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Date and Time Sun. Map and Directions View Map. New Horizons: The Darkest Web. View Details. Follow this organiser to stay informed on future events. Vivid Ideas Event creator. Following Follow. Events you might like:. ScienceTech Networking. Share this event. ScienceTech Class. ScienceTech Conference. ScienceTech Seminar. Why IoT? Save This Event Log in or sign up for Eventbrite to save events you're interested in. Sign Up. So even if the Universe went on forever, the light from a galaxy like ours, by time it reached its destination after a long enough travel-time, would have only the burned-out remnants of star systems to encounter.
But there's also one more reason the night sky is dark, and it's a reason that we're all less comfortable with: the fact that our vision, well, kind of sucks. I mean, for our every day purposes, it's great: we're well-adapted to the light that the Sun puts out. But remember that this is only a tiny, tiny fraction like one part in 10 30 of all the electromagnetic radiation that's actually found in the Universe!
Because the Big Bang started from a hot, dense state, the relic radiation leftover from that actually does illuminate the night sky everywhere, in all directions! It's just that it illuminates the Universe at a temperature of about 2. That's exactly what the Cosmic Microwave Background is! And we can't see all the different wavelengths of radiation that abound in the Universe; the Universe is dark to our eyes because of the limited amount-and-types of light that we can see.
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I particularly liked this: "the relic radiation leftover from that actually does illuminate the night sky everywhere, in all directions! Somehow that's never occurred to me before. I have wondered about this for years, but I could never even figure out how to google for the answer!
I don't think so Mike. I gather that some of the astronomy photographs you see are composite images made up of different spectra. But if we could "see" microwaves, at our ambient temperatures everything around us would be glowing, and our eyes too. So we wouldn't be able to see much. We'd have to be cold. I don't think that Olbers paradox is very well stated in most accounts.
The statement is essentially geometrical, but draws too many conclusions from that. That way, you can show that in an infinite universe the light levels would diverge. But if photons behaved, say, like mesons, and decayed as they travelled, then the geometric argument would fail. Incidentally, I've never seen a proof that in an infinite universe every light ray actually does end in a star. It sounds simple to state, but there are infinite universe for which it is false. Actually, now that I think about it, the issue of whether there are rays which never hit a star is rather important.
For example, ask the question of whether there is a ray with largest length to a star. If such a ray exists then the summation over all rays must stop at this largest radius. But If such a ray does not exist then at any distance there still remains area of the sphere which is uncovered. But is this area dense on the sphere? It's temptiong to apply the continuous approximation, but I'm not sure it can be made to work by argument alone.
It would be 'bracing' to see a physicist's perspective on, let's say, the Zimmerman trial [and verdict]. Or, is that not just your [or this blog's] 'beat'? We really are limited by our physical limits. Thankfully, we have science to make up for it. I hesistate to post this because I really don't want to speak for Ethan or anyone else, but personally, I don't think discussion of social issues is really appropriate here. I come to read this blog to learn about and discuss scientific issues. There are MANY places on the internet where you could discuss the Zimmerman trial, why should it be here?
Unless, of course, there is some scientifically interesting aspect of the case, which I don't believe is true in that particular trial. Fabulous article!
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I'm having a problem with one thing though, picturing how a Universe Thank you Sean T! Now I don't have to comment, and I'm afraid mine would have been a little more forceful!
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There are too many social sites as it is! You may be totally right. There is little in the way of science in the case you're talking about, therefore there's nothing to say on it here. PS we do have a plethora of scientists. We have more than one, that means, just in case you didn't know what "plethora" means :-D.
There are additional assumptions in Olbers' Paradox beyond just a static universe that is infinite in age and infinite in extent, but they are minimal and reasonable and unlike the other assumptions still appear to be true as far as we can tell. It also assumes the universe is homogeneous, so the density of stars and galaxies is roughly the same across the universe, and that the distribution is random and not organized in any meaningful way with regard to our point of observation such as your stars only at integer multiples of some unit universe.
This is in essence the Copernican Principle.
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From this it is easy to see and not hard to prove that any line away from earth will eventually end in a star. Or to put it in terms of your decision problem: As distance X approaches infinity, the probability of the question "Is there a line from earth which exceeds distance X without intersecting a star? In the end, Olbers' paradox is false because it's assumptions are false. But the assumptions that are false are the infinite, eternal, static universe, not the Copernican Principle. Here is another way to look at just how tiny a sliver our eyes can detect of the electromagnetic spectrum.
If you were to take the entire spectrum and extend it from Los Angeles to NYC the slice we can see with our eyes would be the size of a dime. It's a little unclear since it's not obvious how it's being counted.
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We can estimate the energy density of starlight in the universe. The quickest reference I have is from Felten ApJ , which is probably off by a factor of 10 or so given it's age, but it gives a metagalactic outside the galaxy energy density for starlight of 0. That's mostly in the visible. So in terms of energy density the two are quite comparable.
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How could he? The blogger makes no mention of the expansion of the Universe. The stars and Planets have been moving apart from one another for the past 13 billion years. In the distant past the sky was brighter. The expansion of space is the underlying reason for it all. Oblers Paradox is best explained by the expansion of space. All the reasons given are products of an expanding universe, not the reason why the sky is dark Olber's Paradox.
I'm not satisfied. Just tell me why light disperses. Isn't that the point of the article? How about point it out that light is a wave or a particle and things like dust can stop it? Don't ask me, just speculating. You don't know if the universe is infinite or finite. Even if it were finite, what is beyond its end? You don't know the age of stars or their longevity. You don't even know what makes them burn.
You don't know what light is or even why we can see it. So quit acting as if you know. I saw articles referring to a large concentration of matter in a cosmic background wimp image, that structure is one of those rings. What about the red-shift? Is that not also a reason for us not to see all the stars we could see, just because they're moving away from us so fast that their light is not visible to us, any more? Mark: He did mention the Big Bang, which includes universal expansion and a finite age for the universe.
Expansion would result in an event horizon where distant objects are moving away from us faster than light, but finite age is a better explanation for the size of the visible universe today.
As the universe becomes increasingly dominated by dark energy which wasn't known when Olbers' Paradox was resolved , then yes, expansion will be the reason there's nothing interesting in the sky outside the local galaxies. But either way that's not the reason why stars have finite age or our eyes see only a limited portion of the spectrum. Paul Revere: The point of the article isn't to establish that light diminishes as the square of the distance. That's pretty simple to show with geometry and conservation of energy, regardless of what light actually is. Hypothetically it could fall off faster than that but empirically does not , but not any slower.
Dust clouds aren't the cause. As Ethan mentioned, that dust would be heated up by all the starlight it absorbed and start glowing on its own. Steffen Moller: As I said to Mark, at some point stars being red-shifted out of our visible universe will be the dominant reason why we can't see distant objects, but today it's the finite age of the universe. Even things that aren't moving away so fast that we couldn't ever see them nevertheless are too far away for their light to have had the chance to reach us.
Both concepts are part of the Big Bang, though. Usul: Correct, as Ethan said, we do not know if the universe is infinite in size or not. The resulting paradox implies that one of those assumptions is wrong. Whether the universe as a whole is infinite in size or not is still unknown.