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Electromagnetic in cosmology

  • Thread starter trv
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  • #1
trv
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Homework Statement



Title should be: ELectromagnetic signals in cosmology.

[itex]
\int\frac{d\rho}{\sqrt{1-k\rho^2}}>=-\int\frac{dt'}{a(t')}
[/itex]

The integrals being from r1 to r and t1 to t respectively.

I can't understand the need for the prime here. Could someone explain to me the significance of the prime?

Homework Equations



The Attempt at a Solution

 
Last edited:

Answers and Replies

  • #2
nicksauce
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Homework Helper
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It's just because they don't want to have the same variable in the integrand and the bounds of integration. Nothing special.
 
  • #3
trv
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Ok so I could just as well write dt, and a(t), i.e. without the prime, as long as I had t1 to t2 or other such in the bounds of the integration?
 
  • #4
nicksauce
Science Advisor
Homework Helper
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yes.
 

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