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The crisis that Hossenfelder is addressing is that there has been no significant progress that's been experimentally verified in fundamental physics since the birth of string theory in the 1980s. Yes, there are a lot of big open problems, but they remain open. Yes, we have recently found experimental evidence for things like the Higgs boson, but that was first predicted in the 1960s. Yes, we can rule out some versions of string theory thanks to LHC results, but there are a vast multitude of string theories, and that's not a lot to show for nearly 40 years.

Some results that I remember just now:

* There is a recent 4.5+4.8 sigma excess in neutrinos oscillation that hints a new neutrino https://arstechnica.com/science/2018/06/weird-neutrino-exces... [technical note, you can't add sigmas naively, 4.5+4.8=6.1]

* The value of the magnetic moment of the muon (g) is too high. IIRC this result has only a 2.5 or 3 sigma, so it's far from confirmed.

* There are some experiment to prove that the neutrino is a majorana particle and that the neutrino and the anti-neutrino is the same particle. I don't remember any good announcement, so I think that the experiments have still too early results or the results are not interesting. [I don't like this theory, but many people that knows more than me like it.]

Do you have a link for the majorana bit?

https://www.symmetrymagazine.org/article/august-2013/neutrin...

https://en.wikipedia.org/wiki/Double_beta_decay#Neutrinoless...

That kind of emphasizes the point rather than disproves it, though. Nearly 40 years of physics to pull your examples from, and you pull something from last month, something not confirmed (there's been tons of 2.5-3 sigma results over the past 40 years, but there's a reason physicists have learned to wait for more sigma), and something that is unannounced and may be uninteresting.

I believe there are some other things in that time frame. I believe the discovery that the universe is accelerating in its rate of separation fits in that time frame, and that's pretty big. We don't know how to fit it in with anything, but it's big. And I'd still say confirming Higgs is big.

But... yeah... it is a pretty short list compared to preceding decades.

When I spoke to an exo collaborator he told me that exo put a really tight limit on the rate of neutrino-less double beta decay. If I was a betting man I would put it in the same category as proton decay, another theoretical physics favorite.

Sorry to nitpick but if we're adding variances, 4.5^2 + 4.8^2 = 6.6^2

Essentially yes (unless you are nearby an tactician or a journal referee). I just copied the number from the article, I guess there is some rounding.

Also, the 6.2 or 6.1 is "unofficial" because it's difficult to mix results from different experiments.

There's the outstanding issue of the proton size.

The fact that the LHC hasn't seen anything new is the entire point here because it yields evidence against SUSY. That puts almost all of mainstream HEP theory in bad position because it has been built around SUSY being real and an accepted hypothesis.

As usual, theoretical physics is taking the wrong message from this, sticking to their guns and claiming SUSY evidence is yet above 10 TeV instead of stepping back and re-evaluating their fundamental assumptions. Of course they won't because many have built their careers on this hypothesis.

I forsee a reckoning for the whole field (which will take on economic dimensions) in the future.

I agree with you, and I would add that, from a Popperian view, the LHC has helped falsify some of the possible string-theoretic universes from being our universe, by failing to pick the lower-hanging particle-fruits of supersymmetry from its relatively low-powered tests.

Nothing is falsified by the failure of an experiment to observe the expected.

Can you give an example of a falsified result?

All swans are white.

I can sit for day after day not observing a black swan. This proves nothing, it does not prove the theory "there is no non white swan". But if I see a black swan then the theory that all swans are white is up the chute.

There's a distinction here. An experiment may measure a parameter to be zero instead of some nonzero value that everyone expected. That isn't subject to the black swan fallacy. Only when you are sampling is the black swan fallacy relevant.

Yes agree, although the mechanism of measurement is important.

    Hypothesis 0 - all adult swans have largely white plummage.

    Expectation - all observed swans "are white".

    Observation - some swans "are black".

>"Nothing is falsified by the failure of an experiment to observe the expected." //

The experiment failed to observe the expected. The hypothesis was falsified.

    Hypothesis 1 - all swans are white or black.

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Even with something like "we expected to find a Top quark at ~100GeV and found nothing" then the experiment has falsified that there is Top that would appear in such an experimental framework. We usual project that result beyond it's technical bounds, to say there is no top below that limit, is that what you're trying to get at?

