What is Cosmic background: Definition and 25 Discussions

The cosmic microwave background (CMB, CMBR), in Big Bang cosmology, is electromagnetic radiation which is a remnant from an early stage of the universe, also known as "relic radiation". The CMB is faint cosmic background radiation filling all space. It is an important source of data on the early universe because it is the oldest electromagnetic radiation in the universe, dating to the epoch of recombination. With a traditional optical telescope, the space between stars and galaxies (the background) is completely dark. However, a sufficiently sensitive radio telescope shows a faint background noise, or glow, almost isotropic, that 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, and earned the discoverers the 1978 Nobel Prize in Physics.
CMB is landmark evidence of the Big Bang origin of the universe. When the universe was young, before the formation of stars and planets, it was denser, much hotter, and filled with an opaque fog of hydrogen plasma. As the universe expanded, both the plasma and the radiation filling it grew cooler. When the temperature had dropped enough, protons and electrons combined to form neutral hydrogen atoms. Unlike the plasma, these newly conceived atoms could not scatter the thermal radiation by Thomson scattering, and so the universe became transparent. Cosmologists refer to the time period when neutral atoms first formed as the recombination epoch, and the event shortly afterwards when photons started to travel freely through space is referred to as photon decoupling. The photons that existed at the time of photon decoupling have been propagating ever since, though growing fainter and less energetic, since the expansion of space causes their wavelength to increase over time (and wavelength is inversely proportional to energy according to Planck's relation). This is the source of the alternative term relic radiation. The surface of last scattering refers to the set of points in space at the right distance from us so that we are now receiving photons originally emitted from those points at the time of photon decoupling.

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  1. S

    I Photons being blueshifted when crossing evolving voids?

    I was reading this paper (https://academic.oup.com/mnras/article/288/2/387/960778) where they analysed how CMB radiation is affected by evolving voids in an expanding spacetime (particularly through the Rees-Sciama effect and the integrated Sachs-Wolfe effect). This effect predicts that photons...
  2. H

    B Questions about cosmic background radiation

    I'm trying to get a better understanding of CBR. Unfortunately the internet has limited information, I guess it's not a cool enough of a topic to discuss. This is some of what I found, is it correct? CBR is electromagnetic radiation. Microwaves travel at the speed of light. CBR was a result of...
  3. S

    Hawking radiation versus the cosmic background

    Is the cosmic backround radiation incident on a black hole sufficient to make up for the energy lost through Hawking radiation? And what if we include the average energy flux from discrete objects like galaxies, as seen in intergalactic space?
  4. T

    How is the horizon length related to the power law spectrum

    Homework Statement For a power spectrum density fluctuations ##P(k) \propto k^n##, I need to find the scaling (with respect to ##a##) of the horizon wavenumber ##\frac{2\pi}{\chi_H}## in a matter dominated universe in terms of ##n##. ##\chi_H(a)## is the evolving particle horizon, in a flat...
  5. S

    I Has cosmic background radiation been measured underground?

    I am interested to know if cosmic microwave (160 Ghz) or cosmic radio (20-50 Mhz) background radiation has ever been measured/detected underground or underwater? This may seem like an odd question as you’d expect lots of rock and water to attenuate or block the cosmic radiation photons, but I...
  6. N

    I Where Would Ancient Intelligent Life Have Seen Cosmic Background Radiation?

    If intelligent life had evolved on some planet 6.8 billion years ago (half the time to the big bang 13.6 bilion years ago) and they had sent the equivalent of the COBE / Planck satellite to map the cosmic background radiation, where in the electromagnetic spectrum would they have seen the...
  7. SanderStols

    B Why do we still see cosmic background radiation

    In a discussion with a friend I am unable to explain to him why at this moment we still can detect cosmic background radiation. According to his reasoning the radiation that originated from the big bang should have passed us long ago. Where in fact does this radiation that we now detect come...
  8. T

    B How does the cosmic background radiation help us measure expansion in cosmology?

