Discovery of cosmic microwave background radiation

This article concerns the accidental discovery of cosmic microwave background radiation
Cosmic microwave background radiation
In cosmology, cosmic microwave background radiation is thermal radiation filling the observable universe almost uniformly....

. Although predicted by earlier theories, it was first found accidentally 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...

as they experimented with the Holmdel Horn Antenna.

History

Timeline of the discovery of the CMB
Important dates and persons
>1946	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... estimates a temperature of 50K
>1946	Robert Dicke predicts a microwave background radiation temperature of "less than 20K" (ref: Helge Kragh), but later revised to 45K (ref: Stephen G. Brush)
>1948	Ralph Alpher and Robert Herman Robert Herman Robert Herman was a United States scientist, best known for his work with Ralph Alpher in 1948-50, on estimating the temperature of cosmic microwave background radiation from the Big Bang explosion.... re-estimate Gamow's estimate at 5K.
>1949	Alpher and Herman re-re-estimate Gamow's estimate at 28K.
>1960s	Robert Dicke re-estimates an MBR (microwave background radiation) temperature of 40K (ref: Helge Kragh)
>1964	A. G. Doroshkevich A. G. Doroshkevich A. G. Doroshkevich is a Russian theoretical astrophysicist and cosmologist.He is best known for his work with Igor Novikov on the recognition of Cosmic microwave background radiation as a detectable phenomenon in the spring of 1964.... and Igor Novikov Igor Dmitriyevich Novikov Igor Dmitriyevich Novikov is a Russian theoretical astrophysicist and cosmologist.Novikov formulated the Novikov self-consistency principle in the mid-1980s, an important contribution to the theory of time travel.Novikov gained his Ph.D. degree in astrophysics in 1965 and the Russian D.Sc.... publish a brief paper, where they name the MBR phenomenon as detectable.
>1960s	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... measure the temperature to be approximately 3 K.

By the middle of the 20th century, cosmologists had developed two different theories to explain the creation of the universe. Some supported the steady-state theory, which states that the universe has always existed and will continue to survive without noticeable change. Others believed in the Big Bang

Big Bang

The Big Bang theory is the prevailing cosmological model that explains the early development of the Universe. According to the Big Bang theory, the Universe was once in an extremely hot and dense state which expanded rapidly. This rapid expansion caused the young Universe to cool and resulted in...

theory, which states that the universe was created in a massive explosion-like event about 13.7 billion years ago.

The first published recognition of the cosmic microwave background (CMB) radiation as a detectable phenomenon appeared in a brief paper by Soviet

Soviet Union

The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....

astrophysicists A. G. Doroshkevich

A. G. Doroshkevich

A. G. Doroshkevich is a Russian theoretical astrophysicist and cosmologist.He is best known for his work with Igor Novikov on the recognition of Cosmic microwave background radiation as a detectable phenomenon in the spring of 1964....

and Igor Novikov

Igor Dmitriyevich Novikov

Igor Dmitriyevich Novikov is a Russian theoretical astrophysicist and cosmologist.Novikov formulated the Novikov self-consistency principle in the mid-1980s, an important contribution to the theory of time travel.Novikov gained his Ph.D. degree in astrophysics in 1965 and the Russian D.Sc....

, entitled "Mean Density of Radiation in the Metagalaxy and Certain Problems in Relativistic Cosmology", in the spring of 1964.

