Lambda-CDM theory - Woo or not?

[edd]

Isn't it true to say that the negative refers purely to the direction of the resulting force and not that the pressure is negative in absolute terms.

No, not really. You put whatever stuff you have in a box and then try to change the size of the box. The volume in the box changes quite unambiguously in the direction of either larger or smaller when you do this.

The energy inside the box also changes quite unambiguously to be larger or smaller as a result of the work you do in changing the box's size.

This leads naturally to an unambiguous definition of pressure which is not dependent on the direction of the force (which is essentially which side of the box you happened to push or pull upon).

edit to add: Perhaps another way of thinking of it is that while the force has a direction, the area you are considering the force to act upon also has a direction - the normal vector through the plane for example. Then you can define the pressure to be a scalar quantity from those two vectors.

 

[Michael Mozina]

It is inappropriate. It's the equation of state of an ideal gas.

The whole entire physical universe is thinly dispersed bit of idealized gas, dotted with material *structures* that keep in organized. I didn't make up the definition of "pressure", it comes from any ordinary chemistry or physics definition of pressure. The only logical way to treat 'pressure' here is to begin with *at least* this much understanding of kinetic energy in motion. Even the best vacuums of Earth, and the best vacuums of space have atoms in them, even if they are separated by great distances. Even if we remove the kinetic energy of the atoms, from some arbitrary region of "space", the photons flowing through it produce "kinetic energy" as "positive pressure" at the level of QM.

The whole idea behind dark energy is that it has a different equation of state. It's not an ideal gas.

It's going to have to 'accelerate" a system that resembles an ideal "plasma" with massive structures creating an organizing effect in some way. This is a reasonable and acceptable definition of "pressure" considering the makeup of this physical universe.

 

[Ziggurat]

And there you go again....

Your whole show is blown entirely *out of the water* and all you can do is play games.

[qimg]http://upload.wikimedia.org/wikipedia/commons/6/6d/Translational_motion.gif[/qimg]

Uh, no. You're the one playing games, not me. You substituted a picture meant to represent kinetic energy, not pressure, for an actual argument. You can't even figure out how to define pressure for anything other than an ideal gas. And guess what? At room temperature and 1950 atmospheres of pressure, Helium is not an ideal gas. Ever hear of the van der Waals equation? Of course you haven't: that's more complicated than highschool chemistry class. The van der Waals equation makes no sense if you define pressure in terms of the ideal gas law. But it makes perfect sense if that's not how you define pressure. And guess what? Nobody does! Except you, of course. Because you've got no idea what pressure actually means.

That my friend is what kinetic energy is all about. There is *pressure* in that chamber from the particles in that chamber.

In the case of a gas, yes. But it's not the pressure you get from an ideal gas, because the ideal gas law is an approximation.

Once we remove every particle from that vacuum, you end up at *zero* pressure, and it is entirely impossible to reach a "negative pressure" in a vacuum.

The ideal gas law doesn't permit negative pressure solutions. But guess what: the van der Waals equation actually does. Guess which one is a better fit to the real world?

The fact that you can only think about these issues in reference to the ideal gas law shows that your knowledge of basic physics is woefully inadequate. I was right to focus on such basic issues, because that's where your comprehension fails.

 

[Michael Mozina]

No, not really. You put whatever stuff you have in a box and then try to change the size of the box. The volume in the box changes quite unambiguously in the direction of either larger or smaller when you do this.

The energy inside the box also changes quite unambiguously to be larger or smaller as a result of the work you do in changing the box's size.

This leads naturally to an unambiguous definition of pressure which is not dependent on the direction of the force (which is essentially which side of the box you happened to push or pull upon).

edit to add: Perhaps another way of thinking of it is that while the force has a direction, the area you are considering the force to act upon also has a direction - the normal vector through the plane for example. Then you can define the pressure to be a scalar quantity from those two vectors.

All you are doing by changing the volume of the box is increasing the distance between the bouncing objects, and thereby "lowering" the pressure. We can reach a zero pressure state, if and only if there are no more atoms in the box. That's never going to happen. The asymptote of pressure is *ZERO*, and it cannot become negative even if every atom is removed from the box.

 

[edd]

The whole entire physical universe is thinly dispersed bit of idealized gas, dotted with material *structures* that keep in organized.

In other words "I declare the universe to contain no forms of energy other than ideal gases and a smattering of dust that doesn't really matter, therefore the universe cannot contain any dark energy."

I hope you realise the problem with that logic.

I didn't make up the definition of "pressure", it comes from any ordinary chemistry or physics definition of pressure.

Indeed, you can't have made up the definition of pressure since you don't understand the physics involved.

 

[edd]

All you are doing by changing the volume of the box is increasing the distance between the bouncing objects, and thereby "lowering" the pressure.

Radiation pressure. Read about it.

 

[Michael Mozina]

Uh, no. You're the one playing games, not me. You substituted a picture meant to represent kinetic energy, not pressure, for an actual argument.

It is the "kinetic energy" of the atoms that *create the "pressure"*! Man oh man oh man are you digging your hole deeper and deeper and deeper.

