Discovery of cosmic microwave background radiation

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The discovery of cosmic microwave background radiation constitutes a major development in modern physical cosmology. In 1964, US physicist Arno Allan Penzias and radio-astronomer Robert Woodrow Wilson discovered the cosmic microwave background (CMB), estimating its temperature as 3.5 K, as they experimented with the Holmdel Horn Antenna. [1] [2] The new measurements were accepted as important evidence for a hot early Universe (big bang theory) and as evidence against the rival steady state theory [3] as theoretical work around 1950 [4] showed the need for a CMB for consistency with the simplest relativistic universe models. In 1978, Penzias and Wilson were awarded the Nobel Prize for Physics for their joint measurement. There had been a prior measurement of the cosmic background radiation (CMB) by Andrew McKellar in 1941 at an effective temperature of 2.3 K using CN stellar absorption lines observed by W. S. Adams. [5] Although no reference to the CMB is made by McKellar, it was not until much later [6] after the Penzias and Wilson measurements that the significance of this measurement was understood.

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History

Bell Labs' Horn Antenna on Crawford Hill in Holmdel NJ - In 1964 while using the Horn Antenna, Penzias and Wilson stumbled on the microwave background radiation that permeates the universe. Bell Labs Horn Antenna Crawford Hill NJ.jpg
Bell Labs' Horn Antenna on Crawford Hill in Holmdel NJ – In 1964 while using the Horn Antenna, Penzias and Wilson stumbled on the microwave background radiation that permeates the universe.

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 theory, which states that the universe was created in a massive explosion-like event billions of years ago (later determined to be approximately 13.8 billion years).

In 1941, Andrew McKellar used W. S. Adams' spectroscopic observations of CN absorption lines in the spectrum of a B type star to measure a blackbody background temperature of 2.3 K. McKellar referred to his detection as a "'rotational' temperature of interstellar molecules", without reference to a cosmological interpretation, stating that the temperature "will have its own, perhaps limited, significance". [5]

Over two decades later, working at a Bell Telephone Laboratories facility atop Crawford Hill in Holmdel, New Jersey, in 1964, Arno Penzias and Robert Wilson were experimenting with a supersensitive, 6 meter (20 ft) horn antenna originally built to detect radio waves bounced off Echo balloon satellites. [2] To measure these faint radio waves, they had to eliminate all recognizable interference from their receiver. They removed the effects of radar and radio broadcasting, and suppressed interference from the heat in the receiver itself by cooling it with liquid helium to −269 °C, only 4 K above absolute zero.

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, the Sun, or our galaxy. 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, Jim Peebles, and David Wilkinson, astrophysicists at Princeton University just 60 km (37 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, albeit as microwaves, due to a massive redshift.

When his friend Bernard F. Burke, a professor 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 what they believed was a new 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. Dicke, Peebles, Wilkinson and P. G. Roll 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. [3] In a second note, jointly signed by Penzias and Wilson titled, "A Measurement of Excess Antenna Temperature at 4080 Megacycles per Second," they reported the existence of a 3.5 K residual background noise, remaining after accounting for a sky absorption component of 2.3 K and a 0.9 K instrumental component, and attributed a "possible explanation" as that given by Dicke in his companion letter. [1]

In 1978, Penzias and Wilson were awarded the Nobel Prize for Physics for their joint detection. They shared the prize with Pyotr Kapitsa, who won it for unrelated work. [7] In 2019, Jim Peebles was also awarded the Nobel Prize for Physics, “for theoretical discoveries in physical cosmology”. [8]

Bibliography

Related Research Articles

<span class="mw-page-title-main">Big Bang</span> Physical theory

The Big Bang is a physical theory that describes how the universe expanded from a primordial state of high density and temperature. It was first proposed as a physical theory in 1931 by Roman Catholic priest and physicist Georges Lemaître when he suggested the universe emerged from a "primeval atom". Various cosmological models of the Big Bang explain the evolution of the observable universe from the earliest known periods through its subsequent large-scale form. These models offer a comprehensive explanation for a broad range of observed phenomena, including the abundance of light elements, the cosmic microwave background (CMB) radiation, and large-scale structure. The overall uniformity of the universe, known as the flatness problem, is explained through cosmic inflation: a sudden and very rapid expansion of space during the earliest moments. However, physics currently lacks a widely accepted theory of quantum gravity that can successfully model the earliest conditions of the Big Bang.