If you mean experiments aren't perfect then I don't see how that truism is useful. There have been a couple of potentially massive results in recent years that have fallen to poor experimental process.

When a particle is observed at some energy the theories that predict that no such particle can exist are invalidated. It fault of the experiment to see something is just that, the experiment has failed. The causality of the failure is unknown, also if you do make the observation then the causality of the observation if unknown; Newton's observations and all the observations made by people who believed in a Newtonian universe were not unobserved when relating came along. I believe that the probabilistic approach to observation and observe to rule out approach in HEP now is a big error.

The problem here is that in Aristotelian logic, which deals strictly in statements that are true or false and nothing in between, non-existent evidence is not evidence of non-existence. But this cute phrase, over-quoted and generally badly misunderstood, is not true because of the way the obvious, naive reasoning would lead you to believe... it is true because Aristotelian binary logic doesn't deal in anything like "evidence" at all. Non-existent evidence is not evidence of non-existence, because under this logic there is straight-up no such thing as evidence. There is only proof.

However, while this form of logic is a great thing to teach children for their first (and likely only) one, and while your fancier logics probably ought to have some sort of Correspondence Principle for this style of logic, this rigid style of logic is not terribly useful in the real world, where statements of rigid, solid, 100%-confidence mathematical truth are in short supply. In any probabilistic logic, non-existent evidence is evidence of non-existence. It is not proof. But it is evidence. It is true the human mind may have a tendency to overweight the evidence, but that's fixed by math.

So, while there is a sense in which the oft-trotted out phrase is true, in logics useful in the real world, it is simply false.

After all... what other evidence of non-existence do you expect to gather? If you do not believe in the invisible, intangible unicorn that lives in your garage that Sagan liked to talk about, what other actual evidence for that belief do you have other than a complete lack of evidence it exists? There is no way for you to disprove it under Aristotelian logic. (And this style of logic doesn't have a great story for statements it can neither prove nor disprove, which is another reason why mathematics moved past it a long, long time ago.)

If string theory is wrong, what other evidence for that can we gather other than the predictions of string theory being false? Remember, we can build physics models based on, say, Loop Quantum Gravity that excludes strings and may seem to predict the universe correctly, but that does not logically prove that there are not also strings in the universe. We exclude strings or other broken models only by consistently failing to collect evidence they are true.

>>We exclude strings or other broken models only by consistently failing to collect evidence they are true

Which is not a reason to consider them excluded. There is no reason to believe in the unicorn, or strings it there are powerful predictive alternate theories that explain the observed facts. But science creates contingent knowledge, not truth, that is all.

"Remember, we can build physics models based on, say, Loop Quantum Gravity that excludes strings and may seem to predict the universe correctly, but that does not logically prove that there are not also strings in the universe." - from just the previous sentence.

Incidentally, that post gored some oxes, apparently. Despite the firm mathematical foundation I stand on with great confidence for the entire post, it's sitting at -2. Seems a lot of people have a very emotional reaction to hearing "absence of evidence is not evidence of absence" is untrue.

The Michelson-Morely experiment is a famous experiment that pretty conclusively falsified the theory about aether.

The experiment originally set out to detect and confirm the existence of the aether, but ended up falsifying the theory instead.

https://simple.wikipedia.org/wiki/Michelson%E2%80%93Morley_e...

So you disbelieve dark matter because it's not been directly observed?

Perhaps not absolutely, but in a Bayesian sense it should make us less sure of the theory's truth. "Falsification" is really just severe scepticism, after all, nothing can be absolutely proven in any direction.

I think that Bayesian reasoning applies to a different category of knowledge; there are things for which we have no predictive theories that we have to reason about probalistically and Bayes is good for that. But thinking about how things are and probability seems a poor duo - after all, we can end up 99.999% sure that something is true, observe one counter example and now know that 100% it is false... Bayes doesn't do that.

Any theory that predicts something other than the "expected" can be falsified by observing the "expected".

To use the swan argument from down-thread: If a theory predicts a) All swans are drawn from a single distribution of colors and b) 1% of swans will be black, then the observation of a few thousand white swans will be sufficient to rule out said theory.

