# Electrical conductivity of absolute vacuum

#### crutschow

Joined Mar 14, 2008
31,149
A vacuum tube of course does not have a vacuum in it ....
But it's a pretty good approximation, since they typically have a getter to remove stray molecules.

#### MrAl

Joined Jun 17, 2014
9,638
My limited interpretation tells me that an absolute vacuum is NOT the absence of EVERYTHING in the volume of the absolute vacuum.

There’s always SOMETHING there.

Consider a thought experiment. Place a large magnet in a glass (or any non-magnetic material) containment vessel. Before evacuating the vessel, measure the strength of the magnetic field at the periphery of the vessel. Do you get a reading? Write it down. Then start evacuating the vessel. At a pre-determined vacuum delta values, document the degree of the vacuum and the measured magnetic field.

Vote. How many say the magnetic strength will change? How many believe it will be constant.

My point is that while particles maybe absent, a field will still exist in a vacuum.
Hi,

The field will change if there was something in the vessel to begin with, but depending on what was in there it may change a lot or jsut a little.

But isn't that the same thing though as the bucket example?
Just because you can put stuff in the bucket does not mean it can never be empty.

Move the magnet into deep space, then measure the fields just outside of the vessel.

#### Darkstar

Joined Sep 3, 2010
177

The air around you is filled with about 10 quintillion air molecules—that's 10,000,000,000,000,000,000—in every cm^3.
https://van.physics.illinois.edu/qa/listing.php?id=28738&t=making-a-vacuum-chamber

Even the most advanced scientific laboratories can't produce a perfect vacuum. The best they can do is about 100,000 atoms in each centimeter cube. Out between the stars, there are only about three atoms in each cm^3.
https://van.physics.illinois.edu/qa/listing.php?id=28738&t=making-a-vacuum-chamber
This is about 10^-16 torr. http://www.virginia.edu/ep/SurfaceScience/class2.html)

The most nearly perfect vacuum exists in intergalactic space, where it is estimated that on the average there is less than one molecule per M^3.
https://encyclopedia2.thefreedictionary.com/Partial+vacuum

Even at the best vacuum normally used in surface science experiments, ~10^-11 Torr, there are still plenty of molecules in the gas phase, about 300 hundred thousand per cm^3.
http://www.virginia.edu/ep/SurfaceScience/class2.html

Vacuum tube 10^−7 to 10^−10 torr , mean free path 1 km to 1,000 km , 10^9 to 10^6 molecules/cm^3
Cryopumped Molecular beam epitaxy chamber 10^−9 to 10^−11 torr , mean free path 100 km to 10,000 km , 10^7 to 10^5 molecules/cm^3
https://en.wikipedia.org/wiki/Vacuum

I've routinely worked in the 10^-9 to 10^-10 torr range on a mass spectrometer. Less than this in the electronics manufacturing industry.

#### Darkstar

Joined Sep 3, 2010
177
Hi,

The field will change if there was something in the vessel to begin with, but depending on what was in there it may change a lot or jsut a little.

But isn't that the same thing though as the bucket example?
Just because you can put stuff in the bucket does not mean it can never be empty.

Move the magnet into deep space, then measure the fields just outside of the vessel.
I'm curious to see how people will vote on this possible change in magnetic field strength. Please give some reason for your choice so we don't have to guess.

#### MrAl

Joined Jun 17, 2014
9,638
I'm curious to see how people will vote on this possible change in magnetic field strength. Please give some reason for your choice so we don't have to guess.
Hi,

The short answer is if there are steel ball bearings inside the vessel before evacuated then there's gong to be a huge change in field once they are removed.
The long answer is that everything is magnetic to some extent even if it is weakly interacting. That means air as well as frogs too. Yes frogs can be levitated with a strong enough field ha ha. So does the field change before and after the frog or air is removed? The answer must be yes, but of course it could be hard to measure.

So we dont usually see a 'perfect' vacuum, that's a side issue i believe.