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...

in Holmdel, New Jersey, in 1964, Arno Penzias

Arno Allan Penzias

Arno Allan Penzias is an American physicist and Nobel laureate in physics.-Early life and education:Penzias was born in Munich, Germany. At age six he was among the Jewish children evacuated to Britain as part of the Kindertransport rescue operation...

and Robert Wilson

Robert Woodrow Wilson

were experimenting with a supersensitive, 6 meter (20 ft) horn antenna

Horn antenna

A horn antenna or microwave horn is an antenna that consists of a flaring metal waveguide shaped like a horn to direct the radio waves. Horns are widely used as antennas at UHF and microwave frequencies, above 300 MHz...

originally built to detect radio wave

Radio Wave

Radio Wave may refer to:*Radio frequency*Radio Wave 96.5, a radio station in Blackpool, UK...

s bounced off echo balloon satellite

Echo satellite

Project Echo was the first passive communications satellite experiment. Each of the two American spacecraft was a metalized balloon satellite acting as a passive reflector of microwave signals. Communication signals were bounced off of them from one point on Earth to another.-Echo 1:NASA's Echo 1...

s. To measure these faint radio waves, they had to eliminate all recognizable interference

Electromagnetic interference

Electromagnetic interference is disturbance that affects an electrical circuit due to either electromagnetic induction or electromagnetic radiation emitted from an external source. The disturbance may interrupt, obstruct, or otherwise degrade or limit the effective performance of the circuit...

from their receiver. They removed the effects 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 radio broadcasting, and suppressed interference from the heat in the receiver itself by cooling it with liquid helium

Helium

Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...

to −269 °C, only 4 °C above absolute zero

Absolute zero

Absolute zero is the theoretical temperature at which entropy reaches its minimum value. The laws of thermodynamics state that absolute zero cannot be reached using only thermodynamic means....

.

When Penzias and Wilson reduced their data they found a low, steady, mysterious noise that persisted in their receiver. This residual noise was 100 times more intense than they had expected, was evenly spread over the sky, and was present day and night. They were certain that the radiation they detected on a wavelength of 7.35 centimeters did not come from the Earth

Earth

Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

, the Sun

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...

, or our galaxy

Milky Way

The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...

. After thoroughly checking their equipment, removing some pigeons nesting in the antenna and cleaning out the accumulated droppings, the noise remained. Both concluded that this noise was coming from outside our own galaxy—although they were not aware of any radio source that would account for it.

At that same time, Robert H. Dicke

Robert H. Dicke

Robert Henry Dicke was an American physicist who made important contributions to the fields of astrophysics, atomic physics, cosmology and gravity.-Biography:...

, Jim Peebles, and David 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...

, astrophysicists 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....

just 60 km (37.3 mi) away, were preparing to search for microwave radiation in this region of the spectrum. Dicke and his colleagues reasoned that the Big Bang must have scattered not only the matter that condensed into galaxies but also must have released a tremendous blast of radiation. With the proper instrumentation, this radiation should be detectable.

When a friend (Bernard F. Burke, Prof. of Physics at MIT) told Penzias about a preprint paper he had seen by Jim Peebles on the possibility of finding radiation left over from an explosion that filled the universe at the beginning of its existence, Penzias and Wilson began to realize the significance of their discovery. The characteristics of the radiation detected by Penzias and Wilson fit exactly the radiation predicted by Robert H. Dicke and his colleagues at Princeton University. Penzias called Dicke at Princeton, who immediately sent him a copy of the still-unpublished Peebles paper. Penzias read the paper and called Dicke again and invited him to Bell Labs to look at the Horn Antenna and listen to the background noise. Robert Dicke, P. J. E. Peebles, P. G. Roll and D. T. Wilkinson

David Todd Wilkinson

interpreted this radiation as a signature of the Big Bang.

To avoid potential conflict, they decided to publish their results jointly. Two notes were rushed to the Astrophysical Journal Letters. In the first, Dicke and his associates outlined the importance of cosmic background radiation as substantiation of the Big Bang Theory. In a second note, jointly signed by Penzias and Wilson titled, "A Measurement of Excess Antenna Temperature at 4080 Megacycles per Second," they noted the existence of the residual background noise and attributed a possible explanation to that given by Dicke in his companion letter.

In 1978, Penzias and Wilson were awarded the Nobel Prize for Physics for their joint discovery.

General

"Astronomy and Astrophysics Horn Antenna.". National Park Service, Department of the Interior.

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