Why the sky is dark in the night

[exchemist]

It will be in order to thank me too as I started this thread so that we all understand something, despite my/PB games......such an innocuous point, evidenced daily and has a wonderful history....

On the contrary. You failed to mention Olber's Paradox to explain what you wanted to talk about and left it to others to make sense of the subject of your OP. Sort of faintly arseolean of you - and, I have to say, quite in character.

 

[Daecon]

Thats true, billions of stars are not able to make the sky any bright...but why ? Thats the point.

Because each of those billions of points of light is surrounded by trillions of points of not-light.

Cantor dust, that's the name of the thing I was trying to remember. Each speck of "dust" is a star and the empty space is the night sky. Imagine how many iterations you'd have to go through until each star, white dwarf, red giant, etc. is the size of a speck in the night sky.

 

[The God]

On the contrary. You failed to mention Olber's Paradox to explain what you wanted to talk about and left it to others to make sense of the subject of your OP. Sort of faintly arseolean of you - and, I have to say, quite in character.

Forget it, you seem to be in the habit of spoon feeding, Origin did some work/or knew it and came up with this, you did not.....anyways you learnt about this paradox, you can acknowledge and thank this thread for this if not me...

 

[paddoboy]

You jump to conclusion...this happens because of need of you to refer to google again and again (lack of formal knowledge)...If you knew that for this paradox red shift also plays a crucial role...you would not have made this comment.

I conclude nothing. I state accepted facts as evidenced over many years.
Red shift plays a role over the larger scales obviously. You still seem hung up on the decoupling of our local group from the larger scale expansion.
Read slower and let it sink in.

Now if CMBR was 3500 K after t = 380000 years from t = 0 (not ago as you mention), then I am sure if our solar system was to be there in present form (assume) then the night sky would have been bright at 3500 K.....so what is that CMBR temperature and time after t = 0 at which the darkness came ?

You have your answer: It appears it isn't the one you want.
Perhaps the answer at post 7 made with "tic" might fit your agenda better.
[tic mode on]
And God said “Let there be light,” and there was light. God saw that the light was good, and he separated the light from the darkness. God called the light “day,” and the darkness he called “night.” And there was evening, and there was morning the first day.

Is this what you are after?

 

[Russ_Watters]

This should have been your first post, rather than making that cryptic first post.

1. In the early universe ( as per Big Bang) there should have been tremendous brightness, this got fainted as the expansion (inflation onwards) continued....the point it raises is that there should have been an epoc after which slowly the sky darkness would have started, the brightness started diminishing...ignoring the birth time of Earth, what was that time or alternatively what was CMBR value (present around 2.7 K) at which darkness was not there ?

That's up to you to define how you like. If you want, you can consider the CMB to be a positive answer to the paradox: everywhere you look is indeed filled with "light", terminating on a bright surface (the surface of last scattering). It's just red-shifted. How that all works is described here:
https://en.wikipedia.org/wiki/Cosmic_microwave_background

2. There is no red shift between andromeda (and few other Galaxies) with respect to us, there are billions of stars in our own Galaxy and add billions from other non red-shifted stars from andromeda galaxy, still darkness ?

Andromeda is blue shifted. It is moving towards us, not away from us. Anyway, I'm not really sure what you are asking: if you are in a place away from city lights, you can look up in the sky and see both the Milky Way and Andromeda. They don't entirely fill the sky with light because they are too small and nowhere near dense enough.

3. Ultimately it boils down to the amount of photon energy we receive from these stars, will we get desired darkness level if we calculate the energy received from stars ?

Sure.

Technically before we declare Big bang / Red shift as the solution of Paradox, should we not find out the energy received from our Galaxy stars (sun excluded) and andromeda stars and prove that they cannot cause any significant brightness in the night..

As I said, you can go outside and look and see them.

4. Are there planets, which are bright always, receiving significant light from multiple/two stars throughout their spin.

That's vague, so I'll say yes.

 

[The God]

I conclude nothing. I state accepted facts as evidenced over many years.
Red shift plays a role over the larger scales obviously. You still seem hung up on the decoupling of our local group from the larger scale expansion.
Read slower and let it sink in.

You have your answer: It appears it isn't the one you want.
Perhaps the answer at post 7 made with "tic" might fit your agenda better.
[tic mode on]
And God said “Let there be light,” and there was light. God saw that the light was good, and he separated the light from the darkness. God called the light “day,” and the darkness he called “night.” And there was evening, and there was morning the first day.

