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The quantum source of space-time

nature.com

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Re: The quantum source of space-time

#71

Post by lisper »

semi-extrinsic wrote: post #66
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…

(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…

> I believe this interpretation fails to explain experiments where people have entangled particles with timelike separation [1]

I don't have time to read that paper right now, but it sounds like simple entanglement transfer, not unlike what is done for "quantum teleportation." In any case, the math behind QIT is simply the math of QM, so anything that QM can explain, QIT can explain.

[UPDATE:] There was a published version of the C&A paper but I can't look it up right now (I'm on the road with very limited internet connectivity). But it turns out that the C&A position is essentially the same as decoherence/many-worlds. There is essentially no dispute over the facts any more. The problem is with the rhetoric in which those facts are wrapped. Even "many-worlds" is highly misleading.

Re: The quantum source of space-time

#72

Post by madaxe_again »

bytelayer wrote: post #55
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…

This is a fascinating idea. Could you elaborate on how you think the additional computational complexity would give rise to attraction between particles in matter-dense regions?

Spacetime just stretches to reduce the effective density in a flat universe and maintain an effectively constant information density - thus gravity and time dilation.

Re: The quantum source of space-time

#73

Post by dschiptsov »

dools wrote: post #65
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.

Is this a proof?

Western philosophy, so far, succeed in separating these concepts as being a priory which is perfectly reasonable, considering that any sensory input which is subsequently used to train and condition our mind is coming serialized by out sense organ, so, for a mind, which is a result of conditioning by the senses, the notion of succession is a priory. Conditioning by shared physical environment gives us cycles, so the notion of a cycle is also a priory. Succession days into nights in the environment and ageing of other people's bodies gives us notion of a continuous change. But change is not time.

Eastern philosophy (and modern cognitive neuroscience) would suggest that this a priory is related to our minds, not to photons or forces. So?

Re: The quantum source of space-time

#74

Post by duaneb »

madaxe_again wrote: post #46
taliesinb wrote: post #17

Here's a recent lecture by Erik Verlinde in which he tries to explain both dark energy and dark matter using entropic gravity: https://www.youtube.com/watch?v=PSYXt3Xu3xI I'm not a physicist, but he seems to be invoking similar ideas to Raamsdonk: that spacetime and gravity are emergent properties that boil down to entanglement somehow. But the loop quantum gravity people have been saying something like that for ages…

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…

Why do you (and others) tend towards arguments suggesting simulations?

To me, the language here is important. Both simulation and computation imply (to me) a tool and a user of the tool. Even a broader interpretation of computation as, umm, the efficient transfer of precise information through spacetime in certain shapes (which is easily providable by our understanding of physics today) requires an observer to extract the computation from the otherwise non-semantic system.

It definitely makes sense to think of the universe as a projection of a higher dimension, or a holograph, or however you want to look at it, but that's a far cry from implying a simulation.

EDIT: hologram -> holograph

Re: The quantum source of space-time

#75

Post by andyjohnson0 »

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.

Why stop there? Field, black hole, wormhole, string, force, spin, colour, charm, strangeness. All of these terms and more are used by physicists and have very different meanings to those used in "everyday life".

Re: The quantum source of space-time

#76

Post by ThomPete »

madaxe_again wrote: post #46
taliesinb wrote: post #17

Here's a recent lecture by Erik Verlinde in which he tries to explain both dark energy and dark matter using entropic gravity: https://www.youtube.com/watch?v=PSYXt3Xu3xI I'm not a physicist, but he seems to be invoking similar ideas to Raamsdonk: that spacetime and gravity are emergent properties that boil down to entanglement somehow. But the loop quantum gravity people have been saying something like that for ages…

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…

Isn't that what Wolfram is also getting at with his irreducible complexity concept?

I wonder if the trick about this is not really to find a true explanation but the right perspective and more and more simulation seems to be a very valuable perspective to put on this.

Disclaimer — I am not a physicist so apologies if my question is stupid.

Re: The quantum source of space-time

#77

Post by PolLambert »

cjg wrote: post #28
ars wrote: post #27

"The theory holds that gravity is geometry: particles are deflected ... not because they feel a force ... but because space and time around the object are curved." Can anyone explain to me why it can't simply be a force? If you accept that gravity is caused by energy and not mass (which is obviously the case), then I see no reason a photon can not experience a force. So what is the reason to insist it's geometry? And…

That explanation that "things are always moving - through time" is exactly correct. You need to think of the full four dimensional spacetime. It is that spacetime which is curved rather than just space. The crucial concept is Newton's first law (objects continue on their trajectory if a force is not applied). The straight lines in the 4D spacetime (geodesics) - the lines that an object would follow if no force is app…

In order to help people think about curvature and gravity, look at the following examples:

- The surface of the earth is a 2 dimensional positive curved space. To see this, draw a triangle with corners on the north pole, on the equator near Somalia and on the equator in Equador. The resulting triangle has a sum of all corners > 180 degrees.

- In a negative curved space, the sum would be less than 180 degrees. In a flat space, it is equal to 180 degrees.

- Another way to see the curvature of the surface of the earth is to observe that it's impossible to draw 2 parallel lines that do not intersect.

- The 2D torus (e.q. the surface of a donut) is flat. Test it with triangles.

- The towers of the Verrazano–Narrows Bridge are wider at their top than at their base. This has nothing to do with the earth have a positive curvature. Test it with a torus.

- 3D space is nearly always flat in the universe, especially at the surface of our planet.

- 4D space-time is not remotely flat. If I throw up a ball, it will come down. This is due the mass of the earth curving its surrounding 4D space-time. The straight line for a ball in the curved space-time looks like the ball changes directions and comes down in our flat 3D space.

- If you try to find the triangle of a sphere with the biggest sum of corners, you'll discover that the outside and inside of a triangle are interchangeable. We've entered the field of topology now and this has nothing to do with its curvature.

Re: The quantum source of space-time

#78

Post by PolLambert »

ajmurmann wrote: post #11

Do I understand this right that if the conjecture can be proved correct and the remaining issue about time gets solved we effectively have a grand unified theory?

No. Our space-time is definately NOT Anti de Sitter (AdS). AdS/CFT is nothing more than very nice mathematics with applications in different fields of physics. It's not applicable to our universe.

Re: The quantum source of space-time

#79

Post by lisper »

armitron wrote: post #70
lisper wrote: post #52

Earlier quoted context omitted.

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.

I realize that a lot of people think it's an open question. These people are wrong.

And the difference between me and a religious nutcase is that I can back up my position with math.

Re: The quantum source of space-time

#80

Post by lisper »

kgwgk wrote: post #54
lisper wrote: post #48

Earlier quoted context omitted.

No. Collapse doesn't actually happen. Collapse is an approximation to the truth. It's a very (very!) good approximation for systems with a large number of mutually entangled degrees of freedom, but it is an approximation nonetheless. See the links I pointed to earlier to understand why.

Doesn't "the truth" involve any change in state at all? I'll look at your answer to quantum mysteries when I have time. But I suspect your original comment could have been phrased "the standard interpretation of quantum mechanics has to die"...

My complaint is more about rhetoric and pedagogy than it is about facts. There is essentially no serious dispute about the facts. But yes, it is true that the Copenhagen interpretation (by which I mean the idea that measurement involves some mysterious non-unitary process called "collapse") is untenable except as an approximation. There is no serious dispute over this.
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