The question as to whether time travel is actually possible is one of the most enduring in science.
Imagine if we could go back in time, visit key moments in history, perhaps even prevent certain disasters from happening.
Or we could travel far into the future and see what ultimately becomes of the human race.
For some, these concepts are a dream come true, while others might believe that even if time travel is really possible, the past and future should be left alone.
Why do we only travel forward in time?
But I suppose if we think about it, we do appear to travel in time, as we live from day to day.
Which begs the question: if time is one of the four dimensions of the Universe, why can we only travel forward in time?
It’s true that we live in four dimensions, with three dimensions of space and one of time.
However, the time dimension is different to the three space dimensions because of the way we choose to define it and the way the Universe is constructed.
Nevertheless, one of the remarkable features of physics is that travel into the past does appear to be possible.
According to Einstein, time flows more slowly in stronger gravity.
Imagine two people, one on Earth and the other near a black hole, where time flows more slowly because of the stronger gravity.
We view them on Monday, but by the time the person on Earth reaches Friday, the person near the black hole has only reached Wednesday.
If there was a bridge between the two – Einstein’s theory permits one known as a wormhole – it would be possible for the person on Earth to travel back from Friday to Wednesday.
That would effectively mean it was indeed possible to travel back in time.
