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Closed timelike curves 
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#1
Jul611, 04:41 AM

P: 157

do they exist in reality or in nature?



#2
Jul611, 09:58 AM

Emeritus
Sci Advisor
PF Gold
P: 5,597

We have no evidence that they exist in our universe. There is also a conjecture, which I think is widely considered plausible, http://en.wikipedia.org/wiki/Chronol...ion_conjecture that a spacetime that doesn't already have CTCs can't acquire them.



#3
Jul611, 03:21 PM

P: 157




#4
Jul611, 03:26 PM

Emeritus
Sci Advisor
PF Gold
P: 5,597

Closed timelike curves



#5
Jul711, 12:02 AM

P: 157




#6
Jul711, 06:31 AM

P: 608

http://arxiv.org/PS_cache/arxiv/pdf/...708.2324v2.pdf though this is technically a hypothesis (CTCs) within a hypothesis (Cauchy horizon) within a theory (black hole/event horizon). The CTCs are also within a boundary called the turnaround radius which some predict is supposed to send an infalling object out through a (very hypothetical) white hole http://casa.colorado.edu/~ajsh/phys5770_08/bh.pdf (page 23) so even at this level of prediction, there seems to be some level of protection from reaching the CTCs (though a white hole would be just as elusive as CTCs, it's normally best to say that the Cauchy horizon is the barrier of predictability). 


#7
Jul711, 07:30 AM

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P: 7,620

The Kerr Newman metric is probably unlikely to exist in our universe, though  it's basically idealized and inherently unstable. From what I've read it's so unstable that it can't selfconsistently describe a single particle falling into the inner horizon  such a particle would acquire infinite blueshift, infinite energy  and distort the geometry into something that wasn't a Kerr Newman metric.



#8
Jul711, 11:21 AM

Emeritus
Sci Advisor
PF Gold
P: 5,597

Here are some good review articles on CTCs:
http://plato.stanford.edu/entries/timetravelphys/ http://arxiv.org/abs/0710.4474 http://philsciarchive.pitt.edu/archive/00004240/ 


#9
Jul711, 06:58 PM

P: 157




#10
Jul711, 07:11 PM

Sci Advisor
PF Gold
P: 5,059

An exact, symmetric, treatment says if 10 hunters in a circle fire toward the center at the same time, you get a metal ball stationary in the center. You want to try this some time? Pervect is saying the Kerr metric is idealized in a similar sense. Presumably, even less likely than the proposed method of manufacturing ball bearings. 


#11
Jul711, 09:23 PM

P: 157




#12
Jul711, 09:35 PM

Emeritus
Sci Advisor
PF Gold
P: 5,597

PAllen's example of the hunters exists as a solution of Newton's laws, but it has never happened on our planet. 


#13
Jul811, 01:57 AM

P: 157




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