Robert H. Dicke
Encyclopedia
Robert Henry Dicke was an American physicist
who made important contributions to the fields of astrophysics
, atomic physics
, cosmology
and gravity.
, Dicke completed his bachelor's degree
at Princeton University
and his doctorate, in 1939, from the University of Rochester
in nuclear physics
. During the Second World War he worked in the Radiation Laboratory at the Massachusetts Institute of Technology
where he worked on the development of radar
and designed the Dicke radiometer, a microwave receiver. He used this to set a limit on the temperature of the microwave background radiation, from the roof of the Radiation Laboratory, of less than 20 kelvin
s.
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. An important contribution to the field of Spectroscopy
and Radiative Transfer was his prediction of 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 Mössbauer effect
for gamma rays.
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
. A highlight experiment was the classic test of the equivalence principle by Roll, Krotkov and Dicke, a factor of 100 more accurate than previous work. He also 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.
Dirac had noted that the Gravitational constant
, G is very roughly equal to the inverse age of the universe
(in certain 'natural' units), and had concluded that G must vary to maintain this equality. Dicke realized that Dirac's relation could be a selection effect: fundamental physical laws connect G to the lifetime of what are called main sequence
stars, such as our Sun, and these stars, according to Dicke, are necessary for the existence of life. At any other epoch, when the equality did not hold, there would be no intelligent life around to notice the discrepancy. This was the first modern application of what is now called the weak anthropic principle.
In the early 1960s, work on Brans-Dicke theory led Dicke to think about the early Universe, and with Jim Peebles
he re-derived the prediction of a cosmic microwave background (having allegedly forgotten the earlier prediction of George Gamow
and co-workers). Naturally, Dicke, with David Todd Wilkinson
and Peter G. Roll immediately set about building a Dicke radiometer to search for the radiation, but they were famously scooped
by the accidental detection made by Arno Penzias and Robert Woodrow Wilson
(also using a Dicke radiometer), who were working at Bell Labs
just a few miles from Princeton. Nevertheless, Dicke's group made the second clean detection, and their theoretical interpretation of Penzias & Wilson's results showed that theories of the early universe had moved from pure speculation into well-tested physics.
Dicke (1970) gave an interesting argument that the universe must have very nearly the critical density of matter needed to stop it expanding forever. Standard models
of the universe pass through stages dominated by radiation, matter, curvature etc. Transitions between stages are very special cosmic times which a priori could differ by many orders of magnitude. Since there is a non-negligible amount of matter, either we are coincidentally living close to the transition to or from the matter-dominated stage, or we are in the middle of it; the latter is preferred since the coincidences are highly unlikely (an application of the Copernican principle
). This implies a negligible curvature, so the universe must have almost critical density. This has been called the "Dicke coincidence" argument. In fact it gives the wrong answer, since we seem to be living at the time of transition between the matter and dark energy
stages. An anthropic explanation of the failure of Dicke's argument was given by Weinberg.
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. Many of Dicke's experiments capitalize on lock-in in some way or another.
In 1970, Dicke was awarded the National Medal of Science
. In 1973 he was awarded the Comstock Prize in Physics
from the National Academy of Sciences
.
descent, was born in Barrow-in-Furness
in England
in 1920 and as a young girl immigrated to Rochester, NY, via Australia and New Zealand, of which Annie had very fond memories. To her dying day, Annie would state that Australia was nice but New Zealand was Utopia.
At the beginning of World War II
Robert was asked to assist the war effort by applying his skills to the development of radar with the Massachusetts Institute of Technology. Therefore, this is where they began their married life. During this time, Annie became friends with a number of the wives of other professors working on similar projects. However due to security concerns none of them knew what their husbands' work entailed and could never discuss it.
At the end of the war, Robert and Annie moved to Princeton, New Jersey where Robert was on the faculty at Princeton University. Robert died there March 4, 1997. Annie continued to live in Princeton until 2002. For the last years of her life she lived in Hightstown, New Jersey at Meadow Lakes Retirement Community until her death in 2005.
They had one daughter, Nancy born in 1945, and two sons, John born in 1946 and James born in 1953. At the time of Robert's death they had six grandchildren and two great grandchildren.
Physicist
A physicist is a scientist who studies or practices physics. Physicists study a wide range of physical phenomena in many branches of physics spanning all length scales: from sub-atomic particles of which all ordinary matter is made to the behavior of the material Universe as a whole...
who made important contributions to the fields of astrophysics
Astrophysics
Astrophysics is the branch of astronomy that deals with the physics of the universe, including the physical properties of celestial objects, as well as their interactions and behavior...
