Is time travel possible? Of course it is…into the future. You and I are travelling in time right now. And travelling into the far future also is also a reality using Einstein’s principle of time dilation when you travel at high speeds or are near a really high gravity source.
If you travel at nearly the speed of light, your time could slow so much that a day for you may be 10 years on earth.
What doesn’t appear to be possible is travel into the past. So if you did travel into the future, you wouldn’t be able to come back to your previous time. Time travel into the past presents paradoxes, the most famous of which is the “grandfather paradox” where a traveler goes back in time, and murders his own grandfather. This alters the course of history in a way that the traveler couldn’t have been born to travel back in time to kill his grandfather.
These paradoxes cannot exist in nature according to the Hawking chronology protection conjecture. So the idea of time travel as your current self is likely not possible.
However, going back to a past version of yourself cannot be ruled out. This means that using any technology to go back to your past would bring you back to a younger version of yourself, but you would not know that you had travelled back in time.
The events that took place during that earlier time would play out EXACTLY like they did as before.
Now, this would not be much fun because you would just be reliving a past that would be no different, and you would simply relive it exactly as you did before. You could not change anything because it is already written in stone, and no information or knowledge would have travelled back with you.
It turns out this type of travel back in time is theoretically possible, and there are three methods to do this.
1) Caroline Mallary a phD student at the University of Massachusettes, Dartmouth proposed this. You would take two long spaceships and park them in parallel.
One car moves forward really fast, while the other is parked. A time loop forms between the two cars such that space and time folds on itself.
You also need to have a special kind of matter in the two cars, consisting of infinite density. In other words you would need a bare and observable singularity. A point in space with such a huge density that it breaks through the fabric of space and time. Of course, we don’t have a way to create such a singularity, or know whether this kind of singularity even exists.
2) Professor Ben Tippett at the University of British Columbia worked out a theoretical way you could travel back in time. His math is based on Einstein’s theory of general relativity. Since massive objects can bend space and time, they cause the space time fabric to curve.
His time machine uses this concept of bending the fabric of space-time to an extreme degree such that it forms a circle instead of just a bent fabric. That circle could take us back in time.
To build his time machine we would need a theoretical particle known as negative matter – which has not been found yet.
Tippett calls his time machine, “Traversable Acausal Retrograde Domain in Space-time” or TARDIS – From Dr. Who.
3) This is from the master himself. Einstein said that if it were possible to travel faster than the speed of light, then it would be equivalent to travelling back in time.
It turns out that Einstein’s equations apply to speeds slower than the speed of light, as well as speed faster than the speed of light. They just break down AT the speed of light.
In fact, the reason we are seemingly limited to stay below the speed of light is because as you approach the speed of light, according to his equations, time slows down. And it stops completely at the speed of light, and forms a singularity.
However, if you could somehow break this speed barrier, like Chuck Yeager broke the sound barrier, then you would find yourself travelling back in time.
There is nothing in Einstein’s equations that precludes the backward trajectory of time. All the equations of physics would apply whether time was flowing forward or backward.
Or let’s make it really simple…how about someone from the future…where I’m sure they’ve figured this out …could come back, and show us how to build a time machine. So what if that causes a paradox and destroys the world, at least I would get to kick that 3rd grade bully’s ass.
