Yeah, but WHY is c the speed limit of the universe?

I do not know about “physics commentators”, but one would have to be the world’s worst physicist to declare that there is nothing left to discover, let alone understand.

I don’t think this is quite what Sabine means though. I think it’s more that looking at things from a mathematical elegance point of view, and trying to pare down to a simpler model has been a bit fruitless post-standard model.

The brainpower bang for buck has not been great, so maybe a change of emphasis is needed. I don’t think she’s asserted we know it all, or that such an approach should be stopped altogether.

And I’m not saying this as one of the many Sabine fanboys; I often disagree with her.

That’s a complete misrepresentation of her position. Her point is that the efforts to characterize physics in terms of the elegance of purely mathematical approaches such as M-theory have lead to effectively unfalsifiable hypotheses that are not fruitful or used to justify increasingly complex “big science” proposals such as the massive Future Circular Collider, and such approached have resulted in a lack of advancement in the foundations of physics in the last few decades.

This isn’t a novel point of view; it is a common topic of discussion among theoretical high energy physicists, and is evident by the distribution of Nobel Prizes in Physics. Noodling about with infinitely tunable mathematical models requiring large numbers of unobservable or compactified dimensions doesn’t seem to be getting us any closer to unifying gravitation with the Standard Model, or understanding the fundamental basis of quantum mechanics, or resolving the “Crisis in Cosmology”, and in general has led to an approach in theoretical physics of ‘research’ by creating elaborate mathematical models with little or no connection to observable reality.

There is obviously plenty of basic research to do in many applied areas of condensed matter physics, superconductivity, quantum field theory, plasma and stellar physics, geophysics, biophysics, et cetera that are competing for the limited funding while big projects get billions, as well as observational astrophysics and cosmology that could potentially provide the answers we are seeking about fundamental particle physics without constructing multibillion dollar machines that use as much power as a small European country. Hossenfelder has some personal prejudice in this matter because of her career experiences (and in topics outside of her domain of particle physics she often gets out over her skis or fails to provide comprehensive views), but she’s also not wrong to question both the research focus and funding priorities on areas that are not really returning much in the way of fundamental physical insights or providing anything of utility even in the long view.

Stranger

To be sure –
If the limit was different, it would be because we defined our units differently or because something else changed that affected how our defined unit standards behaved. The numerical value of the speed of light does not directly affect how our understanding of physics works, since it doesn’t exist in the theory.

A naive alien lands in the US. He is told, “Your height is 58 inches.”

He then flies to France. He is told, “Your taille is 147 centimeters.”

He has just measured a universal constant (let’s call it b) equal to roughly 147/59 centimeters/inches.

He makes a very good experiment to measure it better, finding b = 2.54~\mathrm{cm/in}.


Ask yourself: “How different would the universe be if we set b = 3.5~\mathrm{cm/in} instead?” Does that question make any sense?

It does not. It is the same with c. Instead of relating the fixed height of something moved from US to France, c relates the size of a fixed interval rotated between space and time. Measurements of “US height” and "French taille" are actually measuring the same type of thing (the alien just wasn’t used to that), and so too are measurements in space and time. We just label them differently and thus find c showing up all over our equations.

Mostly repeating Stranger’s comments, but in different clothes.

Sabine is mostly a lot grumpy that there is so much time and money wasted on what has proven to be a pretty barren path. And in truth it is hard to disagree with her viewpoint. At least as far as the nature of modern physics research goes. A lot of people hold down nice jobs doing little more than navel gazing with nothing to show for it other than a lifetime of useless research papers read by few others than other researchers in the same field. And a further cohort hold down nice jobs demanding very large amounts of money from governments to fund a new round of experiments (aka a bigger collider) on little more than a vague promise of maybe there will be new physics. Well over half a century ago there was new physics. And before that, we saw a huge amount of new physics that changed the landscape of the world order. So for a while there might have been some enthusiasm for this enterprise. But it has been quite a long time between drinks, and little new to show for it other than a few very expensive holes in the ground.
I would paraphrase Sabine as saying that those physicists might better serve humankind by applying themselves to other more pressing problems. That, and stop asking for billions of dollars to fund what is almost certainly a waste of money and time. Those billions could and should go into other research. A few tens of billions on a new collider is a few tens of billions that is, at least in part, missing from science in other disciplines.
Perhaps the more clear point is that particle physics isn’t the poster child for hard science that it was. There may be many further and worthy Nobel physics prizes awarded. But in particle physics, we may well be done. Breathless popular science reporting not withstanding. Which is part of the problem.

Where I get frustrated with Sabine is that even though she tries to widen her scope looking at other areas of science, she is still very blinkered missing how insanely far other areas of science have gone in the same time physics has been moribund. She will prattle on about lack of progress in science in general, and seems blind to things like the science fiction level advances that have occurred in biology and biochemistry, and also how far these areas still have to go. Put string theory up against this sort of progress and it becomes more than embarrassing.

