Photons Behind Bars, Busting Loose

Quantum mechanics teaches us that light has both wave and particle qualities. For decades Niels Bohr's Complementarity Principle was thought to prevent the wave and particle qualities of light from being measured simultaneously. Recently physicist Shahriar Afshar proved this wrong with a very simple experiment. As a reward, the physics community attacked everything from Afshar's religion to his ethnicity. Prevented from publishing a paper, even on arxiv, he "went public" to NEW SCIENTIST magazine.

Afshar's apparatus is based upon the familiar two-slit experiment. Because of the wave nature of light, beams passing through Pinhole 1 and Pinhole 2 form an interference pattern of light and dark fringes. Here Afshar put light behind bars, adding a grid corresponding to the null (dark) fringes. Behind this he placed a lens to refocus the light onto photon detectors.

Because the bars correspond to null fringes, no light is lost in passing through. The photon count at the far end is exactly the number of photons going in. This demonstrates both wave and particle nature of light in a single experiment. This doesn't necessarily conflict with quantum mechanics, but it does prove Bohr's interpretation wrong.

Despite the simplicity and importance of Afshar's experiment, or maybe because of it, he was treated too poorly to describe. Where have we seen behaviour like that? It could have been worse--he could have been female. Afshar's paper will finally be published in Foundations of Physics.

Old theories about light are bound to change. For decades teachers would tell us to shut up, the speed of photons is flat, like the Earth. There is still huge resistance to a changing speed of light. Now look how far we have come!

New Scientist's cover features "DARK ENERGY: It's the Biggest Mystery in the Universe." At one time repulsive energy was thought to solve many problems, even providing support to inflation. This would lead to more respect and funding for physicists. As Lawrence Krauss and others agree, the repulsive energy hypothesis is falling apart. Now the big brains are at a complete loss.

"That honeymoon period is now well and truly over. Although dark energy is a ubiquitous term in cosmological conversations, no one actually knows what it is. As (Rocky) Kolb says, 'Naming is not explaining.'

"Although there are plenty of tentative explanations, each one seems to suffer from some fatal flaw. The simplest of the solutions on offer is the so-called cosmological constant...unfortunately physicists are having trouble finding a way to fit a cosmological constant into their best existing theories.

"A small non-zero dark energy is more difficult to explain than zero," says Sean Carroll, "so we are driven to wilder ideas...dark energy could be the ether of the 21st century."

As readers know, a simple equation like GM = tc^3 solves the problem precisely, without any hypothetical energies. It also provides a successor to inflation. It makes predictions about the speed of light, the CMB, the 4.507034% of baryons and many other things. Finding the answer to a problem is very, very satisfying.