Have you ever wished you could go back in time to right a wrong, to make a different decision or even completely alter the course of history? Time travel is a tricky business, especially when escaping to the past. But is it even possible? And if it is, could we ever do it?
Traveling into the Past
It turns out that we time travel all the time. As we experience our lives here on Earth we are constantly moving into the future. Unfortunately, we have little control over how quickly time passes.
But what about traveling into the past? According to Einstein's theory of relativity, time only flows in one direction: forwards. If time flowed the other way, we would remember the future instead of the past. (Weird, huh?)
So on the face of it, it seems that traveling into the past would be a violation of the laws of physics. But not so fast.
Black holes, Wormholes and "Looking-glasses"
In the famous tale Alice in Wonderland our heroine falls into the "looking-glass" and is whisked away to a strange land. In some ways, this is a prime depiction of what time travel may look like.
The idea of building a time machine, like those often depicted in science fiction films, is likely the stuff of dreams. But one could possibly harness the power of a black hole to venture through time and space.
Once thought to be completely unstable, and therefore un-traversable, recent advances in physics theory has shown that these constructs could, in fact, provide a means of traveling through time. Though we have almost no idea what to expect by doing so.
Theoretical physics is still centuries away from being able to predict what would happen inside a wormhole, assuming one could even approach one. And even then, we are even further behind from an engineering perspective in terms of attempting such a feat.
But, if it were possible to pass through a wormhole, it would probably be a lot like Alice falling through the rabbit hole. Who knows what we would find on the other side.
Causality and Alternate Realities
The idea of traveling into the past raises all sorts of paradoxical issues. (Here is a great rundown of some of the issues, as described by eminent astrophysicist Michio Kaku.) For instance what happens if you go back in time and kill your parents before you are born?
The common solution to this problem is that you effectively create an alternate reality, or parallel Universe. So if you did travel back and prevent your birth, a younger version of yourself would never come to be in that reality. But the reality that you left would carry on as if nothing is changed.
By going back in time, one would create a new reality. And would, therefore, never be able to return to the reality they knew before. (If they then tried to travel into the future, they would see the future of the new reality, not the one they knew before. Confused yet?)
Warning! This Next Section May Make Your Head Spin!
There brings us to another issue that is rarely discussed. The nature of wormholes is to take you to a different point in time and space. So if a traveler left Earth and traveled through a wormhole, they could be transported to the other side of the Universe (assuming they are even still in the same Universe we currently occupy). If they wanted to travel back to Earth they would either have to travel back through the wormhole they just left (bringing them back, presumably, to the same time and place), or journey by more conventional means.
Assuming the travelers would even be close enough to make it back to Earth in their lifetimes from wherever the wormhole spat them out, would it still be the "past" when they returned? Since traveling at speeds approaching that of light makes time slow down for the voyager, time would proceed very, very quickly back on Earth.
So while they exited the wormhole in the past (relative to time on Earth), by being so far away it's possible that they wouldn't make it back to Earth until after they left! This would negate the whole purpose of time travel all together!
I warned you that time travel was confusing.
So, is it Really Possible?
Possible? Yes. Probable? No, at least not with our current technology and understanding of physics. But perhaps some day, thousands of years into the future, man could harness enough energy to make time travel a reality. But until that time, it will just have to stay regulated to the pages of science-fiction.