Olber's Paradox

Jzz

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Olber′s paradox, which was first formulated by the German physicist ands astronomer Heinrich Olbers, states that the sky is not uniformly bright although it contains, to all intents and purposes, an infinite number of stars. In other words going strictly by the facts, the night sky should be as bright as day, the paradox lies in the fact that this is not the case. But does the present day explanation that Olber′s paradox exists because the Universe is expanding and that light from distant stars has not yet reached us, make sense? Keeping in mind that Olber's paradox had been formulated in 1823, when the Milky Way Galaxy had not even been identified, how pertinent is Olber's paradox in today's world. The answer is that Olber's paradox is even more pertinent today than when it was first formulated, because as both the JWST and the HST demonstrate, every bit of space in all directions seems to be filled with stars. Revisiting Olber's paradox reveals several new and surprising facts about light.

Imagine walking on a moor on a moonless night, the power is out and only candles are available. Everything around is in darkness, even the path is very indistinct. Suddenly, as you look up you see the light from a candle. There are several weird things about this candle light, (1) the first is that only the candle flame is visible nothing around it is visible, the reflected light from objects close to the candle cannot be seen (2) if you take a step back the light from the candle light disappears, it is no longer visible. What is happening? The first question to ask is: Why does the light disappear? Obviously, the answer is that there is not enough intensity in the candle light to travel further, the light from the candle can travel so far and only so far before its intensity becomes too low to detect. The question is why; power is still available, the candle is still burning, obviously enough tallow and wick is present to keep the candle burning, why then does the light stop at the precise boundary that you have perceived? How is it that given the fact that the light follows the inverse square law as it travels, meaning that it spreads out directly according to the square of the distance travelled (isotropic light), that only the candle is visible, nothing around its immediate surroundings or your own surroundings is made visible by the light from the candle. Why? Surely, if light spreads out according to the direct square of the distance travelled, some small portion of the surroundings should be illuminated? But this is not the case, the light seems to be visible as a point of brightness and nothing more. What is happening? For anyone, standing on the circumference of the place where you are standing, and with the candle at the centre, the candle flame is clearly visible, but nothing else? Could this have anything to do with the rectilinear nature of light? Numerous experiments have shown that the energy of the photons detected on the circumference that the light covers all have the same energy and therefore intensity. One thought that comes to mind is that light varies not only in frequency but in intensity and in this particular instance, only the most intense light makes it to your location. This would account for the pin point nature of the candle light and also for why stars appear as points in the sky and not as a spread out illumination.

Surely, this is a far more cogent explanation for Olber′s paradox than to think that the Universe is expanding so rapidly and so fast that the light from distant stars never reaches us? Namely, that for a given amount of power, light travels a given distance, it cannot go any further than that power allows. Increase the power and increase the distance over which light is detectable, keep the power at a fixed level and it doesn′t matter for how long that light is on, it cannot travel one iota further than the power supplied to it allows.

It is possible that one could improve the sensitivity of the receiver but that is beside the point, the fact to take cognisance of is the manner in which light travels, not all light is equal it would seem, the most intense light travels further and it is only as one gets closer to the light that other features begin to emerge. Also , whatever, the sensitivity of the receiver used to detect the light, the fact remains that light only travels as far as the power that supplies it.
 
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We have telescopse could detect a candle flame on the Moon. You want to see one farther away? Just build a bigger mirror.
Olber's Paradox is resolved by the fact that there is a lot of dust in the universe. Also, there is not an infinite number of stars. And the visible universe is of finite radius as observed from Earth.
 
But does the present day explanation that Olber′s paradox exists because the Universe is expanding ...
Yes. There was a time period when all the sky was extremely bright everywhere. This happened at Recombination, when atoms first formed. The temperature was around 3000K and you would only see a matter of a few mm prior to atoms forming.

That same glow is there but the expansion has moved that glow to beyond the visible range, so we only see stars (galaxies, etc.) that formed much later.

It wasn't until the early 1930s that an expanding universe idea became respected. Until then, everyone assumed the universe was static. Friedmann seems to have given Einstein the first hint, but he rejected it.

It is hard to imagine that space isn't a nothing. How can something so frictionless carry galaxies away? It's amazing BBT every came about. It did so, IMO, because Einstein's math equations of GR favored expansion, but he, and others, rejected the idea. They kept trying to patch things, as was the case of Einstein's cosmological constant, which pushed galaxies just enough to keep them from their collapse together due to gravity.

