We also cannot suppose that an individual’s thinking survives bodily death, since that destroys the organisation of the brain, and dissipates the energy which utilised the brain tracks. If this be so, we cannot suppose that a solitary electron or proton can ‘think’ we might as well expect a solitary individual to play a football match. Mental phenomena seem to be bound up with material structure. The energy used in thinking seems to have a chemical origin for instance, a deficiency of iodine will turn a clever man into an idiot. What we call our ‘thoughts’ seem to depend upon the organisation of tracks in the brain in the same sort of way in which journeys depend upon roads and railways. There are some who maintain that physiology can never be reduced to physics, but their arguments are not very convincing and it seems prudent to suppose that they are mistaken.

His body, like other matter, is composed of electrons and protons, which, so far as we know, obey the same laws as those not forming part of animals or plants. Of this physical world, uninteresting in itself, Man is a part. The laws of these changes can apparently be summed up in a small number of very general principles, which determine the past and the future of the world when any small section of its history is known. Probably their changes are not continuous, as used to be thought, but proceed by jerks, which are never smaller than a certain minimum jerk. It is thought matter consists of electrons and protons, which are of finite size and of which there are only a finite number in the world. It is thought that the universe is of finite extent in space, and that light could travel round it in a few hundred millions of years.

Both upward and downward, both in the large and in the small, science seems to be reaching limits. The physical world is large compared with Man - larger than it was thought to be in Dante’s time, but not so large as it seemed a hundred years ago. His thoughts and his bodily movements follow the same laws that describe the motions of stars and atoms. Man is a part of Nature, not something contrasted with Nature.

What i believe by bertrand russell