[zgramana]

The real takeaway is that researchers may have found a potential test for string theory.

Its presumed lack of falsifiability has been one of its drawbacks and has been the source of some of the controversy around it.

Finding a potential test that could be conducted with telescopes instead of high energy particle accelerators would be a big moment in modern physics.

[pdonis]

> The real takeaway is that researchers may have found a potential test for string theory.

Not really. All this paper is really saying is that they have found solutions in classical theories of gravity with extra dimensions that, in four dimensions, can look like standard black holes. So even observing effects predicted by these models would not be evidence for string theory. It would at best be evidence for possible extra dimensions of spacetime at the classical level.

Also, the paper only compares its models with the standard Schwarzschild black hole. But first, most black holes are spinning so the comparison should be with Kerr, not Schwarzschild; and second, as the paper notes early on, there are many other proposed models of compact objects that can look similar to standard black holes. Any given set of observations would have to be tested against all proposed models, not just this one.

[raylad]

Given that there is no absolute position in spacetime and everything is relative, in what sense is a black hole "spinning"?

Can't we just pick as a reference the black hole, and say that the everything else is spinning, just as well?

[pdonis]

> in what sense is a black hole "spinning"?

There are several equivalent ways of stating it:

(1) The hole's spacetime geometry is axisymmetric but not spherically symmetric;

(2) The hole has a Killing vector field that is timelike at infinity but is not hypersurface orthogonal;

(3) The hole has nonzero angular momentum as viewed in the asymptotically flat region at infinity.

> Can't we just pick as a reference the black hole, and say that the everything else is spinning, just as well?

No. All three of the above conditions are invariant and only depend on the spacetime geometry; they are unaffected by any choice of coordinates or the motion of any outside observers.

[adastra22]

No, spinning is an accelerated reference frame. If you spin on a carousel, you won’t feel the same as standing still.

Now what does it mean for a black hole, which we assume to be a singularity occupying no space at all, to be spinning? We don’t know. That’s one of the gaps in our theory. But as the collapsed remnants of an object that was spinning, they should have done residual angular momentum.

[pdonis]

> spinning is an accelerated reference frame

Not necessarily. The three definitions for a "spinning" black hole that I gave upthread do not require the presence of any accelerated frames or observers.

> what does it mean for a black hole, which we assume to be a singularity occupying no space at all

This is not correct. A black hole is a finite region of spacetime enclosed by an event horizon. The singularity is inside the hole but is not all of the hole.

> to be spinning? We don’t know.

Yes, we do. We have known since the 1960s that the Kerr solution to the Einstein Field Equation describes a spinning black hole, and all of the geometric properties of that solution have been known for almost as long as that.

> That’s one of the gaps in our theory.

No, it's not. See above.

> as the collapsed remnants of an object that was spinning, they should have done residual angular momentum.

This is correct, but it does not imply or support your other claims.

[adastra22]

You're missing the point that none of the three definitions you provided offer a mechanistic explanation.

[pdonis]

You're missing the point that, since a black hole is purely made of spacetime geometry, there is no "mechanistic explanation" of its spin in the sense you mean.

[georgyo]

Not a physicist, but no.

An object can spin relative to itself. Particles away from the center are constantly accelerating. Gravity or physical connection are the forces that prevent these particles from flying away.

Thinking about it, I am not even sure an object can spin relative to another object. Orbit sure, but not spin.

[pdonis]

> An object can spin relative to itself. Particles away from the center are constantly accelerating. Gravity or physical connection are the forces that prevent these particles from flying away.

This is a reasonable description of spin for an ordinary object, but it can't be used for a black hole, because a black hole is a vacuum solution; it has no "particles". See my other post upthread for better ways to view spin for a black hole.

> I am not even sure an object can spin relative to another object. Orbit sure, but not spin.

The usual definition of "spin" makes use of the object's center of mass frame, yes. Orbital angular momentum is thus separated out.