#### BR-549

Joined Sep 22, 2013
4,928
We need better definitions for space and vacuum. Both are sorta relative. If we measure and detect an area of space anywhere near this universe......it will have many fields in it. These fields are not from the space. The fields only have temporary residence in space.

For clean space and PERFECT vacuum.....the area is empty. Impossible in our region.

Some academics believe this "vacuum foam" is a fundamental state of space. A path to the beginning.

It's litter. It's not the source, it's the dump. An extremely old dump.

To me, the greatest mystery about space charge is, where does it go and when or if it combines. There are huge amounts of high velocity free charge being spayed from the stars.

I wonder if anyone takes that mass into consideration when computing mass to energy solar conversions.

This charge is accelerated for long distances for long times. A true mystery. I think I know, but it's just a guess.

Where does all this charge go? It has to be equal negative and positive charge. Why doesn't it try to combine? There could be several reasons for that. One might be relative velocity. The manner in which charge interacts, depends on relative velocity.

We have all heard this a thousand times.........it all depends on relative velocity. WHY IS THAT? Did anyone ever tell you why that is?

Velocity has direction and speed. These set the relative rates and duration of interaction. And the charge interactions......have directional and rate specifications. This can change the rate of interaction or even prevent it.

It also might be something simple. Such as the mode of acceleration from the sun, this might misalign the charge for combination, while under acceleration.

Remember, there is every reason to believe that this occurs with all stars. Where does it go? We have measured our solar stream and it seems to accelerate out to somewhere around Neptune, last I heard. I wonder if it slows after the acceleration. Does it leave the system? Does our system lose mass?

When and IF and where ever this charge combines......it should wink at us. Why isn't all space around all stars winking at us.

Charge in a vacuum. Wouldn't it be wild......that a vacuum velocity prevents charge interaction for the rest of time?

#### Darkstar

Joined Sep 3, 2010
177
Here's my answer (and more): Air has a relative magnetic permeability of 1.00000037. Being slightly larger than 1 (vacuum) there should be a very slightly weaker magnetic field in the vacuum compared to air. See here: https://en.wikipedia.org/wiki/Permeability_(electromagnetism)
For water (& frogs) it is 0.999992. Being <1 means water is diamagnetic so is repelled by a magnetic field of any polarity.
With a strong enough magnet you can see a dimple form on the surface of water in a dish as it is repelled by a magnetic field below it. Bismuth (0.999834) and pyrolytic graphite (0.9996) are the most diamagnetic materials known. I can repel pure carbon from a pole of my magnet.
Liquid oxygen is paramagnetic and will form a mass surrounding a strong magnet pole.
Iron, 99.8% pure has a relative permeability of 5000, so it will concentrate the magnetic field. This ferromagnetic property is around a billion times stronger than the diamagnetic repulsive property so very strong magnets are needed to demonstrate the diamagnetic effect.
The values in the Wikipedia table are approximate as the relative permeability varies with field strength and frequency.

I've done experiments dropping copper (0.999994) and aluminum (1.000022) through a field I estimate to be near 1 Tesla and they fall at less than 1 inch/second. I don't even have a Neodymium magnet. They have surface fields less than a Neodymium but make up for it in size. A typical small Neodymium has a strong field close to the surface but is practically undetectable a few inches away. Just some of my magnets put together weigh in at about 70 lbs and have poles as much as 72.5 sq inches. They can be detected about 10 feet away. If handled improperly they could probably take my fingers off. Think of a 31 lb mousetrap with sharp metal edges snapping onto another magnet faster than you can blink. It can be scary.

In an MRI machine the magnetic field aligns the spins of electrons on hydrogen atoms in the water of your body. When it is switched off some spins will flip back to their non-aligned position and in doing so emit a weak signal which is monitored by a small antenna placed over the part of the body being examined.

Placing an ionized gas in a strong magnetic field will split the emission lines of elements. I've done this in college. It can be seen in spectra from the sun because it has strong localized fields.

So MrAl, you are correct, everything interacts with magnetic fields to some extent.

