Why is space black??

[Hawkpalmer]

Hey all,

Just curious as to why space/universe is mainly the colour black? Is there a valid/logical reason for it to be black or is it because we (humans) are limited by what the eyeball can see??

Sorry if it's a dumb question and been covered already but my knowledge of these things is very basic but I d like to day dream and think, lool

Thanks

Richard

[Macavity]

A little light(?) reading: Olbers' paradox - Wikipedia, the free encyclopedia

[barkis]

HehHeh!, you beat me to it Mac. I was going to refer him to 'Olbers Paradox' .

Ron.

[Earl]

Space is not black it has no colour so appears black, which is also only true in the spectrum of light we can see, space is far from empty blackness with the aid of HA CCD imaging.

[Hawkpalmer]

Thanks for the link Macavity on Olbers paradox but was hoping for more of an idiots guide to an explanation, lol my head hurts after reading that link.

@ Earl_uk thanks for that.

I appreciate that space isn't empty blackness ect but why/how is it we perceive it as black??

I remember watching a documentary about light and what humans can/can't see and it said that we can only see approx (I think) a small % of the actual colours that's are out there or something?? Also remember something about a blind/partially blind person who could only see in infra red spectrum and/or see colours the average person cannot??

So do other living animals/creatures ect see the same colours/lights as humans??

An idiots guide maybe better for my brain to understand please? Lool

[Macavity]

Thanks for the link Macavity on Olbers paradox but was hoping for more of an idiots guide to an explanation, lol my head hurts after reading that link.

It's a tricky concept. Otherwise: I'd just say something like (most of) space is a "Black Body" at about 3 deg Kelvin (The cooled-off Big Bang!) and the "colour" (or rather spectrum) of this is determined by fundamental "Physics"... This is perceived by our eyes (stars, nebulae etc. excepted) as being: BLACK. It spectrum actually corresponds to the Cosmic Microwave Background - Which of course, being microwaves, we cannot see.

Wikipedia links can "go on a bit", but it's in here somewhere:

Thermal radiation - Wikipedia, the free encyclopedia

Black body - Wikipedia, the free encyclopedia

[DarkStar7]

Olbers' paradox - Wikipedia, the free encyclopedia

I believe it's something to do with the fact the universe is expanding and so very distant light can never reach us .

[Space Bat]

Space isn't black

we only see what is termed the visible spectrum....so for the stuff that is there emitting at different wavelengths other than visible - we can't see it so is not in our capability to observe.

Just as some social insects see in visible down to UV and other species of animals see visible to infrared

Some deep see aquatic animals see with vibration of water molecules and sound....etc

We just don't have to ability to see that Space isn't black

[AllanJ]

Space is beige.

See the NASA picture of the day from 2009 at

APOD: 2009 November 1 -The Average Color of the Universe

I quote "What color is the universe? More precisely, if the entire sky were smeared out, what color would the final mix be? This whimsical question came up when trying to determine what stars are commonplace in nearby galaxies. The answer ... is a conditionally perceived shade of beige. "

Allan

[lw24]

As humans, we 'see' visible light, therefore making the space seem black (it is in visible light) to us. We see visible light due to the light our sun produces. It predominantly produces visible light, and therefore life on Earth has adapted to see, and analyse visible light.

Life on other planets orbiting different suns may have adapted to see and analayse different light (on the Electro Magnetic Spectrum). So, for example, they may see Infared. Therefore, to them, space may not be black.

Clear Skies

Luke

[Earl]

I appreciate that space isn't empty blackness ect but why/how is it we perceive it as black?? l

Simply our eyes do not see the wavelengths of light that is emitted so we see nothing hence the blackness.

The expansion of the universe is why we are not in a sea of light from all the stars in the universe. There is a point where space expands faster than the speed of light, anything beyond that point will always be invisible. Now I dont know if this point is a fixed radius from us, or is a shrinking POV due to the acceleration of the expansion of space.

[acey]

The colour of space is "microwave", with peak wavelength at about 2mm. This is because if you look anywhere in space you will have cosmic microwave background radiation coming at you. But our eyes can't see that wavelength, and even if they could, they would also need to be very sensitive in order to see the glow.

Cosmic microwave background radiation - Wikipedia, the free encyclopedia

The night sky viewed from Earth is not really black: radiation is re-emitted by atmospheric molecules producing airglow even in the complete absence of other light pollution.

