61o5star
Favorite Answer
There is and there isn't. Don't worry, it's not as confusing as it sounds. The biggest and most referred-to vacuum is the universe, so I'll use that for the example. In the universe, there are stars and planets and other rocks, etc. So in that sense, there's stuff in it. But in between all that stuff, there is nothing. No particles, molecules, anything. The universe has no atmosphere-like thing. It can be a hard concept to grasp, but in the space between the spheres, there is just nothingness. A pure emptiness, if you will.
Think of the universe as a buffet table. There's a dish of hash-browns here, a basket of rolls there, a tray of pastries further on. Imagine that each planet or asteroid or star in the universe is a tray/basket/dish of food. There's food isolated in certain areas, but between the dishes of food, there is no food. This food represents the matter in the universe. The space between the matter cannot be filled with matter, otherwise it be a very messy buffet table!
PhysicsHead
a vaccum by definition is empty space. there are NO molecules in a pure vaccum. outer space on the other hand is not a pure vaccume but has particles every once in a while.
Chug-a-Lug
A "perfect" vacuum is some space totally without any matter of any kind or size. There's no such thing as a perfect vacuum though. Even in the deepest regions of outer space there are still a few molecules drifting around.
cosmo
Quantum field theory tells us that the vacuum, even if it's empty and in the lowest energy state, still has some zero-point energy density in the fields.
This is really not at all well understood. It may have a lot to do with "Dark Energy".