Note, though, that strictly speaking, in relativity there is no invariant way to make this split. It works very well as an approximation for most objects (like planets and stars), but there are complications when one tries to apply it to things like black holes. That's one reason why physicists prefer other ways of defining "spinning" for black holes that don't involve any split between orbital and spin angular momentum.

[x3n0ph3n3]

> But first, most black holes are spinning

Have any been detected that are not spinning?

[adastra22]

Well technically no black holes have ever been directly detected.

[simiones]

I think there are all sorts of other potential tests of string theory. The problem is that for all the actual tests that were ever proposed, it failed (supersymmetry, various proposals for sizes of the extra dimensions).

[sigmoid10]

To be fair, what failed is low-energy Supersymmetry and large extra dimensions, because these things were actually accessible by current gen experiments. But there's a huuuge amount of room left unexplored.

[simiones]

That's my point: what experiments could be performed have been performed, and have failed.

Also, it is a massive weakness of the theory that it can be used to predict such varied values. This is a big part of why it is not exactly a scientific theory: it is not really falsifiable, since you can tweak it to predict any value you want. If we had the kind of particle accelerators needed to test high-energy supersymmetry, and if it failed again, it could be adjusted to predict higher-energy supersymmetry, and since the number line extends towards infinity, this would never stop.

[peteradio]

I think you are correct, ST is closer to mathematical abstraction than an actual physical theory. I think that makes it more useful than less useful though.

[mensetmanusman]

Wouldn't that mean it is just more useful in mathematical reality but less useful in physical reality?

[GoblinSlayer]

Can't you disprove string theory by disproving quantum physics?

[dcsommer]

Not without fine-tuning. The issue is that high-energy supersymmetry no longer removes the "ugly constants" of the standard model -- it just shifts them somewhere else. Disclaimer: not a physicist, but I learned a lot reading "Lost in Math: How Beauty Leads Physics Astray".

[Pet_Ant]

…by Sabine Hossenfelder.

I treat her like Jordan Peterson. Obviously smart, but also obviously bitter and if/when they have a valid point I’m sure someone else has said it in a less grating manner.

[TheOtherHobbes]

Physics needs more insider critics. She's oppositional but - unlike Peterson - she does know what she's talking about.

[monkeydreams]

Sabine argues the data, in good(ish) faith, but she does carry a chip on her shoulder.

Peterson does not argue data - he suggests analogies and then holds those analogies as iron-clad transitive relationships to argue his preconceived position.

[snapcaster]

I hear this a lot from people. As a non-physicist who enjoys her content, what am I missing? is she wrong on any specific physics? Without specific criticism this comes off as insiders being upset that a fellow insider is critical of the field

[JBits]

Part of the issue for me is that I don't think her research on quantum foundations is viewed very highly. Some would probably consider it completely pointless. In her videos, she claims that the majority of physicists do not understand quantum mechanics and that AI might find patterns in the randomness of quantum mechanics. This doesn't put her tendancy to tell lay people how everyone else's research is a waste of time in a good light. She's just arguing that her research is more deserving of funding.

Plenty of her points aren't without merit but she's frequently disengenious and doesn't give the full argument for what she criticises.

An example is her criticism on "decoherence solves the measurement issue" where she explains the average of multiple particles doesn't tell you what happens to just one of the particles involved. She's not wrong in the example she gives but decoherence actually can be applied to a single particle. Compare with PBS space time, they present both sides and offer an opinion as their opinion not fact.

I recently watched a lecture on issues in particle physics. Naturalness was mentioned due to a need to ensure the theory gave sensible answers, to ensure it was renormalizable, that's far more reasonable to how Sabine presents it.

[throwaway81523]

I'm no insider but I haven't found Hossenfelder's stuff that impressive. Her reasoning tends to take the form "X is true, therefore Y", where "if X then Y" is a valid deduction, and X hasn't been proven false, so we can't say she's wrong on specific physics. But the presumption that X is true is unjustified even if X hasn't been proven false. Example: she likes superdeterminism instead of quantum mechanics with its various weird consequences. Ok, her version of superdeterminism hasn't been proven wrong, but that's a long way off from saying that it is right. It comes down to her saying "I believe X and I haven't been proven wrong, even though most other physicists believe not-X, but I like my theory better, so there". Perfectly fine and legit, but I'll take X seriously when I see more recognition for it from the rest of physics.

