Current Physics Conjectures

This page is a summary of my conjectures regarding unresolved issues in physics.

Disclaimers

* I am not a physics professional, just a generalist educated layman who had read a lot about a wide range of academic and professional writing on the topic. The topics I am summarizing here have right or wrong answers, but even professional physicists do not have consensus answers to them - they are unsolved problems in physics. These are not statements of established and proven physical conclusions, but neither are they divorced from the empirical evidence, the physics literature, and reasonable inferences that can be drawn from them.

* These are not dogmatic or ideological views. I am open to changing my views in the face of new observational evidence and theoretical insights. 

* If you want to convince me of something, please try to do so on the linked blog posts and not here.

Physics Conjectures

Table of contents:

* Dark matter, dark energy and gravity.

* Cosmological inflation

* Matter creation and B-L conservation

* Neutrinos

* Catalog of fundamental particles

* Fundamental particle rest mass and mixings

* Lepton universality violations.

Dark matter, dark energy and gravity

The physicist closest to an accurate understanding of gravity is Alexandre Deur. 

His approach to quantum gravity is largely vanilla, but is informed by knowledge of the mathematics and phenomenology of quantum chromodynamics (the physics of the strong force), and in particular, the self-interaction of gluons which is parallel to the self-interaction of gravitons.

Deur's approach to quantum gravity (although most of his insights are not inherently quantum and could also be formulated on a classical field basis), differs from conventional classical general relativity primarily in ways generic to any quantum gravity theory (e.g. gravitational energy can be localized in quantum gravity, but not in conventional GR), and from its treatment of gravitational field self-interactions, which are present in conventional GR to some extent in strong fields, but are not modeled correctly in weak fields.

In this approach, the phenomena attributed to dark matter and dark energy are emergent weak field quantum gravity effects that arise primarily from self-interactions of a massless graviton that couples to all other particles with a strength proportional to mass-energy.  There are no dark matter particles and there is no substance (e.g. such as quintessence or vacuum energy) that constitutes dark energy. 

Gravity can be entirely derived, in principle anyway, from the properties of a massless spin-2  graviton with a coupling constant functionally related to Newton's constant, "G", Planck's constant, and the speed of light in a vacuum, "c".

While it may be possible to think of gravity as a warping of space-time, it is usually more helpful to think of gravity as a quantum field theory involving gravitons in Minkowski space in weak fields. Einstein's equations of general relativity as conventionally applied is accurate to the full extent of available observational precision in strong fields such as the vicinity of black holes, neutron stars and the Big Bang, which conventional wisdom has it is almost perfectly reproduced by the behavior of a massless spin-2 graviton with a coupling strength that is a function of Newton's constant. 

To the extent that a graviton based approach in Minkowski space is distinguishable from a geometric approach from general relativity, I suspect that the former and not the latter is correct. 

I strongly suspect that the strong equivalence principle of general relativity is not correct, although the equivalence of gravitational mass and inertial mass is correct. Thus, external field effects are possible. I also suspect that Deur's theory is really a subtle modification of GR rather than just vanilla GR, although it could simply arise due to his consideration of non-perturbative effects in non-spherically symmetrical systems (which are insufficiently studied).

Renormalization effects on the strength of the gravitational coupling constant, if any, are too small to be discerned in almost all applications except the first few moments after the Big Bang and slight details relevant in the immediate vicinity of black holes.

While the graviton is very likely a spin-2 particle, its weak field properties in astronomy applications are well approximated by a massless spin-0 even parity graviton.

Dark matter effects arise as a second order effect due to graviton self-interaction that is discernible only in weak fields and arise only in systems that are not spherically symmetric. Dark matter effects are strongest in systems that can be well approximated as two point masses with a gravitational flux tube running between them. In spiral galaxies, gravitons self-gravitate to cling to the plane of the disk creating an effective 1/r force rather than a 1/r^2 force in the weak field. In elliptical galaxies, dark matter effects are strongest to the extent that the galaxies is non-spherical.

Dark energy effects arise when gravitons that would otherwise have radiated out from a spherically symmetrical system are instead confined to a galaxy or galaxy cluster or other system, weakening the pull between systems in which dark matter phenomena are present. This is why the inferred amount of dark matter and the inferred amount of dark energy are of the same order of magnitude.

