(Image source: ifa.hawaii.edu)
The first ray of dawn of creation
God said: There must be light. So 380,000 years after the creation of the world, there was finally light.
In 1964, Bell Labs engineers Arno Penzias and Robert Wilson were debugging an antenna and found that there was a background noise no matter which direction the antenna was heading, even cleaning up the bird droppings on the antenna and reassembling the antenna, it was lingering.
At the same time, a group of astronomers are pursuing the cosmic background radiation predicted in the theory of the universe Big Bang and are unsuccessful.
According to the theory of the Big Bang, at the beginning of the Big Bang, stars and galaxies had not yet been formed, and the universe was filled with dense, high-temperature hydrogen plasma and radiation. As the universe expands and cools, ions and electrons recombine almost instantly to form neutral particles. From then on, photons and begin to unimpeded in the universe, rather than being constantly scattered by plasma. This event is called photon decoupling. The universe suddenly becomes transparent at this moment. At this time, the age of the universe is 380,000 years.
The photon that came out of chaos when the photon was decoupled, carried the information of creation and kept traveling through the universe until it hit the human detector. This kind of radiation is "cosmic background radiation", just like the legacy of the Big Bang, so it is also called or "legacy radiation".
The expansion of the universe will make these photons darker, longer and longer wavelengths, and lower and lower energy. According to the theory, today's cosmic background radiation should be equivalent to 3K bold radiation, also known as " microwave background radiation ".
The engineer's story was soon discovered by astronomers, and in this way, mankind saw the first ray of dawn of Genesis. The 1973 Nobel Prize in Physics was also awarded to Penzias and Wilson, who discovered the radiation of the universe's background.
Penzias and Wilson discovered the Holmdel horn-shaped antenna for background radiation (picture source: NASA)
Inhomogeneity of cosmic background radiation
Based on the basic principles of cosmology, on a large scale, the universe is uniform and isotropic, so the universe background radiation should also be isotropic. The observation results are generally the case, but on an almost uniform basis, there is still a fluctuation of about 5%.
These subtle inhomogeneities are caused by the interaction between background photons and celestial bodies during their journey, so they also carry the information of these celestial bodies. So microwave background photons are like messengers, bringing us news from the depths of the universe. In 2006, the Nobel Prize in Physics awarded John Mather and George Smoot, who precisely measured the radiation of the cosmic background. There are many theories currently for the inhomogeneity of the background radiation . The latest highest resolution cosmic microwave background radiation map drawn by the Plank satellite (Picture source: ESA/NASA/JPL-Calteck)
Sunyaev-Zel'dovich effect
Sunyaev-Zel'dovich effect
Sunyaev-Zel'dovich effect points out the phenomenon that photons of cosmic background radiation and high-energy electrons in celestial bodies such as galaxy cluster cause inverse Compton scattering, resulting in changes in the observed temperature distribution.
is scattered by inverse Compton, and part of the energy of the high-energy electrons is transferred to low-energy photons in the background radiation, so the number of low-energy photons decreases, the number of high-energy photons increases, and the total energy of the photons increases, and background radiation is no longer an ideal blackbody radiation.
ALMA (Atacama Large Millimeter Wave/Submillimeter Wave Array) is the first SZ effect to be observed (Image source: Reference [4])
Baryon Sound Oscillation
Baryon Sound Oscillation (BAO) is a regular periodic density fluctuation of baryon matter that can be seen in the universe. Just as supernovae can be used as standard candlelight, the mass of matter of baryon acoustically oscillating can also be used as a standard ruler for measuring cosmological distances. The length of the standard ruler
(currently about 490 million light-years) can be measured by large-scale structural surveys. By measuring baryon acoustic oscillations, we can limit cosmological parameters more, thus understanding the properties of the dark energy that causes the accelerated expansion of universe .
baryon sonic oscillation art rendering (Picture source: Big Science and Technology)
integral Sachs-Wolfe effect
The universe is not completely uniform, so there are gravitational potential wells everywhere. When the background radiation photons fall into the gravitational potential well, energy will be obtained, and when climbing out of the potential well, energy will be lost. If the potential well does not change over time, positive and negative cancellation, the final energy of the photon will not change. In the straight cosmology of general relativity adding matter density equals critical density, on a large scale - that is, the gravitational potential in the linear region does not change with time, so photon energy remains unchanged. However, if any of the above three conditions (straight universe, general relativity, and matter-dominated) are not met, the gravitational potential on the linear scale will change with time, resulting in the energy obtained when the photon falls into the potential well and the energy lost when the photon climbs out of the potential well cannot be strictly offset. The photon energy changes, causing the temperature of the background radiation. This new microwave background anisotropy, the integrated Sachs-Wolfe (ISW) effect, was proposed by astronomers R.K. Sachs and A.M. Wolfe in 1967.
Because this effect is the accumulated effect of all gravitational potential changes on the photon path, it is called the integral Sachs-Wolfe effect, so it is distinguished from the microwave background temperature disturbance, that is, the Sachs-Wolfe effect, caused by the change of gravitational potential on the last scattering surface of the photon. A low temperature zone of cosmic microwave background radiation detected by the WMAP satellite is suspected to be caused by the ISW effect (Image source: wikipedia)
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Reference
[1] Penzias, Arno A., and Robert Woodrow Wilson. "A measurement of excess antenna temperature at 4080 Mc/s." The Astrophysical Journal 142 (1965): 419-421.
[2] Mather, John C., et al. "Measurement of the cosmic microwave background spectrum by the COBE FIRAS instrument." The Astrophysical Journal 420 (1994): 439-444.
[3] Sunyaev, R. A., and Ya B. Zel'Dovich. "Microwave background radiation as a probe of the contemporary structure and history of the universe." Annual review of astronomy and astrophysics 18.1 (1980): 537-560.
[4] Birkinshaw, M., S. F. Gull, and H. Hardebeck. "The Sunyaev–Zeldovich effect towards three clusters of galaxies." Nature 309.5963 (1984): 34-35.
[5] Sachs, Rainer K., et al. "Republication of: Perturbations of a cosmological model and angular variations of the microwave background (By RK Sachs and AM Wolfe)." General Relativity and Gravitation 39.11 (2007): 1929-1961.
[6] https://en.wikipedia.org/wiki/Baryon_acoustic_oscillations
[7] https://en.wikipedia.org/wiki/CMB_cold_spot
[8] http://blog.tianya.cn/blogger/post_show.asp?BlogID=24697PostID=20654389
[9] http://www.dkj1997.com/?post=608
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