Split Thread Michael Mozina's thread on Dark Matter, Inflation and Cosmology

Michael Mozina said:
Carmir's work is fine. It's your personal understanding of that work that's messed up.
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And yet its my personal understanding that agrees with the wikipedia article itself, and with numerous other websites. And you who doesn't seem to understand what a boundary condition is or that neutrinos are utterly irrelevant. Oh, and its you who can't understand the difference between pressure and gas pressure.


It's simply a "relative" pressure, just like my wing analogy.
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The problem with analogies is they're useless (or worse) if they are wrong.

The arrows and the foam all represent the "greater pressure" that exists on one side of the plate and the lower pressure on the other.
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I don't really know what the blue blobs are meant to be, but the other diagram is clearly labeled as "Casimir forces on parallel plates".
 
Michael Mozina said:
What exactly do you think those blue arrows are supposed to represent?
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Uh, let me (yet again)!
They are blue arrows. Thus they have a direction, magnitude and the context is that they are involved in the Casimir effect.
This rules out pressure.
The remaining contender is force.

But no one here is the author of the diagram and that author is the only person who knows since the arrows are not labeled.

Michael Mozina,
What exactly do you think those blue arrows are supposed to represent?

ETA:
Since this thread has degenerated into MM's usual discussion of Wikipedia diagrams, perhaps we should discuss the history of the diagrams.
The first one used to have much smaller labels. MM - does this affect the Casimir effect?
The second one was edited significantly 3 times: The colors of the bubbles was changed from red to blue, "Made the bubbles bubblier" and "changed colors of the plates". MM - does this affect the Casimir effect?
 
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Michael Mozina said:
I didn't ask you. I want to hear *HIS* answer, not yours.
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It is fairly obvious what his answer will be.

If you just look at the diagram then the blue arrows are nothing because they are not labeled.

If you know something about physics then you can deduce that the blue arrows are probably forces.

If you know something about physics then you can deduce that the blue arrows cannot be pressure (pressure has no direction).

Also:
First asked 4 February 2010
Michael Mozina,
What exactly do you think those blue arrows are supposed to represent?
(and why would be good)
 
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I try to completely avoid the Casimir discussion, but let me point out that BOTH of the Casimir plate pictures MM refers to are the work of Wikipedia user "Emok". Emok's edit history on Wikipedia consists almost entirely of metalworking articles ("shot peening", "silicon carbide", etc.). His Wikimedia upload history consists almost entirely of (a) maps and (b) illustrations of surface-finishing processes and surface measurements. The two Casimir things are his only contributions to anything in physics.

It is not an illustration from a textbook or a science article. It's a cartoon uploaded to Wikipedia by some random machinist or something. Keep that in mind before you read too many tea leaves into it ("why are there nodes at the plates"?)
 
Michael Mozina said:
You've simply confused the concept of relative pressure (outside vs. inside) with absolute pressure which you're calling "negative pressure".
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Look carefully at what you're saying. You're saying that the vacuum---the space outside the plates---has a positive pressure, despite there being (for the purposes of the Casimir effect) no real particles in it. No atoms, no photons, no blackbody radiation. You're saying that the vacuum between the plates has a slightly lower positive pressure---again, despite there being no atoms, no photons, no blackbody radiation. Is that right?

(Don't pull out the "no vacuum is perfect" business---nobody is getting residual-gas pressure or radiation pressure mixed up with the actual Casimir force, neither in theory nor in experiment.)

I just want to point out:

a) You can't tell us what the pressure is outside the gap? Is it one atmosphere, 1000 atmospheres, 10^34 torr, what? Why don't we see any such pressure limit in experiments? Why doesn't this pressure, rather than hbar c pi^2/ 240a, determine the force?

b) Elsewhere in the thread, you've been passionately opposed to the idea that the vacuum itself has a nonzero positive energy density of 10^-29 g/cc. You're really violently offended by the idea. But when it comes to the Casimir effect, you're suddenly totally happy with assigning an utterly invisible 10^24 torr pressure (or something---won't you tell us?) to empty space itself. This "vacuum pressure" you are shoving at us: it's a pressure we can't see, can't turn on and off, can't experiment with except insofar as it matches your interpretation of a diagram on Wikipedia. It's as "non-empirical" as anything you could possibly imagine. Heck, the only way to experiment with such a pressure (not pressure differences, the pressure itself) would be to look for the effects of its gravitational stress-energy tensor on the equations of motion of some test particle. Just like, um, Perlmutter and Reiss and everyone else are doing.

