What is the vacuum level of the universe?

Answer 1

It can be difficult to specify the "vacuum level of the universe" because the density of space varies. From black holes where density goes out of sight high to deep space where only a proton or perhaps an electron is seen hanging around in a cubic meter of "nothing" but spacetime. Let's look at a couple of possibilities. So how much pressure or vacuum is out there? The average is nearly zero, and that's because it's difficult to quantify the pressure created by, say, one hydrogen atom per cubic meter. We often see that (one hydrogen atom per cubic meter) cited as the average density of the universe. There are something on the order of 10 to 100 atoms of hydrogen per cubic meter in intergalactic space. That's 10 to 100 times the average density of the universe, as you can see. The figure can climb as we approach intergalactic space in the vicinity of galactic clusters. But what value can we actually assign to the vacuum of deep space? 10-10 Torr? 10-15 Torr? 10-20 Torr? It depends on where you measure it. Additionally, the pressure of gas ions in those thin reaches could be quite high because the temperature of the ions can be high. Relative to the couple of degrees K that represents some kind of "average" temperature of deep space, that is. That ion isn't just "hanging in space" out there. It's on the move 'cause it has moderately high kinetic energy. This "answer" must include an apology for it's tendency to jerk you around. It's not that the goal was to do that. It's just that there isn't a "pat" answer like there is to, say, a question on the number of prime pairs with three or less digits. A link is included, and you are encouraged to do just a bit of reading there. That link is below.