You can't even figure out how to define pressure for anything other than an ideal gas.

If we are going to describe and work with a description of "pressure" related to a "vacuum", it's the only rational definition to work with. You're tap dancing now all over the place because you really, really, really, don't understand what "pressure" is all about at the level of kinetic energy and actual physics. If you did understand that relationship you wouldn't have bitched about my use of that image.

In the case of a gas, yes. But it's not the pressure you get from an ideal gas, because the ideal gas law is an approximation.

It approximate asymptote is zero! This is absurd at this point. I've handed you two perfectly rational ways to describe pressure in a "vacuum" and both of them demonstrate that you are wrong. You refuse to embrace the real kinetic energy that results in "pressure" so you really just don't "get it" at all at the level of "physics".

Like I said before, when it comes to math, you folks are in a class by yourself. When it comes to physics however, your conceptual understanding is zero, and you get a big fat F.

Guth blew it in exactly the same way you're blowing it right now. You can't get "negative pressure" from a vacuum. It's never going to happen. Guth's theory is DOA at the level of physics. It might work on paper in a math formula, but when we look at the actually physics, what Guth is proposing and what you are proposing is physically impossible. You still don't even "get it" even with nice pretty pictures, mathematical support of my position, and everything.

 

[Michael Mozina]

Radiation pressure. Read about it.

What about it? It's just "kinetic energy in motion", albeit at the subatomic scale.

 

[Michael Mozina]

In other words "I declare the universe to contain no forms of energy other than ideal gases and a smattering of dust that doesn't really matter, therefore the universe cannot contain any dark energy."

I hope you realise the problem with that logic.

No, it's:

I will stick to known forces of nature, including EM fields, while attempting to describe nature.

The Lambda theory is like:

"I declare that the universe was created by a dead inflation deity, and dark energy faeries who save us from the evil monopole nation and keep the universe accelerating forever and ever, and here is the math to prove it, almen."

 

[Ziggurat]

I didn't make up the definition of "pressure", it comes from any ordinary chemistry or physics definition of pressure. The only logical way to treat 'pressure' here is to begin with *at least* this much understanding of kinetic energy in motion.

Completely and utterly wrong. I don't know of a single physics or chemistry textbook that defines pressure by the ideal gas law. Every single one I've ever seen defines pressure first, and only then talks about either the derivation or measurement of the ideal gas law. In fact, looking at the book I used in intro physics ("Physics for Scientists and Engineers", by Paul Tipler), I note that pressure is actually introduced in the section regarding liquids. And he defines it as P=F/A (equation 11.9, page 336). Not identical to the definition I gave you, but actually completely compatible (but demonstrating that takes math, which you don't have). No reference to gasses of any sort is needed to define pressure. Tipler doesn't introduce the ideal gas law until 160 pages later, in a completely different section.

Or how about Kittel & Kroemer, "Thermal Physics 2nd Ed". Page 66, eq. 26:
[latex]$p=-\frac{\partial U}{\partial V}$[/latex].
Looks a lot like my definition. They then derive the ideal gas law from this definition, which then shows up ten pages later as eq. 73.

Or how about Zumdahl's "Chemistry 3rd ed.", page 186:

However, since pressure is defined as force per unit area,
[latex]$Pressure=\frac{force}{area}$[/latex]
the fundamental units of pressure involve units of force divided by units of area.

Which is the same thing as Tipler. The ideal gas law doesn't show up until page 192. So once again, we see that definitions of pressure always precede the ideal gas law, and are never derived from it.

I can give you more sources if you want which say the same thing, but at this point I don't think that will make any difference.

 

[edd]

What about it? It's just "kinetic energy in motion", albeit at the subatomic scale.

Because you said this. Radiation follows a different equation of state and

All you are doing by changing the volume of the box is increasing the distance between the bouncing objects

is not true. You are lowering the energy of individual photons as well as increasing their separation. It was pointing out the flaw in your logic when you try to apply the same reasoning to dark energy. If dark energy exists then when you change the volume of the box you are quite clearly not merely changing the distance between bouncing objects.

I recognise that you find the idea of such a substance disfavourable. We all do. However the evidence for it is good and the arguments you are putting forward against it do not hold water.

If you wish to steadfastly insist that it's too weird for you to believe that's one thing, but the physical arguments you have made that pressure must be positive are not valid.

 

[DeiRenDopa]

[...]

I can give you more sources if you want which say the same thing, but at this point I don't think that will make any difference.

(bold added)

Wrt a certain JREF Forum member with a very high daily post count ...

Was there any point at which it would have made any difference (and not just to the definition of pressure)?

 

[Ziggurat]

It is the "kinetic energy" of the atoms that *create the "pressure"*!

Not in the case of liquids. And there are textbooks (including the one I mentioned above) which start with pressure in liquids before treating pressure in gasses. Which is, historically speaking, the actual sequence in which it was done anyways. The folks who discovered the ideal gas law measured pressures using liquid columns, and you need to be able to calculate the depth dependence of pressure in a liquid (which is NOT a function of kinetic energy) before you can use that technique.

