Maybe the smallest structures in space-time should be pictured as ‘superstrings’, or perhaps they are pieces of cotton wool tied together as is advocated by Ashtekar and his followers. Maybe you tend to believe, as I do, that the dominant structures at the smallest possible scale are microscopic black holes. Each time, one conclusion seems to be inevitable: the amount of information one can store inside a tiny piece of space appears to be limited. Now, anyone who has worked with computers knows that information can be represented by series of zeros and ones. If an ‘interaction’ takes place, the zeros and ones are replaced by other zeros and ones.

Does this mean that the world we live in is nothing but a giant supercomputer? Every book about the foundations of quantum mechanics will tell you that this would be too much of a simplification of matters. The laws of quantum mechanics, we read, are incompatible with any ‘mechanical’ explanation of what we see happening in Nature. Our future is not determined from the past by unambiguous, ‘deterministic’ rules.

This statement is based on a thought experiment invented by Einstein, Podolski and Rosen. It is an ingenious scheme designed such that quantum mechanics predicts an outcome that cannot possibly be reconciled with a deterministic theory. John Bell at CERN later turned this argument into an accurately formulated mathematical theorem. Thus we can imagine experiments for which the laws of quantum mechanics as we know them predict accurately what we will observe.