Redshift Definition and 368 Threads

I'm new to the Physics forum and thought I'd start with a couple of stupid questions. 1) How do we know that black holes are not stellar nuclei that have just collapsed to a volume less than their mass dependent Schwarzschild radius (the radius at which the speed of light is the escape...

If as a result of the equivalence principle we can derive the gravitational red shift entirely from the perspective of an accelerating body with no reference to gravity and no reference to gravitational time dilation then one is essentially just working out the Doppler shift of a signal...

I am a bit confused here. Is cosmological redshift the same as doppler redshift? This is from wikipedia: "The redshift z often is described as a redshift velocity, which is the recessional velocity that would produce the same redshift if it were caused by a linear Doppler effect (which...

In several threads where I've seen the redshift issue discussed there's been some confusion about this point, Must we treat cosmological redshift as a purely kinematic (relativistic)doppler effect or as the time dymamics of the metric space? Or both views can be made to converge?

Gravitational redshift is given by the following approximate equation; \frac{\lambda}{\lambda_o} = 1 - \frac{GM}{r c^2} From http://scienceworld.wolfram.com/physics/GravitationalRedshift.html Where \lambda is the shifted wavelength and \lambda_o is the rest wavelength. r is...

condidering a photon in expanding cosmos, it 's said that the wavenumber k remains unchanged, the wavelength \lambda increases, proportional to the scale factor a(t) of the universe, and the frequency w decreases in the opposite way, that is the cosmic redshift. so, why does k...

The CMB is believed to have started [or ended] 13.7 billion years ago. Recent estimates of Hubble constant are around 70 km/s/Mpc, or 228 km/s/Mlyr. When we look at CMB we are looking back 13700 million years into the past. Multiplying 228 by 13700 gives us 1.04 times the speed of light as...

redshift ""first year astronomy"" how do i find distance using redshift? please keep in mind that this is first year astronomy course i am currently taking having some trouble doing it. don't know where to start

From what I understand: 1. The more massive the object, the stronger the gravitational field. This leads to the light being emitted from the surface to shift down in frequency. 2. The rate of expansion of the universe causes a redshift proportional its distance away. I'm new to this, but...

Homework Statement I am trying to calculate, from their redshifts, the speed at which each of the following galaxies is moving away from us. Give your answers in both km/s and as a fraction of the speed of light. The galaxies are: Galaxy 1: Observed wavelength of hydrogen line is 659.2...

How do I calculate the redshift of a galaxy that is 650 Mpc away if I am only told its spectral lines should show a redshift z=.15?

Why is it that Quasars don't red-shift? Any ideas or speculations? http://www.physorg.com/news190027752.html Surely all the measurements across all these quasars can't all be wrong. Is it possible that the Big Bang theory is wrong? Is it possible that the universe is not expanding? If...

This might be a tired topic but please help me to understand. Assume a photon moving in vacuum, ignore potential interstellar medium absorption and re-emission since it is not relevant to discussion of space expansion in this context. Redshifted photons will undergo energy loss between *right...

I have a question.. So far, from what I've browsed on the forums, I haven't found an answer to it, and I figured this would be the best place for it. I'm aware of the balloon analogy, but I have a question regarding blueshifts and redshifts. If you take the balloon analogy, everything in the...

A redshift survey has identified a galaxy cluster for which it infers a di stance of 520 Mpc. At what redshift is this cluster observed to be? You may use H0 = 72 km s−1 Mpc−1 Now call me old fashioned but don't i need some kind of relativistic speed to calculate the redshift, i mean i have a...

I know about cosmic expansion, but I was just curious, could the observations of redshift be caused because space is cooling, not expanding. From what I understand, as things cool they redshift. If the universe started cooling after the big bang, wouldn't everything we saw from the early...

Hello. This is one of my coursework questions I was wondering if I could get some insight here.. here is the question: The size of the Universe if conveniently parameterized by a scale factor, a(t), which simply describes how big the Universe is at other times relative to its present size...

