05 October 2007

Airports, Oppenheimer, and the positron

First, did you see Safiri's note about airport paranoia?

Second, here's a passage from American Prometheus, a book about Robert Oppenheimer that my brother-in-law gave me. I hadn't known about his role in postulating the existence of the positron. (Oppenheimer's, not Bryan's. But one never knows.)

"On February 14, 1930, Oppenheimer finished writing a seminal paper, 'On the Theory of Electrons and Protons.' Drawing on Paul Dirac's equation on the electron, Oppenheimer argued that there had to be a positively charged counterpart to the electron -- and that this mysterious counterpart should have the same mass as the electron itself. It could not, as Dirac had suggested, be a proton. Instead, Oppenheimer predicted the existence of an 'anti-electron -- the positron.' Ironically, Dirac had failed to pick up on this implication in his own equation, and he willingly gave Oppenheimer the credit for this insight -- which soon impelled him, Dirac, to propose that perhaps there existed 'a new kind of particle, unknown to experimental physics, having the same mass and opposite charge to an electron.' What he was very tentatively proposing was the existence of antimatter. Dirac suggested naming this elusive particle an 'anti-electron.'

Initially, Dirac himself was not at all comfortable with his own hypothesis. Wolfgang Pauli and even Niels Bohr emphatically rejected it. 'Pauli thought it was nonsense,' Oppenheimer later said. 'Bohr not only thought it was nonsense but was completely incredulous.' It took someone like Oppenheimer to push Dirac into predicting the existence of antimatter. This was Oppenheimer's penchant for original thinking at its best. In 1932 the experimental physicist Carl Anderson proved the existence of the positron, the positively charged antimatter counterpart to the electron. Anderson's discovery came fully two years after Oppenheimer's calculations suggested its theoretical existence. A year later, Dirac won the Nobel Prize."


1 comment:

Anonymous said...

Thank you for the link! I must exist!
Safiri, now home and slightly less paranoid