Quote Of The Day

The sociology in the simulation community seems to be to assert complete success in explaining everything at all times until the next batch of simulations completes running, then point out all the improvements. Everything is explained all the time, only more so as time goes on.

- From Stacy McGaugh at Triton Station on June 18, 2026.

Quote Of The Day

We live in the wrong kind of world to be described by string theory. No physicist has ever won a big prize for string theory. I can tell you with absolute certainty that it is not the real world that we live in. So we need to start over.

- Lenny Suskind (a famous theoretical physicist) via Peter Woit's blog.

Quote Of The Day

This paper is both novel and correct, but the novel part is not correct and the correct part is not novel.

From a peer review of an academic journal article attributed to physicist Wolfgang Pauli.

Dark Matter Is Still Probably The Wrong Answer

Stacy McGaugh has a reaction blog post to the Scientific American article "What if We Never Find Dark Matter?" by Slatyer & Tait.

It nicely sums up the sociological conundrum in astrophysics that has led the discipline to throw a lot of weight and support behind a deeply flawed dark matter particle hypothesis with a particle that hasn't been detected and no hypothetical particle that can fit the astronomy observations and no theory that has made many significant ex ante predictions, rather than MOND and modified gravity that is a much better fit to the astronomy observations and has made many significant ex ante predictions.

He is spot on. Some good quotes:

In the 1980s, cold dark matter was motivated by both astronomical observations and physical theory. Absent the radical thought of modifying gravity, we had a clear need for unseen mass. Some of that unseen mass could simply have been undetected normal matter, but most of it needed to be some form of non-baryonic dark matter that exceeded the baryon density allowed by Big Bang Nucleosynthesis and did not interact directly with photons. That meant entirely new physics from beyond the Standard Model of particle physics: no particle in the known stable of particles suffices. This new physics was seen as a good thing, because particle physicists already had the feeling that there should be something more than the Standard Model. There was a desire for Grand Unified Theories (GUTs) and supersymmetry (SUSY). SUSY naturally provides a home for particles that could be the dark matter, in particular the Weakly Interacting Massive Particles (WIMPs) that are the prime target for the vast majority of experiments that are working to achieve the exceptionally difficult task of detecting them. So there was a confluence of reasons from very different perspectives to make the search for WIMPs very well motivated.

That was then. Fast forward a few decades, and the search for WIMPs has failed. Repeatedly. Continuing to pursue it is an example of the sunk cost fallacy. We keep doing it because we’ve already done so much of it that surely we should keep going. So I feel the need to comment on this seemingly innocuous remark:

although many versions of supersymmetry predict WIMP dark matter, the converse isn’t true; WIMPs are viable dark matter candidates even in a universe without supersymmetry.

Strictly speaking, this is correct. It is also weak sauce. The neutrino is an example of a weakly interacting particle that has some mass. We know neutrinos exist, and they reside in the Standard Model – no need for supersymmetry. We also know that they cannot be the dark matter, so it would be disingenuous to conflate the two. Beyond that, it is possible to imagine a practically infinite variety of particles that are weakly interacting by not part of supersymmetry. That’s just throwing mud at the wall. SUSY WIMPs were extraordinarily well motivated, with the WIMP miracle being the beautiful argument that launched a thousand experiments. But lacking SUSY – which seems practically dead at this juncture – WIMPS as originally motivated are dead along with it. The motivation for more generic WIMPs is lacking, so the above statement is nothing more than an assertion that runs interference for the fact that we no longer have good reason to expect WIMPs at all. . . . 

I can save everyone a lot of time, effort, and expense. It ain’t WIMPs and it ain’t axions. Nor is the dark matter any of the plethora of other ideas illustrated in the eye-watering depiction of the landscape of particle possibilities in the article. These simply add mass while providing no explanation of the observed MOND phenomenology. This phenomenology is fundamental to the problem, so any approach that ignores it is doomed to failure. I’m happy to consider explanations based on dark matter, but these need to have a direct connection to baryons baked-in to be viable. None of the ideas they discuss meet this minimum criterion.

