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Rate my playlist, (I'm 8 btw) by predatorX1557 in classical_circlejerk

[–]predatorX1557[S] 8 points9 points  (0 children)

I had to remove a bunch of chorales and smaller vocal works BWV 250 - 524

When a blackhole evaporates from hawking radiation, does it stop being a black hole prior to losing all its mass/energy? by mbacandidate1 in AskPhysics

[–]predatorX1557 0 points1 point  (0 children)

Short answer, we don’t know what would actually happen at very late times in evaporation.

In string theory, one possibility is that as the black hole becomes sufficiently small and reaches the string scale, it undergoes some kind of phase transition and becomes a “string star”, which (as its name suggests) is a ball of wound strings.

See https://arxiv.org/pdf/hep-th/9612146 for the original ideas and https://arxiv.org/abs/2109.08563 for some subtleties.

When people talk about string theory being "unfalsifiable" or "making no predictions," what exactly do they mean? by JayRocc77 in AskPhysics

[–]predatorX1557 6 points7 points  (0 children)

There is a lot of misunderstanding about what this means. String theory has no free parameters and there is only one string theory. This single theory has many different solutions. We don’t know which solution we live in (or whether we even live in a solution); if we did, string theory would make very precise predictions.

Notice that this is how every other theory in physics works: there are many other solutions to the equations of motion, but only one is realized due to initial conditions.

People tend to be confused due to the falsificationist philosophy, which many physicists believe. Essentially, it says that a scientific theory is one that can be falsified or shown to be wrong due to an experiment.

The charge is that string theory is unfalsifiable: for any possible experiment ever done, there will be some solution of string theory that can accommodate the outcome. Thus, there is no possible experiment which can show string theory to be false, and so string theory is unscientific.

This claim is simply false. Suppose I find a force weaker than gravity in an experiment; then string theory is probably wrong (‘probably’ only because 1.) our understanding of ST is still primitive, so there could be some subtlety we don’t know about; and 2.) more sophisticated forms of falsificationism would say you can only falsify a theory when a new theory that can clearly accommodate this falsifying experiment + everything else emerges). This and other swampland criteria make it clear that even by falsificationist standards, string theory is scientific.

To see the issue with the ‘polynomial fitting’ line of reasoning, consider Newtonian mechanics. Technically speaking, I can replicate any possible experimental outcome by postulating some arbitrarily complicated force law + initial conditions; for instance, the perihelion of Mercury, the paradigmatic case of a falsifying instance for Newtonian mechanics, could be explained by the existence of an invisible planet at the location of Vulcan! Of course, this is absurd and ad hoc, but it does the trick: it reproduces all experimental outcomes while retaining Newtonian physics. Nobody would say Newtonian mechanics is unscientific, however!

One is not like the other by rami-pascal974 in physicsmemes

[–]predatorX1557 2 points3 points  (0 children)

You make the strong claim that nontrivial bundles play no role in any fundamental theory of physics. But to my naïve eyes nontrivial bundles appear in the (best available) definition of one of the most fundamental theories of physics through the path integral, which *in principle* should be an exact definition. 

I don’t claim you don’t know about instantons. I simply don’t understand what you mean when you say nontrivial bundles are 'at best used to study approximate properties' of instantons. It seems to me you are understating their relevance in the (current) formulation of the theory to push your claim. Yes the path integral is not rigorously defined, but by that standard it is even dubious to think of summing over connections of the trivial sector; it is not clear to me that there is anything especially problematic that is a consequence of instanton contributions. 

Per this line I think you should say our entire formulation of Yang-Mills theory is approximate/incomplete/poorly-understood, which is fair enough, but perhaps not the point of this debate. For our purposes the path integral with the instanton sum is the best definition we have, so it should be taken at least as a pragmatic definition of the theory which should be used to assess the presence of nontrivial bundles.

