If it [the universe] was expanding fairly slowly, the force of gravity would cause it eventually to stop expanding and then to start contracting. However, if it was expanding at more than a certain critical rate, gravity would never be strong enough to stop it, and the universe would continue to expand forever.
I think the human race doesn't have a future if we don't go into space. We need to expand our horizons beyond planet earth if we are to have a long-term future. We cannot remain looking inward at ourselves on a small and increasingly polluted and overcrowded planet. We need to look outward to the wider universe.
Think of our dna. In the last million years, our dna hasn't changed at all. It's really much the same as it was in the jungle, a million, two millions years ago. But in the last 200 years, our destructive capacities have increased many, many millions of times over. Why don't we see intelligent signals from outer space? Because in all likelihood, once the civilization reaches the point our civilization has reached, it destroys itself.
If the rate of expansion one second after the big bang had been smaller by even one part in a hundred thousand million million, it would have recollapsed before it reached its present size. On the other hand, if it had been greater by a part in a million, the universe would have expanded too rapidly for stars and planets to form.
If we can avoid disaster for the next two centuries, our species should be safe as we spread into space. If we are the only intellegent beings in the galaxy we should make sure we survive and continue. . . . Our only chance of long-term survival is not to remain inward looking on planet earth but to spread out into space. We have maderemarkable progress in the last hundred years. But if we want to continue beyond the next hundred years, our future is in space.
As those who have seen jurassic park will know, this means a tiny disturbance in one place, can cause a major change in another. A butterfly flapping its wings can cause rain in central park, new york. The trouble is, it is not repeatable. The next time the butterfly flaps its wings, a host of other things will be different, which will also influence the weather. That is why weather forecasts are so unreliable.