James Hopwood Jeans Quotes

The complete closed world consists of three parts-substratum, phenomenal world, and observer. By our experiments we drag up activities from the substratum into the phenomenal world of space and time, but there is no clear line of demarcation between subject and object, and by performing observations on the world, we alter it, much as a fisherman dragging up fish from the depths of the seas disturbs the waters and also damages the fish.

In the interior of the atom, Bohr had tried the plan of retaining the particle-electron and modifying the classical mechanics. Heisenberg took the opposite course, his procedure amounting in effect to retaining the classical mechanics, at least in form, and modifying the electron. Actually, the electron dropped out all together, because it exists only as a matter of inference and not of direct observation. For the same reason, the new theory contains no mention of atoms, nuclei, protons, or of electricity in any shape or form. The existences of all these are matters of inference, and Heisenberg's purely mathematical theory could no more make contact with them than with the efficiency of a turbine or with the price of wheat.

The motion of the stars over our heads is as much an illusion as that of the cows, trees and churches that flash past the windows of our train.

Heisenberg now approached the problem from a new philosophical angle. He discarded all models, pictures and parables, and made a clear distinction between sure knowledge we gain from observation of nature and the conjectural knowledge we introduce when we use models, pictures and parables. Sure knowledge... can only be numerical, so that Heisenberg's results were inevitably mathematical in form, and could not disclose anything about the true nature of physical properties or entities.

If we assume that the last breath of, say, Julius Caesar has by now become thoroughly scattered through the atmosphere, then the chances are that each of us inhales one molecule of it with every breath we take.

The laws which governed the spontaneous jumps of the kangaroos were shown to be of the simplest; out of any number of kangaroos a certain proportion always jumped within a specified time, and nothing seemed to be able to change this number. Also, before the jumps took place, there was nothing in the world of phenomena to distinguish those kangaroos that were about to jump from those that were not... to help fill the quota demanded by the statistical law. As discontinuity marched into the world of phenomena through one door, causality walked out through another.

A second conspicuous landmark... is the enunciation of the fundamental law of radioactive disintegration by Rutherford and Soddy in 1903. This law was in no sense a consequence or development of Planck's theories; indeed fourteen years were to elapse before any connection was noticed between the two. The new law asserted that the atoms of radioactive substances broke up spontaneously, and not because of any particular conditions or special happenings. This seemed to involve an even more startling break with classical theory than the new laws of Planck; radioactive break-up appeared to be an effect without a cause, and suggested that the ultimate laws of nature were not even causal.

Another conspicuous failure of classical mechanics was with one aspect of the problem of radiation. ...Imagine a crowd of steel balls rolling about on a steel floor. ...There must... be a steady leakage of energy from... causes, such as air resistance and the friction of the floor, so the balls will eventually lose energy, and, after no great length of time, will be found standing at rest on the floor. The energy of their motion seems to have been lost... most of it has been transformed into heat. The classical mechanics predicts that this must happen; it shows that all energy of motion, except possibly a minute fraction of the whole, must be transformed into heat whenever such a transformation is physically possible. It is because of this that perpetual-motion machines are a practical impossibility.

When two hypotheses are possible, we provisionally choose that which our minds adjudge to be simpler, on the supposition that this is the more likely to lead in the direction of truth. It includes as a special case the principle of Occam's razor-entia non multiplicana praeter necessitatem.

Physics and philosophy are at most a few thousand years old, but probably have lives of thousands of millions of years stretching away in front of them. They are only just beginning to get under way...

...experimental physics was particularly interested in the processes taking place inside the atom, and in this field the classical mechanics was failing conspicuously and completely. Perhaps its most spectacular failure was with the fundamental problem with the structure of the atom.

And the substance out of which this bubble is blown, the soap-film, is empty space welded onto empty time.

...a detailed mathematical discussion shows that whatever kind of wave-packet we select to represent the electron, the product of the two uncertainties of position and momentum can never be less than h, which is precisely what Heisenberg found...

Into such a universe we have stumbled, if not exactly by mistake, at least as the result of what may properly be described as an accident. The use of such a word need not imply any surprise that our earth exists, for accidents will happen, and if the universe goes on for long enough, enough, every conceivable accident is likely to happen in time. It was, I think, Huxley who said that six monkeys, set to strum unintelligently on typewriters for millions of millions of years, would be bound in time to write all the books in the British Museum. If we examined the last page which a particular monkey had typed, and found that it had chanced, in its blind strumming, to type a Shakespeare sonnet, we should rightly regard the occurrence as a remarkable accident, but if we looked through all the millions of pages the monkeys had turned off in untold millions of years, we might be sure of finding a Shakespeare sonnet somewhere amongst thein, the product of the blind play of chance. In the same way, millions of millions of stars wandering blindly through space for millions of millions of years are bound to meet with every kind of accident; a limited number are bound to meet with that special kind of accident which calls planetary systems into being.

Precisely similar ideas are applicable to the molecules that form the air in a room. ...The classical mechanics now predicts that the whole energy of motion will be changed into radiation [heat], so that the molecules will shortly be found lying at rest on the floor... In actual fact they continue to move with undiminished energy, forming a perpetual-motion machine in defiance of classical mechanics. ...We have passed from one to another of three worlds... from the man-sized world to the world of the electron.