Einstein in 1931 quickly adopted Lemaitre's expansion model thanks to the help from both Eddington and deSitter.

and that light from distant stars has not yet reached us, make sense?
But even then we will see gaps between all the galaxies.
Keeping in mind that Olber's paradox had been formulated in 1823, when the Milky Way Galaxy had not even been identified, how pertinent is Olber's paradox in today's world. The answer is that Olber's paradox is even more pertinent today than when it was first formulated, because as both the JWST and the HST demonstrate, every bit of space in all directions seems to be filled with stars. Revisiting Olber's paradox reveals several new and surprising facts about light.
The elimination of the paradox is one of many arguments favoring the BBT.


One thought that comes to mind is that light varies not only in frequency but in intensity and in this particular instance, only the most intense light makes it to your location. This would account for the pin point nature of the candle light and also for why stars appear as points in the sky and not as a spread out illumination.
In a static universe with infinite stars, there would be candles behind the candles adding more and more flux, so it would never become dim.

The expanding universe would redshift the more distant candles so that they would become invisible causing the forward candle to dim with greater and greater distance.

Surely, this is a far more cogent explanation for Olber′s paradox than to think that the Universe is expanding so rapidly and so fast that the light from distant stars never reaches us? Namely, that for a given amount of power, light travels a given distance, it cannot go any further than that power allows. Increase the power and increase the distance over which light is detectable, keep the power at a fixed level and it doesn′t matter for how long that light is on, it cannot travel one iota further than the power supplied to it allows.
That is quite correct with one candle in the universe. But what if the observer is surrounded by candles?
 
Olber's Paradox is resolved by the fact that there is a lot of dust in the universe.
Given enough time for an infinite universe with an infinite number of stars, which was the view before, say 1900, even the dust would glow white hot.
Also, there is not an infinite number of stars. And the visible universe is of finite radius as observed from Earth.
Yes, and at some point all the starlight of the more distant regions has redshifted beyond the visible range.
 

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Yes. There was a time period when all the sky was extremely bright everywhere. This happened at Recombination, when atoms first formed. The temperature was around 3000K and you would only see a matter of a few mm prior to atoms forming.

During the recombination stage, electrons protons and neutrons combined into atoms, which were mainly hydrogen atoms at this early stage. How does light enter into the picture? Light is made up of photons, and the frequency of all visible light lies in the range of Terahertz per second. The accepted view is to regard photon frequency as non-existent and to think of atoms as emitting and absorbing photons in a one-off kind of process: an electron (cloud?) within the atom absorbing a photon, transitioning to a higher level and then dropping down to a lower energy level and emitting a photon that has an energy value equal to the difference in energy levels. I think that this is a very stunted view of the photon emission and absorption processes within the atom. This is especially so when one looks at smart phones where data is processed at the Gigahertz rate. If data can be processed at such a rate, it is almost a given, considering the infinitesimal distances that the electron has to oscillate, that electrons oscillate at the rate of hundreds of trillions of times per second and absorb and emit photons at those rates. The working of atomic clocks bears out this view of the rate of absorption and emission of photons by electrons. It is supposed that any recombination of sub-atomic particles into matter would also have been accompanied by the creation and emission of photons. Therefore, this early wall of light must have been composed of unimaginably large numbers of photons. The recombination process could have continued for hundreds of thousands and even millions of years. What happened to all those photons, they could not have passed over the edge of the Universe, since by definition nothing exists there, they therefore accumulated in the Universe and form the background medium that allows for the propagation of light as observed today.


It wasn't until the early 1930s that an expanding universe idea became respected. Until then, everyone assumed the universe was static. Friedmann seems to have given Einstein the first hint, but he rejected it.

The theory of an expanding Universe, ignores a very important aspect of the expansion. Since light has a finite speed, when we speak of light that reaches us after travelling billions of light years surely the light that reaches us tells us how the Universe was billions of years ago and not as it is now? Therefore, when we examine light from such huge distances, we are in fact looking back into the past. This fits in very well with the BBT since the further back (i.e., the more distant) we look, the further back into time we are seeing and the faster things appear to be moving. It therefore, makes perfect sense that the more distant stars appear to be travelling away at greater speeds than stars that are closer.