If we are going to describe and work with a description of "pressure" related to a "vacuum"

No. The proper way to do this is to use a universal definition of pressure, one which can be applied to any situation. Yours cannot. It can't even be applied universally to gasses. It is, in fact, wrong. As comparison with the van der Waals equation would have told you.

It approximate asymptote is zero!

Approximate is not good enough. Our definitions should never be approximations.

Guth blew it in exactly the same way you're blowing it right now. You can't get "negative pressure" from a vacuum.

According to you, one cannot get negative pressure in liquids either. And yet, people do. And it fits perfectly well with the definitions of pressure I've given, and with the definitions found in an actual physics or chemistry textbook.

 

[Michael Mozina]

Completely and utterly wrong. I don't know of a single physics or chemistry textbook that defines pressure by the ideal gas law. Every single one I've ever seen defines pressure first, and only then talks about either the derivation or measurement of the ideal gas law. In fact, looking at the book I used in intro physics ("Physics for Scientists and Engineers", by Paul Tipler), I note that pressure is actually introduced in the section regarding liquids.

Not in the case of liquids.

!?!?!?!?!? What the heck do "liquids" have to do with *this specific set of circumstances*?

You keep *intentionally* making comparisons that do not apply to *this set of circumstances*! Guth did *NOT* talk about "pressure in a "liquid". Guth specifically is attempting to create 'negative pressure', not inside a liquid, but rather inside of a "vacuum". A "vacuum" is not a "liquid". You are intentionally and willfully using an *inappropriate* analogy because Guth is describing the pressure of a *vacuum* where the ideal gas laws *would apply*, and definitions of pressure in a "liquid" would *not* apply.

 

[Tubbythin]

!?!?!?!?!? What the heck do "liquids" have to do with *this specific set of circumstances*?

You keep *intentionally* making comparisons that do not apply to *this set of circumstances*! Guth did *NOT* talk about "pressure in a "liquid". Guth specifically is attempting to create 'negative pressure', not inside a liquid, but rather inside of a "vacuum". A "vacuum" is not a "liquid". You are intentionally and willfully using an *inappropriate* analogy because Guth is describing the pressure of a *vacuum* where the ideal gas laws *would apply*, and definitions of pressure in a "liquid" would *not* apply.

Another epic fail I see. Please tell us all why using an approximation, derived using classical mechanics, for a classical gas is appropriate for a quantum system of virtual photons?

 

[DeiRenDopa]

Another epic fail I see. Please tell us all why using an approximation, derived using classical mechanics, for a classical gas is appropriate for a quantum system of virtual photons?

I know! I know!

*kinetic energy*!

... or is it *EM fields*!! ?

maybe "neutrinos", or *neutrinos*, or "*neutrinos*"???

 

[Tubbythin]

You folks cannot tell a *force* from "negative pressure". *Read the WHOLE article* (not just one sentence) and look at the directional components of the blue arrows! This is not "negative pressure". Hoy. It says *FORCE*, not "negative pressure", in fact the term "negative pressure" does *NOT* even appear in the article. You people are in pure denial at this point. Pressure and force are not the same thing.

Yes. We're all in denial. Along with all the major first year undergrad physics text books used at all the most prestigious university in the world. And all the lecturers at those Universities. And only Michael Mozina is correct. All this despite the fact that he wishes to use classical mechanics to describe an effect of second quantization. What is the world coming too.

 

[Ziggurat]

!?!?!?!?!? What the heck do "liquids" have to do with *this specific set of circumstances*?

They demonstrate that the way you define pressure doesn't work. The definition of pressure should not depend upon the conditions under which you want to measure it, but should be universal. Yours is not. Hell, it doesn't even work that well for gasses. That you don't understand this demonstrates that you don't really understand pressure.

You are intentionally and willfully using an *inappropriate* analogy because Guth is describing the pressure of a *vacuum* where the ideal gas laws *would apply*, and definitions of pressure in a "liquid" would *not* apply.

No. Not only does the definition of pressure need to be universal (and the definitions I gave above are), the ideal gas law isn't even sufficient for calculating the pressure. Among other things, it ignores radiation pressure. You cannot calculate radiation pressure using the ideal gas law. And I'm not just talking virtual photons here (ie, Casimir effect), it won't even work for real photons.

 

[Tubbythin]

I know! I know!

*kinetic energy*!

... or is it *EM fields*!! ?

maybe "neutrinos", or *neutrinos*, or "*neutrinos*"???

What do you reckon is next? My bet is on Coulomb's law to describe the force of gravity between the Earth and the Sun. I can't see how that is any more wrong than using the ideal gas equation to describe the Casimir effect.

 

[Michael Mozina]

They demonstrate that the way you define pressure doesn't work. The definition of pressure should not depend upon the conditions under which you want to measure it, but should be universal. Yours is not.

Bull. Guth selected a *very specific set of circumstances* and criteria. He created a "vacuum" and gave it "negative pressure". The only definition that I need for pressure is one that approximates the pressure of a vacuum, and the "best" such definition I have to work with would be an ideal gas law definition. I can specifically and methodically eliminate liquid pressure formulas, formulas related to solids, ect. There is approximately *zero* pressure in a vacuum.