# Electrical conductivity of absolute vacuum

#### HotFurnace

Joined Mar 31, 2018
29
Hi,
In a vacuum there's no particle to form a current (with the exception of capacitor charge&discharge, we are talking about DC current& static field here), so could the absolute vacuum conduct electricity? I heard that with high enough electric field, virtual particles could form and then a current can flow in absolute vacuum. How high this field is? And what happen with even higher electric field?

#### crutschow

Joined Mar 14, 2008
24,725
Of course a current can flow in a vacuum.
It occurs in all vacuum tubes (valves), else they wouldn't work.
The electrons are emitted from the cathode and travel through the vacuum to the positively charged anode (Plate).
No virtual particles needed.

xox

#### panic mode

Joined Oct 10, 2011
1,829
just ask yourself - what property of vacuum would stop something from traveling through it...

#### ebp

Joined Feb 8, 2018
2,332
Can you have an "absolute vacuum" if you're spewing electrons into it?

#### Papabravo

Joined Feb 24, 2006
13,528
Can you have an "absolute vacuum" if you're spewing electrons into it?
Close enough for government work. The electron cloud has virtually no measurable effect on the vacuum. Electrons are vastly different things than oxygen and nitrogen molecules.

#### crutschow

Joined Mar 14, 2008
24,725
Can you have an "absolute vacuum" if you're spewing electrons into it?
I believe the definition in this case is nothing in the space until you introduce the electrons.

#### Papabravo

Joined Feb 24, 2006
13,528
I believe the definition in this case is nothing in the space until you introduce the electrons.
Undt tell me what is the partial pressure of an electron cloud?

#### nsaspook

Joined Aug 27, 2009
7,181
Hi,
In a vacuum there's no particle to form a current (with the exception of capacitor charge&discharge, we are talking about DC current& static field here), so could the absolute vacuum conduct electricity? I heard that with high enough electric field, virtual particles could form and then a current can flow in absolute vacuum. How high this field is? And what happen with even higher electric field?
Forget all you think you know about virtual particles. The scientific definition of a quantity of electricity (archaic usage) is defined as the coulomb (charge), that's not by definition energy only a movement of charge. If what you mean is can absolute vacuum conduct (transport) electrical energy, then the answer is yes. In modern physics the word 'electricity' means a study of a thing.

#### HotFurnace

Joined Mar 31, 2018
29
I mean a volume that have absolute no particles in it. Let's further assume that the cathode and anode are near absolute zero temperature so they hardly emit any electron after all.
Of course vacuum could transport energy, but what i mean here, that is without the cathode emitting electron, without particles inside the volume considered, only the electric field strength is raised very slowly (for example bringing two plate closer), then could the plates lose charge?

#### nsaspook

Joined Aug 27, 2009
7,181
I mean a volume that have absolute no particles in it. Let's further assume that the cathode and anode are near absolute zero temperature so they hardly emit any electron after all.
Of course vacuum could transport energy, but what i mean here, that is without the cathode emitting electron, without particles inside the volume considered, only the electric field strength is raised very slowly (for example bringing two plate closer), then could the plates lose charge?
Sure, you could have field emission at 0K (a QM process not a classical thermal emission) with absolute vacuum (field emission works better as vacuum quality increases) and eventually avalanche breakdown from that field emission with a strong electrostatic field.
http://www.cas.unt.edu/~skg001/SKG Thesis/SKG Thesis Chapter 2.pdf

Field emission used in semiconductors.

Last edited:
xox

#### KL7AJ

Joined Nov 4, 2008
2,225
just ask yourself - what property of vacuum would stop something from traveling through it...
The lack of anything traveling through it.

#### Papabravo

Joined Feb 24, 2006
13,528
I believe most particle beams will go right through a glass bulb with a vacuum inside.

#### nsaspook

Joined Aug 27, 2009
7,181
I believe most particle beams will go right through a glass bulb with a vacuum inside.
It depends on the glass (doping in SiO2 layers on silicon wafers) but most cause beam loss when the particles collide with the glass. Most of the beam view ports use leaded glass to reduce X-ray emission from the Bremsstrahlung process if high energy charges strike the glass.

