Is a Vacuum that isn't empty a Vacuum?

Brian Greene's book Fabric of the Cosmos is a great source of info on our current state of understanding (or lack thereof, depending on how you prefer to frame it). It's an easy read and he writes in a style that is nicely balanced for all readers. The part on the "frozen Higgs field" addresses your question. It's really way beyond the scope of a simple comment but the simple answer appears to be yes, there is something there, exactly what it is doesn't seem to be entirely clear, depending on what you mean by clear or what or is...

When we say it's a vacuum environnement, it's because this environnement don't have air. Space don't have air. But you can have a ton of other things...

Not quite true. If you evacuate a jar by filling it with water, then seal it so there is only one entry point, a tube with a valve to open and close it, will you create a vacuum if you remove water by applying suction to the tube with the valve open and then close the tube? NO, you will not have a complete vacuum. Although there is no air (mostly nitrogen and oxygen, with traces of other gases) there will be plenty of water vapor! A true vacuum is the absence of any particles. TRUE, interplanetary space is only a partial vacuum, with tiny "dust" particles, molecules, and atoms, between the larger masses of matter (the planets, moons, stars...oops, didn't mean to sound like a Lucky Charms commercial!). But the particle density is extremely small, even smaller for interstellar space. In practical terms, this is a vacuum.

That is why sound waves will not travel through space. Sound waves are mechanical energy that depends on the presence of matter as a medium, solid, liquid, or gaseous, to travel. Light (and any other electromagnetic energy, like radio, gamma rays, etc.), does NOT depend on matter for transmission, although it can be affected by matter (solids block, reflect, and refract light; metals block, reflect, and refract radio waves). It is not surprising that magnetic fields should have an effect on electromagnetic energy (don't call it a wave or a particle, it has characteristics of both!), however this has nothing to do with whether or not space is a vacuum. Let's put it this way, despite the whooshing sounds from spacecraft on SciFi TV and films, if two astronauts on a space walk had a bullhorn and external microphone attached to their spacesuit headsets instead of radios to talk to each other, they would never hear a thing. Yet, let them touch helmets, glass-to-glass and they can communicate because mechanical sound energy flows through the air particles, to the glass and is conducted into the glass and air of the other helmet!

I guess I thought a vacuum was an area of space without particles with mass, but that may be wrong. In truth, the reason I asked the question was because I can't find a clear definition. After all, every bit of the vacuum of space is filled with photons, and photons a re particles of a sort, they just don't have mass.

Either way, saying it simply is a place with no air is a vacuum isn't enough, because the ocean doesn't have air but we wouldn't call it a vacuum.

It its pure sense, there is no such thing as a vacuum.

The only obvious exception to that rule would be the many politicians that dwell there.

I agree, with both comments ;)

"In Space, no one can hear you Scream!"

BUWHAHAHAHAHAHAHAHA!

Does this offer an alternate explanation of the bending of light as it passes a massive body vs. Einstein's theory.

Now that is an interesting comment. I think not for this particular case, because what I read indicated it changed linear polarized light to circularly polarized light, so the polarization matters here where it wouldn't for Einstein's theory. However, if space can have one kind of index of refraction, it could have another, so I think that we can't say it couldn't account for it. Really an interesting thought.