Questions tagged [redshift]

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2answers
103 views

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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3answers
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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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3answers
3k views

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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2answers
104 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
59 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
134 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
365 views

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
1k 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
417 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
989 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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0answers
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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
246 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
171 views

Given a fixed spectral resolution, what is the minimum detectable redshift?

Given an spectral resolution $R$ (for example $R=1000$), what is the minimum redshift which I can measure? How is this related to the minimum velocity among galaxies? If this velocity is related with ...
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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 ...
53
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4answers
11k views

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
448 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
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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2answers
64 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
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
522 views

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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1answer
142 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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3answers
119 views

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
141 views

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
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
144 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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5answers
282 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
621 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
129 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
690 views

(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
53 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
169 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
126 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
405 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
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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2answers
219 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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0answers
844 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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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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2answers
166 views

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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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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1answer
93 views

Are far objects really accelerating away at that huge rate? [duplicate]

Discutssions around this question Why is light bent but not accelerated? got me thinking. Specifically, hsinghal said "The absorption lines appeared to be red shifted (de accelerated photons) they ...
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0answers
26 views

How is the CMB used to determine the age of the universe? [duplicate]

Bear with me if this question sounds dumb, I don't understand relativistic redshift and general relativity very well. To imagine it, I picture the universe as being on the surface of an expanding ...
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1answer
187 views

Why pulse of light spread as time goes by? [closed]

I read in the A Brief History of Time by Stephen Hawking that as time goes by, a pulse of light spreads out. In the book he says: As we have seen, Maxwell's equations predicted that the speed of ...
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2answers
132 views

Galaxies moving relative to other galaxies?

I've been going through "Astrophysics in a Nutshell" for a college course. I'm not asking for an answer to a problem - but the author makes an aside in a problem that confused me. At the end of a ...
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3answers
527 views

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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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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1answer
507 views

Conservation of Momentum and The Expansion of The Universe [duplicate]

As I understand it, the cosmological red shifting of light is one of the effects of the expansion of the universe. But as the wavelength of light increases, the momentum given by: p = $\frac{h}{\...
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1answer
1k views

How can the rest-frame spectrum of redshifted light be determined? [duplicate]

The redshift effect must work on all frequencies, so blue would be shifted down to some lower frequency, and ultra violet would be shifted down also, into the visible area. How would you know what ...
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1answer
571 views

Observed wavelength of moving distant star (Doppler shift) with hydrogen cloud absorption [closed]

A star is moving away from a stationary observer with known velocity $V_* = 3 \cdot 10^5 m/s$. Between the star and observer, there is a moving hydrogen gas cloud, which is approaching the stationary ...
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1answer
380 views

Redshifted blackbody intensity and brightness temperature

The spectral radiance1 (units of $\rm W \ sr^{-1} \ m^{-2} \ Hz^{-1}$) of a blackbody is given by the Rayleigh-Jeans law in the low frequency limit: $$B_\nu(\nu) = \frac{2 \nu^2 k_B T}{c^2}$$ The ...