Mystery of Dark Energy: Unravelling the GR Expansion of Universe

[quasar987]

Another one of the physics teacher working at the college I attended (see my previous post) wrote a book on basic http://universite.deboeck.com/Resources/Titles/28011100266200/Images/28011100266200L.gif . In this book it says that the expansion of the Universe is due to the expansion of space itself and that this expansion of space is entirely predicted by Einstein's theory of GR. Now, if this is so, where does the DARK ENERGY (suposedly a MYSTICAL force of repulsion between matter) fit it ?!

 

[Nenad]

this dark energy is a result of a constant that Einstein added to his equation. A positive cosmological constant predicts that there must be a sort of anti - gravity in the universe.

 

[pervect]

Another one of the physics teacher working at the college I attended (see my previous post) wrote a book on basic http://universite.deboeck.com/Resources/Titles/28011100266200/Images/28011100266200L.gif . In this book it says that the expansion of the Universe is due to the expansion of space itself and that this expansion of space is entirely predicted by Einstein's theory of GR. Now, if this is so, where does the DARK ENERGY (suposedly a MYSTICAL force of repulsion between matter) fit it ?!

Here's a very brief history of cosmology post-Einstein:

1) Einstein comes up with GR.
2) Einstein proposes a static universe, with a cosmological constant to keep it from collapsing from its own gravity
3) Hubble observes that the universe isn't static, that it's expanding
4) Einstein recans the cosmological constant.
5) Varioius people make more and more observations of the rate of expansion, to compare it with the model predicted by General Relativity, called the Einstein-Friedmann cosmology. The cosmological constant goes in and out of fashion
6) Recent measurements of the rate of expansion put the cosmological constant back "in fashion" again, because certain experimental results are not fitting otherwise. The cosmological constant is given a new popular name, 'dark energy" (which could also include mechanisms that are like Einstein's original cosmological constant in effect, but different in origin).

 

[marcus]

Another one of the physics teacher working at the college I attended (see my previous post) wrote a book on basic http://universite.deboeck.com/Resources/Titles/28011100266200/Images/28011100266200L.gif . In this book it says that the expansion of the Universe is due to the expansion of space itself and that this expansion of space is entirely predicted by Einstein's theory of GR. Now, if this is so, where does the DARK ENERGY (suposedly a MYSTICAL force of repulsion between matter) fit it ?!

in the einstein equation (1915-1917) the cosmological constant Lambda was just some additional curvature built into space over and above that caused by matter.

we are used to thinking of all the kinds of matter and energy there are in the world being summed up in an overall "energy density" function----some fraction of a joule per cubic meter.

if you know SI metric units you will recognize the unit "joule per cubic meter" as a Pascal (it is the same unit as saying "Newton per square meter")

in the 90 years theyve had the einstein equation people have gotten used to thinking of all curvature (on the LHS of the eqn) as resulting from the Pascals of matter on the RHS of the eqn----the energy density and pressure. that is:"Matter shapes space and the shape tells matter how to flow." (Bingo. Cuckoo. whatever)

the cosmological constant might be some extra curvature on the LHS which is not caused by any matter on the RHS it might just be some intrinsic curvature space was born with.
but this is not the habit.
the habit is to attribute the extra curvature to the presence of some postulated energy which also has a postulated pressure, and which has the observational effects associated with the extra curvature.
we are obliged by 90 years of habit to imagine the existence of dark energy because energy density is where curvature ordinarily comes from

keep skeptical and have fun

 

[marcus]

if you have any interest in dark energy at all then you should get
familiar with the Friedmann equations

they are what cosmologists use instead of the raw Einstein equation
because they are much much easier to work with

and they show the energy density and the pressure explicitly on the RHS

and there should be a link to them, or a post about them, in the
Astronomy Cosmology Reference Sticky at PF General Astronomy forum.
I'll see if i can find it. Otherwise just google Friedmann equation.

 

[RingoKid]

could dark matter be "strings" joined together to become very long and dense hence the reason we can't see them as they are only Planck length wide but anywhere up to infinitely long ?

...dark strings

 

[Garth]

could dark matter be "strings" joined together to become very long and dense hence the reason we can't see them as they are only Planck length wide but anywhere up to infinitely long ?

...dark strings

Actually this post is about Dark Energy, but no matter, we cannot see Dark Energy or Dark Matter (it is too dark) or 'strings' for that matter (they are too small). Dark Energy and Matter are only observed in the depths of space where the observations are theory dependent. That theory being GR, if the theory changes then the observations will change, or disappear altogether.

Unless we come up with something that actually is observed, not only in the depths of space but also in the laboratory, then perhaps all we are doing is 'adding extra epicycles' to make the standard theory work.

