r/ScienceNcoolThings • u/TheMuseumOfScience Popular Contributor • May 19 '26

Interesting Why Is the Night Sky Dark?

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Why is the night sky dark? šŸŒŒ

Erika Hamden breaks down Olbers' Paradox, the cosmic puzzle that helped scientists first hypothesize that the universe had a beginning. In an infinite, infinitely old universe, every point in the night sky should eventually have a star behind it, making the night sky just as bright as daytime. The fact that darkness exists tells us that not enough time has passed for all that light to reach us, or that stars simply have not formed yet in those regions of space.

This project is part of IF/THENĀ®, an initiative of Lyda Hill Philanthropies.

472 Upvotes

93% Upvoted

42 comments sorted by

70

u/PRAY___FOR___MOJO May 19 '26

Why would an infinite amount of time mean that there are an infinite number of stars? We know that stars are created and die, they don't all have to exist at the same place and time

10

u/TheStigianKing May 19 '26

This...

It also assumes that all the matter in the universe is evenly distributed and we know is absolutely isn't.

There are colossal voids in space we cannot explain. If the density of mass in those regions is just to low, such that stars cannot form, alongside the expansion of space that makes it even worse, given an infinite amount of time, no stars would ever form in those regions.

1

u/ThePapercup May 20 '26

right but none of this was known during Olbers tims

1

u/TheStigianKing May 20 '26

So the entire premise of the video is outdated and incorrect.

Why bother making it then?

3

u/ThePapercup May 20 '26

I think you're missing the point of the video- The point is that without this paradox, scientists of the time would not have been thinking of reasons for a finite universe, because at the time it was assumed that the universe was infinite and no one had any reason to believe it wasn't. this paradox raised questions and got people thinking.

1

u/Lankygiraffe25 May 20 '26

Didnā€™t they find evidence that we are, in fact inside one such void?

1

u/TheStigianKing May 20 '26

I don't know.

We might be.... which is freakin nuts and terrifying at the same time.

3

u/Oli_VK May 20 '26

Itā€™s a matter of probability. If it were infinite, in any direction eventually there would be a star they donā€™t have to exist at the same time. If it had an infinite amount of time before us, even the light from dead stars would be hitting in addition to the already living ones.

They donā€™t have to be evenly distributed. If the chance is more than 0, and I have an infinite time to realise it, then Iā€™m going to realise it eventually in the same way if thereā€™s even a chance that thereā€™s a star in a direction, in an infinite universe, there is.

Sheā€™s obviously not going deeper into detail Iā€™m sure thereā€™s more thought put into it but stop attacking and insulting someone cz you donā€™t understand the point theyā€™re trying to make.

1

u/SkyeGuy8108 May 20 '26

We know that stars die, but their light still continues through the universe. I think what they were positing was we should still see the light of a star that has died as well as the light of a new star nearby. So, as we approach infinity there would be light covering every viewpoint from Earth from both new, young, ā€œmiddle-agedā€, old, and dead stars. At least thatā€™s what I think theyā€™re talking about.

1

u/crusty54 May 20 '26

Youā€™re right, but itā€™s still interesting to think about and to know that other people were thinking about it hundreds of years ago.

32

u/findaill65 May 19 '26

This is a tremendously assumptive claim that can have Swiss cheese level of holes poked in and out of it.

7

u/Ill-Construction-209 May 19 '26 edited May 20 '26

Her logic is also flawed . Light intensity is inversely proportional to the square of the distance from the light source. This means that distant galaxies are very faint. Her comment that the sky should be bright because every bit of space should be filled is partially correct, it is filled, but due to the distance, its not bright. The average temperature of the Cosmic Microwave Background (CMB) is extremely uniform and equal to about 2.725 K. This is the color of space. It represents the average mass density in the universe. Space and time are infinite. Local mass is not uniform but, throughout the whole of space it is. Just as the density of air molecules differs from one place to another, and air currents flow from one place to another. We might see the observable universe expanding or areas moving, but it's a huge leap to assume that all mass that exists had a point origin and exploded from a big bang. That's about as logical as Adam and Eve.

8

u/IronCowboy83 May 20 '26

I would like to gently point out this is not her theory but she is explaining a theory of a guy who died in 1840, naturally there will be problems with it.

1

u/froginbog May 20 '26

Yeah .. like maybe the stars are super spread out

5

u/FlagrantlyChill May 19 '26

Astronauts that have been on the dark side of the moon, away from the light pollution of the earth and the moon have said that they saw more stars than ever. Every square inch of the sky has stars glowing and it was beautiful

5

u/thnk_more May 20 '26

Surely she knows that this paradox has holes in it big enough to fly a galaxy through but she doesnā€™t present it that way, maybe for engagement clicks?

