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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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Doppler Effect and the concept of relative velocity in GR

While reading Sean Carroll's book on General Relativity, I understood that the concept of velocity is ill-defined over large distances in arbitrarily curved manifolds, like the one used to describe ...
V Govind's user avatar
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About redshift and distant objects observation

I did a few Time&Length dilation factor calculations. This is for a distant clock away from any field and a clock on Earth on the equator with the moon passing over clock coordinates, the factors ...
olivierlambert's user avatar
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Does gravitational redshift conserve energy?

It is claimed that redshift due to cosmological expansion doesn't conserve energy. Does this exception also apply to gravitational redshift? Why or why not?
Derek Seabrooke's user avatar
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Factor for observed redshift - light dispersion (chromatic aberration) caused by a gravitational lensing

This thought tortured me for a while now, and I can't find if this has been hypothesized/discussed before, and if so, is there a consensus: Can redshift be to at least some degree a result of a ...
Andris's user avatar
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Stars that have fairly high gravitational redshift and calculation of their surface temperature by Planck emition spectra?

How high can the ratio between gravitational redshift and planck emition spectra be depending on the mass of the star so by how much this gravitational redshift could elongate the Planck spectra of ...
Krešimir Bradvica's user avatar
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Distance needed for visible light to be cosmologically redshifted to microwave

What distance will it take for visible light to become a microwave due to cosmological redshift? I'm not sure how to calculate this, as I'm never good at complex math. I tried googling but didn't find ...
X3R0's user avatar
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Could the increasing anisotropy of the universe lead to an additional blueshift?

I'm contemplating the possible sources of a wavelength-shift within our universe: The CMB had a lot more energy when it was produced (around 3000 K). Due to the expansion of the universe, it has been ...
MartyMcFly's user avatar
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$I_{\nu}/\nu^{3}$ which is Lorentz invariant is also invariant for cosmological redshift?

$I_{\nu}/\nu^{3}$ is Lorentz invariant, therefore an observed intensity is boosted by $\delta^{3}$, where $\delta$ is the Doppler factor. If the cosmological redshift is same physical process with ...
Chanwoo Song's user avatar
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Are there structures or systems that can have a high angular momentun that are not made by protons and/or neutrons?

Cosmic structures such as neutron stars, white dwarfs or black holes can have high amounts of angular momentum (high spin velocities). However, these are all made by protons and neutrons (black holes ...
vengaq's user avatar
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11 votes
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Redshift of the CMB

Has the $z\sim 1100$ redshift of the CMB been actually measured by comparing the fingerprint (absorption spectrum) of the CMB with the theoretical radiation pattern of a $2.725\,\mathrm{K}$ blackbody, ...
Yuan Liu's user avatar
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Does someone falling into a spinning black hole see the end of the universe?

It is well known that if you fall into the Schwarzschild black hole you cannot see the entirety of the outside spacetime since there are photons which cannot catch up with you before you reach the ...
bkocsis's user avatar
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In a fast moving space ship, can you harvest energy from the radiation background?

In a fast moving space ship (let's say a meaningful portion of c), radiation coming from the front is blue-shifted, while the one coming from behind is red-shifted. Meaning the part of the universe ...
kutschkem's user avatar
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Cosmological redshift and distance calculus

I am somewhat puzzled when it comes to understanding the general relationship between the cosmological redshift of a galaxy and its distance, and none of the other questions in the forum have ...
Gorga's user avatar
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Resolution of Einstein prediction of brightness loss with acceleration

Stars moving at velocities relative to us nearer to light speed are predicted to have lower brightness as well as red shift. Brightness loss has not been observed, however. Could this be due to ...
Hugh's user avatar
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Up-tunneling of vacuum with high-energy events?

I was reading these papers by Sean Carroll (https://arxiv.org/abs/1405.0298 ; https://arxiv.org/abs/1505.02780) in which, among other things, he argues against vacuum up-tunneling occurring in the ...
vengaq's user avatar
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Why are physicists not more concerned that there are too many explanations for redshift in the universe?

There are speculative explanations for red shift such as the tired light theory, but I am not referring to those. There are three mainstream explanations Red shift due the expansion of the universe ...
John Hobson's user avatar
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Why do successive redshifts multiply rather than add?

I understand the argument presented in the answer to this question on how successive redshifts combine, such that $$1+z = (1+z_1)(1+z_2) = 1 + z_1 + z_2 + z_1z_2 \\ \therefore z = z_1 + z_2 + z_1z_2.$$...
Josh's user avatar
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Cosmological redshift without approximations

The classical proof of cosmological redshift that leads to the relation: $\frac{\lambda_0}{\lambda_e}=1+z=\frac{a\left(t_0\right)}{a\left(t_e\right)}$ is quite well known as for example (among many ...
Vincent ISOZ's user avatar
1 vote
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Is cosmological redshift associated with recession velocity when the light left or when it arrived?

