Empty space?

[claymore]

what does the space between galaxies consist of. Is it totally empty or is it home to wandering comets, asteroids and other debris that has not been captured by the gravitational pull of any of the galaxies ?

[4GS]

As far as I know it consists of dark matter

[Loosehead]

Very little exists in intergalactic space, the odd hydrogen atom knocking about I would imagine. Comets are left over debris from solar system creation so you won't find them outside galaxies.

I stand to be corrected on this 4GS but as I understand it dark matter is needed for the cohesion of galaxies. Essentially Dark matter/energy cannot be detected but has effectivley been deduced to exist mathematically as there is no way Galaxies would stay together with the matter that we can detect. I therefore doubt that much dark matter exists between galaxies.

95% of the universe is dark matter/energy. It''s mind boggling to know that all the galaxies/stars etc we can see are only 5% of the picture!

[jake-the-peg]

Let's expand on that a bit.

Normal matter that is the stuff that is all around us is concentrated in galaxies and in bewteen them there is very little matter indeed. Comets and the like inhabit the regions between stars - check out the Oort cloud.

However we know from the way that the universe is held together by gravity there is far more mass than we can account for and this is known as Dark Matter.(DM)

D M almost certainly exists everywhere not just in between galaxies but all around you now. Infact it was the discovery that spiral galaxies cannot hold together without DM in them that reawakened all the interest in it

There are a number of opinions as to what it might be but personally my favorite is neutrinos.

Neutrinos were thought to be massless, we know that there are countless numbers of them. One is created every time a photon is and at low energies they interact very weakly, they could sail through a light year of lead without noticing it.

However it now seems that they are very likely to have a very very tiny mass. However there are so many of them that they could have an appreciable effect

But I dont think there's any reason to believe that DM is any more common between galaxies than in them and may well be much less common between them.

[heathfield]

For what it's worth, I remember reading that a volume of space the size of the Earth contains enough hydrogen atoms to fill a matchbox at atmospheric pressure.

[MatydaLover]

Dark matter and dark energy are useful concepts when you haven't a clue. Recent observations show that something funny is out there, but exactly what it is ... is mostly speculation ... we're all in the dark. We'll have to wait for the answer.

Meanwhile, how about another idea ... at any point in space you can always see stars and things. So light constantly passes through, therefore there's always something there.

[kwicky]

If you point your receiver to anywhere in the universe you will receive background noise emitted by the Big Bang showing at least there are particles in that region.

[mibn2cweus]

Omega, the overall average density of the universe is estimated to be in the neighborhood of 3H2/8pG = 5 � 10^30 g/cm^3 which is equivalent to about
~ 3 hydrogen atoms per cubic metre.

The less occupied regions, (devoid of planets, stars and galaxies, etc.), would be expected to have an even lower concentration of matter than that!

[kwicky]

For the budding physicists there was a program on BBC3 tonight called ATOM. After delving into the higher analytical reaches of space concluded that space does not exist but is used by matter and self cancelling anti-matter leaving a visible void which wasn't. Help!!!