptions akin the the epicycles to explain celestial mechanics that preceded the discovery that their motions could be explained to all precision available at the time with Newtonian gravity.

It will take time, but I expect that cosmological inflation will ultimately be ruled out.

I expect that new advances in astrophysics will rule out faster than light travel or information transfer and wormholes.

I don't think that we will have a conclusive explanation of baryogenesis and leptogenesis, even within my grandchildren's lives, but I do think that a mirror universe hypothesis that there is an antimatter universe that exists before the Big Bang in which time runs in the opposite direction will become one of the leading explanations. This is because I think that we will make significantly more progress towards ruling out new high energy physics and any possibility of matter creation in periods closer and closer to the Big Bang. This will make non-zero baryon number and lepton number in increasingly short time frames immediately after, although not at, the Big Bang impossible.

I think that there are even odds that we will discover that sphaleron interactions are actually physically impossible in any physical possible scenario doesn't their theoretical possibility in the Standard Model, possibly due to a maximum local mass-energy density.

In the area of high energy physics, I don't expect any new particles to be discovered (apart from possible evidence for the existence of a massless graviton), and I expect the Standard Model to stand the test of time. I do expect some refinements of our theories of wave function collapse and quantum interpretations. I don't expect new high energy physics at higher energies. I don't expect that we will find new heavy elements in islands of stability.

I expect that neutrinos will be found to have Dirac rather than Majorana mass that is somehow made possible without new particles despite the current lack of a clear path to do so. Most likely, our understanding of neutrino mass and of the Higgs field Yukawas of the Standard Model particles will involve a dynamical balancing of the Higgs vev between particles that can transform into each other in W boson interactions via W boson interactions, as opposed to giving such a central role to the coupling of these particles to a Higgs boson. Self-interactions with the fields to which the various fundamental particles couple will also play a role in generating their masses.

I expect that, as our measurements of the fundamental particle masses get more precise, that the sum of the square of the masses of the fundamental particles will indeed be found to equal the square of the Higgs vev. Vast amounts of ink will be spilled once this is confirmed, over why fundamental boson masses give rise to slightly more than half of the Higgs vev, while fundamental fermions give rise to slightly less than half of it. This could reduce the number of free independently experimentally measured mass and coupling constant parameters of the Standard Model from eighteen (fifteen masses and three coupling constants) minus one for the electroweak relationship between the W and Z boson masses and coupling constants, to eight or fewer (three coupling constants, the W, two fermion masses, and two lepton masses).

I expect that we will have a good first principles explanation of the full spectrum of observed hadrons and that we will have first principles calculations of all of their parton distribution functions.

I expect that we will be able to work out the residual strong force that binds nucleons exactly from first principles, and that we will be able to calculate with quantum computers that there are no undiscovered islands of stability in heavy elements or isotopes.

There are even odd that we will discover a deeper explanation for the values of the parameters in the CKM and PMNS matrixes by sometime in my grandchildren's lives, and better than even odds that we will be able to reduce the number of free parameters in those two matrixes to less than the current eight. I wouldn't be surprised if the CP violating parameters of the CKM and PMNS matrixes were found to have an independent source from the other six parameters of those matrixes.

I don't think that we will develop a Lie group Grand Unified Theory or Theory of Everything, or that string theory will ever work, although I do think that we are more likely than not to develop a theory of quantum gravity that can be integrated into the Standard Model more cleanly. Indeed, gravitationally based dark matter phenomena may turn out to be a quantum gravity effect that is actually absent from classical general relativity.