The elimination of the paradox is one of many arguments favoring the BBT.
True, but has Olber’s paradox been truly eliminated, or eliminated solely because of dust and the expansion of the Universe? If we accept the fact that the further away we look, the closer to the Big Bang we are seeing, then surely the speeds with which stars and Galaxies are travelling would also vary with the time line? That having been said, the amount of energy that each star puts out should also play a part. Stars and galaxies would have varying ages and varying amounts of energy to output. Would this contribute to the solution of Olber’s paradox.

Lastly, I hope that my reply is not taken personally, but in the spirit of enquiry, so important to a better understanding of science.
 
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The CMBR - Cosmic Microwave background - fills all space. We cannot see microwaves but can detect them so in a way the sky is lit by light almost everywhere. So, no paradox.
 

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We have telescopse could detect a candle flame on the Moon. You want to see one farther away? Just build a bigger mirror.
Olber's Paradox is resolved by the fact that there is a lot of dust in the universe. Also, there is not an infinite number of stars. And the visible universe is of finite radius as observed from Earth.
Do you think this statement actually makes makes sense? Could an earth bound telescope really see a candle on the moon? Surely not. Think of all the noise, the light from great cities interfering with the signal. Even ignoring all this, surely, the amount of light available would vary as the inverse of the square of the distance? Which is to say that since the sun is 149,597,870,700 metres from the sun or roughly 150 billion metres from the sun, then the luminosity of the candle would reduce from 1 candle, to 1/2.25 x 10^22 times. If a lumen is about 1 w, then it would be reduced to 4.44 x 10^-23 W by the time it reaches earth. I doubt if any optical telescope would be able to detect such a low signal.
 
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Not only can we detect a candle on the moon, we can detect it in full moonlight. Lots of noise. We can now detect signals far below and inside the noise.

Radio, invisible light has come a long way. Some transmission methods appear to transmit a band of noise.

If you were to listen to it, it would just sound like a small increase in background static. But the true signal could be a high res video signal.
 
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Jzz

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Not only can we detect a candle on the moon, we can detect it in full moonlight. Lots of noise. We can now detect signals far below and inside the noise.

Radio, invisible light has come a long way. Some transmission methods appear to transmit a band of noise.

If you were to listen to it, it would just sound like a small increase in background static. But the true signal could be a high res video signal.
Nice answer but perhaps overly pretentious and overbearing. In fact, I had visited the Keck Observatory web site where the boast had originally been made, that their keck telescope could detect a single candle on the moon. Guess what? They have no record of it and no information either, in fact the original link ( https://keckobservatory.org/geninfo/about.php#INSTRUMENTATION ) has been removed and I for one need no second guesses as to why this is so. In any telescope there are two main factors both of which are dependent on each other and both problems are resolved in the same way. The two factors that every Telescope depends on are resolution and sensitivity. To be useful the lens of the telescope has to be equal to the wave length of the EMR being observed. With radio waves and micro waves wave-lengths of a few metres are common but with light you are dealing with 0.0000005 m long wave lengths and very difficult to resolve. If the atmosphere is taken into account it becomes worse. . Very important is the power available from the signal which in this case is 2.25 x 10^-23 W !
 
I remember reading, many years ago, that a big telescope could detect a candle on the Moon. I don't know the source.
I do know that we have detectors that can count individual photons. I also know that the number of photons put out by a candle is astronomical. It is only reasonable to assume that at least one of them would reach a large telescope at the distance of Earth.

The number of photons is equal to Planck's constant times c divided by the wavelenth of the light. For yellow light at 600 nm, this is 3e-19 J. A candle flame is about 80 watts, thus puts out 3e20 photons per second.
Those photons paint the inside of a sphere of the same radius as Earth is from the Moon. Area equals about 2e19 m^2.

So the candle would be sending 1.5 photons per second to each square meter on Earth.

Thus the statement that a telescope on Earth could detect a candle on the Moon is accurate. It could not image it as anything but a point, but a 100 meter telescope on Earth would be getting about 10 thousand hits per second.
 
The light of the total chaos of background universe is so fantastically luminously lit it ascends and descends into darkness! The darkness of too much light . . . too much accumulation of chaos . . . thus an infinity of point-horizon universes, an "Infinite MULTIVERSE Universe," and the collapsed cosmological constant (/\) of Planck/Big Bang 'Mirror Horizon' . . . altogether the same nonlocal, nonrelative, background in superposition!

Illustrations of the "observable universe," illustrated in the "past histories past light cone," light the infinitely light filled background so little, so finitely, as if the infinite density of light information therein wasn't in fact dark!
 
