Stack Exchange Network

Stack Exchange network consists of 175 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

Questions tagged [cosmic-microwave-background]

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.

1
vote
2answers
121 views

Where does the 379,000 year recombination prediction of the Big Bang theory come from?

The Big Bang theory postulates that recombination happened 379,000 years after the Big Bang. However, I have never seen a single statement as to how this number came about. I don't imagine they ...
0
votes
1answer
43 views

On universe homogeneity. Why “shouldn't be” so? [closed]

I start by apologising if I have took sparse sentences to literally. If I didn't understand something that's is why I am asking. In more or less divulgative literature, here, and also in the few ...
0
votes
0answers
23 views

Is the universe be expanding at different rates depending on its temperature and density?

As I understand it, when observing different regions of the universe we get a different rate of expansion (the two Hubble constants), specifically the more distant observation seems to return a lower ...
1
vote
1answer
39 views

How far was the surface of last scattering at the moment of recombination?

If I understand correctly, then the surface of last scattering (the last particles off of which CMB photons scattered before traveling for 13 billion years and reaching us) is currently at a distance ...
13
votes
1answer
4k views

Why can’t you see at the start of the Big Bang?

I’m quite confused with regards to photon emission throughout the creation of the universe. From what I’ve heard, there was no light (of any frequency) in the universe until 300,000 years after the ...
8
votes
2answers
393 views

What wavelength was the CMB originally?

What wavelength was the light that became the CMB after factoring out redshift? Is it safe to assume that what we're seeing in the CMB was emitted at a distance of approx: ...
3
votes
1answer
51 views

Future of the cosmic microwave background pattern

Does the comoving size and the observed angular diameter of CMB hot and cold patches change with time in the future?
3
votes
1answer
166 views

What is the temperature of the black night sky, outside the atmosphere?

The sky at night is rather black. If it were completely black, it would correspond to a black body at absolute zero. But the sky is not completely black. Is there a way to assign a temperature value ...
0
votes
0answers
35 views

Tests of inflation theory

So I'm following a course in Early Universe Cosmology right now. For the next lecture we have to solve a few questions about inflation, just as preparation. I read some closely related lecture notes ...
2
votes
1answer
73 views

Why is Cosmic Microwave Background Radiation attributed to the Big Bang? [duplicate]

When searching for CMBR all articles start by stating as a fact that it is a remnant of the Big Bang. Why? Why is it well understood and accepted? Why sure that it's not an effect of something else ...
2
votes
0answers
24 views

Scale factor at surface of last scattering

Is there an exact theoretical scale factor associated with the CMB? More specifically, since the CMB is associated with a temperature of around 3000K (as I understand), is there an exact thermodynamic ...
4
votes
2answers
3k views

Do we need dark matter and dark energy, if the behaviour of the universe in its initial stages was similar to that of the Sun? [closed]

According to CMBR the universe was a cloud of plasma and was a perfect black body, $380,\!000$ years after big bang. But the Sun in our solar system also is in the state of plasma, thus making it a ...
0
votes
0answers
34 views

Proving that universe is a blackbody

How can you theoretically explain why cosmic microwave background seems to be coming from a perfect blackbody given that the universe is no longer at thermal equilibrium?
1
vote
1answer
57 views

Which decoupled first? The dark matter or the CMB photons?

According theories that work best for the structure formation which happened first in the history of the evolution of the Universe, the decoupling of dark matter or the decoupling of photons? How sure ...
0
votes
0answers
24 views

How can CMB anisotropies be due only to inhomogeneities?

I'm studying from these lecture notes (Author: Wayne Hu, title: Lecture Notes on CMB Theory: From Nucleosynthesis to Recombination). At the very end of page 10 and beginning of page 11 he says: ...
7
votes
1answer
106 views

The Cosmic Microwave Background Paradox

I was reading an article on Olbers' Paradox (why the universe isn't as bright as the sun) and the more I read on it, the more the same question came to mind... We know the observable universe is ...
0
votes
0answers
35 views

How come we can treat space as a blackbody?

I thought that the condition to be a black body was that an object had to absorb all incident radiation without reflecting any. My understanding is, electrons in atoms absorb the incoming radiation. ...
1
vote
0answers
72 views

How to relate CMB acoustic peak to BAO in galaxy surveys to better than a factor 2?

