According to the General Theory of Relativity Wormholes and thereby limited Time Travel is possible.

According to Stephen Hawking Wormholes are very vulnerable to feedback. He also came up with the chronology protection conjecture that basically says physics will not allow time travel.

So I'm going to write an exploration of the idea that Time Travel can only happen if no parodox will occur as a result.

If you attempt to enter the wormhole to go back and a parodox will result then the wormhole begins to destabilize. If you insist on going the wormhole will collapse, preventing your transit.

So scientists have a working Time Machine that they can't use. Apparently parodoxes are very easy to make. So In desperation the scientists start allowing anyone to try.

The story follows the one person who is able to make the trip.