Observational cosmology

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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.

Contents

Early observations

The science of physical cosmology as it is practiced today had its subject material defined in the years following the Shapley-Curtis debate when it was determined that the universe had a larger scale than the Milky Way galaxy. This was precipitated by observations that established the size and the dynamics of the cosmos that could be explained by Albert Einstein's General Theory of Relativity. In its infancy, cosmology was a speculative science based on a very limited number of observations and characterized by a dispute between steady state theorists and promoters of Big Bang cosmology. It was not until the 1990s and beyond that the astronomical observations would be able to eliminate competing theories and drive the science to the "Golden Age of Cosmology" which was heralded by David Schramm at a National Academy of Sciences colloquium in 1992. [1]

Hubble's law and the cosmic distance ladder

Distance measurements in astronomy have historically been and continue to be confounded by considerable measurement uncertainty. In particular, while stellar parallax can be used to measure the distance to nearby stars, the observational limits imposed by the difficulty in measuring the minuscule parallaxes associated with objects beyond our galaxy meant that astronomers had to look for alternative ways to measure cosmic distances. To this end, a standard candle measurement for Cepheid variables was discovered by Henrietta Swan Leavitt in 1908 which would provide Edwin Hubble with the rung on the cosmic distance ladder he would need to determine the distance to spiral nebula. Hubble used the 100-inch 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]

The lookback time of extragalactic observations by their redshift up to z=20. Look-back time by redshift.png
The lookback time of extragalactic observations by their redshift up to z=20.

In 1927, by combining various measurements, including Hubble's distance measurements and Vesto Slipher's determinations of redshifts for these objects, Georges Lemaître was the first to estimate a constant of proportionality between galaxies' distances and what was termed their "recessional velocities", finding a value of about 600 km/s/Mpc. [4] [5] [6] [7] [8] [9] He showed that this was theoretically expected in a universe model based on general relativity. [4] Two years later, Hubble showed that the relation between the distances and velocities was a positive correlation and had a slope of about 500 km/s/Mpc. [10] This correlation would come to be known as Hubble's law and would serve as the observational foundation for the expanding universe theories on which cosmology is still based. The publication of the observations by Slipher, Wirtz, Hubble and their colleagues and the acceptance by the theorists of their theoretical implications in light of Einstein's General theory of relativity is considered the beginning of the modern science of cosmology. [11]

Nuclide abundances

Determination of the cosmic abundance of elements has a history dating back to early spectroscopic measurements of light from astronomical objects and the identification of emission and 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

the CMB seen by WMAP Ilc 9yr moll4096.png
the CMB seen by WMAP

A cosmic microwave background was predicted in 1948 by George Gamow and Ralph Alpher, and by Alpher and Robert Herman as due to the hot Big Bang model. Moreover, Alpher and Herman were able to estimate the temperature, [14] but their results were not widely discussed in the community. Their prediction was rediscovered by Robert Dicke and Yakov Zel'dovich in the early 1960s with the first published recognition of the CMB radiation as a detectable phenomenon appeared in a brief paper by Soviet astrophysicists A. G. Doroshkevich and Igor Novikov, in the spring of 1964. [15] In 1964, David Todd Wilkinson and Peter Roll, Dicke's colleagues at Princeton University, began constructing a Dicke radiometer to measure the cosmic microwave background. [16] In 1965, Arno Penzias and Robert Woodrow Wilson at the Crawford Hill location of 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 dark matter has heavily influenced theoretical modeling of structure and galaxy formation. When trying to calibrate the Hubble diagram with accurate supernova standard candles, observational evidence for dark energy was obtained in the late 1990s. These observations have been incorporated into a six-parameter framework known as the Lambda-CDM model which explains the evolution of the universe in terms of its constituent material. This model has subsequently been verified by detailed observations of the cosmic microwave background, especially through the WMAP experiment.