I just want to point out the contradiction. I don't give a hoot what you think about the Casimir effect---I like the Jaffe/Kardar view that it can be viewed as loop diagrams which couple to the plates---but it provides yet another example of your habit of picking up random half-baked physics statements that you barely understand and defending them like they were the basis of your entire self-image.
 
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Dark Matter and Ultra Faint Dwarf Galaxies

Michael Mozina said:
http://arxiv.org/abs/1002.0504
FYI, they found some more of that "missing mass" in our own galaxy, and oh ya, it's "baryonic material" we just never identified until now, not some new and exotic type of mass. Get used to that scenario. It's happens a lot and it's going to keep happening.
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Your ignorance is showing again.

First, the paper in question:
Big fish, small fish: Two New Ultra-Faint Satellites of the Milky Way
Belokurov, et al., accepted for publication in Astrophysical Journal Letters
Abstract: We report the discovery of two new Milky Way satellites in the neighboring constellations of Pisces and Pegasus identified in data from the Sloan Digital Sky Survey. Pisces II, an ultra-faint dwarf galaxy lies at the distance of ~180 kpc, some 15 degrees away from the recently detected Pisces I. Segue 3, an ultra-faint star cluster lies at the distance of 16 kpc. We use deep follow-up imaging obtained with the 4-m Mayall telescope at Kitt Peak National Observatory to derive their structural parameters. Pisces II has a half-light radius of ~60 pc, while Segue 3 is twenty times smaller at only 3pc.

Now, our Milky Way has a baryonic mass no more than 1011 solar masses and a total virial mass of about 1012 solar masses, so the baryons constitute only about 10% of the total mass of the Galaxy, assuming of course that we are using the right law of gravity (Xue, et al., 2008). So if the "dark matter" is made up of all these ultra faint systems, they have to cover 90% of the mass. But of course, the reason they are ultra faint is that they are ultra small, meaning ultra low in mass. The Belokurov, et al., paper cited by Mozina compares Picsces II to other dwarf galaxies, Leo IV & Leo V. Those two show dynamical masses of 1.5x106 solar masses & 3x105 solar masses respectively (Moretti, et al., 2009, Walker, et al., 2009). But these masses could be to low because they are derived from stellar samples that may reveal only the central mass (the motions of stars can only reliably determine the dynamical mass at lesser, but not greater distance from the center of the system). It has been proposed that the combination of Leo IV + Leo V could be as high as 8x109 solar masses (de Jong, et al., 2009), but this does require an abnormally high mass to light ratio. Segue 3, on the other hand, carries only a "few tens of stars", as the Belokurov, et al., paper tells us, and so is insignificant.

It should come as no surprise to anyone that smaller, less massive systems are dimmer, and larger, more massive systems as brighter. So we face the dilemma of 10% of the stellar mass (i.e., the baryonic mass of the Galaxy) being hugely bright, while 90% of the stellar mass is in such ultra faint systems that they are barely visible at all. I take it the unbiased reader can understand that this is a hard thing to believe.

