Can pressure be negative?

[Ziggurat]

0 in the vacuum seems as likely as 0°K.

That's the problem: when you don't actually know the physics, what seems to be the case is often quite wrong. For example, did you know that negative absolute temperatures exist?

 

[Tubbythin]

Yep. That's exactly what it would take too. You'd have to remove all heat/photons as well as all atoms inside the vacuum, all neutrinos, and all forms of kinetic energy.

No you don't. The vacuum energy is there even when a volume is a vacuum not only when it is a vacuum.

 

[Michael Mozina]

Let's say we've got a chamber filled with He at 1 atmosphere.

How many times did you intend to move the goalposts?

 

[Ziggurat]

How many times did you intend to move the goalposts?

I haven't moved any goalposts. I've just pointed out how wrong you are. Two different causes of pressure don't need to interact the way you think they must interact, and so your reasoning for why we can't treat YOUR OWN example as pressure is simply wrong. And non-interacting pressures are observable even in very simple, non-quantum cases.

Now answer my question. The energy density of the electric field (or photons, if you like) between the plates is constant and positive. The more space there is between the plates, the more energy there is between the plates. The energy is positive, and it scales with the volume. Do you actually disagree with any of this paragraph?

This is a very simple question. Your determination to avoid answering it is making you look like a fool.

 

[Michael Mozina]

No you don't. The vacuum energy is there even when a volume is a vacuum not only when it is a vacuum.

That's because the neutrinos and other forms of kinetic energy exist everywhere, even in a 'vacuum". Neutrinos blow through everything, vacuums and matter alike.

 

[Michael Mozina]

I haven't moved any goalposts.

Sure, you did. First we started discussing *ONE* thingy in a vacuum (Guth's claim). Then you started discussing *TWO* things in a vacuum (casimir effects and charged plates). Then you added MORE STUFF to a vacuum (third object), and now you've removed the vacuum *ENTIRELY*. You couldn't move the goalposts any faster if you tried.

I've just pointed out how wrong you are.

No, you've just shot your own claims it the foot with your own analogies and statements. If you were correct, we'd see a drop in the pressure in the vacuum chamber the moment we turned on the power. We don't. Case closed.

 

[Ziggurat]

Sure, you did. First we started discussing *ONE* thingy in a vacuum (Guth's claim). Then you started discussing *TWO* things in a vacuum (casimir effects and charged plates). Then you added MORE STUFF to a vacuum (third object), and now you've removed the vacuum *ENTIRELY*. You couldn't move the goalposts any faster if you tried.

Apparently you don't know what goalposts are either.

Now answer my question. The energy density of the electric field (or photons, if you like) between the plates is constant and positive. The more space there is between the plates, the more energy there is between the plates. The energy is positive, and it scales with the volume. Do you actually disagree with any of this paragraph?

It's a yes/no question. It's quite simple. Why are you so afraid to provide an answer?

 

[Tubbythin]

That's because the neutrinos and other forms of kinetic energy exist everywhere, even in a 'vacuum". Neutrinos blow through everything, vacuums and matter alike.

No. it isn't anything to do with that.

 

[Skwinty]

Michael,
Here is a free book called "The Structured Vacuum. Thinking about nothing" by Johann Rafelski and Berndt Muller.

It was written in 1985 and takes the form of a conversation between the authors.

http://www.physics.arizona.edu/~rafelski/Books/StructVacuumE.pdf

 

[Michael Mozina]

Michael,
Here is a free book called "The Structured Vacuum. Thinking about nothing" by Johann Rafelski and Berndt Muller.

It was written in 1985 and takes the form of a conversation between the authors.

http://www.physics.arizona.edu/~rafelski/Books/StructVacuumE.pdf

Thanks! That looks like a really wonderful presentation. I'll definitely check it out, but I doubt I'll get through the whole thing today. I appreciate it.

 

[Calrid]

That's the problem: when you don't actually know the physics, what seems to be the case is often quite wrong. For example, did you know that negative absolute temperatures exist?

I was always told achieving 0k was impossible so if that is not the case then I can believe there can be nothing in a vacuum too, even though of course any literature I've read says the minimum atomic distribution in the void is never 0 for any significant part of space-time.

I'd like to a see a link not that I don't believe you, I am just interested particularly in experiments that have gone below 0k.