, atomic physics
Atomic physics
Atomic physics is the field of physics that studies atoms as an isolated system of electrons and an atomic nucleus. It is primarily concerned with the arrangement of electrons around the nucleus and...
, cosmology
Physical cosmology
Physical cosmology, as a branch of astronomy, is the study of the largest-scale structures and dynamics of the universe and is concerned with fundamental questions about its formation and evolution. For most of human history, it was a branch of metaphysics and religion...
and gravity.
Biography
Born in St. Louis, MissouriSt. Louis, Missouri
St. Louis is an independent city on the eastern border of Missouri, United States. With a population of 319,294, it was the 58th-largest U.S. city at the 2010 U.S. Census. The Greater St...
, Dicke completed his bachelor's degree
Bachelor's degree
A bachelor's degree is usually an academic degree awarded for an undergraduate course or major that generally lasts for three or four years, but can range anywhere from two to six years depending on the region of the world...
at Princeton University
Princeton University
Princeton University is a private research university located in Princeton, New Jersey, United States. The school is one of the eight universities of the Ivy League, and is one of the nine Colonial Colleges founded before the American Revolution....
and his doctorate, in 1939, from the University of Rochester
University of Rochester
The University of Rochester is a private, nonsectarian, research university in Rochester, New York, United States. The university grants undergraduate and graduate degrees, including doctoral and professional degrees. The university has six schools and various interdisciplinary programs.The...
in nuclear physics
Nuclear physics
Nuclear physics is the field of physics that studies the building blocks and interactions of atomic nuclei. The most commonly known applications of nuclear physics are nuclear power generation and nuclear weapons technology, but the research has provided application in many fields, including those...
. During the Second World War he worked in the Radiation Laboratory at the Massachusetts Institute of Technology
Massachusetts Institute of Technology
The Massachusetts Institute of Technology is a private research university located in Cambridge, Massachusetts. MIT has five schools and one college, containing a total of 32 academic departments, with a strong emphasis on scientific and technological education and research.Founded in 1861 in...
where he worked on the development of radar
Radar
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...
and designed the Dicke radiometer, a microwave receiver. He used this to set a limit on the temperature of the microwave background radiation, from the roof of the Radiation Laboratory, of less than 20 kelvin
Kelvin
The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...
s.
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
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...
and measuring the gyromagnetic ratio of the electron. An important contribution to the field of Spectroscopy
Spectroscopy
Spectroscopy is the study of the interaction between matter and radiated energy. Historically, spectroscopy originated through the study of visible light dispersed according to its wavelength, e.g., by a prism. Later the concept was expanded greatly to comprise any interaction with radiative...
and Radiative Transfer was his prediction of 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 Mössbauer effect
Mössbauer effect
The Mössbauer effect, or recoilless nuclear resonance fluorescence, is a physical phenomenon discovered by Rudolf Mössbauer in 1958. It involves the resonant and recoil-free emission and absorption of γ radiation by atomic nuclei bound in a solid...
for gamma rays.
He spent the remainder of his career developing a program of precision tests of general relativity
General relativity
General relativity or the general theory of relativity is the geometric theory of gravitation published by Albert Einstein in 1916. It is the current description of gravitation in modern physics...
using the framework of the equivalence principle
Equivalence principle
In the physics of general relativity, the equivalence principle is any of several related concepts dealing with the equivalence of gravitational and inertial mass, and to Albert Einstein's assertion that the gravitational "force" as experienced locally while standing on a massive body is actually...
. With Carl H. Brans
Carl H. Brans
Carl Henry Brans is an American mathematical physicist best known for his research into the theoretical underpinnings of gravitation elucidated in his most widely publicized work, the Brans–Dicke theory....
, he developed Brans-Dicke theory
Brans-Dicke theory
In theoretical physics, the Brans–Dicke theory of gravitation is a theoretical framework to explain gravitation. It is a well-known competitor of Einstein's more popular theory of general relativity...
of gravitation, an equivalence-principle violating modification of general relativity inspired by Paul Dirac
Paul Dirac
Paul Adrien Maurice Dirac, OM, FRS was an English theoretical physicist who made fundamental contributions to the early development of both quantum mechanics and quantum electrodynamics...
's large numbers hypothesis
Dirac large numbers hypothesis
The Dirac large numbers hypothesis is an observation made by Paul Dirac in 1937 relating ratios of size scales in the Universe to that of force scales. The ratios constitute very large, dimensionless numbers: some 40 orders of magnitude in the present cosmological epoch...
and Mach's principle
Mach's principle
In theoretical physics, particularly in discussions of gravitation theories, Mach's principle is the name given by Einstein to an imprecise hypothesis often credited to the physicist and philosopher Ernst Mach....