@BR-549, you are correct about how charges emitted by stars can be accelerated for long distances. This is the source of cosmic rays, particles that have been traveling along the magnetic field lines of galaxies and spinning pulsars and neutron stars to very high energies. As for where they go and why do they not interact, well, space is big, positive and negative particles in the same field will go in opposite directions. They just fly around until they hit something.

NASA announced in 2013 that Voyager 1 had encountered the heliopause on 25 August 2012, when the spacecraft measured a sudden increase in plasma density of about forty times.[2] This was at a distance of 121 AU (18 billion km) from the Sun. (1 AU is the distance from Earth to the Sun.) This is the point at which the pressure of the solar wind and interstellar wind are in balance. In 2018, NASA announced that Voyager 2 had traversed the heliopause on 5 November of that year.[3] Because the heliopause marks the boundary between matter originating from the Sun and matter originating from the rest of the galaxy, the two Voyagers, which have departed the heliosphere, can be said to have reached interstellar space.
https://en.wikipedia.org/wiki/Heliosphere and
https://www.nasa.gov/vision/universe/solarsystem/voyager-interstellar-terms.html

#### MrAl

Joined Jun 17, 2014
9,638
Hi,

Some interesting stuff.

Yes the definition of a vacuum is "a space completely void of any matter".
So if it has a relatively small amount of matter then it's just a pseudo vacuum, and then it starts to depend on the practical application whether or not it can just be called a vacuum. For example what degree of a vacuum occurs when an air conditioning system is evacuated. It's probably not as good as some scientific research project requires.

#### Danko

Joined Nov 22, 2017
1,493
Yes the definition of a vacuum is "a space completely void of any matter".
Then definition of an ocean is: "a water completely void of any waves, whirlpools, streams [energy]".

#### bogosort

Joined Sep 24, 2011
696
Yes the definition of a vacuum is "a space completely void of any matter".
That is the 19th century definition. In modern physics, space is comprised of various fields -- the fields are space -- and so notions such as "empty space" don't even make sense. Instead, physicists use the word vacuum to refer to the ground state (i.e., lowest energy state) of some particular field.

Note that this isn't just a pedantic distinction in terminology; we cannot cogently reason about electrons using classical concepts (such as empty space). The past century of physics history makes this abundantly clear.

#### MrAl

Joined Jun 17, 2014
9,638
Then definition of an ocean is: "a water completely void of any waves, whirlpools, streams [energy]".
Hi,

Ha ha. So how do you know what a grazing field is if there are no cows grazing.
If you say you know what a vacuum isn't, then you must know what a vacuum is.

#### Ya’akov

Joined Jan 27, 2019
6,858
The problem is that every practical vacuum is a matter of degree. It's like a bald man, if you pluck one hair at a time, when does he become bald?

#### MrAl

Joined Jun 17, 2014
9,638
That is the 19th century definition. In modern physics, space is comprised of various fields -- the fields are space -- and so notions such as "empty space" don't even make sense. Instead, physicists use the word vacuum to refer to the ground state (i.e., lowest energy state) of some particular field.

Note that this isn't just a pedantic distinction in terminology; we cannot cogently reason about electrons using classical concepts (such as empty space). The past century of physics history makes this abundantly clear.
Hi,

That's the definition in the English language.
But you could not know what you know unless you know what a perfect vacuum is. You'd never have the word.
I know that things have changed, no question there, but we know they changed because we know the concept of a perfect vacuum.
How would we know we have an imperfect vacuum without that.

There's probably no such thing as a pure crystal either but we know it is impure when it has impurities in it. But what is it that has impurities? It's a pure crystal. We have the concept.

Also, i already stated that it comes down to the application what is a vacuum and what is not for the practical cases.

