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Questions tagged [redshift]

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BAO : Relation between redshift, Hubble constant and radial

From this link https://en.wikipedia.org/wiki/Baryon_acoustic_oscillations#Measured_observables_of_dark_energy , I can't get this relation : $$c\Delta z = H(z)\Delta \chi\quad\quad(1)$$ with $z$ ...
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1answer
41 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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3answers
106 views

Is cosmological redshift at a given time has a constant value?

On one hand, people say that various cosmic events occurred at various redshift values. For example, recombination happened at $z=1100$. This would imply that at any given point in time, in the ...
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1answer
76 views

Cosmological redshift : “time of emission” vs “during travel”

Let’s consider a very distant galaxy, suppose it has no peculiar velocity, and let’s assume space expansion; If I understand correctly there would be a redshift due to the value of space expansion at ...
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1answer
73 views

How is red shifting explained with quantum mechanics? [duplicate]

Light travels as waves through space, and since space is expanding, the light gets stretched out. This is the explanation for red shifting I learned before. Now I know some more and that explanation ...
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1answer
43 views

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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1answer
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Cause of observed galactic red shift or acceleration in expansion of the universe: velocity vs gravity.

Scientist look out at the universe and observe red shifts for galaxies that are roughly proportionate from their distance from us and attribute it to a velocity away from us. Also there is an ...
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1answer
58 views

Is the expansion of the universe really accelerating? Or does it just look like it?

I pulled this quote from an article on the Hubble Constant: "...for example, if the Hubble Constant was determined to be 50 km/s/Mpc, a galaxy at 10 Mpc, would have a redshift corresponding to a ...
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Is the space between galaxies that are close to each other contracting? [closed]

The Milky Way and Andromeda are moving towards each other as indicated by blueshift. Are they just moving towards each other through space or the space between them contracting?
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2answers
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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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1answer
73 views

How scientists know that the Redshift is because of moving objects and not due to local phenomena

I'm from engineering background and not firmly familiar with cosmological equations and concepts. but i know what Redshift is and how it is related to the Doppler effect. My question is how ...
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Does converting light's linear momentum into angular momentum (SAM or OAM) cause it to redshift?

Can all of an electromagnetic wave's momentum be changed to orbital angular momentum? I'd imagine this would be easier to test with radio waves.
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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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Does the Earth's rotation affect redshift measurements?

How do you account for the spin of the earth in the mechanical sense, when measuring redshift? Does the relatively slow speed of the earth have a major change in the measurement because of distance?
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How is the redshift related to the energy and time?

Cosmologists talk about redshifts instead of time to describe the past of the Universe. For example, the recombination happens at $z=11.00$. Knowing the redshift how can I convert it to the energy and ...
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2answers
64 views

How certain do science believe the universe is expanding?

The continue and increased rate of expansion is backed up by red shift, but that can also be true for a slowing down universe. Can the acceleration of expansion be reducing, still causing red shift ...
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5answers
2k views

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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1answer
49 views

Light speed and red shift

D. Giovanni et al. showed that the speed of photons through space can be variable if certain structure is imposed on the photons themselves (see their arxiv submission or their published work in ...
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1answer
72 views

Converting from spherical to Cartesian in cosmology

So I want to find the distance between two different objects at different red shifts. My plan so far is to calculate the line of sight (LOS) co moving distance using the formula $$D_C=D_H\int_0^z \ \...
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3answers
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Proof for photon energy loss due to cosmological redshift

According to Doppler redshift, the frequency of the EM radiation decreases if the emitting object is receding from the observer - this produces the problem in the quantisation of energy - the observed ...
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1answer
47 views

How do you calculate the recession velocity?

$$ \begin{alignat}{7} && \frac{\Delta \lambda}{\lambda} & = \frac{v}{c} \\[2.5px] &\therefore & v & \approx \frac{\Delta \lambda}{\lambda}c \end{alignat} $$ If you want to find ...
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1answer
85 views

Given redshift how do I obtain distance in parsec? [duplicate]

I have a catalog I am experimenting with that has some spectroscopic red shift data available (in the range from 0.5-1) as well as total Ks (K -short band) flux data available, how would I go about ...
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3answers
75 views

Redshift - How can Z be greater than 1?

