Why Do We See Darkness in a Universe Full of Stars?

[Joe30174]

Because if stars are radiating light in every direction, shouldn't there be light all over? And we only see the light/photons that our eyes are receiving? Though there may be dark spots from where crests meet troughs? Or am I completely wrong and missing something?

 

[phinds]

https://en.wikipedia.org/wiki/Olbers'_paradox

 

[DaveC426913]

Because if stars are radiating light in every direction, shouldn't there be light all over? And we only see the light/photons that our eyes are receiving? Though there may be dark spots from where crests meet troughs? Or am I completely wrong and missing something?

Light (generally) travels in straight lines from its source.
We can only see photons that actually enter our eye (along one of those straight lines).
The solar system is rife with photons just passing through from left to right or above to below, but we don't see them unless something (such as a planet or dust) redirects them into our eyes.

If you shine a flashlight or laser pointer into a clear sky, you will not see a beam of light emanating from it, because those photons aren't directed into our eye - unless something reflects or refracts it.

 

[Ibix]

Because if stars are radiating light in every direction, shouldn't there be light all over?

There should be light coming from everywhere there's a star, yes, but that isn't all of the sky - have a look at the resolution section of the Wiki article linked by @phinds.

It might help you to draw a diagram. Draw a point somewhere and draw straight arrows coming out from it in all directions. The arrows are light paths coming off a star. Put the tip of your finger on the page somewhere - that's an astronaut in space. Which directions are arrows that pass under your fingertip coming from? Every direction, or just from the direction to the star?

 

[DrStupid]

Because if stars are radiating light in every direction, shouldn't there be light all over? And we only see the light/photons that our eyes are receiving? Though there may be dark spots from where crests meet troughs? Or am I completely wrong and missing something?

You are right. There is sunlight almost everywhere in the solar system and you just don't see it if you do not look into the Sun. That implies that space crafts in the inner solar system always need some kind of protection from the light. It is quite hard to have something in darkness in space. One of the rare examples is the James Webb Space Telescope which is placed in Earth Lagrange point L2 (in the shadow of Earth).

 

[PeroK]

Because if stars are radiating light in every direction, shouldn't there be light all over? And we only see the light/photons that our eyes are receiving? Though there may be dark spots from where crests meet troughs? Or am I completely wrong and missing something?

The solar system is permanently flooded with light from the Sun. But, unless that light scatters or reflects off something, we can't see it.

For example, you can only see the beam of a torch or car headlights at night because some of the light scatters off particles in the air. If you shine a torch through a vacuum, you will see nothing - unless the torch is pointing at your eyes.

At night, when you look up, there is plenty of light from the Sun surrounding the Earth (*) and moving away into space. But, as there is virtually nothing except the odd planet to reflect off, there is no way to see it.

(*) Except, of course, in the Earth's shadow.

 

[Joe30174]

There should be light coming from everywhere there's a star, yes, but that isn't all of the sky - have a look at the resolution section of the Wiki article linked by @phinds.

It might help you to draw a diagram. Draw a point somewhere and draw straight arrows coming out from it in all directions. The arrows are light paths coming off a star. Put the tip of your finger on the page somewhere - that's an astronaut in space. Which directions are arrows that pass under your fingertip coming from? Every direction, or just from the direction to the st

There should be light coming from everywhere there's a star, yes, but that isn't all of the sky - have a look at the resolution section of the Wiki article linked by @phinds.

It might help you to draw a diagram. Draw a point somewhere and draw straight arrows coming out from it in all directions. The arrows are light paths coming off a star. Put the tip of your finger on the page somewhere - that's an astronaut in space. Which directions are arrows that pass under your fingertip coming from? Every direction, or just from the direction to the star?

That's how I was picturing it. I underatand what we see is the light coming "straight" from the source. But if we had a camera that instead of a normal lense receives photons, sends signals put to detect photons and made an image off of that, everything would be lit up?

 

[PeroK]

That's how I was picturing it. I underatand what we see is the light coming "straight" from the source. But if we had a camera that instead of a normal lense receives photons, sends signals put to detect photons and made an image off of that, everything would be lit up?

It's not possible to have signals (of what?) bouncing off photons! The only way to detect light is to absorb it.

That said:

https://www.mpq.mpg.de/4861203/13-11-15-seeing-a-photon-without-absorbing-it

 

[bbbl67]

Also, a lot of the original light from the Big Bang, which is now called the Cosmic Microwave Background radiation, has stetched out to microwave frequencies, and our eyes don't see in microwave. If we did, then we'd see a lot of light constantly hitting us, especially at night.

 

[phinds]

Also, a lot of the original light from the Big Bang, which is now called the Cosmic Microwave Background radiation, has stetched out to microwave frequencies, and our eyes don't see in microwave. If we did, then we'd see a lot of light constantly hitting us, especially at night.

The CMB is NOT "from the Big Bang". It is from the Surface of Last Scattering which happened some 400,000 years after what I think you mean when you say "the Big Bang" (which, by the way, has nothing to do with the Big Bang Theory which does not include the singularity that I assume you are referring to).

 

[bbbl67]

The CMB is NOT "from the Big Bang". It is from the Surface of Last Scattering which happened some 400,000 years after what I think you mean when you say "the Big Bang" (which, by the way, has nothing to do with the Big Bang Theory which does not include the singularity that I assume you are referring to).

Yes, yes, you're very clever, thank you.

 

[berkeman]

One of the rare examples is the James Webb Space Telescope which is placed in Earth Lagrange point L2 (in the shadow of Earth).

Interesting. I was confused at first, because it seems like solar panels would not work at L2, but it is far enough away from the Earth to still get some sunlight that makes it around the Earth (given the relative sizes and angles of the Sun and Earth).

https://space.stackexchange.com/que...2-how-will-the-james-webb-telescope-be-powere

 

[sophiecentaur]

@phinds directed the thread to the Olber Paradox, higher up.
If you look in any direction in the sky, there is a star (mostly in some distant galaxy). If it were not for the expansion of the Universe then we would be receiving all the light flux in a solid arc from every star. But the expansion causes red shift so the light from the most distant stars has been more and red shifted until it is not visible so there are invisible (far red) gaps between the visible stars.

 

[PeroK]

I guess you mean the Olbers' paradox?

 

[sophiecentaur]

I guess you mean the Olbers' paradox?

Danged autocorrect! Plus my brain is getting olber!

 

[phinds]

Danged autocorrect! Plus my brain is getting olber!

Yeah, when typing on a computer, auto-correct is our worst enema.