Of course it could be that MOND – either as modified gravity or modified inertia, an important possibility that usually gets overlooked – is essentially correct and that’s why it keeps having predictions come true. That’s what motivates considering it now: repeated and sustained predictive success, particularly for phenomena that dark matter does not provide a satisfactory explanation for. . . . 

The equation coupling dark to luminous matter I wrote down in all generality in McGaugh (2004) and again in McGaugh et al. (2016). The latter paper is published in Physical Review Letters, arguably the most prominent physics journal, and is in the top percentile of citation rates, so it isn’t some minuscule detail buried in an obscure astronomical journal that might have eluded the attention of particle physicists.

Bonus quote from the comments:

It’s exactly the same crap as with string theory, and supersymmetry, and inflation, and dark sectors, and many other research bubbles in the foundations of physics. It is mathematical fiction; it’s nothing to do with reality any more.

- Sabine Hossenfelder (YouTube link).

Quote Of The Day

Civilization exists by geologic consent, subject to change without notice.

—Historian Will Durant

Making More Nails

4gravitons has an excellent post entitled Making More Nails. It begins as follows:

They say when all you have is a hammer, everything looks like a nail.

Academics are a bit smarter than that. Confidently predict a world of nails, and you fall to the first paper that shows evidence of a screw. There are limits to how long you can delude yourself when your job is supposed to be all about finding the truth.

You can make your own nails, though.

Quote Of The Day

CERN buildings not only have evacuation instructions for the building in case of a fire, but also evacuation instructions for the whole site.

From 4gravitons.

Genius In Action

I went to a conference which was totally about my specialization, and one Ph.D student gave his presentation, sounding very nervous. I could barely follow his talk, and thought I must have forgotten a lot of things, it seemed beyond my knowledge. 

At the any questions stage, someone stood up, and suggested one part was wrong, with an alternative explanation, which seemed convincing - lots of people nodding, as he said what would have happened if the student speaker had been right. 

Then instantly a second person stood up and said the first critic was right about the error, but his explanation was wrong, and explained why it was wrong and gave a second alternative explanation. Wow, criticizing an explanation and alternative explanation on a complex subject he had just heard 10 seconds ago. Lots of people nodding and ooing "oh yes." 

Then a third person stood up, gave his name and was immediately recognized as a Nobel prize winner, (who just happened to be in town visiting an friend), but not a specialist in the topics of the conference. He told the original presenter what their error was, then told the first critic what was really wrong with his alternative explanation, told the second critic that he was wrong in each alternative he had offered (including his wrong explanation of what was wrong) and then explained what was really really going on.

Silence. Every one sat going through what this not a specialist had said about everything, and slowly we all started nodding in agreement. We were all wiped out by how he could correct things outside of his own specialism and also how we all took so long to work out he was right. Genius is truly impressive when it swings into action.

From here (with minor spelling and punctuation edits and paragraph breaks added). 

Quote Of The Day

One red flag that a theory might be in trouble is when one has to invoke tooth fairies to preserve it. These are what the philosophers of science more properly call auxiliary hypotheses: unexpected elements that are not part of the original theory that we have been obliged to add in order to preserve it.

- Stacy McGaugh at his Triton Station blog.

Quote Of The Day

I have been Chair of the CWRU Department of Astronomy for over seven years now. Prof. Mihos served in this capacity for six years before that. No sane faculty member wants to be Chair; it is a service obligation we take on because there are tasks that need doing to serve our students and enable our research.

- Stacy McGaugh posting at Triton Station.

Academia is an area where the urge to "move up" into the direct management level position of department chair is not strong.

This fact is widely known by those in academia (incidentally, it also applies to the position of chief judge in most courts), and little known outside it.

Quote Of The Day

If an elderly but distinguished scientist says that something is possible, he is almost certainly right; but if he says that it is impossible, he is very probably wrong.

- Arthur C. Clarke

Quote Of The Day

A wise person (I think it was @AlbrechtPhysics) once told me: the first important bar that a successful theory passes is the ‘ego’ test: you hear an enthusiastic talk on the theory and it is not given by one of its inventors.

From here. 

Quote Of The Day

 

Naturalness And Similar Delusions

"Naturalness" is not a real physics problem. The "hierarchy problem" and the "strong CP problem" and the "baryon asymmetry of the Universe problem", are likewise not real physics problems. These are just cases of unfounded conjectures about how Nature ought to be that are wrong.

