Can pressure be negative?

[Michael Mozina]

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

As long as you stick to elements on the periodic table when constructing stars, why should I care? If you're going to claim that stars of made of SUSY particles, I'd first like to see you produce a few SUSY particles. Is that too much to ask?

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

No RC, it has not. You've either measured the EM attraction between TWO things (which you do not have in GUTH's creation mythos), or you've measured *RELATIVE KINETIC PRESSURE* on *BOTH* sides of the plates. Either way, the PRESSURE OF THE VACUUM is *irrelevant*. The same exact process works at virtually any "pressure" we put into the chamber! It therefore has NOTHING to do with the "pressure" of the chamber or the pressure of a vacuum.

 

[Reality Check]

Both types of "pressures" are directly related to the transfer of particle kinetic energy and they are both POSITIVE.

You are wrong. The pressure form gas atoms (and photons) is POSITIVE.

The pressure from virtual particles depends on the situation and can be either positive or negative. It is nothing to do with any kinetic energy of the virtual particles.

Why is the the calculated pressure exerted by the Casimir effect negative?
Why is the the measured pressure exerted by the Casimir effect negative?
First asked 7 April 2011

 

[Tubbythin]

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

Has lab-based experiment justification. Is also a result of QED, the most precisely tested theory in the history of physics.

2. Inflation

Is consistent with multiple subsequent empirical observations.

3. Expansion of space

A direct result of general relativity which has been lab tested, tested via Earth-moon experiments, Earth-satellite experiments and observational experiments.

4. Derk Energy

No idea what that is, sorry.

5. SUSY theory (the one real hope you have for any sort of empirical vindication)

Clearly not (see above).

Virtually your *ENTIRE* theory (at least 96%) is dependent upon what you CANNOT demonstrate in the lab,

So what. The lab is a matter of human conveinience. The only reason to restrict ones scientific understanding to experiments conducted in the lab is if one thought the laws of the Universe were designed to be understood on scales that were practical for humans. The only reason someone would think that is if they thought the Universe was designed specifically for humans.

and only 4% is based on empirical physics that you can justify in an empirical manner.

Nope. Empirical just means information that has come from experiment rather than theory. The evidence for, dark matter say, is thus close to 100% empirical.

How is that not a 'religion" in terms of having "faith in the unseen" (in the lab)?

Err, I think assuming that all facets of the Universe must be determinable on a scale of human convenience is a million times more religious than the practice by which information is synthesized from as many available avenues as possible? Don't you?

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.

You get "bashed" because you make bold, unsupported statements about fields you have no experience in or little knowledge of and assume, rather arrogantly, that if you don't understand something it must be the theory, not your comprehension, that is lacking.

 

[Michael Mozina]

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

http://physicsworld.com/cws/article/news/37241

It's not. It entirely depends on the geometry and QM interactions in the chamber RC. Since the process works at *VIRTUALLY ANY PRESSURE*, and only with EM types of materials, your claim that the Casimir effect is an example of negative pressure in a vacuum is obviously erroneous. You might want to start by explaining why *IF* there was an actual negative pressure between the plates, the type of material even matters.

 

[Reality Check]

As long as you stick to elements on the periodic table when constructing stars, why should I care?

Whys does the existence of elements mean that stars exist?
There have been no stars in labs so by your logic stars do not exist!

No RC, it has not.

Yes MM, it has: negative pressures have been measured in Casimir experiments.

 

[Reality Check]

http://physicsworld.com/cws/article/news/37241

It's not. It entirely depends on the geometry and QM interactions in the chamber RC.

I know that MM.
So now do you aknowledge that with a given configuration a negative pressure is produced by the Casimir effect (as stated in your citation )?

 

[mike3]

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.

But is this really "negative pressure" like what would happen if you could get a negative reading on a barometer? Below vacuum pressure, so that objects have a sort of uniform outward force applied to them, like how that when an object is submerged in an atmosphere it has a uniform inward force applied? You say it "pulls them together" -- but that isn't what I expect from negative pressure: I'd think the term would mean in outward, apart effect, not an inward together effect, regardless of whether or not it's from an external inward push or internal inward pull. It's the "inwardness" that's the problem.

 

[Tubbythin]

Both types of "pressures" are directly related to the transfer of particle kinetic energy and they are both POSITIVE.

No they are not.

Try comprehending that.

Why comprehend something that is not only unsupported but directly contradicted by experiment?

All "pressure" is directly related to PARTICLES and MOVEMENT/Kinetic energy of those particles.

No it isn't. How is the pressure from the weight of an elephant related to kinetic energy?

The complete removal of all particle kinetic energy is *IMPOSSIBLE* so all vacuums have a "positive' pressure, and positive kinetic energy.

No. If the pressure due to the vacuum energy is more negative than the gas pressure then the net pressure is negative.

You cannot make a vacuum contain negative kinetic energy.

Nobody said they could. But then nobody is claiming that negative pressure is associated with negative kinetic energy.

