Illegitimate source that there is no such thing as a true vacuum

Re: Vacuums

Where did you hear this from? I too have heard the mention of things such as this, also that nothingness contains a quantum ammount of spacial value as well. Both of which were from also, illegitimate sources.

 

Re: Vacuums

It really is impossible in practice, at least over long time scales. All materials have a vapor pressure; that is, atoms detach all the time. (The vapor pressure increases exponentially with temperature; if it reaches atmospheric pressure, the solid will sublimate to gas even in a closed container.) So it's not possible to have a container-enclosed pure vacuum indefinitely, at least. The time scale depends on the enclosed area, the container material, and the temperature.

(This doesn't consider the fact that the vacuum would also be immediately filled with photons.)

 

Re: Vacuums

There needs to be some additional context to understand what is meant by 'true vacuum'. Torricelli really irked the Pope in the 17th century with his column, and some cosmological models claim the universe is in a false vacuum state.

Those two uses of the term 'vacuum' are tenuously connected- can you provide additional context?

 

Re: Vacuums

From an engineering point of view you can't make a perfect vacuum, because even if you made a perfect pump molecules would boil off the surface of the walls. The best laboratory vacuums are about 1million-billion atoms/m^3 , even in deep space there is an atom every few m^3,

From a cosmological point of view you can't have a perfect vacuum because even in a completely empty universe it is possible for pairs of particles/anti-particles to appear form nothing. This is called a quantum vacuum.

 

Re: Vacuums

First limit is the pump technology.
Imagine a displacement pump (like a bike pump) you open a valve and the pressure equalises inside the vacuum and the pump body, you then close the valve and squeeze that volume down until it reaches atmospheric pressure and spray out the captured molecules to the air. This only works down to the point where the number of molecules left in the pump when you go back to the vacuum is equal to the number coming in from the vacuum, for rotary pumps this is about 1/000 mBar

Then you switch to turbo pumps, these have angled blades running at very high speed. When an atom drifts up to them it gets hit by the blades and thrown toward the other end of the chamber (where another pump removes it) ultimately when the vacuum gets very low the chance of an atom hitting a blade gets too low and just as many atoms drift back from the collection side as get pushed toward it. About 1/millionth of a mBar or 10^-9 atmospheres.

Then you use cryopumps. You take a material with a very large surface area like activated charcoal or ceramic pellets and cool them to liquid Nitrogen and then liquid Helium temperatures. Any molecule hitting this surface loses it's energy and sticks.
This can't pump huge volumes of gas because the surface of the material (called a getter) will fill up but it does give you very high vacuums.
But ultimately there is a small chance of an atom or molecule having enough energy to boil off the surface, even at absolute zero molecules don't actualy have zero energy.

The main need for very high vacuums is in particle accelators, so achieving a vacuum of 10^-12 of an atmosphere in a pipe 30mi long is quite good. Especially when a single pin head sized drop of water or oil, or even the grease from a finger print, left inside would mean that you would have a vacuum a million times worse.

ps. Yes getting ultra high vac even in a small cryostat for say a camera is a very long and tedious job, especially when it takes 2 days to pump and cool the chamber to discover a problem and a day to warm it up again.