but that's not the same thing as saying we will ever know everything, or even that we will know everything there is to know.

Some things are probably fundamentally unknowable, or at least, fundamentally unprovable. That's what Godel showed us in mathematics, that there are some true propositions that can not be proven to be true.

I suppose there is no reason we can't survive forever as a civilization, perhaps that is our destiny, to spread out across the universe. But even if that is the case, we will surely change to the point of unrecognizability.

Will we physically evolve into a different biological form, or into many? Will that evolution be natural, or directed? Will our machines take over from us? Personally, I don't think so. Our record of progress and growth is remarkable, but it has been so short, so recent, and so long in getting started it would be foolish to think it must continue indefinitely. It's like saying, "My tooth stopped hurting a few seconds ago, so I don't need to go to the dentist." I believe our future as a species will run out in about a million years. Several million years seems to be about average for most species, and if we are different, it is just as likely our adaptability and aggressiveness will be a liability as it is an asset. Of course, I have no way of proving that, either way. Some things we'll just have to wait and see.

The Romans and the Greeks died out, too, but much of their civilization still survives, in many forms; law, language, architecture, knowledge and ideas, art and philosophy, technology and culture. If they had never existed, the world would be very different. Other civilizations, like the Chinese, came from other roots, and we can see how different they are.

We are tending to become homogenized, the same, and this is why I believe space travel is so important to our species. As the world becomes smaller, we are becoming more similar, more uniform. Amongst the stars, the distances between us will keep us separate, and diversity will be preserved. We will not become the same, and we will evolve to meet local conditions and to respond to our isolation. By forcing us to become different from our colonies, some of us will survive, no matter what happens to the universe, or in it. And who knows, perhaps one day, in the far distant future, our expanding sphere of inhabited worlds will intersect another, one from another place and another time.