Can pressure be negative?

[Michael Mozina]

That would depend on how they interacted with the vacuum. But yes, the Casimir effect (an example of negative pressure in a vacuum) can pull objects together from inside. Michael likes to pretend that it's really a push from outside, but that explanation actually fails rather dramatically under serious scrutiny.

It really doesn't make a darn bit of difference if they are "pushed" together or "pull' each other due to atomic attraction. You don't have another PLATE to work with in a vacuum, just your *SINGLE* clump of 'stuff' and the vacuum itself. If you had *ANOTHER* clump of separate stuff, *THEN* and only then would your analogy have any merit. Since you don't have two things to even work with in the first place, your two plate analogy is MEANINGLESS to Guth's claim.

 

[Ziggurat]

It really doesn't make a darn bit of difference if they are "pushed" together or "pull' each other due to atomic attraction.

You're wrong.

You don't have another PLATE to work with in a vacuum

You're right: the plate isn't in the vacuum.

It's the boundary of the vacuum.

Since you don't have two things to even work with in the first place, your two plate analogy is MEANINGLESS to Guth's claim.

I'm not talking about Guth yet. You don't know enough to talk about Guth yet either.

 

[JohnnyG]

Negative pressure is indeed possible in metastable liquids.

http://discovermagazine.com/2003/mar/featscienceof

 

[edd]

Inflation isn't about the pressure acting directly as a force/area. It's about the gravitational effect of the energy content. This has been explained at length, repeatedly, to the point of ridiculousness.

 

[Michael Mozina]

No it doesn't. The ideal gas law is wrong. Even for a single atom.

Only if you have something OTHER THAN atoms in chamber!

No matter what type of particle you put into that vacuum, it's going to have POSITIVE KINETIC energy, and there is no such thing a NEGATIVE kinetic energy. Even light is going to exert POSITIVE kinetic energy on everything it bumps into, as will all those neutrinos in the vacuum. You can't even show me one experiment that achieves a ZERO pressure in a vacuum (and only a vacuum). The only way you've even been able to construct ANY sort of "negative pressure" argument is by using TWO OBJECTS and Guth only has one! Your analogy isn't even applicable, nor is it an example of 'negative pressure in a vacuum". If you actually were achieving a "negative pressure' in that chamber with two plates, then the type of material that was used would be utterly and completely irrelevant. It's not. There *MAY* actually be a "pull' from the other plate for that matter, but even that is not related to the pressure of the vacuum, just the distance between the plates!

 

[Michael Mozina]

Inflation isn't about the pressure acting directly as a force/area. It's about the gravitational effect of the energy content. This has been explained at length, repeatedly, to the point of ridiculousness.

Inflation didn't even have a scientific precedent before Guth literally "made it up" in his head. You can't even construct an experiment using inflation, so there goes any hope of any empirical demonstration of concept.

You're literally "making up" the properties of inflation and then "INSISTING* that I agree with them. Forget it.

 

[Ziggurat]

Only if you have something OTHER THAN atoms in chamber!

Nope. The ideal gas law is wrong. It's wrong for ALL gasses. It's wrong even if you have nothing else in your chamber.

Really, your continued willful ignorance on such a fundamental and simple issue should be embarrassing.

 

[Michael Mozina]

Nope. The ideal gas law is wrong. It's wrong for ALL gasses. It's wrong even if you have nothing else in your chamber.

Really, your continued willful ignorance on such a fundamental and simple issue should be embarrassing.

The fact you've been reduced to trying to use *TWO* things in a vacuum to demonstrate your claim about negative pressure is what is embarrassing. Your whole bang theory is predicted on having ONE and only one CLUMP of material, surrounded by nothing but a "vacuum". The fact you don't realize it's all about kinetic energy is also pretty damn embarrassing from my perspective.

 

[Reality Check]

FYI, RC's question relates back to the pressure of a VACUUM in the total absence of anything *OTHER THAN* the vacuum itself.

No. My question is about pressure in general. VACUUM is not meantioned at all in the OP.

The pressure of a VACUUM by defintion has no pressure. But a vacuum is never in total absense of anything *OTHER THAN* the vacuum itself. There are virtual particles and these exert pressure.

The formula PV=nRT

Is the ideal gas law and applies to an ideal gas.

 

[edd]

The fact you've been reduced to trying to use *TWO* things in a vacuum to demonstrate your claim about negative pressure is what is embarrassing. Your whole bang theory is predicted on having ONE and only one CLUMP of material, surrounded by nothing but a "vacuum". The fact you don't realize it's all about kinetic energy is also pretty damn embarrassing from my perspective.

