Space curvature allows time travel to the past!

[Gamish]

Is it true that space can be curved around and loop itself to a point in the past? If this is true, then time travel to the future and the past should be theoreticly posible. I'm trying to further uderstand relativity, this is why I ask. If we could travel to the past, maybe we can really see the origin of the universe :tongue2:


"There are 3 types of knowledge in the world, knowledge, understanding, imagination."

[pervect]

The possibility that wormholes in General Relativity might act as time machines is still an unresolved issue, though last I heard the general feeling was that quantum gravity would _probably_ prevent this. Since nobody has a definite theory of quantum gravity yet, there's a lot of room for argument over what quantum gravity would or would not prevent. The main issue is that quantum vacuum fluctuations are predicted to occur which are likely to destroy any wormhole which attempts to become a time machine.

There are some theorems in GR which prohibit finite sized time machines without "exotic matter", which is matter with a negative energy density. (Dark energy would also do, in a pinch as far as satisfying the theoretical requirements).

[Gamish]

So do worn holes curve space? And if so, what is "Curving of space" anyway? As far as I know, time can be slowed through the warping of space, but what is a "curvature"? :wink:

[Nereid]

So what is warping if not curvature?

More generally, worm holes are nice implications from theory, but as pervect said, without a theory of quantum gravity, and no pertinent observational (let alone experimental) results whatsoever, they must remain rather speculative for now. But to answer your question, worm holes (should they exist) most definitely would 'curve space'!

[Rob Woodside]

Wormholes tell you how spacetime is connected and curvature tells you how it is bent. Wormholes are topological invariants, curvature is not. You can mathematically cut and paste flat space-times to make all the wormholes you want. (Is space-time a material substance that can be cut and pasted?) Einstein's equations link mechanical properties such as energy density, momentum density, energy flux, and stresses to curvature. In discussing wormholes the curvature comes from the mechanical properties of the material fields via Einstein's equations. The idea is that these fields can hold up the wormhole and stop it from collapsing. Unfortunately this appears to happen only with exotic fields that have negative energy densities and enormous tensions. The contribution of quantum ideas remains to be seen.