Solve Obler's Paradox: Calculate Universe Size in Parsecs & Light Years

  • Thread starter J.Welder12
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In summary, to avoid Olbers' Paradox, the universe would have to be large enough for a photon to hit another particle before reaching the edge, with the size depending on the total cross section per unit mass and the number of atoms per unit mass.
  • #1
J.Welder12
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Homework Statement


Suppose all stars had the same radius as the Sun, and they were distributed throughout the universe with the same density as we have nearby- about 1 star per cubic parsec. Approximatly how bigh in parsecs and light years would the universe have to be in order to avoid Oblers Paradox?


Homework Equations


Think of light as a particle- how far does the photon have to go until it hits another particle?



The Attempt at a Solution


photon- particle relation xr= 1/an
tr= 1/anc
κ= nσr/ρ where (n/ρ) is the number of atoms per unit mass and κ= total cross section per unit mass
 
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  • #2
The universe must be as large as necessary for the photon to hit another particle before it reaches the edge of the universe. Therefore, the size in parsecs and light years would depend on the total cross section per unit mass and the number of atoms per unit mass.
 

Related to Solve Obler's Paradox: Calculate Universe Size in Parsecs & Light Years

1. How do you solve Obler's Paradox?

To solve Obler's Paradox, you need to use the formula for luminosity distance, which takes into account the expansion of the universe, and the speed of light. This formula is: D = (c/H)1/3 * z * (1 + z)-1, where D is the distance in parsecs, c is the speed of light, H is the Hubble constant, and z is the redshift of the object.

2. What is the Hubble constant?

The Hubble constant is a measure of the rate at which the universe is expanding. It is denoted by the symbol H and has a value of approximately 70 km/s/Mpc (kilometers per second per megaparsec).

3. How do you calculate the size of the universe in parsecs?

The size of the universe in parsecs can be calculated by using the formula for luminosity distance, which takes into account the expansion of the universe, and the speed of light. This formula is: D = (c/H)1/3 * z * (1 + z)-1. The resulting value will be the distance to the object in parsecs.

4. What is the speed of light?

The speed of light is a fundamental physical constant that is denoted by the symbol c. It is approximately 299,792,458 meters per second in a vacuum and is considered to be the fastest possible speed in the universe.

5. How do you convert parsecs to light years?

To convert parsecs to light years, you can use the conversion factor of 1 parsec = 3.26 light years. So, if you have the distance in parsecs, you can multiply it by 3.26 to get the equivalent distance in light years.

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