The same goes for this stuff about tests of string theory. As far as I can tell, string theory is perfectly good physics whether or not it is experimentally testable. That is, there is a viewpoint called "naive Popperianism" that if something isn't experimentally testable then it it isn't science, but from what I can tell, that viewpoint is not truly decisive (thus "naive"), and its proponents don't have the authority that they wish they did. As a comparable situation, there is not much dispute that general relativity (GR) is perfectly good physics except at the center of a black hole, where it predicts a singularity which people consider non-physical. Particularly, GR makes predictions about the interior of black holes (points inside the event horizon) that are considered perfectly good except at the center. But, since there is no way to observe the inside of a black hole, those predictions of GR are also not verifiable. So I'm not bothered by unverifiability. Theory is good if it has explanatory or interpretive power, not just testable predictive power.

[consilient]

> is she wrong on any specific physics?

She's not wrong about any of the empirical content of physics (so far as we know), but neither are the people she criticizes. It's a philosophical conflict. Most physicists are at least weakly inclined towards scientific realism, whereas Hossenfelder is a radical instrumentalist - and doesn't seem to think any other view is even worth engaging with.

[gloryjulio]

Jordan Peterson now is so far gone into the far right now it's not remotely comparable.

Maybe been you mean Jordan Peterson the year 1 edition where he was still talking about personal responsibility.

[runsWphotons]

Jordan Peterson has had many iterations. The year -5 edition had good psychology lectures and I disagree with the above poster who says he doesn't know what he is talking about. Within his academic realm, I think he did, although there would be points other academics would contest (this is what academics do). He has then gone through at least two transformations.

[s17n]

Hm, that seems like the opposite of Jordan Peterson (who is obviously an idiot, but has a good voice for TV)

[noobermin]

"low-energy Supersymmetry" oh, you mean 8 TeV wasn't enough? This kind of reasoning is just like the ether, people keep harping on a god of the gaps explanation for the failure of the search.

[progrus]

Yeah, it’s more they might have found a way to test the latest fix, than anything.

[ravenstine]

Even if it were testable, and the test failed to validate string theory, I don't think that would convince string theorists one way or another. Strings are a de facto religion within physics.

[colechristensen]

This line of talk is way overplayed. Like people who have an enthusiast amount of knowledge follow a few people who have professional knowledge who are just unreasonably fixated on what other physicists pursue.

Doubt and questioning are a part of science but this "religion" meme about string theory et al is silly. If you're really upset that somebody is pursuing something is a blind alley, go ahead and do some physics that shows results, otherwise I really wish people would tone the unhelpful criticisms down.

[senttoschool]

I agree. If every physicist quit string theory because we haven’t thought of a way to test it, like what @ravenstein might want, then that would be a sad day.

I don’t see the problem with physicists working on or even promoting string theory.

[kagakuninja]

I am not a physicist, but what I have read from critics (badly paraphrased):

During the hype phase of string theory, every major university wanted to get in on the game, and devoted large amounts of funding towards hiring researchers with a background in string theory. If you weren't one of those people, you were at a severe disadvantage, and might not get hired at all.

String theory hovered up tons of cash in university budgets, and majorly fucked over a lot of careers. The result of all this money has been no actual scientifically proven results despite decades of research.

[consilient]

> devoted large amounts of funding towards hiring researchers with a background in string theory. If you weren't one of those people, you were at a severe disadvantage, and might not get hired at all.

> String theory hovered up tons of cash in university budgets, and majorly fucked over a lot of careers.

This is pretty misleading. An argument could be made - though I'm not necessarily endorsing it - that string theory has crowded out other quantum gravity research programs in the last few decades. But quantum gravity is a small and poorly funded subfield: we're talking about no more than a few hundred people total in the US, fighting over one medium-sized experiment worth of grant money. None of it makes any difference to the overwhelming majority of physicists.