. A highlight experiment was the classic test of the equivalence principle by Roll, Krotkov and Dicke, a factor of 100 more accurate than previous work. He also made measurements of solar
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
oblateness which were useful in understanding the perihelion
Apsis
An apsis , plural apsides , is the point of greatest or least distance of a body from one of the foci of its elliptical orbit. In modern celestial mechanics this focus is also the center of attraction, which is usually the center of mass of the system...
precession of Mercury's
Mercury (planet)
Mercury is the innermost and smallest planet in the Solar System, orbiting the Sun once every 87.969 Earth days. The orbit of Mercury has the highest eccentricity of all the Solar System planets, and it has the smallest axial tilt. It completes three rotations about its axis for every two orbits...
orbit
Orbit
In physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...
, one of the classical tests of general relativity.
Dirac had noted that the Gravitational constant
Gravitational constant
The gravitational constant, denoted G, is an empirical physical constant involved in the calculation of the gravitational attraction between objects with mass. It appears in Newton's law of universal gravitation and in Einstein's theory of general relativity. It is also known as the universal...
, G is very roughly equal to the inverse age of the universe
Age of the universe
The age of the universe is the time elapsed since the Big Bang posited by the most widely accepted scientific model of cosmology. The best current estimate of the age of the universe is 13.75 ± 0.13 billion years within the Lambda-CDM concordance model...
(in certain 'natural' units), and had concluded that G must vary to maintain this equality. Dicke realized that Dirac's relation could be a selection effect: fundamental physical laws connect G to the lifetime of what are called main sequence
Main sequence
The main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Hertzsprung and Henry Norris Russell...
stars, such as our Sun, and these stars, according to Dicke, are necessary for the existence of life. At any other epoch, when the equality did not hold, there would be no intelligent life around to notice the discrepancy. This was the first modern application of what is now called the weak anthropic principle.
In the early 1960s, work on Brans-Dicke theory led Dicke to think about the early Universe, and with Jim Peebles
Jim Peebles
Phillip James Edwin Peebles is a Canadian-American physicist and theoretical cosmologist who is currently the Albert Einstein Professor Emeritus of Science at Princeton University. Peebles was born in Winnipeg and completed his bachelor's degree at the University of Manitoba...
he re-derived the prediction of a cosmic microwave background (having allegedly forgotten the earlier prediction of George Gamow
George Gamow
George Gamow , born Georgiy Antonovich Gamov , was a Russian-born theoretical physicist and cosmologist. He discovered alpha decay via quantum tunneling and worked on radioactive decay of the atomic nucleus, star formation, stellar nucleosynthesis, Big Bang nucleosynthesis, cosmic microwave...
and co-workers). Naturally, Dicke, with David Todd Wilkinson
David Todd Wilkinson
David Todd Wilkinson was a world-renowned pioneer in the field of cosmology, specializing in the study of the cosmic microwave background radiation left over from the Big Bang. He was born in Hillsdale, Michigan, and earned his Ph.D. in physics at the University of Michigan under the supervision...
and Peter G. Roll immediately set about building a Dicke radiometer to search for the radiation, but they were famously scooped
Discovery of cosmic microwave background radiation
This article concerns the accidental discovery of cosmic microwave background radiation. Although predicted by earlier theories, it was first found accidentally by Arno Penzias and Robert Woodrow Wilson as they experimented with the Holmdel Horn Antenna....
by the accidental detection made by Arno Penzias and Robert Woodrow Wilson
Robert Woodrow Wilson
For the American President, see Woodrow Wilson.Robert Woodrow Wilson is an American astronomer, 1978 Nobel laureate in physics, who with Arno Allan Penzias discovered in 1964 the cosmic microwave background radiation...
(also using a Dicke radiometer), who were working at Bell Labs
Bell Labs
Bell Laboratories is the research and development subsidiary of the French-owned Alcatel-Lucent and previously of the American Telephone & Telegraph Company , half-owned through its Western Electric manufacturing subsidiary.Bell Laboratories operates its...
just a few miles from Princeton. Nevertheless, Dicke's group made the second clean detection, and their theoretical interpretation of Penzias & Wilson's results showed that theories of the early universe had moved from pure speculation into well-tested physics.
