J. Richard Gott III

GOTT: One of the things we might like to know about is how long the human race is likely to last. We can be helped by determining this by using the Copernican principle. The Copernican principle is named after Nicholas Copernicus who proved to everyone that the earth was not at a special location at the center of the universe. It is simply the idea that your location is not likely to be special. It has been one of the most successful scientific hypotheses in the history of science. It works simply because, by definition, there's only a few special places and many non-special places, so you're more likely to be at one of the many non-special places.

Well, how can we use this to estimate the longevity of something we're observing? Let's say you're observing something that has a beginning and an end on a continuum. The end comes either when it no longer exists or when no one left to see it. If you're not special, you're located somewhere randomly in this interval. That means that there's a 95-percent change that you're located in the middle 95 percent. That's not the first two and a half percent and not the last two and a half percent. Why have I chosen 95 percent here? Well, that's because scientists usually like to make predictions that have a 95-percent chance of being correct, and you have a 95-percent chance of being in the middle 95 percent.

Now, what if you're at the very beginning of this region? Well, two and a half percent is one fortieth of the total line, so if you were sitting right at the beginning, one fortieth is past, and 39/40th's remain in the future. So in that case, the future would be 39 times as long as the past.

But suppose you were way over here at the end? Then 39/40th's has passed and only 1/40th remained in the future. In that case, the future is 1/39th as long as the past. If you're in between these two limits, that means that the future is bigger than the past divided by 39, but not as long as 39 times as long as the past.

Let's apply this to something important that we care about. Our species, Homo sapiens, has been around for 200,000 years. Now, 200,000 divided by 39 is about 5100. If you multiply by 39, you get 7.8 million. So if there's a 95 percent chance that you're in the middle 95 percent of human history, and that means that the future longevity of the human race is at least 5100 years but less than 7.8 million. Those numbers are interesting because they give us a total longevity that's quite similar to other species. Mammal species have an average longevity of two million years. Our ancestor, Homo erectus, lasted 1.6 million years, and the Neanderthals lasted 300,000 years. So this is quite in line with those numbers.

One way we might improve our survival prospects would be to colonize off the earth, giving ourselves more chances. Now, what's the chance of that happening? Well, unfortunately, the human space program has a past duration of only 37 years, and if you apply the formula, it says its future longevity at 95 percent chance is at least 11 more months but less than 1443 years. The number of years projected for the space program is therefore much smaller than projected human longevity , which suggests that we have a brief window of opportunity to colonize off the earth, and if we don't take advantage of that opportunity then we'll be stuck on the earth where, again, we're exposed to similar risks of other species and we may expect to have a longevity similar to them.

QUESTION: Is there a sense of urgency for humans to get to another planet?

GOTT: I think it's a good life insurance policy for us to not have all our eggs in one basket. If we were to colonize Mars, that would give us a life insurance policy against some unexpected catastrophe that might occur on earth. Since the space program hasn't been around very long, we should be taking advantage of this opportunity to colonize Mars while we have the chance.

QUESTION: Do we have time to wait for freelance space exploration?

GOTT: I would say there's some urgency because I remember in the '60's people saying, "Well, let's go to the moon." "It's so expensive now, let's wait till the '90's when it'll be a lot easier." Now we've found it's more difficult to go in the '90's, not because of technology but because we are willing to spend less money. It concerns me that at some point the decision could be taken to quit the space program. So the real space race, it seems to me, is whether we colonize before we foolishly decide to quit the space program.

The great thing about a self-supporting colony is that the people on the colony would vote to continue it. Colonization is a great bargain because it's the colonists that do all the work, you know, and they multiply there. Colonies can found other colonies.

Let's say you put four astronauts on Mars. You've taken eight months to get them there; they've landed safely on Mars. Then if you'd like to bring them back and trade them with four other astronauts on the earth, well, I would say: let's leave them there, and add more astronauts to them. For this, you have to get astronauts who are willing to be the founders of the Mars colony, and you might as well do that at the outset.

QUESTION: Does the notion that a species has a two to three million year lifespan apply to us?

GOTT: We're intelligent observers who can ask questions like this that other species have not. An interesting observation is that our species, Homo sapiens, has been around for 200,000 years, and this is comparable, in order of magnitude, to the mean duration of mammal species, which is two million years. So we observe that we're smarter than the other species, but we haven't been around the time scale much longer than the typical time scale you would have expect for a species. I think one of the factors here is that if we stay on the earth, we're exposed to pretty much the same risks that they are, and it's dangerous to stay on the earth. This is a planet full of the bones of extinct species, you know. The Tyrannosaurus Rex lasted for two and a half million years, and it was the most potent thing around — and something caught it by surprise.