As WOH pointed out, one hypothesis says you can only go back as far as when a species learns to time travel, and your analogy is spot on!
Stehen Hawking tried to test this, and left invitations for time travellers from Cambridge to join him for afternoon tea and discussion. No kidding. He set up the tea and goodies, and waited, and nobody showed up. That seems to indicate that at least contact is not something that is likely to happen, and just might support the above notion!
This is the methodology. Break it into little pieces, and see what we can lay out on the table.
LINK - The party that didn't go off with a Big Bang: Stephen Hawking held a party for time-travellers - but no-one turned up..
'Einstein's general theory of relativity seems to offer the possibility that we could warp space-time so much that we could travel back in time.
'However, it is likely that warping would trigger a bolt of radiation that would destroy the spaceship and maybe the space-time itself.'
Still, if at some time in the future (or back in the past), you find yourself talking to Prof Hawking at a party, you may ask him his views on people who have seen UFOs.
The response he gave to Ars Technica is: 'Evidence that intelligent life is very short-lived is that we don't seem to have been visited by extra terrestrials.
'I'm discounting claims that UFOs contain aliens. Why would they appear only to cranks and weirdos?
You think I am confusing? Read the above, and then this.
All you need is a wormhole, the Large Hadron Collider or a rocket that goes really, really fast
Hello. My name is Stephen Hawking. Physicist, cosmologist and something of a dreamer. Although I cannot move and I have to speak through a computer, in my mind I am free. Free to explore the universe and ask the big questions, such as: is time travel possible? Can we open a portal to the past or find a shortcut to the future? Can we ultimately use the laws of nature to become masters of time itself?
Time travel was once considered scientific heresy. I used to avoid talking about it for fear of being labelled a crank. But these days I'm not so cautious. In fact, I'm more like the people who built Stonehenge. I'm obsessed by time. If I had a time machine I'd visit Marilyn Monroe in her prime or drop in on Galileo as he turned his telescope to the heavens. Perhaps I'd even travel to the end of the universe to find out how our whole cosmic story ends.
To see how this might be possible, we need to look at time as physicists do - at the fourth dimension. It's not as hard as it sounds. Every attentive schoolchild knows that all physical objects, even me in my chair, exist in three dimensions. Everything has a width and a height and a length.
Is it possible or not? Even the smartest man in the world can give you both sides of that coin.
Edited by psyche101, 31 January 2013 - 01:18 AM.