Wednesday, January 29, 2014

Our quantum reality problem

When the deepest theory we have seems to undermine science itself, some kind of collapse looks inevitable

‘On this view, a dust grain is actually a little galaxy of collapse points, winking instantaneously in and out of existence’

On this view, a dust grain is actually a little galaxy of collapse points, winking instantaneously in and out of existence’

In 1909, Ernest Rutherford, Hans Geiger and Ernest Marsden took a piece of radium and used it to fire charged particles at a sheet of gold foil. They wanted to test the then-dominant theory that atoms were simply clusters of electrons floating in little seas of positive electrical charge (the so-called ‘plum pudding’ model). What came next, said Rutherford, was ‘the most incredible event that has ever happened to me in my life’.

Despite the airy thinness of the foil, a small fraction of the particles bounced straight back at the source – a result, Rutherford noted, ‘as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you’. Instead of whooshing straight through the thin soup of electrons that should have been all that hovered in their path, the particles had encountered something solid enough to push back. Something was wrong with matter. Somewhere, reality had departed from the best available model. But where?

The first big insight came from Rutherford himself. He realised that, if the structure of the atom were to permit collisions of the magnitude that his team had observed, its mass must be concentrated in a central nucleus, with electrons whirling around it. Could such a structure be stable? Why didn’t the electrons just spiral into the centre, leaking electromagnetic radiation as they fell?

Such concerns prompted the Danish physicist Niels Bohr to formulate a rather oddly rigid model of the atom, using artificial-seeming rules about electron orbits and energy levels to keep everything in order. It was ugly but it seemed to work. Then, in 1924, a French aristocrat and physicist named Louis de Broglie argued that Bohr’s model would make more sense if we assumed that the electrons orbiting the atomic nucleus (and indeed everything else that had hitherto been considered a particle) either came with, or in some sense could behave like, waves.
 
For the rest of the story: http://aeon.co/magazine/nature-and-cosmos/our-quantum-reality-problem/

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