Lambda-CDM theory - Woo or not?

[Michael Mozina]

Michael, I'm pretty sick of trying to discuss this with you, mainly because it never seems to go anywhere. But when I read comments like that, all I can think is that you've just totally misunderstood something somewhere.

There's only one constant. It's one number. It's only allowed to have one value. And as a result, the theory really is very predictive, because (at least in principle) you can determine that number with just one observation, and then every other observation you make is a test of the theory.

For my own reasons I just read a paper about an alternative to lambda-CDM, where you set lambda to zero but assume we're in the middle of a giant void (i.e. a spherical region with fewer galaxies in it than the average). It turns out you can get away with setting lambda to zero in such models - but the price you pay is that you have to assume that for some reason the earth is almost at the exact center of this big spherical void. In other words, that the earth really is at the center of the universe.

And the other price you pay is that the theory is much less predictive, because it has many numbers in it (the density is a function of radius) that need to be fixed by data, and so it's a lot easier to adjust it to match whatever observations get made. But it's still possible to distinguish from lambda CDM, and it seems that within a few years one or the other will be ruled out by data.

I realize that you're trying really hard to communicate here sol and I appreciate it, I really do.

Try as I might, I simply "lack belief" that any constant in that GR formula is related to 'dark energy', just as I lack belief that the same constant in that same formula is related to 'fill in the metaphysical/religious blank energy'. It's the empirical disconnect between the observation of acceleration of physically massive objects, and the demonstration that "fill in the blank" has any effect on mass than I find to be lacking.

I also have a hard time with the notion of "predictive value". The constant was there while the mainstream 'predicted' the universe was slowing down over time. It was then CHANGED to "postdict a fit". Yes, I understand it can then be 'tested' in all directions, but again, it's just a number. The number is not a 'cause'.

I really do think we are "stuck" due to this difference between us, and I simply don't know how to bridge that gap, even though I do see you side of the argument:

http://www.internationalskeptics.com/forums/showpost.php?p=7642705&postcount=4979

 

[ben m]

Try as I might, I simply "lack belief" that any constant in that GR formula is related to 'dark energy',

You don't have to.

You just have to agree that the lambda constant (or something very like it) needs to be in the GR formula, in order for GR to agree with precision cosmology observations.

And that it's not unempirical bunny God magic to say so.

 

[edd]

Think http://profmattstrassler.com/articl...ysics-basics/virtual-particles-what-are-they/ is nice, and pertinent to certain misunderstandings of the Casimir Effect.

 

[Michael Mozina]

No I'm not. I haven't claimed that the Casimir effect is the same as Guth's inflationary hypothesis....

Then you haven't followed this whole debate TBT. That's where the whole Casimir claim stems from in the first place! I balked while reading Guth's original inflation paper when Guth pulled his negative pressure vacuum claim out of his back pocket. Your side threw up Casimir experiments of an example where a vacuum contains negative pressure. The pathetic part is that the vacuum MUST contain positive pressure because no experiment on Earth can even reach a zero pressure ideal state. The Casimir effect isn't even dependent upon the pressure in the chamber to begin with! The PLATE is ATTRACTIVE to the SECOND PLATE. It has nothing to do with the PRESSURE of the VACUUM.

No. I mean the pressure in the vacuum between the plates is negative.

No! The vacuum always contains positive pressure, and positive kinetic energy everywhere in the vacuum. I has FEWER VP's and a LOWER VP pressure between the plates and MORE VP's and a HIGHER VP pressure outside of the plates. In the venacular of edd's last article, the "disturbance in the field/force" is greater on the outside of the plates than between them. Most of you folks still don't know squat about kinetic energy in a vacuum. Definitely no merit badge for you.

 

[ben m]

No! The vacuum always contains positive pressure, and positive kinetic energy everywhere in the vacuum.

Positive kinetic energy: yes indeed. Positive pressure: nope, you're still thinking of kinetic pressure, i.e. virtual particles bumping into things and pushing on them.

Take the gravitational effect, i.e. the GR consequences, of that positive kinetic energy density. (It goes into the source terms of GR, like any energy density.) The gravitational effect of a vacuum energy density is the same as that of a negative pressure.

 

[Tubbythin]

Then you haven't followed this whole debate TBT. That's where the whole Casimir claim stems from in the first place! I balked while reading Guth's original inflation paper when Guth pulled his negative pressure vacuum claim out of his back pocket. Your side threw up Casimir experiments of an example where a vacuum contains negative pressure.

