Interstellar space is not a true vacuum but full of particles

Evidence

What I am learning now is that far from being empty, space is full of stuff. And some of it even qualifies as sound. — George Michelsen Foy, Zero Decibels, 270

Categorization

• corroborated: 2 independent passages support this claim — George Michelsen Foy, Zero Decibels: The Quest for Absolute…, 270
• XREF: connects to: Air is a seething low-density molecular gas with constant collisions