Question for a friendly cosmologist. Let's define the sound horizon as $s = \int_0^{t_{ls}} c_s (1+z) dt$ where $c_s$ is speed of sound in primordial plasma (roughly $c/\sqrt{3}$ but you can include ...
0
votes
1answer
58 views

What will happen with the cosmic microwave background radiation if the Big Rip theory is true?

There are three things I can imagine happening: It appears one light year further away every year, which would be a bit weird, because it would be behind the universal event horizon, but still ...
0
votes
0answers
16 views

Express polarization moments in terms of temperature quadrupoles

I am trying to compute the polarisation moments in the tight coupling limit which is an exercise from Dodelson's Modern cosmology where the evolution equation is given by $$\dot{\Theta}_p+ik\mu\...
0
votes
1answer
36 views

Why isn't the cosmic microwave background a solid 3D volume?

This is the cosmic microwave background radiation: It's a Mollweide Projection, which maps the surface of a sphere. Like, this is a map of Earth (also Mollweide Projection): And it only shows the ...
0
votes
1answer
42 views

How does the CMB constrain the baryon asymmetry?

The CMB contains information about baryon acoustic oscillations in which baryons (I assume protons and electrons) and photons form a plasma exhibiting sound waves. How is information about the baryon ...
0
votes
1answer
141 views

Horizon Problem: How did different regions of space acquire different temperatures?

I'm trying to understand the Horizon Problem. Inflation describes how non-causally connected parts of the universe (that we see today) could once have been in causal contact. The reasoning goes that ...
2
votes
1answer
57 views

Picturing the density inhomogeneity of matter at recombination

The CMB was formed at the time of recombination which suggests that the analysis of the temperature anisotropies of the CMB helps to infer the profile of density fluctuations at the time of ...
2
votes
0answers
77 views

Are deductions from CMB much less accurate than claimed, owing to approximations in the FLRW model?

My question concerns "timescape cosmology" and measurements of dark energy based on CMB radiation. The background to the question is Lawrence H. Dam, Asta Heinesen, David L. Wiltshire, "Apparent ...
1
vote
1answer
57 views

Is there a bound on the number of sterile neutrinos from cosmological observations?

The right-handed sterile neutrinos $\nu_{R}$ are electroweak singlets. They do not contribute to the electroweak anomaly, and therefore, their number is not fixed by the requirement of the anomaly ...
2
votes
1answer
49 views

Thermal equilibrium of objects in deep space

I've read somewhere (not a reliable source though) that an object in space and far enough away from any heat source other than the CMB would eventually cool to 3K, the CMB's temperature, but no colder....
-6
votes
1answer
80 views

Why is the mainstream theory of cosmological redshift inconsistent with the mainstream theory of gravitational redshift

Gravitational redshift Cause : A reduction in the decompression of space* over distance (due to the presence of mass). Mainstream theory: Photons are emitted in a region of higher gravity with ...
0
votes
1answer
105 views

What is the present day photon density, $\rho_{\gamma, 0}$?

I'm attempting to perform the integration that will yield the sound horizon at recombination: $$ c_s^2 = \frac{c^2}{3}\left[\frac{3}{4}\frac{\rho_{b,0}(1+z)^3}{\rho_{\gamma,0}(1+z)^4} + 1\right]^{-1}...
0
votes
0answers
21 views

What is the simple way to calculate the content of dark energy from CMB probe? Do i have to find out the power or anular spectrum

And which data should i use, after getting data which software can plot it. Here are software in this site but dont know which one to choose- https://lambda.gsfc.nasa.gov/toolbox/ , since i am ...
3
votes
1answer
253 views

How did the Planck Study calculate the angular size of the sound horizon?

The Planck Collaboration has quoted the angular size of the Sound Horizon:$$\Theta_*= 0.0104$$I decided I'd try a rough, back-of-the-envelope calculation to understand how they arrived at this value. ...
0
votes
1answer
41 views

What happened to the antielectrons and antiprotons and $\mu^-,\tau^-$ at the time of recombination?

Recombination is the time when the Universe was made up of electrons $e^-$ and protons $p^+$ and the electrons attached to the protons to form the first hydrogen atom. What happened to the ...
1
vote
0answers
54 views

If there is no destination does light actually get emitted? [closed]

If the action of least principle says light needs a destination what happens when we shine a laser into the dark region of the microwave background radiation? Alternatively, if we put a light source ...
1
vote
1answer
107 views

What is the age of a universe with positive, negative, and zero curvature?

