Monday, April 14, 2008

John Wheeler, dead at 96

John Archibald Wheeler, one of the last great physicists of a bygone era, has died. He outlived most of his contemporaries (Bohr, Einstein, Oppenheimer) and even some of his students, like Feynman.
NYTimes: John A. Wheeler, a visionary physicist and teacher who helped invent the theory of nuclear fission, gave black holes their name and argued about the nature of reality with Albert Einstein and Niels Bohr, died Sunday morning at his home in Hightstown, N.J. He was 96.

...One particular aspect of Einstein’s theory got Dr. Wheeler’s attention. In 1939, J. Robert Oppenheimer, formerly the head of the Manhattan Project, and a student, Hartland Snyder, suggested that Einstein’s equations had made an apocalyptic prediction. A dead star of sufficient mass could collapse into a heap so dense that light could not even escape from it. The star would collapse forever while spacetime wrapped around it like a dark cloak. At the center, space would be infinitely curved and matter infinitely dense, an apparent absurdity known as a singularity.

Dr. Wheeler at first resisted this conclusion, leading to a confrontation with Dr. Oppenheimer at a conference in Belgium in 1958, in which Dr. Wheeler said that the collapse theory “does not give an acceptable answer” to the fate of matter in such a star. “He was trying to fight against the idea that the laws of physics could lead to a singularity,” Dr. Charles Misner, a professor at the University of Maryland and a former student, said. In short, how could physics lead to a violation itself — to no physics?

Dr. Wheeler and others were finally brought around when David Finkelstein, now an emeritus professor at Georgia Tech, developed mathematical techniques that could treat both the inside and the outside of the collapsing star.

At a conference in New York in 1967, Dr. Wheeler, seizing on a suggestion shouted from the audience, hit on the name “black hole” to dramatize this dire possibility for a star and for physics.

The black hole “teaches us that space can be crumpled like a piece of paper into an infinitesimal dot, that time can be extinguished like a blown-out flame, and that the laws of physics that we regard as ‘sacred,’ as immutable, are anything but,” he wrote in his 1999 autobiography, “Geons, Black Holes & Quantum Foam: A Life in Physics.” (Its co-author is Kenneth Ford, a former student and a retired director of the American Institute of Physics.)

In 1973, Dr. Wheeler and two former students, Dr. Misner and Kip Thorne, of the California Institute of Technology, published “Gravitation,” a 1,279-page book whose witty style and accessibility — it is chockablock with sidebars and personality sketches of physicists — belies its heft and weighty subject. It has never been out of print. ...

I mentioned the history of black holes in general relativity in an earlier post on J.R. Oppenheimer:

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.

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