Questions tagged [redshift]

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How to calculate redshift for a very large object?

I've been scratching my head on this concept of redshift. I can understand redshift for a pointlike object that is either coming towards an observer or going away. However, I am confused on what color ...
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Cosmological, gravitaitonal and doppler redshift power?

I am trying to get my head around the concept of redshifts and their relation to powers. Consider the observe $O$ at rest (who is measuring the power) and emitter $E$ in one of the three following ...
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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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1answer
148 views

At what distance will the furthest objects redshift beyond detection?

62–65 billion light years away is the “future visibility limit”, according to Wikipedia. Does this also mean that objects past this 62–65 gyr range have red-shifted already? And that’s why we’ll ...
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1answer
286 views

Can the wave length of a photon be stretched out caused by expansion of spacetime? [closed]

Strictly speaking perhaps it is not right to say that a photon is a wave so its wave length can't be stretched out; a photon is actually just a point. So is its wave property only a relativistic ...
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273 views

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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1answer
754 views

Does redshift only affect particles of visible light?

May seem really daft but I don't know of any ways of detecting redshift in the rest of the EM spectrum, so was just wondering
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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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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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3answers
143 views

How much does surface gravity of a star shift color and who observes the shift?

Reading Richard Muller's new book Now he explains that since the gravitational field near the surface of star causes time to run slower relative to time further away from the surface, the frequency of ...
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2answers
414 views

Gravitational wave redshifts and LIGO [duplicate]

When I heard about the LIGO gravitational wave detection, I wondered if the distance to the event was determined by the inverse square law of radiation and/or by measured red shifts. Which is/are the ...
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627 views

What is the QUANTUM mechanical “explanation” for the “red shift?” [closed]

On another thread, users have asked for an explanation of the "red shift" of photons (the apparent loss of energy of photons due to the expansion of the universe.) All they ever got was a GENERAL ...
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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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2answers
631 views

Red-shift formula

What is the true redshift formula that we can use it in every question? I somewhere read that it is: $z= \frac{v}{c}$ and in another place it says: $1+z = \sqrt\frac{c+v}{c-v}$ so $z = \sqrt\frac{c+...
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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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1answer
157 views

Why does universe expansion introduce redshift - doppler effect should not apply

If we think of a projectile being launched from a distant object to us, and the object is not moving away from us, then the projectile will arrive with the same velocity local to us - whether the ...
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0answers
73 views

Is red-shift a violation of the conservation of energy? [duplicate]

Light loosing frequency equals to a loss of energy as far as I understood. So where does this energy go, given that the law of conservation of energy is correct?
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2answers
167 views

Could the universe be shrinking? [duplicate]

It is thought the universe is expanding because of the red shift of most galaxies but if all the matter in the universe was actually falling into a massive black hole wouldn't most galaxies still be ...
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3answers
46 views

redshifted or scaled light?

In relation to the emitted light, at reception the radiation has a wavelength that is shifted, or should it be called scaled light ? ( Imo, shift is to addition term as scale is to a multiplication ...
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2answers
262 views

Redshift - Relativistic or Classical doppler effect?

So we know that Hubble found evidence that the universe was expanding through finding redshift / blueshift of light from distant stars. My question is, was he using the relativistic or classical ...
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2answers
100 views

Redshifting light in an expanding universe

It's evident and well known that light traveling across an expanding FLRW universe is redshifted via an equation: $$\frac{\lambda_{arriving}}{\lambda_{emitted}}=\frac{a_{now}}{a_{then}}$$ Where $a$ is ...
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1answer
226 views

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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1answer
53 views

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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0answers
369 views

Where does the energy of a redshifted photon go to? [duplicate]

When traveling through the vacuum, electromagnetic waves experience an increase of wavelength (redshift). According to this equation: $$E=\frac{hc}{\lambda}=h\nu$$ ( Where, as we know, h is the ...
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1answer
124 views

Absolute frequency shift of red shift 11.9 [closed]

According to a 2012 article about the Hubble Telescope, the Hubble found the most distant galaxy at a red shift of "11.9". What does this mean in terms of THz frequency? For example, I know that the ...
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2answers
6k views

Redshift-distance relation, and redshift-scale factor relation

For a universe described by the RW metric, a relation between the scale factor at the time of emission of light and the redshift can be derived, and yields $$ a(t_e) = \frac{1}{1+z} $$ The above ...
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3answers
492 views

Is a light wave's amplitude stretched, along with the “red shift” stretch - making it brighter?

