Observational cosmology

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Full-sky image derived from nine years' WMAP data
Early universe
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Expansion · Future
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Structure
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Scientists
Subject history

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.

Early observations

The science of

National Academy of Sciences colloquium in 1992.[1]

Hubble's law and the cosmic distance ladder

Main articles: Hubble's law and cosmic distance ladder

Distance measurements in astronomy have historically been and continue to be confounded by considerable measurement uncertainty. In particular, while

Hooker Telescope at Mount Wilson Observatory to identify individual stars in those galaxies, and determine the distance to the galaxies by isolating individual Cepheids. This firmly established the spiral nebula as being objects well outside the Milky Way galaxy. Determining the distance to "island universes", as they were dubbed in the popular media, established the scale of the universe and settled the Shapley-Curtis debate once and for all.[2]

lookback time of extragalactic observations by their redshift up to z=20.[3]

In 1927, by combining various measurements, including Hubble's distance measurements and

General theory of relativity is considered the beginning of the modern science of cosmology.[11]

Nuclide abundances

Main articles: cosmochemistry and astrochemistry

Determination of the

absorption lines which corresponded to particular electronic transitions in chemical elements identified on Earth. For example, the element Helium was first identified through its spectroscopic signature in the Sun before it was isolated as a gas on Earth.[12][13]

Computing relative abundances was achieved through corresponding spectroscopic observations to measurements of the elemental composition of meteorites.

Detection of the cosmic microwave background

Main article: Discovery of cosmic microwave background radiation
the CMB seen by WMAP

A

Bell Telephone Laboratories in nearby Holmdel Township, New Jersey had built a Dicke radiometer that they intended to use for radio astronomy and satellite communication experiments. Their instrument had an excess 3.5 K antenna temperature which they could not account for. After receiving a telephone call from Crawford Hill, Dicke famously quipped: "Boys, we've been scooped."[17] A meeting between the Princeton and Crawford Hill groups determined that the antenna temperature was indeed due to the microwave background. Penzias and Wilson received the 1978 Nobel Prize in Physics
for their discovery.

Modern observations

Today, observational cosmology continues to test the predictions of theoretical cosmology and has led to the refinement of cosmological models. For example, the observational evidence for

WMAP
experiment.

Included here are the modern observational efforts that have directly influenced cosmology.

Redshift surveys

Main article: Redshift survey

With the advent of automated

Great Wall, a vast supercluster of galaxies over 500 million light-years wide, provides a dramatic example of a large-scale structure that redshift surveys can detect.[18]

3D visualization of the dark matter distribution from the Hyper Suprime-Cam redshift survey on Subaru Telescope in 2018[19]

The first redshift survey was the

spectrograph; a follow-up to the pilot program DEEP1, DEEP2 is designed to measure faint galaxies with redshifts 0.7 and above, and it is therefore planned to provide a complement to SDSS and 2dF.[23]

Cosmic microwave background experiments

For a more comprehensive list, see List of cosmic microwave background experiments.
This section is an excerpt from Cosmic microwave background § Discovery.[edit]
The Holmdel Horn Antenna on which Penzias and Wilson discovered the cosmic microwave background.[24]
The first published recognition of the CMB radiation as a detectable phenomenon appeared in a brief paper by
Bell Telephone Laboratories in nearby Holmdel Township, New Jersey had built a Dicke radiometer that they intended to use for radio astronomy and satellite communication experiments. The antenna was constructed in 1959 to support Project Echo—the National Aeronautics and Space Administration's passive communications satellites, which used large earth orbiting aluminized plastic balloons as reflectors to bounce radio signals from one point on the Earth to another.[24] On 20 May 1964 they made their first measurement clearly showing the presence of the microwave background,[27] with their instrument having an excess 4.2K antenna temperature which they could not account for. After receiving a telephone call from Crawford Hill, Dicke said "Boys, we've been scooped."[28][29][30]: 140  A meeting between the Princeton and Crawford Hill groups determined that the antenna temperature was indeed due to the microwave background. Penzias and Wilson received the 1978 Nobel Prize in Physics for their discovery.[31]
The interpretation of the cosmic microwave background was a controversial issue in the late 1960s. Alternative explanations included energy from within the solar system, from galaxies, from intergalactic plasma, from multiple extragalactic radio sources. Two requirements would show that the microwave radiation was truly "cosmic". First the intensity vs frequency or spectrum needed to be shown to match a thermal or blackbody source. This was accomplished by 1968 in a series of measurements of the radiation temperature at higher and lower wavelengths. Second the radiation needed be shown to be isotropic, the same from all directions. This was also accomplished by 1970, demonstrating that this radiation was truly cosmic in origin.[32]

