Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: jeffreyH on 17/02/2018 14:02:57

Title: If there was only vacuum what fields could be defined?
Post by: jeffreyH on 17/02/2018 14:02:57
In a universe containing only vacuum could different fields still be defined? Could the quantum fluctuations generate such fields?
Title: Re: If there was only vacuum what fields could be defined?
Post by: jeffreyH on 17/02/2018 19:40:15
While thinking about this one bear in mind that there are vacuum solutions for gravitation.
Title: Re: If there was only vacuum what fields could be defined?
Post by: saspinski on 17/02/2018 23:31:51
There is a reflexion about vaccum solutions and the energy moment tensor in https://arxiv.org/pdf/1605.09236.pdf
The author seems to agree with the Mach idea that we can not speak of a spacetime without its fields. Or that spacetime and fields are the same. But he disagrees that sources requires the energy moment tensor.

I compare the vacuum solutions of GR to the Poisson equation for classical gravity: ∇²Φ = 4πGρ. Out of the Earth for example, ρ=0, so ∇²Φ = ∇.a = 0. But the divergence of acceleration being zero doesn't mean that each of its parcial derivatives are zero.

In the same way, each component of the Ricci tensor is a sum of components of the Riemann tensor. The later can be non zero while the former are zero.
Title: Re: If there was only vacuum what fields could be defined?
Post by: yor_on on 18/02/2018 02:21:10
A vacuum as a geometry?

that's difficult, how should I define a magnitude?
Title: Re: If there was only vacuum what fields could be defined?
Post by: Bill S on 18/02/2018 19:20:35
Are we considering an “absolute” vacuum, or a “quantum-type” vacuum?

If it is the former; where would quantum fluctuations come from?

If the latter; then there must be something filling the “vacuum”, so, I would think, there must be fields already present. 
Title: Re: If there was only vacuum what fields could be defined?
Post by: petelamana on 19/02/2018 01:00:57
Please define the degree of vacuum you are considering.  For example...

A perfect vacuum is defined as a state with no matter particles, and also no photons. This state is impossible to achieve experimentally because it is nearly impossible to remove the matter, and is impossible to eliminate all the photons. Since there is also some energy available, virtual particles can hop into and out of existence.
Title: Re: If there was only vacuum what fields could be defined?
Post by: jeffreyH on 19/02/2018 12:34:03
It is THE vacuum containing vacuum energy.
https://en.m.wikipedia.org/wiki/Vacuum_energy
Title: Re: If there was only vacuum what fields could be defined?
Post by: petelamana on 19/02/2018 12:41:24
Fascinating.  Thank you jefferyH.  I now have something to study this week.
Title: Re: If there was only vacuum what fields could be defined?
Post by: Bill S on 20/02/2018 20:49:33
Quote from: Jeffrey
It is THE vacuum containing vacuum energy.
https://en.m.wikipedia.org/wiki/Vacuum_energy

That clears "vacuum = nothing" out of the way, so there should be nothing to prevent the "development" of fields associated with any particle that might be present.

Would the fact that they are virtual particles complicate the situation?
Title: Re: If there was only vacuum what fields could be defined?
Post by: jeffreyH on 20/02/2018 21:06:58
Quote from: Bill S on 20/02/2018 20:49:33
Quote from: Jeffrey
It is THE vacuum containing vacuum energy.
https://en.m.wikipedia.org/wiki/Vacuum_energy

That clears "vacuum = nothing" out of the way, so there should be nothing to prevent the "development" of fields associated with any particle that might be present.

Would the fact that they are virtual particles complicate the situation?

That is a very good question. To which I have no answer.
Title: Re: If there was only vacuum what fields could be defined?
Post by: geordief on 27/02/2018 22:43:47
Do virtual particles require  (exchange? mediate?) energy from the system they are associated with ?

I know little of this.