Wednesday, February 22, 2017

Notable Views Regarding Physics


If you review a large amount of information about a subject and don't have an opinion, you aren't paying attention. Needless to say, I have opinions about a great many matters that I have reviewed at the "tree level" over the years in the area of physics.

If you are a long time reader of this blog, you know the views that I have expressed on a variety of notable issues in physics. But, if you are relatively new to this blog, you might be less familiar with these views. 

It is not my purpose to mislead anyone into thinking that there is a scientific consensus regarding an observation that I make that may be a minority view regarding a controversy or issue, or may even be one that I am the only person currently actively advocating. And, anyone reading this blog should know the assumptions, preconceptions and hypotheses that I come to my coverage holding.

Also, I want to make clear that none of my views on these physics issues are set in stone. They represent my current synthesis of the available evidence. I have changed my mind about some of them in the past, and no doubt will in the future as new evidence becomes available. Each new data point refines the picture, sometimes confirming it with greater certainty, sometimes providing greater detail, and sometimes resulting in a paradigm shift.

This post is a summary of conclusions. It does not purport to even attempt to cite to posts at this blog where I marshal evidence in favor of a view or analyze why I believe it to be correct. This has happened over the course of many hundreds of posts and would be too time consuming and voluminous to include here.

Substance - My Most Notable Views About Physics

I. Gravity, Dark Matter, Dark Energy and Astronomy

A. In my view the most unimportant unsolved problem in fundamental physics is how the phenomena attributed to dark matter arise.

B. There are two primary paradigms: particle based dark matter theories and gravity modification theories. The available evidence does not refute all models advanced in either approach, although much of the potential dark matter parameter space has been ruled out by observation and analysis, and some gravity modification theories have likewise been ruled out.

C. I believe that a gravity modification theory is considerably more likely than a particle based theory to explain dark matter phenomena.

D. I believe, at a lower level of certainty, following the work of Deur, that:

(1) the correct gravity modification arises from a quantum gravity theory that conceptualizes gravity as an exchange of gravitons rather than primarily as a geometric bending of space-time;

(2) this quantum gravity theory differs from the predictions of general relativity predominantly in weak gravitational fields (as opposed, for example, to near the Big Bang or black holes);

(3) the quantum gravity modification largely arises from the failure of general relativity to accurately reflect second and greater order effects arising from graviton interaction with other gravitons in a manner analogous to gluon interactions with other gluons;

(4) in principle this quantum gravity theory introduces no new fundamental constants not found in GR (although it may operationally need one or two constants that are in practice derived even though they could in principle be determined from existing constants);

(5) in this theory the amount of ordinary matter and the shape of the geometric distribution of matter both impact the second order quantum gravity effects;

(6) much or all of the effects of dark energy result from gravitons being diverted to make gravitational pulls stronger in ways that manifest in dark matter phenomena, leading to gravitational forces between systems that manifest dark matter phenomena to be weaker than they would be without this effect; and

(7) there are solid indications that the amount of dark energy or the size of the cosmological constant, as the case may be, is materially overestimated experimentally, which makes it more likely that substantially all dark energy effects are side effects of dark matter phenomena.

E. If, the less probable case is true and in fact, gravity is not modified and the source of dark matter is a particle:

(1) dark matter phenomena are predominantly the product of not more than two kinds of particles (a fermion singlet (which may or may not be composite) and a boson that interacts only with dark matter), and quite possibly only one kind of particle (indeed, most likely only one kind of particle); 

(2) those particles are warm dark matter scale for the fermion or less; and

(3) the dark matter particles have essentially no non-gravitational interactions with ordinary matter through any of the three Standard Model forces (electromagnetic, strong and weak).

II. Cosmology

A. In my view, the most likely explanation for the matter-antimatter asymmetry in the universe is that there is an antimatter dominated universe "before" the Big Bang in which the second law of thermodynamics runs in the other direction that balances the matter dominated nature of our own universe. This implies that a new source of extreme CP violation is unnecessary. But, I do not hold this view with a high level of confidence.

B. In my view, the evidence to support the events of the early moments of the Big Bang prior to Big Bang nucleosynthesis, including "inflation" is not solid enough to constitute scientific proof and is merely a plausible hypothesis.

C. I believe that the multiverse and anthropic principle are being used in fundamentally unscientific ways at this time.

III. Neutrino Physics

A. I think that neutrinos are very unlikely to have Majorana mass.

B. I think that neutrinos have a "normal" mass hierarchy.

C. I think that cosmology based caps on the sum of the neutrino masses are accurate and can be integrated with other data to accurately estimate the neutrino masses.

D. I think that we don't understand the mechanism of neutrino mass generation or neutrino oscillation beyond the current phenomenological model. But, I think that seesaw models of neutrino mass are almost surely wrong. I think that there is a reasonable possibility that some sort of boson mediates neutrino oscillation.

E. I think that neutrino oscillation almost surely has a CP symmetry violating term.

F. I think that neutrino oscillation does not involve any maximal mixing angles.

G. I think that neutrinoless double beta decay never happens, nor do any other forms of sub-GUT scale lepton number violation or baryon number violation (such a proton decay).