In the 1970s numerous studies showed that tiny deviations from isotropy in the CMB could result from events in the early universe.[32]: 8.5.1 

Harrison,[33] Peebles and Yu,[34] and Zel'dovich[35] realized that the early universe would require quantum inhomogeneities that would result in temperature anisotropy at the level of 10−4 or 10−5.[32]: 8.5.3.2  Rashid Sunyaev calculated the observable imprint that these inhomogeneities would have on the cosmic microwave background.[36]

After a lull in the 1970s caused in part by the many experimental difficulties in measuring CMB at high precision,[32]: 8.5.1  increasingly stringent limits on the anisotropy of the cosmic microwave background were set by ground-based experiments during the 1980s. RELIKT-1, a Soviet cosmic microwave background anisotropy experiment on board the Prognoz 9 satellite (launched 1 July 1983), gave the first upper limits on the large-scale anisotropy.[32]: 8.5.3.2 

The other key event in the 1980s was the proposal by

cosmic inflation. This theory of rapid spatial expansion gave an explanation for large-scale isotropy by allowing causal connection just before the epoch of last scattering.[32]
: 8.5.4  With this and similar theories, detailed prediction encouraged larger and more ambitious experiments.

The NASA Cosmic Background Explorer (COBE) satellite orbited Earth in 1989–1996 detected and quantified the large scale anisotropies at the limit of its detection capabilities.

The NASA COBE mission clearly confirmed the primary anisotropy with the Differential Microwave Radiometer instrument, publishing their findings in 1992.[37][38] The team received the Nobel Prize in physics for 2006 for this discovery.
Inspired by the COBE results, a series of ground and balloon-based experiments measured cosmic microwave background anisotropies on smaller angular scales over the[
cosmic inflation was the right theory of structure formation.[45]
WMAP and Planck

(March 21, 2013)

Inspired by the initial COBE results of an extremely isotropic and homogeneous background, a series of ground- and balloon-based experiments quantified CMB anisotropies on smaller angular scales over the next decade. The primary goal of these experiments was to measure the angular scale of the first acoustic peak, for which COBE did not have sufficient resolution. These measurements were able to rule out

cosmic inflation
was the right theory.

During the 1990s, the first peak was measured with increasing sensitivity and by 2000 the
interferometers provided measurements of the fluctuations with higher accuracy over the next three years, including the Very Small Array, Degree Angular Scale Interferometer (DASI), and the Cosmic Background Imager
(CBI). DASI made the first detection of the polarization of the CMB and the CBI provided the first E-mode polarization spectrum with compelling evidence that it is out of phase with the T-mode spectrum.

Telescope observations

Radio

The brightest sources of low-frequency radio emission (10 MHz and 100 GHz) are

megaparsecs
. Because radio galaxies are so bright, astronomers have used them to probe extreme distances and early times in the evolution of the universe.

Infrared

Far

Stratospheric Observatory For Infrared Astronomy, and the Herschel Space Observatory. The next large space telescope planned by NASA, the James Webb Space Telescope
will also explore in the infrared.

An additional infrared survey, the

Two-Micron All Sky Survey
, has also been very useful in revealing the distribution of galaxies, similar to other optical surveys described below.

Optical rays (visible to human eyes)

Optical light is still the primary means by which astronomy occurs, and in the context of cosmology, this means observing distant galaxies and galaxy clusters in order to learn about the

celestial coordinates
can be used to gain information about the other two spatial dimensions.