In a previous life I saw a lot of how major funding was dished out for research. Like law and sausages, best not to know what goes on in the back rooms. Often really big money was liberated from the taxpayer by nothing more than appealing to the vanity of key politicians in control of the purse strings. Then it was snouts to the trough.

Part of the pedagogic issue is that Newtonian Mechanics is a universe where it is, under this analogy, physically impossible to move anything from the US to France or back. If that was the case the conversion between “height” and “taille” would be entirely meaningless. Americans and Frenchmen could be giants or midgets relative to each other and no one would be the wiser.

Similarly in Newtonian Mechanics, you can never “line up” a time interval against a space interval, so a conversion factor between the two is meaningless. It’s new physics in SR that says an interval that one observer experiences as pure time, another observer will experience as time+space that makes the conversion meaningful.

Thanks for posting that. It helped me…see the light on why this is difficult to answer straight up. And now all the other posts will reveal themselves to me and I just might have a better understanding about this than before.

Aren’t these two very different problems, by an order of magnitude? How much support does a string theorist need other than a pad, a pencil, and a computer with LaTex and Maple installed? Don’t forget they typically have a teaching gig on the side. Also, is string theory slowly running out of air? I ask that because the social sciences at least are prone to faddishness, with some academic industries going into decline as the questions get smaller and squirrelier. Yes, there are other countervailing pressures.

The question regarding when the world should start building its next multi billion dollar collider is a good one though. I say put it off unless someone in Asia wants to do it first.

In terms of money, yes. In terms of how it affects physics research in the large, not so much. Sabine is taking issue with a lot of things. Her book Lost in Math is an interesting read. As noted above, she is particularly scathing about theories that have mathematical beauty as their leading (or only) attribute. So the problem with string theory is set in the context of what she regards as a misguided approach to doing science - sometimes to the point where there is no actual science being done. When a generation of bright young physicists have their PhDs and research careers dashed against the rocks of string theory, the damage is wider. Some got jobs working on derivatives for financial traders, but it isn’t great. Within the body of physics research, the shadow cast is large. It might not be big money, but it tips the scales in unfortunate and long lasting ways. At least for a time the reason to do string theory given by graduate students was that it was the only game in town. Which is also a bad start.

The very lucrative popular physics publication gravy train is replete with books extolling the virtues of these beautiful ideas. Some have it in their titles. Some just peddle woo. And have that in the title as well.

Then again, IMHO, any actual theory that works, will be simple \ddagger and probably elegant. It may however bring with it mind melting technical challenges in use. In practice, the described reality may well be just as wretched as Sabine suggests.

\ddagger For some as yet unknown value of simple.

I had never seen any of Hossenfelder’s stuff, although I was aware of the name. I just sorted her YouTube channel by “Popular” and watched a few videos, including “What’s going wrong with particle physics”.

My head hurts from all the face palming :person_facepalming: I was doing. She has clearly made a good business of being the “edgy” one, and she’s skilled at constructing long-form arguments that appear to make sense. But that’s because she is free to set up her own picture for how things are and argue against that strawman for thirty minutes. The pieces of her arguments are at best distorted but certainly hand-crafted throughout. Inconsistencies also abound, but that’s far from my main complaint. My main complaint is that every other sentence draws heavily on the techniques of (say) politicians whose goal is to win rather than be correct. She chose her conclusion and then figured out how to say things to support it (and how definitely not to say things that refute it.) It’s a disappointing watch because I know I am in a position to see where she’s repeatedly pulling wool for the sake of a click-bait-y conclusion, but I also know that she will be convincing to non-experts because of her scriptwriting skill and freedom to select and distort just so the essential inputs to her arguments.

(To add: the inputs of concern aren’t limited to the physics. How budgets work, how publishing works, how research choices are made, how success and failure work (and how they compare across all fields of science)… all of these aspects suffer from the issues above. But, the approach she takes is presumably fruitful in the content creation space.)

And thus the question is how many of her viewers know enough physics to critique her. I once caught Up and Atom in a major mathematical error and commented on it (And was ignored. I didn’t check to see if it was deleted) meaning she didn’t care. But how many others would have noticed that error?

Although Hossenfelder certainly makes the point about the waste of intellectual talent on pursuing seemingly untestable theses in M-theory and cosmology, her broader complaint is twofold; one is that it leads to “groupthink” adoption of certain fundamental precepts and methodology even though they have not been shown as validated which limits new and broader ways of integrating different areas of science, and the other is the pressure to build ever-larger and more powerful apparatus to look for particles for which there is no actual evidence of existence.

