True Vacuum

[petrushkagoogol]

Does a true vacuum exist in space? No matter, no energy. CMBR is ubiquitous, isn't it.....

[CraigD]

Does a true vacuum exist in space? No matter, no energy. CMBR is ubiquitous, isn't it.....

Ordinary, open-to-the-rest-of-the universe space isn’t a perfect vacuum.

 

As you note, the CMBR is everywhere, even in intergalactic space, far from stars where there isn’t much higher-energy light. There are about 400 photons of from it in every cm³ of space.

 

The universe is also full of neutrinos, though they interact so weakly with everything else they’re barely detectable. There are about 300 of them per cm³.

 

The universe is also, on average, a very diffuse gas, mostly of hydrogen. The average matter density of the universe is about 0.2 hydrogen atoms per m³. Parts of the universe, known as voids, are about 1/10th as dense as the average.

 

Even if you manage to contrive to keep all matter and EM radiation out of some volume of space (I don’t know of any way, theoretically, to keep out neutrinos, but imagine somehow you could), according to quantum mechanics, even a perfect vacuum has energy.

 

Sources: Wikipedia articles Outer Space, Friedmann equations, Vacuum energy.

[sanctus]

Yeah, to elaborate more on the vacuum energy, a simple way to see it is that thanks to QM you have non-stop particles and corresponding antiparticles created which annihilate each other right away. So as CraigD said, pure vaccuum does not exist.