Last edited:

#### panic mode

Joined Oct 10, 2011
1,829
The lack of anything traveling through it.
fair enough but i think this is either a common misconception or - my misunderstanding (lack of sleep can do that)

lets elaborate my view, lets use A and B as substitutes.

my understanding of original question is:
"is it possible for A to travel through B?"

you seem to understand it as follows:
"is it possible for B to travel through B?"

but A and B are not the same thing.

So in this case:
A = current (moving charged particles); B = vacuum

but if you like, you can use any other analogy:
A = deer; B = field
A = bird; B = air
A = fish; B = water
A = bullet; B = bone
etc.

water ("pure" or "just water") is not the same as water with some fish swimming in there - just ask any fisherman.

so why do we still call it "water"?

because it is:
a) MOSTLY water
b) DIFFICULT (IMPOSSIBLE) to refer to it if we are going to use "detailed" naming such as "water with some fish, sand, one shark, lost sandal, sunk ship, bikini bottom, human remains, fish remains, algae, lost treasure ....".

It is so much more practical and ingrained into our minds to just call it "water"

So what is in B that prevents A from moving through B?

the other point would be what exactly is "pure" vacuum or how would you define it? i don't think it can exist... even if we treat it as pure thought experiment (hypothetical pure vacuum)... after all even in such vacuum, there has to be some vacuum in it. ;-)

and that's without going into quantum physics

or how do you interpret it?

#### nsaspook

Joined Aug 27, 2009
7,181

#### bogosort

Joined Sep 24, 2011
959
The best model we have says that what we call space is really a set of quantum fields. "Space" is never empty. The vacuum state of a field is simply its ground state, its lowest energy state. It's no use trying to picture an electron moving through empty space; that image is unphysical. A ripple in the electron field is a better visualization.

#### nsaspook

Joined Aug 27, 2009
7,181
The best model we have says that what we call space is really a set of quantum fields. "Space" is never empty. The vacuum state of a field is simply its ground state, its lowest energy state. It's no use trying to picture an electron moving through empty space; that image is unphysical. A ripple in the electron field is a better visualization.
A ripple in the electron field is not very useful when you need to calculate the needed electron density to neutralize a surface charge. Plain old particles moving in empty space works just fine for that. The best model is the one that works correctly and easily for your application.

#### bogosort

Joined Sep 24, 2011
959
A ripple in the electron field is not very useful when you need to calculate the needed electron density to neutralize a surface charge. Plain old particles moving in empty space works just fine for that. The best model is the one that works correctly and easily for your application.
Sure, but the original question was theoretical in intent, asking specifically about empty space and rightfully being confused by such a notion.

#### BR-549

Joined Sep 22, 2013
4,938
I believe in clean space. It's the only thing that can fill eternity.

The space anywhere near this universe is filthy with waste products, both field and matter.

#### Darkstar

Joined Sep 3, 2010
117
Hi,
In a vacuum there's no particle to form a current (with the exception of capacitor charge&discharge, we are talking about DC current& static field here), so could the absolute vacuum conduct electricity? I heard that with high enough electric field, virtual particles could form and then a current can flow in absolute vacuum. How high this field is? And what happen with even higher electric field?
In my chem & physics classes back in the 70's we were told the same thing about no current flow. The vacuum was a place that the electron was forbidden to occupy (I too thought of vacuum tubes). It wasn't long before quantum tunneling was discovered in which an electron could disappear from one location and reappear on the other side of a barrier without ever having been inside the forbidden barrier zone.

Another way to have charges move through a perfect vacuum is to have 2 plates very close together. I forget the dimensions, but it is too small for an atom to fit between them so it has to be a perfect vacuum in that respect. However, it is not a perfect vacuum because it contains energy. If my memory serves me, this is called the zero point energy. It is everywhere. When the 2 plates mentioned are close enough, particles can form in the gap, produced by the energy contained therein. I forget specifically what particles they are but I think they have opposite charges so each can travel to one of the plates. This is supposed to be happening naturally all over space but with no place to go, the particles simply recombine and turn back into energy. The net result looks like nothing has happened but on a quantum level it has. I don't remember any mention of voltages on the plates being the energy source for the formation of the particle pairs, it was the natural energy in empty space. That's the way I remember it anyway.