According to Einstein's theory of relativity, if you travel faster than light, time would slow down so I could go into the future. But how do I come back from the future? Is there any science proving I could somehow come back from the future and not be stuck there forever?
The faster you travel the faster outside time is for you and slower it is for you locally. If you travel at the speed of light everything happens instantly for you.
That means that if a photon is emitted from the sun, from our perspective it takes 8 minutes to get from the sun to us, but from its perspective that journey happened isntantly.
Now if you go FASTER than light, mathematically, it is interpretted that you start going backwards in time. I am not read up on how the equation bares out but I would assume the faster you go the faster you travel back as well till you hit the same point where you travel so fast all of time is an instant.
Consequences of this is that it a theory that anti-particles are traveling back in time which if true, your ship/person would become anti-particles and it would go boom.
Another 2 ways to travel back in time that is being worked on are Wormholes. If you take a wormhole, open it up and then hold one end and throw it out and then have it come back on side is connected to Time A and the other to Time B and you simply need to go in one end and out the other. Similarly you can use a massive gravity well which is being experimented with.
The problem with both of these, supposing you could get them to work for a human or ship is that you can only go back as far as when the time gate/machine first was able to successfully work. So if these were created in 2020, you went to 2100 and wanted to come back, you could (if the machine was active that whole time) go from 2100 to 2020, but you couldn't go to 2000.
Further, with the Wormhole version you can only go back the set interval. For example, if it was created in 2000 and the other end was in 2050 you could only travel 50 years forward or back (on 1 trip) and only as far back or forward as it was maintained. So if you want to get to 2025 from 2100, you'd have to go back to 2050, then 2000, then wait for 25 years, or conversly wait 25 years and then travel back to 2075 and then 2025. This isn't a problem if you can travel fast though, because you can just travel forward in time to the time interval needed and just go back then.