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TrickyDicky
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What is the formula used to convert the measured redshift into a velocity?, not the approximated formula for low speeds v=cz , but the more general and accurate one.
Thanks.
Thanks.
Do you want the answer for special relativity or cosmology or both?TrickyDicky said:What is the formula used to convert the measured redshift into a velocity?, not the approximated formula for low speeds v=cz , but the more general and accurate one.
Thanks.
Passionflower said:Do you want the answer for special relativity or cosmology or both?
TrickyDicky said:For cosmology, the one used to get a velocity from the redshift and plug it in the Hubble Law formula.
TrickyDicky said:I think , this is the one
v=[((1+z)^2-1)/((1+z)^2+1)]c=Ho*D
c=light speed constant
Ho=Hubble constant
D=distance
v=velocity
TrickyDicky said:I think , this is the one
v=[((1+z)^2-1)/((1+z)^2+1)]c=Ho*D
c=light speed constant
Ho=Hubble constant
D=distance
v=velocity
George Jones said:No, this isn't correct. See section 3 from
http://arxiv.org/abs/astro-ph/0310808.
It is fairly easy to derive equation (1) from this paper.
This is not exactly what I wanted. I asked for the way to translate from z to velocity for high z or at least >1, this must be a very common formula for cosmologists, I'd say.Calimero said:I don't think it is correct. For zero density universe it is:
[tex]v=H_{0}D[/tex]
[tex]D=(c/H_{0})ln(1+z)[/tex]
TrickyDicky said:The one I wrote is exactly equation (2) from that paper.
Calimero said:I don't think it is correct. For zero density universe it is:
[tex]v=H_{0}D[/tex]
[tex]D=(c/H_{0})ln(1+z)[/tex]
George Jones said:This expression and the expression that TrickyDicky gave in post #5 are both true in special relativity, i.e., in an empty universe. The conventions used for distance, however, are different in posts #5 and #7, and this leads to differing expressions for speed.
TrickyDicky said:...and anyway this is a cosmology debate that I find artificial and tiresome and I don't really want to get into it , I think it's been discussed enough in these forums, just remember that people as prestigious as David Hogg supports the view of cosmological redshift as Doppler.
TrickyDicky said:What is the formula used to convert the measured redshift into a velocity?, not the approximated formula for low speeds v=cz , but the more general and accurate one.
TrickyDicky said:For cosmology, the one used to get a velocity from the redshift and plug it in the Hubble Law formula.
Redshift is measured by comparing the observed wavelength of an object's light to the expected or known wavelength. This can be done using a spectrometer or spectrograph.
The formula for converting redshift to velocity is v = c * (z + 1), where v is the velocity, c is the speed of light, and z is the redshift. This is known as the Hubble-Lemaître law.
Converting redshift to velocity allows scientists to determine the speed at which objects in the universe are moving away from us. This is a crucial component of understanding the expansion of the universe and the cosmic distance ladder.
The redshift to velocity formula is considered accurate for small redshift values, typically less than 0.1. However, for larger redshift values, the formula may not accurately reflect the true velocity due to the effects of general relativity and the expansion of the universe.
Yes, redshift can be used in combination with the Hubble-Lemaître law to estimate the distance of an object from Earth. This is known as the cosmological redshift and is a key tool in measuring the distances of objects in the universe.