T om eone of the best movies made that cn show the "Issues" with TIME TRAVEL if it was ever able top be done would be TIME COP, and showing the need of a force to basically police TIME and make sure people werent altering or making profit off the past.

But I agree, To m e time is something that I think cant be bent or changed, And if people have come from the future and visited the past of course we wouldnt have any history of it, They woul dnot wanna be seen or known that they are not from a time that they are in. The would dress in the clotes of the era, etc and just observe. I highly doubt they would announce themselves to the people around them.

The Philadelphia experimant though is a very interesting test that was done, what they ACTUALLY where trying to do wont ever be known unless you have access to the info but something did happen that was not expected or planeed, when a whole ship vanishes and then comes back with burned bodies, Whatever they did try I think altered TIME around the ship and did something for sure.