Earlier this month, a NASA satellite detected a stellar explosion so big that it could be seen by the naked eye...even though it happened halfway across the visible universe. The gamma ray burst actually occurred before Earth was even formed--the light from the blast traveled over 7 billion years before it reached Earth.
This is something I need to remind myself whenever I look at the stars. That some of the light I'm seeing has traveled millions of years to reach my eyes. My mind starts to fold in on itself when I try to imagine how far away those stars must be. And then I have to remind myself about all the stars and galaxies and dark matter I can't see.
An article in Scientific American by Lawrence M. Krauss and Robert J. Scherrer has upped the ante of these thoughts for me. They argue that due to the fact that the universe is expanding, there will eventually be a time when distant galaxies will become invisible to observers on Earth. They explain that we live in a very unique time in which astronomers are able to observe evidence that that big bang occured. Scientists of the future may live in a world where that evidence has passed beyond the event horizon. What, then, will astronomers 100 billion years from now be able to observe? And how will that affect their conclusions about the orgins and nature of the universe? Will they think they live in the center of one lone galaxy that makes up the entire universe?
While you're thinking on all of that, you might find the ringtone above from Space helps you keep things in perspective.