No.

 

[Reality Check]

The bottom line is that you can't get a single *REAL* vacuum down to even an absolute ZERO pressure state, let alone a negative one.

You are wrong.
The bottom line is that when scientists have measured negative pressure in lots of *REAL* vacuums, e.g. Tests of new physics from precise measurements of the Casimir pressure between two gold-coated plates

 

[Michael Mozina]

No. My question is about pressure in general. VACUUM is not meantioned at all in the OP.

No, of course not because then the jig is just up. If you don't have liquids and/or solids to muddy the question with, your whole argument falls apart immediately. Even your Casimir effect requires ONE MORE ITEM than Guth had to work with. If you limit yourself to ONE THING in the vacuum and you only talk about the pressure of a vacuum (not liquids and solids), your whole belief system crumbles and you have no *POSSIBLE* way to avoid the obvious.

The pressure of a VACUUM by defintion has no pressure. But a vacuum is never in total absense of anything *OTHER THAN* the vacuum itself. There are virtual particles and these exert pressure.

If the vacuum is not empty, it contains *POSITIVE KINETIC ENERGY* and therefore positive pressure. You can't get any particle to contain "negative kinetic energy".

Is the ideal gas law and applies to an ideal gas.

That ideal gas law also clearly demonstrates the limits of pressure in a vacuum. It's zero, not negative infinity.

Let's see you justify *GUTH's* claim. He didn't have two plates inside the vacuum, just ONE THING. Which experiment demonstrates that ONE THING inside of a vacuum can be surrounded by "negative pressure" that the vacuum itself exerts on any surface of a *SINGLE* object in the chamber?

 

[Reality Check]

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?

An example of negative pressure is the pressure exerted by the Casimir effect:

• h bar is positive.
• c is positive.
• pi is positive.
• pi squared is definitely positive!
• 240 is positive.
• a is the separation (positive again!)
• a to the fourth power is definitely positive!

There is a negative sign in front of multiplying and dividing these positive quantities. Theerfore the pressure is negative.

 

[edd]

Seriously Michael, if you can't figure out that it's not a clump of matter sitting in a vacuum, you're not ready to think about inflation. You need to figure out the Big Bang generally and understand that first before getting wound up about anything else.

 

[Michael Mozina]

You are wrong.
The bottom line is that when scientists have measured negative pressure in lots of *REAL* vacuums, e.g. Tests of new physics from precise measurements of the Casimir pressure between two gold-coated plates

BS. That's ONE MORE ITEM than Guth had to work with RC. You're already using an analogy that isn't even the least bit appropriate.

The worst part is that the material itself makes a difference, and the actual "pressure" of the chamber does not matter. Either the plates are "pushed' together by the energy of the 'vacuum", or they are "pulled together" by the attraction between the atoms inside the two plates, but either way, there is no region in the vacuum itself that experiences "negative pressure". The whole thing still occurs in a POSITIVE pressure scenario, so it can't possibly be "vacuum pressure" related in the first place. You can have high and low pressures in a chamber, and high and low absolute temperatures, but you can't have negatives of either one.

 

[Michael Mozina]

Seriously Michael, if you can't figure out that it's not a clump of matter sitting in a vacuum, you're not ready to think about inflation.

I read Guth's paper edd. I saw him try to claim his "vacuum" had a "negative pressure". Inflation doesn't have any effect on "pressure" in any experiment on Earth. You're just "making it up" and then expecting me to agree with you - or else. The "or else' part is a ton of ridicule and claims about how "I just don't understand". It's like an astrologer telling me the I'm not ready to think about astrology yet because I don't agree with their claim before we begin.

You need to figure out the Big Bang generally and understand that first before getting wound up about anything else.

I understand that Guth had NO PRECEDENT at all before 'whipping up' his mythical inflation deity in his head. Whatever you *THINK* it does is a pure act of faith on your part because you absolutely cannot demonstrate your claims here on Earth in a real controlled experiment.

 

[Tubbythin]

Oh boloney. If we added just ONE atom to your mystical sort of "vacuum" then the formula and the recorded pressure EXACTLY matches the ideal gas law and it is a COMPLETELY valid method of determining the pressure. It has a POSITIVE pressure.

Nope. It doesn't even make sense to discuss gas pressure with a single atom. After all, the atom cannot exert a force on all walls simultaneously. For example, the IGL contains a variable, T, for temperature. But temperature is only defined for macroscopic quantities.

