The universe should be billions of times brighter than the Milky Way?

In summary, Olber's Paradox is resolved by the fact that the universe is not infinite and unchanging, did not exist forever, and is not infinite in size. Additionally, the paradox also assumes a static universe and does not take into account the effects of dust or relativistic effects.
  • #1
kmarinas86
979
1
The universe should be billions of times brighter than the Milky Way?

The sun is 1 AU away.
  1. The center of the galaxy is 2 billion AU away.
  2. A sun at 2 billion AU away is 4 billion billion times dimmer than our sun.
  3. There are about 200 billion stars within the radius of the sun's orbit.
  4. It would take less than 20 million billion times as many stars to be as bright as our sun.
  1. The Virgo SuperCluster is 6 trillion AU in radius.
  2. A sun at 6 trillion AU away is 36 trillion trillion times dimmer than our sun.
  3. There are about 10 trillion stars at the Virgo SuperCluster (10% of visible mass and 1% of virial mass).
  4. It would take less than 3.6 trillion times as many stars to be as bright as our sun.
  1. The visible "Big Bang" universe is 900 trillion AU in radius.
  2. A sun at 900 trillion AU away is 810 thousand trillion trillion times dimmer than our sun.
  3. There are about 70 thousand billion billion stars[1] in the visible "Big Bang" universe
  4. It would take less than 12 million times as many stars to be as bright as our sun.

Overall:
Our overall galaxy is less than 20 million billion times dimmer than our sun.
Our overall super cluster is less than 3.6 trillion times dimmer than our sun.
Our overall universe is less than 12 million times dimmer than our sun.
But this would mean that the brightness reaching us from the rest of the universe is greater than the brightness coming from our super cluster which is more than the brightness coming from our galaxy! But we do not observe this! The universe does not appear to be billions of times brighter than our galaxy! Something is wrong with the calculations or something is wrong with current theory!

I miscalculated =P

The sun is 1 AU away.
  1. The center of the galaxy is 2 billion AU away.
  2. A sun at 2 billion AU away is 4 billion billion times dimmer than our sun.
  3. There are about 200 billion stars within the radius of the sun's orbit.
  4. It would take less than 20 million times as many stars to be as bright as our sun.
  1. The Virgo SuperCluster is 6 trillion AU in radius.
  2. A sun at 6 trillion AU away is 36 trillion trillion times dimmer than our sun.
  3. There are about 10 trillion stars at the Virgo SuperCluster (10% of visible mass and 1% of virial mass).
  4. It would take less than 3.6 trillion times as many stars to be as bright as our sun.
  1. The visible "Big Bang" universe is 900 trillion AU in radius.
  2. A sun at 900 trillion AU away is 810 thousand trillion trillion times dimmer than our sun.
  3. There are about 70 thousand billion billion stars[1] in the visible "Big Bang" universe
  4. It would take less than 12 million times as many stars to be as bright as our sun.

Overall:
Our overall galaxy is less than 20 million times dimmer than our sun.
Our overall super cluster is less than 3.6 trillion times dimmer than our sun.
Our overall universe is less than 12 million times dimmer than our sun.

It was my calcs.. nvm!
 
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  • #2
Don't forget about all of the dust blocking our view, and the relativistic effects too... there is a paradox named after this, but can't think of the name at the moment.
 
  • #3
Olber's Paradox.

This is how we know that
- the universe is not infinite and unchanging
- it did not exist forever
- it is not infinite in size
 
  • #4
DaveC426913 said:
Olber's Paradox.

This is how we know that
- the universe is not infinite and unchanging
- it did not exist forever
- it is not infinite in size

Olbers' Paradox ony arises when the following conditions are met:
* The universe is homogenous with lumninous matter evenly spread (on average) through the universe
* The universe existed in that state either for infinite time and is infinite in size

So, in theory (and purely on the basis of Olbers' Paradox) the universe can be infinite in size and infinite in time, when it did not always contain luminous matter, or it could be infinite in size but not in time and at any moment evenly spread with luminous matter, or it could be finite in size but infinite in time and evenly spread with lumnious matter.
 
  • #5
Additionally, the paradox bases on the assumption that space is static and the paradox is also resolved dropping this assumption. In an infinite, eternal universe with homogeneous luminous matter in which space expands there is no Olbers paradox. For example, a de-Sitter universe, as postulated in the Steady-State Cosmology.

As an interesting aside, the paradox is also resolved for an infinite, eternal and static universe with a fractal distribution of light sources with fractal dimension less than two. This is not difficult to prove. Peebles analizes in detail this scenario in his book "Principles of Physical Cosmology" when discussing the cosmology that was proposed by Benoit Mandelbrot.
 
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1. What does it mean for the universe to be billions of times brighter than the Milky Way?

When we say the universe is "brighter" than the Milky Way, we are referring to the overall luminosity or brightness of all the galaxies, stars, and other celestial objects in the observable universe. This is typically measured in terms of energy output per unit time, or watts.

2. How is the brightness of the universe calculated?

Calculating the total brightness of the universe is a complex process that involves measuring the luminosity of individual galaxies and stars, and then using statistical methods to estimate the total brightness of the universe. This can be done by observing the light emitted from distant galaxies and using models to estimate the total number of galaxies in the observable universe.

3. Why is the universe expected to be billions of times brighter than the Milky Way?

The brightness of the universe is expected to be much greater than that of the Milky Way because the universe is much larger and contains billions of galaxies, each with their own stars and other luminous objects. The Milky Way is just one of many galaxies in the universe, so its brightness is just a small fraction of the total brightness of the universe.

4. Are there any factors that could affect the estimated brightness of the universe?

Yes, there are several factors that could affect our estimated brightness of the universe. One major factor is the presence of dark matter, which we cannot directly observe but is thought to make up a significant portion of the universe's mass. Additionally, the expansion of the universe and the varying distances of galaxies from Earth can also affect our calculations.

5. How does the brightness of the universe impact our understanding of the cosmos?

The brightness of the universe is a key factor in understanding the structure and evolution of the cosmos. By studying the brightness and distribution of galaxies, scientists can gain insight into the formation and evolution of the universe, the role of dark matter and dark energy, and the fate of the universe. It also helps us understand the vastness and complexity of the universe and our place within it.

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