 

[Ziggurat]

I was always told achieving 0k was impossible

It is impossible. It's also unnecessary in order to reach negative temperatures (see below). But if you don't know why it's impossible, then it can seem like it's equivalent to reaching 0 pressure. But it's not equivalent, not at all.

so if that is not the case then I can believe there can be nothing in a vacuum too, even though of course any literature I've read says the minimum atomic distribution in the void is never 0 for any significant part of space-time.

One doesn't need zero atoms to achieve zero pressure. Practically speaking, it's probably easier to achieve zero or even negative absolute pressure with LOTS of atoms - for example, water in a sealed piston. You can tune the pressure from positive to zero to negative by simply pushing or pulling on the piston.

I'd like to a see a link not that I don't believe you, I am just interested particularly in experiments that have gone below 0k.

This is actually a perfect example of not knowing the physics: when I tell you that negative temperatures are possible, you assume that this means a temperature BELOW 0 Kelvin. That's not an unreasonable assumption, but it's wrong. Negative temperatures exist above infinite temperature, not below 0 Kelvin. And the reason is that in thermodynamics, temperature is actually less fundamental than inverse temperature. As the energy of a system increases, the inverse temperature decreases. In most systems, the inverse temperature can never actually reach 0, but can only approach it asymptotically. But for some systems, the inverse temperature can pass through zero and go negative. That means there's a discontinuity in temperature: we go to infinite positive temperature, then infinite negative temperature, back to finite negative temperature. So negative temperatures are "hot", not "cold". Note also that even though there's a discontinuity in temperature, there is no discontinuity in inverse temperature, and that's actually the more fundamental property.

Negative temperatures violate most people's conception of what temperature is and what it means, but that's because most people don't really understand it in the first place. And why would you, if you haven't studied it? I certainly didn't have a clue about what negative absolute temperatures were until I took a thermodynamics class, and I don't expect anyone else to.

Anyways, Wikipedia has a page on negative temperatures if you're curious to learn more. They're fairly esoteric since only systems with a maximum possible energy can obtain negative temperatures, and if you place a system which can support negative temperatures in thermal contact with a system which cannot (and that's most systems), equilibrium will always be positive temperature.

 

[Michael Mozina]

This is actually a perfect example of not knowing the physics: when I tell you that negative temperatures are possible, you assume that this means a temperature BELOW 0 Kelvin. That's not an unreasonable assumption, but it's wrong. Negative temperatures exist above infinite temperature, not below 0 Kelvin.

Um, even if we *assumed* that was true, you're the one creating all the confusion then by calling it a "negative temperature". What the heck is "above infinite temperature"? It's like you're making up these bizarre and physically impossible claims as you go based on a wing, a prayer and a fascination with Buzz Lightyear. I don't suppose you have any empirical evidence of a lab experiment where they achieved either a "negative temperature" or a temperature above infinity do you?

 

[Ziggurat]

Um, even if we *assumed* that was true, you're the one creating all the confusion then by calling it a "negative temperature".

This is standard thermodynamics, Michael. Pick up a textbook some time. The fact that you are confused by it is of no consequence. Actual physicists understand it quite well. And there are damned good reasons to call it negative temperature, namely because it IS negative using the standard thermodynamic definition of temperature. But given your inability to grasp the definition of pressure, I seriously doubt you've got a clue about the definition of temperature.

What the heck is "above infinite temperature"?

Higher energy than an infinite temperature state. I thought I made that clear.

It's like you're making up these bizarre and physically impossible claims as you go based on a wing, a prayer and a fascination with Buzz Lightyear.

This is standard textbook thermodynamics. Perhaps before accusing me of making stuff up, you should have followed the link I gave.

I don't suppose you have any empirical evidence of a lab experiment where they achieved either a "negative temperature" or a temperature above infinity do you?

I do.
http://prola.aps.org/abstract/PR/v81/i2/p279_1
And you could have found such evidence easily yourself, if you had bothered to google the topic. But you didn't. Instead, you mouthed off about a subject of which you are wholely ignorant, and have thus beclowned yourself.

 

[Michael Mozina]

This is standard thermodynamics, Michael. Pick up a textbook some time.

Yes Zig I ultimately know this too because I have access to Google and textbooks, just like you do. It's ultimately the verbiage I'm bitching about, including calling a higher energy state a "negative" and referring to a limited energy state as "infinite".

The fact that you are confused by it is of no consequence.

It's not just me that doesn't "understand" your use of terms it's pretty much any "outsider" that might ever be first introduced to the idea that is likely to be confused. First science teaches everyone that Kelvin is the absolute measurement of temperature with ZERO being the lowest possible energy state. Then you start talking about "negative temperatures' when what you really mean is that these are actually "excessively high" temperatures, not not actually higher than INFINITY temperatures.