If we now remove that SINGLE ATOM from that very same vacuum chamber, the pressure drops to zero. That *IS* the appropriate function for the pressure of a vacuum. The lowest limit of pressure in a vacuum is zero.

No it isn't. It completely ignores the Casimir force.

This whole conversation demonstrates just how little any of you understand KINETIC ENERGY. You seem to have some irrational belief that the pressure in a vacuum is somehow completely physically detached from kinetic energy. It's not. When the temperature goes up, the atoms have more kinetic energy and exert more pressure on the sides of the chamber.

Its a vacuum, there are no atoms.

As you cool the atoms, they have less kinetic energy and exert less pressure on the sides. If you removed ALL the kinetic energy you achieve ZERO pressure in a vacuum.

No, if you remove all atoms there is zero gas pressure. You do realise that not all pressures are gas pressures. You do realise that when you stand up your weight exerts pressure on the floor. Would you try to describe that with the ideal gas equation? Because that kind of situation has more in common with an ideal gas than the Casimir effect does.

There is no such thing as "negative kinetic energy", so there is no such thing as 'negative pressure'.

Pressure isn't defined in terms of kinetic energy so the second half of the sentence is completely meaningless.

You folks are utterly clueless at the level of particle kinetic energy, and that's your same problem as it relates to MR theory as well.

Says the person who is, yet again, trying to use the ideal gas law (which is classical (ie non-relativistic), classical (ie non-quantum) and number is conserved) to describe the pressure exerted by virtual particles (which are relativistic quanta with where number is not conserved). Can you not see these situations are completely different.

 

[Reality Check]

Even your Casimir effect requires ONE MORE ITEM than Guth had to work with.

Guth did not work with a vacuum. The universe is not a vacuum.

If you limit yourself to ONE THING in the vacuum and you only talk about the pressure of a vacuum (not liquids and solids), your whole belief system crumbles and you have no *POSSIBLE* way to avoid the obvious.

Only an idiot would limit themselves to a vacuum with absolutely no contents.
Casimir considered the virtual particles in a vacuum.
Guth considered the entire universe with all of its mass and energy (in a vacuum)

f the vacuum is not empty, it contains *POSITIVE KINETIC ENERGY* and therefore positive pressure. You can't get any particle to contain "negative kinetic energy".

KE = 1/5mv^2
But this has nothing to do with pressure which is the consequence of a force on a surface. A repulsive force exerts a positive pressure. An attractive force exerts a negative pressure.

That ideal gas law also clearly demonstrates the limits of pressure in a vacuum. It's zero, not negative infinity.

That ideal gas law also clearly demonstrates the limits of the pressure of an ideal gas in a vacuum. It's unlimited (temperatures can be negative).
But in reality ideal gases always have positive pressure.

Let's see you justify *GUTH's* claim

Done: It is simple to show that a cosmological constant in GR results in a negative pressure.

ETA
Whoops, I assumes that you knew what you were talinkg about MM .
Actually Guth made no claim about negative pressures in GR.

• Einstein made that claim.
• Everyone who has ever worked with GR makes that claim.
• Any one who can read and understand the relatively simple math that shows that a cosmological constant means negative pressure makes that claim.
• Wikipedia makes that claim!
• Scholarpedia makes that claim.

Guth's scientific theory ("claim") is the inflationary period of the early universe driven by a negative-pressure vacuum energy density. Its ppredictions have been verified by observations.

 

[Ziggurat]

I read Guth's paper edd.

But you didn't understand it.

 

[Michael Mozina]

Micheal Mozina,
Why is the the calculated pressure exerted by the Casimir effect negative?

It's done that way for the same reason the lift of a wing, or the pressure on a wing might be calculated relative *ONLY* to the top of the wing. It's a RELATIVE measurement of pressure, not an ABSOLUTE pressure. There is MORE kinetic energy hitting the outside surfaces of the plates and LESS kinetic energy pushing on the inside of the plates.

You're whole argument is stupid because it's impossible for any vacuum to achieve even a zero pressure here on Earth. We don't even have the technology to construct a "vacuum" that is anything other than a "positive pressure" environment.

The other thing that makes you claim ridiculous is that the type of material makes a difference and that wouldn't happen if it was really a "negative pressure" between the plates.

The *WORST* part of your analogy however is that it's *COMPLETELY AND UTTERLY INAPPROPRIATE* because Guth didn't have *two* things to rub together in the first place, just one!