The cosmic microwave background (CMB) is the electromagnetic radiation in the microwave band which can be observed throughout the whole universe, not connected to any astronomical object. Its spectrum follows a very precise black-body radiation with a temperature of about 2.7 K.

learn more… | top users | synonyms

0
votes
1answer
31 views

Do we really need inflation for horizon problem?

This is a very fundamental doubt. I think i am missing something in inflation. The inflation theory solves the horizon problem by stating all of the universe started from a very small region in ...
2
votes
1answer
38 views

Cosmological fluctuations: what is gaussian?

When we are speaking about gaussianity and non-gaussianity in a cosmological context, what is gaussian or non-gaussian in the CMB? What would a non gaussian CMB look like compared to a gaussian one? ...
1
vote
1answer
34 views

Particle Horizon and CMB

If particle horizon is the maximum distance we can see presently in the universe, how come we are able to see CMB? CMB is radiation from surface of last scattering happened at t~380k years. Suppose ...
-1
votes
0answers
29 views

When was the temperature of the CMB between 0°C? When was it 100°C? [duplicate]

The current temperature of the CMB is something like 3°K. When was the CMB temperature between 0° and 100° Celsius?
2
votes
1answer
122 views

If we go to space why isn't the temperature high? [duplicate]

We know that the temperature in space (which has vacuum) is low. If I go to space will I feel sweaty and hot or chilly? I think I will feel sweaty and hot because the radiation (UV, IR, etc) of the ...
0
votes
1answer
47 views

CMB anisotropy, temperature and doppler effect

How would you derive the following equation: $$ T' = T_{CMB} \left( \frac{\sqrt{1-v^2}}{1+v\cos{\theta}} \right) $$ which describes how the temperature of the CMB varies due to the speed $v$ of the ...
5
votes
2answers
83 views

Would the presence of B-modes in the CMB provide evidence for quantum gravity?

Finding B-modes in the CMB (which aren't due to foreground contamination) would be evidence for gravitational waves, because they cannot be produced by density perturbations (to first order, is my ...
2
votes
2answers
112 views

Why the CMB has not been dispersed so far?

Imagine you have a box of black body radiation. What happens if you open the box for a long time? It becomes dispersed and no radiation remains in the box. Now, apply this example to the Cosmic ...
2
votes
0answers
64 views

How do we get the power spectrum through the CMB?

How do we get the power spectrum through observing the CMB?
1
vote
0answers
62 views

Has the cosmic alignment of Earth and the Solar System been explained (CMB anisotropy)

The Cosmic Microwave Background anisotropy is currently aligning Earth and the Solar System with the largest and earliest structure of the universe. Has this been explained yet? Or are the theories ...
2
votes
2answers
74 views

What is the process by which the density fluctuations that were detected in the CMB evolved into the first stars?

We can detect very slight fluctuations in the temperature (mass distribution) when the CMB was released (decoupling). It is believed that these fluctuations led to the first stars. However, these ...
0
votes
1answer
37 views

Energy variations of cosmic background radiation

Has anyone been able to measure a difference in the energy density of Cosmic Background Radiation in a gravity well compared to zero gravity?
0
votes
0answers
28 views

How is the formation of the first atoms related to the cosmic microwave background? [duplicate]

Common atoms formed when the universe finally got cool enough for electrons to bind with atomic nuclei around the year 380,000. From what I understand this shift in state from plasma to discrete atoms ...
0
votes
0answers
56 views

Assuming the universe is finite, at some point, CMB should go away, right?

I'm not talking about gradual red-shifting, that happens slowly anyway, but with a universe of finite size, we should actually see Cosmic Background Radiation turn off in a sense, first at a point, ...
1
vote
1answer
41 views

What made up the cosmic microwave background and the first stars?

I am trying to figure out how the first stars formed and I'm looking for information on what made up the gas/radiation that they formed from. Most of our evidence for the make up of these formations ...
0
votes
0answers
66 views

CMB parameter, what's the meaning of the matter power spectrum normalization sigma_8?