At Quanta magazine, another article about the “naturalness problem”, headlined A Deepening Crisis Forces Physicists to Rethink Structure of Nature’s Laws. This has the usual problem with such stories of assigning to the Standard Model something which is not a problem for it, but only for certain kinds of speculative attempts to go beyond it. John Baez makes this point in this tweet:

Indeed, calling it a “crisis” is odd. Nothing that we really know about physics has become false. The only thing that can come crashing down is a tower of speculations that have become conventional wisdom.

James Wells has a series of tweets here, starting off with

The incredibly successful Standard Model does not have a Naturalness problem. And if by your criteria it does, then I can be sure your definition of Naturalness is useless.

He points to a more detailed explanation of the issue in section 4 of this paper.

My criticisms of some Quanta articles are motivated partly by the fact that the quality of the science coverage there is matched by very few other places. If you want to work there, they have a job open.

From Woit's "Not Even Wrong" blog.

I share Woit's opinion that Quanta is, on average, one of the better sources of science journalism directed to educated laypersons in the English language.

Even Science Is Resistant To The Scientific Method

A new scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die and a new generation grows up that is familiar with it. . . . An important scientific innovation rarely makes its way by gradually winning over and converting its opponents: it rarely happens that Saul becomes Paul. What does happen is that its opponents gradually die out, and that the growing generation is familiarized with the ideas from the beginning: another instance of the fact that the future lies with the youth.

— Max Planck, Scientific autobiography, at pgs. 33 and 97 (1950). Related:

Never trust an experimental result until it has been confirmed by theory.

- Astronomer Arthur Eddington who died on November 22, 1944 (discussed here noting that: "In general, Eddington’s advice is good: when an experiment contradicts theory, theory tends to win in the end." But acknowledging exceptions and discussing Hume's take on it).

A comment makes the good point, however, that ossification of views is less of a problem in fields that are new and rapidly emerging, rather than those that have settled down a bit with enough time for competing camps over unresolved issues to emerge.

But scientists are persuaded by new evidence sometimes, as documented in this paper.

High Energy Physics Quote Of The Day

Quantum chromodynamics (QCD) calculations have been lagging behind experimental tests of it in precision for the last 40 years, at least. Feynman concluded his short introduction to quantum mechanics, "QED" (1985) with almost the same observation.

When particle physicists try to model experiments, they confront an impossible calculation — an infinitely long equation that lies beyond the reach of modern mathematics.  

Fortunately, they can generate largely accurate predictions without seeing this arcane math all the way through. By cutting the calculation short, scientists at CERN’s Large Hadron Collider in Europe make forecasts that match events they actually observe when they send subatomic particles barreling toward each other around a nearly 17-mile track. 

Unfortunately, the era of agreement between forecast and observation may be ending. As measurements grow more precise, the approximation schemes theorists use to make predictions may not be able to keep up.

From here. 

I explained the issue at greater length in a recent comment at the Physics Forums:

QCD calculations are not very precise, and this isn't just a matter of imprecise measurements.

For example, we have measured the mass of the charged pion to a precision of 1.5 parts per million. But we can only calculate that mass from first principles to a precision of a few parts per thousand.

We understand why this is the case quite well. The strong force coupling constant has been measured only to about one part per thousand. The high numerical value of the dimensionless strong force coupling constant relative to one means that even at five loops you only have about one part per thousand theoretical precision compared to one part per 61 billion theoretical precision in QED calculations to five loops in which the dimensionless QED coupling constant is much smaller relative to one. Photons don't have self-interactions and only have one charge plus polarization, greatly reducing the number of possible Feynman diagrams per loop of calculation and qualitatively reducing the potential complexity involved, while gluons have self-interactions and three colors in addition to polarization requiring far more Feynman diagrams per loop. We can observed free photons and charged particles, while quarks and gluons (apart from top quarks) are confined so we have to infer their properties from composite particles.