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I remember reading, many years ago, that a big telescope could detect a candle on the Moon. I don't know the source.
I do know that we have detectors that can count individual photons. I also know that the number of photons put out by a candle is astronomical. It is only reasonable to assume that at least one of them would reach a large telescope at the distance of Earth.

The number of photons is equal to Planck's constant times c divided by the wavelenth of the light. For yellow light at 600 nm, this is 3e-19 J. A candle flame is about 80 watts, thus puts out 3e20 photons per second.
Those photons paint the inside of a sphere of the same radius as Earth is from the Moon. Area equals about 2e19 m^2.

So the candle would be sending 1.5 photons per second to each square meter on Earth.

Thus the statement that a telescope on Earth could detect a candle on the Moon is accurate. It could not image it as anything but a point, but a 100 meter telescope on Earth would be getting about 10 thousand hits per second.
The problem might be found in the noise. A terrestrial scope is stuck with a light flux from the sky that isn't that insignificant, especially with today's light pollution. A space scope will still have to see Earthshine on the dark side of the Moon.

[I can't imagine how a candle could be seen on a full Moon since each tiny surface feature on the reflecting Moon would vary in brightness often more than the candle. Perhaps I'm wrong.]

By chance, I was reading a little astro history and just read that the 100" Hooker, IIRC, was deemed capable of detecting a candle at 15,000 km. [It didn't say if this was with or without a camera, so I assume this is a visual statement.]
 
Yes, noise would be an issue and it would need to be done with a shadow background and no skyglow.
I backpacked up into the Andes to photograph Halley. I wanted to get as high an altitude as possible. I got to 10,000 feet, set up, it got dark. Skyglow was so bright it was not a dark sky. Like a hazy glow everywhere.
 
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Yes, noise would be an issue and it would need to be done with a shadow background and no skyglow.
I backpacked up into the Andes to photograph Halley. I wanted to get as high an altitude as possible. I got to 10,000 feet, set up, it got dark. Skyglow was so bright it was not a dark sky. Like a hazy glow everywhere.
Ug, that was a worse experience than my travel south for 60 miles to see the comet. It was a clear night and as I was establishing my focus on Saturn when, suddenly, the focus became worse and worse. I looked up and within seconds the entire sky was overcast.

But, we were near a tank (pond) and I had a flashlight. With a little effort we got a nice comet-looking reflection off the lake. ;) We showed our wives that image and they took it hook, line and sinker. Of course, we did tell them soon thereafter.

I've mentioned it before, but even at high elevations particle counts can be too high for good seeing. I read where the night Hubble imaged his variable in M31 the count was a level 1, which is when the Mt. Wilson closes the dome. [The next night was much better and he added, IIRC, 5 minutes extra to his imaging in order to nail the variable or nova.] McDonald Obs. also monitors particle counts and will shut down when too high.

When stars that are as hot as the Sun, or hotter, have a distinct yellow tint and are relatively high altitude, you can bet it's about time to close the dome. This happened to me during a lunar eclipse viewing through their [McDonald] 8" Dob when they showed us a red dwarf companion to a hotter than the Sun star. The dwarf was very red, which is unusual, and the white hot star was definitely yellowish. This was back when I was pushing the Sun has not a hint of a tint of yellow (seen from space). It shocked me since with the notion that I could be wrong -- me, the world's only heliochromoloigst. ;) I assumed the air to be more pristine at such elevations.
 
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I sat one night in the hills near Characato, near Arequipa, far south of Peru, up in the mountains. Arequipa had the same population as San Francisco, but, in 1986 had nothing but incandescent and sodium street lighting. What they had was sparse. It was a golden yellow that did not interfere the least with sky observations. The air was very clear. Off to the north Vocan Misti showed a small plume of steam. It was surreal.
One night up in the mountains I was setting up my tent when two men showed up with AK's. In Spanish they said they were there to protect me from bandits. Stayed all night, left in the AM. These were villagers. Shining Path was active at the time.
 
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I wrote about 10,000 words on the trip, it was a great one. It's in a Wordstar file somewhere. Probably on a floppy. I have hard copy but its like 15 pages, too much to scan. I have photos around somewhere, I'll look.

I can summarize the most important learning: Go to any town in Peru, there will be a guy in native garb, sitting on the sidewalk with a blanket piled high with small green leaves. Get some. Chew them. Thank me later.
 
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