Meanwhile, I noted above that "Your ignorance is showing again". In this case, specific ignorance of the "missing satellites problem":
Where Are the Missing Galactic Satellites?
Klypin, et al., The Astrophysical Journal, Volume 522, Issue 1, pp. 82-92; September 1999
Abstract: According to the hierarchical clustering scenario, galaxies are assembled by merging and accretion of numerous satellites of different sizes and masses. This ongoing process is not 100% efficient in destroying all of the accreted satellites, as evidenced by the satellites of our Galaxy and of M31. Using published data, we have compiled the circular velocity (Vcirc) distribution function (VDF) of galaxy satellites in the Local Group. We find that within the volumes of radius of 570 kpc (400 h-1 kpc assuming the Hubble constant h=0.7) centered on the Milky Way and Andromeda, the average VDF is roughly approximated as n(>Vcirc)~55+/-11(Vcirc/10 km s-1)-1.4+/-0.4 h3 Mpc-3 for Vcirc in the range ~10-70 km s-1. The observed VDF is compared with results of high-resolution cosmological simulations. We find that the VDF in models is very different from the observed one: n(>Vcirc)~1200(Vcirc10 km s-1)-2.75 h3 Mpc-3. Cosmological models thus predict that a halo the size of our Galaxy should have about 50 dark matter satellites with circular velocity greater than 20 km s-1 and mass greater than 3x108 Msolar within a 570 kpc radius. This number is significantly higher than the approximately dozen satellites actually observed around our Galaxy. The difference is even larger if we consider the abundance of satellites in simulated galaxy groups similar to the Local Group. The models predict ~300 satellites inside a 1.5 Mpc radius, while only ~40 satellites are observed in the Local Group. The observed and predicted VDFs cross at ~50 km s-1, indicating that the predicted abundance of satellites with Vcirc~50 km s-1 is in reasonably good agreement with observations. We conclude, therefore, that unless a large fraction of the Local Group satellites has been missed in observations, there is a dramatic discrepancy between observations and hierarchical models, regardless of the model parameters. We discuss several possible explanations for this discrepancy including identification of some satellites with the high-velocity clouds observed in the Local Group and the existence of dark satellites that failed to accrete gas and form stars either because of the expulsion of gas in the supernovae-driven winds or because of gas heating by the intergalactic ionizing background.

So we see that one of the problems that has faced the Lambda-CDM concordance cosmology has long been that we see far fewer dwarf satellite galaxies than we expected to see.

Fast forward to ...
The Kinematics of the Ultra-faint Milky Way Satellites: Solving the Missing Satellite Problem
Simon & Geha, The Astrophysical Journal, Volume 670, Issue 1, pp. 313-331; November, 2007
Abstract: We present Keck DEIMOS spectroscopy of stars in eight of the newly discovered ultra-faint dwarf galaxies around the Milky Way. We measure the velocity dispersions of Canes Venatici I, Canes Venatici II, Coma Berenices, Hercules, Leo IV, Leo T, Ursa Major I, and Ursa Major II from the velocities of 18-214 stars in each galaxy and find dispersions ranging from 3.3 to 7.6 km s-1. The six galaxies with absolute magnitudes MV<-4 are highly dark matter dominated, with mass-to-light ratios approaching 1000 Msolar/Lsolar,v. For the fainter galaxies we find tentative evidence for tidal disruption. The measured velocity dispersions of the ultra-faint dwarfs are correlated with their luminosities, indicating that a minimum mass for luminous galactic systems may not yet have been reached. We also measure the metallicities of the observed stars and find that the new dwarfs have mean metallicities of [Fe/H]=-2.0 to -2.3 these galaxies represent some of the most metal-poor stellar systems known. The six brightest of the ultra-faint dwarfs extend the luminosity-metallicity relationship followed by more luminous dwarfs by a factor of ~30 in luminosity. We detect metallicity spreads of up to 0.5 dex in several objects, suggesting multiple star formation epochs. UMa II and Com, despite their exceptionally low luminosities, have higher metallicities that suggest they may once have been much more massive. Having established the masses of the ultra-faint dwarfs, we re-examine the missing satellite problem. After correcting for the sky coverage of the Sloan Digital Sky Survey, we find that the ultra-faint dwarfs substantially alleviate the discrepancy between the predicted and observed numbers of satellites around the Milky Way, but there are still a factor of ~4 too few dwarf galaxies over a significant range of masses. We show that if galaxy formation in low-mass dark matter halos is strongly suppressed after reionization, the simulated circular velocity function of CDM subhalos can be brought into approximate agreement with the observed circular velocity function of Milky Way satellite galaxies.

Note from the abstract above: Having established the masses of the ultra-faint dwarfs, we re-examine the missing satellite problem. After correcting for the sky coverage of the Sloan Digital Sky Survey, we find that the ultra-faint dwarfs substantially alleviate the discrepancy between the predicted and observed numbers of satellites around the Milky Way, but there are still a factor of ~4 too few dwarf galaxies over a significant range of masses. Far from being a problem for dark matter, as Mozina says, the discovery of ultra faint dwarf galaxies like this is in fact a big deal in confirming that dark matter cosmology is consistent with observations, by bringing the number of observed dwarf satellite galaxies up to the number expected from theory. As noted in the Simon & Geha paper, there remained a significant deficit of observed versus expected galaxies. But as we are able to see deeper & dimmer, we continue to discover more ultra faint dwarf galaxies, closing the gap between observation and theory.

