If someone was from the future, how could they prove it? They can't it is impossible to prove. Anything they say can be shot down by some other explaination. Even it you had them write you a history book before it happened and then compared it as time went along, you could say that either they are psychic or just lucky. Even a high tech device from the future or even the time machine itself can be hoaxed by a brilliant mind. The only way to prove time travel is to do it yourself on your own. Even then you wouldn't be able to prove it to anyone else. Good luck.