Questions tagged [redshift]

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Is the GW170817 event evidence or counter evidence for Dark Energy?

I've always figured there must be a simpler explanation for the observed lack of red shifting that has lead astronomers to hypothesize Dark Energy. Or at least there must be a simpler explanation of ...
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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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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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4answers
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What is a layman explanation for why the wavelength of light increases when space itself expands?

I understand that the universe is generally agreed to be expanding based on observations. What I have read is that space itself is expanding. My question is why does this expansion of space affect the ...
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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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How do we know that Dark Energy has homogeneous energy density? [duplicate]

I’ve read places that the density of Dark Energy is the same throughout the universe. If the expansion density of dark energy were the same throughout the universe, why don’t all galaxies have the ...
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Does space expansion affect the CMB photon frequency?

I have read this question: Effect of expansion of space on CMB where Ted Bunn says: For definiteness, let's consider a wave packet of electromagnetic radiation with some fairly well-defined ...
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2answers
48 views

Why does the expansion of space lead to cosmic redshift?

I have always thought of light as a point-like object in space, with the EM field strengths dependent on time. However, stretching of space would not affect a point-like object. Thus, I assume that ...
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1answer
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does dark mass/energy change cosmic red shift [closed]

Virtually all cosmology is based on the observation that galactic light is red-shifted. The Hubble Law defines that the red-shift is proportional to distance photons traveled. Further, this ...
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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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1answer
123 views

Redshift of a black hole [duplicate]

Is that ring the "redshift" of a black hole ?
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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
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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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Cosmological Inflation: If Photon expands, why not other matter?

I keep repeatedly reading in many Stack Exchange and Quora questions that space of universe expands but particles (matter) don't, see e.g. this Phys.SE post. The reason given is that particles are ...
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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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What wavelength was the CMB originally?

What wavelength was the light that became the CMB after factoring out redshift? Is it safe to assume that what we're seeing in the CMB was emitted at a distance of approx: ...
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What can I see if I hold a ruler that stretches into a distant receding galaxy? [closed]

If my clones were to form a line along that metric ruler that bridges Milky Way galaxy and a still red shifting galaxy far far away, would any of me notice anything about the scale of the ruler? Now ...
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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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Why does the black hole's matter ring in the image released on April 10th seem to lack blue/red shift? [duplicate]

If the matter around a black hole is spinning around it at nearly the speed of light, then the blue/red shift on each side should be quite visible (even though we're watching at an angle). But in this ...
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1answer
51 views

Can expanding space stretch the wavelength of GWs? [duplicate]

I have read this question: Redshifting of Light and the expansion of the universe Now analogously, we could talk about GWs traveling in the empty voids of space, where the expansion of space is ...
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When space expands where do the energy of the gravitational wave dissipate to? [duplicate]

I think it is safe to say that gravitational wave do not dissipate unless it met matter along the way imparting some of it's energy to cause some distortion or when it's frequency is stretched even ...
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4answers
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Why hasn't anybody done a two-telescope test on the speed of starlight?

It seems that even though it wouldn't be too hard, nobody has taken the trouble to use a pair of telescopes to confirm that light originating from red-shifted / distant stars is indeed traveling at c. ...
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2answers
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On Distant Lanterns and Relative Speed [closed]

It is said, that by measuring distant sources, we can gather information about the past state of the universe. The further we measure, the faster things appear to recede, which brings me to my ...
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1answer
86 views

Redshift z values and galactic age

Redshift for astronomical objects is often discussed in terms of z-value which I understand to be $\dfrac{\lambda_{obsv} - \lambda_{emit}}{\lambda_{emit}}$, where $\lambda$ is the wavelength. Is this ...
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1answer
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If I held up a glass lens and looked at a star through it, could I see the spectrum of the light?

Given that I can see light from stars with my naked eye. And also some lenses suffer chromatic aberration. I would think that with enough training I could simply hold up a lens to a star and look at ...
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2answers
181 views

$z$ (redshift) at the inflation start up time?

The $q$ parameter is at present -ve which implies accelerated expansion , hence we can approximate our universe now to be dominated by dark energy since dark energy provides exponential growth $~e^{\...
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1answer
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Hubble - Cosmological vs Doppler Red Shift

When we learnt about the Hubble Constant at school we were taught that Hubble had observed Red Shift due to the Doppler Effect, and thus the universe (and space time itself?) must be expanding. ...
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5answers
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Is redshift path-dependent?

Is redshift dependent simply upon the relative velocity and gravitational potential of transmitter and receiver? Or is it path dependent; say the receiver runs away for billions of years then changes ...
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1answer
65 views

Does the redshift have anything to do with Compton scattering? [duplicate]

The more I think about it the more I can't help but feel that the redshift must be caused by a form of Compton scattering and the interaction between particles of light and electrons. Is this ...
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1answer
67 views

Relative size of galaxy calculation

So this is a past exam problem, however I am confused to a question which is related to this graph and the questions states: Question: On the graph, one galaxy is labelled A. Determine the size of ...
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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 ...
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2answers
168 views

Event horizon and particle horizon

The furthest distance that we can see is defined by the radius of the particle horizon, which is nearly 46 Gly. However, the event horizon is nearly 16 Gly. Does this mean the galaxies that are ...
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2answers
54 views

Looking for redshift database or data

I am looking for data wich contains the redshift values(z) of observed supernova or galaxies with their observed distanced(so the distance between the object and earth how we observe it now and not ...
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5answers
996 views

Why doesn't the escape of electromagnetic waves from a microwave depend on the reference frame, because of the Doppler effect?

If an observer traveling towards a microwave oven at almost the speed of light blue shifts the microwaves enough to be visible light, how can the mesh on the oven door still stop to waves from ...
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2answers
91 views

How can the red shift due to Hubble flow be consistent with the law of conservation of energy? [duplicate]

Given that there is no change in relative kinetic energy attributable to the expansion of the universe, what accounts for the difference in energy emitted vs energy absorbed (i.e. the red shift ...
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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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4answers
110 views

Determining the acceleration of the Universe from a single star?

It Occurs to me we might be able to find an entirely independent method of determining the Universe's acceleration using a single source. If one was to watch a single high source consistently one ...
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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
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What part of special relativity is factored in in relativistic redshift velocity equations?

While doing research into redshift equations (doppler redshift and cosmological redshift), both types of redshift had two equations for finding recession velocity: a 'non-relativistic' equation and a '...
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1answer
107 views

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
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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
183 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
191 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
107 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
73 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
92 views

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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2answers
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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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2answers
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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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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
98 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 ...