Hello. This is question for my course work, I was wondering if I could get some insight, here is the question: Assume that the vast majority of the photons in the present Universe are cosmic microwave radiation photons that are a relic of the big bang. For simplicity, also assume that all the...

I've been trying to find out more about cosmic background radiation, but I am unable to find any information on the variations in the measured cosmic background radiation. I'm talking about these WMAP images. Most of the images you'll find on Internet are the versions after being corrected...

the figure 1.73 is approximate...given uncertainties, somewhere around 1.7. We see galaxies out beyond z = 7, of course, and the ancient background light has redshift 1090, so we see ancient matter emitting light, before it even formed stars and galaxies. But as of now, the standard model...

http://img76.imageshack.us/img76/2711/virgocluster.jpg Look at this image of the Virgo cluster of galaxies, for images of galaxies extending as far as the eye can see, some appear to exist in a swarm around the sub cluster at the core, others are in streamers and wisps of galaxies extending...

I am reading Wald's book. There is a problem confused me: page 158, problem 4,(b). An symptotic statoinary flat space, two stationary observer connected with a rope. One observer A is at finite r and the other B is at infinity. Observer B is really stationary by other forces and holding the...

I’ve made several efforts to provide a simple description of how the cosmological redshift works. Each has been closer to the mark than its predecessor, and now I think I’ve got it nailed. The premise underlying the redshift is simply that a photon must travel at a local velocity of c through...

If an atom in a distant galaxy emits a uv photon, the photon would have had enough energy to cause photoelectric emission from a negatively charged zinc plate. By the time the photon reaches me on Earth it has been sufficiently 'redshifted' so that it could not cause photoelectric emission if...

While objects closer to us tend to shift both in direction red or blue, depending on their movement in relation to us, distant objects such as galaxies tend to only shift to the red. As I understand this is the base of the idea that the universe is expanding. But how are we sure that is the...

I was looking at section 7.6 of Longair's Galaxy Formation, and in it, he is talking about the flatness problem, or fine-tuning problem. In it, he shows that if you define a general (i.e. varies with cosmic time and hence with redshift) density parameter \Omega_m for matter by analogy with...

Here is an interesting observation, which I would like to know the validity of. The momentum of a relativistic 'cosmological' particle in a homogeneous universe can be written as ^{[1]} L = \gamma m a v_{pec} = K where \gamma=(1-v_{pec}^2/c^2)^{-0.5}, m the rest mass, v_{pec} the peculiar...

If light is moving on a curve, for instance, if light were bent around a massive body thus curving due to gravity, does it undergo any redshift of blueshift? I ask this because the universe may not be expanding (what we see as redshift), but may just be affected by gravity, and curving, thus...

Surely it is possible to take a spectrum, deduce the redshift, then use this as a definitive distance indicator for all distances. Why is it we use the distance ladder?

I am stuck on a few cosmological points I could use some help on. The first being "redshift" as an indication of inflation. To me red shift just seems like it's a result of the degradation of light quanta over long distances. Since light slows down in environments close to absolute zero...

It seems quite common to more or less equate gravitational redshift to gravitational time dilation. For example, the two might be explained as follows. We have two observers. A is standing on the surface of the earth, B on the top of a tower. A sends light up to B with some frequency, B...

Gravitational redshift seems to be measured as if gravitational time dilation has no effect upon it. What effect if any does gravitational time dilation have on the measurement of gravitational redshift?

Are there any alternative theories/explanations of why light from distant galaxies is redshifted by an amount proportional to the distance away from us, other than the popular universal expansion explanation? Maybe some theory about light losing energy when traveling over such large distances...

does the expansion itself redshifts photons (if so, does the expansion affect the photon in his frame of referance?) or is it because the distant object that emits them is seemingly moving away from us (in cases where the expansion is much more dominant of course)? The latter doesn't makes much...