[senttoschool]

If there was a more promising theory to investigate in, we would have done that, right?

Even today, we don't really have anything much better than string theory.

[ravenstine]

No one is saying that string theory shouldn't be investigated.

[senttoschool]

Apologies. It was unclear what your desired goal from your original post.

[MichaelDickens]

> Strings are a de facto religion within physics.

I don't think string theorists are being unreasonable by not having changed their minds yet, given that no evidence has come out one way or the other.

I don't think we can extrapolate from "string theorists didn't update when presented with no evidence" to "string theorists won't update when presented with evidence".

[noslenwerdna]

There has been evidence though. All tests so far have been negative. Low energy SUSY, extra dimensions

[asdfman123]

“Science advances one funeral at a time”

- Max Planck

[Accujack]

Sadly, this is true of many things these days.

[SV_BubbleTime]

I don’t think it’s a these days thing at all.

I think it’s a human thing and every generation has to deal with the fanatics or believers or whatever you want to call it of their time.

We’re in a time where a great number of people are extremely religious without having any idea they are. The people that live by what their screen tells them. If you didn’t see some of this in the last three years that there is religion without it being labeled as such, I don’t know I’ll be able to reach you now.

[mitchdoogle]

We all live by what our screens tell us. We don't know anything outside of our own direct experience without depending on others. And for the most part we choose to trust others and it usually works out ok. That's not religion - that's an efficient way to intake information about the world, because an individual doesn't have the resources to learn about everything or go every place. If someone abuses our trust, then it's not a problem with the delivery method, it's a problem with them. So the fact that we get a lot of information via a screen is irrelevant.

Though I'm not sure what that has to do with the notion that bad ideas only die when the people who hold them die.

[mr_toad]

Just because all religions are a belief doesn’t mean all beliefs are a religion.

https://en.wikipedia.org/wiki/Affirming_the_consequent

[asdfman123]

I agree with your first sentence for sure.

It’s human nature for older people to be more conservative. Transcends time and culture.

[SV_BubbleTime]

Are you sure you’re not emphasizing my second point by thinking what I wrote was an attack of one ideology vs another?

[getcrunk]

Lol … I think the technical term for this is “hater”

[nathan_compton]

I don't see how this is testable, given what is written here.

[noobermin]

>If the researchers can discover an important observational difference between topological solitons and traditional black holes, this might pave the way to finding a way to test string theory itself.

This is a big if. For now they've just shown that once again something in the string theory landscape could look like something in real life.

[jgeada]

I know it is the standard nomenclature, but I object to it being called string theory, as it is at best a hypothesis, if not even just philosophical speculation with more math.

It can make no predictions, it is not falsifiable, it meets none of the constraints that allow something to be science.

[lo_zamoyski]

> just philosophical speculation with more math

Speaking of nomenclature, this is not a good characterization of what philosophy is, if your intention is to reduce philosophy to what you seem to have in mind for “philosophical speculation”. Metaphysical theory thoroughly supported by argument (hylomorphic dualism, theory of act and potency) is actually stronger than mere empirical science. Empirically testable predictions do not transcend reasoned argument as observation is interpreted though the body of propositions of prior theory and enters into scientific argument as argument.

[behringer]

I think string theory is so pupular is exactly because it can make predictions that classical particle theory cannot.

[vlovich123]

Are you sure? I thought that was why it had largely fallen out of favor. The predictions it makes are not testable.

[whynotkeithberg]

String theory is basically just noodles on the wall these days trying to find what sticks. mostly without basis and 99.9% of it falls off eventually as it's not backed by anything of substance.

[eikenberry]

> Its presumed lack of falsifiability has been one of its drawbacks[..]

Given that the definition of a theory is an hypothesis that can be tested for falsehood, it isn't a theory by definition. It is a hypothesis.. but presumably "string hypothesis" doesn't sound as nice.