Is Any Part of the Universe Truly Empty?

[TRUGONOWFOR]

I have just recently read a book entitled THE HOLOGRAPHIC UNIVERSE in which it is suggested that what we now call empty space is only called empty because we are like fish that cannot see the water they swim through. Is there a reason to consider that any area of the universe is empty?

 

[suyver]

Well... there is always the gravitational argument: mass attracts mass. So if a region of space does not attract other mass, then you can assume it's empty (or rather: not very full). Also, from spectroscopy outside the visible range (mainly infrared) you can make a pretty good guess as to how many elements there are in "empty space", as well as which elements they are. I believe that the real "empty" places have about 100 hydrogen molecules per qubic kilometer (correct me if I'm wrong!) and also trace amounts of helium. Not a lot!

 

[russ_watters]

It depends on what you mean by "blind." Our eyes aren't the only thing we can use to see. It also depends on what you mean by "empty" because space is generally considered to not be completely empty, just ALMOST completely empty.