Time travel is happening all the time; even as you are reading this article, time is travelling around you and causing you to age by the minute. If you were cryogenically frozen, you would cease to age, proving that time travel and its effects are happening to you and not the other way around.
Relativistic time dilation via the Twin Paradox is a good example of “time travel”. An experimental demonstration of this requires two twin brothers, with one travelling into space at the speed of light and the other staying on earth. Time travels at different rates relative to where you are and if both brothers are the same age when the experiment begins, then the brother that remains on earth will be biologically older than the space-faring brother, even though the passing of time has remained constant for both of them in their respective worlds. This demonstrates the possibility of time travel (though not a physical movement through the time-space continuum; this isn’t Doctor Who after all). However, travelling at the speed of light would require an exorbitant amount of energy and any vehicle travelling that fast would probably be destroyed.
The Grandfather Paradox disproves the notion of time travel via a sequence of causal events. If you were to go back in time and kill your grandfather, preventing him from having one of your parents and thus hindering your parents from having you, how would you even be born to perform the action in the first place? Another popular argument against limitless time travel is that even if a time machine were built, the furthest place you could travel back to is the point in time where you created the machine in the first place.
The concept of our universe having a chronological ‘beginning, middle and end’ is subjective, constructed by the human mind to categorise the world around us into terms that are fathomable. Our perception is compromised by the fact that we ourselves are ensconced in time and therefore cannot observe it objectively. Time travel may be possible because, even though time is fixed, it can move forward at different rates. Whilst travelling through time may not be as tangible as travelling through, let’s say, Spain, time can be manipulated to produce a different effect from the one it normally exhibits, eliciting “time travel”.
(Image courtesy of Robert van der Steeg)