Can pressure be negative?

[edd]

Michael. In the early universe in the inflationary picture both matter and radiation exist at vastly higher positive pressures and densities than they do now. The point is that there exists a negative and larger vacuum energy that drives inflation.

That it is a vacuum energy does not imply that it only operates in a vacuum. It merely implies it would still exist without the matter and radiation present.

Your claim that we disregard any lesser positive pressure in a negative-pressure dominated situation is ridiculous.

 

[temporalillusion]

Yes you are. You're ignoring the fact that every single atom in that Casimir chamber still has kinetic energy and it exerts PRESSURE and everything it hits.

So if there were no atoms inside the Casimir chamber, there would be nothing to measure? What about no atoms, neutrinos, or photons?

The photons also carry POSITIVE KINETIC ENERGY. There's more of it on the outside of the plates and less of it on the inside of the plates.

How does that happen? What about Casimir experiments that use spheres, why is there more on the one side of a sphere than on the other?

Guth didn't have two plates to work with, so what are the "boundary" conditions of his "vacuum"?

Unnecessary, a uniform field has negative pressure.

 

[Tubbythin]

Yes you are. You're ignoring the fact that every single atom in that Casimir chamber still has kinetic energy and it exerts PRESSURE and everything it hits.

That would be the gas pressure.

You're ignoring the kinetic energy of the neutrinos,

I calculated this a previous thread. There would be of order one neutrino interaction per plate per year.

the EM field and everything inside the 'vacuum'.

No. We are explicitly NOT ignoring the EM field. It is from the EM field which the Casimir pressure comes. Using only the ideal gas equation is, however, ignoring the EM field.

In fact the fact you believe that photons do not have kinetic energy just demonstrates the problem!

Kinetic energy is the amount of energy required to accelerate a body from rest to its current velocity. This does not apply to photons. Photons have energy and they have momentum. But this does not depend on their mass (they don't have one) or their velocity. So, please explain to me, under what definition do photons have kinetic energy?

How do you figure the secondary of the coil in your car ends up with "current flow" if no kinetic energy transfers take place?

What are you talking about?

The photons also carry POSITIVE KINETIC ENERGY. There's more of it on the outside of the plates and less of it on the inside of the plates.

Photons do not carry kinetic energy. Why do you keep insisting the pressure must come from kinetic energy? Does the pressure an elephant exerts on the ground come from kinetic energy?

Guth didn't have two plates to work with, so what are the "boundary" conditions of his "vacuum"?

Inflation isn't the Casimir effect.

No, it's not inappropriate to determine the lower limit of pressure in a vacuum because all vacuums contain SOME gas.

But that does not define the lower limit of pressure. It defines the lower limit of gas pressure. If you only use the ideal gas equation you'll only get the pressure of an ideal gas. If there is pressure from something else then you'll get the wrong answer.

Actually, in terms of their ability to transfer kinetic energy they aren't all that different. It's still just "kinetic energy".

Photons do not have kinetic energy. And even if they did they'd still be completely different since photon number is not conserved.

 

[Michael Mozina]

Michael. In the early universe in the inflationary picture both matter and radiation exist at vastly higher positive pressures and densities than they do now. The point is that there exists a negative and larger vacuum energy that drives inflation.

What endowed the vacuum with "negative energy"? What is "negative energy"? How does inflation affect anything related to "vacuum pressure"?

That it is a vacuum energy does not imply that it only operates in a vacuum. It merely implies it would still exist without the matter and radiation present.

What still exists? Kinetic energy in some form? How would that "pull" on any ONE THING we added to an otherwise "basic vacuum"?

Your claim that we disregard any lesser positive pressure in a negative-pressure dominated situation is ridiculous.

My claim is that you ignore the kinetic energy aspects entirely and that no "Vacuum" can achieve an absolute NEGATIVE pressure.

 

[Tubbythin]

My claim is that you ignore the kinetic energy aspects entirely and that no "Vacuum" can achieve an absolute NEGATIVE pressure.

The point is that your claim has not been backed up by anything other than a completely inappropriate use of the ideal gas equation.

