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The quantum source of space-time

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Re: The quantum source of space-time

#31

Post by abdullahkhalids »

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…

Good questions.

It could be a force - if someone finds a theory that describes all the observational data. They haven't.

The reason to insist geometry is that general relativity manages to predict extremely accurately the result of all gravitational experiments/observations as of 2015. In science, prediction comes before explanation, meaning if you have to accept whatever explanation the best predictive theory offers and not vice versa.

Well, its has been explained - you just haven't gone through the right books. There are two answers, which I will simplify. One, the Big Bang threw everything all over the place and now masses are moving so as to reach the state of minimum energy. Two, there are 3 other forces in the universe which can cause masses to move. For example you can use electromagnetic forces during the combustion of rocket fuel to send a satellite in space. The satellite then moves in orbit because of the geometry of spacetime. Same when stars explode - this involves all three forces.

Re: The quantum source of space-time

#32

Post by abdullahkhalids »

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?

Probably not. But it will be a big step in the direction.

There are two unifications that need to happen. One is the unification of the strong force with electro-weak force(the unified version of electromagnatic force and weak force). The other is gravity with the unification of the three forces.

As far as I understand, this work is concentrating on the second unification, and not the same. Though it might open the door for the first one too. Someone closer to this area should comment.

Re: The quantum source of space-time

#33

Post by mrob »

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…

>It is that spacetime which is curved rather than just space.

This is the crucial point that many discussions overlook. The concept of "curvature of space" is obvious nonsense because curvature is measured with respect to space. For space itself to curve implies the existence of meta-space (and as many nested metaspaces as you like). But "spacetime" does not work like "space", and there actually is no metaspace. Talking about "space" curving or expanding is unnecessarily confusing.

Re: The quantum source of space-time

#34

Post by zby »

lisper wrote: post #29

"Entanglement lets the measurement of one particle instantaneously determine the state of a partner particle, no matter how far away it may be" No. No! No!!! This meme has really got to die. A measurement of one entangled particle does NOTHING to the other particle. Its state is exactly the same as it was before. In fact, the whole concept of "before" and "after" a remote measurement doesn't even make sense because i…

'determine' does not mean 'change' - does it?

Re: The quantum source of space-time

#35

Post by kgwgk »

mrob wrote: post #33
cjg wrote: post #28

Earlier quoted context omitted.

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…

>It is that spacetime which is curved rather than just space. This is the crucial point that many discussions overlook. The concept of "curvature of space" is obvious nonsense because curvature is measured with respect to space. For space itself to curve implies the existence of meta-space (and as many nested metaspaces as you like). But "spacetime" does not work like "space", and there actually is no metaspace. Talk…

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.

Re: The quantum source of space-time

#36

Post by lisper »

zby wrote: post #34
lisper wrote: post #29

"Entanglement lets the measurement of one particle instantaneously determine the state of a partner particle, no matter how far away it may be" No. No! No!!! This meme has really got to die. A measurement of one entangled particle does NOTHING to the other particle. Its state is exactly the same as it was before. In fact, the whole concept of "before" and "after" a remote measurement doesn't even make sense because i…

'determine' does not mean 'change' - does it?

The issue is not so much with the word "determine" as it is with the word "instantaneously". You could say "Entanglement lets the measurement of one particle instantaneously frob the state of a partner particle" without knowing or specifying what the word "frob" means and you'd have the same problem: you're claiming that measuring one particle does something to the other particle, and does it instantaneously and, moreover, that this is mysterious because the two particles are far apart (hence the slogan "spooky action at a distance"). All this is wrong. There is no "spooky action at a distance" because there is no action. Whether that action is "determining" or "frobbing" the state of the other particle is irrelevant.

The correct story is that measurement and entanglement are the same physical phenomenon. The creation of an EPR pair is the first step in any measurement process. The correlations in EPR measurements derive from exactly the same physical process as the correlations in "ordinary" measurements (I put "ordinary" in scare quotes because, as I said, even "ordinary" measurements start with the creation of an EPR pair). When you "measure" the two halves of an EPR pair what you are really doing is performing two measurements on whatever system produced the EPR pair to begin with. When you look at it that way it is not at all surprising that the measurements should be correlated.

For more details see:

https://www.youtube.com/watch?v=dEaecUuEqfc

http://www.flownet.com/ron/QM.pdf

Re: The quantum source of space-time

#37

Post by semi-extrinsic »

contravariant wrote: post #30
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…

Well, with these kind of articles you can usually safely replace "physicists" with "some physicists". Anyway, the part that I know, and which is well established, is that there seems to be a correspondence between a d+1 dimensional quantum gravity theories, and d dimensional quantum field theories (e.g the standard model). A while ago this was still purely conjecture, but Maldacena showed that this correspondence was…

I believe Maldacena's 1999 paper [1] proving the AdS/CFT correspondence is the most cited in theoretical physics in the last 50 years. It's an incredibly nice result that is almost impossible to explain to laymen. (You did a pretty good job.)

[1] https://scholar.google.no/scholar?cluster=132568844183140142...

Re: The quantum source of space-time

#38

Post by mrob »

kgwgk wrote: post #35
mrob wrote: post #33

Earlier quoted context omitted.

>It is that spacetime which is curved rather than just space. This is the crucial point that many discussions overlook. The concept of "curvature of space" is obvious nonsense because curvature is measured with respect to space. For space itself to curve implies the existence of meta-space (and as many nested metaspaces as you like). But "spacetime" does not work like "space", and there actually is no metaspace. Talk…

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.

Re: The quantum source of space-time

#39

Post by Confusion »

lisper wrote: post #29

"Entanglement lets the measurement of one particle instantaneously determine the state of a partner particle, no matter how far away it may be" No. No! No!!! This meme has really got to die. A measurement of one entangled particle does NOTHING to the other particle. Its state is exactly the same as it was before. In fact, the whole concept of "before" and "after" a remote measurement doesn't even make sense because i…

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.

Re: The quantum source of space-time

#40

Post by semi-extrinsic »

lisper wrote: post #36
zby wrote: post #34

Earlier quoted context omitted.

'determine' does not mean 'change' - does it?

The issue is not so much with the word "determine" as it is with the word "instantaneously". You could say "Entanglement lets the measurement of one particle instantaneously frob the state of a partner particle" without knowing or specifying what the word "frob" means and you'd have the same problem: you're claiming that measuring one particle does something to the other particle, and does it instantaneously and, mor…

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
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