September 28, 2006

The Double-slit experiment

One of the classic experiments that helped establish Quantum Physics is Thomas Young's double-slit experiment. It had been shown to work not only with a continuous wavefront but with single particles -- electrons, photons, etc... It now seems to work with single macroscopic objects. From PhysOrg News:
Single-particle interference observed for macroscopic objects
With a variation on the famous double-slit experiment of quantum mechanics, scientists Yves Couder and Emmanuel Fort from the University of Paris 7 are rewriting the textbooks. Their accomplishment, however, has less to do with quantum mechanics than with an observation once considered experimentally impossible: the wave-particle double nature of a macroscopic object (an oil droplet and its associated surface wave).

The droplet, which is about 1mm (10 million times larger than an atom), is also one million times larger than the second largest object--a 2-nm molecule called a buckyball--whose wave-particle duality was observed in 2003.

"The interest of our result comes from the fact that we observe single particle diffraction and interference with a classical system," Couder told PhysOrg.com. "This phenomenon was thought to be reserved to the quantum scale."

Although there is no specific dividing line between the quantum and macroscopic scales, an object larger than an atom generally has much too small a wavelength to be detected. Wave-particle duality, one disturbing chapter of quantum mechanics, means that all objects (quantum and macroscopic) sometimes behave like waves and show interference, and other times like particles--objects that have mass and obey conservation laws. Duality, though strange, could explain why objects seem to be in two places at the same time and communicate instantaneously across distances. These abilities, to scientists, would be even more difficult to reckon with than wave-particle duality, which is accepted as an "interpretation" of the world rather than a literal description.

Couder and Fort have recently designed an experiment that enabled them to detect the interference pattern of an object they call a "walker"--a droplet of silicon oil and the surface wave packet it emits, which should be thought of as one entity. The scientists forced the droplet to bounce indefinitely on the surface of a vibrating fluid. At a certain instability threshold, the droplet emits a wave packet which in turn makes the droplet "walk" on the liquid surface.
double_slit.jpg
I love Quantum Physics -- it is simultaneously beautiful and really weird. I do not profess to understand it but I love it. Two great Quantum quotes:
Everything we call real is made of things that cannot be regarded as real.
~~Niels Bohr.

If you think you understand quantum mechanics, you don't understand quantum mechanics.
~~Richard Feynman
Posted by DaveH at September 28, 2006 10:24 PM | TrackBack
Comments

If you think you understand quantum mechanics, you don't understand quantum mechanics.
~~Richard Feynman

That doesn't mean if you think you don't understand quantum mechanics, you understand quantum mechanics.

The two statements combined: nobody understands quantum mechanics.

In a "quantum way": any given person at any given time is a superposition of two states: one is understanding quantum mechanics and the other is not understanding quantum mechanics. The proportions of these states are different for different people at different times. The probability of any pair of people to have the same proportion at any time is 0 as dictated by continuum.

Posted by: Eugene at July 16, 2013 11:40 AM