An Astronomer's View of the Universe by Sir James Jeans is the opening of book The Mysterious Universe. It is a splendid demonstration of his power to communicate a vision of the universe with fluency and clarity.
The littleness of our home, the Earth in space when measured is unimaginably small in the universe. The number of stars in the universe is like the number of grains of sand on all the seashores of the world. The majority of the stars are so large that millions of earths could be packed inside each.
The majority of stars are wandering about in space. A few journey in company, but the majority are solitary travellers. And they travel through a universe so spacious that it is an event of almost unimaginable rarity for a star to come anywhere near to another star.
The stars we see in the sky are intensely hot. In course of time, the expelled fragments of the sun gradually cooled down. Afterwards, one of these cooling fragments gave birth to life. From these simple beginnings emerged life. It seems that humanity came into existence in some such way as this. If we attempt to discover the nature and purpose of the universe, our first impression is similar to terror. We find the universe terrifying because of its vast distances, our extreme loneliness and insignificance of our home in space. Above all, we find the universe terrifying because it appears to be indifferent to life like our own. The universe even appears to be hostile to life like our own.
We have fallen into such a universe, by mistake or as the result of an accident. Our calculation shows that the number of planetary systems can at most be very small in comparison with the number of stars in the sky. Planetary systems are exceedingly rare objects in space. Life on earth could only originate on planets like the earth. It needs suitable conditions for its appearance; the most important is a temperature at which substances can exist in the liquid state.
The stars themselves are far too hot. We may think of them as a vast collection of fires scattered throughout space. Away from the fires there is cold of hundreds of degrees of frost. Close up to them is a temperature of thousands of degrees, at which all solids melt, all liquids boil.
Life can only exist inside a narrow temperate zone between the extremes of temperature zones. Outside these zones life would be frozen; inside, it would be dried-up. At a rough estimate, these zones within which life is possible constitute less than a thousand million millionth part of the whole of space. Just for this reason it seems unbelievable that the universe have been designed to produce life like our own.
We do not know if suitable physical conditions are sufficient in themselves to produce life. According to one school of thought, the earth gradually cooled, it was natural, and unavoidable, that life should come. Another holds that after one accident had brought the earth into being, a second was necessary to produce life. The constituents of a living body are ordinary chemical atoms, carbon, hydrogen, oxygen, nitrogen and so on. Every kind of atom necessary for life must have existed in the new born earth. At intervals, a group of atoms might happen to arrange themselves in the way in which they are arranged in the living cell. Indeed, given sufficient time, they would be certain to do so. But would they then be a living cell? Is it merely atoms, or is it atoms plus life? Or, to put it in another way, could a skilful chemist create life out of the necessary atoms and then make it go? We do not know the answer.