Visit this site and print out the form once you’ve decided on a time and place to return to from the future. This way, we can show everyone that time travel is (will be?) possible. Seriously, though, this particular argument is perhaps the most convincing proof that time travel is impossible; I think Stephen Hawking said that the main argument against the possibility of time travel is that we haven’t had any time travellers from the future visit us. Or have we?