Michael Mozina said:
Get used to that scenario. It's happens a lot and it's going to keep happening.
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That's right Mozina, get used to it. The more of these ultra faint dwarf systems we find, the better dark matter cosmology looks and the worse you look.
 
ben m said:
Look carefully at what you're saying. You're saying that the vacuum---the space outside the plates---has a positive pressure, despite there being (for the purposes of the Casimir effect) no real particles in it. No atoms, no photons, no blackbody radiation. You're saying that the vacuum between the plates has a slightly lower positive pressure---again, despite there being no atoms, no photons, no blackbody radiation. Is that right?

(Don't pull out the "no vacuum is perfect" business---nobody is getting residual-gas pressure or radiation pressure mixed up with the actual Casimir force, neither in theory nor in experiment.)

I just want to point out:

a) You can't tell us what the pressure is outside the gap? Is it one atmosphere, 1000 atmospheres, 10^34 torr, what? Why don't we see any such pressure limit in experiments? Why doesn't this pressure, rather than hbar c pi^2/ 240a, determine the force?
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This is exactly where this whole Casimir thing went a year ago in a different thread. Originally MM said 1 atmosphere, but seemed to back away from that (because of how silly it being 1 atmosphere would be is maybe). I asked him to show how to calculate what this ambient pressure is (i.e. how do I calculate it using Casimir's or someone else's formula) but never got any response.
 
Reality Check said:
PS is inaccurate.
Einstein is not the only person ever to have worked on GR.
In 1917 de Sitter showed that the cosmological constant acts as a cosmological acceleration. So the cosmological constant has been re-introduced to explain an observed cosmological acceleration that has been part of GR for over 90 years.
The relevant posts are:
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I read those posts and found it strange that in spite of reading so many books and papers (for decades) on GR and cosmology that the input of Lemaitre, de Sitter, Eddington took such a back seat that it never came to my attention.
I can only conclude that those in the mainstream of GR and cosmology had rejected the CC as did Einstein, except for the musings I mentioned about the ultimate fate of the universe. I can quite vividly recall reading articles (in periodicals like Scientific American) written by respected mainstream physicists that took the death of the CC as a given.
Now, I am not claiming that there is any problem with reinstating the CC in the context of dark energy; I am only agreeing that MM's perspective of the history of events has merit.
 
Perpetual Student said:
Now, I am not claiming that there is any problem with reinstating the CC in the context of dark energy; I am only agreeing that MM's perspective of the history of events has merit.
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I don't understand---what about MM's story do you think is accurate, or what version of our story is inaccurate? That Einstein didn't know that the CC term gives acceleration? That the CC term does not give acceleration?
 
ben m said:
Look carefully at what you're saying. You're saying that the vacuum---the space outside the plates---has a positive pressure, despite there being (for the purposes of the Casimir effect) no real particles in it.
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No, that's absolutely not what I'm saying. I'm saying that inside the chamber are "real particles" that carry the EM field and those particles "push" against all sides of all the plates.
 
Michael Mozina said:
No, that's absolutely not what I'm saying. I'm saying that inside the chamber are "real particles" that carry the EM field and those particles "push" against all sides of all the plates.
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I just said: you are wrong, there are not "real particles that carry the EM field". Real EM force carriers are photons, and photon pressure is (a) miniscule and (b) trivial to distinguish from the Casimir force---utterly trivial.

I'd say that's worse than the inconsistency I had attributed to you. You're ignoring the Casimir physics and inventing new behaviors for electromagnetism.
 
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ben m said:
I just said: you are wrong, there are not "real particles that carry the EM field". Real EM force carriers are photons, and photon pressure is (a) miniscule and (b) trivial to distinguish from the Casimir force---utterly trivial.

I'd say that's worse than the inconsistency I had attributed to you. You're ignoring the Casimir physics and inventing new behaviors for electromagnetism.
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MM has been told this before but I do mot remember actual values given to him. So here is more physics for him to ignore:
From Teaching the photon gas in introductory physics (PDF)

Photon pressure P = bT4/3 where b is a constant involving h, c and k. This is constant at constant temperature. In controlled empirical experiments*, the pressure between 2 parallel plates varies with their separation. A good review is Casimir force between real materials: experiment and theory (23 Feb 2009).