 

[Ziggurat]

My claim is that you ignore the kinetic energy aspects entirely

There is no kinetic energy aspect. Photons have no kinetic energy, because they have no mass. Their energy is simply a field energy, the same energy that, say, a charged capacitor (where NOTHING is moving) stores.

and that no "Vacuum" can achieve an absolute NEGATIVE pressure.

That's demonstrably false.

 

[edd]

What endowed the vacuum with "negative energy"? What is "negative energy"? How does inflation affect anything related to "vacuum pressure"?

It's not negative energy. You have to stop making these incredibly basic errors before you can legitimately claim there's a problem.

What still exists? Kinetic energy in some form? How would that "pull" on any ONE THING we added to an otherwise "basic vacuum"?

What? No! Vacuum energy.

My claim is that you ignore the kinetic energy aspects entirely and that no "Vacuum" can achieve an absolute NEGATIVE pressure.

We're clearly not on the same page here Michael. You can't criticise the last chapter when you're still struggling to read the initial dedication.

 

[Reality Check]

Why is the the calculated pressure exerted by the Casimir effect negative

It's a RELATIVE measurement of pressure, not an ABSOLUTE pressure.
...snipped usual rant...

That is ignorant of you MM. The derivation of the pressure only looks at the pressure within the plates. Casimir effect

In the original calculation done by Casimir, he considered the space between a pair of conducting metal plates at distance a apart. In this case, the standing waves are particularly easy to calculate, since the transverse component of the electric field and the normal component of the magnetic field must vanish on the surface of a conductor.

There is no other pressure to be RELATIVE to. Thus it is an ABSOLUTE pressure.

So lets try again:
Micheal Mozina,
Why is the the calculated pressure exerted by the Casimir effect negative?

Why is the measured pressure exerted by the Casimir effect negative?

 

[Perpetual Student]

 

[rwguinn]

This all seems to be a matter of semantics and convention at the quantum level. My expertise and knowledge ends at a more macro level.
Hell-I left the EE programs when they started talking about "holes" moving.
Just as Newtonian physics is a very good approximation for relatively low (HA!) velocities, the IGL is a good representation of gas behavior for a reasonable value on "n" and "T".
I freely admit that the IGL falls apart as n->0, or as T->0. I think that was part of my point originally, anyway.
For all practical purposes T is always 0 or greater, and P is always 0 or greater. Electron spin measurement is way beyond my idea of practicality...
ETA: with my knowledge and training, and desire--you folks could be lying through your teeth, and I'd never know...

 

[Reality Check]

I've already done so. No experiment of a vacuum on Earth takes place in anything other than a POSITIVE PRESSURE scenario. It's not even humanly possible to construct a 'zero pressure' vacuum. That alone should get you to drop your outrageous claim, but NOOOOOOO.

More ignorance from you, Michael Mozina.
Of course laboratory vacuums are not perfect vacuums!

An idiot would assume that the pressure in experimental vacuum chambers is zero. A total idiot would assume that other people think that.

There is a reason why Casimir effect measurements are not done at room pressures. It is to reduce the POSITIVE PRESSURE exerted by any gas atoms left in the apparatus to a negligible level. Maybe you have herd of the ideal gas law? It has the number of particles in it . Keep T and V constant, reduce n and P decreases. Remove enough particles and P is smaller than other source of pressure, e.g. the Casimir effect .

To put it simply for you:
A tiny replusive force exerting a POSITIVE PRESSURE.
A big attractive force exerting a NEGATIVE PRESSURE.
Add the tiny replusive force to the big attractive force. You get a slighty smaller attractive force and a NEGATIVE PRESSURE.

 

[edd]

This all seems to be a matter of semantics and convention at the quantum level. My expertise and knowledge ends at a more macro level.

If it's semantics and convention, Michael's using the wrong semantics and convention for discussing cosmology.
Also, I don't believe it particularly needs quantum theory to explain either - and Michael's objections appear to be based on a certain class of laboratory experiment rather than any theoretical concerns - he simply claims negative pressure has not been observed in the laboratory and therefore its existence cannot be justified.
I think that this latter claim is unnecessarily conservative.

 

[Michael Mozina]

The point is that your claim has not been backed up by anything other than a completely inappropriate use of the ideal gas equation.

