Lambda-CDM theory - Woo or not?

[Michael Mozina]

In the interests of finding some common ground, I ask this:

Michael Mozina, do you agree that a gravitational effect has been observed and measured, yes or no?

Which effect? Repulsion? No. Attraction between objects made of mass? Yes.

If yes, and without any speculations whatsoever on the cause, do you agree that that effect must necessarily have a cause, yes or no?

The attraction process certainly has a cause, yes.

If you can't anwser yes to both those questions, then there really is no point at all.

What evidence here on Earth suggest to you that gravity does repulsive tricks?

 

[D'rok]

Plainly, there is no point at all. Mozina simply denies basic facts.

 

[ben m]

There's nothing "mythical or exotic" until you claim that your 'missing mass' isn't composed of "normal" matter.

The missing mass is not of normal matter. Nice hypothesis, Michael, but that hypothesis makes astrophysical predictions which are ruled out by astrophysics data. Baryonic dark matter = false. Discard this hypothesis, move on to another hypothesis.

What in the universe makes you believe it's made of anything other than the normal matter we find on Earth?

I think you know this one by now. Sing it with me! To the tune of "Ermuntre Dich Mein Schwacher" (BWV 43)! CMB/CMBpol/LSS/BAO/BBN/galaxies/cluster gas/cluster dynamics/weak lensing/strong lensing/microlensing/LyA/Bullet Cluster. Repeat twice and remain standing for the organ solo.

 

[Michael Mozina]

Plainly, there is no point at all. Mozina simply denies basic facts.

You evidently have a hard time distinguishing between a "fact' and an "assumption". It is a 'fact' that photons are redshifted. It is an "assumption" that the phenomenon of redshift is somehow related to the "expansion of space".

 

[D'rok]

You evidently have a hard time distinguishing between a "fact' and an "assumption". It is a 'fact' that photons are redshifted. It is an "assumption" that the phenomenon of redshift is somehow related to the "expansion of space".

It is a fact that gravitational effects on visible matter have been observed and measured. You deny this fact. You are delusional.

 

[edd]

You evidently have a hard time distinguishing between a "fact' and an "assumption". It is a 'fact' that photons are redshifted. It is an "assumption" that the phenomenon of redshift is somehow related to the "expansion of space".

What about BAO measurements compared to the sound horizon measured at the CMB?

 

[Michael Mozina]

It is a fact that gravitational effects on visible matter have been observed and measured.

I agreed with you that the ATTRACTIVE effect of gravity has been observed. Did you miss that?

You deny this fact. You are delusional.

No I don't. I deny that you have ever physically demonstrated that "dark energy" has any physical effect at all on objects with mass.

 

[Michael Mozina]

The missing mass is not of normal matter.

You don't know that Ben, you ASSUME that.

Nice hypothesis, Michael, but that hypothesis makes astrophysical predictions which are ruled out by astrophysics data. Baryonic dark matter = false. Discard this hypothesis, move on to another hypothesis.

What "other" hypothesis? Do you even have another one to work with Ben?

 

[ben m]

No I don't. I deny that you have ever physically demonstrated that "dark energy" has any physical effect at all on objects with mass.

Sure we did. Galaxies have mass. Galaxies are observed to be doing something inconsistent with the GR effect of positive pressure matter. There you go. Done.

That is happening even though we don't know what the cause is.

Not knowing what the cause is does not make the data go away.

Not knowing what the cause is does not make the "ordinary matter is responsible" hypothesis actually work. (It doesn't work, remember?)

Not knowing what the cause is does not mean that we can't give it a name, "dark energy", and hypothesize about how it works.

 

[ben m]

You don't know that Ben, you ASSUME that.

No, I know it. The laws of physics that govern gas, plasmas, planets, stars, neutrinos, and photons are known. Those laws, applied to a "baryons are the dark matter" hypothesis, make predictions. Those predictions are falsified by the data. Therefore the hypothesis "baryons are the dark matter" is scientifically proven false. This is not an assumption, it's a fact.

What "other" hypothesis? Do you even have another one to work with Ben?