See my post #10 https://www.physicsforums.com/showthread.php?p=284031#post284031

 

[RingoKid]

thanx Garth...

so where do you propose this paradigm will shift to...can any variant of string/brane theory currently account for dark matter or energy, eg a dark string speculation ?

and isn't it true that inflation requires early universe matter to be flung out at speeds exceeding c making it another contradiction of GR ?

cheers

 

[Garth]

so where do you propose this paradigm will shift to...can any variant of string/brane theory currently account for dark matter or energy, eg a dark string speculation ?

You may be interested in my thread "Self Creation Cosmology - a new gravitational theory" https://www.physicsforums.com/showthread.php?t=32713 because SCC does not require Inflation, unknown Dark Matter or Dark Energy. There is Dark Matter but it is ordinary baryonic matter such as hydrogen and helium, it is dark in the sense of being non-luminous and not being an unknown substance. The theory may or may not stand up but it is falsifiable and is at present about to be tested by the Gravity Probe B satellite.

and isn't it true that inflation requires early universe matter to be flung out at speeds exceeding c making it another contradiction of GR ?

No - the restriction on not going faster than light only applies within space-time. Inflation is talking about space-time itself expanding at an enormous rate, objects (not that there were any then!) within space-time would have been carried along with that general expansion. At present with the Hubble flow, or expansion of the universe, the galaxies are not moving within space-time but it is space-time itself which is expanding and we, and everything else, are simply being carried along with it. Distant galaxies beyond our event-horizon are moving away from us at velocities greater than the speed of light, that is why we cannot see them.

 

[sol2]

The thing is, if you look at the http://wc0.worldcrossing.com/WebX?14@174.GuiAcZYuBaw.0@.1ddf4a5f/57 as consistant, at what point would this be so?

If you have consider how pearls and chains are formed in a universe that is cooling, and you need some framework in which to comprehend the interlinking capability.

So in the beginning we look at how supersymmetrical states would have existed and how the expansitory universe, would neuronically connect.

http://astro.uchicago.edu/~andrey/soft/p3d/p3d_evol.gif

http://www.gsfc.nasa.gov/gsfc/spacesci/pictures/20020812gamma/denset.jpg

Scharf and Mukherjee's new research compared a catalog of 2,469 galaxy clusters with the Compton database. Using sophisticated statistical techniques, they showed that the sky surrounding the most massive clusters was systematically brighter in gamma rays than other regions.

"The more massive the cluster (and greater the gravitational potential), the brighter the gamma-ray halo," said Mukherjee. "The enhancement observed was very similar to that predicted by the Loeb-Waxman theory

http://www.gsfc.nasa.gov/topstory/20020812gamma.html

 

[Nereid]

Another one of the physics teacher working at the college I attended (see my previous post) wrote a book on basic http://universite.deboeck.com/Resources/Titles/28011100266200/Images/28011100266200L.gif . In this book it says that the expansion of the Universe is due to the expansion of space itself and that this expansion of space is entirely predicted by Einstein's theory of GR. Now, if this is so, where does the DARK ENERGY (suposedly a MYSTICAL force of repulsion between matter) fit it ?!

This question is about theory; at least as important - since this is science, arguably more important - is experiment and observation.

AFAIK, there are two classes of observations (no experiments ) which support 'dark energy', distant supernovae and 'all cosmologically relevant observations'

1) Distant supernovae. Ever since Hubble first published obsevational results which pointed to an expanding universe, astronomers have been keen to characterise that expansion as accurately as possible - over all distance scales, and in all directions. To do this, they need independent measures of both distance and recession speed. The latter is relatively easy to measure, with great precision - the 'redshift' of galaxies and quasars; the former has proven immensely difficult, and only in the last decade has a broad consensus emerged (there is still considerable 'observational error', and there are still some dissenters). Distance can be measured by a number of different types of observations, and the 'distance ladder' is now reasonably well established, out to perhaps as much as 10 billion light years.

While redshifts are relatively easy to measure, their interpretation as 'recession due to the expanding universe' has had its challenges and upsets. Perhaps the biggest was 'http://cow.physics.wisc.edu/~ogelman/guide/gr8a/ '; apparently there is an awful lot more mass in the local part of the universe (~100 Mpc) than can be 'seen'.

So, the 'expanding universe' hypothesis predicts that the universe is, and has been, expanding uniformly - in all directions, and at all times (at least, after any inflation ended; observationally we can't directly see any earlier than ~300,000 years after the BB, well after any inflation finished), over sufficiently large chunks of the universe (superclusters have sufficient mass so 'expansion' of objects within a supercluster may be small compared with net gravitational attraction from masses within the supercluster).