It does, though it is not the same as inflation.

The pathetic part is that the vacuum MUST contain positive pressure because no experiment on Earth can even reach a zero pressure ideal state.

It doesn't matter in the slightest.

The Casimir effect isn't even dependent upon the pressure in the chamber to begin with! The PLATE is ATTRACTIVE to the SECOND PLATE. It has nothing to do with the PRESSURE of the VACUUM.

Yes it does.

No! The vacuum always contains positive pressure,

No it doesn't. P=-dE/dV by definition. If dE/dV is positive then pressure is negative. So unless you can show how dE/dV is always negative, then you're making claims that you cannot justify.

and positive kinetic energy everywhere in the vacuum.

Why do you you keep mumbling on about positive and negative kinetic energy? Not one person has tried to invoke negative kinetic energy.

I has FEWER VP's and a LOWER VP pressure between the plates and MORE VP's and a HIGHER VP pressure outside of the plates.

Pardon?

In the venacular of edd's last article, the "disturbance in the field/force" is greater on the outside of the plates than between them. Most of you folks still don't know squat about kinetic energy in a vacuum. Definitely no merit badge for you.

Thanks. I'll take that as a compliment.

 

[Reality Check]

Try as I might, I simply "lack belief" that any constant in that GR formula is related to 'dark energy', just as I lack belief that the same constant in that same formula is related to 'fill in the metaphysical/religious blank energy'.

Your religous beliefs have nothing to do with it MM .
The science is simple. A positive cosmological constant in GR results in a negative pressure. A negative pressure is a property of dark energy. Thus a positive cosmological constant is good candidate for dark energy.

Of course a positive cosmological constant is one candidate for dark energy. There are others. But if you 'lack belief' in the standard physics that is GR then you will totally 'lack belief' in the more exotic physics that is evoked in those theories.
Constant? Constant? Who needs a ****** constant? We need a quintessence field to 'fill in the metaphysical/religious blank energy' (in your inane words).

It was then CHANGED to "postdict a fit".

Wrong: It was always there. It was CHANGED to match the observations.
This is what happens with any physical constant. If you have problems with the cosmological constant being changed to match observations then you will also have problems with the other constants changing to match observations, e.g. electron mass.

 

[Farsight]

All: apologies for not being around. Work has been tough and we've been having the central heating and bathrooms done at home. As a result I've had zero free time. And the electrician starts the rewiring tomorrow.

 

[Michael Mozina]

Positive kinetic energy: yes indeed. Positive pressure: nope, you're still thinking of kinetic pressure, i.e. virtual particles bumping into things and pushing on them.

That is EXACTLY how they act Ben. You folks seem to have a physical disconnect when we get to subatomic physics. There is simply more kinetic energy on the outside of the plates and LESS kinetic energy between them.

Take the gravitational effect, i.e. the GR consequences, of that positive kinetic energy density. (It goes into the source terms of GR, like any energy density.) The gravitational effect of a vacuum energy density is the same as that of a negative pressure.

Oh brother. "Take our belief system and see how it results in "negative pressure from a vacuum"! Boloney.

 

[Michael Mozina]

Your religous beliefs have nothing to do with it MM .

Pffft. You're the one throwing away MILLIONS on your impotent on Earth sky entities, not me.

The science is simple. A positive cosmological constant in GR results in a negative pressure. A negative pressure is a property of dark energy. Thus a positive cosmological constant is good candidate for dark energy.

Like I said, you folks understand math, but at level of actual physics, your clueless. A constant in a math formula is NOT a PHYSICAL CAUSE RC. It's just a constant in a math formula.

 

[Tubbythin]

Oh brother. "Take our belief system and see how it results in "negative pressure from a vacuum"! Boloney.

So this is the point that I remind you of P=-dE/dV and you show us how dE/dV must be negative for a vacuum. Or that would be what you would do if you had any kind of argument at all.

 

[Michael Mozina]

So this is the point that I remind you of P=-dE/dV and you show us how dE/dV must be negative for a vacuum. Or that would be what you would do if you had any kind of argument at all.

If you had any argument at all you could slap a pressure gauge to the vacuum of your experiment and demonstrate your case. Since you can't empirically demonstrate anything of the sort, and you're completely clueless about kinetic energy at the subatomic level, you go right back to ignoring the fact that you CANNOT change the volume of the vacuum in "Guthianity"!

