# Vacuum, hello? is there anyone?

1. Dec 27, 2004

### Clausius2

I think you're going to hate me for talking again about the vacuum.

Yesterday I saw a TV program about CERN. A physicist (spanish by the way) talked about the vacuum is not so vacuum as we could think.

Let's suppose I have a reservoir in which it has been made a high vacuum. A manometer measures 1e-5 Pa. Surely the manometer has an instrumental error so maybe that measure has some internal error. I suppose that physicist do not try to explain vacuum from manometers, so the first question is:

1. how can be sizable the small perturbations of the vacuum? What instrumental have used the physicist to know that the vacuum is not so vacuum? Or is merely a theoretical assumption?

2. The same physicist said (translated into english) the next: "the mass is caused by the friction against the vacuum". What does it mean?.

Thanks. I'm only a layman in this part of physics.

2. Dec 27, 2004

### dextercioby

Sorry,i missed the previous part... :tongue2: Was it interesting??

There's no such thing as vacuum.We should use this word:"vacuum".

a)The thermodynamical/technical "vacuum" is one thing defined in thermodynamics (think at the fundamental formula of kinetic theory of ideal gases:$p=nkT$.Assume u have a "vacuum" pump which is taking out molecules from an enclosed volume.As u can see,at constant temperature (mean kinetic energy/molecule) the pressure and the concentration of molecules are proportional:the more molecules u take out,the least pressure the gas has.
b)"Perturbations of <<vacuum>>" has to do with the concept of "vacuum" thought by the QFT (Quantum Theory of Fields).I believe putting together the classical theory of special relativity and the quantum principle of uncertainty energy-time gives us the idea that we have about the "vacuum":a gazzilion of virtual particles which annihilate and create at the same moment of time.They are called "virtual particles" not because they would not exist (according to theory they do),but we cannot see them,as their "lifetime" is very,very small.So yes,it is a theoretical assumption which cannot be infirmed by experience.

He was probably speaking about the ellusive (unfound yet,but predicted by theory in 1964) Higgs boson and the quantum "vacuum" in the electroweak interactions.The part with the "friction" is a metaphor :tongue2: ,friction has nothing to do with fundamental particles/interactions.I don't know,the Higgs mechanicsm is pretty complicated and to explain it in nontechnical words is rather difficult,as least for me.Maybe Marlon could find the appropriate words and no formulas to tell about the Higgs boson and the quantum "vacuum". :uhh:

You're welcome.BTW,"vacuum" is trully vacuum only in SR and GR.Those theories have nothing in common with Heisenberg's principle.

Daniel.

3. Dec 27, 2004

### Clausius2

No, there are not any previous part. The only thing I usually see at PF forums is a lot of people talking about vacuum. Mine is something similar to those who ask themselves about the recurrent topic of lift or new heat engines developments.

So you imply there is not any evidence of such quantum fluctuations of the vacuum. I cannot imagine an experimental device able to measure it. In addition of having its inherent error, Heisenberg's principle adds an additional error.

I would be glad of hearing some explanation about that. The problem here is why you call vacuum to something that is not vacuum. I may think that vacuum cannot exist due to Heisenberg's principle, is that correct?.

4. Dec 30, 2004

### Kane O'Donnell

There is plenty of evidence that the quantum vacuum is the way dextercoiby has described. For example, the Casimir effect, where two plates very close together in a vacuum feel an attractive force proportional to the fourth power of their separation.

Another example is the Lamb shift (a slight shift in atomic energy levels) and indeed spontaneous emission of light is *itself* a result of vacuum fluctuations - people often ask the question "what makes the electron jump back down into a lower state if it's in a stationary state", and the answer (from QED) is fluctuations in the electromagnetic field.

You are correct in saying that the classical vacuum doesn't exist as far as we can tell.

Cheerio,

Kane O'Donnell