What do observations show? The best distance indicator for very distant objects is Type 1a supernovae - we think we understand their behaviour sufficiently well so good observations of their lightcurves can be turned into estimates of distance (this 1998 poster gives more details). Plotting distance against redshift shows that the data are not on the curve predicted by 'uniform expansion' (it's not quite as clear-cut as this; different models of the universe - e.g. with different amounts of dark matter - give different curves, but no model that is consistent with other observational data - e.g. WMAP - goes near the data). What model curves will go through the data? Those in which the rate of expansion of the universe is increasing!

'Dark energy' is the shorthand that is used for whatever might be causing the observed acceleration of the universal expansion.

But not so fast! How can astronomers be so certain that there aren't other effects involved? Initially, quite a bit of work had to be done to nail these down, e.g. do we understand Type 1a SN sufficiently well? what if the distant SN are partly obscurred by dust? and so on. Many of these 'systematic errors' have now been characterised and their effects on the data taken into account. However, some feel that at least an OOM more of good data are needed (http://snap.lbl.gov/ to the rescue?)

2. All 'cosmologically relevant observations': As Garth correctly points out, this is a bit of chicken and egg. Basically, you take all observations that have relevance to cosmology - WMAP and others on the CMBR, large scale structure (e.g. 2dF, SDSS), primordial nuclide abundances, the Hubble relationship, the distant SN data, ... - and see what sort of cosmological model is most consistent with it all. The idea is that there is more than enough data to constrain models, so if the models are wrong, there will be obvious inconsistencies. The good news is that there are models which are consistent with all the data ... but only those which have 'dark energy' in them!

Further reading: Wikipedia
APOD
Snowmass 2001, Yellow Book on Dark Energy
short article - model-independent dark energy
nice, bite-sized physicsweb summary

 

[Garth]

The good news is that there are models which are consistent with all the data ... but only those which have 'dark energy' in them!

Not quite "only those with Dark energy in them"!

As we have discussed in a previous thread an Indian team, consisting of Gehaut, Lohiya et al., have been looking at the strictly linearly expanding or "freely coasting" universe. It fits exactly all the constraints!

Their papers can be found at:
A Concordant "Freely Coasting Cosmology"
http://arxiv.org/abs/astro-ph/0306448

A "Freely Coasting" Universe
http://arxiv.org/abs/astro-ph/0209209

They say "A strictly linear evolution of the cosmological scale factor is surprisingly an excellent fit to a host of cosmological observations. Any model that can support such a coasting presents itself as a falsifiable model as far as classical cosmological tests are concerned." (Taken from the abstract of the first paper above)

One theory that does indeed "support such a coasting" is SCC - in its Jordan Frame formulation- without requiring Dark Energy. [See my paper "Self Creation Cosmology - An Alternative Gravitational Theory" http://arxiv.org/abs/gr-qc/0405094 (to be published in 'Progress in
General Relativity and Quantum Cosmology Research', Nova Science
Publishers, Inc. New York.)]

 

[marcus]

...
'Dark energy' is the shorthand that is used for whatever might be causing the observed acceleration of the universal expansion.

Hi Nereid, at one time I thought you made a nuanced distinction between
the cosmological constant and dark energy. Does this "whatever might be causing" definition get rid of any earlier distinction you may have made and simply lump the two? I'm not certain I understand why you have dark energy in quotes, and consistently write 'dark energy'. I don't recall your doing this before (perhaps you did and I simply failed to notice). It would be interesting to know if your thinking has been changing about this. Would you care to clarify your own view?

 

[sol2]

Maybe she is softening like Peter Woit? Maybe one day, I will convert you too, Marcus.

Oh Marcus, could you correct your quote?

 

[marcus]

Maybe he is softening like Peter Woit?

he?

Who do you mean sol?

Nereid is a she. Both she and Peter Woit are crisp thinkers, in my view, and soften rarely. On the other hand, even when you might be joking you have intuitions about people that are worth listening to, so I will consider it a possibility

 

[Nereid]

Hi Nereid, at one time I thought you made a nuanced distinction between
the cosmological constant and dark energy. Does this "whatever might be causing" definition get rid of any earlier distinction you may have made and simply lump the two? I'm not certain I understand why you have dark energy in quotes, and consistently write 'dark energy'. I don't recall your doing this before (perhaps you did and I simply failed to notice). It would be interesting to know if your thinking has been changing about this. Would you care to clarify your own view?

Thanks for the clarification marcus!

In these discussions it can be quite difficult to write something brief that also reflects all the major aspects in play ... let alone ALL aspects which can be said to fit (somehow). Garth's post is a good example of this - a cosmological model which the authors claim to be consistent with all the observational data, and one which differs markedly from the 'concordance model' (no doubt there are others out there too ... with relatively weak observational constraints, theoreticians can have the most marvellous fun imaginable ).