I am trying to calculate the age of universes with different curvatures using the Hubble constant and Friedmann equation. What does it mean when we say that the universe started out at equipartition ...
4
votes
1answer
140 views

How is pressure calculated in the early universe?

I'm trying to calculate the sound horizon from the start of time to decoupling. To do this I need to know the speed of sound and how it changes as the universe grows. The speed of sound in a fluid ...
0
votes
1answer
31 views

What is the best book for learning how to model the CMB Power Spectrum?

I would like to understand the science behind the CMB Power Spectrum. How the harmonics are calculated (distance to surface of last scattering, sound horizon), how the amplitudes are predicted (...
4
votes
0answers
45 views

Where did the energy from the CMBR go? [duplicate]

Basically the title. The wavelength of light from the CMBR has expanded as the universe expanded and so it has lost energy since it is inversely proportional to the wavelength. Where did this energy ...
2
votes
2answers
55 views

Does the pattern of CMB anisotropies change over cosmic time?

Currently, the Universe is about 14 billion years old, and we now see a certain pattern of anisotropies in the cosmic microwave background (CMB). If we wait another 14 billion years, and repeat the ...
1
vote
1answer
42 views

Is dark energy just a cooling effect of CMB?

(1) Cosmic microwave background cooled down from about 3000K billions of years ago to a couple of Kelvin nowadays. (2) Adiabatic expansion causes gas (of photons in this case) to cool. (3) Dark energy ...
5
votes
3answers
130 views

CMB homogeneity: Inflation vs. common initial conditions?

As I understand it, inflation was proposed to provide a mechanism by which now-causally disconnected regions of the universe could have once been in causal contact, and thus explain correlations in ...
18
votes
2answers
4k views

Did the big bang create an infinite number of photons?

We will always be able to see the cosmic microwave background (CMB) at about [the age of the universe] light years away. Always. Does that mean that infinite photons were created at that time? If ...
7
votes
1answer
247 views

Why does the first peak of the temperature power spectrum of CMB imply a flat Universe?

According to Wikipedia, the first peak of the temperature power spectrum of CMB determines the curvature of the Universe. And this answer by @pela says that the first peak is consistent with a flat ...
0
votes
3answers
165 views

What is the current value for the temperature at which Recombination took place?

I'm looking for the most recent, most accepted value for the temperature at which the photon first decoupled from the atoms during the Epoch of Recombination? That is, what was the temperature of the ...
0
votes
2answers
82 views

What is the future of the CMBR?

Galaxies farther away than let's say z=2 are beyond our reach. If we today receive a message from such a galaxy, our response message will never reach back to them. So goes the current knowledge. This ...
2
votes
1answer
82 views

Quantum fluctuations producing CMB fluctuations also cause inflation to be eternal?

It is believed that quantum fluctuations in the inflaton field caused inflation to end at different times in different places, which led to CMB fluctuations (1 part in 100,000). Eternal inflation ...
2
votes
1answer
87 views

What does the gravitational potential of the Milky Way do to the CMB?

We sit in a gravitational potential, so there should be a blue shift on the CMB light from the potential of the Milky Way. Is this blue shift dependent on direction? Is it being subtracted from the ...
0
votes
0answers
25 views

what are possible explanations for the larger scale anomaly in Planck satellite's data?

In the Planck satellite's image of the Cosmic Microwave Background (CMB), there have been anomalies, the most important of which is a deficit in the signal at large angular scales on the sky, which is ...
2
votes
2answers
109 views

How to Interpret WMAP's statement they have “nailed down the curvature of space to within 0.4% of ”flat“ Euclidean””

I find myself slightly frustrated when I'm reading a NASA page and they claim they have “nailed down the curvature of space to within 0.4% of "flat" Euclidean” 0.4% of what? Mathematically this ...
-2
votes
1answer
44 views

CMB details of wavelength, amplitude and frequency

Hi could someone help me with a small project with the CMB signal. I need the details of wavelength, amplitude and frequency of the cosmic microwave background. Thank you from Marc.
5
votes
1answer
117 views

Results of WMAP mission

The NASA WMAP mission mapped the cosmic microwave background (CMB), the the residual high temp photons from the condensed space 380000 years after big bang that expanded into the much high volume we ...