Suppose that we are not the sole intelligent life-form in the Universe. Discovery of another life-form and subsequent communication with it would be one of the most important events in the history of the human race. But how should we go about searching for such a life-form, let alone communicate with it? The question of […]

We have a basis for understanding the synthesis of elementary proteins. This is but the first rung on the ladder towards the evolution of life as we know it. As we climb this ladder, the system adapts itself more strongly to the terrestrial environment and so it is from here on that the divergences between […]

We have seen that the primitive atmosphere of the Earth would have contained, at a very early stage, organic compounds of varying degrees of complexity. Indeed, the picture described so far is likely to be a fairly common one wherever planetary systems have formed; no extraordinary events have been postulated. The next step must be […]

Given that other stars have planetary systems, what is the likelihood that the planetary system resembles our Solar System ? If we can answer that, we may be able to decide whether the evolution of life on Earth has any relevance to life elsewhere in the Universe. The only planetary system we have any knowledge […]

How likely is it that systems similar to the Solar System exist elsewhere in the Galaxy ? This, like many of the questions raised when discussing extraterrestrial life, is a highly controversial issue. It should be remembered that we have no direct evidence for the existence of any planetary system other than the Solar System. […]

Life is the most complex state of organization of matter known in the Universe. Living systems achieve this state of organization by using energy that they extract from their environment. Many physical systems do this, but a living system is distinguished in that it uses the energy to convert the material taken from its surroundings […]

A typical galaxy contains some hundred billion stars, most of which are not unlike our own Sun. The largest telescopes can photograph some billions of galaxies. The observable Universe therefore contains some 1020 stars! How likely is it that the Sun is the only one among these which is orbited by a life-bearing planet? This […]