What is Cosmic microwave background: Definition and 54 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 Can the integrated Sachs-Wolfe & the Rees-Sciama effects have any influence on matter?

    CMB photons can be affected by the expansion of the universe through the linear integrated Sachs-Wolfe effect (ISW) [1] and the non-linear ISW effect or also called Rees-Sciama effect [1]. In particular, according to the ISW effect, the photons crossing superclusters would leave them having a...
  2. SherLOCKed

    I Maximizing S/N in Angular Power Spectrum Signals

    The signal-to-noise ratio for angular power spectrum signal Cl under theoretical noise Nl, where Cl and Nl are functions of multipole l, is given as (S/N)^2= \sum (2l+1) (Cl/Nl)^2To increase the S/N we bin the power spectrum signal, if bin width \Delta l, this in principle decreases Nl by a...
  3. M

    I Cosmic Microwave Background Surveys

    If I understand correctly, by reference say here, the results seem to relate to a survey of the Milky Way. 1. Is the Milky Way a 'closed' system? 2. Whether or not, were the surveys based on data from the visible Universe, or restricted in all or part to the data form 'within' the Milky Way.
  4. K

    A Is it possible for variable speed of light in a vacuum?

    <unacceptable reference deleted> As our universe is expanding, that is, our vacuum is becoming more and more sparse, I believe it is possible that some key characterics of our vacuum is also variable.
  5. PainterGuy

    I Some questions about Cosmic Microwave Background radiation

    Hi, I have some questions about cosmic microwave background radiation, CMB, and I thought it's better to ask them together. I have combined all related content for each question to make the question clearer, understandable, and to provide proper context for any person like who stumbles upon...
  6. PainterGuy

    I Blackbody radiation and the cosmic microwave background

    Hi, The following is my basic understanding of blackbody radiation spectrum. The important sections are in boldface. Source: https://en.wikipedia.org/wiki/Black-body_radiation#Spectrum Question 1: The quote above says that at room temperature (let's say 20 C or 293 K) the emission is in the...
  7. J

    I Journey of an Observed Cosmic Microwave Background Photon

    Suppose we receive a cosmic microwave background (CMB) photon from space. According to the Big Bang model, this photon became free to travel when the universe was about 0.38 million years (Myr) old. At that time, it was about 42 million light years (Mly) away from our location. Because of the...
  8. P

    I How do we observe the CMB at all?

    So, as I understand it, the photons from the microwave background were the result of photon decoupling. Now, if I remember correctly, because of the accelerated expansion of the universe, the diameter of the universe is not about 28 Gyr, but about 90 Gyr, the consequence of which is that there...
  9. R

    I How Does The Cosmic Microwave Background Show That The Universe is Expanding?

    I've been searching for weeks and still with the doubt. I just know scientist look the content of the CMB and with general relativity calculates the expansion rate today that is 73 km/s/Mpc, but nowhere does it say how exactly. What does the contents of the universe have to do with the...
  10. PainterGuy

    B Questions about the cosmic microwave background radition and its discovery

    Hi, I have few questions about cosmic microwave background radiation (CMBD) and trying to find simple answer at a basic level. I really appreciate your help and time! The universe is almost 13.799 billion years old and currently has radius of around 46.5 billion light-years. It is said that...
  11. nmsurobert

    I Cosmic microwave background observations

    If my understanding is correct... From Earth the cmb is fairly uniform around us. From a galaxy that is 12 billion light years away, would they also see a uniform distribution of the cmb? to add to that question, would the radiation be less redshifted. From my understanding on why we aren't...
  12. Ebanflo

    I Is any attention being given to Conformal Cyclic Cosmology?

    Conformal Cyclic Cosmology, or CCC, is a hypothesis put forward by Roger Penrose in the early 2000s. My understanding of physics is lacking so my explanation will not be that clear, but I will summarize it here. Essentially, the existence of a previous spacetime, or "aeon," is postulated. This...
  13. S

    I Where Does the Cosmic Microwave Background Come From and How is it Measured?

    Hello! I am reading some basic stuff in cosmology and I am a bit confused by the microwave background. As far as I understand, it is the radiation produced at the beginning of the universe, when the matter density was not that high so the photon can escape and travel freely. So the microwave...
  14. T

    I Why hasn't the light from the CMB already passed us?

    If the cosmic microwave background occurred at the moment that electrons and protons joined together and photons were now free to travel across the universe, then why haven't those photons already passed it. I'm having a hard time understanding why we can see the CMB forever if it was simply a...
  15. S

    B Understanding the Cosmic Microwave Background

    When a "layman" hears of the cosmic microwave background, and this layman also has a passing knowledge of big bang theory, it can be difficult for said layman to wrap his head around what the CMB really is. That layman might ask, wouldn't this primordial radiation have "passed" us by now, and...
  16. jfizzix

    Can fast objects get cooked by Cosmic Microwave background?

