is it just nothing? if i went to space with an open jar, closed it in space, and then studied what was inside, would there just be nothing? not a single atom? a photon maybe? how is space black if it is nothing?
In: Physics
There is a small amount of stuff in most places. Close to the Earth there is still some oxygen, water, nitrogen and such which have escaped the Earth atmosphere but is not quite out of the gravitational well yet. Some of these are captured in the magentic Van Allen belt around the Earth. The Sun have a similar field of particles around it but much less dense and it goes much further out. Even going beyond all the planets. The Voyager probes are currently crossing the boarders of this region and have probably crossed most of it. Beyond the solar system there is also a gas and dust cloud throughout the galaxy. Some places this becomes dense enough that it blocks light, although only when several light years deep. Even between the galaxies there is a thin vail of gas and some dust. As for the density of any of this it is very low. Your jar is probably not going to contain any single atom even as low as the orbit of the ISS.
Space is (mostly) black because there has been no time since the big bang for the light of most stars to reach us. It is not really black, it’s just dark.
Space is basically the absence of matter it is very nearly a vacuum with occasional hydrogen atoms and a few others wandering past.
The amount of “stuff” in space varies depending on how far out you go.
Just beyond the limit of our atmosphere, which is defined as either 50 miles or 100km, there is enough stuff their to actually slow down spacecraft by friction.
Then you move further out to inter-planetary space (inside our solar system), interstellar space (outside our solar system but inside our galaxy) to intergalactic space. Estimates are that there is on average one proton per cubic meter in intergalactic space ([source](https://www.universetoday.com/30280/intergalactic-space/)).
So your jar would likely be empty. Actually it would probably contain a few molecules that jumped out of the glass wall of the jar, I would guess. However if you sent up something bigger, like a truck, you would probably get a proton or two. Once you got back to earth and started to examine it, you wouldn’t find any difference between the intergalactic proton and the matter on earth.
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