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

Redshift surveys

With the advent of automated telescopes and improvements in spectroscopes, a number of collaborations have been made to map the universe in redshift space. By combining redshift with angular position data, a redshift survey maps the 3D distribution of matter within a field of the sky. These observations are used to measure properties of the large-scale structure of the universe. The 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 HSCSDMmap2018.gif
3D visualization of the dark matter distribution from the Hyper Suprime-Cam redshift survey on Subaru Telescope in 2018

The first redshift survey was the CfA Redshift Survey, started in 1977 with the initial data collection completed in 1982. [20] More recently, the 2dF Galaxy Redshift Survey determined the large-scale structure of one section of the Universe, measuring z-values for over 220,000 galaxies; data collection was completed in 2002, and the final data set was released 30 June 2003. [21] (In addition to mapping large-scale patterns of galaxies, 2dF established an upper limit on neutrino mass.) Another notable investigation, the Sloan Digital Sky Survey (SDSS), is ongoing as of 2011 and aims to obtain measurements on around 100 million objects. [22] SDSS has recorded redshifts for galaxies as high as 0.4, and has been involved in the detection of quasars beyond z = 6. The DEEP2 Redshift Survey uses the Keck telescopes with the new "DEIMOS" 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

This section is an excerpt from Cosmic microwave background § Microwave background observations.[ edit ]
Comparison of CMB results from COBE, WMAP and Planck (March 21, 2013) PIA16874-CobeWmapPlanckComparison-20130321.jpg
Comparison of CMB results from COBE, WMAP and Planck
(March 21, 2013)

Subsequent to the discovery of the CMB, hundreds of cosmic microwave background experiments have been conducted to measure and characterize the signatures of the radiation. The most famous experiment is probably the NASA Cosmic Background Explorer (COBE) satellite that orbited in 1989–1996 and which detected and quantified the large scale anisotropies at the limit of its detection capabilities. 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 strings as the leading theory of cosmic structure formation, and suggested cosmic inflation was the right theory.

During the 1990s, the first peak was measured with increasing sensitivity and by 2000 the BOOMERanG experiment reported that the highest power fluctuations occur at scales of approximately one degree. Together with other cosmological data, these results implied that the geometry of the universe is flat. A number of ground-based 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.

In June 2001, NASA launched a second CMB space mission, WMAP, to make much more precise measurements of the large scale anisotropies over the full sky. WMAP used symmetric, rapid-multi-modulated scanning, rapid switching radiometers to minimize non-sky signal noise. [24] The first results from this mission, disclosed in 2003, were detailed measurements of the angular power spectrum at a scale of less than one degree, tightly constraining various cosmological parameters. The results are broadly consistent with those expected from cosmic inflation as well as various other competing theories, and are available in detail at NASA's data bank for Cosmic Microwave Background (CMB) (see links below). Although WMAP provided very accurate measurements of the large scale angular fluctuations in the CMB (structures about as broad in the sky as the moon), it did not have the angular resolution to measure the smaller scale fluctuations which had been observed by former ground-based interferometers.

A third space mission, the ESA (European Space Agency) Planck Surveyor, was launched in May 2009 and performed an even more detailed investigation until it was shut down in October 2013. Planck employed both HEMT radiometers and bolometer technology and measured the CMB at a smaller scale than WMAP. Its detectors were trialled in the Antarctic Viper telescope as ACBAR (Arcminute Cosmology Bolometer Array Receiver) experiment—which has produced the most precise measurements at small angular scales to date—and in the Archeops balloon telescope.

On 21 March 2013, the European-led research team behind the Planck cosmology probe released the mission's all-sky map (565x318 jpeg, 3600x1800 jpeg) of the cosmic microwave background. [25] [26] The map suggests the universe is slightly older than researchers expected. According to the map, subtle fluctuations in temperature were imprinted on the deep sky when the cosmos was about 370000 years old. The imprint reflects ripples that arose as early, in the existence of the universe, as the first nonillionth of a second. Apparently, these ripples gave rise to the present vast cosmic web of galaxy clusters and dark matter. Based on the 2013 data, the universe contains 4.9% ordinary matter, 26.8% dark matter and 68.3% dark energy. On 5 February 2015, new data was released by the Planck mission, according to which the age of the universe is 13.799±0.021 billion years old and the Hubble constant was measured to be 67.74±0.46 (km/s)/Mpc. [27]

Additional ground-based instruments such as the South Pole Telescope in Antarctica and the proposed Clover Project, Atacama Cosmology Telescope and the QUIET telescope in Chile will provide additional data not available from satellite observations, possibly including the B-mode polarization.

