Playing around with the Double-Slit Experiment
Very clever hack on the classical
Double-Slit Experiment.
From
PhysOrg:
Physicists Modify Double-Slit Experiment to Confirm Einstein's Belief
Work completed by physics professors at Rowan University shows that light is made of particles and waves, a finding that refutes a common belief held for about 80 years.
Shahriar S. Afshar, the visiting professor who is currently at Boston's Institute for Radiation-Induced Mass Studies (IRIMS), led a team, including Rowan physics professors Drs. Eduardo Flores and Ernst Knoesel and student Keith McDonald, that proved Afshar’s original claims, which were based on a series of experiments he had conducted several years ago.
An article on the work titled "Paradox in Wave-Particle Duality" recently published in Foundations of Physics, a prestigious, refereed academic journal, supports Albert Einstein’s long-debated belief that quantum physics is incomplete. For eight decades the scientific community generally had supported Niels Bohr’s ideas commonly known as the Copenhagen Interpretation of Quantum Mechanics. In 1927, in his “Principle of Complementarity,” he asserted that in any experiment light shows only one aspect at a time, either it behaves as a wave or as a particle. Einstein was deeply troubled by that principle, since he could not accept that any external measurement would prevent light to reveal its full dual nature, according to Afshar. The fundamental problem, however, seemed to be that one has to destroy the photon in order to measure either aspects of it. Then, once destroyed, there is no light left to measure the other aspect.
And what did Afshar do:
In this modified double-slit experiment, a laser beam hits a screen with two small pinholes. As a particle, light goes through one of the pinholes. Through a lens system, the light is then imaged onto two detectors, where a certain detector measures only the photons, which went through a particular pinhole. In this way, Afshar verified the particle nature of light. As a wave, light goes through both pinholes and forms a so-called interference pattern of bright and dark fringes.
“Afshar’s experiment consists of the clever idea of putting small absorbing wires at the exact position of the dark interference fringes, where you expect no light,” Knoesel said. “He then observed that the wires do not change the total light intensity, so there are really dark fringes at the position of the wires. That proves that light also behaves as a wave in the same experiment in which it behaves as a particle.”
Very clever! They have done the double-slit experiment with single photons so it is definitely a particle and a wave simultaneously.
Posted by DaveH at March 15, 2007 3:37 PM