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.
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Measuring one way speed of light using CMB dipole and quantum entanglement ;) [duplicate]
Edit: before saying this is similar to other questions please at least explain why using quantum entanglement to synchronize clocks has no benefit over the classical way of doing it. I linked an ...
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Why does the CMB have a spectrum like a black-body radiation?
Equilibrium distributions of particles (Maxwell, Boltzmann, Saha) are achieved by the particle collisions. On the other hand, photons do not interact with each other. From the introductory course in ...
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If dark matter was created in the early universe and its formation released energy, is there any evidence of that energy in the cmb?
When atomic nuclei fuse, energy is released. Is there anything about the CMB energy distribution that suggests that dark matter could have formed from other particles that released energy?
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Does Cosmic Background radiation transmit heat?
The Cosmic Background Radiation can be considered as the after-glow of the Big Bang, but does it transmit heat to objects in space? It is thermal radiation and is basically charged photons ...
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How is Hubble's constant (the expansion rate) predicted from LCDM and the CMB?
I know this will probably be far more technical than I actually understand, but how does the $H_0 = 68$ km/s/Mpc come about?
When we use the distance ladder to make local measurements, it is 74 km/s/...
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CMB dipole anisotropy maping to earth visualization
I do not see how this dipole anisotropy is due to the motion of the earth (and thus a doppler effect). Does anyone have a visualization of how this maps onto the earth and the motion of the earth such ...
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Understanding the CMB power spectrum 02
I've read many posts, books, articles and so on about the CMB power spectrum (this page for example http://background.uchicago.edu/~whu/intermediate/map5.html) to try to understand it, but I seem to ...
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Could a Relativistic Rocket convert the heat of Doppler shifted Cosmic Background Radiation into usable energy? [closed]
This page on mathdept.ucr.edu about relativistic rockets states:
As you approach the speed of light you will be heading into an
increasingly energetic and intense bombardment of cosmic rays and
other ...
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If our universe could be simmilar to the surface of a sphere is then obvious that CMBR photons should move in all directions on that continuum?
If our universe is open and flat then my question does not really make sense but if we could somehow compare it with a closed surface of a sphere which is expanding like a baloon is then obvious that ...
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$\Lambda$CDM's observations and the universe's matter content
It's known that the current value of the universe's total density parameter $\Omega_0=1$.
According to the $\Lambda$CDM model, the current density parameter of baryonic matter $\Omega_P \sim 0.04$, ...
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Where are CMB or galactic photons travelling to?
I'd like to describe my problem in an example:
Let's say one "generation" of CMB photons reaches Earth and
the passing ones arrive at Mars ~20 min later.
As CMB is coming from all directions ...
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Cosmic neutrino background temperature
In my cosmology lecture course, we derived the temperature of the cosmic neutrino background as
\begin{equation}
T_{\nu} = \left(\frac{4}{11}\right) ^ {1/3} T_{\gamma} \,.
\end{equation}
Since the ...
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Inflation and CMB power spectrum
So the inflation is evoked to solve the horizon problem so that every point in the CMB was in causal contact. Does this then contract to the calculation without inflation of the angular size of the ...
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Horizon problem and relation to cosmological principle
I am taking an introductory course in cosmology and we have just introduced inflation as a way to solve the horizon problem (why the CMB is so uniform if not all parts of it have been in causal ...
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Is the cosmic background radiation random and Kolmogorov complexity
In the article https://arxiv.org/pdf/physics/0510102.pdf the idea arises that if there was a Creator of the Universe and wanted to send us a message, then the "right" place to do it, would ...
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Sachs-Wolfe time shift
The term $-(2/3) \delta \phi /c^2 $in the Sachs-Wolfe effect, due to photons in the high density region experiencing the last scattering earlier, intuitively why is that?
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Sachs-Wolfe effect
So for photons at the bottom of the well at the time of last scatter, they will climb out of it losing energy. But, from there on, the potential wells (density fluctuations) do not just disappear, so ...
