Illustrating Olbers' paradox

Hello,

What the title says. I'll use instructions from Wikipedia: - "To show this, we divide the universe into a series of concentric shells, 1 light year thick. Thus, a certain number of stars will be in the shell 1,000,000,000 to 1,000,000,001 light years away. If the universe is homogeneous at a large scale, then there would be four times as many stars in a second shell between 2,000,000,000 to 2,000,000,001 light years away. However, the second shell is twice as far away, so each star in it would appear four times dimmer than the first shell. Thus the total light received from the second shell is the same as the total light received from the first shell."

If we start with 10 bright stars in the first shell, then there should be 40 stars 4 times less bright in the second shell, like this:

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...so the total amount of light received from both shells is the same.


Right?

 

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Hi there. While I'm not a moderator on this forum, you should expect the same treatment from me here as you got on PF if you act the same way here. Likely even via copying and pasting messages from PF that you've chosen to ignore.

So: are you going to make more of an effort here to learn, or is this going to be more of the same game? You didn't post a question or thesis yet, so it isn't possible yet to know where you want to go with this.

If your goal is to learn, I recommend you start by learning how to do basic lighting intensity calculations, then apply them to olbers paradox.

 

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For the love of drugs, you are everywhere! Look, I'm too old for that condescending attitude of yours, it's inappropriate. Point out what you believe is wrong and put forward what you think is right, anything else is unnecessary. My goal is to find the truth, the more there is to learn on the way the better.

Now, would you please quote my sentence and insert the actual image in between those two lines so people can see?

And welcome, my dear archenemy.

 

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Bring it on. Rrrrhh!

 

Your general description of Olber's paradox is correct. The main reason the sky is not all white is that the age of the universe is finite.

 

Ok, so if we correctly illustrate the paradox we should get completely white image, right?

 

I have a question. What is the average life of a star, and does the fact that they burn out eventually affect your illustration?

 

For a G2 Sun like star, its around 10 billion years.
For red dwarfs its much much longer, and for O type stars and Wolf Rayet stars, just a few 10's of millions of years.

 

Whatever the paradox says. I think the assumption was that new stars form from dead stars, so statistically it's the same as if they have infinite lifespan. In any case the number of stars in the paradox universe is considered to be infinite.

 

I don't think that's quite specific enough: according to the paradox, the entire sky should be as bright as the surface of the sun.

 

All the same to me, so what color would that be?

 

Roughly white.

 

Maybe, but the input so far is the the age of the visible universe is finite, stars have finite lives, and the universe is observed to be expanding. Those seem to me to be enough to defeat Olbers'.

 

New stars do not form from old stars. New stars form from molecular clouds. What happens when a star 'dies' really depends on the starting size of the star but none of the 'deaths' involve the 'dead' star ever becoming a new star.

 

I am fortunate enough to live in an area with a very dark sky (no city lights). I can see the andromeda galaxy with my naked eye as a slight light smudge. The galaxy is only 2.5 million light years away and covers an area of about 6 times the diameter of the full moon. In the small area there about 400 billion stars. So again all I can see is a slight smudge to indicate where all of these vast number of 'close' stars are. Based on that I am not surprised in the slightest that the sky is dark. Olbers paradox seems to be kind of silly to me.

 

Well yes - it is around 200 years old, from a time when astronomers had very little understanding of what stars are. It doesn't have much value now that we know what is wrong with all of the assumptions that went into it. Perhaps it would be instructive to list all of those assumptions.

 

True. Here is a site that discusses Olbers paradox and several other aspects of the universe in a very simple, clear and concise way.

 

interesting

 

Perhaps. However, if Olbers' paradox is flawed and its conclusion false, it would make room for one more explanation, which is the effect on brightness caused by the inverse-square law. Therefore the question we are supposed to answer here is whether the conclusion of the paradox is valid or not. I'll be advocating the paradox is flawed, that if we correctly illustrate it we will not actually obtain uniformly bright (white) image, and I suppose everyone else will be arguing the opposite. But for the sake of truth, even if you don't agree with me you could join my side and play the devil's advocate, which is really what I am doing. I don't have a horse in this race, I couldn't care less whether the universe is really finite or infinite, expanding or not expanding, or whatever.

So, let's begin. If you look at those two images of the first and second shell you will notice how much darker the second shell is. Now, if we continue to draw other shells the stars in every subsequent shell are only going to get dimmer and dimmer, so how is that supposed to produce uniformly bright (white) image? Did I make some mistake in drawing those first two shells, or maybe brightness of those dim stars is somehow eventually supposed to add up, or what?

 

A question I have that I have not seen anyone raise is that except for a very few stars no matter what the magnification the star will never be more than a point source and as such doesn't that mean that the stars have a zero angular diameter, so they literally could not 'cover' the sky.