Most CMB experiments like WMAP and Planck include a certain cosmological parameter called $\sigma_8$. My understanding is that normalization of the matter power spectrum is not a theoretical ...
1
vote
1answer
70 views

absorption of cosmic microwave background radiation

My understanding of the CMB radiation is that it comes from everywhere, and goes in every direction. But how can this be the case, when there is a lot of matter in space which could absorb, or for ...
1
vote
0answers
52 views

Convert angular power spectrum to spatial power spectrum

If we have a signal projected on a sphere, one routinely decomposes this in spherical harmonics, in analogy to a Fourier decomposition in flat space. One can then make the decomposition: ...
0
votes
0answers
24 views

What does velocity relative to CMB mean? [duplicate]

I've see some velocities such as that of the Sun quoted as "relative to the cosmic microwave background"? How is this different to measuring velocities relative to that old, discredited idea, the ...
3
votes
3answers
103 views

Average temperature of the universe

Is it possible to define some average temperature of the universe? If yes, what fixes this temperature and how t estimate today's temperature? Is it different from the temperature of the black-body ...
1
vote
1answer
59 views

Confusion with the meaning of CMB

We say that CMB is the radiation leftover from big bang. When we measure the radiations i.e., the flux of photons in a given microwave range (say 0.1cm to 70cm, for example), in deep sky, there are ...
3
votes
0answers
34 views

Thomson scattering on the elections does not produce any circular polarization?

All references on CMB polarization has this statement as if it is a trivial fact. But I have to admit that I completely don't understand what this sentence is telling us.
3
votes
0answers
51 views

What is the latest findings on the topology and size of the universe?

The paper G. Aslanyan & A.V. Manohar, The Topology and Size of the Universe from the Cosmic Microwave Background, JCAP 06 (2012) 003, arXiv:1104.0015, uses the 7-year WMAP data. Has any ...
9
votes
2answers
398 views

Could I see the cosmic microwave background if it were Doppler shifted enough?

If I traveled fast enough, my current understanding is that visible light would be blueshifted to the blue/UV range, but also that microwaves and longer wavelength waves would be blueshifted into the ...
6
votes
1answer
113 views

Angular Power Spectrum of CMB

I was wondering, if anyone could guide me through the different peaks of this spectrum (See below)? I've been reading and reading numerous pages about this, but I can't seem to get my head around ...
2
votes
3answers
180 views

Cosmic Background Radiation and redshift vs. temperature

I get that the CMB has gone from high energy photons, to low microwave photons today. And that is probably due to the redshift from the expanding Universe. But, since CMB is a black body it is ...
-2
votes
1answer
89 views

How can we detect cosmic background microwave radiation? [closed]

From my understanding this stuff expands at or near the speed of light -- and it's origins are that of the creation of this universe (via big bang). Obviously, our planet does not expand from origin ...
11
votes
1answer
560 views

The status of the BICEP2 'discovery' after Planck 2014

The tumultous period after the original announcement that the BICEP2 experiment had supposedly detected strong evidence of cosmological inflation in the form of B-mode polarization in the cosmic ...
0
votes
0answers
19 views

Direction of CMB and magnetic fields?

Measurements show the CMB is warmer to the North. Could more photons coming from that direction of the sky, cause metals in the Earth to move in that particular direction? As the Earth orbits the ...
12
votes
3answers
899 views

What is meant by the temperature of the CMB?

This is what I commonly read: The CMB came to existence when atoms where formed and photons weren't constantly absorbed anymore. In other words, the universe became "transparent". Because of the ...
3
votes
2answers
166 views

What is the origin of CMB fluctuations?

I have read somewhere that CMB (cosmic microwave background radiation) fluctuations in temperature are linked to mass distribution fluctuations in the early universe (at ~350000 years after Big Bang, ...
1
vote
1answer
63 views

Does the CMB signal get weaker over time?

If the universe is infinite or flat, then this isn't true (I guess). But if the universe is finite, then as it expands wouldn't the CMB signal weaker at any given point over time?
3
votes
1answer
151 views

Is the Universe still believed to be flat?

I have read a handful of old articles from mid 2013 expressing that the Universe may, in fact, be curved. http://www.nature.com/news/universe-may-be-curved-not-flat-1.13776 ...
2
votes
1answer
71 views

Why is the graph of CMB/black-body radiation asymptotic?