On the first point, she opines that this has resulted in the already pervasive “publish or perish” model of academic research being further perverted by essentially leveraging already untested theories into an entire field of what is essentially fictioneering pseudoscience, not only in particle physics but also in cosmology (specifically, “multiverses”, the “simulation hypothesis”, and other vaguely defined theses that will never be physically falsifiable because they occur outside of the context of physics). All of the work that has gone into developing the various aspects of M-theory, for instance, while interesting (and has provided some general insights into linear algebra, ring theory, and noncommutative geometry) as produced nothing that can actually be experimentally tested or provides further physical insights, and yet has exploded in terms of how it dominates theoretical fundamental physics, largely pushing out work on competing theories (which are also problematic but at least offer a diversity of thought). That the field has somewhat stagnated is not just because it is probably a dead end but that it also encouraged a general trend in research of following whatever avenue seemed to be getting the most publication and not to question it too hard, which is a bad way to do groundbreaking science.

To be clear, research science always has blind allies and involves wasted effort by the nature of the process; sometimes, the question that you were trying to answer is actually the wrong question, or badly formulated, and we shouldn’t expect some kind of linear process for basic discovery, but when nearly everyone in the entire field is going down the same path just to latch on to a fashionable but unproven theory it creates a propensity to just do more of the same. I’m currently seeing this trend in AI research with feed forward neural network models which are software-on-digital-hardware and ‘experts’ of various stripes religiously declaring that this the only viable approach and is producing language-trained models that have ‘a spark of consciousness’, ‘deep models of world’, ‘will surpass human intelligence and creativity’, and other claims that are not only unverified but for which there isn’t even a plausible mechanism, and yet when you start pointing out the limitations of this approach, and major deficiencies such as the massive amount of training data required to get a model that does anything useful, the problem of getting such models to be reliable even about basic factual statements, and the enormous amount of energy required per unit of effective computation compared to animal brains, you get shouted down as an nonbeliever and a Luddite who just doesn’t understand how these systems work.

On the second point, the Large Hadron Collider was useful because not only did it prove the existence of the Higgs boson as predicted by the Standard Model but it has other utility, particularly in studying heavy ion collisions at energies much higher than the Relativistic Heavy Ion Collider. However, the proposed next generation Future Circular Collider (FCC) is specifically intended to look for supersymmetric particles and hypothetical ‘dark matter’ candidates, even though there is no observed reason to believe that these actually exist, or will be found within in the energies that can be achieved by the FCC. It is essentially a massive, multi-tens-of-billions dollars tool looking for a problem to solve. She’s actually said that she doesn’t opposing building a new collider at some point, but only when there is some particle that is specifically predicted by a credible theory rather than just throwing particles against a wall to see what sticks. Given the cost and energy consumed by such as system, I think that is a rational argument, but of course, that doesn’t create more jobs as CERN.

I don’t think this is quite right; she’s certainly acknowledged progress in other areas of physics and other sciences, and it would be impossible to credibly argue that there haven’t been radical advances in biosciences. However, she does regularly complain that advances are often exaggerated by popular science articles and sometimes by the researchers themselves, and about the lack of rigorous falsification and reproducibility, which is a very wide problem across essentially all areas of science. Outside of string theory, I think she’s probably been most critical of quantum computing (and the general effort to stuff “quantum” and “AI” into everything), and quite frankly I think that complaint is becoming increasingly valid, at least in regard to scaling quantum computers to a useful level of complexity with the current approaches. And when she gets far afield from the physical sciences, I basically don’t assign her any credibility beyond a layperson just expression personal opinion, which is a problem of many scientists who believe that their expertise extends to all fields of knowledge and endeavor, e.g. Robert Milliken, Francis Crick, Lynn Margulis, Richard Dawkins, et cetera ad nauseam.

That is an eminently fair criticism; Hossenfelder definitely uses strawman arguments, and of course doesn’t offer competing views to refute them. She also gets in tiresome internet ‘debates’ with other scientists that are either unresolvable or are essentially a matter of opinion with no objective factual basis. In areas where I have some degree of expertise, I can see how she cherry-picks her arguments and mostly presents only evidence that supports her position. I certainly wouldn’t take anything she says as gospel (and frankly, I don’t think she would argue that you should), and her entire schtick is being a contrarian rather than just an objective science communicator.

But when the argues about the lack of progress in the foundations of physics in the last few decades, she’s objectively not wrong. I don’t think it is just because of the obsession with fashionable theories like M-theory, but I suspect we’re at a point that requires some entirely new approach other than looking for symmetries and other mathematical elegances. Constructor theory and “complexity physics” seems to be kind of the hot new items but who knows if that will actually provide any fundamental insights or breakthrough advances; we might just be at a point where the threshold of energy required to reveal new fundamental physics is beyond our current technological development, or understanding more complex mechanics of the underlying world is just beyond our limited cognitive capacity. That doesn’t mean we should stop doing basic research but it does argue for diversity in approaches (and a lot more introspection and criticism) instead of trying to brute force a particular theory to fit observations rather than make falsifiable predictions.

