In case you didn’t know it, wormholes are a theoretic conduit through 4-dimensional space-time – not just space according to Stephen Hawking and others. They have posited that wormholes might theoretically be utilized for travel through time in addition to traveling through space. But only to the future and not to the past which they believe will never be possible and the reason is too much potential for paradoxes and self-destructive feedback loops.
Albert Einstein and Nathan Rosen first proposed the existence of “bridges” through space-time in 1935 using the theory of general relativity to explain how two different points in space and time might connect – offering a short cut that could reduce travel time and distance. The phrase was coined (in 1957) by the American physicist John Wheeler. Wormholes are like black holes in that they have never been observed directly.
Some theorists believe that wormholes could be used as a tunnel or short-cut for high-speed space travel between distant points or even for time travel. However most believe that wormholes are inherently highly unstable and would probably collapse in a much shorter time than it would take to get through to the other side.
Here is what Hawking thinks in his own words:
Closely related to time travel, is the ability to travel rapidly from one position in space, to another. As I said earlier, Einstein showed that it would take an infinite amount of rocket power, to accelerate a space ship to beyond the speed of light. So the only way to get from one side of the galaxy to the other, in a reasonable time, would seem to be if we could warp space-time so much, that we created a little tube or wormhole. This could connect the two sides of the galaxy, and act as a short cut, to get from one to the other and back while your friends were still alive. Such wormholes have been seriously suggested, as being within the capabilities of a future civilization. But if you can travel from one side of the galaxy, to the other, in a week or two, you could go back through another wormhole, and arrive back before you set out. You could even manage to travel back in time with a single wormhole, if its two ends were moving relative to each other.
One can show that to create a wormhole, one needs to warp space-time in the opposite way, to that in which normal matter warps it. Ordinary matter curves space-time back on itself, like the surface of the Earth.
However, to create a wormhole, one needs matter that warps space-time in the opposite way, like the surface of a saddle. The same is true of any other way of warping space-time to allow travel to the past, if the universe didn’t begin so warped, that it allowed time travel. What one would need, would be matter with negative mass, and negative energy density, to make space-time warp in the way required.
Via: Stephen Hawking, Space and Time Warps