Other than SUSY? Sure, are you kidding? Particular hypotheses I've spent time on include: axions, quark nuggets (technically they're baryonic, but not the way you're thinking of), and hidden sectors.

 

[ben m]

I also just want to point out the difference between MM's approach to his preferred dark matter theories, and the (mainstream) nonbaryonic alternatives.

When told that diffuse plasma had been ruled out as a dark matter candidate, he decided that the baryons were actually dwarf stars. When he learned that dwarf stars were ruled out he switched to free-floating planets, or rocks, or meteors, or dust.

One thing he did not say was this:

I'm certainly aware of the fact that SUSY particles dark baryons have *CONSISTENTLY* failed to show up in the lab telescopes for over 20 40 years now, including those billion dollar LHC multimillion dollar microlensing survey experiments. I'm aware of the fact that virtually all the papers used to support the 'cold dark matter' aspect of Lambda-CDM plasma cosmology are based on SUSY particles huge amounts of diffuse cosmic plasma. What's it going to take to falsify a falsified theory anyway?

What IS it going to take?

By the way, a mistake: no, none of the evidence for cold dark matter (CMB/CMBpol/LSS/BAO/the usual) has anything to do with SUSY. The word "WIMP" refers to any cold weak particle, whether it's a SUSY neutralino or a KK heavy boson or a hidden-sector fourth-generation technihydrogen. Get it straight.

 

[sol invictus]

But therein lies the rub edd, you can't even tell me where dark energy comes from! It's really a little like whack a metaphysical mole around here. I can demonstrate that all those papers that astronomers wrote about mythical WIMPs doing gamma ray dances at midnight went up in smoke in the lab.

Nobody knows where "dark energy" comes from, let alone demonstrate it actually has a material effect on anything. The inflation entity is dead, so the odds of seeing it do anything to anything in a real controlled experiment on Earth are zip. The one and *ONLY* sky entity I could ever hope to falsify or verify was the "dark matter" genie, but alas it too seems to be incredibly impotent around the lab.

If a direct failure of exotic brands of "dark matter" mythologies in a multi-billion euro lab won't kill of the dark matter mythology, what will?

You've got all sorts of different things mixed up in your head, Michael. Here are some facts that almost certainly won't help you get them straight:

Fact: Newtonian gravity cannot account for the way galaxies rotate unless there is some (literally) dark matter in and around them - matter that we do not see with telescopes.

Fact: General relativity is very well approximated by Newtonian gravity when it comes to galaxy rotation, and therefore the same statement applies to GR.

Fact: In addition to galaxy rotation, at least four other independent lines of evidence also demonstrate the existence of extra matter. They all agree at least roughly on its abundance (roughly 5 times ordinary matter) and distribution (big diffuse mostly spherical clouds around galaxies).

Fact: Dark matter is almost certainly not baryonic, because all baryonic possibilities have been ruled out by direct searches and/or by various other effects it would have produced.

Fact: There are many types of particles already known to exist, many of which are massive and not baryonic - but none of which can account for dark matter.

Fact: General relativity cannot account for the overall expansion history of the universe (the rate at which clusters of galaxies move away from each other over time) unless there is some (literally) dark energy present - energy that we cannot see with telescopes, and that has a certain (rather peculiar) property in how its density changes with expansion. One such form of energy is a positive cosmological constant.

Fact: General relativity might be wrong. Since all of the above conclusions rely on GR, if it is wrong, there might be no dark matter or dark energy. However, GR has passed many experimental tests, and no viable alternative is presently known. Many mainstream physicists are actively searching for alternatives, however.

Fact: many supersymmetric extensions of the standard model of particle physics contain a dark matter particle. However, the existence of non-existence of SUSY is completely independent of the above facts.

 

[Reality Check]

Hijacking the thread won't change the fact that SUSY theory seems to have been falsified in the lab, along with your beloved dark sky religion.
...usual religous rant snipped...

Your ignorance will not change the fact that SUSY theories actually have been restricted to a smaller parameter space by the LHC results.

 

[Reality Check]

Like what? Surely you must realize how much this sounds like a "mythical exotic dark matter of the gaps" argument, right?