I'm having trouble understanding the equation for redshift: z = Δλ/λ ≈ Δf/f ≈ v/c If z = v/c and c = speed of light, how can z>1 (as nothing can exceed the speed of light)?
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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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2answers
123 views

Recession velocity, redshift and different cosmological models?

Equation 1 (page 5) in “Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the universe” by Davis and Lineweaver gives the general relativistic ...
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1answer
71 views

What is the minimum detectable redshift?

Given an spectral resolution $R$ (for example $R=1000$) which is the minimum redshift I can discern? How is this related to the minimum velocity among galaxies and If this velocity is related with the ...
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1answer
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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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4answers
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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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1answer
90 views

Redshift of matter-radiation equality from $T^4$

I am trying to solve the following problem. Argue on dimensional grounds that the energy density of blackbody radiation at temperature T should scale as $T^4$. Use this to find the redshift of ...
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1answer
22 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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2answers
54 views

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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1answer
42 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
67 views

What is the cosmological redshift drift effect? [closed]

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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1answer
131 views

If an arbitrary “signal” at an arbitrary frequency was received at Earth, would there be any way to tell if it was redshifted?

I've been thinking a lot about SETI and aliens, and, just for fun (layman), learning a lot about redshift: why it's possible despite $c$ being constant, how we know stars are red- or blueshifted. But ...
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How do astronomers know what wavelength the body will emit when it is at rest? [duplicate]

In the book of The First Three Minutes by Weinberg, at page 21, he talks about how do astronomers measure the speed of a luminous body along the line of sight by Doppler affect, i.e. the fractional ...
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2answers
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Understanding a plot obtained from the 2dF redshift survey

The diagram below (taken from here) represents the distribution of Galaxies obtained from 2dF redshift survey. I have a few very naive questions about this. Which point does the centre correspond ...
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1answer
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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
130 views

Does the energy of a photon remain the same as the universe expands? [closed]

A team of two researchers far away from each other agree to perform a simple experiment. The first researcher emits a photon with wavelength $\lambda$ toward his colleague. As the photon travels to ...
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0answers
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Issues with formula for redshift

I have a textbook that is telling me that redshift is given by $\frac{v}{c}=-\frac{\Delta\lambda}{\lambda}$ where $\Delta\lambda$ is the difference between the emitted and observed wavelength of the ...
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5answers
209 views

Do the distances and velocities observed from galaxies other than Milky way really show that every point in the universe is the center?

Hubble's observation from redshift shows a pattern that the speed of the galaxies is proportional to their distance, by using those informations we can map the position of the galaxies. But these ...
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1answer
209 views

Parallax versus Redshift when measuring astronomical distances?

From my understanding, the most common method for calculating how far away stars and galaxies are relative to us is by accounting for their redshift. I feel that this method could be inaccurate, ...
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1answer
75 views

Concerning the origin of cosmological redshift

I stumbled across this paper, which is published in MNRAS, that wants to show that the cosmological redshift is not due to some "stretching of space," by showing that this interpretation is coordinate ...
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2answers
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(How) does gravitational lensing affect red shift?

In all the measurements taken over the years, has anyone ever observed any effect of gravitational lensing on red shift? So: if we would look at 2 galaxies at, say, 250 million lightyears away, where ...
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1answer
43 views

Why is void making CMBR lose energy as inflation speeds up?

The expansion of space is speeding up, so many voids are getting bigger. CMBR lose energy when moving through this void and then gain back the same energy as it leaves the void except in the case when ...
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1answer
100 views

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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1answer
73 views

Interpretation of Hubble Diagram

According to my professor's notes, this is the Hubble Diagram. Unfortunately, I do not know what the y-axis is referring to. Is it the absolute luminosity?
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2answers
199 views

Why does the redshift formula hold true when measuring the expansion of the universe?

As far as I understand, photons get 'stretched' as the universe expands, and the expansion rate is not constant. This means that the redshift observed on Earth is the sum of individual redshifts ...
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1answer
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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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116 views

Cosmological Redshift Data

Is there somewhere on the internet I can find cosmological redshift data. In particular, I would like to know the redshift around the time when the acceleration of the Universe began to accelerate.
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260 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 ...