#### MrAl

Joined Jun 17, 2014
9,638
The problem is that every practical vacuum is a matter of degree. It's like a bald man, if you pluck one hair at a time, when does he become bald?
Hi,

Yes, and the real crux of the issue is what application are we working with. One mans vacuum is another man's junk yard

#### Darkstar

Joined Sep 3, 2010
177
Hi,

Yes, and the real crux of the issue is what application are we working with. One mans vacuum is another man's junk yard
That quote can cover so much ground. Like, one man's old computer in his garbage is another man's source for recycled gold or a kid's source for electrical parts for a new homemade computer and is another man's source for someone's personal info left on the hard drive. Like you say, it all depends on your application. With 2 rooms full of hobby stuff to get rid of, collected over 53+ years, I can really relate to that these days.

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#### MrAl

Joined Jun 17, 2014
9,638
That quote can cover so much ground. Like, one man's old computer in his garbage is another man's source for recycled gold or a kid's source for electrical parts for a new homemade computer and is another man's source for someone's personal info left on the hard drive. Like you say, it all depends on your application. With 2 rooms full of hobby stuff to get rid of, collected over 53+ years, I can really relate to that these days.
Hi,

Oh wow yeah i can relate to that too, i have containers and containers of electrical parts that i dont use anymore. Decades worth. Might donate to Rutgers University which is not too far from here (5 miles).
It's crazy what i have collected over the years.

#### nsaspook

Joined Aug 27, 2009
10,715
Hi,

Oh wow yeah i can relate to that too, i have containers and containers of electrical parts that i dont use anymore. Decades worth. Might donate to Rutgers University which is not too far from here (5 miles).
It's crazy what i have collected over the years.
There are times when you just need to let it go.

#### BR-549

Joined Sep 22, 2013
4,928
I certainly wouldn't give it to the 1 percenters at an university. Give it to a ham club, robot club, drone club or micro controller club.

Or a vocational school.

They will appreciate it.

#### bogosort

Joined Sep 24, 2011
696
That's the definition in the English language.
But you could not know what you know unless you know what a perfect vacuum is. You'd never have the word.
I know that things have changed, no question there, but we know they changed because we know the concept of a perfect vacuum.
How would we know we have an imperfect vacuum without that.
You're missing the point. There's nothing wrong with talking about vacuum -- in the sense of empty -- in appropriate contexts. But in the particular context of electron physics, that word has a very different meaning than the common usage. The OP had a question about electrical conductivity (electron physics) in "absolute vacuum" (common usage), which is a bit like asking if leeching can fix chromosomal damage. The two concepts are not in the same scope.

Also, i already stated that it comes down to the application what is a vacuum and what is not for the practical cases.
In QFTs, there is only one notion of vacuum. There is, however, a scary possibility that we're living in a false vacuum, i.e., that the apparent equilibrium of the universe's energy state is only a local minimum. A universe in true vacuum is stable, but a universe in false vacuum is meta-stable and will eventually decay to its ground state. If this happens, the universe as we know it would be destroyed. Experimental data strongly suggests that the electroweak field is indeed in a false vacuum. Since vacuum decay propagates at the speed of light, it's possible the process has already started somewhere in the universe. Sweet dreams!

#### nsaspook

Joined Aug 27, 2009
10,715
You're missing the point. There's nothing wrong with talking about vacuum -- in the sense of empty -- in appropriate contexts. But in the particular context of electron physics, that word has a very different meaning than the common usage. The OP had a question about electrical conductivity (electron physics) in "absolute vacuum" (common usage), which is a bit like asking if leeching can fix chromosomal damage. The two concepts are not in the same scope.

In QFTs, there is only one notion of vacuum. There is, however, a scary possibility that we're living in a false vacuum, i.e., that the apparent equilibrium of the universe's energy state is only a local minimum. A universe in true vacuum is stable, but a universe in false vacuum is meta-stable and will eventually decay to its ground state. If this happens, the universe as we know it would be destroyed. Experimental data strongly suggests that the electroweak field is indeed in a false vacuum. Since vacuum decay propagates at the speed of light, it's possible the process has already started somewhere in the universe. Sweet dreams!
The eventual fate of the universe because of unstable AdS vacuum regions? Loud snoring, wake me up in several billion years to check that.