<span class="mw-page-title-main">Cosmic microwave background</span> Trace radiation from the early universe

The cosmic microwave background is microwave radiation that fills all space in the observable universe. It is a remnant that provides an important source of data on the primordial universe. With a standard optical telescope, the background space between stars and galaxies is almost completely dark. However, a sufficiently sensitive radio telescope detects a faint background glow that is almost uniform and is not associated with any star, galaxy, or other object. This glow is strongest in the microwave region of the radio spectrum. The accidental discovery of the CMB in 1965 by American radio astronomers Arno Penzias and Robert Wilson was the culmination of work initiated in the 1940s.

Cosmic noise, also known as galactic radio noise, is a physical phenomenon derived from outside of the Earth's atmosphere. It is not actually sound, and it can be detected through a radio receiver, which is an electronic device that receives radio waves and converts the information given by them to an audible form. Its characteristics are comparable to those of thermal noise. Cosmic noise occurs at frequencies above about 15 MHz when highly directional antennas are pointed toward the Sun or other regions of the sky, such as the center of the Milky Way Galaxy. Celestial objects like quasars, which are super dense objects far from Earth, emit electromagnetic waves in their full spectrum, including radio waves. The fall of a meteorite can also be heard through a radio receiver; the falling object burns from friction with the Earth's atmosphere, ionizing surrounding gases and producing radio waves. Cosmic microwave background radiation (CMBR) from outer space is also a form of cosmic noise. CMBR is thought to be a relic of the Big Bang, and pervades the space almost homogeneously over the entire celestial sphere. The bandwidth of the CMBR is wide, though the peak is in the microwave range.

<span class="mw-page-title-main">Wilkinson Microwave Anisotropy Probe</span> NASA satellite of the Explorer program

The Wilkinson Microwave Anisotropy Probe (WMAP), originally known as the Microwave Anisotropy Probe, was a NASA spacecraft operating from 2001 to 2010 which measured temperature differences across the sky in the cosmic microwave background (CMB) – the radiant heat remaining from the Big Bang. Headed by Professor Charles L. Bennett of Johns Hopkins University, the mission was developed in a joint partnership between the NASA Goddard Space Flight Center and Princeton University. The WMAP spacecraft was launched on 30 June 2001 from Florida. The WMAP mission succeeded the COBE space mission and was the second medium-class (MIDEX) spacecraft in the NASA Explorer program. In 2003, MAP was renamed WMAP in honor of cosmologist David Todd Wilkinson (1935–2002), who had been a member of the mission's science team. After nine years of operations, WMAP was switched off in 2010, following the launch of the more advanced Planck spacecraft by European Space Agency (ESA) in 2009.

<span class="mw-page-title-main">Cosmic Background Explorer</span> Historic NASA cosmology mission

The Cosmic Background Explorer, also referred to as Explorer 66, was a NASA satellite dedicated to cosmology, which operated from 1989 to 1993. Its goals were to investigate the cosmic microwave background radiation of the universe and provide measurements that would help shape our understanding of the cosmos.

<span class="mw-page-title-main">Robert Woodrow Wilson</span> American astronomer (born 1936)

Robert Woodrow Wilson is an American astronomer who, along with Arno Allan Penzias, discovered cosmic microwave background radiation (CMB) in 1964. The pair won the 1978 Nobel Prize in Physics for its discovery.

<span class="mw-page-title-main">Arno Allan Penzias</span> American physicist (1933–2024)

Arno Allan Penzias was an American physicist and radio astronomer. Along with Robert Woodrow Wilson, he discovered the cosmic microwave background radiation, for which he shared the Nobel Prize in Physics in 1978.

<span class="mw-page-title-main">Holmdel Horn Antenna</span> Microwave horn antenna in New Jersey, US

The Holmdel Horn Antenna is a large microwave horn antenna that was used as a satellite communication antenna and radio telescope during the 1960s at the Bell Telephone Laboratories facility located on Crawford Hill in Holmdel Township, New Jersey, United States. It was designated a National Historic Landmark in 1989 because of its association with the research work of two radio astronomers, Arno Penzias and Robert Wilson.

Observational cosmology is the study of the structure, the evolution and the origin of the universe through observation, using instruments such as telescopes and cosmic ray detectors.

