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## Main Question or Discussion Point

If QM requires a constant universal time, does this rule out closed time-like curves?

- Thread starter Endervhar
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If QM requires a constant universal time, does this rule out closed time-like curves?

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Quantum mechanics involves wave equations, which are differential equations. Differential equations are local things, so there is no problem with stating them in a space that has unusual global properties.

You might have issues, for example, with constraints that prevent the existence of solutions for certain boundary conditions. But this isn't a specifically quantum-mechanical issue. You get the same issue classically. This is basically just the grandfather paradox.

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I was re-reading an article from New Scientist 10 June 2006; Marcus Chown's "Do the Cosmic Twist" and I recalled that I had been puzzled by the following first time round:

"The trouble is, quantum theory requires time to be "universal" - there should never be closed loops of time isolated from the time in the rest of the universe".

Information about quantum time always seems to contain a lot of off-putting equations, so I was hoping for something a bit less technical.

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The part about "isolated from [...] the rest of the universe" may be what's relevant, but I can't tell what he's talking about just from the isolated quote. Unfortunately the article is paywalled, so it's going to be difficult for anyone here to puzzle out what he really means.I was re-reading an article from New Scientist 10 June 2006; Marcus Chown's "Do the Cosmic Twist" and I recalled that I had been puzzled by the following first time round:

"The trouble is, quantum theory requires time to be "universal" - there should never be closed loops of time isolated from the time in the rest of the universe".

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No.

But you could post a quote from it with enough context for us to see what he's saying.

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Marcus Chown’s Article. Looking at the work of Pawel Mazur and George Chapline.

Almost everything we see in the universe rotates, yet most cosmologists believe the cosmos does not rotate.

GR seems to require the universe to look the same in every direction. Obviously, an axis of rotation (although not prohibited in itself) would give the universe a preferred direction.

The article goes on to describe spinning cosmic strings and the formation of CTCs.

M & C developed the idea that GR breaks down in

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Chown doesn't seem to have posted any papers on arxiv.org.

Pawel O. Mazur has: http://arxiv.org/find/gr-qc/1/au:+Mazur_P/0/1/0/all/0/1

These seem relevant:

http://arxiv.org/abs/0911.2326

http://arxiv.org/abs/astro-ph/0509230

http://arxiv.org/abs/gr-qc/0407033

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Bill_K

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The various developments of quantum field theory in curved space-time have left the false impression that general relativity and quantum mechanics are compatible as long as one considers the length scales well above the Planck length [p. 2]

From http://arxiv.org/abs/gr-qc/0407033 :It turns out that certain predictions of classical general relativity such as closed time-like curves and event horizons are in conflict with a quantum mechanical description of space-time itself. In particular, a quantum mechanical description of any system requires a universal time. In practice, universal time is defined by means of synchronization of atomic clocks, but such synchronization is not possible in space-times with event horizons or closed time-like curves. [p. 2]

They describe the conventional wisdom, and say the conventional wisdom is wrong. However, they don't seem to give any explanation of what they think is wrong with the conventional wisdom.The various developments of quantum field theory in curved space-time have left the false impression that gen- eral relativity and quantum mechanics are compatible. Actually though certain predictions of classical general relativity such as closed time-like curves and event hori- zons are in conflict with a quantum mechanical descrip- tion of space-time itself. In particular, a quantum me- chanical description of any system requires a universal time. In practice, universal time is defined by means of synchronization of atomic clocks, but such synchroniza- tion is not possible in space-times with event horizons or closed time-like curves.

Their claim that event horizons are automatically incompatible with quantum mechanics seems to me to be something that is clearly not accepted in general.

This may have something to do with the fact that in quantum mechanics, time is not an operator, but simply a parameter.

I'm going to ask that thread be this be moved into Beyond the Standard Model, where I think we can probably get more competent answers than I would be able to provide.

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Uh oh. My kook alarms were already going off, but now they're really, really going off.On the other hand, he doesn't believe in black holes!

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There is no suggestion in the article that either Mazur or Chapline doubt the existence of black holes. In fact the bit about CTCs forming around cosmic strings is followed by:

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But: http://www.nature.com/news/2005/050328/full/news050328-8.htmlThere is no suggestion in the article that either Mazur or Chapline doubt the existence of black holes.

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