If you have an ideal gas of 1.00 mol of monatomic argon at P = 1.01 105 Pa, V = 2.473 1022 m3, and T =300 K then the photon pressure is 2.04 10-6 Pa.
The only way to get the gas pressure and photon pressure to comparable values it to increase the temperature. The controlled empirical experiments* on the Casimir effect are not done at the temperatures of ~105 K needed for this.

* = MM speak.
 
Michael Mozina said:
No, that's absolutely not what I'm saying. I'm saying that inside the chamber are "real particles" that carry the EM field and those particles "push" against all sides of all the plates.
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This isn't what the Casimir force is.

The Casimir effect is due to the zero-point energy of the EM field. Every mode of the EM field has a lowest-energy state which is non-zero. The allowed modes are restricted by the fact that the field must be zero on the surface of the plates. When the plates are closer together, there are fewer allowed modes and a lower zero-point energy.

What of the field outside? Well, if you can imagine the plates being contained in a large conducting box, so that the EM field has to be zero on its walls, then there would also be an attractive force between the plates and the walls. However, it'd be extremely weak, as the Casimir force falls off with the fourth-power of distance. The walls would (weakly) pull at the plates, and the plates would more strongly pull at each other. Nothing is being pushed.

If the walls are moved increasingly far away, the force between the plates and the walls vanishes. The only force acting on the plates would be the attractive Casimir force between them. The vacuum on the outside exerts no force, and thus no pressure. In spite of this, the plates attract. In order for the "relative pressure" to be negative, the pressure between the plates must be negative.
 
Michael - do you agree that when the plates are closer, there is a lower energy density between them?
 
ben m said:
I don't understand---what about MM's story do you think is accurate, or what version of our story is inaccurate? That Einstein didn't know that the CC term gives acceleration? That the CC term does not give acceleration?
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This was my original post:

MM does make a good point that Einstein introduced his CC to avoid instabilities in GR that would lead to a collapsing universe. After Hubble's discoveries he abandoned it and called it his "biggest blunder."

As far as I know, the CC has since been a matter of debate related to questions about the ultimate fate of the universe (e.g.: continuing to expand eternally, ceasing to expand, ultimately collapsing) . So re-introducing it as a way to explain cosmological acceleration would be a new application. I believe this is a fairly accurate summary of the history of the CC. Can anyone demonstrate otherwise?
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That's all I'm saying. The range of possible values given to the CC may very well account for varying degrees of expansion and/or acceleration (positive or negative). I cannot imagine that Einstein did not know that.
The fact is that Einstein was seeking only stability and that was the point MM was making.
 
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schrodingasdawg said:
This isn't what the Casimir force is.

The Casimir effect is due to the zero-point energy of the EM field. Every mode of the EM field has a lowest-energy state which is non-zero. The allowed modes are restricted by the fact that the field must be zero on the surface of the plates. When the plates are closer together, there are fewer allowed modes and a lower zero-point energy.
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When you talk about "zero point energy", what you mean is that the universe contains kinetic energy, even if we could remove all the atoms from the chamber. We can select a 'low' energy state as the "relative zero" starting point, but we can never achieve an "absolute" zero energy state. Sometimes the energy state can be slightly lower than our "relative zero", sometimes higher, but it has nothing to do with negative pressure in a vacuum.

Nothing is being pushed.
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*Everything* is being pushed, some sides more than others.

The vacuum on the outside exerts no force, and thus no pressure.
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That's simply not so. The vacuum energy exerts kinetic energy on everything.

In spite of this, the plates attract. In order for the "relative pressure" to be negative, the pressure between the plates must be negative.
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No. The pressure between the plates simply has to be "less than" the overall ambient "pressure" from the EM field in the chamber. Those blue arrows point into all sides of all plates. Likewise the QM "foam" is everywhere, exerting kinetic energy everywhere. That's because we can never achieve a zero energy state. We can't even remove every atom from a "vacuum", let alone every EM carrier particle and every neutrino, etc. There will always be positive kinetic energy everywhere inside that chamber, and it will effect all sides of all plates.
 
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Michael Mozina said:
When you talk about "zero point energy", what you mean is that the universe contains kinetic energy
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Not kinetic. Why do you insist on slapping the word "kinetic" in front of every energy you can find? You were doing this with plasma physics too---you always wanted the magnetic energy to be "kinetic". (ETA: Or, wait---if you actually believe this residual-gas picture, then it would be all kinetic energy.)