Dicke (1970) gave an interesting argument that the universe must have very nearly the critical density of matter needed to stop it expanding forever. Standard models
Friedmann equations
The Friedmann equations are a set of equations in physical cosmology that govern the expansion of space in homogeneous and isotropic models of the universe within the context of general relativity...
of the universe pass through stages dominated by radiation, matter, curvature etc. Transitions between stages are very special cosmic times which a priori could differ by many orders of magnitude. Since there is a non-negligible amount of matter, either we are coincidentally living close to the transition to or from the matter-dominated stage, or we are in the middle of it; the latter is preferred since the coincidences are highly unlikely (an application of the Copernican principle
Copernican principle
In physical cosmology, the Copernican principle, named after Nicolaus Copernicus, states that the Earth is not in a central, specially favored position. More recently, the principle has been generalized to the relativistic concept that humans are not privileged observers of the universe...
). This implies a negligible curvature, so the universe must have almost critical density. This has been called the "Dicke coincidence" argument. In fact it gives the wrong answer, since we seem to be living at the time of transition between the matter and dark energy
Dark energy
In physical cosmology, astronomy and celestial mechanics, dark energy is a hypothetical form of energy that permeates all of space and tends to accelerate the expansion of the universe. Dark energy is the most accepted theory to explain recent observations that the universe appears to be expanding...
stages. An anthropic explanation of the failure of Dicke's argument was given by Weinberg.
Robert Dicke is also responsible for developing the lock-in amplifier
Lock-in amplifier
A lock-in amplifier is a type of amplifier that can extract a signal with a known carrier wave from an extremely noisy environment . It is essentially a homodyne with an extremely low pass filter...
, 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. Many of Dicke's experiments capitalize on lock-in in some way or another.
In 1970, Dicke was awarded the National Medal of Science
National Medal of Science
The National Medal of Science is an honor bestowed by the President of the United States to individuals in science and engineering who have made important contributions to the advancement of knowledge in the fields of behavioral and social sciences, biology, chemistry, engineering, mathematics and...
. In 1973 he was awarded the Comstock Prize in Physics
Comstock Prize in Physics
The Comstock Prize in Physics is awarded by the U.S. National Academy of Sciences "for recent innovative discovery or investigation in electricity, magnetism, or radiant energy, broadly interpreted."...
from the National Academy of Sciences
United States National Academy of Sciences
The National Academy of Sciences is a corporation in the United States whose members serve pro bono as "advisers to the nation on science, engineering, and medicine." As a national academy, new members of the organization are elected annually by current members, based on their distinguished and...
.
Marriage and family life
Dicke married Annie Currie in 1942. Annie, of ScottishScottish people
The Scottish people , or Scots, are a nation and ethnic group native to Scotland. Historically they emerged from an amalgamation of the Picts and Gaels, incorporating neighbouring Britons to the south as well as invading Germanic peoples such as the Anglo-Saxons and the Norse.In modern use,...
descent, was born in Barrow-in-Furness
Barrow-in-Furness
Barrow-in-Furness is an industrial town and seaport which forms about half the territory of the wider Borough of Barrow-in-Furness in the county of Cumbria, England. It lies north of Liverpool, northwest of Manchester and southwest from the county town of Carlisle...
in England
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
in 1920 and as a young girl immigrated to Rochester, NY, via Australia and New Zealand, of which Annie had very fond memories. To her dying day, Annie would state that Australia was nice but New Zealand was Utopia.
At the beginning of World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
Robert was asked to assist the war effort by applying his skills to the development of radar with the Massachusetts Institute of Technology. Therefore, this is where they began their married life. During this time, Annie became friends with a number of the wives of other professors working on similar projects. However due to security concerns none of them knew what their husbands' work entailed and could never discuss it.
At the end of the war, Robert and Annie moved to Princeton, New Jersey where Robert was on the faculty at Princeton University. Robert died there March 4, 1997. Annie continued to live in Princeton until 2002. For the last years of her life she lived in Hightstown, New Jersey at Meadow Lakes Retirement Community until her death in 2005.
They had one daughter, Nancy born in 1945, and two sons, John born in 1946 and James born in 1953. At the time of Robert's death they had six grandchildren and two great grandchildren.
External links
- National Academy of Sciences biography
- BAAS 29 (1997) 1469, obituary
- A Look at the Abandoned Contributions to Cosmology of Dirac, Sciama and Dicke (arxiv:0708.3518)
- Oral History interview transcript with Robert Dicke 2 May 1983, American Institute of Physics, Niels Bohr Library and Archives
- Oral History interview transcript with Robert Dicke 18 June 1985, American Institute of Physics, Niels Bohr Library and Archives