When light waves are stretched and "red-shifted", is the amplitude of the light wave stretched as well, affecting the intensity/brightness of the light wave?
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2answers
102 views

Why is the possibility of the universe having a centre around which everything orbits not considered feasible?

I'm sure there is some kind of reason as to why this isn't considered as a legitimate theory but upon giving it though it seemed to make sense to me. I figure if all gravitational orbits are ...
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2answers
454 views

Which materials redshift light?

I'm currently researching ways to get the human perceived colors red, green and blue when you only have a mostly blue spectrum available at your source (using electroluminescence). The solution should ...
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2answers
355 views

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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1answer
137 views

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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2answers
1k views

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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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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2answers
1k views

Cosmic Scale Factor $R$ and redshift

I'm slightly confused by an idea of redshift: If we assume the distance between two points is given by: $$d = R Δx$$ we can assume that $$λ_0 = R_0 Δx$$ And when we receive the emission it will ...
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1answer
2k views

How can we find out the distance to a galaxy using redshift?

As redshift occurs due to Doppler effect and universe expansion, how do we know what part of the shift is responsible for which, in order to determine the distance to the object emitting the waves? Is ...
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0answers
44 views

Doppler shift of light from stars and galaxies [duplicate]

I was reading about how we can ascertain whether a cosmic object is receding from or approaching us by studying the doppler shift of its spectrum- I mean the redshift and blue-shift. But we have no ...
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2answers
584 views

How'd you explain Red shift and Blue shift with respect to Doppler Effect

I understand Doppler effect in Sound and Water because there we can observe relative speeds. But in case of light, the speed is same in all references so is the change in relative wavelength due to ...
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0answers
29 views

Why don't big bang photons conserve mass and energy? [duplicate]

A photon from the big bang has lost most of its momentum and energy. What does it push against? Does it break the 'laws' of conservation of energy and momentum? Is there any possibility that momentum ...
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1answer
755 views

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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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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2answers
1k views

Calculating the redshift in cosmological constant dominated universe

How can the redshift be found when $\rho_m = \rho_\Lambda$ and when the cosmological constant begins to dominate from matter? Given that $\Omega_M \approx 0.3$ and $\Omega_\Lambda \approx0.7$ . I've ...
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1answer
58 views

Can we produce energy by red-shifting light

The answer on my question Does light accelerate as it nears a black hole? leads me to think that light 'gains' the gravitational energy by shifting to a frequency with a higher energy (blue). Is this ...
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1answer
157 views

How do we know that light isn't redshifted by space itself? [duplicate]

Do we know if light is red-shifted by traveling through space? If it isn't, how do we know? I guess my pondering has lead me to wonder if the observed accelerating space-expansion is a ...
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1answer
52 views

Energy conservation in Hubble Expansion [duplicate]

So space expands due to Hubble Flow. Some light is observed, which is seen to be red-shifted due to the space expansion. It is less energetic. Where did the energy go?
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3answers
476 views

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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1answer
210 views

Quasar redshift

The quasar 3C 273 has a redshift z=0.158. A question in a textbook: could this be a gravitational redshift instead of cosmological (=resulting from the expansion of space)? My answer: no. Firstly, ...
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0answers
77 views

Red shift and expansion of universe [duplicate]

We have been led to believe that in the theory of universe expansion, the farthest object is moving faster away from us than the nearest object, attributing the difference to red shift. Question: is ...
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6answers
1k views

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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1answer
194 views

How to explain Doppler redshift of light?

For other waves like water or sound, it is easy to understand Doppler effect, because for those waves, the speed of wave in different inertia reference frames changes. But for light wave, the speed ...