Is the cosmological redshift $z$ associated with the recession velocity when the light left, when it arrived, or something in-between?
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Blueshift and redshift of a radially infalling photon [closed]

An observer, initially at rest in infinity, is radially infalling through a Schwarschild black hole of mass M. Also a photon is radially infalling, almost cathing up the observer at a radial distance ...
qwerty's user avatar
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Would continuously increasing curvature of space explain seeming expansion of the universe? [closed]

Could expanding universe phenomenon be explained by slowly but continuously increasing curvature of space around masses like galaxies and galaxy clusters? In other words, I am curious whether the ...
Roland Pihlakas's user avatar
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Advantage of a single large telescope over many small ones for optical/infrared spectroscopy?

In a thought experiment where we would like to do optical/infrared spectroscopy on distant galaxies, and in which we would like to increase as much as possible the resolution of the spectroscopy (...
Vincent's user avatar
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2 votes
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Gravitational redshift inside tunnel that goes to the center (where the light comes from) of massive body of radius $R$ a distance $r$ from the center

I'd like to know the general formula of the gravitational red shift for light emitted from the center of a massive body of density $\rho$ and radius $R$ where the light is emitted from the center of ...
Relativist's user avatar
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Is there a formula for gravitational time dilation at the cosmological scale?

There is a standard formula for gravitational time dilation used in eg the operation of the global positioning system. It is based on the integration of g(h) where g is a function relating ...
John Hobson's user avatar
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Why only Lyman alpha transition suffer Redshift in the epoch of Recombination in Cosmology?

I was reading Baumann's book on cosmology (topic: Effective three level system). There it is said that in the epoch of recombination to form Hydrogen molecule two type of transition happens. $$ 2S \to ...
Kazi Abu Rousan's user avatar
1 vote
1 answer
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Redshift near Kerr Black Hole

The question is related to Sean Carroll's Spacetime and Geometry ex 6.6. Consider a Kerr black hole with an accretion disk of negligible mass. Particles in the disk follow geodesics. Some iron in the ...
Tachon's user avatar
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How to derive deceleration parameter in terms of redshift?

How do I get q in terms of $z$ specifically of this form: I want to derive the second equation from the first but I'm getting an additional $ \frac{a^2}{H^2}\ $ in the second term $$ q= -\frac{\ddot{a}...
Scribbles and scratches's user avatar
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2 answers
90 views

If the expansion of space causes the elongation of light waves, why isn't this elongation observed within the Milky Way?

The elongation of light waves occurs not because galaxies are moving away from each other, but because light waves are stretching along with the fabric of expanding space (cosmological redshift). ...
Dinislam Maushov's user avatar
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Clocks at different redshift: does calculating luminosity distance shift the frame of reference?

Luminosity is energy per time. When we calculate a luminosity distance, using angular diameter distance times $(1+z)^2$, I think we are correcting the energy (from redshifted photons) by $(1+z)$ and ...
MikeHelland's user avatar
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Maths behind red/blue-shifting [closed]

I watched this video of silly science facts, on of which stated "you can avoid red lights by travelling at around 114,000,000mph (51,000,000m/s) because the red light would be blue shited enough ...
Ethan's user avatar
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How can we accurately tell distances of celestial bodies when considering superluminal expansion [closed]

If parts of the universe are moving away from each other faster than the speed of light relative to my position in space, how can we accurately tell the age or distance of other celestial bodies ...
Spatium et Tempore's user avatar
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170 views

Constraints on the CMB temperature redshift dependence at matter-radiation equality?

As pointed out in the 2011 paper Constraints on the CMB temperature redshift dependence... here the relation between redshift and the CMB temperature, $T_{CMB}(z)=T_0(1+z)^{1-\beta}$ (with $\beta=0$ ...
Mr Anderson's user avatar
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1 vote
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The linear growth factor of perturbations today should be 1 but I am unable to derive it

The definition of the linear growth factor $D(z)$ of perturbations in a cosmological setting is usually normalized to unity at redshift $z=0$. So, $$\delta(z) = D(z)\times \delta(z=0) \tag{1}$$ where $...
Matrix23's user avatar
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Casimir Effect & Redshifting

The classic plate experiment highlights how omitted wavelengths of light create an energy differential and pressure. This pressure is dependent on the distance between the plates, including how this ...
Eric Roche's user avatar
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How fast would you have to go in space to be warmed to a comfortable temperature?

