Quantum foam and discreteness of spactime for an idiot

[PianoDentist]

Hello,

Im doing an essay on time travel, and as of yet have done nowhere near enough mathematical stuff to be able to grasp the mathematics behind these concepts.

but anyway I was looking at wormholes and I think I am right in that in quantum foam you get loads of little wormholes among other stuff.

What was confusing me was I've read people say this stuff is totally real, but then at the same time say at this scale space and time cannot be defined. how can something that can't be defined be real? am I just confused or should I stop using youtube for research?

and if spacetime is quantised or whatever, does this mean that quantum foam isn't really there, would the minimum size? of spacetime be big enough that you never saw all the tiny wormholes and tiny universes and stuff?

thanks in advance for any answers

 

[Careful]

Hello,

Im doing an essay on time travel, and as of yet have done nowhere near enough mathematical stuff to be able to grasp the mathematics behind these concepts.

but anyway I was looking at wormholes and I think I am right in that in quantum foam you get loads of little wormholes among other stuff.

What was confusing me was I've read people say this stuff is totally real, but then at the same time say at this scale space and time cannot be defined. how can something that can't be defined be real? am I just confused or should I stop using youtube for research?

and if spacetime is quantised or whatever, does this mean that quantum foam isn't really there, would the minimum size? of spacetime be big enough that you never saw all the tiny wormholes and tiny universes and stuff?

thanks in advance for any answers

You ask many questions ! Concerning the issue of time travel itself, one should start at the beginning. Let us first ask this question within the theory of general relativity, there has been written a great deal about this and I can recommend you the following paper http://arxiv.org/abs/gr-qc/0109029 by Krasnikov as well as other papers of his on the same issue. Now, in classical GR there is no grandfather paradox since there is no free will but in quantum mechanics there is, so one need further insights here; there is a beautiful little paper about that in the book Quo Vadis quantum mechanics which can also be found here http://arxiv.org/abs/quant-ph/0506027. Now, all this has nothing to do with quantum space time; the kind of causal loops which might come about in a quantum theory of gravity are microscopic tiny ones.

Regarding your more philosophical questions about the meaning of quantum spacetime, I can only say that it has no meaning, period. If you speak french, there is a nice video on youtube from Tibault Damour explaining several of these things.

Careful

 

[PianoDentist]

You ask many questions ! Concerning the issue of time travel itself, one should start at the beginning. Let us first ask this question within the theory of general relativity, there has been written a great deal about this and I can recommend you the following paper http://arxiv.org/abs/gr-qc/0109029 by Krasnikov as well as other papers of his on the same issue. Now, in classical GR there is no grandfather paradox since there is no free will but in quantum mechanics there is, so one need further insights here; there is a beautiful little paper about that in the book Quo Vadis quantum mechanics which can also be found here http://arxiv.org/abs/quant-ph/0506027. Now, all this has nothing to do with quantum space time; the kind of causal loops which might come about in a quantum theory of gravity are microscopic tiny ones.

Regarding your more philosophical questions about the meaning of quantum spacetime, I can only say that it has no meaning, period. If you speak french, there is a nice video on youtube from Tibault Damour explaining several of these things.

Careful

thanks, I'll have a look at the links later.

I'd been reading some book which said it may be possible for some advanced civilisation to use inflation to increase the size of these mini-wormholes. sounded like bollocks to me but I thought I'd discuss it if there was space.

I nearly did my essay on the physics of free will, but decided against it as I also have to do a 15 minute presentation and didnt think the topic area was wide enough to fill all that time...still a very interesting area.

 

[Careful]

I nearly did my essay on the physics of free will, but decided against it as I also have to do a 15 minute presentation and didnt think the topic area was wide enough to fill all that time...still a very interesting area.

I don't know if physics of free will is the correct word. If you want to hear interesting views on these issues, there are very good videos about this on youtube figuring Hans Peter Durr and Ilya Prigogine. There are some in english, most of them are in french and german however...

These ones of Prigogine are in english , and .

Careful