Talk:Redshift

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Edit 6 March[edit]

Can you explain why "none of these edits really helped"? Especially since it's my understanding that the current text is factually wrong. Banedon (talk) 01:13, 7 March 2014 (UTC)

suspected error in redshift for theta= 0 formula[edit]

under redshift formulae in the dopler effect section it says:

1+ z = \frac{1 + v \cos (\theta)/c}{\sqrt{1-v^2/c^2}}

and for motion solely in the line of sight (θ = 0°), this equation reduces to:

1 + z = \frac{1}{\sqrt{1-v/c}}

I'm pretty sure this is simply not true. I cannot get to that form.

can anyone verify?

Indeed, I fixed it. Thanks for pointing out! Banedon (talk) 14:24, 11 November 2014 (UTC)

Error/lack of clarity in geodesic equation[edit]

The geodesic equation is quoted as:

ds^2=0=-c^2dt^2+\frac{a^2 dr^2}{1-kr^2}

and all symbols other than "r" are defined. Generally an equation in physics should work no matter what system of units is chosen but this not the case here and "r" and "dr" do not appear to be related in the way one would expect.

Elsewhere I found that "k" can only take values 1, 0, and -1 (dimensionless). 1-kr^2 also has to be dimensionless so this should be written as 1-\frac{kr^2}{Rmax^2} where Rmax is some maximum value of r (which has to be the case if k = 1). Alternatively, if "r" is by convention a dimensionless fraction of Rmax (which should be explained) then one assumes "dr" is also dimensionless and something needs to be added to the expression c^2dt^2 to make that dimensionless.

88.10.216.37 (talk) 11:46, 23 November 2015 (UTC)Alan Williams-Key