Robert H. Dicke
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Robert Henry Dicke (May 6, 1916 – March 4, 1997) was an American experimental physicist, who made important contributions to the fields of astrophysics, atomic physics, cosmology and gravity.
[edit] Biography
In 1946, he returned to Princeton University, where he remained for the rest of his career. He did some work in atomic physics, particularly on the laser and measuring the gyromagnetic ratio of the electron.
He was instrumental in early measurements of the cosmic microwave background radiation, whose physics he worked out with Philip James Edwin Peebles, David Todd Wilkinson and Peter G. Roll (having forgotten the earlier prediction of George Gamow). The Dicke radiometer has been used for many measurements of the background radiation, including that of Arno Penzias and Robert Woodrow Wilson.
He spent the remainder of his career developing a program of precision tests of general relativity using the framework of the equivalence principle. With Carl H. Brans, he developed Brans-Dicke theory of gravitation, an equivalence-principle violating modification of general relativity inspired by Paul Dirac's large numbers hypothesis and Mach's principle. He made measurements of solar oblateness which were useful in understanding the perihelion precession of Mercury's orbit, one of the classical tests of general relativity.
Together with Philip James Edwin Peebles he was instrumental in transforming cosmology into a respectable field of inquiry in physics. He may be credited by some for originating the concept now called the weak anthropic principle by noting that the coincidence that certain parameters or conditions of the universe hold only at the present epoch in the universe's history, so we appear, coincidentally, to be living at a very special time. Together with Brandon Carter, Dicke noted the fact that this epoch coincided with the lifetime of what are called main sequence stars, such as our sun. At any other epoch, there would be no intelligent life around to measure the physical constants in question. So this coincidence had to hold, simply because there would be intelligent life around only at the particular time that the coincidence did hold. This has been referred to as "Dicke's coincidence".
Robert Dicke is also responsible for developing the lock-in amplifier, which is an indispensable tool in the area of applied science and engineering. Some believe that Robert Dicke deserved a Nobel prize just for the invention of such a powerful and ubiquitous device.
Robert Dicke contibuted also notably contributed to the field of Spectroscopy and Radiative Transfer by means of predicting the phenomenon called Dicke narrowing (aka collisional narrowing): When the mean free path of an atom is much smaller than the wavelength of one of its radiation transitions, the atom changes velocity and direction many times during the emission or absorption of a photon. This causes an averaging over different Doppler states and results in an atomic linewidth that is much narrower than the Doppler width. Dicke narrowing occurs at relatively low pressures in the millimeter wave and microwave regions (where it is used in atomic clocks to improve precision). Dicke narrowing is analogous to the Mossbauer effect for gamma rays.
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[edit] References
- J. R. Kuhn, K. G. Libbrecht and R. H. Dicke, "The surface temperature of the sun and changes in the solar constant", Science 242, 908 (1988).
- J. G. Williams, R. H. Dicke, P. L. Bender, C. O. Alley, D. G. Currie, W. E. Carter, D. H. Eckhardt, J. E. Faller, W. M. Kaula, J. D. Mulholland, "New test of the equivalence principle from lunar laser ranging", Phys. Rev. Lett. 36, 551 (1976).
- P. J. E. Peebles and R. H. Dicke, "Origin of the Globular Star Clusters", Astrophys. J. 154, 891 (1968).
- R. H. Dicke and H. M. Goldenberg, "Solar Oblateness and General Relativity", Phys. Rev. Lett. 18, 313 (1967)
- R. H. Dicke, P. J. E. Peebles, P. G. Roll and D. T. Wilkinson, "Cosmic Black-Body Radiation", Astrophys. J. 142, 414 (1965).
- P. G. Roll, R. Krotkov and R. H. Dicke, "The Equivalence Of Inertial And Passive Gravitational Mass", Ann. Phys. 26, 446 (1964).
- R. H. Dicke, "Mach's Principle And Invariance Under Transformation Of Units," Phys. Rev. 125, 2163 (1962).
- C. Brans and R. H. Dicke, "Mach's Principle And A Relativistic Theory Of Gravitation," Phys. Rev. 124, 925 (1961).
- R. H. Dicke, "The Effect of Collisions upon the Doppler Width of Spectral Lines", Phys. Rev. 89, 472 (1953).