Stranger

Which leads me to postulate the ultimate science boondoggle: a hypothesis that true AGI can be achieved by an exotic quantum process that to demonstrate would require a new 100TeV collider.

Yep. As I said upthread, I disagree with Sabine a lot, but I think within this science communicator space she is a breath of fresh air. Even if she’s a bit of a dick at times, and may strawman opposing positions, there aren’t many voices publicly questioning the direction of particle physics and the construction of yet bigger colliders, who also have the physics chops.

And I like that Sabine updates her position on things. My biggest bugbear with her used to be that she was way too invested in MOND. In the last year or so her position has shifted substantially and the last video on it I think she was trying to stay agnostic.

If you “try to stay agnostic” on MOND, you’ll quickly come to the conclusion that it doesn’t make sense. Absolutely everything about MOND is nothing but the pointless navel-gazing that she claims is the problem.

It is no surprise that the giant industrial human enterprise of figuring out how the universe works is complicated. Any adequate high-level discussions about it deserve, nay require, way more bandwidth than a message board allows. This is also why Hossenfelder’s 30-minute videos on “big issues” are rather content-dense. But “content-dense” means short cuts and approximations have been taken. And generally, when a situation is complicated or nuanced, approximations in the discussion make things simpler but also more extreme (one way or the other), especially if one has a goal in mind.

This is common in many pop sci sources, and it echoes in this thread. When short cuts lead to a hyperbolic stance on some piece of the puzzle, it can amplify other coinciding approximations that now seem more valid. (It’s like the nucleation of a phase transition, if I may drop in an unnecessary analogy.) Kernels of truth will be everywhere, but critical context or nuance has been lost, and in this case, the lost stuff is too important for understanding the big picture correctly.

In the list below, I do not aim to characterize anyone’s specific stated position. I instead aim to list just a sampling of points that are at times misconstrued, misunderstood, or just wrong in these approximated discussions. Any single item would require a full thread of its own to discuss adequately. Each stems from a (sometimes sensationalist) casting away of nuanced discussion or an echoing/amplification of “things heard”.

Points that are problematically simplified or worse include:

  • that experimental testability should be the immediate goal of all parts of the research enterprise

  • that string theory, quantum gravity, and various outflows have significantly pushed out other work or creative avenues

  • that talent is somehow wasted or even just more wasted here than with other theoretical areas

  • that the diverse field of experimental particle physics is represented by one big machine

  • that physicists are marching like lemmings to a new big machine

  • that there are no mysteries in the models worthy of explanation

  • that discovery is pointless if it doesn’t lead to a change in predictions

  • that science funding is arbitrarily fungible

  • that the diversity in pop sci topics is representative of the diversity in actual science

  • that the pop sci amplification of any one theory is representative of anything other than the pop sci market

  • that the field is problematically stagnant, and especially in comparison to others

  • that quantum computing is at a loss for direction

  • that mathematical tool development and theoretical connections are not part of scientific advancement

…among others. Again, each is a full thread topic on its own, so I have not even attempted to elaborate on any single item here.

I re-opened that Hossenfelder video about particle physics to maybe add to the above list. I shouldn’t have, for my own peace of mind. While there are another half dozen easy additions to the list, I had to come back here instead just to state more strongly than I did earlier how wildly disingenuous and self-inconsistent she is throughout that video.

She uses sterile neutrinos as an example of silly physicists looking for silly made-up particles. Ten minutes later she gives her sage insight that it is okay to try new models when there are inconsistencies in the data to motivate it. Well, yeah, and that’s exactly why the sterile neutrino searches exist in the first place. So, which is it? (Answer: she doesn’t care, because her general audience won’t catch her out on such things.)

She also doesn’t seem to understand (except… surely she does, so interpret it as you will) that a model that fits even her ideals typically offers a range of possible realizations, and a single limited null search doesn’t kill the whole idea. There’s a reason for sequential searches for well-motivated ideas. It’s hard, and it proceeds in steps.

If she lost her keys on a 10-mile mountain hike, she would I guess go back the next day, search the first mile, and then insist that any searching in the next nine miles is just stupid physicists looking for made-up keys. And heaven forbid different search strategies are used to cover reasonable possibilities (e.g., a drone overhead vs. a metal detector).

Don’t take these examples as any indication that my complaints are limited to them. Issues in the video are ten-fold these, generally amounting to false equivalences, invalid analogies, and the like that she knows she won’t get called out on.

Has anyone asked why pi is 3.14onandonandon?

A proof that Pi is transcendental? Sure. Such things worried mathematicians.