Very deep observations (which is to say sensitive to dim sources) are also useful tools in cosmology. The

Hubble Extreme Deep Field, and Hubble Deep Field South
are all examples of this.

Ultraviolet

See Ultraviolet astronomy.

X-rays

See X-ray astronomy.

Gamma-rays

See Gamma-ray astronomy.

Cosmic ray observations

See Cosmic-ray observatory.

Future observations

Cosmic neutrinos

Main article: Cosmic neutrino background

It is a prediction of the

cosmic microwave background radiation
. The microwave background is a relic from when the universe was about 380,000 years old, but the neutrino background is a relic from when the universe was about two seconds old.

If this neutrino radiation could be observed, it would be a window into very early stages of the universe. Unfortunately, these neutrinos would now be very cold, and so they are effectively impossible to observe directly.

Gravitational waves

Main article: Gravitational wave background

See also

References

  1. ^ Arthur M. Sackler Colloquia of the National Academy of Sciences: Physical Cosmology; Irvine, California: March 27–28, 1992.
  2. ^ "Island universe" is a reference to speculative ideas promoted by a variety of scholastic thinkers in the 18th and 19th centuries. The most famous early proponent of such ideas was philosopher Immanuel Kant who published a number of treatises on astronomy in addition to his more famous philosophical works. See Kant, I., 1755. Allgemeine Naturgeschichte und Theorie des Himmels, Part I, J.F. Peterson, Königsberg and Leipzig.
  3. ^ S.V. Pilipenko (2013-2021) "Paper-and-pencil cosmological calculator" arxiv:1303.5961, including Fortran-90 code upon which the citing chart is based.
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  7. ^ Reich, E. S. (27 June 2011). "Edwin Hubble in translation trouble".
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  8. ^ Livio, M. (2011). "Lost in translation: Mystery of the missing text solved".
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  10. ^ Hubble, E. (1929). "A relation between distance and radial velocity among extra-galactic nebulae".
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  11. Time Magazine's listing for Edwin Hubble in their Time 100 list of most influential people of the 20th Century. Michael Lemonick recounts, "He discovered the cosmos, and in doing so founded the science of cosmology." [1]
  12. ^ The Encyclopedia of the Chemical Elements, page 256
  13. ^ Oxford English Dictionary (1989), s.v. "helium". Retrieved December 16, 2006, from Oxford English Dictionary Online. Also, from quotation there: Thomson, W. (1872). Rep. Brit. Assoc. xcix: "Frankland and Lockyer find the yellow prominences to give a very decided bright line not far from D, but hitherto not identified with any terrestrial flame. It seems to indicate a new substance, which they propose to call Helium."
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  16. ^ R. H. Dicke, "The measurement of thermal radiation at microwave frequencies", Rev. Sci. Instrum. 17, 268 (1946). This basic design for a radiometer has been used in most subsequent cosmic microwave background experiments.
  17. ^ A. A. Penzias and R. W. Wilson, "A Measurement of Excess Antenna Temperature at 4080 Mc/s," Astrophysical Journal 142 (1965), 419. R. H. Dicke, P. J. E. Peebles, P. G. Roll and D. T. Wilkinson, "Cosmic Black-Body Radiation," Astrophysical Journal 142 (1965), 414. The history is given in P. J. E. Peebles, Principles of physical cosmology (Princeton Univ. Pr., Princeton 1993).
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  19. ^ Duffy, Jocelyn (October 2, 2018). "Hyper Suprime-Cam Survey Maps Dark Matter in the Universe". Carnegie Mellon University. Archived from the original on April 12, 2022. Retrieved December 7, 2022.
  20. ^ See the official CfA website for more details.
  21. S2CID 6906627.{{cite journal}}: CS1 maint: numeric names: authors list (link) 2dF Galaxy Redshift Survey homepage Archived 2007-02-05 at the Wayback Machine
  22. ^ SDSS Homepage
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  24. ^ a b 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.
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  26. ^ Dicke, R. H. (1946). "The Measurement of Thermal Radiation at Microwave Frequencies".
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  33. ^ Harrison, E. R. (1970). "Fluctuations at the threshold of classical cosmology".
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