But the problem of the slow convergence of the infinite series path integrals we use do to QCD calculations isn't simply a case of not being able to throw enough computing power at it. The deeper problem is that the infinite series whose sum we truncate to quantitatively evaluate path integrals isn't convergent. After about five loops, using current methods, your relative error starts increasing rather than decreasing. From the link in this paragraph:

When you can get to parts per 61 billion accuracy at five loops as you can in QED, or even to the roughly one part per 10 million accuracy you can in weak force calculations to five loops, this is a tolerable inconvenience since our theoretical calculations still exceed our capacity to measure the phenomena that precisely. But when you can only get to parts per thousand accuracy at five loops as is the case in perturbative QCD calculations, an inability to get great precision by considering more loops is a huge problem when it comes to making progress.

You can't even measure the fundamental constants with more accuracy due to this problem, because you do that by theoretically reverse engineering the precisely measured observable quantities of composite particles like the charged pion and proton and neutron masses, with QCD theoretical formulations, to figure out the values of the fundamental constants that produce those experimental values in the theory.

Now, this isn't necessarily insurmountable. It might be possible to use math tricks to do better. For example, mathematically speaking, one can resort to techniques along the lines of a Borel transformation to convert a divergent series into a convergent one. And, path integral formulations are limitations associated with perturbative QCD calculations that can be overcome by using non-perturbative QCD methods like lattice QCD. But getting great precision in QCD calculations is as much a theoretical problem as a practical one.

Quote Of The Day

Not only do they make up everything, they are also feckless, because they are prone to acting randomly.

Hat tip to Dr. Jennifer Grant of the University of Wisconsin-Stout.

Bonus gag:

Meta: This blog is actually two posts in excess of its 3% humor quota, so I guess I'm going to have to dial it back now.

Quote of the Day

The current problems with fundamental physics have nothing to do with mathematical abstraction, but with the refusal to give up on bad physical ideas that don’t work. Thirty-six years ago Witten and many other leaders of the field fell in love not with a mathematical abstraction, but with a bad physical idea: replace fundamental particles with fundamental strings. One reason they fell in love with this idea was that it could be fit together with two other bad ideas they had been dallying with at the time, that there are new forces mixing leptons and quarks (GUTs), and that you can relate bosons and fermions with the square root of translation symmetry (SUSY).

Unfortunately it seems to me that many theorists have now drawn the wrong conclusion from the sorry story of the last forty-some years, deciding that what they need to do is to stay away from unwholesome mathematics, and stick to the wholesome experimentally observable and testable. But what if the underlying reason you got in a bad relationship with a seriously flawed love interest was that there weren’t (and aren’t) any experimentally testable ones to be found? Maybe what you need to do is to work on yourself and why you stay in bad relationships: the mathematically abstract love of your life might still be out there.

Witten yesterday posted a definitely not mathematically abstract paper on the arXiv, Searching for a Black Hole in the Outer Solar System. It’s basically a proposal for finding a physical black hole we could then go and get into a relationship with. I can’t help thinking the probabilities are that getting into a healthy relationship with a new mathematical abstraction is more likely to work out than this. 

Woit at "Not Even Wrong" (April 30, 2020). 

The Ethical Obligations Of Scientists

Yes, it is funny. But, should scientists spend more time thinking about whether they should, instead of merely whether they can? This certainly isn't part of the culture we instill as we train scientists.

The quote is from Jurassic Park (1993), which is closer to the realm of the possible than you might think.

Quote Of The Day (Regarding AdS/CFT)

It isn’t widely appreciated, but in the standard model of particle physics coupled to gravity there is actually only one global symmetry: the one described by the conservation of B-L (baryon number minus lepton number). So this is the only known symmetry we are actually saying must be violated! 

What Harlow doesn’t mention is that this is a result about AdS [ed. anti-deSitter] gravity, and we live in dS [ed. deSitter], not AdS space, so it doesn’t apply to our world at all. Even if it did apply, and thus would have the single application of telling us B-L is violated, it says nothing about how B-L is violated or what the scale of B-L violation is, so would be pretty much meaningless.

Via Not Even Wrong (this is really a double quotation, the portion in italics is from physicist Daniel Harlow, the remainder is from Peter Woit, the author of the blog).