Is this what you are after?

Take a walk....

 

[Russ_Watters]

Thats true, billions of stars are not able to make the sky any bright...but why ? Thats the point.

You can easily model the problem with a spreadsheet and calculate how bright the Milky Way is. The simple answer though is that billions of stars is nowhere near enough to fill up the night sky.

 

[Russ_Watters]

You can easily model the problem with a spreadsheet and calculate how bright the Milky Way is. The simple answer though is that billions of stars is nowhere near enough to fill up the night sky.

Actually, there is a pretty simple geometry exercise that would be very instructive for you, which I am certain you will not attempt:

1. Google for the following information: Andromeda's size, distance, number of stars and the average size of a star (roughly).
2. Use simple geometry to calculate what fraction of Andromeda is sight-lines that end on the surface of stars and fraction pass through open space between them.

This assumes that none of the stars are blocked by other stars or dust, which isn't quite true but doesn't substantially affect the conclusion.

 

[The God]

This should have been your first post, rather than making that cryptic first post.

It could be cryptic for you......

That's up to you to define how you like. If you want, you can consider the CMB to be a positive answer to the paradox: everywhere you look is indeed filled with "light", terminating on a bright surface (the surface of last scattering). It's just red-shifted. How that all works is described here:
https://en.wikipedia.org/wiki/Cosmic_microwave_background

No, CMBR at 2.7 K takes care of BB light, it does not resolve it fully....you also missed what if CMBR was at 100 K or say at 27 K, will it still be dark ?

Andromeda is blue shifted. It is moving towards us, not away from us. Anyway, I'm not really sure what you are asking: if you are in a place away from city lights, you can look up in the sky and see both the Milky Way and Andromeda. They don't entirely fill the sky with light because they are too small and nowhere near dense enough.

Sure. Don't bother about why andromeda is blue shifted, the idea is that not all the light received is red shifted, the MW and Andromeda both put together have billions of stars, light is not red shifted also...........your argument is that light from these billions of stars is not sufficient to brighten up the sky...I can extend the same argument to all the star lights, that light as received from all the stars (even if red shift was not there)is not sufficient to brighten the sky.....why do I need redshift to resolve this ? Would the sky be bright with present distribution of stars in finite universe if red shift (expansion) is not there ?

 

[origin]

Sure. Don't bother about why andromeda is blue shifted, the idea is that not all the light received is red shifted, the MW and Andromeda both put together have billions of stars, light is not red shifted also...........your argument is that light from these billions of stars is not sufficient to brighten up the sky...I can extend the same argument to all the star lights, that light as received from all the stars (even if red shift was not there)is not sufficient to brighten the sky.....why do I need redshift to resolve this ? Would the sky be bright with present distribution of stars in finite universe if red shift (expansion) is not there ?

I am afraid this thread is going to be like your confusion over the graphic showing how space is bent around a star. Instead of another 20 pages of going round and round perhaps you should just realize this is probably another concept that you just cannot 'get'.

 

[Russ_Watters]

No, CMBR at 2.7 K takes care of BB light, it does not resolve it fully....you also missed what if CMBR was at 100 K or say at 27 K, will it still be dark ?

No, you missed my point. But I'll just spoon feed you an answer, since I don't think that issue will mean anything to you anyway: if by "dark", you mean not emitting visible light, then yes, matter at 100K is dark. You should already know that, though, since you are warmer than that!

...your argument is that light from these billions of stars is not sufficient to brighten up the sky...I can extend the same argument to all the star lights, that light as received from all the stars (even if red shift was not there)is not sufficient to brighten the sky.....why do I need redshift to resolve this ? Would the sky be bright with present distribution of stars in finite universe if red shift (expansion) is not there ?

Correct, you don't really need redshift to resolve Olbers' Paradox, because it is obsolete. However, if you want a more complete/detailed understanding of why the universe appears the way it does, you will.

 

[Russ_Watters]

It could be cryptic for you......

I'll be direct here, because it matters for whether you actually want to learn and have people understand you:

-Did you know this issue had a name (Olbers' Paradox) when you started the thread?

-Did you read the wiki article or any other instructional material about it prior to starting the thread?

-Where did you get the idea that there is no agreement as to the resolution?

 

[paddoboy]

Take a walk....

