We must conclude from the work of those who have studied the origin of life, that given a planet only approximately like our own, life is almost certain to start. Of all the planets in our own solar system we are now pretty certain the Earth is the only one on which life can survive. Mars is too dry and poor in oxygen, Venus far too hot, and so on. But other suns, stars as the astronomers call them, are bound to have planets like our own, and as the number of stars in the universe is so vast, this possibility becomes virtual certainty. There are one hundred thousand million stars in our own Milky Way alone, and then there are three thousand million other Milky Ways, or galaxies, in the universe. So the number of stars that we know exist is now estimated at about 300 million million million.
We can make the same kind of argument, and have in recent years. For example, we think that between 80 and 90 per cent of all stars, like our sun, are circled by planets which may be inhabited. That means that our nearest neighbours are perhaps 4. 3 light years away, which is much too far to think of in terms of visiting them. But even if we never visit them, if we could get at their language, we might be able to communicate with them.
Recently, two Americans made a startling discovery; they have found sound waves in the space between the stars. If such sound waves really exist, they must be the remains of some very large and powerful explosion that took place thousands of millions of years ago. Since these sound waves are spreading outwards at the speed of light, they are by now far out in the universe. And it is also possible that other civilizations have picked up these waves, and are trying to make something of them. This also gives us a new way to look at the universe, and makes us wonder if there are other intelligent beings out there.