Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

The quantum source of space-time

nature.com

Post reply on HN
Print view View original

61–70 of 124 posts

Re: The quantum source of space-time

#61

Post by simonh »

hellofunk wrote: post #57
madaxe_again wrote: post #46

Earlier quoted context omitted.

I am a physicist... The most interesting (to me, at any rate) bit of this article are susskind's observations on computational complexity. As a precocious undergrad I put forward the idea that gravity and time dilation were the same thing, and both stemmed from the universe needing a constant amount of "time" to compute the interrelations between the particles in a volume of space - and if there were more particles m…

Beautiful stuff, man. One of the more interesting questions I've seen asked in my casual hobby readings lately is: "Is the Universe quantized?" Meaning of course, is there a final limit to how small things get, and, with the passing of time, does it flow freely or pass in very tiny quantized periods?

I don't see how that would work with length contraction and time dilation. A unit quantum length object in my frame of reference would have different length to one in a frame at motion relative to mine, and time for it would pass at different quantum clock ticks. I don't see how a universe like that could work when it came to interactions between moving particles.

Re: The quantum source of space-time

#62

Post by tfgg »

taliesinb wrote: post #21
cperciva wrote: post #15

If any two particles are connected by entanglement, the physicists suggested, then they are effectively joined by a wormhole. And vice versa: the connection that physicists call a wormhole is equivalent to entanglement. They are different ways of describing the same underlying reality. In other words, there's no such thing as "spooky action at a distance", because with particles joined by a wormhole there is no dista…

Information transfer was never a problem with spooky action. But if all entangled particles were linked by some kind of funky wormhole it seems a harder task to explain why FTL information transfer isn't routinely possible.

Indeed. When I saw a novel proposal for embedding QM inside GR using closed time-like curves (rather than the usual vice-versa), the main problem seemed to be that a GR-computer is potentially _much_ more powerful than a QM-computer, so you have to explain where the extra power has gone.

Re: The quantum source of space-time

#63

Post by edem »

After reading this article I somehow feel a little correlation between this and the short story "That alien message" on LessWrong which suggested that we are living in a simulated universe.

Re: The quantum source of space-time

#64

Post by dschiptsov »

What is the proof of existence of 'universal time' as physical phenomena instead of being a 'derived property' of some or other physical process?

Rotation of Earth around Sun is just a process, there is no time in it apart from the mind of an external observer. Similarly with any so called "atomic clocks" or any other physical process, including so called expansion of the Universe.

Time, of course, could be derived as a concept from an observable change (a process) by mind, but this does not imply its physical existence, like it is with what we call physical forces.

Space is more subtle, but it is also require an observer and at least two particles related via this or that set of forces.

Two random Photons share nothing, and without an observer there is neither space nor time among them.

Mathematics does not imply existence of described abstraction.

Re: The quantum source of space-time

#65

Post by dools »

dschiptsov wrote: post #64

What is the proof of existence of 'universal time' as physical phenomena instead of being a 'derived property' of some or other physical process? Rotation of Earth around Sun is just a process, there is no time in it apart from the mind of an external observer. Similarly with any so called "atomic clocks" or any other physical process, including so called expansion of the Universe. Time, of course, could be derived a…

Mathematics doesn't imply anything. You can make a model using mathematics and then use it to make predictions, then test those predictions experimentally. By doing this a lot you can discover things and give them names like time, and proper time, and space and whatnot.

Re: The quantum source of space-time

#66

Post by semi-extrinsic »

lisper wrote: post #47
semi-extrinsic wrote: post #40

Earlier quoted context omitted.

Sorrt, but you're flat-out wrong, and the sources you link aren't credible. (That's not even a journal paper.) I suggest you read Scott Aaronson's explanation of why you're wrong (he understands this better than me): http://www.scottaaronson.com/blog/?cat=33

Here's the credible citation: http://arxiv.org/abs/quant-ph/9605002 (It's ironic, BTW, that you should complain that my citation is "not even a journal paper" when yours isn't either.) And BTW2, Aaronson's blog post doesn't contradict my position. The Bell inequality violations are indeed real. They just aren't caused by "spooky action at a distance." They are caused by the classical correlations that arise when you…

(Not constructive, but OK: Obviously a blog is not a journal paper, but it doesn't try to look like one either. It does have references to the journal papers it discusses though. As for the Cerf and Adami paper you linked above: from my searching it appears this is not published anywhere, it's just a 15-year-old preprint on the arXiv.)