<span class="mw-page-title-main">Robert H. Dicke</span> American astronomer and physicist (1916–1997)

Robert Henry Dicke was an American astronomer and physicist who made important contributions to the fields of astrophysics, atomic physics, cosmology and gravity. He was the Albert Einstein Professor in Science at Princeton University (1975–1984).

In physical cosmology, the age of the universe is the time elapsed since the Big Bang. Astronomers have derived two different measurements of the age of the universe: a measurement based on direct observations of an early state of the universe, which indicate an age of 13.787±0.020 billion years as interpreted with the Lambda-CDM concordance model as of 2021; and a measurement based on the observations of the local, modern universe, which suggest a younger age. The uncertainty of the first kind of measurement has been narrowed down to 20 million years, based on a number of studies that all show similar figures for the age. These studies include researches of the microwave background radiation by the Planck spacecraft, the Wilkinson Microwave Anisotropy Probe and other space probes. Measurements of the cosmic background radiation give the cooling time of the universe since the Big Bang, and measurements of the expansion rate of the universe can be used to calculate its approximate age by extrapolating backwards in time. The range of the estimate is also within the range of the estimate for the oldest observed star in the universe.

<span class="mw-page-title-main">Jim Peebles</span> Canadian-American astrophysicist and cosmologist

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<span class="mw-page-title-main">Ralph Alpher</span> American cosmologist (1921–2007)

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<span class="mw-page-title-main">Cosmic background radiation</span> Electromagnetic radiation from the Big Bang

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<span class="mw-page-title-main">Cosmic microwave background spectral distortions</span> Fluctuations in the energy spectrum of the microwave background

CMB spectral distortions are tiny departures of the average cosmic microwave background (CMB) frequency spectrum from the predictions given by a perfect black body. They can be produced by a number of standard and non-standard processes occurring at the early stages of cosmic history, and therefore allow us to probe the standard picture of cosmology. Importantly, the CMB frequency spectrum and its distortions should not be confused with the CMB anisotropy power spectrum, which relates to spatial fluctuations of the CMB temperature in different directions of the sky.

References

  1. 1 2 Penzias, A.A.; R. W. Wilson (July 1965). "A Measurement Of Excess Antenna Temperature At 4080 Mc/s". Astrophysical Journal Letters. 142: 419–421. Bibcode:1965ApJ...142..419P. doi: 10.1086/148307 .
  2. 1 2 Overbye, Dennis (5 September 2023). "Back to New Jersey, Where the Universe Began – A half-century ago, a radio telescope in Holmdel, N.J., sent two astronomers 13.8 billion years back in time – and opened a cosmic window that scientists have been peering through ever since". The New York Times . Archived from the original on 5 September 2023. Retrieved 5 September 2023.
  3. 1 2 Dicke, R. H.; Peebles, P. J. E.; Roll, P. J.; Wilkinson, D. T. (July 1965). "Cosmic Black-Body Radiation". Astrophysical Journal Letters. 142: 414–419. Bibcode:1965ApJ...142..414D. doi:10.1086/148306.
  4. ↑ Sciama, D. W. (1990). Mandolesi, N.; Vittorio, N. (eds.). "The Impact of the CMB Discovery on Theoretical Cosmology". The Cosmic Microwave Background: 25 Years Later. Astrophysics and Space Science Library. Dordrecht: Springer Netherlands: 1–15. doi:10.1007/978-94-009-0655-6_1. ISBN   978-94-009-0655-6.
  5. 1 2 McKellar, A. (1941). "Molecular Lines from the Lowest States of Diatomic Molecules Composed of Atoms Probably Present in Interstellar Space". Publications of the Dominion Astrophysical Observatory. 7 (6). Vancouver, B.C., Canada: 251–272. Bibcode:1941PDAO....7..251M.
  6. ↑ Thaddeus, P. (1972). "The short-wavelength spectrum of the microwave background". Annual Review of Astronomy and Astrophysics . 10: 10(1), 305–334. Bibcode:1972ARA&A..10..305T. doi:10.1146/annurev.aa.10.090172.001513.
  7. ↑ "The Nobel Prize in Physics 1978". NobelPrize.org. Nobel Prize Outreach AB. Retrieved 9 February 2022.
  8. ↑ "The Nobel Prize in Physics 2019". NobelPrize.org. Nobel Prize Outreach AB. Retrieved 9 February 2022.
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