I understand the concept, but not the math. For example, let's say a galaxy is moving away from us, and we observe one absorption line at 400 nm, and another absorption line at 500 nm. Let's also say that we determine that the radiation was emitted originally at 200 nm and 300 nm...

Which statement is true? A The apparent speed of recession of a galaxy is given by the product of the Hubble constant and the distance to the galaxy. B The further away a galaxy is, the lower its apparent speed of motion away from us. C A galaxy with a redshift of 5.37 is situated at a...

I have a hopefully straightforward question. It is well known that in the Schwarzschild metric the gravitational redshift is given by 1+z=(1-r_{s}/r)^{-1/2}. Clearly this is just the ratio of observed to emitted frequencies (or energies). I understand this so far. However, for the case of the...

Apparently my recent thread on the cosmological redshift assumed more general insight into this subject than is the case. So the purpose of this thread is to help dispel some popular misconceptions about the cosmological redshift and hopefully spur a vigorous discussion. This thread is NOT...

It is well established that the cosmological redshift causes both the wavelength and the separation of photons to increase in proportion with the increase in the cosmic scale factor a. The traditional explanation for the mechanism of the redshift is that ‘expanding space’ progressively forces...

Just a physics buff so bear with me, this has been bothering but I am sure there is a simple answer. I watch a lot of physics and science programs on TV. When discussing red shift the explanation is that the light from objects that a further away is more red-shifted than light from closer...

Hi, Do sound waves experience a redshift similar to that of light in a gravitational field? Does anyone know the equation governing the change in frequency of the sound? Is this the same as the Doppler shift for an accelerating source of sound? Thanks.

We all know that nothing can travel faster than the speed of light in a local frame. We also know that distant galaxies in our observable universe have recession 'velocities' relative to us which are far in excess of the speed of light, c, despite the fact that the velocity in their local...

The item of gravitational redshift in the WIKIpedia says that this redshift is referred to the light of others forms of electromagnetic waves. This puzzles me. Other waves except electromagnetic waves have not this phenomenon, like sonic wave ? Is the gravitational redshift a result of...

This may be an easy answer for AtsroPhys vetrans. But I'm assuming since the doppler effect of an accelerating galaxy causes reshift, then the time dilation from a gravitational field would do the same. This is referring to very powerful fields, and also to redshift in all waves (not just...

Some objects, Quasars for example have extremely high redshifts, and come from a time long past, and place far away. When determining distance on such large scales, how do you also factor in the cosmological expansion of the universe, meaning 10 billion years ago the universe was much smaller...

Questions: Gravitational redshift and black holes I have some questions: 1. What does gravitational redshift do to light trying to escape a black hole? Is the light destroyed? 2. And what is the physical cause of this redshift? (I’m not interested in equations and math, only the physical...

There is no "Transverse Gravitatonal Redshift" There has been a lot of noise on this forum lately about A. Mayer's so-called "Transverse Gravitational Redshift." It is not difficult to prove that no such effect exists, yet I have not seen anyone post a calculation to prove it. I have therefore...

I've looked quite a bit on this forum and also elsewhere online and I cannot really find any information on my inquiry. If this is a double post please delete and send me in the right direction. Now I may be totally off on my thought process, but as I understand it the CMB first started off...

I have a homework question I am not sure how to approach: We are told that 1) CMB provides about 10^9 photons/baryons. 2) For matter dominated era, assume flat university with H_o = 73km/s/Mpc 3) Stefan-Boltzman law for energy density: ρ_rad = αT^4 where α = 7.56x10^-15 ergs / cm^3 K^4...

Homework Statement We are to assume the recombination happens at redshift z_{rec} when the number density of photons n_{\gamma}(z_{rec}) capable of ionizing hydrogen is exactly equal to the number density of baryons n_{b}(z_{rec}) . Use the measured number density of baryons, the...