And as for time, that's sort of the point of the Fermi paradox, with this much time there should be evidence of life everywhere, unless you have an unstated assumption that all life is self terminating before it reaches a point where it can leave much of a galactic mark? (In our case then, probably excitingly soon)
Charles Stross has pointed out that interstellar travel is probably prohibitively expensive, so any marks left by other civilizations might have been purely local. How many marks have we left? You'd have to do a pretty thorough search of the other planets and moons to find our various landers - hell, it wasn't until last year that anyone took recent pictures of the American moon landing sight, right? A Japanese satellite, if I remember correctly.
Here's a gedankenexperiment for you. Hire a pilot to fly you from Dallas to El Paso. As you're flying over the panhandle, jump out with a parachute. What are the odds that you'll see signs of civilization? I've made that drive before, and if it weren't for the road that I was on, I'd have sworn the planet didn't even have any vertebrates on it.
Obviously my argument is founded on a current understanding of physics, and I'd love to sound like an idiot tomorrow with the invention of cheap interstellar flight and an ansible.
Ironic you should say: from HN this morning: Researchers 'speak' to dolphins in their own language http://news.ycombinator.com/item?id=3314056
:)
And as for time, that's sort of the point of the Fermi paradox, with this much time there should be evidence of life everywhere, unless you have an unstated assumption that all life is self terminating before it reaches a point where it can leave much of a galactic mark? (In our case then, probably excitingly soon)