Brian Greene, professor of physics and mathematics at Columbia University and co-founder of the World Science Festival, presents what is known about time travel by now.
There are two kinds of time travel which are drastically different. According to Greene, time travel to the future is absolutely probable.
More than hundred years ago Einstein showed us that if you travel in space approximately with the speed of light and return, then your clock will be counting time more slowly. Thus, when you come out it will be the future on planet Earth.
Einstein also demonstrated that if you hang out close to a strong source of gravity – a neutron star or a black hole – and somehow you approach the brink of that object, time would slow down for you. And that is why when you return to Earth, it will again be remote future.
But many oppose to the idea that the other kind of time travel - to the past is possible. The key suggestion that people regard unworthy of attention for traveling to the past is the strange idea of so called wormholes, also discovered by Albert Einstein.
It’s some kind of a bridge, or a channel from one place to another. Einstein made this discovery in 1935, but it was afterwards found out that if you handle the openings of a wormhole – put one close to a black hole or take one on a high-speed travel – then time of the two openings of this wormhole channel will not take off at the identical speed, and you will not simply move from one place to another, but you’ll move in time, depending on the direction, to the past or to the future.
But then again, it is not proven that wormholes exist, and if they exist, if one will be able to pass through them. Although it is generally accepted that time travel in the past is impossible, this option is still not eliminated.