So, to be clear: you are advocating some interpretation of quantum mechanics (for instance, but not limited to, the many worlds interpretation) where the measurement process is really measuring the system that produced the entangled pair?

I believe this interpretation fails to explain experiments where people have entangled particles with timelike separation [1], and then have shown that measurement of the second particle (which has never co-existed with the first particle in any reference frame) collapses the wavefunction of the first particle.

I'm not saying that the Copenhagen interpretation is the absolute truth, in particular many-worlds and superdeterminism are valid alternative interpretations, but I think the one you're advocating doesn't work.

[1] http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.110... (non-paywall: http://arxiv.org/abs/1209.4191 )

Re: The quantum source of space-time

#67

Post by aroberge »

mrob wrote: post #38
kgwgk wrote: post #35

Earlier quoted context omitted.

Curvature is not "measured with respect to [an embedding] space". If you have a triangle and the sum of the angles is not 180 degrees that's a non-Euclidian (curved) space.

But that's not how the word "curved" is used in everyday life. Call it non-Euclidian if it's non-Euclidian. Redefining common words only leads to confusion.

Take a 50-kg object (110 pounds) and carry it in your arms for an hour on a flat road. You will have done no work against gravity. You may complain that this is not how the word "work" is used in everyday life - and that you will have done a lot of "work" against gravity (preventing the object from falling to the ground). However, if you wish to discuss Physics and Mathematics, using terms that have precise definitions in those fields, you cannot object on the basis that these words do not have the same meaning as non-Physicist and non-Mathematicians ascribe to them.

Re: The quantum source of space-time

#68

Post by progman »

hellofunk wrote: post #57
madaxe_again wrote: post #46

Earlier quoted context omitted.

I am a physicist... The most interesting (to me, at any rate) bit of this article are susskind's observations on computational complexity. As a precocious undergrad I put forward the idea that gravity and time dilation were the same thing, and both stemmed from the universe needing a constant amount of "time" to compute the interrelations between the particles in a volume of space - and if there were more particles m…

Beautiful stuff, man. One of the more interesting questions I've seen asked in my casual hobby readings lately is: "Is the Universe quantized?" Meaning of course, is there a final limit to how small things get, and, with the passing of time, does it flow freely or pass in very tiny quantized periods?

> is there a final limit to how small things get

AFAIK yes, the limits are known as Planck Constants. It means that we are living in a digital universe.

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

There are also conjectures about a _holographic_ universe.

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

https://www.youtube.com/results?search_query=holographic+uni...

Re: The quantum source of space-time

#69

Post by lisper »

hellofunk wrote: post #58
lisper wrote: post #47

Earlier quoted context omitted.

Here's the credible citation: http://arxiv.org/abs/quant-ph/9605002 (It's ironic, BTW, that you should complain that my citation is "not even a journal paper" when yours isn't either.) And BTW2, Aaronson's blog post doesn't contradict my position. The Bell inequality violations are indeed real. They just aren't caused by "spooky action at a distance." They are caused by the classical correlations that arise when you…

>It's amazing how the Physics world bifurcates into two camps: those who think that the connection between entanglement and measurement is common knowledge, and those who adamantly deny that it is true. The fact that there are two legitimate camps means that no one knows for sure what is happening. And you are obviously in one of those camps. So to insist the world is a particular way is to deny how much is still unk…

The difference is that one camp has the math solidly on its side, and the other camp has to invoke the extra-physical hypothesis that measurement is somehow different (non-unitary, non-reversible) from everything else.

Re: The quantum source of space-time

#70

Post by armitron »

lisper wrote: post #52
Confusion wrote: post #39

Earlier quoted context omitted.

You are asserting something as true that is actually under dispute. Whether the state of the particle was already determined is the million dollar question. Importantly, under non-local theories, it doesn't have to be. Superpositions can be real and not just mathematical entities.

It's only disputed by people who haven't actually looked at the math. And I didn't say the state of the particle was already determined. It wasn't. Yes, of course superpositions are real. Yes, of course the Bell inequalities are violated. Yes, this eliminates all local hidden variables theories. Yes, it seems like this necessarily leads to the conclusion that there is spooky action at a distance. But that's wrong. To…

You do realize this is an open question right?

No jokeprod paper or video is going to put it to rest. You sound like a religious nutcase.

Post reply on HN