    Awhile ago, I was considering what sort of dangers a spacecraft moving at relativistic speeds would face in interstellar space. Aside from the obvious pieces of space dust being relativistic bullets in the ship's frame of reference, the cosmic microwave background (CMB) would become a big...
  17. resurgance2001

    I Cosmic Microwave Background Radiation Anisotropies

    Hi This question may have already been answered elsewhere. If so please accept my apologies in advance. I am confused! The textbok(s) I am reading describe a whole bunch of different causes for there being temperature fluctuations in the CBM, so I am confused about which one(s) of these...
  18. C

    Energy from cosmic microwave background

    Hello everyone I've a question about the cosmic microwave background which my nephew asked me a couple of days ago. How much energy hits the Earth each year from the CMB? I'm assuming here that it is measurable in this way, but apologies if not. Thanks in advance for your help. Chris
  19. P

    Homemade Cosmic Microwave Background detector

    Hi Guys, I studied physics for my bachelor but still I am not a super expert, although I am still working closely to physics (but not so much astronomy). I was wondering if it would be possible to build a radio, or some other devise (any ideas?) that could be tuned at the frequency where the...
  20. wolram

    Is the CMB unique to our galaxy or present in all galaxies?

    How do we know that the cmb is not just related to just our galaxy, and that all galaxies have there own cmb?
  21. C

    OCR A2 Physics cosmic microwave background radiation question

    I was going over some past papers ( OCR Physics A2 ) and I came across this question about cosmic microwave background radiation-the topic I seem to be struggling with the most :/ and I wasn't sure how to structure my answer. It's worth 5 marks. The question is : Describe the important...
  22. Leandro Souza

    Cosmic microwave background radiation

    "The cosmic microwave background radiation" is an electromagnetic radiation observed in all directions of the sky and presents a profile type black body with about 3 K temperature. The fact that this allows us to infer the conditions of evolution of matter with radiation of the universe?
  23. M

    Is the Cosmic Microwave Background an Absolute Frame of Reference?

    I heard sometime ago that the cosmic microwave background may be a candidate for an absolute frame of reference. Did this idea ever get any credence?
  24. S

    What's the bandwidth of the Cosmic Microwave Background radiation?

    What's the bandwidth of CMB and what was the bandwidth of CMB when it was emitted (at the moment when the Universe was 379,000 years old)?
  25. S

    For how long the Cosmic Microwave Background was emitted?

    When the Universe was 379,000 years old, the radiation could travel into space. From that point in time the CMB started to be emitted in form of visible light. Am I correct? my question is: for how long the CMB was emitted? Or is it still emitted today? If the CMB was emitted for 10...
  26. F

    Cosmic microwave background radiation

    Homework Statement The cosmic microwave background radiation has a blackbody type spectrum. Determine its max frequency and the correspondent wavelenght. Verify if found frequency is a microwave frequency and compare with the following curve: Homework Equations Using the...
  27. J

    Cosmic microwave background question.

    So to detect the EM waves from this background, did the device that measured it focus on one single point in the sky, kinda like hubble, or did it do a full panoramic spherical measurement of the whole sky around it?
  28. G

    Why does the cosmic microwave background make a noise

    For about the 7th time I've been told the story of how Penzias and Wilson discovered a noise the source of which they could not detect. It turned out to be the CMB. Well, why should the cmb make a noise? It's just photons in the microwave spectrum.
  29. R

    Effect of CMB (cosmic microwave background) on objects at relativistic speeds

    A hypothetical question relating to 1) moving a physical object at a significant % of c. 2) interaction with the cosmic microwave background radiation Is it the case that doppler effect and time dilation means that the CMB is going to be physically damaging to the object? Further...
  30. R

    How many degrees of view is cosmic microwave background?

    Is it a section of sky or a full 100% 360 degree panoramic view? I am referring to the cosmic microwave background picture that can be found here: http://en.wikipedia.org/wiki/Cosmic_microwave_background_radiation
  31. T

    'Density' of 2.73K Cosmic Microwave Background

    Never seen this addressed anywhere, and maybe it doesn't matter; but, regarding the cosmic background radiation, in any given instant, how many 2.73K (on average) photons are in a given volume ? See, we would measure the same background temperature with our instruments over a range of...
  32. 4

    Cosmic Microwave Background Radiation, why from 380,000?