In an idealised world the thousand white swans and 10 black swans will be mixed randomly, and you would be right. In the real world bird move in flocks, the presence of one group of birds frightens off different birds. You may live in the hemisphere with only white swans and never as long as you live see a black one, but just over the hill there is a big population, it just lives in a place you haven't looked. In natural systems observations are biased. You reasoning is based on ideal assumptions.

Fundamental physics is not like flocks of birds. It is much more like a system which makes ideal assumptions.

Huh??? What was the Michelson-Morley result then?

MM is a great historical example that the field should remember. However, culturally for the current and previous generations, physicists aren't keen on their history and even if they are they definitely can't place themselves in it.

I'm sorry but that's silly. Everybody in physics knows the Michelson-Morley experiment.

Yes, and it's results confused everyone in physics and made people wonder what was really going on, but it could have been that another "amended" version of aether could have worked out, or it could have been that there was some mess with the experiment, or something else (perhaps) a bit like gravity now (cdm, or something else?) - when Einstein came up with relativity then all of that was blown away because Relativity came with positive predictions that aether didn't come with and these predictions were then observed ("look ma that swan is black, I told ya"). Now, who out there actually believes that cold dark matter is wrong because no one has had a good direct observation so far? It might be wrong, but it isn't ruled out at all.

You're losing the plot here. Recall the original claim:

> Nothing is falsified by the failure of an experiment to observe the expected.

MM definitively falsified the then-prevalent theory that space and time are absolute, and that the earth is moving with respect to the medium through which light waves propagate. The fact that it did not falsify all possible theories of the luminiferous aether does not change this fact.

Not by the result directly, no. But you can take the same data and use it to state that we are this sure the theory is wrong.

The term "failure" is loaded.

The lack of observation of proton decay has falsified several otherwise acceptable theories.

None of what you say contradicts that HEP Theory is in a crisis. That word was thrown around before the LHC confirmed the Standard Model, it's become more acute since.

The crisis is that the foundational ideas about how to make progress in physics: Elegance, beauty, naturalness, symmetries... are not yeilding any insights on the questions you raise. And yet CERN still argues that HL-LHC is important for detecting supersymmetry in their press release today.

The technical core of Hossenfelders argument is here:

https://arxiv.org/abs/1801.02176

Pasting block quote for mobile users:

"Thirty spokes share the wheel's hub; It is the center hole that makes it useful. Shape clay into a vessel; It is the space within that makes it useful. Cut doors and windows for a room; It is the holes which make it useful. Therefore profit comes from what is there; Usefulness from what is not there." Tao Te Ching - Lao Tzu - Chapter 11 (translation by Gia-fu Feng and Jane English)

--- (YC people: it is very telling that you can't find the will/resources to fix this blockquote on mobile problem. I would say it is damning of the whole ethos of YC/HN, in fact, but I'm marginal.)

The blockquotes are fine. It’s for code, not quotes. And they have better things to focus on.

On mobile you can read about 20 characters before hitting the edge of an iframe. It isn't even good for code.

One dev intern could tinker with HN's codebase to improve it. It's not as if YC is a startup that has to have a laser focus on one main chance. This is big business now.

There's plenty of research about the problem of the arrow of time, so o don't think it's fair to say nobody touches them. And what did you mean by "Is there something underlying quantum mechanics?"

> The observation of the apparent non-existence of something (supersymmetry, in this case) is at least as important as the existence of something.

Human imagination can create a large number of theories. It isn't as valuable to prove the non-existence of something you have imagined up than proving the existence of something you have imagined up.

Sure, in this case, it was pretty important to prove an idea (supersymmetry) wrong because it was so widely accepted. But, insofar as physics is an empirical science, not it's important to reflect, how did it happen in the first place that an idea with no empirical support became so widely held? What can be improved in the culture and habits of physics and physics funding. Which traditions should be reconsidered.

Supersymmetry was "beautiful" (i.e. it was produced by the conscious mind) and hence in a sense more "likely", so disproving it is as valuable as proving other "beautiful" theories (e.g. GR and Mercury's orbit).