Lunchtime doubly so.
Entangled toy universe shows time may be an illusion
11–20 of 53 posts
Re: Entangled toy universe shows time may be an illusion
#12Lunchtime doubly so.
Yes! Douglas Adams reference!
Re: Entangled toy universe shows time may be an illusion
#13Question: Why do some physicists believe it's a problem that physics isn't unified? It seems odd to assume that just because throughout history we've unified more and more concepts that all of physics can be unified. What if there's a limit? It's interesting to think that 100,000 years from now, physicists will still be working on the problem since no one would know it's impossible.
Per my understanding, there's less concern over unifying, say, the strong and electroweak interactions. You have to posit some ridiculous coincidences to explain facts like why the charge on protons and electrons are exactly opposite, but nothing whatsoever prevents you from doing so. Then you get separate, compatible theories describing separate domains. That's basically what the Standard Model is: QCD + electroweak, agglomerated as separate interactions, not unified.
However there's better reasons to be concerned with the relationship between general relativity and quantum mechanics. The problem is that while their domains are generally separate, we know they must intersect in cases like black holes or the early universe. And in these scenarios, the theories produce incompatible predictions, leading to issues like the black hole information paradox.
Physicists are very interested in any theory of gravity that makes predictions compatible with quantum mechanics. Some of the contenders unify with the other forces (string theory) while some do not (loop quantum gravity). A unified theory would be huge, but a non-unified "agglomerated" theory that nevertheless makes a single, unified prediction would be almost as exciting.
So the answer to your question is that popular physics writing often uses "unification" as a shorthand for "unified prediction" rather than "a single interaction." That's what this article is doing: the referenced Wheeler-DeWitt equation is NOT a unified theory because it does not explain QCD or electroweak.
Re: Entangled toy universe shows time may be an illusion
#14Question: Why do some physicists believe it's a problem that physics isn't unified? It seems odd to assume that just because throughout history we've unified more and more concepts that all of physics can be unified. What if there's a limit? It's interesting to think that 100,000 years from now, physicists will still be working on the problem since no one would know it's impossible.
Depending on what phenomena a set of equations describe, if the equations break down at some point it becomes of interest to figure out the reason. The situation cannot be ignored because it hints that the phenomena may not be properly understood.
The equations of general relativity do not hold on the quantum scale, and those of quantum mechanics cannot be used when gravity is large. This is a break down. The bridge between the two could be unifying the two "worlds" or have a damn good reason why not. Nature has a good motivator for unifying called black-holes. Inside black-holes you have large gravity and also quantum scale stuff that has been eaten or squished together or just tiny space.
It would be rather difficult to solve the black-hole problem starting from scratch, as black-holes arise out of general relativity equations. So you start from quantum scale and cross-check with the other end or vice versa.
If you are weary of the word "unify" from a philosophical perspective, then it may help to realize that the word unify comes to apply because we (humanity) have discovered and built up more knowledge from imperfect bundles.
Suppose in 1906 (before quantum mechanics or general relativity) Einstein had come up with some universal theory/model that inherently worked everywhere, it probably would never have been termed as a unification theory.
Re: Entangled toy universe shows time may be an illusion
#15Question: Why do some physicists believe it's a problem that physics isn't unified? It seems odd to assume that just because throughout history we've unified more and more concepts that all of physics can be unified. What if there's a limit? It's interesting to think that 100,000 years from now, physicists will still be working on the problem since no one would know it's impossible.
Simple answer -- There are situations (like black holes, or early universe physics) where gravity becomes very strong and important, and so do quantum effects. To understand physics in those regimes, we need a consistent way to put together gravity and quantum mechanics.
The explanation that gravity corresponds to the physics of the large scales and quantum mechanics to the physics of small scales is not quite true -- this description applies in our daily experience, but is not always the case.
Re: Entangled toy universe shows time may be an illusion
#16Time is weird stuff. When you can tell what altitude your atomic clock is by the offset in its notion of time with the clock at your side, you start to get an inkling about that. The professor who taught quantum mechanics at USC when I was there used to joke that God told Adam and Eve that it took 7 days to create the universe, but we know from our observations that it was closer to 14 billion years. Given these two…
Isn't that special relativity(time dilation) that your quantum mechanics teacher talking about there?
Re: Entangled toy universe shows time may be an illusion
#17Earlier quoted context omitted.
It is difficult, perhaps impossible, to come up with a philosophically sound logically consistant explanation for natural phenomenon which isn't unified and connected at a fundamental level. Two incompatible sets of natural explanations are vastly less likely than one unless we're falling back on superstition again. Really? Ancient philosophers argued that it's vastly less likely for there to be such a huge distance…
> Ancient philosophers argued that it's vastly less likely for there to be such a huge distance separating celestial bodies than whatever their pet theory of the day was. Is it me or is that a bit handwavy? The Greeks or whoever else got things awfully right and other things terribly wrong. We have the benefit of hindsight so we can point at the latter category. It doesn't negate the former. Seems like you could take…
I think that's a bit of a strawman. The pattern described was that we are often wrong because there's some factor about which we do not yet have the slightest clue.
Given for how long we've thought that we knew everything, it should hardly be surprising to find out that there's more to things than we know.
Re: Entangled toy universe shows time may be an illusion
#18Time is weird stuff. When you can tell what altitude your atomic clock is by the offset in its notion of time with the clock at your side, you start to get an inkling about that. The professor who taught quantum mechanics at USC when I was there used to joke that God told Adam and Eve that it took 7 days to create the universe, but we know from our observations that it was closer to 14 billion years. Given these two…
Isn't that special relativity(time dilation) that your quantum mechanics teacher talking about there?
Yes, but this is a physics professor making jokes to an audience of physics students. Why shouldn't he refer to special relativity? It's part of his training and the training of everyone who can hear him.
I'd be more surprised if the joke came from, say, the professor teaching egyptian hieroglyphics.
Re: Entangled toy universe shows time may be an illusion
#19Time is weird stuff. When you can tell what altitude your atomic clock is by the offset in its notion of time with the clock at your side, you start to get an inkling about that. The professor who taught quantum mechanics at USC when I was there used to joke that God told Adam and Eve that it took 7 days to create the universe, but we know from our observations that it was closer to 14 billion years. Given these two…
Smolin's book on time is interesting. One of the points he makes is that we are limited in our thinking about the universe by using a language that does not model time - mathematics. Sometimes I wonder if we want things to be fundamentally pure and stateless because we find change so stressful.
Re: Entangled toy universe shows time may be an illusion
#20Question: Why do some physicists believe it's a problem that physics isn't unified? It seems odd to assume that just because throughout history we've unified more and more concepts that all of physics can be unified. What if there's a limit? It's interesting to think that 100,000 years from now, physicists will still be working on the problem since no one would know it's impossible.
Because physicists believe in parsimony? Less flippantly, simply that if the two (on their own, staggeringly accurate) main theories we have about how the universe works are as fundamentally incompatible as the ones we've got, then there's probably something we don't yet understand about the thing they're describing. The search for a ToE isn't so much about "unifying" QM and Relativity as it is about figuring out wha…
I am blasted away by your completely staggering domain-knowledge and my lack of the same. Probably should stop seeing universe docus and study more science