 

[Tubbythin]

If you had any argument at all you could slap a pressure gauge to the vacuum of your experiment and demonstrate your case. Since you can't empirically demonstrate anything of the sort, and you're completely clueless about kinetic energy at the subatomic level, you go right back to ignoring the fact that you CANNOT change the volume of the vacuum in "Guthianity"!

Huh? You're the one making the strong claim. You're the one saying negative pressure in a vacuum is impossible. It's up to you to put up or shut up. Stop shifting the burden of proof.

 

[Michael Mozina]

Huh? You're the one making the strong claim. You're the one saying negative pressure in a vacuum is impossible. It's up to you to put up or shut up. Stop shifting the burden of proof.

Right back at you. You claimed it WAS possible. You've failed *MISERABLY* to show any experiment where you actually achieved "negative pressure" from a VACUUM (not from a second plate). In fact, even your second PLATE experiment completely fails to show what you THINK it shows because not a damn one of you can tell the difference between a RELATIVELY LOWER kinetic energy state and LOWER pressure and a NEGATIVE pressure! Oi Vey!

There are SIX SIDES to those plates TBT. When did you intend to acknowledge that point?

 

[ben m]

Michael,

To calculate the effect of the Sun's internal pressure on the Earth, do you need to imagine putting a six-sided box in the center of the Sun and measuring the momentum of atoms bouncing off it? No: the only effect the Sun's pressure has on the Earth is: it represents an energy density, and energy densities gravitate, and the spacetime near Earth is shaped by the Sun's gravity.

To understand the effect of a vacuum energy density on the entire Universe, which is shaped by everything's gravity ... what's all this about six sided boxes? You should be looking at the energy density, because energy densities gravitate.

 

[Tubbythin]

Right back at you. You claimed it WAS possible. You've failed *MISERABLY* to show any experiment where you actually achieved "negative pressure" from a VACUUM (not from a second plate).

No I didn't. Don't mistake your failure to understand what pressure is for somebody else's failings.

In fact, even your second PLATE experiment completely fails to show what you THINK it shows because not a damn one of you can tell the difference between a RELATIVELY LOWER kinetic energy state and LOWER pressure and a NEGATIVE pressure! Oi Vey!

The Casimir effect has little to do with kinetic energy Michael. The fact that you keep talking about kinetic energy shows you have no understanding of the Casimir effect at all.
Do you not find it funny that all the literature sources disagree with you?

There are SIX SIDES to those plates TBT. When did you intend to acknowledge that point?

That's nice Michael? What is your point?

 

[Tubbythin]

By the way Michael, if I was to say I'd like to calculate the mass, M, of an object using the equation

dM = rho*dV

would you be comfortable with that? What would you conclude if I said that rho was some constant density over the whole volume, V? What would the sign of dM/dV be if rho was a positive constant?

 

[Michael Mozina]

Michael,

To calculate the effect of the Sun's internal pressure on the Earth,......

And to think you accuse *me* of goal post shifting? Holy cow! Your goalposts have twin turbo's! We're not calculating the pressures of various objects on one another, we're calculating the PRESSURE OF A VACUUM on ONE object that might exist inside that vacuum. Guthianity doesn't have second plates or second objects to work with ben. Try again, only start with only one mass blob and a VACUUM. That's all Guthainity has to work with.

 

[Tubbythin]

And to think you accuse *me* of goal post shifting? Holy cow! Your goalposts have twin turbo's! We're not calculating the pressures of various objects on one another, we're calculating the PRESSURE OF A VACUUM on ONE object that might exist inside that vacuum. Guthianity doesn't have second plates or second objects to work with ben. Try again, only start with only one mass blob and a VACUUM. That's all Guthainity has to work with.

Errm. Are we?
What gave you the idea that we start with one mass blob and a vaccum? You do know the big bang wasn't an event that happened in a pre-existing vacuum don't you?

 

[Michael Mozina]

No I didn't. Don't mistake your failure to understand what pressure is for somebody else's failings.

No. Don't step into the middle of a highly charged conversation unarmed.

The Casimir effect has little to do with kinetic energy Michael. The fact that you keep talking about kinetic energy shows you have no understanding of the Casimir effect at all.

Irony overload. I think only sol really appreciates the fact that EM field energy is kinetic energy. The rest of you, well, your statements speak for themselves. We even know that the EM field is the carrier particle of the kinetic energy transfer because the materials make a difference.

When were you going to accept the fact that you've never shown any appreciation for the difference between "relative pressure" and "absolute pressure"? When did you intend to show any evidence that Guth's mythical vacuum contains negative pressure?