Telescope observations

Radio

The brightest sources of low-frequency radio emission (10 MHz and 100 GHz) are radio galaxies which can be observed out to extremely high redshifts. These are subsets of the active galaxies that have extended features known as lobes and jets which extend away from the galactic nucleus distances on the order of 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 infrared observations including submillimeter astronomy have revealed a number of sources at cosmological distances. With the exception of a few atmospheric windows, most of infrared light is blocked by the atmosphere, so the observations generally take place from balloon or space-based instruments. Current observational experiments in the infrared include NICMOS, the Cosmic Origins Spectrograph, the Spitzer Space Telescope, the Keck Interferometer, the 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 large scale structure of the Universe as well as galaxy evolution. Redshift surveys have been a common means by which this has been accomplished with some of the most famous including the 2dF Galaxy Redshift Survey, the Sloan Digital Sky Survey, and the upcoming Large Synoptic Survey Telescope. These optical observations generally use either photometry or spectroscopy to measure the redshift of a galaxy and then, via Hubble's Law, determine its distance modulo redshift distortions due to peculiar velocities. Additionally, the position of the galaxies as seen on the sky in 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 Deep Field, Hubble Ultra Deep Field, 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

It is a prediction of the Big Bang model that the universe is filled with a neutrino background radiation, analogous to 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

See also

Related Research Articles

<span class="mw-page-title-main">Big Bang</span> Physical theory describing the expansion of the universe

The Big Bang is a physical theory that describes how the universe expanded from an initial state of high density and temperature. The Big Bang theory was inspired by the discovery of the expanding Universe by Edwin Hubble. It was first proposed in 1927 by Roman Catholic priest and physicist Georges Lemaître. Lemaître reasoned that if we go back in time, there must be fewer and fewer matter, until all the energy of the universe is packed in a unique quantum. 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">Physical cosmology</span> Branch of cosmology which studies mathematical models of the universe

Physical cosmology is a branch of cosmology concerned with the study of cosmological models. A cosmological model, or simply cosmology, provides a description of the largest-scale structures and dynamics of the universe and allows study of fundamental questions about its origin, structure, evolution, and ultimate fate. Cosmology as a science originated with the Copernican principle, which implies that celestial bodies obey identical physical laws to those on Earth, and Newtonian mechanics, which first allowed those physical laws to be understood.

<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.

<span class="mw-page-title-main">Redshift</span> Change of wavelength in photons during travel

In physics, a redshift is an increase in the wavelength, and corresponding decrease in the frequency and photon energy, of electromagnetic radiation. The opposite change, a decrease in wavelength and increase in frequency and energy, is known as a blueshift, or negative redshift. The terms derive from the colours red and blue which form the extremes of the visible light spectrum. The main causes of electromagnetic redshift in astronomy and cosmology are the relative motions of radiation sources, which give rise to the relativistic Doppler effect, and gravitational potentials, which gravitationally redshift escaping radiation. All sufficiently distant light sources show cosmological redshift corresponding to recession speeds proportional to their distances from Earth, a fact known as Hubble's law that implies the universe is expanding.

<span class="mw-page-title-main">Hubble's law</span> Observation in physical cosmology

Hubble's law, also known as the Hubble–Lemaître law, is the observation in physical cosmology that galaxies are moving away from Earth at speeds proportional to their distance. In other words, the farther they are, the faster they are moving away from Earth. The velocity of the galaxies has been determined by their redshift, a shift of the light they emit toward the red end of the visible spectrum. The discovery of Hubble's law is attributed to Edwin Hubble's work published in 1929.

In modern physical cosmology, the cosmological principle is the notion that the spatial distribution of matter in the universe is uniformly isotropic and homogeneous when viewed on a large enough scale, since the forces are expected to act equally throughout the universe on a large scale, and should, therefore, produce no observable inequalities in the large-scale structuring over the course of evolution of the matter field that was initially laid down by the Big Bang.

