Why isn't the night sky completely lit up with all-white light?

Originally posted by fourthmeal
reply to post by NewAgeMan

 

imagine.gsfc.nasa.gov...
cosmology.berkeley.edu...

Because visible light output drops by a factor of 4 for every doubling of distance. And we are a LOOONG way away from any of those stars.

And the atmosphere blocks a bit of light too.

One question though - that's for distance from a light source, but what of the idea that stars long extinguished who emitted light eons ago is also light passing us now, cumulative light from all stars both alive or dead all along that line of sight..? Some of those photons might have hit something in between but what of all the one's that got through, don't they the photons "stack up"..? I can't help but think that there ought to be a cumulative factor for all photons along each line of sight no matter how far the stars are away or when they lived or died.. help? I still think there's something missing from this apparently simple explanation.

Originally posted by Arbitrageur

Originally posted by elfie
Olber's paradox

A technical explanation.

The inverse square law, as stated above, is also a good explanation.

Actually Olber's paradox assumes an infinite number of stars.

A simpler solution to Olber's paradox is that the number of stars is huge, but finite.

I have never seen this as much of a paradox with a finite number of stars. Some galaxies are so distant that one photon arrives at your eye every few seconds. The light is hitting your eye but that's not intense enough for your eye to detect it.

Simple.

Not so simple when you factor in every photon from every source all along that sightline (whereby every sight line is filled with stars and galaxies and light sources) which has had sufficient time to arrive.

As I understand it, the inverse square law applies to our galaxy, which to a degree IS visible, but as to the rest, the only possible way that the light isn't cumulatively visible, is because it has't got here yet, but then again, the telescope can see it by ultra-magnification..so I guess the inverse square law still applies..

Olber's paradox seems to suggest that there's more to this quandry than "meets the eye"..


bump quote for further pondering

Originally posted by NewAgeMan
However, if you took the Hubble Space Telescope and created a wrap around image enveloping the earth at every point of the sky, and at variying magnifications, what would be seen would not be a black sky dotted with stars, and a hazy river-like Milky Way in one section, or even a nebula here and a galaxy there, with black space in between - but a dome of nothing BUT stars and galaxies without any black in between whatsoever!


Thus, even though we cannot see it with our eyes, seeing "only" the local stars in a very very small sphere of space within the Milky Way Galaxy, what's mind-numbingly AWESOME is that in truth, the whole sky IS "bejeweled" every single point of it, all around the whole earth - think of that next time you look at the sky either during the day (imagining what's behind the blue) or during the night (what's in between the stars that are visible).

Space absorbs energy where it travels into the past. As long as the light generation source is drawing more energy out from the future, there is the balance and the 2nd law of thermodynamics.

reply to post by NewAgeMan

Yes it's simple because photons are coming, but the rate is too low for your eye to detect. If you opened a camera shutter and just collected light for a long enough period of time, eventually enough photons would hit the receptor to be detected and the sky would appear to fill up with much more light than we ordinarily see. The light is there, but the intensity is too low to be detected without long time exposures

Even with a long exposure like the Hubble Deep field, you can see there is black between the light parts.

en.wikipedia.org...:Hubble_ultra_deep_field_high_rez_edit1.jpg


The fallacy in your logic is that you think you know what's along each line of sight, but you don't. As the above image shows in over 3 months of collecting light, there is still more blackness than light, and even where you see light in the above image, most of it is too faint for your eye to detect when looking at the sky, due to the small number of photons reaching your eye. The lights only show up here because months of exposure on the Hubble is way more sensitive than your eye.

reply to post by tkwasny


That's another question which for me defies relativity in that there is only one now, regardless of relative motion or the speed of light. Time cannot be relative, only constant.

reply to post by Arbitrageur

Nice photo!

I'm not sure the paradox is so easily resolved as people think, as can be seen when reading through the wiki article on the Olber's paradox, which reveals that I wasn't an idiot to pose the question.

If anything the "point" I'd like to highlight is that every point in the sky encircling our world, is filled with stars and galaxies - is it bejeweled the entire sphere or dome surrounding the earth.

Remember the Hubble pointed at an apparently blank piece of sky the size of one square millimeter held at arms length..

Originally posted by NewAgeMan
If anything the "point" I'd like to highlight is that every point in the sky encircling our world, is filled with stars and galaxies - is it bejeweled the entire sphere or dome surrounding the earth.

The Hubble Deep Field image suggests to me that this is NOT the case.

We peered into a black area of space, and still, most of it is black!

I'm impressed by the lights we found, but don't overlook that black still dominates the image.

reply to post by NewAgeMan


Hi im from wyoming and when i go camping or go into the hills away from town the sky is nearly completly white, its frickin amazing especially in the mountains

We only see in a certain spectrum, and this channel has some boundaries. Not sure if humans see everything in space, could be that not only is our UV spectrum defined to a narrow 98 FM station, but, our atmosphere does the rest.

reply to post by Arbitrageur


The Hubble image is of a dot of sky the size of a square milimeter held at arm's length.. take that point and add the other 10 or 100 million such points which encircle the globe and you'll start to get the picture in terms of what I mean by "bejeweled".

reply to post by kimmitchell

Are you a fan of the band Max Webster.. re: Kim Mitchell.

Well theory goes, if you believe in the hot big bang (personally i think its the best and most supportive of observational data that we have,, but yep please explain any others to me, I have a masters in Physics and Astronomy and a PhD in physics, and unlike alot of people would say of an academic, i do find theories very very interesting) that as the universe expanded (remember it is an expansion of space, not an expansion in space) the environment was at ultra high energy and what existed was a soup of exotic particles... quark sea people have postulated.