    Hello, I just have a quick question about CMB. Why is it from 380,000 years after big bang? Why not before? Will you please tell me if my explantion is right? Before 380,000 years, the universe was too dense to have any neutral atoms (free electrons and protons / plasma). And...
  33. P

    Cosmic Microwave Background Radiation and Photography

    Hi firstly I am a photographer not a physicist, When taking photos there is always 'noise' in the image, especially at higher ISO. I presumed this is the same noise that we would hear on a radio, or see on a tv? Would it be possible to create a room that blocked out the background radiation...
  34. Orion1

    Hawking radiation and cosmic microwave background radiation

    In order for the black hole to evaporate it must have a temperature greater than that of the present-day black-body radiation of the Universe. Cosmic microwave background radiation temperature: T_u = 2.725 \; \text{K} Hawking radiation temperature: T_H = \frac{\hbar c^3}{8 \pi G M k_B}...
  35. R

    Cosmic microwave background fits the blackbody radiation spectrum

    Homework Statement (a)The cosmic microwave background fits the blackbody radiation spectrum well with a temperature of 2.7 K and a corresponding peak wavelength at 1.9nm. Applying the relationship between the radiant emittance, i.e. the total power emitted per unit area, and the photon energy...
  36. F

    Layman's question on Cosmic Microwave Background

    Hi everyone, I'm a lowly computer programmer who has been interested in the CMB lately and recently became curious about one thing... As I understand it, the CMB is the left-over radiation from the Big Bang spread uniformly throughout the universe. Does this mean that this radiation is...
  37. J

    Link between Universe mass density and Cosmic Microwave Background energy

    Present critical density of Universe rho_crit = 3 H^2 / 8 Pi G H = Hubble Constant = 2.2E-18 sec^-1 rho_crit = 8.6E-27 kg / m^3 What particle mass does this represent? The length scale associated with a quantum particle of mass m is the Compton wavelength lambda where lambda =...
  38. M

    Cooling in Cosmic Microwave Background

    I am a little confused about how exactly the CMB "works". At first hearing, it makes perfect sense that as time goes on and the universe expands radiation would decrese in frequence, but when I think about it a little more deeply I miss something. My thought is how exactly does the light...
  39. D

    Exploring the Variations of CMBR Across Planets

    Is the CMBR distinguished by a particular set of spectrometry signatures? If not, how is it differentiated?
  40. D

    Cosmic Microwave Background

    CMB hot spots have a physical size that corresponds to the size of the horizon at age 300; 000 yrs. Assume one such hot spot region has been expanding together with the universe, how big in physical size (express in unit of light-year) has it become today? For this exercise, use a model of...
  41. S

    Blue shifted cosmic microwave background photons

    I hope this is an appropriate forum for this question. What kind sort of impact might intensely blue shifted cosmic microwave background (CMB) photons have on hawking radiation? Could intensely blue shifted CMB photons drive a portion of newly created electrons and positrons into the even...
  42. R

    Cosmic Microwave Background Origin

    If the light from a distant galaxy was red shifted far enough wouldn't it appear as microwave? Is it possible that the CMB is just more galaxies beyond what we consider to be the "observeable universe?"
  43. M

    Cosmic microwave background radiation

    Question> The fact (simplified) is that our planet is rotating arount the Sun, also our solar system is rotating... Is there available information on direction of CMBR in relation to our planet or to our solar system? THX foun answer myself Re: does the cosmos have direction...
  44. M

    CMB Cosmic Microwave Background

    How does one convert measurements in radio astronomical terms to temperature (Kelvin)? Specifically: Penzias & Wilson's measurement of CMB was "excess temperature at 4080 Mc/s." HOW does this yield a "value of about 3.5 degrees Kelvin higher than expected?" Basically, how do you get from...
  45. L

    Cosmic Microwave Background - why do we see photons from 13 billion years ago?

    I am trying to wrap my head around the Cosmic Microwave Background and how it is that the low frequency ancient photons we observe could be only 'passing' us in space now. If we think of a photon as an entity that is traveling away from the origin of the Big Bang at 300,000km/s, why would these...
  46. B

    Cosmic microwave background and a reference frame

    Dear Friends A fleet of spaceships is given, each equipped with a differential microwave radiometer, just like COBE was, whose detectors are antipodeanly pointing (this way one should catch blue shifted radiation and the other one red shifted). Could their acquisitions be used to...
  47. S

    Exploring the Cosmic Microwave Background

    I was looking at a map of the cosmic microwave background, and began wondering if the cmb would look the same from another vantage point, perhaps Pluto, or a nearby star. Or what about if it were seen from another galaxy? And, in a related question, does the cmb evolve with time? I suppose...
  48. T

    Finding mean energy of cosmic microwave background photons

    Hello all, I was recently assigned a problem in my modern physics class regarding finding the mean energy of Cosmic Microwave Background (CMB) photons. The problem reads as follows: The universe is permeated with primordial microwave radiation that has a mean wavelength of about 2.5 mm...
  49. Q

    Cosmic Microwave Background and Its Temperature

    We know that the CMB has been decreasing in temperature since the big bang. This is due to the continuing expansion of the universe that results to an increase in the wavelengths of the CMB photons. Increased wavelength => less energy => less temperature. My question is why do the photons have...
  50. M

    Will cosmic microwave background disappear?

    According to the standard cosmological model, the description for cosmic temperature falls is:T=A*t^-0.5. So when t-->infinite, T-->0. It means the temperature of microwave background will approach 0k after billions of years. Microwave background will disappear?:confused:
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