Tuesday, May 08, 2007

This Week in Physics History: May 7 - 13

This is from the About: Physics website. It has all the significant physics events that occurred in this week. However, one part of it is puzzling me.

May 9, 1931 - Polish-born American physicist Albert Abraham Michelson dies. Michelson was the first American physicist to win a Nobel Prize in the sciences, with his 1907 Nobel Prize in Physics. He is best known for his work in the famed Michelson-Morley experiment, which helped to disprove the concept of ether and, thus, laid the foundation for wave particle duality.


How does "disproving" ether "laid the foundation" for wave-particle duality? It was Einstein's photoelectric effect, which was a completely separate phenomena (and 1905 paper), that "laid the foundation" for such "wave-particle duality"[1]. The MM experiment simply shows that the speed of light is isotropic in all directions. There is not even a hint of the "particle" behavior in here.

Zz.

[1] I am not fond of this phrase, because it perpetuates the misconception that modern physics, especially quantum mechanics, has two different ways of describing light, which isn't true. While we do use "wave" and "particle" mechanics in different circumstances, this isn't due to a "duality" but rather due to convenience. One can get all those wave-like properties such as diffraction and interference using the SAME QM formulation that make use of the photon picture.

2 comments:

Kent said...

After taking a course in advanced quantum mechanics, I learnt that all the properties of the photoelectric effect can be described by treating the light as a continuous wave. The photoelectric effect has been often quoted as a "proof" that light exists as a "particle" but this is not the case.

Are there any phenomena that you can think of which can only described by treating the light as a particle? One that pops up in my head is Compton Scattering and the Klein-Nishina cross-section... I have not seen a continuous wave description of this yet.

ZapperZ said...

The classical and semi-classical picture do not have the ability to account for the which-way experiment and the photon anti-bunching experiment.[1]

Furthermore, and this has been talked about ad nauseum, beyond just the photoelectric effect, if you go deeper, the intricate details that one get out of (i) resonant photoemission (ii) angle-resolved photoemission and (iii) multiphoton photoemission so far can only be described via the photon picture. No classical or semiclassical anything have been offered to explain all of them as of now.

Zz.

1. H. Paul, Rev. Mod. Phys. v.54, p.1061 (1982).