The terms anti-deSitter and deSitter refer to the topography of the curved spacetime of the universe. The best available experimental evidence suggests that our universe's spacetime has a deSitter topology, although it is very close to flat at a global level. What does this mean? It means that the universe has a positive, sphere-like deSitter curvature, rather than negative, hyperbolic surface-like anti-deSitter curvature. As Wikipedia explains:

In mathematics and physics, n-dimensional anti-de Sitter space (AdS_n) is a maximally symmetric Lorentzian manifold with constant negative scalar curvature. Anti-de Sitter space and de Sitter space are named after Willem de Sitter (1872–1934), professor of astronomy at Leiden University and director of the Leiden Observatory. Willem de Sitter and Albert Einstein worked together closely in Leiden in the 1920s on the spacetime structure of the universe. 

Manifolds of constant curvature are most familiar in the case of two dimensions, where the surface of a sphere is a surface of constant positive curvature, a flat (Euclidean) plane is a surface of constant zero curvature, and a hyperbolic plane is a surface of constant negative curvature. 

Einstein's general theory of relativity places space and time on equal footing, so that one considers the geometry of a unified spacetime instead of considering space and time separately. The cases of spacetime of constant curvature are de Sitter space (positive), Minkowski space (zero), and anti-de Sitter space (negative). As such, they are exact solutions of Einstein's field equations for an empty universe with a positive, zero, or negative cosmological constant, respectively.

A spacetime with an anti-deSitter topography is interesting theoretically because of a correspondence between AdS spaces and conformal field theories that makes it possible to do all sorts of theoretically interesting tricks. As Wikipedia explains:

[T]he anti-de Sitter/conformal field theory correspondence, sometimes called Maldacena duality or gauge/gravity duality, is a conjectured relationship between two kinds of physical theories. On one side are anti-de Sitter spaces (AdS) which are used in theories of quantum gravity, formulated in terms of string theory or M-theory. On the other side of the correspondence are conformal field theories (CFT) which are quantum field theories, including theories similar to the Yang–Mills theories that describe elementary particles. 

The duality represents a major advance in our understanding of string theory and quantum gravity. This is because it provides a non-perturbative formulation of string theory with certain boundary conditions and because it is the most successful realization of the holographic principle, an idea in quantum gravity originally proposed by Gerard 't Hooft and promoted by Leonard Susskind.

Empirically there is no experimental evidence of B-L violation, which is preserved in the Standard Model of Particle Physics, and B-L violation is not obviously violated in any viable candidate for a real world gravitational theory standing alone, that I have seen. 

B and L are separately conserved in the Standard Model except in very high energy sphaleron interactions (which can't be depicted in Feynman diagrams because they are space-like without a time-like element) that have never been observed in reality, but even those interactions conserve B-L.

The recognition that most or all of string theory vacua exist in anti-deSitter space that does not correspond to reality, that are collectively called the "swampland" is one of the main global and generic challenges to string theory as a viable description of reality in physics today.

Lots of cosmologists deeply want B-L violation to exist, even though it is known that it doesn't happen in any detectable amounts at energies up to the 14 TeV of the Large Hadron Collider (LHC), because this is the easiest way to produce our existing universe, in which matter predominates over anti-matter, with a starting point that consists of pure energy rather than a finite and fixed aggregate baryon number and aggregate lepton number for the universe. (Baryon number is the quarks minus anti-quarks divided by three. Lepton number is leptons minus anti-leptons.)

It is also worth sharing one of my conjectures from my linked swampland post here to provide some out of the box context:

For what it is worth, it is also possible that gravity and the cosmological constant observed are not actually topological effects as in General Relativity, but instead closely approximate a mechanism that involves the behavior of gravitons in a Minkowski spacetime that is itself fundamentally flat, rather than being deSitter or anti-deSitter, even though that graviton behavior is similar to and in most circumstances almost exactly equivalent to, a topologically curved spacetime.

This conjecture is just me on physics and doesn't come from any authoritative source, so take it for what it is worth, which is not very much. But, it it were correct, it would eliminate one of the biggest conceptual and mathematical barriers to integrating the Standard Model, which is formulated in Minkowski space (which observes special relativity but not general relativity), but not in a spacetime with a curved topology.