You guys and girls really do have a physical disconnect between particle physics and your math formulas.

Nope. You do not understand that pressure is not defined in terms of kinetic energy.

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".

Sadly for you, multiple experiments say you're wrong.

There's no physical possibility of making any vacuum on Earth reach a "zero' pressure state. The neutrinos alone preclude that from *EVER* happening.

Don't be stupid. A neutrino that passes through a vacuum without interacting (ie all of them) exerts 0 pressure.

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.

It doesn't matter.

The very most you could hope for is a very LOW PRESSURE vacuum, or even "theoretically speaking" at least, a 'zero' pressure vacuum.

No. One can have a close to zero gas pressure and a negtive pressure due to the vacuum energy. You do realise that if a = 1 and b = -2 that c = a + b = -1 don't you?

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"?

Make sure it has a greater negative pressure from vacuum pressure than positive pressure from gas pressure. Obviously.

 

[edd]

I wonder what Michael would think if I said that relativistically speaking pretty much every gas made of atoms has zero pressure.

 

[Tubbythin]

You might want to start by explaining why *IF* there was an actual negative pressure between the plates, the type of material even matters.

I already did this a few hours ago. You have a very short memory. Conductive media require that the vacuum fluctuations have nodes at the surfaces. Non-conductive media do not enforce the same boundary requirement. Different boundary conditions, different results.

 

[mike3]

So what. The lab is a matter of human conveinience. The only reason to restrict ones scientific understanding to experiments conducted in the lab is if one thought the laws of the Universe were designed to be understood on scales that were practical for humans. The only reason someone would think that is if they thought the Universe was designed specifically for humans.

And that the designer wanted to make it easy to understand, too.

You get "bashed" because you make bold, unsupported statements about fields you have no experience in or little knowledge of and assume, rather arrogantly, that if you don't understand something it must be the theory, not your comprehension, that is lacking.

So what would happen if one were to refuse to use all personal attacks, and only use actual arguments? And furthermore, has he actually said that: "I don't understand this, thus it must be wrong?" Or could it be that he does not know he doesn't grasp it? (Dunning-Kruger effects and similar phenomena could be in play. When you don't know, you may not really know that you don't know.)

 

[Perpetual Student]

You get "bashed" because you make bold, unsupported statements about fields you have no experience in or little knowledge of and assume, rather arrogantly, that if you don't understand something it must be the theory, not your comprehension, that is lacking.

How true! Around and around you go with the same fruitless discussion. I have not yet regretted keeping Mozina in ignore. When someone quotes him and I get a glimpse of his anti-scientific ramblings, I cherish the fact that he's only an occasional (4%?) Internet abstraction.

 

[mike3]

How true! Around and around you go with the same fruitless discussion. I have not yet regretted keeping Mozina in ignore. When someone quotes him and I get a glimpse of his anti-scientific ramblings, I cherish the fact that he's only an occasional (4%?) Internet abstraction.

So why not just quit this whole "debate" thing entirely? Just quit?

 

[MattusMaximus]

Pressure doesn't "suck"

Yes, negative pressure can only be below some other value above zero.
Space is a pretty good zero level of pressure.
Suction is negative pressure, but relative to some higher pressure.
It's what makes the coke go up the straw, when you make "negative pressure" in your mouth.
That might be a tenth of a psi less than the static pressure on the surface of the liquid.

Nitpick: "suction" is a misnomer. Suction doesn't exist, because if it did we wouldn't have an upper limit on the height to which mercury could rise in a barometer. If suction were a real effect, then an ever larger evacuated chamber at the top of the barometer tube would "suck" the mercury ever higher, but this never happens because the upper limit isn't the result of "suction", it is the result of an excess pressure from outside of the barometer pushing the mercury up the tube. No matter how much "suction" one provides by a larger vacuum tube, the mercury will only rise up as high as the atmospheric pressure can push it.

In the context in which you put it, "negative pressure" is more appropriately labeled as a pressure differential, where the pressure inside the soda straw is less than that of the atmosphere shoving the liquid up the tube. So while the relative pressure is negative inside the straw, the absolute values of both the pressure inside and outside the soda straw are still positive (it's just a question of which is bigger).

So, in this context, terms like "negative" pressure and "suction" are misnomers. However, when discussing pressure in the limited context of fluids & hydrostatic (and hydrodynamic) scenarios, it is only a subset of ideas of pressure, as was outlined nicely within the OP.

 

[sol invictus]

Regarding the Casimir effect - one might try to argue that the negative pressure between two conductive plates in the classic Casimir experiment arises because the vacuum outside the plates has a higher pressure than the vacuum between them.

There's a very simple way to see that this cannot be the explanation. Consider a variation on the experiment, where the plates are replaced by a periodic boundary condition. In other words, imagine that the universe in at least one direction is wrapped around in a circle (never mind whether it's possible to do this experimentally - although it actually may be - just think of it as a math exercise). There's no distance between the plates (because there are no plates), but there's a distance around the circle that plays the same role. Most importantly, there's no space "outside" the plates.

