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. May 6 is the 126th day of the year in the Gregorian Calendar (127th in leap years). ... Year 1916 (MCMXVI) was a leap year starting on Saturday (link will display the full calendar). ... March 4 is the 63rd day of the year in the Gregorian Calendar (64th in leap years). ... 1997 (MCMXCVII) was a common year starting on Wednesday of the Gregorian calendar. ... ... Spiral Galaxy ESO 269-57 Astrophysics is the branch of astronomy that deals with the physics of the universe, including the physical properties (luminosity, density, temperature, and chemical composition) of celestial objects such as stars, galaxies, and the interstellar medium, as well as their interactions. ... Atomic physics (or atom physics) is the field of physics that studies atoms as isolated systems comprised of electrons and an atomic nucleus. ... Cosmology, as a branch of astrophysics, is the study of the large-scale structure of the universe and is concerned with fundamental questions about its formation and evolution. ... Gravity is a force of attraction that acts between bodies that have mass. ...

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. A LASER (from the acronym of Light Amplification by Stimulated Emission of Radiation) is an optical source that emits photons in a coherent beam. ... In physics, the gyromagnetic ratio or Landé g-factor is a dimensionless unit which expresses the ratio of the magnetic dipole moment to the angular momentum of an elementary particle or atomic nucleus. ...

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. Philip James Edwin Peebles (born April 25, 1935) is an Canadian-American astronomer. ... David Todd Wilkinson (13 May 1935 – 5 September 2002) was a world-renowned pioneer in the field of cosmology, specializing in the study of the cosmic microwave background radiation (CMB) left over from the Big Bang. ... George Gamow (pronounced GAM-off) (March 4, 1904 – August 19, 1968) , born Georgiy Antonovich Gamov (Георгий Антонович Гамов) was a Ukrainian born physicist and cosmologist. ... Arno Allan Penzias (born April 26, American physicist. ... Robert Woodrow Wilson Robert Woodrow Wilson (born January 10, 1936) is an American physicist. ...

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. General relativity (GR) is the geometrical theory of gravitation published by Albert Einstein in 1915/16. ... In relativity, the equivalence principle is applied to several related concepts dealing with gravitation and the uniformity of physical measurements in different frames of reference. ... Carl H. Brans is a physicist on the faculty of Loyola University. ... This article or section is in need of attention from an expert on the subject. ... Paul Adrien Maurice Dirac, OM, FRS (IPA: [dɪræk]) (August 8, 1902 – October 20, 1984) was a British theoretical physicist and a founder of the field of quantum physics. ... The Dirac large numbers hypothesis refers to an observation made by Paul Dirac in 1937 relating ratios of size scales in the universe to that of force scales. ... In theoretical physics, particularly in discussions of gravitation theories, Machs principle is the name given by Einstein to a vague hypothesis first supported by the physicist and philosopher Ernst Mach. ... The Sun is the star at the centre of the Solar System. ... A diagram of Keplerian orbital elements. ... Precession refers to a change in the direction of the axis of a rotating object. ... Note: This article contains special characters. ... In physics, an orbit is the path that an object makes, around another object, whilst under the influence of a source of centripetal force, such as gravity. ...

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". Philip James Edwin Peebles (born April 25, 1935) is an Canadian-American astronomer. ... In physics and cosmology, the anthropic principle is an umbrella term for various dissimilar attempts to explain the structure of the universe by way of coincidentally balanced features that are necessary and relevant to the existence on Earth of biochemistry, carbon-based life, and eventually human beings to observe such... Brandon Carter is a theoretical physicist, most famous for his work on the properties of black holes and for introducing the anthropic principle. ... Hertzsprung-Russell diagram The main sequence of the Hertzsprung-Russell diagram is the curve where the majority of stars are located in this diagram. ...

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. A Lock-in Amplifier (also known as a Phase Sensitive Detector) is a type of amplifier that can extract a signal with a known carrier wave from a noisy environment. ...

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. Extremely high resolution spectrum of the Sun showing thousands of elemental absorption lines (fraunhofer lines) Spectroscopy is the study of matter and its properties by investigating light, sound, or particles that are emitted, absorbed or scattered by the matter under investigation. ... The Mössbauer effect, a physical phenomenon discovered by Rudolf Mössbauer in 1957, refers to the resonant and recoil-free emission and absorption of gamma rays by atoms bound in a solid form. ...

External links

• National Academy of Sciences biography
• BAAS 29 (1997) 1469, obituary

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).