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Multipole ${\it l}$ value for the second acoustic peak in the CMB power spectrum
So according to the Planck paper https://arxiv.org/pdf/1502.01582.pdf page 20, the first peak is ${\it l}$=220, but the second peak is ${\it l}$=537. Not quite the double of the first peak, why? If ...
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How to interpret the velocity from relativistic doppler effect/equation for the redshift of cosmic background radiation?
Value and calculation of redshift of the microwave background radiation:
https://lambda.gsfc.nasa.gov/education/graphic_history/microwaves.html
https://thecuriousastronomer.wordpress.com/2015/07/30/...
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How does apparent brightness (or stellar magnitude) change with distance in an expanding universe
Cosmological redshift causes wavelengths of a distant object to stretch by a factor $1/(1-Hr/c)$ where H is the Hubble constant, r is distance, and c is the speed of light. Consequently the received ...
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How does conservation of energy relate to cosmic microwave background radiation?
I've seen posters on a number of forums, including this one, telling us that conservation of energy doesn't apply to cosmic microwave background radiation. This is of some concern because, for ...
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Inverse of equation with Legendre polynomials [closed]
I have to find the inverse of the equation of the multipole moment of a field
\begin{equation}
\Theta_l(k)=\int_{-1}^1 \frac{d\mu}{2}\mathcal{P}_l(\mu)\Theta(k,\mu),
\end{equation}
where $\mathcal{P}...
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If we have a cosmic microwave background should't we also have a cosmic radio wave background?
I'm a layman in physics, but here is what I understand:
What we see in the sky with naked eyes is a map of electromagnetic waves in the frequency visible to the human vision.
But that kind of ...
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Why are power spectrum plots $l^2 P(l)$ instead of just $P(l)$?
Why is it typically plotted $l^2 P(l)$, or $l(l+1) P(l)$, vs $l$ instead of just $P(l)$ in power spectrum plots?
For example, we can see it in this plot found in Introduction to Gravitational Lensing ...
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How can we still see the CMB? [duplicate]
May seem stupid but i cant wrap my head around it. if a star explodes we eventually see it when the light gets here. but once its got here we see the event and the star is now gone, we cant see it ...
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Correlation functions in cosmology
I'm reading an article about Non-Gaussianity of Large-Scale Cosmic Microwave Background (link) and the authors write that the n-point correlation function of $e^{\varphi(x)}$ where $\varphi(x)$ is a ...
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How can the Cosmic Neutrino Background (CνB) have a temperature? How can any neutrino have a 'temperature'?
The word temperature usually refers to the average velocity of massive particles, correct?
And the Cosmic Microwave Background (CMB) has a 'temperature' based on the temperature of a 'black body' that ...
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Why do we say the universe is isotropic when we are clearly moving w.r.t the CMB?
Modern cosmology is built on the Friedmann equations, which in turn rely on isotropy — the idea that the universe looks the same in every direction — as a fundamental assumption.
However, there's a ...
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How did neutrinos eliminated from dark matter? [duplicate]
I am reading "Dark Matter and Dark Energy" by Brian Clegg.
In Chapter 3 it's discussing about cosmic microwave background radiation and the elliptical shape
of early universe obtained from ...
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Does the gravitational constant $G$ impact the density parameter $\Omega$?
As far as I'm aware, for baryonic matter the estimated mass density is:
$$\Omega_{\rm m} = 0.044 \pm 0.004$$
If in some other universe $G$ was say $22$ times what it is in ours, is there a linear ...
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Implications of the axis of evil in Big Bang theory and cosmological inflation?
According the the axis of evil feature of the CMB map verified twice by space missions our home location is on this center axis of the CMB map! Making our home location sort of the center of the ...
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Calculation of age of Universe
The age of the Universe is about 13.8 billion years, measured by light emitted from the time it emerged from opaqueness. But how was the time from the "beginning" to 380,000 years (era of ...
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Approximation of Spherical Bessel function [closed]
I am currently studying the CMB power spectrum from a numerical approach (easier than the analytical approach). In a Mathematica notebook that I am following, they work with spherical Bessel functions ...