H. I think that there is probably not a right handed neutrino.

IV. Quantum Mechanics And Space-Time

A. Entanglement inherently requires a surrender of at least one of three things: causality, locality and reality. I am not nearly so convinced that causality and locality need to be maintained as many physicists.

B. I think that the non-speed of light paths in the particle propagator of quantum mechanics suggests that the picture of space-time are perfectly smooth and local is likely to be incorrect.

C. I think that the four dimensional nature of space-time may be emergent, but that there are unlikely to be more than four or five dimensions of space-time, and that there are no compactified dimensions.

D. I am not perfectly convinced that quantum mechanical randomness is not just extremely chaotic (in a mathematical sense of a deterministic system highly sensitive to slight changes in initial conditions) rather than truly random behavior.

V. Beyond The Standard Model Theories

A. I believe that some of the most notable experimental anomalies which physics are dealing with today, such as the muon g-2 problem and the muonic proton radius puzzle, are due to some combination of experimental error and a failure to properly apply existing fundamental physical laws to the problems properly, rather than to beyond the Standard Model Physics.

B. I believe that so called "problems" such as the "hierarchy problem" and the "strong CP problem" are not problems at all that need to be solved and are unsound at a basically philosophical level in their very formulation.

C. I believe that there are deeper theories that can explain the relationship of the Standard Model constants, particles and forces to each other from a more fundamental set of rules and constants. For example:

(1) I think that the sum of the square of the fundamental particle masses is functionally related to the Higgs vacuum expectation value.

(2) I think that at least the charged fermion masses relative to each other dynamically through a process that primarily involves W boson interactions and reproduces a relationships approximately captures in Koide's rule.

(3) I think that it is likely that the CKM matrix can accurately be parameterized with one real parameter and one complex parameter.

(4) I think it is plausible that the CKM matrix parameters are related functionally, in some way, to the PMNS matrix parameters.

(5) I think it is plausible that it may be possible to determine the CP violating phases of the CKM matrix and PMNS matrix from first principles.

D. I believe that the barriers to quantum gravity involve more of a shortage of computational tools and lack of creativity, than they do any fundamental theoretical problem.

E. I think that beyond the Standard Model fundamental particles that do not serve merely as preons for Standard Model fundamental particles are generally ill motivated. We might be missing one or two, but if my conjectures regarding dark matter are correct, we don't need any more fundamental particles, and certainly not the multitude suggested by SUSY theories.

F. I think that supersymmetry and supergravity do not accurately describe reality and merely constitute toy models useful for thinking about particle physics to use in more realistic models.

G. I think that there are some operative principles for applying quantum chromodynamics that we do not yet know which are necessary to understand the non-observation of glueballs and the spectrum of scalar and axial vector mesons.

H. I think that string theory is incorrect but may provide valid insights.


Ryan said...

Why do you say that Dark Matter (if it exists) couldn't have more than 2 particles?

andrew said...

Strictly speaking, I say it can't have more than two particles that make a dominant contribution.

In the early days of dark matter models, there were a lot of "mixed dark matter" models that would have several different kinds of particles. But, these models pretty much across the board failed to match observation in simulations as well as more parsimonious models. There were probably a dozen or more papers that came to that conclusion.

Also, the fact that you can make a modified gravity model closely approximate reality with just a couple of free parameters or less, implies that any dark matter particle theory that also approximates reality may have no more degrees of freedom than the modified gravity model does.

You actually could have a dark matter particle model in which just like reality, almost all matter was wrapped up in just a couple of kinds of particles (protons and neutrons in the matter world) and almost all other forms of dark matter were extremely rare and unstable (much like heavier baryons in the matter dominated world), because those very rare and short lived particles don't have a meaningful gravitational dynamics impact. And the dominant dark matter particles, for similar reasons, need not be fundamental - they could be stable composite particles instead.

But, any dark matter particle theory has to boil down to one or two dominant kinds of dark matter with just one dominant fermion and possibly one dominant boson in addition (in self-interacting dark matter models), or one dominant boson without a dominant fermion. But, since the parameter space of SIDM is pretty much non-existent at this point, you really, at this point, need either one dominant fermion or one dominant boson as the sole dominant source of dark matter. So, the parameter space is really even more constrained (although I'm not sure that two nearly degenerate forms of dark matter particles in analogy to the proton+electron v. the neutron, would be detectable with current experimental methods).

Ryan said...

Put it this way:

Suppose we had a perfect understanding of gravity and were trying to model the behaviour of baryonic matter. How simple of a model could we get away with to capture the rough mass distribution?

IIRC most matter is tied up in the intergalactic gas at the galaxy cluster/higher scale, and at the scale of a galaxy a large percentage is in molecular gas clouds. How much would we need to know to model their behaviour in a given environment? Presumably we would need to know about photons and that there is some sort of baryon. Would we need to know about ionization? Looking at some of the models for evolution of the structure of the universe, they have to include the effects of supernova and active galactic nuclei on these media. Do you think we would be able to figure all of that out if the only thing we could observe was the gravitational effects?