This mechanism for dark energy phenomena and the larger theory means that contrary to conventional wisdom about the cosmology constant or other dark energy theories, quantum gravity conserves matter-energy not just locally but globally.

Deur's approach closely approximates the conclusions of the toy model modified gravity theory of Milgrom called MOND, regarding the rotation curves of spiral galaxies, although it can in principle do so without an independent MOND acceleration constant a(0). It also approximates the dark matter phenomena observed in galactic clusters where MOND underestimates dark matter effects.

I suspect that this approach will accurately reproduce 21cm signals in the radiation era transition that predict the wrong temperature of the universe at that time in the presence of dark matter, but is accurate in the absence of dark matter. In this area, the universe may be sufficiently spherically symmetric and sufficiently homogeneous for a no dark matter model of be a good approximation.

I suspect that Deur's approach will solve the "impossible early galaxy" problem, because modified gravity theories that eliminate the need for dark matter generically tend to do so (MOND) also (another modified gravity theory).

There is good reason to believe that the rate at which the universe is expanding (which is governed by the cosmological constant in conventional general relativity and the lambdaCDM standard model of cosmology) is less than the value conventionally assigned to it (and hence, closer in magnitude of inferred dark matter effects) due to methodological issues with how the measurement is done.  See also here. This technical issue is currently unresolved, however.

Contrary to conventional wisdom, there is no particular dark matter theory (and related theory regarding how dark matter came to be distributed as it purportedly is today), that accurately reproduces all dark matter phenomena at the galaxy and smaller scale, or it predictive at that scale. See also, e.g., here and here. Even galaxy cluster data  are problematic for lambdaCDM.

Also, the cosmic background radiation predictions of a dark matter model is less spectacular than it seems, because it is really only predicting a single parameter. Modified gravity theories generalizing MOND have reproduced this feat. Deur's approach does as well and can  also explain the Hubble tension and evolving dark energy.

I strongly suspect that the universe does not have more the four space-time dimensions, although the dimensions that we do have may be emergent.

Cosmological inflation

It is necessarily true that most cosmological inflation scenarios are false, because there are so many mutually inconsistent inflation theories (literally hundreds of them).

Inflation is conventionally believed to take place from 10^-33 seconds to 10^-32 seconds after the Big Bang). 

I am not convinced that it is fruitful or possible to use the laws of physics, and those things it is possible to observe via astronomy, to go back further than the immediate post-inflation era for a set of initial conditions for the universe, a tiny fraction of a second after the Big Bang. There may be a tiny fraction of a second that is unknowable and that tiny bit of cosmic censorship may be harmless. See also here.

The evidence that cosmological inflation is necessary to describe the features of the universe that it claims to describe are likewise dubious.

Matter creation and B-L conservation

The baryon asymmetry of the universe arises from a scenario in which the birth of the Universe arises from a pair of universes, one the CPT image of the other, living in pre- and post-big bang epochs. The CPT-invariance strictly constrains the vacuum states of the quantized fields. Thus, before the Big Bang is a predominantly antimatter universe in which time runs backwards relative to our universe. See also here and here.

I strongly suspect that baryon number and lepton number are not violated outside of Standard Model sphaleron interactions (which conserve B-L). So far, even they have not been observed at the LHC. 

I am not confident that sphaleron interactions actually happen, although whether or not they do at very high energies (beyond what can be reproduced at the current LHC and limited predominately to the first microsecond after the Big Bang) is largely irrelevant to the larger conclusions, because the effect size is too small. A sphaleron requires a roughly 9 TeV energy to be concentrated at a density of about 1000 times that of the mass-energy density of a proton (i.e., a radius of about 8.4 * 10^-17 meters; the Schwarzschild radius of a 9 TeV sphaleron is about 2.4 * 10^-50 meters; the Planck length is about 1.6 * 10^-35 meters). It would probably require a collider at least 100 times as powerful as the LHC to create a sphaleron - probably something that the next generation of more powerful particle colliders will not achieve. 

