Questions tagged [redshift]

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How do you explain cosmological red shifting in terms of gravitons?

We know that the photons from the big bang are continually being red shifted and losing more and more energy. In terms of the graviton view, how would you explain that? Where is the energy going? Are ...
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0answers
51 views

Do redshifted galaxies with $z>1$ look like bigger because red light has a larger diffraction angle?

As a laser beam starts to diverge after a certain distance and has a divergence or diffraction angle which is largest for red light somebody could observe two laser sources distant 1m from each other ...
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1answer
77 views

Would the Doppeler effect be incorrect to use as evidence to support an expanding universe?

In our science class we have a question to answer, which is 'explain how redshift supports the idea of an expanding universe'. I am not sure how to answer this question, as I know that there are '...
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1answer
70 views

How does the redshift - distance graph show the rate of expansion of the universe at every moment in time?

By plotting the graph of redshift against the distance of the object from earth, we are able to obtain a best-fit curve showing the relationship of redshit against the distance. How does this ...
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2answers
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Red-shifting due to emitting gravitational waves

Light waves exert their own gravitational pull and must be emitting gravitational waves, losing energy in the process. Does this mean that light becomes red-shifted as it travels even without the ...
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0answers
843 views

Blackbody temperature with redshift confusion

I am a little confused about proving that the temperature of a redshifted blackbody differs from the intrinsic temperature by the factor (where z is the reshift)$$T=\frac{T_{intrinsic}}{(1+z)}$$ So ...
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0answers
64 views

Proof of an accelerated expansion of the universe

Are there any more "proofs" of an accelerated expansion of the universe other than: $1:$ that galaxies that are farther away from us are also more redshifted. $2:$ using "Baryon ...
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1answer
72 views

What happens to the energy of photon red shifted by expansion of universe?

There are many similar questions but the answers don't satisfy me. I mean it as asked in the title. Some answers given before give the explanation based on gravitational potential energy but consider ...
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1answer
49 views

Ambiguity in measuring the speeds of galaxies

People measure the speeds of galaxies via the redshift effect. However, considering our spacetime as a non-flat manifold implies that measuring the speeds of any two objects not in the same tangent ...
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0answers
42 views

What is the meaning of “current” CMB rest frame or the CMB rest frame at redshift $z$?

As I know that the definition of the CMB rest frame is the comoving frame of the plasma emitting CMB. And the anisotropy of CMB is due to the velocity difference between the earth frame and the CMB ...
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0answers
100 views

Demonstration of comoving volume probed between 2 redshifts

1) I can't manage to find/justify the relation (1) below, from the common relation (2) of a volume. 2) It seems the variable r is actually the comoving distance and not comoving coordinates (with ...
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0answers
55 views

How long does it take for the image of an object falling into a black hole to disappear?

From what I've read on other questions and answers, an outside observer cannot see an object fall into a black hole, but rather the image of the object will look like it is stuck on the surface of the ...
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41 views

Red shift of radio signals

If a radio signal is red-shifted does it still last the same amount of time? Knowing the signal wavelength is now longer but still is traveling at the speed of light one would assume the radio message ...
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2answers
101 views

If light speed determines the rate of time, could the speed of light be varying over time and we be unaware of it?

Is this a valid implication/alternative explanation of universal red-shift? I thought I'd ask this when I read this question about light clocks. I had speculated this way: If light speed determines ...
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0answers
129 views

At what rate does a photon blue shift as it falls toward a black hole and red shift as time slows close to a black hole?

Perhaps I am thinking about this incorrectly when a photon arrives at an event horizon, from an observers perspective time has essentially stopped for it and the photon has red shifted completely. ...
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2answers
94 views

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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1answer
84 views

are redshift and Doppler effect identity with speed of light?

we know that redshift and Doppler effect say wavelength and energy are relative to the speed of cause body, so how can I understand the special relativity which said that the speed of light is same ...
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1answer
85 views

How to shift AGN x-ray spectrum to rest frame

I have limited information to shift a spectrum (in the x-ray 0.5-10 keV bandpass) at redshift z=2 to rest frame. I have a plot of normalized (photon) counts s$^{-1}$ keV$^{-1}$ by energy (keV), and so ...
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0answers
247 views

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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0answers
71 views

Local acceleration of mirror in flat 1+1 spacetime

Setup: I am reading a paper (Carlitz and Willey. Phys.Rev.D. Vol35. pp.2327-2335. 1987) where the authors model Hawking radiation using a point-like accelerating "mirror" in 1+1 dimensional flat ...
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0answers
47 views

How does the number density of supernovae change with red shift

I am interested to know more about how the number of supernovae found changes according to their distance/red shift. I have heard but I can't remember where that the number of supernovae is greater ...
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2answers
157 views

Light and Gravity

The gravitational force does not affect the speed of light rather affects the frequency of light (hence light changes colors, red to blue and vice-versa). I know this has been verified but I have 2 ...
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1answer
41 views

How would distant objects in a contracting universe look?

Our current universe is expanding, and distant galaxies are redshifted, with a redshift that increases as the distance to the galaxy increases. After a certain distance, the galaxies move faster than ...
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1answer
14 views

Red shift for an observer outside the gravitational field

Assuming there are no forces around,consider the situation: A multi storey laboratory is accelerating in free space, for convenience say vertically. In it a light pulse is generated. The people in ...
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24 views

How, if at all, do Tachyons experience redshift?

