Life In The Universe

Life in the Universe

In this talk, I would like to speculate a little, on the development of life in

the universe, and in particular, the development of intelligent life. I shall

take this to include the human race, even though much of its behaviour

through out history, has been pretty stupid, and not calculated to aid the

survival of the species. Two questions I shall discuss are, 'What is the

probability of life existing else where in the universe?' and, 'How may life

develop in the future?'

It is a matter of common experience, that things get more disordered and chaotic with time.

This observation can be elevated to the status of a law, the so-called Second Law of

Thermodynamics. This says that the total amount of disorder, or entropy, in the universe,

always increases with time. However, the Law refers only to the total amount of disorder. The

order in one body can increase, provided that the amount of disorder in its surroundings

increases by a greater amount. This is what happens in a living being. One can define Life to

be an ordered system that can sustain itself against the tendency to disorder, and can

reproduce itself. That is, it can make similar, but independent, ordered systems. To do these

things, the system must convert energy in some ordered form, like food, sunlight, or electric

power, into disordered energy, in the form of heat. In this way, the system can satisfy the

requirement that the total amount of disorder increases, while, at the

same time, increasing the order in itself and its offspring. A living being

usually has two elements: a set of instructions that tell the system how

to sustain and reproduce itself, and a mechanism to carry out the

instructions. In biology, these two parts are called genes and

metabolism. But it is worth emphasising that there need be nothing

biological about them. For example, a computer virus is a program that

will make copies of itself in the memory of a computer, and will transfer

itself to other computers. Thus it fits the definition of a living system,

that I have given. Like a biological virus, it is a rather degenerate form,

because it contains only instructions or genes, and doesn't have any

metabolism of its own. Instead, it reprograms the metabolism of the

host computer, or cell. Some people have questioned whether viruses

should count as life, because they are parasites, and can not exist

independently of their hosts. But then most forms of life, ourselves included, are parasites, in

that they feed off and depend for their survival on other forms of life. I think computer viruses

should count as life. Maybe it says something about human nature, that the only form of life we

have created so far is purely destructive. Talk about creating life in our own image. I shall

return to electronic forms of life later on.

What we normally think of as 'life' is based on chains of carbon atoms, with a few other atoms,

such as nitrogen or phosphorous. One can speculate that one might have life with some other

chemical basis, such as silicon, but carbon seems the most favourable case, because it has the

richest chemistry. That carbon atoms should exist at all, with the properties that they have,

requires a fine adjustment of physical constants, such as the QCD scale, the electric charge,

and even the dimension of space-time. If these constants had significantly different values,

either the nucleus of the carbon atom would not be stable, or the

electrons would collapse in on the nucleus. At first sight, it seems

remarkable that the universe is so finely tuned. Maybe this is

evidence, that the universe was specially designed to produce the

human race. However, one has to be careful about such

arguments, because of what is known as the Anthropic Principle.

This is based on the self-evident truth, that if the universe had not

been suitable for life, we wouldn't be asking why it is so finely

adjusted. One can apply the Anthropic Principle, in either its

Strong, or Weak, versions. For the Strong Anthropic Principle, one supposes that there are

many different universes, each with different values of the

physical constants. In a small number, the values will allow the

existence of objects like carbon atoms, which can act as the

building blocks of living systems. Since we must live in one of

these universes, we should not be surprised that the physical

constants are finely tuned. If they weren't, we wouldn't be

here. The strong form of the Anthropic Principle is not very satisfactory. What operational

meaning