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Starlight Where Are You


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If sixteen stars the size of our sun were four times the distance, they would occupy the same area of sky and provide the same amount of light to the Earth that the sun does. Distance of stars do not make them dimmer, just reduces the area of sky that they occupy.

 

If we add up all of the stars in our visible universe, how large of an area of sky would be covered? Surely the area of stars is comparable if not greater than the area occupied by the sun.

 

So where is the light? What is the status quo explanation for this?

 

 

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See Olber's Paradox

 

The assumption is for a universe that is infinitely old, with an infinitely large number of stars distributed homogenously in an infinite space.

 

In that case, the entire sky would be as bright as the surface of a star.

 

The resolution is the observed fact that the universe is finitely old and is expanding. This, coupled with the finite speed of light means that only a finite number of stars can be observed from Earth. Also, redshift of light, caused by the expansion, shifts observable light into the microwave range, as we see in the cosmic microwave background which does indeed fill the entire sky just not in the visible light range.

 

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INVERSE SQUARE LAW:

 

Over a greater distance the less photons you will receive from stars, at some distance due to the inverse square law you will receive a NON-DETECTABLE number of photons.

 

Olber's paradox does not apply because of the inverse square law as well, at some distance over the entire life of a star NO photons will reach the earth over the area of the detector over any possible exposure time.

 

So it is possible that the universe is infinitely old and infinitely large and NOT have a 'as bright as the sun' sky. 

 

The resolution is that even if the universe is infinitely old and infinitely large, the sources of the light are NOT shining for an infinite time and the inverse square law means that over the life of a star at a certain distance from that star no photons or next to no photons will reach the earth.

 

The other resolution of the paradox is that the night sky IS NOT as bright as the sun, brightness is also a function of distance and not just area.

 

Hubble deep field was detecting (at any one point) something like one photon every 8 seconds, when looking at very distant objects. So 1 photon every 80 years, or 8000 years is impossible to detect. That is why the night sky is not like a sun all the time.. 

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If sixteen stars the size of our sun were four times the distance, they would occupy the same area of sky and provide the same amount of light to the Earth that the sun does. Distance of stars do not make them dimmer, just reduces the area of sky that they occupy.

 

If we add up all of the stars in our visible universe, how large of an area of sky would be covered? Surely the area of stars is comparable if not greater than the area occupied by the sun.

 

So where is the light? What is the status quo explanation for this?

 

 

So imagine another alien race viewing our sun from their planet light years away. The technology not yet available to them either for such distance traveling. 

We assume the aliens have high-tech, but they could be in our version of the 1800's ..

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  • 1 month later...

As others have already stated the visible universe is finite and just does not have enough stars to light up all of the sky.

 I did wonder if dust clouds between the stars might be absorbing a lot of the starlight so it wouldn't shine through to us. But apparently scientists tell us that the dust itself would absorb so much energy from the starlight that eventually it would glow as hot and bright as the stars themselves. So I guess dust the dust cloud idea is a non-starter.

For a good comprehensive answer to this post’s question, I recommend the reference below.

https://spaceplace.nasa.gov/dr-marc-dark-sky/en/ 

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