Skyglow - Wikipedia, the free encyclopedia

But our eyes aren't good at detecting that either. Hence space looks black.

[themos]

A beautiful picture of the "airglow" in the upper atmosphere

[ollypenrice]

EE Barnard debated long and hard over whether his dark nebulae were holes through which the depths of space could be seen or obscuring patches of dark material. The presence of something or the absence of anything? By the end of his life he had concluded that they were obscure patches of dark stuff - correctly as it now seems.

In this Pelican NAN, note the dark sooty obscuring clouds of dust between the main nebulae, far darker than the background sky.

Olly

http://ollypenrice.smugmug.com/Photography/Widefield-images-including/NAN-FINISHED/1140503434_oQfB2-XL.jpg

[Space Bat]

But the dark stuff aint that dark in other wavelengths such as IR

[scogyrd]

It's black because of the same reason the grass is green, e.g. our brains are wired up in such a way that it appears black to us. If you were a dog the grass would be grey and if you were a snake the sky would be multicoloured because (I think) they can see infrared.

However I could be wrong about this.

[DarkStar7]

Simply our eyes do not see the wavelengths of light that is emitted so we see nothing hence the blackness.

The expansion of the universe is why we are not in a sea of light from all the stars in the universe. There is a point where space expands faster than the speed of light, anything beyond that point will always be invisible. Now I dont know if this point is a fixed radius from us, or is a shrinking POV due to the acceleration of the expansion of space.

I have a real problem with statement. It is a statement made on numerous occations by respected scientists. How can it be justified? Space is some 'thing' and as such can not be perceived to travel faster than light relative to a stationary observrer. It seems a cheat of Einsteins ideas. I can understand superluminal speed can happen because of the perspective of observing. But surely nothing can be perceived to travel faster than light relative to me as an observer. Even in entanglement of particles, no particle is actually traveling faster than light. Please can someone try and convince me otherwise.

[JulianO]

Light is just the fastest way information can travel across space. But space can expand at any speed.

If you think of the oft quoted balloon analogy, and start blowing up a balloon. You transfer information using trained ants that can walk at 1cm/s, they are the speed of light. They have no problem delivering stuff to nearby places, but if you blow the balloon up quite quickly, if they try and get something to the other side (and this is a balloon that never bursts no matter how big it gets) if the balloon is blowing up fast enough, they'll never get there.

E.g., if the balloon's other side is 10cm away, and an ant sets off there. After 1 second its covered 1cm, but the balloon is blowing up, and the other side is now 15cm's away. So its made 1cm progress but is now effectively further away than it was when it started out.

In this model, as ants are the fastest thing in this world, you can never know whats beyond a certain distance, and you'll never be able to reach the other side.

[themos]

But space can expand at any speed

There is no way that you can make the "inflation" of spacetime (which is measured in % per year) come out like a speed (which is measured in meters/second).

[AstroGnome]

We see visible light due to the light our sun produces. It predominantly produces visible light, and therefore life on Earth has adapted to see, and analyse visible light.

Nearly right. The reason some life evolved to see the visible is more to do with our atmosphere which is nearly totaly transparent at visible wavelengths but blocks a lot of UV and IR either side of it. So our eyes evovled to detect the band of radiation that was most prevelant.

See: http://www.udel.edu/Geography/DeLiberty/Geog474/spectrum.jpg

M....

[JulianO]

There is no way that you can make the "inflation" of spacetime (which is measured in % per year) come out like a speed (which is measured in meters/second).

Ok...... ermmm - No way? That's quiet a bold statement

How about the red shift velocity, or recessional speed of distant galaxies, or the hubble parameter itself (which is usually quoted in terms of km/s / Mpc) which one way of looking at is it expresses how fast a galaxy one Mpc away is receding in km/s?

To an ant on a balloon looking at a distant point it looks very much like a velocity.

[Space Bat]

Does time travel faster than Space expansion or Light ?

[JulianO]

Time travels at 1second/second... :-)

[themos]

How about the red shift velocity, or recessional speed of distant galaxies, or the hubble parameter itself (which is usually quoted in terms of km/s / Mpc) which one way of looking at is it expresses how fast a galaxy one Mpc away is receding in km/s?

That involves a particular length scale and so the units come out looking just like a velocity.

[JulianO]

That involves a particular length scale and so the units come out looking just like a velocity.

So there IS a way