Thursday, September 17, 2009

Fun with Space Time

Let's say that you, at age 20 go out on a cloudless night with an immensely powerful telescope, aim it at another, far distant planet 50 light years away. Light, leaving that planet will take 50 years to reach you. At the exact same time, on that far distant planet a member of another sentient species sits out on a cloudless night pointing a telescope back at you. Both of you, looking directly at the spots where each of you are sitting will see nothing. Empty space. Because the light each of you are seeing left that point on the other planet 50 years before each of you got there.

So you see nothing, but, on a lark each of you waves at the nothing you both perceive.

Fast forward 50 years. You're both 70 now, and for fun you both return to the same spot you took your telescopes to fifty years prior. Nostalgically you look back to the same point in space where you once waved to an imaginary alien, an empty spot of soil. Amazingly you now both behold a creature sitting at the spot that 50 years ago was empty. They seem to be young creatures, both peering back at you through a telescope. Excited that your sight-seeing didn't return empty-handed this time you both wave excitedly. And, in seeming recognition of your gesture, the creature on either other end of the telescope waves back.

Of course that wave happened 50 years ago, and was in response to seeing nothing. But, in a sense, there is real contact in the present. At least in the minds of each of our observers. And that's likely the closest we'll come to traveling in time. But it's enough. The farther away we peer into the cosmos, the farther back in time we're seeing. It's very possible that one day we may find another sentient civilization in some far flung part of the universe. But we may be seeing things that happened hundreds or thousands (or hundreds of thousands) of years earlier. By the time we find them, they may already be gone. But we can still watch their past. Observe them as our two stargazers observed each other fifty years in each other's pasts. We can observe but we can't participate.

Time travel is a spectator sport only.

No comments:

Post a Comment