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If CMB came from the big bang, how come we got to where we are before the CMB arrived? [duplicate]
I have read that the cosmic background radiation was formed 380,000 years after the big bang, when stuff changed from being opaque to light, because of free electrons, to becoming transparent.
However,...
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Cosmic ray GZK limit calculation: subtleties with four-vectors
I'm considering an ultra-relativistic cosmic proton colliding with a CMB photon, creating a neutral pion, as depicted by this equation:
$$\tag{1}
p + \gamma \rightarrow p + \pi.
$$
This process is ...
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Matter-antimatter annihilation and CMBR [duplicate]
Does this intensity of microwave background radiation correspond to the huge amount of gamma photons that could be released during the theoretical annihilation of matter and antimatter at the time of ...
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Wouldn't Miller's planet be fried by blueshifted radiation?
In Interstellar, wouldn't Miller's planet be fried by blueshifted radiation? The 61,000x time dilation multiplier would make even cosmic background radiation photons into extreme UV photons.
I was ...
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Wouldn't the cosmic background radiation (CMB) produce drag and thus create a preferential inertial frame?
Because the CMB is everywhere and is isotropic, if an object would have a certain velocity, it could have a pressure differential produced by the CMB which would produce drag till it would stop with ...
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Does photon-photon scattering influence classical vacuum E&M dynamics?
At a purely classical level, Maxwell's equations are completely linear, and associated with a linear coupling to a conserved current in the electrodynamical Lagrangian. When this Lagrangian is ...
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How can recombination lead to photon decoupling if scattering can still occur with neutral particles?
During the recombination era, two things happened:
Electrons and protons bonded to form neutral hydrogen atoms.
As a result of #1, Compton scattering is no longer efficient enough to keep photons and ...
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If the universe expands uniformly in all directions, wouldn't that make the basis for an universal and absolute "now" and reference frame? [duplicate]
Let's consider a universe with constant expansion for simplicity's sake. In such a universe, the Hubble Parameter drops to half its value after double the time. If it happens to be 70 km/s/Mpc today, ...
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Cosmic rest frame breaking Lorentz invariance
Is it surprising given that the existence of a preferred frame in the universe (from the cosmic microwave background), the cosmic rest frame, that there are no preferred observers? (Lorentz invariance ...
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Will a clock that is isolated and stationary with respect to the CMB report the highest possible value for the age of the universe?
We have a very special clock that has existed since the dawn of time. Its purpose is to measure the age of the universe. It is always very far from any massive body or gravitational field and it is ...
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Is CMB slowing down all moving objects in the universe?
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Object moving relative to the CMB frame of reference will see the CMB blue shifted where it is heading and red shifted where it came from.
Correct?
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The blue photons ahead should have more ...
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On which speed the relic microwave background radiation becomes dangerous for the people on space ship?
If we travel with speed close to the speed of light, the light waves becomes shorter and their energy increases (because we flight through much more light for the same time).
So, even background ...
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Why the CMBR redshift is so higher than the redshift of the most distant therefore oldest galaxies in the universe?
Why the CMBR redshift is so higher than the redshift of the most distant therefore oldest galaxies in the universe? We know that cosmological redshift rises with distance from the object but at ...
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Question: Is our Universe finite? [duplicate]
Is it at all possible to compare our three-dimensional space with the two-dimensional surface of an expanding ball where recombination-induced radiation from the point at the top of the ball travels ...
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Is the blackbody curve of the cosmic microvave background maintained as the Universe expands?
The cosmic microwave background is observed to have a blackbody spectrum. What happens to it as the Universe expands and is a blackbody curve
maintained with the expansion? I know that the spectrum ...
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How can a photon emitted when the universe was just a few lightyears in diameter, travel for billions of years without bumping into something?
Admitted: I find it already surprising that a photon can travel for billions of years without bumping into something in a universe that has the size of current observable universe but there I guess ...
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Planck's law and CMBR
Rereading statistical mechanics notes, I was recently struck by a fact that seemed very surprising to me. In the notes I am reading, one derives Planck's formula for the energy distribution of photons ...
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