Hi, I've been watching a few of those time traveller footages on the internet ie: the woman talking on a mobile in the 1928 Charlie Chaplin film. I have a few plausible theories that make sense. 1) it could be modern computor enhanced trickery. 2) The film director's deliberately put an extra talking on what they may of believed would be the phone of the future. We do it all the time in our films, we use scfi props.. 3) There is a parallel advanced planet to Earth and we were visted by Human's but not of our planet. Time travel is possible in theory but only through actual space travel we would have to cross the solar system to then return back to Earth.. To travel back to the past would not be possible as the past does not exsist in the sense that we could not build a machine to alter time to take us back. Although it may be possible to travel through our subconscious ie: whilst we are hypnotised or sleeping, but I am not sure if we would be visible to the people in the time we have travelled back too.