Is that the best you can do?

 

[paddoboy]

It could be cryptic for you......

It seems it was cryptic and confusing and just plain wrong to everyone.

No, CMBR at 2.7 K takes care of BB light, it does not resolve it fully....you also missed what if CMBR was at 100 K or say at 27 K, will it still be dark ?

The CMBR along with the other reasons all aptly explain why Olber's paradox is not really a paradox.

Sure. Don't bother about why andromeda is blue shifted, the idea is that not all the light received is red shifted, the MW and Andromeda both put together have billions of stars, light is not red shifted also...........your argument is that light from these billions of stars is not sufficient to brighten up the sky...I can extend the same argument to all the star lights, that light as received from all the stars (even if red shift was not there)is not sufficient to brighten the sky.....why do I need redshift to resolve this ? Would the sky be bright with present distribution of stars in finite universe if red shift (expansion) is not there ?

No, the expanding universe, the 2.7K CMBR, the intensity of the light and distance, the photon energy etc etc.

In essence as you have shown many times in many threads, you don't appear interested in an answer, unless perhaps in this case it is the one given tic at post 8.
Just a continuation of your hopeless evangelistic mission to somehow invalidate science.

 

[river]

First the Universe does not have a infinite amount of stars ; otherwise there would be no night sky .

Second ; space ; there is an enormous amount of space between stars and galaxies. And light with little oxygen doesn't get scattered ; light therefore is very focused .

Just saying .

 

[DaveC426913]

"Why the sky is dark in the night"

Short answer: It isn't.

It is literally awash with microwave radiation, left over, and attenuated, from the BB.

Perhaps the better question you want to be asking is: why is the night sky not full of visible light (radiation in the 400 - 700 nm range)?

 

[river]

"Why the sky is dark in the night"

Short answer: It isn't.

It is literally awash with microwave radiation, left over, and attenuated, from the BB.

Perhaps the better question you want to be asking is: why is the night sky not full of visible light (radiation in the 400 - 700 nm range)?

Dave common now we know what the OP of the thread is getting at ; technically your right but hardly the point of the thread its self.

 

[The God]

The discussion cannot proceed meaningfully and will derail, if everytime we associate agenda (like Paddoboy does) or we refuse to accept a question as question (like Russ_Watters) or we associate incompetence with the poster to understand the mainstream (like Origin does).

All responses on the paradox are mostly inane and blindly support what mainstream says.....all the critical analytical skills are put to backbenches...and if anyone asks he becomes a crank....even people with passing knowledge of subject (like Exchemist) become some kind of final voice...nothing but demonstration of a parrotised mentality.

The OP text very clearly says there are some issues, everyone is in hurry to demolish it, everyone is worried that they should not be branded as anti mainstream lest others will ridicule, come on guys, it is forum discussion only the dark or bright sky is not falling......kill the argument with valid points not by declaring someone as crank or stupid or incapable or by making contentless thoughless copy pastes....

Now let us see, how the Olbers paradox, can still haunt...

1. Resolution of Olbers' Paradox is used as the suppport for Big Bang and finite expanding universe...This instantly raises questions...

a. The CMBR was not always 2.7 K, it has come to this level from a very very high temperature with present redshift being a very high value due to inflation/expansion,...so there must have been a stage when CMBR was high enough (Russ is stuck with 27k/100K example) to cause bright sky...what was that CMBR value and till when from BB this happened ? No positive argument on this, yet..

2. That was with BB, the other part of resolution is finite universe and finite speed of light...This is also creates few questions..

a. Number of stars as taken from a web link.....Kornreich used a very rough estimate of 10 trillion galaxies in the universe. Multiplying that by the Milky Way's estimated 100 billion stars results in a large number indeed: 100 octillion stars, or 100,000,000,000,000,000,000,000,000,000 stars, or a "1" with 29 zeros after it....And I am sure he must be talking about stars who are not the part of those galaxies which are receding at >c, surely we would be getting few photons from each of them and despite their comparatively small redshift (compared with CMBR redshift which is very high) energy input should be substantial to cause some brightness ? None offered a calculation that this won't be substantial, none attempted to go beyond wiki, just the abuses.