I recently attempted to answer this question, to which I felt qualified because the possibility of Tachyons had been discussed when I took a course on Special Relativity. In that same course I learned ...
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1answer
23 views

Interpreting recession velocity (red / blue shift)

I just had to teach something that I myself have never learned, concerning recessional velocity of galaxies. Awkward! The question was: "A line in a hydrogen spectrum has a wavelength of 486.1nm ...
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1answer
36 views

Calculating the redshift drift

I am trying to calculate the redshift drift where its written as $$\frac{dz}{dt} = (1+z)H_0 - H \tag{1}$$ We also know that $$1+z = a(t_o) / a(t_e) \tag{2}$$ and $$H_0 = \frac{\dot{a}(t_0)}{a(t_0)}$$ $...
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17 views

Parallax and redshift - has anyone used Gaia data to match objects with redshift data?

Given the recent Gaia parallax data out to large distances, has anyone used that data to match objects with observed redshift data? I have taken as much Gaia object data as I can and compared it with ...
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1answer
23 views

How to tell a population 3 star in red shifted galaxy?

I read that population 3 are metal poor stars especially those very very massive ones will quickly exhaust their fuel and goes into supernovae when their internal pressure drops due to pair ...
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2answers
187 views

Conservation of Charge vs. Conservation of Energy

Is conservation of charge ever violated like conservation of energy is violated during cosmological expansion? I am trying to understand this with respect to Noether's Theorem.
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1answer
54 views

How do we determine both the distance to and speed of distant stars?

My understanding is that we can measure the distance to far away stars by using their color to infer the absolute magnitude of the light they emit and compare that to the observed magnitude of the ...
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0answers
32 views

Bad or valid expression for gravitational redshift

In my lecture of General Relativity, teacher takes the following metric : $g_{\mu\nu}(x)=\eta_{\mu\nu}+h_{\mu\nu}(x),~ {\rm with}\ h_{\mu\nu}\ll1$ Qquestion 1) I understand its first demonstration ...
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26 views

What is the current most accurate measurement of the cosmological transition redshift

Does anyone know what the current most accurate measurement of the redshift for when the Universe's expansion changed from decelerating to accelerating (with a reference)?
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1answer
49 views

Disregarding expansion of space, are there any processes which can redshift light over billions of light-years?

Assume there are 10 molecules per cubic meter, on average, in interstellar space--in effect, a very thin gas. Assume that the source of light is ten billion light years away, the tunnel through which ...
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0answers
34 views

Can the age of the universe at the time of emitted light be calculated with Hubble's Law?

Let there be an object being observed, distance D away. D equals the speed of light times the time it takes the light to arrive (but space expands while the light is propagating, which is most likely ...
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1answer
39 views

Is the mean CBM frequency more red-shifted since discovered in the 1960's?

If the universe is uniformly expanding at rate x, is possible to measure that the CBM has increased its red-shift value over time? If the red-shift is a static value, is it possible that the ...
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1answer
23 views

Information contained in red shifted “light”.

A source of light is traveling away from us at .95c. Its emr reaches us with a big redshifted wave pattern yet still arrives at the speed of light. So if our light source moves away from us at say 1....
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1answer
92 views

Original distance from us to galaxy at redshift of z=6 if we know the current distance and taking into account universe expansion?

So I'm given that a galaxy cluster is currently at redshift z = 6 and the question asks "what was its distance from us at the time the light left the cluster?" We only know the redshift, but the ...
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1answer
37 views

Hubble Expansion

Just to add a simple question but maybee I'am to simple to answer it on my own in calculations about the size of the observable universe and hubble spheres and all of that how do you determine the ...
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1answer
102 views

How to manage to solve for the scale of factor increase between two galaxies?

The greatest redshift known corresponds to the cosmic microwave background (CMB, CBR) at redshift z 1100 (although the redshift is obtained theoretically rather than observationally). UDFy-38135539 ...
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0answers
109 views

Can redshift occur from relative velocity or just from expanding space

With sound the Doppler effect is caused by the wavelength of the sound being affected by the relative velocity between the observer and emitter, eg. If they are moving toward each other the observed ...
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1answer
150 views

How can the angle to a pulsar be determined by measuring its redshift?

Suppose we (a spacecraft, probe, or similar) know our location only to within a few billion km (a few Tm) in any direction in 3D space, and we want to determine our location to a higher degree of ...
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1answer
52 views

Entanglement thought experiment with redshift

Thought experiment: 2 entangled photons, one escape from galaxy to galaxy without hitting an electron and another one got caught between 2 perfect mirrors. Would the redshift (wavelength becomes ...
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1answer
104 views

Red shift and the expanding universe pertaining to gravity wells

is it possible that gravity's effect on the energy level of light could be causing the red shift in light arriving from other galaxies and not an expanding universe? it is impossible, after all, to ...
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1answer
177 views

Tired light question

How do we arrive at the conclusion that redshifted light from cosmological sources has 'lost' energy during its transit from source to us? If in fact no actual measurement of the energy of the ...
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1answer
100 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 ...