Gaurav Sagar’s Reviews > The Emperor's New Mind > Status Update

The angular momentum of a body persists in time so long as the body is not disturbed by frictional or other forces. This, indeed, is what quantum-mechanical spin is, but now it is the 'spinning' of a single particle itself that concerns us, not the orbiting motion of myriads of individual particles about their common centre of mass (which would be the case for a cricket ball).

Quantum theory as we know it today arose out of two independent later schemes, which were initiated by a pair of remarkable physicists: a German, Wemer Heisenberg, and an Austrian, Erwin Schrodinger.

The real number system does not, as it turns out, have a monopoly with regard to mathematical power and elegance. There is still a certain awkwardness in that, for example, square roots can be taken only of positive numbers (or zero) and not of negative ones.

The concept of computability is a very important and beautiful mathematical idea. It is also a remarkably recent one as things of such a fundamental nature go in mathematics having been first put forward in the 1930s. It is an idea which cuts across all areas of mathematics (although it may well be true that most mathematicians do not, as yet, often worry
themselves about computability questions).