er… infinite and expanding that is…
Olber’s Paradox doesn’t show the sky is dark because the universe is infinite and expanding. It shows the universe is infinite and expanding because the sky is dark.
Actually the point of the original column was ‘why is the sky dark’ and the person who asked the question even stated ‘aren’t we overlooking the obvious here’. So I posted the obvious. It has been roundly criticized.
Perhaps you could explain what you mean by “pixel-ating” the sky.
You lost me at that point.
Just a point of light in the sky, a small unit of lit up space. Like a pixel on a monitor.
If you look at the hubble deep field, every object would represent a pixel, and there are 10,000 of them. It would be like putting 10,000 LCD pixels on a dime 75 meters away. Now spread that out over the entire sky.
I’ve done this on the Dope often enough before, but I’ll again recommend Ed Harrison’s book Darkness at Night (Harvard, 1987) for a history of the issue and why the different explanations proposed over the years either do or don’t work.
Including lengthier explanations of John’s point about why it’s not enough just to claim that it’s because the distant stars in the “gaps” are too faint to be visible.
I have made a most marvelous discovery that will just fit inside the margins of this text box. When a guest to a message board makes a post about science that he does not understand, the chances that when he returns his next post will not a) apologize for his previous mistakes or b) understand where he went wrong or the explanations to correct him exceed 100%. This can only be true if the amount of ignorance in the universe is a) infinite and b) expanding. I predict that Mapcase’s Paradox will live through the ages and be rediscovered by future commentators and I also predict it will be misunderstood by those with insufficiently deep minds.
Why am I still cranky when what sparker1776 says in post #18 is clearly true? Because it is trivially true. What he writes amounts to no more than saying the night sky is dark because there isn’t enough light. This is obvious - looks up at night sky; yep, it’s dark - but it in no way addresses Olbers’ Paradox. It may the first thought of those who don’t understand the problem, but it’s dismissed by those who do because it has no explanatory power except on itself (which it must because of its circularity). It doesn’t contradict anything, old or not. It’s just a statement of what everybody knew then and everybody knows now.
The true question that Olbers was asking was: what is the basic underlying structure of the universe? That’s a deep problem and one that would take decades to solve.
However, it is not true that:
No it doesn’t. Olbers’ Paradox is answered by showing that at least one of the two assumptions it makes - again, 1) The number of stars is infinite and 2) The universe is of fixed size - is not true. The paradox itself shows nothing. Only the answer as to why it is not a paradox shows anything. As I took care to demonstrate earlier, an infinite universe is not required. A sufficiently large finite number of stars would provide the illumination. A sufficiently large finite number of stars would be bright enough even if the universe were expanding, though that would be a true buttload of stars. A sufficiently small number of stars would also explain the finding even if the size of the universe were fixed.
While the paradox is easily shown to be nothing of the kind, figuring out the parameters of the actual universe to answer the questions of its size, density, age, light speed, shape, expansion, and other qualities is a much more difficult process and one that is still not fully answered. (Astronomers don’t know whether the universe is infinite or not. An infinite universe would have to be infinite from the moment of creation but this plays havoc with the physics as we know it. Olbers’ paradox can’t possibly show that the universe is infinite when nobody even knows whether that’s true.)
The “obvious” has probably never been the right answer in the entire history of astronomy. Real scientists go much deeper than the “obvious” to get answers: answers that often contradict earth-bound “common sense.”
If you come across a problem in astronomy or any of the sciences don’t expect to blurt out the first thought that comes into your mind and have anyone do anything other than roll their eyes. And eye-rolling makes some people cranky. 
“figuring out the parameters of the actual universe to answer the questions of its size, density, age, light speed, shape, expansion, and other qualities is a much more difficult process and one that is still not fully answered.”
You don’t need to do all this in order to show what I’m talking about, it just overcomplicates the question.
I also don’t need a lecture on how science works.
I think the differences between us on this thread are due to you having to defend things perpetually here for a long time. You saw my post and though ‘oh another person attacking this’. But I’m not. I don’t think you gave my post enough consideration to get past your initial incredulity.
However, I wrote my original posts quickly as I was in a hurry - it was a simple enough concept so I didnt think anything more refined was really necessary. I had no idea I would be entering a pissing contest, so I didn’t spend much time on it. So I apologize if my post was not clear enough.
So, since we both claim to be educated and sane, let’s start over here. I’ll write this up in a more precise way:
___________________________________ <----- starting over here
There are two sides to the question “why is the night sky dark”, as evidenced by the initial post which stated “Excuse me, but aren’t we overlooking the obvious here?”.
