Think about this, Stephen Hawking!

My housemate was watching Yellow Submarine yesterday. As I was going to shower I started to listen to the movie too. I heard the thing about time travel in the movie while I was shaving in the bathroom. They got smaller and smaller as they went back in time. Also their moustache vanished. As they went back to the future (or present time) they grew back. (Both, the Beatles and their moustaches.)

This made me think. If you would shave your face, then travel back in time and you get younger and younger. When you go past (or before, however you wanna think about it) your puberty and your hair growth stops, you stop the time travel there. Then travel back to the future, or the present, anyways, to what now is now.

Does your beard, fingernails and hair grow that long as you would never cut them before?

And if they grow, where does the energy come from? Otherwise, the energy to grow back must be there somewhere when you are young (but where?), but as you have cut fingernails and hair along your live, the matter is lost - where does the energy come from when you travel back to your own time? I think you might be quite hungry then.

Hm.. Maybe this could be a perfect weight-loss treatment. Go back in time, then travel back into the present and transform fat into hair and fingernails and simply cut the extra fat off like hair.

Also, as H. G. Wells wrote in "The Time Machine" (1895), you can't change the past. As in, you can't just check the lottery numbers and go back in time to tell them to yourself. Since from where you came, it didn't happen.

You can meet your friends in the past, like in The Time Machine. So can you meet yourself, like Hunter S. Thompson in a club in San Francisco? If you can, can you shake hands with yourself, or do you vanish, like in van Damme's Time Cop? And if you vanish, where does the matter go? And if you can meet yourself, shake hands with your self and have a conversation with yourself, do you remember shaking hands with yourself twice when you go back to your own time from the past? (1st time in the past, 2nd time when you travel to the past.)