b. Now this will create further hostility and abuses.......I am of the opinion that we can get light from those galaxies which are receding at or higher than 'c'.......My argument is that consider a Galaxy which is just outside the visible Sphere (The volume in which all the Galaxies are receding at less than c), now this Galaxy may be in Gravitational locking with a Galaxy which is inside this sphere (like MW and Andromeda), there is no reason why they cannot be....so if this inner Galaxy is getting light from a Galaxy >c then there is no reason why we cannot receive that light.........

c. Even Hubbles expansion is also epoc related, the receding speed must decrease as the time passes, so there will be a time (suficiently large) when we will get more stars/Galaxies giving light to us, thus in a very remote future, it is quite possible that our night sky starts getting bright

We get agog and lap up when BH business tycoon Hawking says that it will take a stellar mass BH to evaporate in 10^67 years (whatever that means), then what stops us from discusing that by 10^33 years probably our sky will be bright all around ? Why only selective science ?

The present explanation of finite universe (well, octillion is semantically non infinite), and not getting light from those Galaxies which are receding >c, appears to be incomplete.

 

[river]

The discussion cannot proceed meaningfully and will derail, if everytime we associate agenda (like Paddoboy does) or we refuse to accept a question as question (like Russ_Watters) or we associate incompetence with the poster to understand the mainstream (like Origin does).

All responses on the paradox are mostly inane and blindly support what mainstream says.....all the critical analytical skills are put to backbenches...and if anyone asks he becomes a crank....even people with passing knowledge of subject (like Exchemist) become some kind of final voice...nothing but demonstration of a parrotised mentality.

The OP text very clearly says there are some issues, everyone is in hurry to demolish it, everyone is worried that they should not be branded as anti mainstream lest others will ridicule, come on guys, it is forum discussion only the dark or bright sky is not falling......kill the argument with valid points not by declaring someone as crank or stupid or incapable or by making contentless thoughless copy pastes....

Now let us see, how the Olbers paradox, can still haunt...

1. Resolution of Olbers' Paradox is used as the suppport for Big Bang and finite expanding universe...This instantly raises questions...

a. The CMBR was not always 2.7 K, it has come to this level from a very very high temperature with present redshift being a very high value due to inflation/expansion,...so there must have been a stage when CMBR was high enough (Russ is stuck with 27k/100K example) to cause bright sky...what was that CMBR value and till when from BB this happened ? No positive argument on this, yet..

2. That was with BB, the other part of resolution is finite universe and finite speed of light...This is also creates few questions..

a. Number of stars as taken from a web link.....Kornreich used a very rough estimate of 10 trillion galaxies in the universe. Multiplying that by the Milky Way's estimated 100 billion stars results in a large number indeed: 100 octillion stars, or 100,000,000,000,000,000,000,000,000,000 stars, or a "1" with 29 zeros after it....And I am sure he must be talking about stars who are not the part of those galaxies which are receding at >c, surely we would be getting few photons from each of them and despite their comparatively small redshift (compared with CMBR redshift which is very high) energy input should be substantial to cause some brightness ? None offered a calculation that this won't be substantial, none attempted to go beyond wiki, just the abuses.

b. Now this will create further hostility and abuses.......I am of the opinion that we can get light from those galaxies which are receding at or higher than 'c'.......My argument is that consider a Galaxy which is just outside the visible Sphere (The volume in which all the Galaxies are receding at less than c), now this Galaxy may be in Gravitational locking with a Galaxy which is inside this sphere (like MW and Andromeda), there is no reason why they cannot be....so if this inner Galaxy is getting light from a Galaxy >c then there is no reason why we cannot receive that light.........

c. Even Hubbles expansion is also epoc related, the receding speed must decrease as the time passes, so there will be a time (suficiently large) when we will get more stars/Galaxies giving light to us, thus in a very remote future, it is quite possible that our night sky starts getting bright

We get agog and lap up when BH business tycoon Hawking says that it will take a stellar mass BH to evaporate in 10^67 years (whatever that means), then what stops us from discusing that by 10^33 years probably our sky will be bright all around ? Why only selective science ?

The present explanation of finite universe (well, octillion is semantically non infinite), and not getting light from those Galaxies which are receding >c, appears to be incomplete.

Hear, Hear !!!!!!!!

 

[paddoboy]

"Why the sky is dark in the night"

Short answer: It isn't.

It is literally awash with microwave radiation, left over, and attenuated, from the BB.

Perhaps the better question you want to be asking is: why is the night sky not full of visible light (radiation in the 400 - 700 nm range)?

Bingo! Well put!