The pressure between the plates simply has to be "less than" the overall ambient "pressure" from the EM field in the chamber.
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The overall ambient pressure from EM in the chamber? What IS that overall ambient pressure? Go ahead and calculate the blackbody photon pressure at room temperature, it's really easy. (The equation is on Wikipedia.) Compare it to the Casimir calculation and Casimir results. THEY'RE DIFFERENT THINGS.

We can't even remove every atom from a "vacuum", let alone every EM carrier particle and every neutrino, etc.
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We don't need to. The residual atoms, residual blackbody photons, and neutrinos (!!!) do NOT cause the observed 1/a^4 force. What makes you guess that they do?
 
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Michael Mozina said:
Yes.
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Great.

Consider a classical gas with positive pressure. It pushes out on the two plates. In doing so, it performs work - the pressure P, times the area A, is a force F, which pushes the plates apart a distance d. The work done is F.d.

The volume change is A.d. The gas loses energy to perform the work, and cools down. Its internal energy drops, the work goes into pushing the plates apart.

Now, in the case of the stuff between the plates in the Casimir effect, the volume change is the same, but the stuff in the middle gains energy (remember you just agreed that a volume drop causes a drop in the energy density, and the converse that a volume increase also causes an increase in its density also holds true). As the energy change in the middle is the opposite sign, the work done must be negative rather than positive, so the force F is negative.

The pressure, being just F/A is therefore also negative.

How can you maintain the two contradictory points of view you've just displayed?
 
Tubbythin said:
Were you intending doing the experiment in the vicinity of a supernova?
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confused.gif
 
edd said:
Great.

Consider a classical gas with positive pressure. It pushes out on the two plates. In doing so, it performs work - the pressure P, times the area A, is a force F, which pushes the plates apart a distance d. The work done is F.d.

The volume change is A.d. The gas loses energy to perform the work, and cools down. Its internal energy drops, the work goes into pushing the plates apart.

Now, in the case of the stuff between the plates in the Casimir effect, the volume change is the same, but the stuff in the middle gains energy (remember you just agreed that a volume drop causes a drop in the energy density, and the converse that a volume increase also causes an increase in its density also holds true). As the energy change in the middle is the opposite sign, the work done must be negative rather than positive, so the force F is negative.

The pressure, being just F/A is therefore also negative.

How can you maintain the two contradictory points of view you've just displayed?
Click to expand...

That's a great explanation, thanks.
 
Michael Mozina said:
When you talk about "zero point energy", what you mean is that the universe contains kinetic energy, even if we could remove all the atoms from the chamber.
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No, what I mean is
schrodingasdawg said:
Every mode of the EM field has a lowest-energy state which is non-zero.
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Every mode of the electromagnetic field is a quantum harmonic oscillator. Read the wiki article for more details,
http://en.wikipedia.org/wiki/Quantum_field_theory#Second_quantization_of_bosons
In particular,
Wikipedia said:
These are precisely the relations obeyed by the ladder operators for an infinite set of independent quantum harmonic oscillators, one for each single-particle state.
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Here is another Wiki article on the quantum harmonic oscillator,
http://en.wikipedia.org/wiki/Quantum_harmonic_oscillator
In particular
Wikipedia said:
Secondly, the lowest achievable energy is not zero, but \hbar\omega/2, which is called the "ground state energy" or zero-point energy.
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Does this clarify things any?
 
edd said:
Great.

Consider a classical gas with positive pressure. It pushes out on the two plates. In doing so, it performs work - the pressure P, times the area A, is a force F, which pushes the plates apart a distance d. The work done is F.d.

The volume change is A.d. The gas loses energy to perform the work, and cools down. Its internal energy drops, the work goes into pushing the plates apart.

Now, in the case of the stuff between the plates in the Casimir effect, the volume change is the same, but the stuff in the middle gains energy (remember you just agreed that a volume drop causes a drop in the energy density, and the converse that a volume increase also causes an increase in its density also holds true).
Click to expand...

I'm with you to this point.

As the energy change in the middle is the opposite sign, the work done must be negative rather than positive, so the force F is negative.
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The energy density and force from that energy density is simply 'greater' on the outside of the plates, and 'less' between them. There is still some small force pushing into the insides of the plates. That force is simply "less than" the energy density that is pushing the plates together.