Baloney. It's "backed up" by the fact human beings are physically incapable of creating even a ZERO pressure vacuum!

 

[Tubbythin]

Baloney. It's "backed up" by the fact human beings are physically incapable of creating even a ZERO pressure vacuum!

It doesn't matter in the slightest. So long as the vacuum pressure is bigger or comparable in magnitude to the gas pressure it will still be observed.

 

[Michael Mozina]

It doesn't matter in the slightest. So long as the vacuum pressure is bigger or comparable in magnitude to the gas pressure it will still be observed.

What exactly is 'vacuum pressure' *BESIDES* particles with kinetic energy?

You seem to have a physical disconnect somewhere between your beloved math formulas and empirical physics. The "pressure" of a gas is increased when the temperature of the gas increases. That is because the particles contain 'kinetic energy" and they move around FASTER than a cold gas. That change in kinetic energy is why pressure is related to temperature.

Photons also contain and transfer 'kinetic energy' even if they don't have 'mass' (according to theory). They are still capable of transferring kinetic energy, just like a neutrino or an atom. Now a vacuum is typically not 'empty". It has particles of mass embedded in it. They bounce around and transfer particle kinetic energy to the sides of the chamber that we record as 'pressure" in the vacuum. If (and only if) we can remove *EVERYTHING* from the chamber, particle kinetic energy reaches zero (assuming photons and neutrinos are also removed). At that point *THEORETICALLY AT LEAST* we *MIGHT* achieve a zero kinetic energy state in the vacuum.

In terms of the "pressure" in a "Vacuum" that's as low as it gets boys and girls, *ZERO* pressure. I know you have a physical disconnect here because you cannot even tell me what you would add or subtract from that 'pure vacuum" state to achieve a "negative" pressure. You're (as a group) clueless when it comes to particle physics, and you're therefore equally incapable of explaining what you would physically do the the vacuum to make it have 'negative pressure"".

 

[Reality Check]

What exactly is 'vacuum pressure' *BESIDES* particles with kinetic energy?
...snipped usual rant...

MM, applying a little reading comprehension will help you a lot.

It is obviously vacuum pressure as opposed to gas pressure. In Casimir experiments you have 2 sources of pressure

1. The residual gas inside the apparatus that exerts a gas pressure.
2. The virtual particles inside the apparatus that exert a vacuum pressure.

In terms of the "pressure" in a "Vacuum" that's as low as it gets boys and girls, *ZERO* pressure.

Stop displaying your ignorance to the boys and girls, MM

There are pressures from

• Gas
  Arranged to be negligible in experiments by removing as much gas as needed.
• Photons
  Arranged to be negligible in experiments by not applying EM fields or shining lasers into the chamber!
• Virtual particles

 

[Michael Mozina]

If it's semantics and convention, Michael's using the wrong semantics and convention for discussing cosmology.
Also, I don't believe it particularly needs quantum theory to explain either - and Michael's objections appear to be based on a certain class of laboratory experiment rather than any theoretical concerns - he simply claims negative pressure has not been observed in the laboratory and therefore its existence cannot be justified.
I think that this latter claim is unnecessarily conservative.

Do you really think it's unnecessarily conservative? Let's take a good hard look at what you CANNOT justify or verify in the lab. Most of the list CANNOT EVER be verified in the lab due to physical limitations either related directly to your claim, or just real physical limitations:

1. Negative pressure in a vacuum
2. Inflation
3. Expansion of space
4. Derk Energy
5. SUSY theory (the one real hope you have for any sort of empirical vindication)

Virtually your *ENTIRE* theory (at least 96%) is dependent upon what you CANNOT demonstrate in the lab, and only 4% is based on empirical physics that you can justify in an empirical manner. How is that not a 'religion" in terms of having "faith in the unseen" (in the lab)? If I don't "bow" to your will, you (collectively not personally) seem more than happy to bash me personally, so the peer pressure is exactly the same as far as I can tell.

 

[Reality Check]

How many stars have been measured in a lab, MM

:
1. Negative pressure in a vacuum
2. Inflation
3. Expansion of space
4. Derk Energy
5. SUSY theory (the one real hope you have for any sort of empirical vindication).

Now with your obsession with measuring things in a lab. How many stars have been measured in a lab, MM?

