Something will happen to Earth eventually, it’s just a question of time. Eventually the sun will expand and destroy all life on Earth, so we do need to move at some point, or at least be a multi-planet species. [...] You have to ask the question: do we want to be a space-flying civilisation and a multi-planet species or not? [...] It's a question of what percentage of resources should we devote to such an endeavour? I think if you say 1 per cent of resources, that's probably a reasonable amount.

We are so far from being able to move a good fraction of the population anywhere else. Even if Elon Musk and other private individuals manage to start sending humans to Mars, we may be a few hundred years away from putting any sizable population there—and we have to fix Earth right now. Eventually, if we’ve been irresponsible enough to create problems in our world, moving to a new one won’t necessarily solve the problem because we might do the same thing in the future.

I don't think the human race will survive the next thousand years, unless we spread into space. There are too many accidents that can befall life on a single planet. But I'm an optimist. We will reach out to the stars.

Human migration beyond Earth is our destiny, not as in something preordained, but in the sense of it being inevitable and necessary. The lot of humanity seems to be that of expanding consciousness into new territory.

Man will not always stay on earth; the pursuit of light and space will lead him to penetrate the bounds of the atmosphere, timidly at first, but in the end to conquer the whole of solar space.

And then, the Earth being small, mankind will migrate into space, and will cross the airless Saharas which separate planet from planet and sun from sun. The Earth will become a Holy Land which will be visited by pilgrims from all the quarters of the Universe. Finally, men will master the forces of Nature; they will become themselves architects of systems, manufacturers of worlds.

An optimistic view of the future would indicate that before long, the clear necessity of expanding humanity's horizons would cause ... space settlements to be built. The construction would also serve as a great project that not only would be clearly of great benefit, but might induce human cooperation in something large enough to fire the heart and mind, and make people forget the petty quarrels that have engaged them for thousands of years in wars over insignificant scraps of earthly territory.

It’s time for the human race to enter the solar system.

The time will come when a spacecraft carrying human beings will leave the earth and set out on a voyage to distant planets to remote worlds. Today this may seem only an enticing fantasy, but such in fact is not the case. The launching of the first two Soviet Sputniks has already thrown a sturdy bridge from the earth into space, and the way to the stars is open.

I don't think the human race will survive the next thousand years, unless we spread into space.

Humanity is destined to explore, settle, and expand outward into the universe.

Behind every man now alive stand thirty ghosts, for that is the ratio by which the dead outnumber the living. Since the dawn of time, roughly a hundred billion human beings have walked the planet Earth.

Now this is an interesting number, for by a curious coincidence there are approximately a hundred billion stars in our local universe, the Milky Way. So for every man who has ever lived, in this Universe there shines a star.

But every one of those stars is a sun, often far more brilliant and glorious than the small, nearby star we call the Sun. And many — perhaps most — of those alien suns have planets circling them. So almost certainly there is enough land in the sky to give every member of the human species, back to the first ape-man, his own private, world-sized heaven — or hell.

How many of those potential heavens and hells are now inhabited, and by what manner of creatures, we have no way of guessing; the very nearest is a million times farther away than Mars or Venus, those still remote goals of the next generation. But the barriers of distance are crumbling; one day we shall meet our equals, or our masters, among the stars.

Men have been slow to face this prospect; some still hope that it may never become reality. Increasing numbers, however are asking; 'Why have such meetings not occurred already, since we ourselves are about to venture into space?'

Why not, indeed? Here is one possible answer to that very reasonable question. But please remember: this is only a work of fiction.

The truth, as always, will be far stranger.

The likelihood is that, in 100,000 years time, we shall either have reverted to wild barbarism, or else civilisation will have advanced beyond all recognition – into colonies in outer space, for instance. In either case, evolutionary extrapolations from present conditions are likely to be highly misleading.

I don’t have much to say except a warning. Life reached an evolutionary milestone when it climbed onto land from the ocean, but those first fish that climbed onto land ceased to be fish. Similarly, when humans truly enter space and are freed from the Earth, they cease to be human. So, to all of you I say this: When you think about heading into outer space without looking back, please reconsider. The cost you must pay is far greater than you could imagine. *