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Beyond Einstein: Physicists find surprising connections in the cosmos
- mike_ivanov 8y ago"black holes have a temperature that arises because each particle that falls into a black hole has an entangled particle that can escape as heat" o_O
- rhn_mk1 8y agoI believe this is referring to Hawking radiation. 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.
- mike_ivanov 8y ago"virtual ones .. a counterpart which ends up being "radiated"." -- but this is not how Hawking radiation works.
- Pharmakon 8y agoTo be fair, it is the usual way HR is described in pop science articles. The reality of pair production outside of the event horizon, and one particle falling in while the other “steals” a bit of energy from the hole’s gravitational field is not described as often. It’s also equivalent to the same pair being produced with the inflating partner having negative energy.
- rhn_mk1 8y agoCare to point out the error?
- mike_ivanov 8y agoIt's a form of redshift effect in curved spacetime. Any massive object stretches the spacetime in a way that the spectrum of the light emitted by that object shifts down from the point of view of a remote observer (remote - this is important). The larger the mass, the stronger the effect. 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.
- Pharmakon 8y agoThat’s part of it, but then you have to account for the role the event horizon plays, and inherently complicated things like wave packets scattering off of it. I can’t pretend to understand the process well enough to talk about it without resorting to heuristics.
- mike_ivanov 8y agoPerhaps this could also help - https://physics.stackexchange.com/questions/251385/an-explanation-of-hawking-radiation https://physics.stackexchange.com/questions/251385/an-explan...
- antidesitter 8y agoI wish science communicators would abandon the whole “virtual particle” terminology altogether. It creates a lot of confusion.
- Pharmakon 8y agoMatt Strassler has a good blog post on the subject. https://profmattstrassler.com/articles-and-posts/particle-physics-basics/virtual-particles-what-are-they/ 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.
- __john 8y ago> normally particles don't have an entangled counterpart. I believe this assumption is incorrect. Most particles do have an entangled counterpart. https://www.quora.com/What-percentage-of-subatomic-particles-are-quantum-entangled https://www.quora.com/What-percentage-of-subatomic-particles...
- isolli 8y agoIt's difficult for a non-specialist to place this article in a broader historical context. I thought string theory was by now more or less considered a dead-end, so I wonder if this article is an attempt to revive it, or the first sign that it may actually go somewhere after all. Maybe someone knowledgeable can weigh in?
- dkural 8y agoIt is still considered a dead-end. This is a puff / PR piece going over well known old arguments to promote it to the lay public.
- MockObject 8y agoDoes that mean there's nothing promising anymore in AdS/CFT correspondence?
- Pharmakon 8y agoIt’s interesting mathematically, but we don’t live in an AdS universe so there’s that. Recently there’s been some progress extending the notion fromthe AdS toy model to a dS toy model, but the degree to which any of that applies to anything real’s questionable. “Interesting, but with no indication of a valid physical interpretation in the universe” is probably the best way to sum up the world of string theory. 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.
- peteradio 8y ago
- anthony_doan 8y agoThe 5th dimension have already been experimentally conducted. https://www.youtube.com/watch?v=3HYw6vPR9qU 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 https://arxiv.org/abs/1801.08160
- mike_ivanov 8y agoDid you mean "experimentally ruled out"? From the paper: "gravitational waves propagate in D=3+1 spacetime dimensions, as expected in general relativity."
- anthony_doan 8y agoYep it was ruled out there is an extra dimension that's hiding gravity's strength that was the conclusion of the paper.
- brink 8y agoIn other words, it appears that there are no extra dimensions that interact with gravity like space-time does. 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.
- ivalm 8y agoAdS/CFT correspondence is a pretty old idea, whether it will yield something useful is still to be seen. Our world is not an N=4 Yangs Mills CFT, and our space is not AdS, so both sides of the correspondence are basically toy models that have been known for a while and haven't produced verifiable predictions (other than supersymmetric partners we haven't seen).
- auntienomen 8y agoNeither of these models predicts superpartners. The AdS theory doesn't include the standard model. The N=4 theory doesn't even have particles. They're toy models, albeit rather sophisticated ones. Their utility is that they can give us concrete demonstrations of various conjectures about gravity, holography, and gauge theories.
- ivalm 8y ago> The AdS theory doesn't include the standard model 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.
- TomMckenny 8y agoGiven this explanation of gravity, can anyone hint (to a layman) how the-force-due-to-acceleration works in this model?
- blaze33 8y agoDoes assuming some ultimate law ruling the universe what mainly drives research? 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?
- goldfeld 8y agoM-Theory posits that yes, the laws of nature and physics have evolved as the miltudimensional space evolved, they may not always have been the same as now.
- blaze33 8y agoThanks, didn't knew about M-theory, I'll look it up! 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...