How fast would you have to go in space, not near a star, such that the Cosmic Microwave Background is blueshifted enough to warm you to a comfortable temperature (70 F or 21.111 C)? Expressing it in ...
Jonathan's user avatar
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How is a photon being consumed by electron in QM?

I'm not a physicist in any way, but I'm curious enough to watch and attend some pop-science lectures. Let's imagine the following situation - there is a free-standing unbound electron. It has its wave-...
abyss.7's user avatar
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1 vote
3 answers
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Why do we See Black Holes?

The image of things falling into a Black Hole stays frozen on the event horizon forever. So how is it that we don't see the image of a dying star where a Black Hole formed? We see the black, with an ...
talanum1's user avatar
6 votes
3 answers
837 views

"Artificially" time dilated photons

If you bang on the table you create a single thump, but if you keep doing so with shorter and shorter intervals, eventually it'll start to sound like a note with a particular pitch. Now, if I used a ...
Cosmo's user avatar
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1 answer
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Was doppler effect for light proven experimentally?

If so, provide me with the data sources. From what I read, doppler for light is taken for granted. Or sometimes based on theoretical formulas. But if one wants to theorise, light is a mix of photons ...
MrFramm's user avatar
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Detectability of cosmological redshift in an empty part of universe

I'm pretty new to the concept and I want to get a better idea about it. I've seen a video in which a light wave is stretched since the space itself is stretching. Another analogy is that cosmological ...
Shirish's user avatar
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Since the general formula of redshift only depends on the metric of the source and the observer, how do we end up with Integrated Sachs-Wolfe effect?

To my knowledge, the most general expression of the redshift in cosmology is the following: $1+z=\frac{\left(g_{\mu\nu}k^{\mu}u^{\nu}\right)_{S}}{\left(g_{\mu\nu}k^{\mu}u^{\nu}\right)_{O}}$ where : $...
Vincent's user avatar
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1 vote
1 answer
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Mass redshift degeneracy for binary black holes at all order in post-Newtonian perturbation theory

When you compute the inspiral signals of a binary black hole to lowest order in the post-Newtonian formalism, and study how this solution propagates through an expanding spacetime, you find that the ...
konstle's user avatar
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Has the speed of light always been constant? [duplicate]

Is there any evidence to suggest that the speed of light (or its other properties) has been unchanged since the beginning? The particular curiosity stems from the redshift observed in distant galaxies....
A McKelvy's user avatar
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8 votes
2 answers
739 views

At what distance can I assume peculiar velocity is negligible compared to expansion velocity, to use Hubble's law?

I am working on a high school physics assignment and am trying to figure out a method to determine if the star is a giant or main sequence from its spectral and photometric data (from SDSS). I picked ...
Hossam Dahshan's user avatar
3 votes
1 answer
300 views

Do LIGO O4 Gravitational waves observations distance estimates account for redshift?

A new LIGO detection today has a mean distance estimate of 7412 Mpc. Does that mean that this LIGO distance calculation does not account for redshift, since that mean distance estimate translates to ...
Max Kislik's user avatar
0 votes
1 answer
499 views

Methods for calculating the orbital speed of a star in a binary system

As I understand it, to calculate the speed of rotation of a star in a binary system that is receeding, that is in the same plane as us (inclined at 0 degrees) the method is use the Doppler formula: Δλ/...
tomd7824's user avatar
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-4 votes
1 answer
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Is it possible to measure the one way speed of light with redshift [duplicate]

By this I mean say you had and entire galaxy to work with, and you could measure the exact wavelengths of the waves you send out and record it. You would shoot this light beam across the galaxy and ...
Baker Rentmeister's user avatar
2 votes
1 answer
72 views

Why does a distant observer experience gravitational redshift and not blueshift?

The model I am learning to explore Schwarzschild spacetime is where solution modes to the scalar equation originate at null infinity, propogate through a massive body (only inside the mass is the ...
Tawny's user avatar
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1 vote
1 answer
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Taylor Expansion of the scale factor in terms of redshift

I was reading about the Taylor expansion of the scale factor from visser,2004 He writes: $$ \frac{a(t)}{a_0} = 1 +H_0 (t -t_0) - \frac{q_0}{2} {H_0}^{2}(t-t_0)^2 + \frac{j_0}{3 !} {H_0}^{3}(t-t_0)^3 ...
Alucard's user avatar
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1 answer
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Why does redshift happen?

If an object B does NOT move away from us, doesn't matter whether it's 10 km or 5,000,000 km away from us, I think redshift wouldn't happen. Now, if the object is moving away from us, it's said that ...
Matt's user avatar
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