As the universe expanded the energy density reduced until eventually stable matter 'condensed' out of high energy gamma rays. Now there is an issue about how this happens, it would produce equal amounts of matter and anti-matter. However the theoretical fix for this is CP violation in the quark and lepton sectors... it has been observed in the quark and there have been hints in the leptons...

So when this condensation happened, it represents the point at which the universe switched from being photon dominated, and matter dominated. Photons do remain from this process... these are redshifted down from being high energy gamma rays to a couple of kelvin energy microwaves. If you look at the night sky in microwave, you do indeed see a constant glow everywhere, it is in fact extremely uniform as you expect.


On objects that are far away at the edge of what you see... well these objects are probably made up of super massive stars, the early galaxies that formed would probably have contained very dense gases compared to what we see now. Stars that are big, are very short lived also... so the early universe would have been a mix of supermassive stars forming and going nova, along with smaller red stars that probably still exist today, slowly burning away their fuel.

The sun is a second or maybe third generation star, and is actually quite unusual as is one of the heaviest 5% of all stars in the galaxy.

Furthermore, you cannot look in all directions in the optical, we are blocked off by dust when we look towards the galactic centre, we have no idea what is behind it really.

because it's like the man wants to make you think you are on a planet but it's all just a matrix man

reply to post by syrinx high priest

Or maybe we're supposed to be the jewel in the crown framed by a non-local, holographic universe, which would be very embarassing for us, you would think - bad enough that we've already gone and transmitted "I Love Lucy" and Hitler's Olimpic Games radiating outwardly at the speed of light.

Originally posted by NewAgeMan
The Hubble image is of a dot of sky the size of a square milimeter held at arm's length.. take that point and add the other 10 or 100 million such points which encircle the globe and you'll start to get the picture in terms of what I mean by "bejeweled".

It's a DARK patch of sky. If you look there with your eye you see almost nothing. Even with Hubble's super-huge light gathering capability compared yo your eye, and even with a super-long time exposure, it's still mostly black. I think the idea that it's full of light is a mental construct in your mind that's not supported by photographic evidence in reality, and what light exists is so faint we can't see it.

If you pick 10 random points in that Hubble deep field image, probably at least 9 of them will be black. The absence of light far outweighs the light even in that extreme image. And even where there is light in that image, it's not visible to the naked eye for the most part.

reply to post by NewAgeMan


Whoa now! "I Love Lucy" is one of the greatest shows of all time. Don't hate!

In answer to your question, I think there are a whole host of factors involved, most of which should be pretty obvious.

Light pollution, atmospheric interference, space dust, the wavelength of the light....

reply to post by Arbitrageur


Ok forget about the light - there are 10,000 galaxies on average in every square millimeter of the sky, all around the sphere of the earth, for which there are something like 10,000,000 or more.. such points, that's what we're really in the middle of, aside from our own galaxy, just think about it - anyone's who's not awed by that doesn't have their head screwed on right.

reply to post by NewAgeMan


Reason one: clean your glasses
Reason two: stop spanking it
Reason three: step out your front door and look up
Reason four: go to the country side
Reason five: maybe you use up your lucky stars
Reason six: comb back your hair
Reason seven: forgot to take off your sleeping cap
Reason eight: Stop smoking the weed
Reason nine: maybe you need to move away from Washington state
Reason ten: Maybe you are on the wrong planet

anyhow I see all the stars every night unless cloudy. so maybe you live in the city where lights take away the view of stars, or you live next to HAARP and under a dark cloud most the time.... anyhow hope you find your lucky star soon.

reply to post by NewAgeMan


Regions of neutral atomic hydrogen effectively absorb photons at sufficient energies:

H I region

For our galaxy, these regions are nearly everywhere.

An area where H I is minimized:

Lockman Hole

Originally posted by ErosA433
Well theory goes, if you believe in the hot big bang (personally i think its the best and most supportive of observational data that we have,, but yep please explain any others to me, I have a masters in Physics and Astronomy and a PhD in physics, and unlike alot of people would say of an academic, i do find theories very very interesting) that as the universe expanded (remember it is an expansion of space, not an expansion in space) the environment was at ultra high energy and what existed was a soup of exotic particles... quark sea people have postulated.

As the universe expanded the energy density reduced until eventually stable matter 'condensed' out of high energy gamma rays. Now there is an issue about how this happens, it would produce equal amounts of matter and anti-matter. However the theoretical fix for this is CP violation in the quark and lepton sectors... it has been observed in the quark and there have been hints in the leptons...

So when this condensation happened, it represents the point at which the universe switched from being photon dominated, and matter dominated. Photons do remain from this process... these are redshifted down from being high energy gamma rays to a couple of kelvin energy microwaves. If you look at the night sky in microwave, you do indeed see a constant glow everywhere, it is in fact extremely uniform as you expect.


On objects that are far away at the edge of what you see... well these objects are probably made up of super massive stars, the early galaxies that formed would probably have contained very dense gases compared to what we see now. Stars that are big, are very short lived also... so the early universe would have been a mix of supermassive stars forming and going nova, along with smaller red stars that probably still exist today, slowly burning away their fuel.

The sun is a second or maybe third generation star, and is actually quite unusual as is one of the heaviest 5% of all stars in the galaxy.

Furthermore, you cannot look in all directions in the optical, we are blocked off by dust when we look towards the galactic centre, we have no idea what is behind it really.

Here's another question

Originally posted by fourthmeal
reply to post by NewAgeMan

 

imagine.gsfc.nasa.gov...
cosmology.berkeley.edu...

Because visible light output drops by a factor of 4 for every doubling of distance. And we are a LOOONG way away from any of those stars.

And the atmosphere blocks a bit of light too.

Why does light, in the vacuum of space follow the inverse square law - what's stopping or limiting the photons according to that law, why don't the photons just continue on..?