It’s a worry of time travelers everywhere. What if they go back in time and do something terrible, like prevent their parents from meeting or killing their grandfather? Such a time-traveling “oops” could prevent them from ever being born. Therefore, they would have never existed to travel back in time in the first place.
This “grandfather paradox” has had want-to-be time travelers scratching their heads ever since we dreamed of traveling back in time. Does this mean that time travel is not possible? Does it mean that each decision we make creates several different branching worlds? This conundrum may have been cleared up (at least mathematically) by fourth-year undergraduate student Germain Tobar of the University of Queensland.
Time Travel and Philosophy
One way to solve the grandfather paradox? Time travel isn’t possible at all.
This is probably the easiest, yet least fulfilling, of potential solutions. Time travel isn’t possible, let’s wash our hands of any possibility and forget about it. And this very well may be the case.
However, in general relativity, things called closed time-like curves can exist, and are a way to solve general field equations. It’s like stepping on a train, taking a wonderful trip through the mountains, and returning to the same spot you left off, both in space and in time. That means the moment where you step off the train is both in the past and future of when you got on the train in the first place. In a closed time-like curve, an object returns to the same place and time that it was in the past, completing a loop. It’s unclear if closed time-like curves exist in our universe, but if they do, mathematically, they would allow for time travel.
Then there’s option two. In this quantum mechanical model, each choice opens up another universe. If time travelers changed something in the past, they would enter another parallel universe. The original timeline would still exist, one among many branching worlds. In such a model, it might be very hard for time travelers to return to the universe they came from.
Finally – time travel is possible, but time travelers can only do certain things. A time traveler who went back in time, for example, could not kill Hitler, no matter what he tried. This raises all sorts of philosophical problems – does the time traveler still have free will? It’s difficult to say time travel is possible while simultaneously destroying freedom of choice.