Negative pressure in a vacuum has been measured (Casimir effect)

 

[Tubbythin]

What exactly is 'vacuum pressure' *BESIDES* particles with kinetic energy?

The pressure exerted due to the vacuum energy. The latter having nothing to do with kinetic energy.

You seem to have a physical disconnect somewhere between your beloved math formulas and empirical physics. The "pressure" of a gas is increased when then temperature of the gas increases. That is because the particles contain 'kinetic energy" and they move around FASTER than a cold gas. That change in kinetic energy is why pressure is related to temperature.

The change in kinetic energy is why gas pressure is related to temperature. But we're not talking about a gas.

Photons also contain and transfer 'kinetic energy' even if they don't have 'mass' (according to theory).

No, they still have momentum and energy but no work is done in accelerating them from 0 to c.

They are still capable of transferring kinetic energy, just like a neutrino or an atom.

No, they are still capable of transferring energy, but the processes are somewhat different to particles which obey different conservation laws.

Now a vacuum is typically not 'empty". It has particles of mass embedded in it. They bounce around and transfer particle kinetic energy to the sides of the chamber that we record as 'pressure" in the vacuum.

Ok...

If (and only if) we can remove *EVERYTHING* from the chamber, particle kinetic energy reaches zero (assuming photons and neutrinos are also removed). At that point *THEORETICALLY AT LEAST* we *MIGHT* achieve a zero kinetic energy state in the vacuum.

If you insist. I've never really heard anyone talk in such terms before though.

In terms of the "pressure" in a "Vacuum" that's as low as it gets boys and girls, *ZERO* pressure.

No it isn't. You are ignoring the pressure due to the vacuum energy.

I know you have a physical disconnect here because you cannot even tell me what you would add or subtract from that 'pure vacuum" state to achieve a "negative" pressure.

It is not me that has the physical disconnect. I am not the one repeatedly asking what needs to be added to or removed to change the pressure. When was pressure defined in terms of the number of items in the system? Never. That's when. It is because you continually and repeatedly insists, with zero justification, that gas pressure is the only relevant form of pressure that you keep coming up with the wrong answer.
Do you understand the following statement: "There are forms of pressure other than gas pressure. Some of these forms of pressure do not depend on the number of items in the system. Pressure is not defined by the number of items in the system".

You're clueless when it comes to particle physics,

I'm not the one invoking neutrino pressure or trying to use the ideal gas equation to describe the pressure of the vacuum energy. So excuse me if I scoff at your claims of my cluelessness.

and you're therefore equally incapable of explaining what you would physically do the the vacuum to make it have 'negative pressure"".

No I'm not. You're just completely incapable of seeing past the ideal gas equation.

 

[Michael Mozina]

MM, applying a little reading comprehension will help you a lot.

It is obviously vacuum pressure as opposed to gas pressure. In Casimir experiments you have 2 sources of pressure

1. The residual gas inside the apparatus that exerts a gas pressure.
2. The virtual particles inside the apparatus that exert a vacuum pressure.

1. 
   
   Both types of "pressures" are directly related to the transfer of particle kinetic energy and they are both POSITIVE. Try comprehending that. All "pressure" is directly related to PARTICLES and MOVEMENT/Kinetic energy of those particles. The complete removal of all particle kinetic energy is *IMPOSSIBLE* so all vacuums have a "positive' pressure, and positive kinetic energy. You cannot make a vacuum contain negative kinetic energy.
   
   You guys and girls really do have a physical disconnect between particle physics and your math formulas. You're great at the macroscopic level, but in the microscopic realm, you're like a fish out of water. You just don't "get it".
   
   There's no physical possibility of making any vacuum on Earth reach a "zero' pressure state. The neutrinos alone preclude that from *EVER* happening. It's not even possible to remove every single atom from a 'vacuum' and there is certainly no way to remove every single photon, every single neutrino, etc etc. The very most you could hope for is a very LOW PRESSURE vacuum, or even "theoretically speaking" at least, a 'zero' pressure vacuum. You absolutely will never achieve that here on Earth in your lifetime. You *might* achieve that zero pressure state in "theory". What then are you going to to do to that vacuum to make it have a "negative pressure"?