Why is it not possible to have a perfect vacuum?

Answer 1

Let us analyse the technique of producing vacuum.

Initially the pressure inside the container and that outside will be the same. While pumping out with piston model, we depend mainly on the functions of the valve operating in the evacuating device. Actually valve is a traffic controller who checks the one way traffic. There by the valves are expected to get open only in one direction and thereby allowing the air to move only in one direction. As the pressure goes on reduced to some level, then the air pressure inside the container will become so weak that it cannot even push the valve gate to get opened and come out. This draw back is there in the old devices.

So rotary pump got designed where the rotor would suck those weaker molecules to come out of the container.

Even after following so many techniques in an intelligent way to produce vacuum of the order of 10 -14 mm of Mercury, yet some molecules thousands in number) will be roaming about within the container. So it is impossible to produce perfect vacuum.

In free space too, there are hydrogen molecules with utmost very low density some ten molecules for every cubic meter.