<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> NASA satellite of the Explorer program

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">Observable universe</span> All of space observable from the Earth at the present

The observable universe is a ball-shaped region of the universe comprising all matter that can be observed from Earth or its space-based telescopes and exploratory probes at the present time; the electromagnetic radiation from these objects has had time to reach the Solar System and Earth since the beginning of the cosmological expansion. Initially, it was estimated that there may be 2 trillion galaxies in the observable universe. That number was reduced in 2021 to only several hundred billion based on data from New Horizons. Assuming the universe is isotropic, the distance to the edge of the observable universe is roughly the same in every direction. That is, the observable universe is a spherical region centered on the observer. Every location in the universe has its own observable universe, which may or may not overlap with the one centered on Earth.

The Sunyaev–Zeldovich effect is the spectral distortion of the cosmic microwave background (CMB) through inverse Compton scattering by high-energy electrons in galaxy clusters, in which the low-energy CMB photons receive an average energy boost during collision with the high-energy cluster electrons. Observed distortions of the cosmic microwave background spectrum are used to detect the disturbance of density in the universe. Using the Sunyaev–Zeldovich effect, dense clusters of galaxies have been observed.

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.

The Lambda-CDM, Lambda cold dark matter, or ΛCDM model is a mathematical model of the Big Bang theory with three major components:

  1. a cosmological constant denoted by lambda (Λ) associated with dark energy
  2. the postulated cold dark matter
  3. ordinary matter
<i>Planck</i> (spacecraft) European cosmic microwave background observatory; medium-class mission in the ESA Science Programme

Planck was a space observatory operated by the European Space Agency (ESA) from 2009 to 2013. It was an ambitious project that aimed to map the anisotropies of the cosmic microwave background (CMB) at microwave and infrared frequencies, with high sensitivity and small angular resolution. The mission was highly successful and substantially improved upon observations made by the NASA Wilkinson Microwave Anisotropy Probe (WMAP).

<span class="mw-page-title-main">History of the Big Bang theory</span> History of a cosmological theory

The history of the Big Bang theory began with the Big Bang's development from observations and theoretical considerations. Much of the theoretical work in cosmology now involves extensions and refinements to the basic Big Bang model. The theory itself was originally formalised by Father Georges Lemaître in 1927. Hubble's Law of the expansion of the universe provided foundational support for the theory.

The expansion of the universe is the increase in distance between gravitationally unbound parts of the observable universe with time. It is an intrinsic expansion, so it does not mean that the universe expands "into" anything or that space exists "outside" it. To any observer in the universe, it appears that all but the nearest galaxies recede at speeds that are proportional to their distance from the observer, on average. While objects cannot move faster than light, this limitation only applies with respect to local reference frames and does not limit the recession rates of cosmologically distant objects.

<span class="mw-page-title-main">Archeops</span>

Archeops was a balloon-borne instrument dedicated to measuring the Cosmic microwave background (CMB) temperature anisotropies. The study of this radiation is essential to obtain precise information on the evolution of the Universe: density, Hubble constant, age of the Universe, etc. To achieve this goal, measurements were done with devices cooled down at 100mK temperature placed at the focus of a warm telescope. To avoid atmospheric disturbance the whole apparatus is placed on a gondola below a helium balloon that reaches 40 km altitude.

In physical cosmology and astronomy, dark energy is an unknown form of energy that affects the universe on the largest scales. Its primary effect is to drive the accelerating expansion of the universe. Assuming that the lambda-CDM model of cosmology is correct, dark energy is the dominant component of the universe, contributing 68% of the total energy in the present-day observable universe while dark matter and ordinary (baryonic) matter contribute 26% and 5%, respectively, and other components such as neutrinos and photons are nearly negligible. Dark energy's density is very low: 6×10−10 J/m3, much less than the density of ordinary matter or dark matter within galaxies. However, it dominates the universe's mass–energy content because it is uniform across space.