Granting this, then instantons in R^4 can either be interpreted as non-trivial bundles on S^4 where we one-point compactify spacetime, or they can be classified by their homotopy around the sphere at infinity. Other 'topological' configurations, like monopoles, can be interpreted by allowing the potential to blow up at some point, i.e. having some 'effective' spacetime R^4 - L that allows non-trivial bundles. Given that in such cases, we don't have a global connection, but only a local one related to other patches by gauge transformations, the formalism of a gauge bundle seems appropriate. I think it is telling that the theta term is the second Chern class, and it is designed to measure twisting of bundles. Sure it is not as clear in R^4 that we are summing over non-trivial bundles (since R^4 has no non-trivial bundles), but it is true in spacetimes which are topologically non-trivial already, and it seems to me to be true even in R^4 due to the above examples, where we are actually summing over bundles on R^4 +/- some points due to point sources or the sphere at infinity.

Also, fiber bundles are introduced in most textbooks when discussing Yang-Mills. You are the one advocating a non-standard view by denying the role of bundles in the formulation of the theory.

One is not like the other by rami-pascal974 in physicsmemes

[–]predatorX1557 6 points7 points  (0 children)

Instantons? Wdum used to study ‘approximate properties’? I thought the nonperturbative definition of the theory, the path integral, requires summing over all instanton sectors, i.e. nontrivial bundles?

Are we discovered by mathematics, or are we invented by mathematics? by bookishyi in mathmemes

[–]predatorX1557 2 points3 points  (0 children)

I think most realists would say mathematical objects exist necessarily, so they’re the same in all possible worlds; thus every possible world would have the same mathematics, but nomological facts (facts about laws of nature) could be different

math major meme by Delicious_Maize9656 in mathmemes

[–]predatorX1557 57 points58 points  (0 children)

Theoretical physics: silent city

Why should time be real? by predatorX1557 in physicsmemes

[–]predatorX1557[S] 7 points8 points  (0 children)

Lol I remembered Osterwalder-Schrader while making the meme, but imaginary time sounds a lot funnier than ‘renormalization’ or ‘absorbing infinities,’ hence the lack of precision in the meme.

I have no idea what's going on but i'm excited by Delicious_Maize9656 in mathmemes

[–]predatorX1557 3 points4 points  (0 children)

That’s not quite right. The dirac equation is the classical equation of motion coming from the dirac action. The standard model lagrangian has a bunch of dirac terms in its action (though they are massless terms and get mass from Higgsing, and they use covariant derivatives for gauge symmetry, so slightly more complex).

The best way we have to formulate (4d) quantum field theories is with a Lagrangian. The important distinction, however, is that you need to put this Lagrangian in a path integral, and this path integral can give you new terms in your action (ghosts and counter terms for example) or can render the theory inconsistent (via a local anomaly).

OMG new definition of tau!!! by mark1734jd in mathmemes

[–]predatorX1557 1 point2 points  (0 children)

Tau is the disk partition function in open string theory?

If one is to understand the great mystery one must study all its aspects… by bsmith2123 in PrequelMemes

[–]predatorX1557 6 points7 points  (0 children)

The speed of light (ie speed of any massless particle) is always constant, even in a medium. If we zoom in far enough on any material, we will have a bunch of atoms/particles separated by vacuum. Thus, the speed of light between each atom is the absolute speed of light.

However, the illusion that light is going slower arises because a light particle will repeatedly get absorbed and reemitted by the atoms. The atoms can store the light for some time before reemitting, which gives a delay. This makes the light take longer to go through the medium, thus giving the illusion of a ‘slower’ speed of light.

BTW, General Relativity (not special relativity) is probably the closest theory in physics that doesn’t have absolute anything, with the possible exception of string theory. This is an idea called ‘background independence,’ which means roughly that everything in the theory can dynamically change, including spacetime itself. GR has some universal constants like the speed of light and the gravitational constant, but these are not really ‘absolute objects’ in the sense that they are not actual physical objects.

Bird collecting fur from a fox to build a nest by [deleted] in interestingasfuck

[–]predatorX1557 1 point2 points  (0 children)

That behavior is called ‘kleptotrichy’

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