This would require a mass-energy density more than nine million times greater than a neutron star, i.e. 10^17 kg/m^3, or the mass-energy density of a minimum sized stellar collapse black hole. A mass-energy density this great has never been observed. This concentrated a mass-energy may not be possible. It is possible and plausible that there is a maximum mass-energy density in the universe, and that this threshold that prevents non-conservation of baryon number and lepton number from occurring at all.

This also implies that (at the tree level) neutrinoless double beta decay cannot occur, that proton decay cannot occur, that neutrinos are not Majorana particles, and that flavor changing neutral currents do not occur. This also rules out some seesaw models of neutrino mass generation.

Neutrinos

There are exactly three electroweak neutrino types and exactly three neutrino mass eigenstates. There are no sterile neutrinos that oscillate with ordinary active neutrinos. There are no right handed neutrinos. 

The neutrinos mass eigenstates have a "normal" rather than an inverted or degenerate mass hierarchy.

None of the neutrino masses is zero, but the lightest neutrino mass eigenstate is probably on the order of a low single digit meV or less. 

Neutrino oscillation exhibits CP violation, but not quite maximal CP violation. This can be explained fully by a single CP violating phase parameter.

The magnetic moment of the neutrino is equal to, or very nearly, the negligible Standard Model value, i.e. 3*10^-19, arising from non-tree level effects, which is too small to measure with existing technology.

Neutrinos are not Majorana particles and do not have Majorana mass. There is no neutrinoless double beta decay.

I don't claim to know how neutrinos do generate their mass, however, and it might not be the same as the mechanism by which other fundamental fermions and fundamental massive bosons in the Standard Model do. But, I do not think that it is a seesaw model.

I don't rule out the possibility of a massive vector boson that gives rise to neutrino mass and facilitates neutrino oscillation including its CP violations, in the way that the W boson and Higgs boson do for other fermions. An "on shell" understanding of neutrino oscillation as a virtual W boson mediated process is plausible. A fundamental boson that addresses this issues is the most likely non-Standard Model particle other than a graviton to exist, if any such particle does.

Catalog of fundamental particles

Fundamental Fermions

There are exactly three generations of fundamental fermions. The fundamental fermions of the Standard Model are a complete set of the fundamental fermions that exist.

The Higgs Boson

The observed Higgs boson has exactly a Standard Model Higgs boson of its measured mass (of approximately 125 GeV). 

There are no charged Higgs bosons. 

There are no Higgs bosons other than the Standard Model Higgs boson, with the possible exception of a massive boson related to neutrino oscillation and mass, which, if it exists, would be much less massive than the W boson or Higgs boson, and which could be scalar, pseudo-scalar, or even vector or tensor in spin.

The observed Higgs boson may actually be some sort of composite particle made up of a combination of a W+ boson, a W- boson, a Z boson, and a photon, whose combined mass in composite combination is greater than the sum of their individual masses, due to quantum corrections or binding forces. But this would not really resemble technicolor theories.

It isn't impossible, particularly if the Higgs boson is in some sense composite, that there are excited states of the Higg boson with the same properties but a different mass. There are some weak hints at a couple of different masses of this possibility. But there is very likely no pseudoscalar or vector or tensor or charged Higgs boson.

The mass of the Higgs boson implies a possibly metastable universe, but including the graviton in the calculation of the beta functions of the Standard Model physical constants may tip the balance at high energies towards the universe being absolutely stable.

The Graviton

There is a spin-2 massless graviton.

Other Fundamental Bosons

The Standard Model is correct that there is a W+ boson, a W- boson, a Z boson, a photon, and gluons that come in eight color charge combinations.

The Standard Model is correct that photons and gluons have no rest mass, and that the rest mass of the W+ boson is identical to the rest mass of the W- boson, its antiparticle.

Color charge may be a topological feature of color charged particles.

Composite Particles

All possible hadrons (i.e. composite particles bound by the strong force) can be created, although two valance quark antiquark mesons and three valence quark or three valence antiquark baryons are much more common since they are more likely to form randomly and more stable. But some common bosonic hadron resonances may have tetraquark and/or glueball components. Protons and bound neutrons are the only stable hadrons with mean lifetimes much more than a microsecond.

