Questions tagged [redshift]
Redshift refers to the difference in frequency of an electromagnetic wave as measured by a source versus a receiver in relative motion.
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Cosmology - an expansion of all length scales
From the link Is non-mainstream physics appropriate for this site?
"a question that proposes a new concept or paradigm, but asks for evaluation of that concept within the framework of current (...
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Redshifted Photon Energy
A photon emitted from a receding source (Doppler redshift) has less energy when detected at an observer's location. Please explain the energy loss from the perspective of energy conservation.
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With redshift, energy is lost. Where does it go? [duplicate]
A photon emitted by a distant source billions of light years away arrives here with a lower frequency hence less energy than it started with. What happened to the energy?
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If space is "expanding" in itself - why then is there redshift?
The "kid's" way of understanding the expanding universe is that: "space" is totally "ordinary", and all the galaxies are expanding through it (like an explosion). Of course, that's wrong.
The usual ...
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Interpretation of cosmological redshift
I was trying to understand why we cannot explain the observed redshift of distant galaxies using special relativity and I came upon this article by Davis and Lineweaver.
Unfortunately when I arrive ...
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Redshift of distant galaxies: why not a doppler effect?
How can I explain to my 17 year old pupils that the observed redshift of distant galaxies cannot be interpreted as a doppler effect and inescapably leads to the conclusion that space itself is ...
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Can gravitational waves be red-shifted?
Whenever the Doppler effect is mentioned, it's typically in the context of sound waves or electromagnetic radiation. On the cosmological scale, red-shifting is also important because of the enormous ...
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Why is "gravitational" red-shift neglected in galaxy and galaxy cluster scales?
The red-shift of the light of a star in a galaxy or that of a galaxy in a cluster of galaxies is generally interpreted as how fast the star or the galaxy is moving, i.e. it is interpreted in a purely ...
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'Doppler redshift' Vs 'Cosmological redshift'
It is not difficult to understand the differences between 'Doppler redshift' and 'Cosmological redshift' conceptually. But how do astronomers distinguish them when doing observations?
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What is the cosmological redshift drift effect?
What is the redshift drift effect in cosmology?
What are the necessary cosmological conditions for there to be a measurable redshift drift effect?
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Redshift of merging black holes
How did they found that the gravitational waves where emitted at redshift $z=0.09$?
I understand the measurement of redshift for an electromagnetic wave where we have measured in a lab various ...
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Red shifted to what?
I searched and found a lot of questions and answers about red shift here but none with the answer to mine. (sorry if it is there somewhere and I did not find it.)
Everyone is saying the light from ...
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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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Does an object's redshift actually decrease with time?
I am trying to determine how an object's redshift (specifically, redshift due just to the expansion of the universe) changes in time. Starting with a definition of the Hubble parameter,
$$H \equiv \...
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A question on the redshift of photons due to cosmic expansion
Given that the universe is expanding over time, in the sense that the (spatial) metric is changing over time, corresponding to the physical distance between objects increasing, naïve intuition leads ...
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Does GR explain cosmological time dilation?
There is plenty of evidence for a cosmological time dilation effect. For instance a supernova that takes 20 days to decay will appear to take 40 days to decay when observed at redshift $z=1$ (see Ned ...
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What is the redshifted amplitude of a gravitational wave?
Consider a gravitational plane wave in flat background spacetime, with amplitude $h$ and frequency $f$. For an observer moving with redshift $(1+z)$ relative to the plane wave, what is the observed ...
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Why is speed measured along the line of sight (LOS) a factor $\sqrt{3} $ smaller for randomly distributed velocities?
I encountered this problem from Introduction to Modern Cosmology by Andrew Liddle.
I had the exact same doubt as the OP of that question had, and the first answer makes sense but I don't understand ...
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Expanding space and red shift
Assuming space is really expanding -
Due to expanding space, distant galaxies are supposed to be moving away from us.
When light leaves a distant galaxy, it's wavelength is red shifted to begin with ...
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Momentum and energy of photon
Does the momentum and energy of photon change when it travels from distant galaxies through the Space?
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Does Redshift depends on wavelength?
I came across this equation on Wikipedia:
$$z=\frac{\lambda_{\text{observed}} - \lambda_{\text{emitted}}}{\lambda_{\text{emitted}}}$$
and it got me thinking: If I measure a wavelength of $700 \;\text{...
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Does red shift evidence necessarily imply that the universe started from a singularity?
We are taught that the universe began as a singularity - an infinitely small and infinitely dense point. At the beginning of time there was a 'Big Bang' or, more accurately, 'Inflation'.
The main ...
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Why isn't the De-Broglie wavelength of massive particles redshifted in an expanding universe
It is pretty straight forward how light is redshifted in an expanding universe, yet I still can't understand why the De'Broglie wavelength of a massive particle isn't redshifted in an expanding ...
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Is there a thermodynamic heuristic argument on why a redshifted blackbody spectrum is a blackbody at a new temperature?
Without calculating it, it isn't obvious to me that if you take Planck's Law for the spectral radiance as a function of temperature of a black body and shift all the frequencies by the same factor, ...
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Can we use redshift measurements to determine absolute velocity?
Here's a thought experiment: suppose I'm in a large box in space without windows or sensors, and I fire a laser in 6 different directions and measure the redshift along each direction. Could that data ...
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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:
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Is there cosmological redshift within the Milky Way?
