In Cambridge University's Cavendish Laboratory works a young Briton of Swiss extraction who is indisputably one of the few great mathematical logicians in the world. His Principles oj Quantum Mechanics is a monument of human cerebration. That book is utterly incomprehensible to ordinary men who had never heard of its author until Paul Adrien Maurice Dirac won a Nobel Prize last year. Only a few of the ablest scholar-scientists can follow the chain of symbolic reasoning in Principles of Quantum Mechanics, and among them none is more articulate, more authoritative, more sensible than Sir James Hopwood Jeans, president of the British Association for the Advancement of Science. Like a modern St. Paul, Sir James has taken it upon himself to preach the Gospel abroad, to explain the groundwork of theory which makes the work of Dirac and his peers possible. Last week appeared the newest Jeans book, Through Space and Time,* into which the 57-year-old astronomer and mathematician has packed the fundamental things 1934 Science knows about the Universe. Sir James has made his story so simple that laymen can digest it without difficulty, so authoritative that no scientist will quarrel with his premises.
The substance of Through Space and Time was delivered last winter as a course of lectures before the Royal Institution, which invites its annual speakers to discourse "in a style adapted to a juvenile auditory." Sir James took for granted almost no qualifications of his audience beyond ability to understand plain English. Highlights of the indisputable universe as presented by Evangel Jeans:
The Earth is so old that if its story were imagined as a 500-page book, recorded history would fit easily into the last word, the Christian era into the last letter. How is this known? The rate at which radioactive substances decay can be experimentally determined, and hence the age of radioactive rock can be told by the amount of decay observed. In Canada there are rocks that reveal an age of 1,230,000,000 years. Yet Earth could not be more than two or three times that old, because otherwise all the radium would have decayed to lead. Thus the time at which Earth and the other planets were thrown off the sun, probably by the gravitational yank of a passing star, is commonly estimated at 2,000,000,000 years ago. Much of this time was spent cooling, shrinking, solidifying: more than half of it passed before evidence of the first microscopic life was left in the rocks. Five hundred million years ago sponges, jellyfish and worms appeared; fishes 400,000,000 years ago; giant reptiles 150,000,000 years ago. Well within the last 100,000,000 years birds and mammals appeared, and within the last million, man. The dates. Sir James admits, are conjectural but the sequence is not.