The pressure, being just F/A is therefore also negative.
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If all we did is look at "pressure" from a single surface (like my wing analogy), you might be "tricked" into believing that the pressure on the top of the wing is "negative". It's not. The pressure under the wing is "greater" that the pressure on top of the wing, and the "pressure difference" causes upward lift. The same analogy is true here. The *whole* chamber has an energy density, not just the region between the plates. The "ambient energy density" is simply greater than the energy density between the plates and the plates are 'pushed together' from the outside force of that ambient energy density.
 
Michael Mozina said:
If all we did is look at "pressure" from a single surface (like my wing analogy), you might be "tricked" into believing that the pressure on the top of the wing is "negative".
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Analogies are worse than utterly useless if the analogy isn't analogous to the thing being described.
 
Michael Mozina said:
[qimg]http://www.internationalskeptics.com/forums/images/smilies/confused.gif[/qimg]
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I'd guess because you'd probably have to be right beside a supernova in order to get enough neutrinos to have them have any impact on a Casimir experiment.

You remember when someone calculated for you that in normal circumstances you'd have to run your experiment for a year before you'd get a single interaction with a neutrino?
 
Tubbythin said:
Analogies are worse than utterly useless if the analogy isn't analogous to the thing being described.
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The analogy is entirely valid and demonstrates the flaw in your argument. The energy density outside the plates is simply "greater than" the energy density between them. There's no form of 'negative pressure' in a vacuum. Those blue arrows and those blue quantum foam bubbles push into all sides of everything in the chamber. The ambient energy density outside the plates is simply greater than the energy density between them.
 
temporalillusion said:
I'd guess because you'd probably have to be right beside a supernova in order to get enough neutrinos to have them have any impact on a Casimir experiment.

You remember when someone calculated for you that in normal circumstances you'd have to run your experiment for a year before you'd get a single interaction with a neutrino?
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I'm not claiming that the neutrino has anything to do with the casimir effect. I think we all agree the energy density in question is related to the EM field. I was simply pointing out that the term "zero point energy" relates to the kinetic energy of everything we can't remove from our experiments.
 
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Michael Mozina said:
The energy density and force from that energy density is simply 'greater' on the outside of the plates
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You are mixing up force, pressure, and energy density. The "force from an energy density" is nonsense. Forces arise only because of changes in energy. Anywhere you look and find a force---springs, newtonian gravity, gases, E&M, etc.---you will find some form of potential energy. Keep track of that potential energy and how it changes, and that's where you find a force showing up; the force arises only because displacing something does work and dW = F dx. You do NOT just look at the "energy density" and say "if the energy density is higher the force is higher." It's simply wrong.

This is called Hamiltonian mechanics and it is more basic than either quantum mechanics or relativity. At my university we teach it to juniors (and the faster sophomores) in full detail. The first-quarter freshmen, even the engineers and premeds, even get a simplified special-case version, F = -dU/dx, which edd just tried to explain to you and whose core ideas you just completely ignored in favor of the same math-free mental image. How many times do we have to do this?

At least, next time, you could begin the thread with "I understand that mainstream physicists explain the Casimir effect using some sort of dU/dx term that I reject. However, I think the Casimir effect arises from (a) real photon pressure (b) imperfect vacuum chambers, and (c) an "energy density = force" effect that I think must be true no matter what dU/dx says." That would be honest and would waste less of everyone's time.
 
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Michael Mozina said:
The analogy is entirely valid
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No, it isn't.

and demonstrates the flaw in your argument.
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No it doesn't.

The energy density outside the plates is simply "greater than" the energy density between them. There's no form of 'negative pressure' in a vacuum.
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Yes there is.

Those blue arrows and those blue quantum foam bubbles push into all sides of everything in the chamber.
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:jaw-dropp. You think the Casimir setup actually has blue arrows in it?

The ambient energy density outside the plates is simply greater than the energy density between them.
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So if you push the plates together what happens?
 
schrodingasdawg said:
Every mode of the electromagnetic field is a quantum harmonic oscillator.

Does this clarify things any?
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Not really because these oscillations occur both outside and between the plates. There are simply more of these oscillations going on outside the plates than between them.
 
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