It turns out when you do that, you get a Casimir force that either tries to make the circle bigger or smaller, depending on the types of particles you have in your theory. So you can have pressure of either sign, and it manifestly has nothing to do with the pressure "outside" - because there is no outside.

 

[Andrew Wiggin]

Working in the hospital environment, we have "negative pressure isolation rooms" where we put patients with TB, for example.

I'm assuming it's negative relative to the pressure outside the room (and that's the only reason it's "negative"), and outside the room we have a digital reading which lets us know whether or not the room is operating correctly. There is also a simple test (quick and dirty so to speak) of dropping a kleenex slightly beyond the threshold and watching it "suck" into the room.

I know the question the OP is asking is mathematical in nature, but I thought I would throw this anecdote in there just for it's novelty value perhaps ...

Ours have a little glass housing mounted over the door. There's a hole in the housing and a thin metal vane that hangs down. If the pressure in the room is less than the pressure in the hallway, air jets through the hole and blows the vane over. There's a rough scale on the glass for how much the vane deflection means in terms of pressure but in practice it just deflects full scale or doesn't deflect at all. I've never really noticed tissues and such being pulled into the rooms, but then again I've always just looked at the indicator.

 

[Cuddles]

Several posts removed to AAH. This thread is about whether pressure can be negative. Do not derail it with general claims about all physics being wrong.

Replying to this modbox in thread will be off topic  Posted By: Cuddles

 

[rwguinn]

Regarding the Casimir effect - one might try to argue that the negative pressure between two conductive plates in the classic Casimir experiment arises because the vacuum outside the plates has a higher pressure than the vacuum between them.

There's a very simple way to see that this cannot be the explanation. Consider a variation on the experiment, where the plates are replaced by a periodic boundary condition. In other words, imagine that the universe in at least one direction is wrapped around in a circle (never mind whether it's possible to do this experimentally - although it actually may be - just think of it as a math exercise). There's no distance between the plates (because there are no plates), but there's a distance around the circle that plays the same role. Most importantly, there's no space "outside" the plates.

It turns out when you do that, you get a Casimir force that either tries to make the circle bigger or smaller, depending on the types of particles you have in your theory. So you can have pressure of either sign, and it manifestly has nothing to do with the pressure "outside" - because there is no outside.

Everything I have read--and I do not pretend to understand it all--indicates that, despite the denial from another poster, this is indeed a quantum effect. Some posters are apparently trying to use it as proof that "Einstein was Wrong^TM"
The curvature of space indicated above is not an observed (or observable) thing, AFAICS, and there may be other reasons for the force between the plates. The phenomenon is still being investigated.
I will stipulate that the Casimir Effect is real, but that's as far as I am willing to go.
In the practical world, Force is a function of mass, acceleration, pressure, area, magnetic force, spring constant, distance, and a large number of other things. While Casimir Effects may (and apparently are) significant in some Nano-technology applications, from my standpoint, it's just something else to be accounted for, and it's actual cause is for the real eggheads to bother over.
Like gravity, inertial, stiffness, magnetic, and other forces, whether it is caused by gravitons, electrons , or gypsy pygmy fairies is of interest to me, but the cause doesn't keep me from considering the effects.

 

[sol invictus]

Everything I have read--and I do not pretend to understand it all--indicates that, despite the denial from another poster, this is indeed a quantum effect.

The Casimir effect is quantum, yes. It's proportional to Planck's constant, which makes it quantum by definition.

The curvature of space indicated above is not an observed (or observable) thing, AFAICS, and there may be other reasons for the force between the plates.

There's no need for curvature of space. You could do the experiment I outlined simply by constraining some field to be non-zero only inside a hoop, and then measure the tension in the hoop. You could (at least in principle) swing the pressure from positive to negative by changing the spin of the field that's non-zero inside the hoop (by changing the material it's made out of, for example).

In any case, my point was that at least if you buy the math behind it, that example (realistic or not) proves that Casimir pressures can be negative, and that the negative pressure cannot be due to a force from outside.

 

[rwguinn]

The Casimir effect is quantum, yes. It's proportional to Planck's constant, which makes it quantum by definition.



There's no need for curvature of space. You could do the experiment I outlined simply by constraining some field to be non-zero only inside a hoop, and then measure the tension in the hoop. You could (at least in principle) swing the pressure from positive to negative by changing the spin of the field that's non-zero inside the hoop (by changing the material it's made out of, for example).

In any case, my point was that at least if you buy the math behind it, that example (realistic or not) proves that Casimir pressures can be negative, and that the negative pressure cannot be due to a force from outside.

but...but...
Forces due to pressure are always due to differential! To be otherwise would require deleting or adding a dimension, I would think.
ETA: "spinning fields"? I done tole ya-I quit EE because of "moving holes". Now you're spinning fields in a Hula-Hoop^TM.

That is my story and I'm sticking to it!