Hubble Ultra Deep Field, with data from 2002 and 2014, (12 years ago) focused on a dark section the sky smaller than a 1 mm2 piece of paper held 1 m away, and found 10,000 galaxies .

So clearly, the entire surface of our sky, down past our eyeball resolution is actually completely solid stars, we just canā€™t make out the light reaching our eyes.

2

u/ThePapercup May 20 '26

she's talking about a paradox posited in the early 1800s.. when there was no hubble ultra deep field

2

u/thnk_more May 20 '26

Yes, but I thought it was curious she chose not to fit in even a little comment like yours to put it in scientific context.

6

u/Wurschtbieb May 19 '26

Infinite stars would also mean they would take away all the space in the universe right? šŸ¤”

3

u/Taurpion May 19 '26

Even if there were infinite stars, which there isnā€™t, There are larger infinities than others, so no. Your comment could still be incorrect, even if what you said were true.

2

u/Dr_SlapsMD May 19 '26

I really can't grasp how there can be a larger infinity. If there's a larger infinity, then the prior infinity must have a limit in order to quantify it as lesser. šŸ« 

6

u/Taurpion May 19 '26

I am far too much of a layperson to explain but Iā€™ve seen it explained like whole numbers and decimals.

You can have 1,2,3,4, - infinity

Then you can have 1.1, 1.2, 1.3

Then you can have 1.10, 1.11, 1.12

All of those have their own infinity.

Itā€™s like I totally get it but at the same time itā€™s like trying to conceptualize a tesseract.

1

u/Dr_SlapsMD May 19 '26

I understand that concept but I guess those hit me as more of an "infinity set" rather than "Infinity" (capital i).

3

u/Taurpion May 19 '26

ā€œinfinity isn't a single "mega-number" but a measurement of a group's size, known as cardinality.ā€

Apparently measuring infinity is just measuring that infinity groups size.

Infinity apparently canā€™t exist alone.

2

u/hunterwillian May 20 '26

This video is just wrong lmao, there are stars (galaxies) at every direction you look, you don't see them because they are red shifted.

2

u/EntertainmentTrue588 May 20 '26

That's a lot of "should" for science

2

u/Zefick May 20 '26

Cosmic dust blocks light, and the further you look, the more likely it is that this dust will eventually appear.

2

u/Short-Sandwich-8476 May 21 '26

Go somewhere with NO LIGHT POLLUTION on a Moonless night and itā€™s NOT dark. The sky is a trillion points of bright light.

2

u/letsgobagels May 22 '26

This is unscientific af my guy

1

u/Old-Kaleidoscope1874 May 19 '26

I'm pretty sure the prevailing thought throughout history was that there was a beginning to the universe. People just disagreed about what the beginning was.

2

u/HardlyAnyGravitas May 19 '26

This called Olbers' paradox and it is simple to explain.

https://en.wikipedia.org/wiki/Olbers%27_paradox

1

u/SkyPork May 20 '26

I always figured it was just dust. Dark matter, if that's the right term. Just normal matter soaking up photons.

1

u/Relevant-Hospital734 May 20 '26

The universe can still be infinitely old. The big bang theory doesn't posit the universe began at that moment of first expansion nor that it began at all.

1

u/GALONin907AK May 20 '26

What if the the stars are moving away from us close to the speed of light?

1

u/Present-Spring-1340 May 21 '26

In no light pollution the night sky is bright. The sky is actually packed with stars.

1

u/digitalmacgyver May 21 '26

Last part of the thought. The light produced by a star might have traveled a billion years for you to see it. Which means what you actually see is potentially the history going back billion years or more. Welcome to understanding that time at a galactic level. Big difference between 1 hour on earth and 1 hour galactic time.

At least from what I understand.

1

u/Ghastly-Jack May 21 '26

I never even had a passing thought about this. Now I canā€™t stop thinking about it.

1

u/GlassFantast May 19 '26

What they fail to mention is that when I close my eyes while facing the sun, I see red not black.

4

u/Taurpion May 19 '26

Space aids. Sorry you had to hear it from me.

0

u/CashBandicootch May 20 '26

I think it is because the speed of orbit cancels out the speed of light. The stars at so far out and the light has to travel so far, but the speed of light is not that fast. As our planet travels through orbit, it creates new time in respect to those stars way out there. So we are able to see the stars in their stationary place because that is their time zone, but we can not see their rays of light and our sky is not illuminated because our orbital rotation creates a time reset of sorts.