In cosmology, baryon acoustic oscillations (BAO) are fluctuations in the density of the visible baryonic matter of the universe, caused by acoustic density waves in the primordial plasma of the early universe. In the same way that supernovae provide a "standard candle" for astronomical observations, BAO matter clustering provides a "standard ruler" for length scale in cosmology. The length of this standard ruler is given by the maximum distance the acoustic waves could travel in the primordial plasma before the plasma cooled to the point where it became neutral atoms, which stopped the expansion of the plasma density waves, "freezing" them into place. The length of this standard ruler can be measured by looking at the large scale structure of matter using astronomical surveys. BAO measurements help cosmologists understand more about the nature of dark energy by constraining cosmological parameters.

<span class="mw-page-title-main">BICEP and Keck Array</span> Series of cosmic microwave background experiments at the South Pole

BICEP and the Keck Array are a series of cosmic microwave background (CMB) experiments. They aim to measure the polarization of the CMB; in particular, measuring the B-mode of the CMB. The experiments have had five generations of instrumentation, consisting of BICEP1, BICEP2, the Keck Array, BICEP3, and the BICEP Array. The Keck Array started observations in 2012 and BICEP3 has been fully operational since May 2016, with the BICEP Array beginning installation in 2017/18.

<span class="mw-page-title-main">Cosmology Large Angular Scale Surveyor</span> Microwave telescope array in Chile

The Cosmology Large Angular Scale Surveyor (CLASS) is an array of microwave telescopes at a high-altitude site in the Atacama Desert of Chile as part of the Parque Astronómico de Atacama. The CLASS experiment aims to improve our understanding of cosmic dawn when the first stars turned on, test the theory of cosmic inflation, and distinguish between inflationary models of the very early universe by making precise measurements of the polarization of the Cosmic Microwave Background (CMB) over 65% of the sky at multiple frequencies in the microwave region of the electromagnetic spectrum.