Speaking of this graph of blackbody radiation, I see that the graph goes to 0 asymptotically: As we go to higher and higher frequencies, the energy of a single photon becomes increasingly high. ...
1
vote
0answers
42 views

A physical understanding of the 2/3 in the Sachs-Wolfe effect

I am trying to develop an intuitive but quantitative understanding of the factor of 2/3 in the Sachs-Wolfe effect. I believe I have a picture that makes sense but it relies on one assumption I don't ...
28
votes
3answers
4k views

How can interstellar space have a temperature of 2-3K?

Several different sources online state that the average temperature of interstellar space (or the universe in general) is around 2-3K. I learned that temperature is basically the wiggling of matter, ...
7
votes
2answers
92 views

What did recombination look like?

I recently remembered that someone worked out what the big bang sounded like and that got me thinking... About 377,000 years after the Big Bang, electrons became bound to nuclei to form neutral ...
2
votes
1answer
78 views

How is CMB related to the temperature of the universe

As I understand it, CMB (cosmic microwave background) is the radiation emitted when matter decoupled at the early stages of the big bang. The thing I don't understand is do all stars emit this kind of ...
0
votes
2answers
98 views

When the Cosmic Microwave Background radiation cools, where does the energy go? [duplicate]

I understand how photons can change wavelength via gravitational redshifting, but that doesn't seem to be what's going on with the CMB radiation. I've heard it explained as happening because of the ...
3
votes
2answers
532 views

What trajectory has the Cosmic Microwave Background radiation taken to get to earth?

I have a few related questions: Where is the CMB coming (emitted/reflected/remitted) from? When CMB hits the earth, is that the first thing those photons hit since they were emitted 400 thousand ...
8
votes
2answers
998 views

Will the CMB ever stop shining?

Will we ever reach a point where all the light that was set free by recombination finally reaches us from our point of view and the CMB stops "shining" for observers on Earth?
7
votes
1answer
188 views

Seeing beyond the CMBR with neutrinos?

As I understand it, you can't see beyond the Cosmic Microwave Background Radiation because the plasma of the early universe was opaque to electromagnetic radiation. What if you had a "neutrino ...
2
votes
1answer
176 views

Redshift of Cosmic Microwave Background

Does the cosmic microwave background radiation have a red shift parameter z? If so what is the value for z?
1
vote
1answer
48 views

Peaks and dips position in the Planck CMB

I am currently looking for the values of the firsts peaks and dips (at least the first 3) in terms of l and angular size for the CMB angular power spectrum measured from Planck. But the only thing I ...
6
votes
2answers
199 views

When was the cosmic background radiation in the visible spectrum?

From what I understand about the Cosmic Microwave Background Radiation is that it was from the big bang, and since space has streched and become bigger since then the wavelength of the CMBR has ...
1
vote
2answers
116 views

Redshift 1+z - CMB Temperature lower?

I know that $\frac{\lambda_2}{\lambda_1} = 1 + z$ Suppose a galaxy had redshfit $z=3$. Does this mean that the wavelength becomes $4\lambda$? Then by wien's law where $\lambda \propto \frac{1}{T}$, ...
5
votes
1answer
117 views

The initial conditions of the CMB spectrum

The CMB spectrum shows the intensity of fluctuation at a certain angular scale: The achievement is the correspondence between the predicted power spectrum and the observed one. My question is as ...
27
votes
8answers
3k views

Why is absolute zero considered to be asymptotical? Wouldn't regions such as massive gaps between galaxy clusters have temperatures of absolute zero?

Why is absolute zero considered to be asymptotical? Wouldn't regions such as massive gaps between galaxy clusters have temperatures of absolute zero? I just do not see why our model must work the way ...
7
votes
1answer
260 views

Frequency of cosmic microwave background

Some people refer to cosmic microwave background's (CMB) frame of reference as an absolute one. If I understand correctly, we can measure 'absolute' velocity in this frame by using the Doppler effect. ...
8
votes
1answer
224 views

$\Delta^+$ decay in GZK process

The dominant channels in the GZK process are $$p+\gamma_{\rm CMB}\to\Delta^+\to p+\pi^0,$$ $$p+\gamma_{\rm CMB}\to\Delta^+\to n+\pi^+.$$ According to the pdg, $\Delta\to N+\pi$ makes up essentially ...