Also, even if spacetime is actually slightly deSitter in real life as General Relativity supposes, a quantum gravity theory formulated in Minkowski space might be close enough to reality to be a good approximation of reality, especially in the weak gravitational field domain of applicability for distances less than or equal to the order magnitude of the immediate vicinity of galaxy clusters (which is all that matters except in the immediate vicinity of black holes, neutron stars and similarly massive object, at scales smaller than cosmological ones, unless one is extremely precise). And, in these strong fields and for universal scale distances, we know experimentally that classical General Relativity is a very good approximation of reality, so resort to quantum gravity in lieu of classical General Relativity isn't usually necessary except in the immediate first moments after the Big Bang.

In the same vein, even though we have very good reason to think that a graviton, if it exists, is a spin-2 particle known as a "tensor" particle, there is also good reason to think that a scalar (i.e. spin-0) graviton approximation is a very good approximation of a spin-2 graviton over a wide domain of applicability, particularly in weak fields. This is because in most contexts, the contribution of the mass-energy of particles to the stress-energy tensor of General Relativity far exceeds that of the other aspects of the stress-energy tensor such as linear and angular momentum, electromagnetic flux, sheer stress, torsion and pressure. A scalar graviton theory is basically a static equilibrium approximation of a full spin-2 graviton theory, which is fine when a system is very far from moving at relativistic speeds (i.e. speeds close to the speed of light) and is in a state reasonably close to equilibrium (such as a fairly stable solar system or galaxy).

One reason to doubt the purely geometric interpretation of gravity from General Relativity is that MOND's external field effect (EFE) violates the "strong equivalence principle" of General Relativity  (i.e. that the outcome of any local experiment (gravitational or not) in a freely falling laboratory is independent of the velocity of the laboratory and its location in spacetime) and there are several recent astronomy observations which suggest that the EFE is a real phenomena.

This matters because there are lot of very difficult technical mathematical challenges to formulating gravity as a theory of a spin-2 graviton in a curved spacetime that are drastically simplified if the approximation of a spin-0 graviton in Minkowski space, that would make it much more feasible to do calculations with the theory. So, if this approximation is a very good one in a wide domain of applicability involving weak gravitational fields, we could have a very workable quantum gravity theory for a very wide range of applications, even though there would be some extreme circumstances in which it would be flawed and the model's analytical and qualitative predictions could not be trusted.

Indeed, in practice, it is common place in many astronomy applications involving scales of galaxy cluster distances of less that involve weak gravitational fields to approximate General Relativity with Newtonian gravity in any case. But, using a spin-0 graviton in Minkowski space approximation is still much more precise, and captures far more non-Newtonian quantum gravity effects, than using a Newtonian gravity approximation does. Since a quantum gravity theory with a spin-0 graviton in Minkowski space would still involve a self-interacting carrier boson, just like QCD does, even this greatly oversimplified approximation of quantum gravity still involves very challenging mathematics that only specialist physics and mathematics PhDs would be capable of mastering and applying confidently and accurately.

A good analogy would be the simplifications that can arise when considering electromagnetic phenomena without considering polarization. It isn't perfect and ignores some important experimentally testable phenomena, but it is also much easier to understand, makes the mathematics  of applying it a lot simpler, and can be safely neglected without significant loss of accuracy in many applications.

UPDATE July 19, 2019: Sabine Hossenfelder has some cogent discussion of why theories related to anti-deSitter space may provide little insight into the real world. An excerpt:

[D]iscontinuous limits should make you skeptical about any supposed insights gained into quantum gravity by using calculations in Anti de Sitter space.

Anti De Sitter (AdS) space, to remind you, is a space with a negative cosmological constant. It is popular among string theorists because they know how to make calculations in this space. Trouble is, the cosmological constant in our universe is positive. And there is no reason to think the limit of taking the cosmological constant from negative values to positive values is continuous. Indeed, it almost certainly is not because the very reason that string theorists prefer calculations in AdS is that this space provides additional structure that exists for any negative value of the cosmological constant, and suddenly vanishes if the value is zero. 

String theorists usually justify working with a negative cosmological constant by arguing it can teach us something about quantum gravity in general. That may be so or it may not be so.