**"If we see further it is because we stand on the shoulders of
giants," ** said Newton (alluding to an earlier phrase, see Bartlett's
Quotations). Here is an amazing gathering of giants.
This photo is from the 1927 Solvay conference on quantum mechanics, which
was held just in the middle of the quantum revolution when many of the
key ideas were being worked out over the course of a few years. Einstein
is in the middle.

I've seen this picture before, but didn't realize until recently the presence of a number of famous physicists who made major contributions to plasma physics and fluid dynamics:

**Irving Langmuir** first used the word "plasma" to define an ionized
gas as the fourth state of matter and was the discoverer of "Langmuir oscillations",
the omega_pe plasma oscillations. He was a great experimentalist
also.

**Petrus Debye **elucidated the important plasma property that bears
his name of Debye shielding.

**Paul Langevin** studied statistical mechanics and random walk processes
(as did **Einstein**), and his "Langevin equation" underlies many statistical
theories in plasma physics. The **Brillouin** limit applies in
a single-species plasma and Brillouin scattering is important in laser-plasma
interactions. **Kramers** and Brillouin popularized the WKB approximation,
and the Kramers-Kronig relations shows certain properties that a dielectric
must have to satisfy causality (and is thus related to Landau damping).

**Werner Heisenberg** is most famous for the Heisenberg uncertainty
principle of quantum mechanics, but also spent much of his career investigating
the complex dynamics of turbulence. **Knudsen** made important
contributions to the study of rarefied gases.

Front row from left to right: Irving Langmuir, Max Planck, Marie
Curie, Hendrik Lorentz, Albert Einstein, Paul Langevin, Charles Eugene
Guye, Charles Wilson, Owen Richardson.

Second row: Petrus Debye, Martin Knudsen, William Lawrence Bragg,
Hendrik Kramers, Paul Dirac, Arthur H. Compton, Louis de Broglie, Max Born,
Niels Bohr.

Back row: Auguste Piccard, E. Henriot, Paul Ehrenfest, Edouard Herzen, Theophile De Donder, Erwin Schrodinger, J.E. Verschaffelt, Wolfgang Pauli, Werner Heisenberg, Ralph Howard Fowler, Leon Brillouin."

(This photo appeared in the New York Times on Dec. 12, 2000, p. F4, and a high-resolution version of it can be purchased from the AIP's Emilio Segre archives.)