The two answers given to the two questions inherent in the overall question ‘why is the night sky dark’ were:
- The whole Olbers paradox solution (there is an unobservable universe so infinity does not come into play)
- “there just aren’t enough stars in the observable universe to fill up the night sky”
The first answer is not up for debate. The second answer is seperate from the first, it is based on a different set of reasoning. Let me reiterate: this post is not at all about Olbers, I am specifically talking about the observable universe.
Later on in the answer there are two further statements, and one contains the correct answer in my opinion:
- We don’t really know how many stars there are. What we do know is that however many there are, we can see only a finite number of them
- The few jillion stars in our corner of the cosmos (AKA the “observable universe”) don’t have the collective candlepower to illuminate the night sky
My hypothesis is that #2 is not correct.
#3 infers that #2 can’t actually be validated at the time of the original statements, since it states we don’t have evidence for #2. It is also no longer true. We have a picture of them back to almost the very edge of the observable universe, called the hubble deep field. #4 seems patently obvious.
But back to the point: #2 is incorrect. Here is why I feel there are “plenty of stars in the observable universe to fill up the night sky”.
a. The hubble deep field has about 10,000 galaxies (collections of stars) within it.
b. This represents one-two millionth of the dark night sky as viewed by an individual (one-twelve millionth of a 360 degree view from earth)
c. You can multiply that out to literally calculate the density of objects from our perspective, and determine if that satisfies you as far as ‘filling up the night sky’ or not
d. After doing the math, in my opinion it’s ‘filled up’ to an amazing, truly incredible actually, degree. Thus #2 above is incorrect.
Ok, so it’s filled up. Why is the night sky still dark? They are too dim from our perspective (#4).
So #1 is true, #4 is true, #2 is not true, and #3 is half true (but not an answer to the original question.)
You may look at this and say ‘well yes, that’s obvious’. Excellent.
Note that part of the original Olber’s Paradox is that an infinite Newtonian universe with a finite number of stars would collapse upon itself. Practically speaking, therefore, an infinite Newtonian universe requires an infinite number of stars. And a Newtonian universe must be infinite.
To “sparker1776”: You can’t just say, “they’re too dim” without blowing off simple fact that the reason they’re dim is that their light falls off with the square of the distance, which is exactly compensated for by the fact that their number, in a hypothetical infinite universe, keeps increasing with the square of the distance.
So unless they’re getting extra dimming from magic, your argument doesn’t pass the math test. The reason has to be of another kind.
I think I see the OP’s misunderstanding. The OP has stated that faraway objects are dimmer because they are distant. That is indeed true, but that cause is one step removed from what we’re actually observing. They’re not dimmer merely because they’re far away… they’re dimmer because their apparent size is smaller. They’re taking up smaller chunks of the visible sky, and that’s the reason they end up contributing less overall light to our sky when we look up.
Taking the example of the Hubble Deep Field, it most certainly is not completely filled up with stars. You see plenty of black in between the galaxies even at that intensely magnified and lengthened exposure. If it was truly “filled up,” then the picture would be solid white. It’s not.
*** Ponder
Having spaces between objects when looking at high magnification would always be true unless we live within a solid sphere, or Olbers wasnt a paradox (ok there are other possibilities but they are too wierd). Interestingly effectively the same thing as far as the Olbers question is concerned though.
The ‘smaller chunks of the sky’ question is great - but it’s exactly what I’m talking about with pixelation. Once the granularity is beyond your eyes capability to detect it, you have it covered in the ‘why is the night sky dark’, individual perspective question. The question wasn’t ‘why is there dark space between objects under high magnification when looking through the most powerful telescopes in the world’.
My calculations show that the granularity would be well beyond the naked eye’s ability to detect it. If every object out there was bright enough to be seen with the naked eye, you would not see any spaces between them as a person who is looking up at the night sky, you would see a pure white sky.
“You see plenty of black in between the galaxies even at that intensely magnified and lengthened exposure”. As I interpret the original question, this is backwards. I interpret this as “At this intensely magnified exposure you can see plenty of black, but if it were not magnified, you would just see a white spot”. You could calculate what kind of magnification you would need to get beyond a white spot, it seems to me it would have to have pretty good magnification… I don’t have time to figure that out right now though, perhaps later.
To be very clear, Im trying to answer the original question regarding ‘the night sky’, which infers the simplest question of an individual merely staring up at it without a telescope.
