Yes, but that isn’t what the objection to Olber’s solution was about. He explained the dark sky as being due to dust blocking the light. His solution was rejected by using the claim that if so, the dust would heat up and glow as bright as the stars. If this objection to his explaining the seeming paradox is wrong, and it obviously is, then his reasoning is sound, and it explains the paradox.
The entire rejection of his solution depends on that one claim. That if dust were obscuring the light, it would eventually glow as bright as the starlight it was absorbing. That we do not observe this, in regards to our very close galactic center, so right now (not at some distant time), we know obscuring dust does not glow as bright as the stars.
Trying to move the goalpost to “but in an infinite universe” doesn’t change the facts right now, as we can observe them.
Don’t forget that the Galactic Centre is not infinite, but has a very small luminosity compared to the hypothetical infinite universe under discussion.
Of course the total luminosity of the galactic centre, including the dust, is the same as the luminosity of the stars in the centre, but the dust radiates at a much lower temperature; this is because it is not surrounded by an ifinite shell of stars.
In an infinite universe the temperature of the dust would be much higher, in the visible range; about 3000 K according to Wikipedia.
In regards to our view, that is nonsense. The Milky Way is just part of the Universe, but close to us, and very very thick with stars. I covers a huge amount of our sky, and is the most luminous thing in the heavens, aside from the sun of course. It doesn’t need to be infinite, in regards to how bright and hot the galactic center is, and how close it is. From our perspective, with out dust blocking the light, it would be far brighter and hotter than the sun.
This assumes it is all dust blocking out the radiant energies. We actually are still discovering what is out there, new discoveries are a multitude. Like the discovery that there is likely a cloud of stars “outside” our galaxy, with as many stars in this huge cloud as there are in the main disk, what we used to think of as “the galaxy”. Which means the amount of light from the stars in our own galaxy is actually twice as much as previously thought. There is also most likely a huge cloud of dust as well, which is why we can’t actually observe these stars.
FXMastermind, imagine that there is nothing in our universe but our galaxy. If you removed all the interstellar dust in our galaxy, would the total amount of radiation from all wavelengths leaving our galaxy increase, decrease, or stay the same?
It was called a paradox in the first place because under the given assumptions, we would expect to see one thing, but instead see something else. Under Olber’s assumptions, we would expect to see incandescent-hot gas clouds, but we don’t see them. This does not mean that Olber was right; it means that there’s still a paradox, and hence Olber’s explanation is useless.
No, that is the error, the assumption is that any dust will reach the same brightness temperature as the starlight it is blocking. Since we do not observe this in our own galaxy, it isn’t happening here. So the dust is the reason the Milky Way isn’t a huge bright “object” in the sky.
The sky seems dark instead. Will the dust someday glow as bright as the galactic core? That doesn’t matter, in regards to the situation now. It’s obscuring dust (and probably other matter) that makes the sky seem dark, when we look at the Milky way.
Assuming no interstellar dust, what percentage of the night sky do you think would be covered in stars from Earth? Just a WAG? I think the answer is much much lower than you seem to think.
We actually have the situation Olbers described, our own Milky Way, and it does not glow like a wall of brightness, and heat, which is the assumption made for the entire sky, if it were solid stars.
So we don’t need to imagine if every point ends in a star, or why a sky full of stars isn’t bright. We have a section of the sky that we know is full of stars, and it isn’t bright. It isn’t bright because the light is being absorbed, and we know the absorbing matter has not become as bright and hot as the stars.
The claim is simple, “Any absorbing interstellar gas or dust would simply heat up until it reradiated all the starlight it absorbed, and the energy reaching us would be the same.” We know that isn’t true, because we actually are observing it has not happened. You can argue that in the future it might, but that has nothing to do with what is real, right now. Right now, in the real Universe, the sky is dark, instead of bright, looking directly at the center of our galaxy. So we know, in reality, that the light and heat isn’t reaching us from a huge galaxy center, which is right there, not millions of light years away.
If you can’t grasp this fact, it’s going to be hard to understand why Olbers was right.
No we do not. The centre of the galaxy is very dense with stars, but the stars are very small, and do not cover the entire sky, even in this region. If it were not for the dust in the galactic hub, we would be able to see right through it.
No, it’s not. It’s an entirely different problem. Explaining why the galactic center of our galaxy is so dark, or even understanding why Andromeda is so dim, isn’t Olbers paradox at all. Olbers explained that the reason we don’t see a sky bright, full of stars, based on the idea that there might be an infinite amount of them, so that every last point in the sky contains a star, is that the light is dimmed. There is simply something blocking out the light (dust).
My point is that it doesn’t even matter if every point in the sky is full of stars (actually it would be galaxies for most of it, but that is still stars). We have two fine examples of thick bright regions, that are for all practical reasons, full of stars. Even if only half of the region is solid stars, or we just look at the galactic center, which is almost a solid mass of starlight, we don’t observe a region of the sky that is bright like sunlight. It just isn’t there. Our Milky Way core would be brighter than the sun if the light wasn’t blocked, due to the sheer size in the sky. (the Milky Way covers almost a tenth of the sky)
The center of Andromeda would also be as bright as the sun. And about one quarter the size of the moon. Instead it’s a very faint object.