Actual physicists understand it quite well.

Hmm. Are you such a person (actual physicist)?

 

[Michael Mozina]

FYI Zig, you might want to take a gander at the WIKI page. It did a better job than you did explaining how it actually works:

http://en.wikipedia.org/wiki/Negative_temperature

In physics, certain systems can achieve negative temperatures; that is, their thermodynamic temperature can be a negative quantity. Negative temperatures can be expressed as negative numbers on the kelvin scale.

Temperatures that are expressed as negative numbers on the familiar Celsius or Fahrenheit scales are simply colder than the zero points of those scales. By contrast, a system with a truly negative temperature is not colder than absolute zero; in fact, temperatures colder than absolute zero are impossible by definition. Rather, a system with a truly negative Kelvin temperature is hotter than any system with a positive temperature (in the sense that if a negative-temperature system and a positive-temperature system come in contact, heat will flow from the negative- to the positive-temperature system).

It says nothing about INFINITY AND BEYOND.....

 

[GeeMack]

FYI Zig, you might want to take a gander at the WIKI page. It did a better job than you did explaining how it actually works:

http://en.wikipedia.org/wiki/Negative_temperature

It says nothing about INFINITY AND BEYOND.....

Yes, Ziggurat, you might want to take a look at that Wiki page. After all, someone who has demonstrated virtually no qualifications to understand physics or math, and barely any qualifications to understand even basic science highlighted a couple sentences from a Wiki page. That interpretation is bound to be a more thorough and valid explanation than something you learned in some dumb old college class on thermodynamics.

 

[Ziggurat]

Yes Zig I ultimately know this too because I have access to Google and textbooks, just like you do. It's ultimately the verbiage I'm bitching about, including calling a higher energy state a "negative" and referring to a limited energy state as "infinite".

Then you're bitching about standard terminology. Because you don't understand it.

It's not just me that doesn't "understand" your use of terms it's pretty much any "outsider" that might ever be first introduced to the idea that is likely to be confused.

Go figure: the subject matter is confusing you. In and of itself, that's quite understandable, and nothing to be ashamed of. But don't blame your confusion on me, especially since my use of terms is the standard one. And if you actually understood the subject matter, you'd understand why that's the standard terminology.

First science teaches everyone that Kelvin is the absolute measurement of temperature with ZERO being the lowest possible energy state.

Quite true. And it contradicts nothing I said, since I rather explicitly pointed out that negative temperatures were high-energy states.

Then you start talking about "negative temperatures' when what you really mean is that these are actually "excessively high" temperatures, not not actually higher than INFINITY temperatures.

No, Michael. I do mean higher than infinite temperature. Because that's what it is. You're confused by the very concepts involved here, because you don't understand what temperature is to begin with.

But I'll give you a bit of a hand: temperature is NOT the same thing as thermal energy. For systems which can support negative temperatures (and thus infinite temperatures as well), the thermal energy at infinite temperature remains finite. Again, negative temperatures only occur in systems with a maximum energy.

Hmm. Are you such a person (actual physicist)?

Why do you care? And what would either answer actually mean here?

 

[Ziggurat]

in fact, temperatures colder than absolute zero are impossible by definition. Rather, a system with a truly negative Kelvin temperature is hotter than any system with a positive temperature (in the sense that if a negative-temperature system and a positive-temperature system come in contact, heat will flow from the negative- to the positive-temperature system).

It says nothing about INFINITY AND BEYOND.....

Translation: I can't figure out anything for myself, I'm too stubborn to ask for an explanation, and I must blame others for my own willful ignorance.

If you had read my previous post, you'd understand what this meant, and you'd see that it agrees with what I said. I pointed out that inverse temperature, Beta = 1/kT, is more fundamental than temperature T. As a system increases in energy, Beta will decrease. What happens to T if Beta passes through zero? Why, T will diverge to infinity, then become negative. So negative temperature systems are hotter (lower Beta) than any positive temperature system. Which is what Wikipedia said. But note what you've done: you're blaming me for having explained more than what Wikipedia said.

Oh, but I used math. And you can't do math. That, really, is your complaint against me.

 

[W.D.Clinger]

I pointed out that inverse temperature, Beta = 1/kT, is more fundamental than temperature T.

I doubt whether Michael Mozina will ask to have that formula carved into his tombstone.