CapitalistImperialistPig

The world looks simpler when we confine ourselves to local interactions. We affect the world mostly by local interactions. If we want to move something, we usually need to push on it. When Newton discovered his law of universal gravitation, with its action at a distance, that conception of locality was profoundly challenged. He didn't like it, but he could discover no satisfactory hypothesis to explain it. Electricity and magnetism turned out to present similar challenges. The invention of the electromagnetic field by Faraday and Maxwell changed all that. Field strengths, and the forces they generated were now determined by the fields and charges in the local neighborhood, in effect pervading space with an ether that transmitted the forces. Einstein showed that the ether had to be Lorentz invariant and that gravity too could be localized, with the gravitational field now being determined by the matter and fields in the neighborhood. One reason this is interesting today is t...

Dennis Overbye, writing in the NYT, has a nice article on the significance of the BICEP2 measurements. He makes a point that I had not understood (I'm assuming that he is right). The gravitons themselves, theory says, are produced by the same process by which black holes leak. It is known as Hawking radiation, after Stephen Hawking of Cambridge University, the renowned black hole theorist, best-selling author and avatar of cosmic mystery who discovered it in a prodigious calculation in 1973. Shortly thereafter, William Unruh, now at the University of British Columbia, showed that you didn’t need black holes to see this radiation, just acceleration in space. In this case, the role of the black hole you can’t get out of is played by the rapidly retreating horizon you can’t reach in the inflating universe. Hawking radiation has been part of the physics firmament for decades; it’s the best-known prediction of quantum gravity. “Now it seems that Hawking and Unruh were right!” sai...