Only in your head, Michael Mozina.
You remain ignorant that there is a body of observational evidence that dark matter exists.

The observational evidence for dark matter means that it is mostly nonbaryonic matter with a tiny component of baryonic matter (e.g. MACHOs)
​

So the main question is what is dark matter?
The theories for the composition of dark matter include SUSY particles. There are other theories. Excluding SUSY particles merely means that dark matter must be something else.

 

[Marshall]

AFAICS Michael M has been well and truly answered on the subject of dark matter.
"Dark Energy" is a different issue. The LambdaCDM theory does not officially require some exotic kind of energy. Lambda is just a CONSTANT with dimensions of inverse area or, equivalently, curvature. Other people may have pointed this out (I didn't read the whole thread.)

Lambda could simply be that and nothing more: just a constant in the law of gravity. This is one possible way to think about (the Lambda in) the LambdaCDM model. It does not need an explanation in the form of some vacuum energy. There are people who talk about it as if they knew for sure that Lambda was produced or explained by the presence of a constant energy density. That way of talking is popular with the press---has a kind of exciting mysterious ring. But there is nothing so far that says it has to be that way. The Law of Gravity (Einstein Equation) could simply have two constants, G and Lambda, in it. It always did, in a way, we just thought for many decades that the second one was zero.

A discussion of this is in a 2010 paper by Eugenio Bianchi and Carlo Rovelli
with a slightly tongue-in-cheek title:
"Why all these prejudices against a constant?"

http://arxiv.org/abs/1002.3966 (just click on "PDF" to see the whole article)
==quote from the abstract==
The expansion of the observed universe appears to be accelerating. A simple explanation of this phenomenon is provided by the non-vanishing of the cosmological constant in the Einstein equations. Arguments are commonly presented to the effect that this simple explanation is not viable or not sufficient, and therefore we are facing the "great mystery" of the "nature of a dark energy". We argue that these arguments are unconvincing, or ill-founded.
9 pages, 4 figures
==endquote==

Michael M is not alone in getting messed up by confusing Lambda with CDM. The media may fail to distinguish sharply because both are called "dark".
Clouds of cold dark matter (CDM) are seen by lensing and mapped out and soforth. The evidence is mounting up that dark matter is a real kind of matter. One that has played an essential role in structure formation. It cools with expansion and gathers into cloudy bunches much like other kinds of matter.
Lambda is different. No evidence of bunching! According to the LambdaCDM model it does not have to correspond to any physical field or substance (it MIGHT or might not). It is quite possibly just a second constant in the Einstein Field Equation.

I see that the Bianchi-Rovelli paper has been cited by 20 other papers mostly from 2011:
http://www.slac.stanford.edu/spires/find/hep?c=ARXIV:1002.3966
I hadn't checked this before. Looking them over could be a way of finding different opinions on this within the research community. Some will be citing the paper because they want to take issue with it, others because they are making a survey of various current viewpoints.

 

[Reality Check]

Ya, including ordinary matter.

Wrong: including a tiny percentage of ordinary matter, e.g. neutrinos.
We know that dark matte ris not ordinary matter. Ther eis a whole thread devoted to your "dark matter = rocks" fantasy.


You still cannot get the simple physics that shows that dark matter is nonbaryonic matter:

• Look at 2 colliding galaxy clusters and see where the light is coming from. This is visible matter.
• Now look at where the matter actually is using gravitational lensing. This is all matter, both visible and not visible.
• Note the separation between them. This means that the non visible matter has interacted weakly (or not at all!) with the visible matter.
  The interaction is electromagnetic. The not visible matter deoes not interatce like the visibale matter. That means it is nonbaryonic matter.

NASA Finds Direct Proof of Dark Matter , another observation and Abell 520

I've yet to hear you folks address that "dust" in space revelation from a few years ago,

You are lying - it has been addressed several times.

or that revelation that galaxies are twice as bright as first thought,

You are lying - it has been addressed several times.

or that "stellar recount" data that that shows that small stars were underestimated by a factor of FOUR!

You are lying - it has been addressed several times.