What then do you make of this?
It’s very interesting, but if it’s 1 billion light years across then there is 12 billion light years of observable stuff in front of and behind it. In my scenario, that area of the sky would be… a little less than 8% dimmer than the rest of it.
But it’s a cool find, it does have important implications.
This is, well, obviously, not true. If there were observable stuff in back or in front of it would be observed. It is not 8% dimmer. It is a black void.
This scientific fact shows that your understanding of astronomy is dead wrong.
I would add it’s also 8% less dense; but for the eye to detect it at all, it would have to be more than 99.98% less dense (which brings it down to high def level of granularity), if my math is correct.
Back to the apparent size dimness thing. You brought up an interesting point so I’ve been thinking about it for a bit. Dimmer because apparent size is smaller is synonomous with dimmer because they are far away - their apparent size is so small because they are far away. But it still brings the question back to dimness rather than density.
More math - fact is, it blows me away how many galaxies are out there, which is why I’m so interested in this question. The hubble deep field is a picture of the sky representing ‘a dime held at 75 meters’, and it has 10,000 objects. If you magnify it 75 times, so that it is one meter away from you, in order to keep the density of the objects relatively identical, you would have to have 750,000 visible objects on that dime. So picure a dime held at arms length in the dark with 750,000 visible-to-the-naked-eye light emitting objects on it. You cannot possibly be able to see the dime behind it.
At arms length in order to get it down to high def (which you have to admit you cannot see the spaces between the pixels at one meter) you would lower the number down to… 750,000 / (however many dimes fit onto a high def screen, lets go with a 42" to be conservative). My extremely rough calculation on that (someone could do a lot better but it should be close) are:
The screen is about 36" x 22". A dime is less than 3/4 of an inch, I’ll round to 3/4. So you should be able to fit… about 1400 dimes on a flat screen.
So in order to drop the granularity down to high def, you would have to drop from 750,000 visible objects to 535 on that dime at one meter. We can debate how much more def than high def is acceptable, but as you can see, we’re so beyond the ballpark it’s truly incredible. Again, if my math is right.
I also understand those pixels would be smaller than a high def pixel in open space, but the atmosphere helps with that quite a bit (like the diffraction on this image: http://upload.wikimedia.org/wikipedia/commons/thumb/e/e1/Lunarcorona.jpg/180px-Lunarcorona.jpg )
Fun stuff.
Actually this isn’t about astronomy, it’s basic geometry.
The observable universe is a sphere 26 billion light years in diameter (actually likely more but Im being conservative), we’re at the center of it (since we are the observers), and this is what the void sits inside of.
The void is not a tube (or cone) 13 billion light years long and a billion light years wide that leads down to earth. It is a sphere (for our purposes) with a 1 billion light year diameter which is sitting inside another 26 billion light year diameter (13bly radius) sphere.
Like this:
us [observable stuff] [void] [observable stuff]
If someone had found a 13-billion-light-year-tube-void that would be different.
How do I know it’s not a tube? Let me quote your post… “The void, which is about 6 billion to 10 billion light years away…” What’s in front of the void? More void?
This shows that your understanding of basic geometry is dead wrong. Wee.
I’m not going to start anything, but if you attack me I’m not just going to bend over and ask for more.
Still, can you just quit the personal attacks already? They are pointless.
I have a serious suggestion. Given that this issue has produced considerable attention from professional astronomers for, oh 400 years now, and given that the professional concensus is that your theory is not correct, perhaps you could/should send your explanation to, oh, say the Astronomy department at Cal Tech, or some similarly important institution. See what they say. :rolleyes:
So we’re back to hiding behind Wikipedia? It’s no longer necessary to think?
By your standards, the bible is the de facto keeper of all scientific fact. Unless we can find some heiroglyphics that show otherwise. Nice.
Fine, I’m done with this thread.
Ok that was unfair. I understand what you are saying, I knew the 400 year thing would come up (where is that 400 year quote from by the way… other than Wikipedia that is…). I uinderstand that your de facto keeper of knowledge is not the bible. It’s Wikipedia.
There are plenty of serious astronomy sites that state exactly what I’m saying. They go so far as to state that the ‘not enough objects’ model is unrealistic. I just thought a site like this would actually be interested in discussing simple topics, beyond just spouting dogma. But it seems the site is really not about that.
Ok I am completely done with this forum and site, I can use wikipedia if I need to look up popular opinion on almost anything.