Friday, June 01, 2007

Oppenheimer on Einstein

A great find -- via Brad DeLong -- from 1966. Trying to teach non-science majors about relativity this quarter has only enhanced my regard for Einstein's genius.

More on Oppenheimer and Einstein from this blog.

Note Added: another great Internet find -- a chess game (Princeton, 1933) in which Einstein defeats Oppenheimer (the latter, playing black, appears to lose his queen on a blunder :-)

New York Review of Books:

... Einstein was a physicist, a natural philosopher, the greatest of our time.

What we have heard, what you all know, what is the true part of the myth is his extraordinary originality. The discovery of quanta would surely have come one way or another, but he discovered them. Deep understanding of what it means that no signal could travel faster than light would surely have come; the formal equations were already known; but this simple, brilliant understanding of the physics could well have been slow in coming, and blurred, had he not done it for us. The general theory of relativity which, even today, is not well proved experimentally, no one but he would have done for a long, long time. It is in fact only in the last decade, the last years, that one has seen how a pedestrian and hard-working physicist, or many of them, might reach that theory and understand this singular union of geometry and gravitation; and we can do even that today only because some of the a priori open possibilities are limited by the confirmation of Einstein's discovery that light would be deflected by gravity.

Yet there is another side besides the originality. Einstein brought to the work of originality deep elements of tradition. It is only possible to discover in part how he came by it, by following his reading, his friendships, the meager record that we have. But of these deep-seated elements of tradition—I will not try to enumerate them all; I do not know them all—at least three were indispensable and stayed with him.

THE FIRST IS from the rather beautiful but recondite part of physics that is the explanation of the laws of thermodynamics in terms of the mechanics of large numbers of particles, statistical mechanics. This was with Einstein all the time. It was what enabled him from Planck's discovery of the law of black body radiation to conclude that light was not only waves but particles, particles with an energy proportional to their frequency and momentum determined by their wave-number, the famous relations that de Broglie was to extend to all matter, to electrons first and then clearly to all matter.

It was this statistical tradition that led Einstein to the laws governing the emission and absorption of light by atomic systems. It was this that enabled him to see the connection between de Broglie's waves and the statistics of light-quanta proposed by Bose. It was this that kept him an active proponent and discoverer of the new phenomena of quantum physics up to 1925.

The second and equally deep strand—and here I think we do know where it came from—was his total love of the idea of a field: the following of physical phenomena in minute and infinitely subdividable detail in space and in time. This gave him his first great drama of trying to see how Maxwell's equations could be true. They were the first field equations of physics; they are still true today with only very minor and well-understood modifications. It is this tradition which made him know that there had to be a field theory of gravitation, long before the clues to that theory were securely in his hand.

The third tradition was less one of physics than of philosophy. It is a form of the principle of sufficient reason. It was Einstein who asked what do we mean, what can we measure, what elements in physics are conventional? He insisted that those elements that were conventional could have no part in the real predictions of physics. This also had roots: for one the mathematical invention of Riemann, who saw how very limited the geometry of the Greeks had been, how unreasonably limited. But in a more important sense, it followed from the long tradition of European philosophy, you may say starting with Descartes—if you wish you can start it in the Thirteenth Century, because in fact it did start then—and leading through the British empiricists, and very clearly formulated, though probably without influence in Europe, by Charles Pierce: One had to ask how do we do it, what do we mean, is this just something that we can use to help ourselves in calculating, or is it something that we can actually study in nature by physical means? For the point here is that the laws of nature not only describe the results of observations, but the laws of nature delimit the scope of observations. That was the point of Einstein's understanding of the limiting character of the velocity of light; it also was the nature of the resolution in quantum theory, where the quantum of action, Planck's constant, was recognized as limiting the fineness of the transaction between the system studied and the machinery used to study it, limiting this fineness in a form of atomicity quite different from and quite more radical than any that the Greeks had imagined or than was familiar from the atomic theory of chemistry. ...


Unknown said...

Hi Steve,

I just read the Oppenheimer piece on Einstein in its entirety and as I was reading I reminded myself that I must thank you for bringing this otherwise forgotten piece to the attention of a wider modern audience. The thought that went through my mind is why people would want to read Walter Isaacson if they could read J. Robert Oppenheimer. Indeed, why read the latest mega-sellers when one can read Tolstoy and Faulkner?

Oppenheimer was also such a fascinating character. You should post something about him, or perhaps about the Tolman-Oppenheimer-Volkoff equation. Many physicists have forgotten that the interior metric has a very nice form also.

Steve Hsu said...


Thanks for your comment -- I completely agree.

For some reason the post below doesn't come up high when you search my blog for Oppenheimer. In that post I made a few comments about Oppenheimer's pioneering work on black holes. Kip Thorne (who was a Wheeler student; Wheeler coined the term black hole in 1967) told me once that almost all the basic results about black holes are already in the Oppenheimer work, but that most of the community had not appreciated it. Oppenheimer's work was done in the 1930s! Of course, events such as the war, the bomb, QED, etc. intervened, focusing the attention of physicists elsewhere.

It took Wheeler et al. to communicate it more broadly; catchy names help!

"Perhaps most important was his work in the 1930's on the endpoint of stellar evolution, with his students Volkoff and Snyder at Berkeley. They explored many of the properties of black holes long before the term "black hole" was coined by Wheeler. Oppenheimer and company were interested in neutron star stability, and gave the first general-relativistic treatment of this complicated problem. In so doing, they deduced the inevitability of black hole formation for sufficiently massive progenitors. They also were the first to note that an infalling object hits the horizon after a finite proper time (in its own frame), whereas an observer orbiting the hole never actually sees the object hit the horizon. The work received amazingly little attention during Oppenheimer's life. But, had Oppenheimer lived another few decades, it might have won him a Nobel prize."

Dave Bacon said...

Show me a master of statistical mechanics and I'll show you a master physicist :)

Unknown said...

Hi Steve,

Why didn’t Oppenheimer et al think of turning on quantum mechanics? Or put another way, why did it take so long for Hawking radiation to be discovered given all these alleged experts on gravity? Of course, in theoretical physics almost everything is obvious in hindsight. One can construct any number of heuristic arguments against the statement that all things inevitably fall into a black hole. Once quantum mechanics is turned on, then particles with de Broglie wavelength longer than the size of the black hole cannot fall in. From this immediately follow finite entropy and the Hawking temperature.

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