About all I see are papers claiming "SUSY did this in the sky, SUSY did that in the sky".

Why whine to us about your ignorance about the possible candidates for dark matter?

There are a lot of papers about the SUSY candidates for dark matter because since that fixes a couple of problems (not just the composition of dark matter).
There are a lot of papers abnout non-SUSY candidates for dark matter - axions for example.

SUSY seems to be dead. What justification do you even have for exotic forms of matter at this point?

The observational evidence for dark matter means that it is mostly nonbaryonic matter with a tiny component of baryonic matter (e.g. MACHOs)

Duh !

 

[Reality Check]

You evidently have a hard time distinguishing between a "fact' and an "assumption". It is a 'fact' that photons are redshifted. It is an "assumption" that the phenomenon of redshift is somehow related to the "expansion of space".

You almost get something right!
It is a deduction from the known laws of physics that the cosmological redshift of galaxies is caused by the expansion of space. This deduction is really simple:

1. The CMB exists and its properties have no other viable explanation other than the universe was once in a hot dense state.
2. GR shows that any light emitted in an expanding universe will redshift.

 

[sol invictus]

"Dark Energy" is a different issue. The LambdaCDM theory does not officially posit some exotic kind of energy. Lambda is just a CONSTANT with dimensions of inverse area or, equivalently, curvature.

It has dimensions of energy density if you factor out Newton's constant.

It could simply be that and nothing more: just a constant in the law of gravity. That is one way to think about (the Lambda in) the LambdaCDM model. It does not require an explanation in the form of a vacuum energy. Some people talk about it as if they knew for sure that Lambda was produced or explained by the presence of a constant energy density. That way of talking is popular with the press---has a kind of exciting mysterious ring. But there is nothing so far that says it has to be that way. The Law of Gravity (Einstein Equation) could simply have two constants, G and Lambda, in it. It always did, in a way, we just thought for many decades that the second one was zero.

That's only kind of true. Vacuum energy (at least as long as it's constant) comes into Einstein's equations in exactly the same way Lambda does - they are physically totally indistinguishable. What we measure is the sum of the two.

Moreover, we know that there were first-order phase transitions in the early universe, which means that the vacuum energy was definitely non-zero back then. So if you'd been around then, you'd have measured a very different value for the sum than you do today.

If you like, the "mystery" of cosmic acceleration is twofold:

1) Is it in fact due to vacuum energy + cosmological constant, or something else?

2) If it is due to VE+CC, why is it so incredibly small, and why is it becoming important exactly when humans are around to measure it?

 

[sol invictus]

I see that the Bianchi-Rovelli paper has been cited by 20 other papers mostly from 2011:
http://www.slac.stanford.edu/spires/find/hep?c=ARXIV:1002.3966
I hadn't checked this before. Looking them over could be a way of finding different opinions on this within the research community. Some will be citing the paper because they want to take issue with it, others because they are making a survey of various current viewpoints.

Perhaps, but I'd recommend reading Weinberg, Carroll, or Polchinski's reviews (cited in refs. 2 and 3 of the Bianchi-Rovelli paper) instead. They represent something closer to the mainstream view (such as it is).

ETA - just read the Biachi-Rovelli paper. Surprisingly I agree with much of it, but it does fail miserably on two rather key points.

First off, the coincidence problem is best phrased as why the time scale set by dark energy is of order the time scale for evolution (e.g. billions of years). Instead it could just as well have been .0000000000000001 seconds, or 10000000000000000 trillion years. How serious of a problem that is is clearly debatable, but they seem to have missed it entirely.

Secondly, the discussion of vacuum energy is flat-out wrong at least in parts (for instance the assertion that since empty boxes don't have huge inertia, vacuum energy cannot gravitate). As I said above, it's just true that according to Einstein's theory, it's the sum of vacuum energy and cosmological constant that is physically measurable. So if you accept his theory - as it seems they do - you must explain why that sum is so small. No two ways about it.

 

[tusenfem]

If a direct failure in the lab won't do it, what exactly WOULD it take to falsify Lambda-CDM anyway?

I guess I am still waiting for your laboratory proof of the CNO cycle.