I found this excerpt on the internet and I want to know if it's true:

 

There was paper by Kirt Godel with a scheme for time travel that would work. It simply required that you spin a cylinder half the size of the solar system [close to] the speed of light, but everybody agrees that if you could do that and then travel along its transverse axis, you would be moved backward in time.

 

Is this true?

It is true that the Godel metric has closed time-like curves.

 

For more details you should have a look at a good book on general relativity.

Yes, I'm familiar with GR.

 

I've also heard that massive rotating objects will not only bend space and time towards itself but will twist them in the direction of their rotation, and that this can somehow create loops in time that could take one into the past. I'm not sure how this works but it sounds similar to the quote above. Is it the same idea?

It simply required that you spin a cylinder half the size of the solar system [close to] the speed of light,

 

Oh, is that all? And here I thought it might be difficult to make...

Space-times that "mix" temporal and angular coordinates tend to have closed time-like curves. So yes, something rotating can create time machines.

Does it have to be that big - or does it just depend on mass? Could you use a a much smaller but very dense sphere - like a neutron star?

i don't think that time travel can be possible. you have to reverse all physical and chemical processes to time travel.

i don't think that time travel can be possible. you have to reverse all physical and chemical processes to time travel.

 

Objects whose world-line is a loop are known as jinn. These were never created and never destroyed. As they get older they need to get younger!

 

Such things are very interesting and seem to break the laws of thermodynamics.

I don't see how this would allow backward time travel. Maybe the slowing of time in that reference frame. Can anyone provide more details?

Edited May 31, 200916 yr by MM6

I don't see how this would allow backward time travel. Maybe the slowing of time in that reference frame. Can anyone provide more details?

 

You mean how rotation creates CTCs?

 

In essence the term [math]dt d\phi[/math] in the metric for a rotating space time makes the periodic angular variable into a timelike coordinate. The Godel and Kerr space-times are typical examples of this.

 

The other typical mechanism for time travel is apparent faster than light propagation. Time machines based on wormholes are of this kind.

i don't think that time travel can be possible. you have to reverse all physical and chemical processes to time travel.

 

- Not all scientists agree but according to Einstein and quantum theory, time travel could be possible