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.
  4. 1 2 Lemaître, G. (1927). "Un univers homogène de masse constante et de rayon croissant rendant compte de la vitesse radiale des nébuleuses extra-galactiques". Annales de la Société Scientifique de Bruxelles A . 47: 49–56. Bibcode:1927ASSB...47...49L. Partially translated in Lemaître, G. (1931). "Expansion of the universe, A homogeneous universe of constant mass and increasing radius accounting for the radial velocity of extra-galactic nebulae". Monthly Notices of the Royal Astronomical Society . 91 (5): 483–490. Bibcode:1931MNRAS..91..483L. doi:10.1093/mnras/91.5.483.
  5. ↑ van den Bergh, S. (2011). "The Curious Case of Lemaitre's Equation No. 24". Journal of the Royal Astronomical Society of Canada . 105 (4): 151. arXiv: 1106.1195 . Bibcode:2011JRASC.105..151V.
  6. ↑ Block, D. L. (2012). "Georges Lemaître and Stigler's Law of Eponymy". In Holder, R. D.; Mitton, S. (eds.). Georges Lemaître: Life, Science and Legacy. Astrophysics and Space Science Library. Vol. 395. pp. 89–96. arXiv: 1106.3928 . Bibcode:2012ASSL..395...89B. doi:10.1007/978-3-642-32254-9_8. ISBN   978-3-642-32253-2. S2CID   119205665.{{cite book}}: |journal= ignored (help)
  7. ↑ Reich, E. S. (27 June 2011). "Edwin Hubble in translation trouble". Nature News . doi:10.1038/news.2011.385.
  8. ↑ Livio, M. (2011). "Lost in translation: Mystery of the missing text solved". Nature . 479 (7372): 171–173. Bibcode:2011Natur.479..171L. doi: 10.1038/479171a . PMID   22071745. S2CID   203468083.
  9. ↑ Livio, M.; Riess, A. (2013). "Measuring the Hubble constant". Physics Today . 66 (10): 41. Bibcode:2013PhT....66j..41L. doi:10.1063/PT.3.2148.
  10. ↑ Hubble, E. (1929). "A relation between distance and radial velocity among extra-galactic nebulae". Proceedings of the National Academy of Sciences . 15 (3): 168–73. Bibcode:1929PNAS...15..168H. doi: 10.1073/pnas.15.3.168 . PMC   522427 . PMID   16577160.
  11. ↑ This popular consideration is echoed in 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."
  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."
  14. ↑ Gamow, G. (1948). "The Origin of Elements and the Separation of Galaxies". Physical Review. 74 (4): 505. Bibcode:1948PhRv...74..505G. doi:10.1103/physrev.74.505.2.Gamow, G. (1948). "The evolution of the universe". Nature. 162 (4122): 680–2. Bibcode:1948Natur.162..680G. doi:10.1038/162680a0. PMID   18893719. S2CID   4793163.Alpher, R. A.; Herman, R. (1948). "On the Relative Abundance of the Elements". Physical Review. 74 (11): 1577. Bibcode:1948PhRv...74.1577A. doi:10.1103/physrev.74.1577.
  15. ↑ A. A. Penzias (1979). "The origin of elements". Nobel lecture . 205 (4406): 549–54. Bibcode:1979Sci...205..549P. doi:10.1126/science.205.4406.549. PMID   17729659 . Retrieved October 4, 2006.
  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 Journal142 (1965), 419. R. H. Dicke, P. J. E. Peebles, P. G. Roll and D. T. Wilkinson, "Cosmic Black-Body Radiation," Astrophysical Journal142 (1965), 414. The history is given in P. J. E. Peebles, Principles of physical cosmology (Princeton Univ. Pr., Princeton 1993).
  18. ↑ Geller, M. J.; Huchra, J. P. (1989), "Mapping the Universe", Science, 246 (4932): 897–903, Bibcode:1989Sci...246..897G, doi:10.1126/science.246.4932.897, PMID   17812575, S2CID   31328798
  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. ↑ Shaun Cole; et al. (The 2dFGRS Collaboration) (2005). "The 2dF galaxy redshift survey: Power-spectrum analysis of the final dataset and cosmological implications". Mon. Not. R. Astron. Soc. 362 (2): 505–34. arXiv: astro-ph/0501174 . Bibcode:2005MNRAS.362..505C. doi:10.1111/j.1365-2966.2005.09318.x. 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
  23. ↑ Marc Davis; et al. (DEEP2 collaboration) (2002). "Science objectives and early results of the DEEP2 redshift survey". Conference on Astronomical Telescopes and Instrumentation, Waikoloa, Hawaii, 22–28 August 2002. arXiv: astro-ph/0209419 .{{cite conference}}: CS1 maint: numeric names: authors list (link)
  24. ↑ Bennett, C. L.; (WMAP collaboration); Hinshaw, G.; Jarosik, N.; Kogut, A.; Limon, M.; Meyer, S. S.; Page, L.; Spergel, D. N.; Tucker, G. S.; Wollack, E.; Wright, E. L.; Barnes, C.; Greason, M. R.; Hill, R. S.; Komatsu, E.; Nolta, M. R.; Odegard, N.; Peiris, H. V.; Verde, L.; Weiland, J. L.; et al. (2003). "First-year Wilkinson Microwave Anisotropy Probe (WMAP) observations: preliminary maps and basic results". Astrophysical Journal Supplement Series . 148 (1): 1–27. arXiv: astro-ph/0302207 . Bibcode:2003ApJS..148....1B. doi:10.1086/377253. S2CID   115601. This paper warns that "the statistics of this internal linear combination map are complex and inappropriate for most CMB analyses."
  25. ↑ Clavin, Whitney; Harrington, J.D. (21 March 2013). "Planck Mission Brings Universe Into Sharp Focus". NASA . Retrieved 21 March 2013.
  26. ↑ Staff (21 March 2013). "Mapping the Early Universe". The New York Times . Retrieved 23 March 2013.
  27. ↑ Planck Collaboration (2016). "Planck 2015 results. XIII. Cosmological parameters (See Table 4 on page 31 of pfd)". Astronomy & Astrophysics. 594 (13): A13. arXiv: 1502.01589 . Bibcode:2016A&A...594A..13P. doi:10.1051/0004-6361/201525830. S2CID   119262962.
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