Cosmological redshift is based on the idea that the universe is expanding. When the universe doubles in size, or scale factor, the wavelength of light doubles. But the Milky Way is not expanding so my ...
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Conversion between extragalactic distances
What is the conversion between redshift $z$ and lightyears?
When an article says that some object is at a distance of $z = 1$, then what distance are we talking about in light years or parsec?
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Does observed red shift indicate expanding universe? [duplicate]
The observed red shift of objects is assumed to indicate that those objects are moving away from Earth but is it possible that there could be another explanation for the observed red shift that does ...
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Cosmological Inflation: If Photon expands, why not other matter?
I keep repeatedly reading in many Stack Exchange and Quora questions that space of universe expands but particles (matter) don't, see e.g. this Phys.SE post. The reason given is that particles are ...
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Cosmology: Is there any experimental evidence for the redshift scale-factor relation?
Modern cosmology relies heavily on the redshift scale-factor relation $$a=\frac{1}{1+z}$$
But what is the experimental evidence for it?
It's derived in textbooks from General Relativity, but for all ...
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Kerr black hole horizons and infinite redshift surfaces
In the Kerr black holes we have infinite-redshift surfaces (where a infalling body is still according to the asymptotic observer) and event horizons (the escape velocity becomes greater than the speed ...
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Redshift of the Cosmic Microwave Background: increasing or decreasing?
$$\dot z\equiv\frac{\mathrm d z}{\mathrm d t_{\text{obs}}}(t_0)=(1+z)H_0-H(z)$$
The picture and equation above are quoted from Liske et al. (2008).
According to the equation, the redshift of the ...
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Where does the energy go when light is redshifted? [duplicate]
Imagine a galaxy millions of lightyears away and, obeying Hubble's law, moving very quickly away from us.
Now imagine the same galaxy emitted a green photon in our direction (a photon with a ...
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How large or small can frequency in the EM spectrum get?
The largest frequency range is gamma rays, but does the EM spectrum 'stop' somewhere? Like is there a limit to how large a frequency can get?
Or how small frequency can get?
Is it one of those things ...
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For an observer NOT in comoving coordinates, won't the Hubble factor be anisotropic?
Since the Earth isn't exactly in comoving coordinates, I would think redshift surveys have to adjust for this?
I couldn't, upon searching, immediately find which direction our CMB dipole shift was in,...
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At what cosmological redshift $z$, does the recession speed equal the speed of light? How is it calculated?
At what cosmological redshift $z$, does the recession speed equal the speed of light?
What equations are used to calculate this number (since at large redshifts, $z=\dfrac{v}{c}$ won't apply)?
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Redshift of mass-dominant universe
What was the value of redshift $z$ when matter started to dominate the universe?
Is there any way to calculate it without knowing the time?
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Does the cosmological redshift of the same object has a same value as it evolves
https://arxiv.org/abs/1802.02444
According to the link above, the following phrase comes out:
" One must keep in mind that in the real universe, the same object( or comoving position) does not ...
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Can Hubble redshift be interpreted as time dilation?
Can we interpret the de Sitter universe as a spherical cosmic horizon null surface of finite radius, centered at Earth, and containing the Hubble volume of space where time is dilated and radial ...
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Is space expansion causing increasing distances between galaxies?
I read/heard that the expansion of the universe would lead to any observer not being able to see other galaxies as time goes on, due to their light not reaching them anymore.
But there's something I ...
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Acceleration of Universe expansion
I have been recently researching the topic of the expansion of the Universe. Specifically, the 1998 discovery by Saul Perlmutter that claims the Universe is expanding at an accelerated pace. From my ...
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CMB - Excess Energy? [duplicate]
Today in physics we were looking at how the energy of a photon is the product of Planck's constant and the frequency of the photon, therefore the lower the frequency, the lower the energy of the ...
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Struggling with Universe Expansion Rate and Redshift Graph
I have read other posts on this but I'm still confused. I'm trying to conclude how an accelerating and decelerating expansion rate graph would look like when it's plotted against the redshift Z. ...
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Distances in cosmology
I want to make sure that I understand the different distance measures is cosmology.
To do that I consider the FLRW metric:
$$ ds^2=dt^2-R(t)^2\left(\frac{dr^2}{1-kr^2}+r^2d\theta^2+r^2\sin^2\theta d\...
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We say Light is Red-Shifted or Blue-shifted from faraway stars and galaxies [closed]
We say Light is Red-Shifted or Blue-shifted from faraway stars and galaxies. Can we find out the distance at which it changed its frequency.
So in another solar system, it might seem to be Green ...
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Effect of redshift on energy conservation [duplicate]
Light coming from galaxies that are going away from us is redshifted. Since the energy of a photon is purely dependent on its frequency one may conclude that the energy of these photons decreases. The ...
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Energy loss of photons crossing a dielectric medium
How much energy do photons lose when crossing an "isotropic" dielectric medium? What would be possible mechanisms.
I assume the straight forward answer would be that the photon loses zero energy and ...
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What if we red shift a photon of the lowest possible frequency?
Properties of photons are quantised right? So what if we red shift the photons with the lowest possible frequency?
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If mass isn't conserved in an expanding universe, why do we assume atomic spectra are constant?
Of the many ways to write a mass in general relativity (Komar, adm and the like), it seems that none of them are conserved in an expanding universe (or more generally for nonstationary metrics).
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