    I have embarked in trying to really do my homework and understand cosmology. From what I understand one of the ways that we can measure expansion is the the cosmic background radiation doesn't expand thereby providing something to compare observed expansion to. Have I got that wrong? tex
  9. bapowell

    Insights A Poor Man's CMB Primer. Part 1: The Birth of a Cosmic Background Radiation - Comments

    bapowell submitted a new PF Insights post A Poor Man's CMB Primer. Part 2: The Birth of a Cosmic Background Radiation Continue reading the Original PF Insights Post.
  10. H

    Cold Spot in Cosmic Background Radiation

    At one time, I read that the universe was, on a very large scale, essentially the same in all directions. Recently I have learned about the Cold Spot in the fairly uniform Cosmic Background Radiation map. Scientists have attributed the artifact to a very very large void in the ordinary matter...
  11. K

    Question about Cosmic Background Radiation

    I was wondering what experiments or observations have shown that the cosmic microwave background radiation exists outside our galaxy in intergalactic space. Have we detected it emanating from sources outside the galaxy? I know we've detected it here on Earth.
  12. Spinnor

    What operator acting on vacuum gives a box of cosmic background radiat

    What operator acting on the vacuum state (vacuum state of the box?) gives a m^3 box of cosmic background radiation at 2.7K? As the temperature 2.7K slowly drops (wait a million years) must our operator above change in time? Do photons scatter via gravitions so that their energy changes...
  13. J

    The lost energy of Cosmic Background Radiation

    Could anyone clarify where is gone the energy lost by CBR as the universe expands? Thank you in advance and happy new year
  14. L

    The source of cosmic background radiation

    All stars and Galaxies appear to give off the whole spectrum of electromagnetic radiation. If one views images of the distribution of background radiation in detail it appears to be filimetary in nature. Also if one views the distribution of visible matter in the universe it also appears...
  15. C

    Can Absolute Velocity be Measured with Cosmic Background Radiation?

    Greetings, I have heard that one can not know one's absolute velocity, only one's velocity relative to other objects. But wouldn't the cosmic background radiation be blueshifted in the direction of motion and redshifted in the oposite direction? Thanks
  16. B

    Cosmic Background Radiation - why is it still here?

    If the Cosmic background radiation was emitted at approximately 384,000 years after the big bang, and it travels the speed of light, with mattter moving at a slower speed, how is it possible that the cosmic rays are still with us and haven't already passed beyond us 13 billion years later...
  17. L

    Cosmic background radiation - redshift, blueshift, anisotropies

    I've been trying to find out more about cosmic background radiation, but I am unable to find any information on the variations in the measured cosmic background radiation. I'm talking about these WMAP images. Most of the images you'll find on Internet are the versions after being corrected...
  18. N

    Do Galaxies and the CMB Share the Same Reference Frame?

    If we look around us with the right instruments, we see CBR all around and it is fundamentally isotropic, that means on average the temperature and frequency is the same no matter which direction we look. (Doesn't it?) Say we are passed by someone traveling at 0.6c. At the moment that...
  19. F

    How can we see the cosmic background radiation?

    I am wondering how it is possible that we see CBR. Here's why: When the big bang occured, there was a sea of particles that gave off radiation. Now, if we are now made out of those particles, then how are we seeing their radiation now? The only way I see this happening is if matter traveled...
  20. W

    How does the cosmic background radiation works

    How does this stuff works (CBR)
  21. B

    Could Cosmic Background Radiation Hold Clues About the Big Bang?

    Problaby a silly thought but if the cosmic microwave backgroud radiation got created in the big bang and traveled outwards at the speed of light, and so did everything else, but traveled at less than the speed of light, would'nt it be "ahead" of us. Or alternatively if the radiation is absorbed...
  22. marlon

    Exploring the Cosmic Background Radiation

    Guys, I really have been wondering how cosmic background radiation has been generated. I mean, as far as i understand it this is just red shifted photons that we receive from very distant places.It cannot come from distant stars because this radiation is a black body spectrum. But the red...
  23. C

    Cosmic Background Radiation & Big Bang

    Dear All, I am trying to understand SPECIFICALLY the physics HOW and WHY the discovery of the 2 Bell scientists is hailed as something like the cosmological equivalent to the "missing link" as regard the Big Bang Theory ? I am looking for any and all links that explain this connection...
  24. J

    Time flow & Cosmic Background Radiation

    Hi, I was wondering if somebody could tell me in what way the following paragraph is incorrect (if it is). Thanks. According to Einstein’s theory, when radio waves travel from one place to another, and both places have a different time flow, the frequency will appear to change. When...
  25. Z

    Cosmic background radiation - alternative proposal

    I've had this idea for years but never had a forum. How do we know we aren't merely measuring the energy emitted by our sun's http://science.nasa.gov/ssl/pad/solar/images/heliosph.gif ?