Hypothetical Particles That Do Not Exist

There are no supersymmetric particles. There are no leptoquarks. The most plausible beyond the Standard Model fermion would be a singlet spin-3/2 gravitino, but I don't think that it exists either. There are no axions. There are no W' or Z' bosons. The hypothetical X17 boson does not exist. There are no dark matter particles (other than gravitons themselves). 

There are no right handed, or sterile, neutrinos.

There are no fundamental particles with electromagnetic charges that are not multiples of 1/3e (or zero). The only particles with electromagnetic charges that are not multiples of e are quarks and antiquarks, and they are almost always confined into hadrons with charges that are multiples of e (quark gluon plasma and isolated top quarks are the only exceptions).

Primordial black holes, if they exist at all, are very rare in the current universe, having either decayed via Hawking radiation, or having grown to be larger than stellar black holes, by now. They may be largely impossible, or even more rare, if a maximum density conjecture holds true.

Muon g-2

The close match between the measured value of muon g-2 and its correctly calculated Standard Model value, strongly suggests that the inventory of fundamental particles set forth above is complete, and that any beyond the Standard Model physics are limited to extremely high energies or to tweaks that don't impact muon g-2 (such as supplementary understandings of how the Standard Model physical constants arise discussed below).

Within The Standard Model Particles

It seems plausible to me that there may be some sort of particle or small number of particles that are more fundamental than the dozen fundamental fermions and half dozen fundamental bosons described above: perhaps some sort of preon or string for which these fundamental particles are the only possible permutations. 

A few theoretical efforts along these lines have appeared promising. But so far, the nature of these more fundamental particles, if they exist at all, remains elusive.

Fundamental particle rest mass and the CKM matrix

Quarks, charged leptons, the Higgs boson, the W+ boson, the W- boson and the Z boson acquire their masses through an electroweak mechanism which either is, or is very similar to, the Standard Model Higgs mechanism. 

The CKM matrix is also an electroweak phenomena and really best thought of as primarily a property of the W boson.

The sum of the square of the rest masses of the fundamental particles of the Standard Model is equal to the square of the Higgs vacuum expectation value.

The Higgs vacuum expectation value is a function of the W boson mass and the coupling constant of the weak force. Thus, these two fundamental constants set the mass scale of fundamental particles the Standard Model.

The Z boson mass is a function of the W boson mass, the coupling constant of the weak force, and the coupling constant of the electromagnetic force, and thus can be chosen to be non-fundamental in a permissible parameterization of the Standard Model experimentally measured constants in the context of electroweak unification.

Illustrations via Wikipedia.

Koide's rule for charged leptons is correct to a precision at least comparable to the ratio of the charge lepton masses to the neutrino masses. The true value of the charged lepton masses may need a small correction that reflects W boson mediated interactions between charged leptons and neutrinos. This reflects a dynamic balancing of charged lepton masses via W boson interactions with them. Charged lepton universality is correct apart from slight distortions due to W boson mediated interactions between charged leptons and neutrinos that import a highly suppressed PMNS matrix driven set of lepton flavor universality violations.

The quark masses reflect a dynamic balancing of quark masses via W boson interactions with them. An extended Koide's rule approximates these masses because it incorporates two of three of the possible W boson mediated interactions of a quark in a Koide triple, but must be adjusted for the third possible W boson mediated interaction, and possibly for higher order loop effects, to be completely accurate. 

The photon, gluons, and the graviton have a rest mass of zero because they do not have weak force mediated interactions.

Forces mediated by bosons with a rest mass of zero cannot have charge parity (CP) conservation violations, which are equivalent to time symmetry violations, because the carrier bosons do not experience time because they are constantly traveling at the speed of light. This is one resolution, among many, of the strong CP problem.

In contrast, weak force interactions via the W boson can have charge parity violations because the W boson is massive and therefore experiences time.

The CKM matrix is more fundamental than the quark masses.

The non-CP violating parameters of the CKM matrix can be reduced to a single parameter in some deeper theory.

In may be the case that quantum gravity is a right handed chiral force in the same way that the weak force is a left handed chiral force - as part of a larger graviweak unification.

Lepton Universality Violations

Experimental deviations from lepton universality were the product of experimental fluke data and analysis errors. Leptons are universal subject to possible deviations so slight from higher loop effects so slight (due to the slight masses of the neutrinos relative to them) that they can be observed with current technology.