This is due to matter between us and the light. There is no other physical explanation.
Olbers said this was the reason the sky is dark. Somebody claimed the dust would glow as bright as the stars the dust is blocking. This has not happened. So for practical reality, what we now observe, it’s the reason the sky seems dark.
If there is some other explanation, I would love to hear it.
This is where you are mistaken. The total luminosity of the stars in the Galactic Centre is around 50 billion suns; at the distance of the galactic centre, this works out to be about magnitude -7; brighter than Venus but less bright than the brightest iridium flare.
And of course this brightness is spread out over several square degrees of the sky, so is diffuse- only visible in a dark sky. The masking effect of the dust is significant, but far from total.
:rolleyes:, yes well done you’ve overturned many years of conventional understanding on this subject and no you are no making basic misunderstanding
Firstly quibbling about what the original paradox is rather useless as it is a matter of history rather than science and as I didn’t state what the assumptions were it is difficult to see which assumption you think was not an assumption. Regardless it is clear from Olbers’ orignal statement of the paradox what his explicit and implicit assumptions were and these assumptions are incompatible with the idea that any interstellar dust could solve paradox or else the paradox would fail for much more trivial reasons which would’ve been clear to Olbers.
The (apparent) paradox is that what we would observe under a set of assumptions (e.g. an eternal, infinite, static Universe) that would’ve seemed reasonable to Olbers is not what we observe. Olbers incorrectly thought that adding dust to the model would resolve the paradox and it doesn’t for precisely the reasons previously stated.
There may be at least 100 billion stars like our sun, and many more not like our sun, nobody actually knows, but if it wasn’t for the dust the Milky Way would be incredibly bright. Look at the infrared image right above the optical one. The Milky Way covers over a tenth of the sky. If the visible light wasn’t blocked, it would be an immense and bright object in the sky. Even with the light spread out over such a large area, it would be a huge amount of light, and heat, reaching us. But it’s dim.
The reason Olbers explanation was rejected was that obscuring dust would glow as bright as the stars it blocked out. The Milky Way is almost as old as the Universe itself, but we don’t see the obscuring dust glowing brightly at all. In fact, it’s dark.
Remember, in reality we can only see about 6000 light years into our galaxy, the center is though to be 28,000 light years away.
Please do the maths before saying someone is wrong on the Straight Dope. We are supposed to be giving the correct facts here. My figure for the magnitude of the Galaxtic Hub assumes that the dust is not present.
100 billion suns is only twice the luminosity I quoted, and may be correct; but at 25,000 ly, assuming no dust, the magnitude of 100 billion suns would be -8.2474; only as bright as a thin crescent moon.
Utter nonsense, as I have demonstrated. Please do not state this again, as you might misinform someone who is serious about learning the facts.
Apparent magnitude of our sun: -26.74
Apparent magnitude of the Milky Way if there were no dust: ~ -5.1
Apparent magnitude of Venus at its brightest: -4.9
This is much lower estimate than my figure, and is likely to be much more accurate; I was assuming that the Milky Way was concentrated at a single point 25,000 light years away, but in fact most of it is much further away.
I’ll do you even better, here’s some info from somebody who knows the maths and the facts, and says it plainly.
That’s just a dozen or so light years across, a tiny little bit of the core, and of course it is an estimate. The core is more like 5,000 light years across, not a dozen. But moving on
But wait. There’s more.
And a lot of those billions are much closer than the center of the core.
BOOM! Just like I have been saying. But that’s just looking right at the tiny little central core. But just that little dozen light years across region would be brighter than the full moon!
Just the tiny little dozen light years across core section would be brighter than that. “If you looked in that direction, you wouldn’t see much else but the combined glow of billions of stars.”
There may be far more stars closer to us than anyone thought when the calculations above were done. Since we can’t actually see more than 6000 light years towards the core, (which might be 25,000 light years away, or 20,000, we don’t actually know), there is little doubt there be a huge amount of star light behind those dust clouds that make it look dark.
Remember I just showed you an impeccable source that claims just the center would be brighter than the full moon.
But none of this is actually about the brightness of the core, or even the Milky Way, it’s about the fact that even with our own galaxy almost as old as the Universe itself, the dust obscuring the stars isn’t glowing as bright as the stars it is blocking.
Which was the assumption used to say Olbers was wrong about his resolution of the paradox. If the assumption is right, that every point we can see is a star, no matter how close or how far away, which was the assumption that started the paradox, if that were true, his reasoning could indeed explain why the sky is dark.
Because it certainly explains why it’s dark when looking directly towards the very near and very dense regions of space that appear as a solid mass of stars, the center of our own galaxy.
You can argue that those esteemed astronomers I used as a source are wrong, but that would be ignoring facts.