Tolman surface brightness test -

In summary, Richard Tolman's surface brightness test states that in an expanding universe with any geometry, the surface brightness of identical objects will decrease by a factor of (1+z)^4. Some sources suggest that the decrease may be (1+z)^2 instead. The surface brightness is equivalent to flux (W/m^2) and it may be confusing because the received flux typically decreases by the distance squared. It is possible that the factor is negligible for small distances from Earth. Urgent help is needed for further clarification.
  • #1
_Andreas
144
1
Tolman surface brightness test -- need help!

Richard Tolman derived that in an expanding universe with any arbitrary geometry, the surface brightness of a set of identical objects will decrease by (1+z)^4.

I have two questions:

1) The surface brightness is the same as the flux (W/m^2), right?
2) My understanding so far has been that the received flux decreases with the distance squared, so reading that it will decrease by a factor of (1+z)^4 is a bit confusing. Is it perhaps a factor that is ignored when the distance from Earth is relatively small (because z is so small)?

Need help urgently!
 
Last edited:
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  • #2
Oh, and another question. Some sources say the SB will decrease by (1+z)^2 instead of (1+z)^4 in an expanding universe. Which is correct?
 
  • #3
I've received answers to the first two questions already, so no need for anyone to bother with them. The question in my second post is still unanswered, though.
 
  • #4
Please only a post in one forum at a time. If you want a post moved, contact a moderator/mentor.
 

1. What is the Tolman surface brightness test?

The Tolman surface brightness test is a method used in cosmology to measure the distance to faraway galaxies by comparing their surface brightness to that of nearby galaxies.

2. How does the Tolman surface brightness test work?

The test works by comparing the apparent brightness of a galaxy at different distances, assuming that the intrinsic luminosity of galaxies is the same. This allows for the calculation of the distance of the faraway galaxy based on its observed surface brightness.

3. What is surface brightness?

Surface brightness is a measure of the amount of light per unit area received from a distant source. It takes into account both the size and brightness of the object being observed.

4. What are the limitations of the Tolman surface brightness test?

The main limitation of this test is that it assumes that the intrinsic luminosity of galaxies is the same, which may not always be true. Additionally, it does not account for the effects of dust and gas in the interstellar medium, which can affect the observed surface brightness.

5. How is the Tolman surface brightness test used in cosmology?

This test is used to measure the distances to galaxies beyond the reach of other methods, such as parallax or redshift measurements. It is also helpful in determining the expansion rate of the universe and in studying the large-scale structure of the universe.

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