Beyond Einstein: Physicists find surprising connections in the cosmos
discovery.princeton.edu
discovery.princeton.edu
I never said AdS includes standard model?
> The N=4 theory doesn't even have particles
Yang Mills is a super symmetric CFT used as a toy model for other super symmetric models (which do have super partners; Yang Mills informs us about our real world only in as much as it informs us about other supersymmetric CFTs).
> Their utility is that they can give us concrete demonstrations of various conjectures about gravity, holography, and gauge theories.
Sure, but there is significant concern about how meaningful those demonstrations are since the theories that are most similar to the toy examples are themselves probably dead ends.
https://www.youtube.com/watch?v=3HYw6vPR9qU
I won't give away the spoiler but this article is written within a few months of the above video (oct vs dec).
The paper in reference is: "Limits on the number of spacetime dimensions from GW170817" Pardo, Fishbach, Holz & Spergel 2018 https://arxiv.org/abs/1801.08160
From the paper: "gravitational waves propagate in D=3+1 spacetime dimensions, as expected in general relativity."
The possibility of dimensions that do not interact with gravity appears to be still open.
Unless I'm missing something; all this experiment really does is shows that there's nothing else "absorbing" gravity apart from space-time.
The other big problem is that a lot of what made it seem natural and elegant has been progressively ruled out, so you’re left with far less simple and elegant versions which could apply to the universe. At that point you have to ask what the appeal is, you know? It’s not unlike the problems with Inflationary cosmology. Originally it was a simple way to resolve outstanding issues of homogeneity and isotropy of the observable universe. That was based on a model with a very natural PE curve, which has been ruled out. Now we’re left with a “curve” every bit as contrived as simply saying “because” in reference to the underlying questions.
In both cases, M-Theiry and Inflation, they persist because of huge investments of time and energy into them, and because as yet no strong competitors have emerged.
Many of the best people in theoretical physics with Edward Witten being the most prominent example have been working on it for ~40+ years now. None of the public detractors have nearly the same stature that Witten has. Of course this is basically an argument by authority and there is a chance that once titans like Witten leave the playing field the following generations will lose more and more influence.
I think there is a fair bit of criticism of String Theory among very good people that is not voiced publicly because there would be no point to it, they have nothing to gain. In many ways it is the "Only Game in Town" (literal quote from my supervisor), just doing high-energy particle phenomenology is not that much more exciting.
String theory has already led to a number of very high profile successes in mathematics (Perelman's Proof of the Poincare Conjecture, Monstrous Moonshine etc.), so it is not like the techniques that have been developed are totally useless.
Aren't there a few alternatives such as Quantum Loop Gravity?
I'd be extremely hard pressed to name a significant result loop quantum gravity has exported to the rest of physics and mathematics.
There's also the asymptotic safety program, which isn't completely implausible, but is kind of stuck in the 'steal underpants' phase.
If we look at the idea of a ”point particle”, it’s clearly something that is never observed elsewhere.
This is what leads to the whole idea of renormalization: that any force that goes to infinity as r->0.
For string theory, adding a second dimension to the particle adds density, which avoids the same amount of infinites. Similarly, loop gravity’s ”chunky” timespace also prevents infinites by essentially adding a minimum distance.
I feel both approaches are wrong. The conceptual model of the particle as a dot still lives on in some regard.
With M-theory, string theory moved more to something like the concept of a particle with density in multiple dimensions.
However, the extreme complexity and the many assumptions needed in string theory made it very unappealing to me.
I would like to see some theory that used the wave nature of particles resolve the infinities - including quantum gravity, then describe some mechanism how these waves could gain dual particle-like behaviour when leaving the Planck length world.
o_O
I'm not an expert, but normally particles don't have an entangled counterpart. Only virtual ones do, and those which fall in can have a counterpart which ends up being "radiated".
Perhaps the confusion is caused by the current understanding that any information (and mass?) that comes in will eventually get emitted back away.
A black hole would create an infinite redshift (due to singularity inside of it) -- but only if infinitesimal EM frequencies were possible, which in turn would imply continuous spectrum. The energy of photons is quantized, therefore no truly infinite redshift is possible. The same applies to other particles.
Basically it's a raster effect that becomes apparent when you zoom up on a magazine photograph, or equivalently -- when you stretch a photograph printed on a rubber sheet, the only difference is that you stretch spacetime, not just space.
https://profmattstrassler.com/articles-and-posts/particle-ph...
Part of the problem however is that science communication has become its own “field” typically staffed by miserably unqualified people on a shoestring budget. There are also few laurels and less money to be had in trying to give the public at large a faithful representation of the real science. By contrast rehashing decades old basics about black holes with lots of hand-waving sells papers, clicks, magazines, etc.
As long as fiendishly complicated subjects are relentless dumbed down in the name of “inspiring enthusiasm” rather than instilling facts, we’re stuck with this.
I believe this assumption is incorrect. Most particles do have an entangled counterpart.
https://www.quora.com/What-percentage-of-subatomic-particles...
Or, what if our so-called laws of nature, just like life, only emerged from the initial big bang? Was there a natural selection of the fittest particles after the big bang?
Science taught me about how everything is made of particles while their interactions follow the laws of nature. Much later, reading Wittgenstein, I understood that the world is not so much about it's particles but more about how things interact together. Because if something never interact at all with anything, it may as well not exist at all. So the very existence of something always comes with its interactions to the world and whatever rules they happen to follow...