From the observational perspective, at the current level of constraint, both a cosmological constant and some kind of 'dark energy' are pretty much indistinguishable, though we are all looking forward to the day when that ceases to be! Since "cosmological constant, 'dark energy', or something else; anyway, whatever gives rise to the observed acceleration of expansion" is anything but shorthand, I think you'll find that 'dark energy' is more convenient (Of course, when talking 'theory', cc and DE are certainly distinguised!)

 

[Nereid]

he?

Who do you mean sol?

Nereid is a she. Both she and Peter Woit are crisp thinkers, in my view, and soften rarely. On the other hand, even when you might be joking you have intuitions about people that are worth listening to, so I will consider it a possibility

Message from the global collective of Nereids, their partners, friends and families: http://members.iquest.net/~jswartz/jks/humor/dog.htm Woof! Woof!

(and no, lady dogs do NOT reveal their breeds :shy: )

 

[marcus]

(Of course, when talking 'theory', cc and DE are certainly distinguished!)

that's my good old Nereid


see sol? crispness

 

[sol2]

he?

Who do you mean sol?

Nereid is a she. Both she and Peter Woit are crisp thinkers, in my view, and soften rarely. On the other hand, even when you might be joking you have intuitions about people that are worth listening to, so I will consider it a possibility

I made correction Marcus in previous post.

Yes if you cook the bacon to long it can become crisp:)

The very foundational principals have to have a basis in which to move from. I scream loudly scientific verification is the only road too and anything less is theoretical speculation. There, I feel better

When one sends out it's tentacles from the mind, it can flop quite freely if you do not have control. So wild speculation would have been loosening a grip to what we have known for certain, and what shakes our foundation.

I often compare it to the view I had of the Grand Canyon and the wide open expanse, yet I held firmly to the rail

 

[marcus]

(and no, lady dogs do NOT reveal their breeds :shy: )

but a guy dog with a good nose can tell if its a lady---forget about breeds we are talking about what matters, nuff said, and WOOF WOOF to you too

 

[sol2]

Message from the global collective of Nereids, their partners, friends and families: http://members.iquest.net/~jswartz/jks/humor/dog.htm Woof! Woof!

(and no, lady dogs do NOT reveal their breeds :shy: )

good one , then I hope you won't laugh at the kind of Bird I am

 

[meteor]

It's important to be familiar with the concept of "Dark energy equation of state", represented by w. It is equal to density/pressure of dark energy. these are the values for the 3 more notorious models of dark energy

cosmological constant: w=-1
phantom energy: w<-1
quintessence: -1<w<-(1/3)

 

[meteor]

chameleon chameleon

I want to present... the chameleon model!
http://arxiv.org/abs/astro-ph/0309300
"Chameleon Fields: Awaiting Surprises for Tests of Gravity in Space"
In a nutshell, in this model quintessence is a chameleon field (i.e. a scalar field that has mass not constant in space and time, but rather depends on the environtment, in particular on the local matter density)

Now i understand why Bowie sang "There's a starman waiting
in the sky..."

 

[Nereid]

It's important to be familiar with the concept of "Dark energy equation of state", represented by w. It is equal to density/pressure of dark energy. these are the values for the 3 more notorious models of dark energy

cosmological constant: w=-1
phantom energy: w<-1
quintessence: -1<w<-(1/3)

Thanks meteor.

AFAIK, there's another difference between various approaches to DE, the question of time variability. The observational data are not consistent with DE varying by OOMs over cosmological time, but slower changes aren't ruled out. Of course, the CC is, by definition, non-varying

What about the others?

Also, can you tell us anything about the 'Generalized Chaplygin gas' which many papers make reference to? How does such a gas differ from good ol' air?

 

[Chronos]

Thanks meteor.

AFAIK, there's another difference between various approaches to DE, the question of time variability. The observational data are not consistent with DE varying by OOMs over cosmological time, but slower changes aren't ruled out. Of course, the CC is, by definition, non-varying

What about the others?

Also, can you tell us anything about the 'Generalized Chaplygin gas' which many papers make reference to? How does such a gas differ from good ol' air?

It is imaginary.

 

[meteor]

I will take on time variability later, but with respect to the GCG, its starnge cause the form of the equation of state differs form that of the other models. For the GCG is
P=(-A)/(d^a)
P=pressure
d=density
A=positive constant
and 0<a<=1
(reference gr-qc/0305086)
and no much information is given about it, is described as "a polytropic gas" or "a perfect fluid".
It's rather curious, in fact is an example of a kind of possible substance candidate to act as dark energy and dark matter at the same time called quartessence, that's why the GCG is also called Chaplygin quartessence. But there are other 2 possibles forms of quartessence: logarithmic quartessence and exponential quartessence

It is imaginary.

Some modern phlogiston?

 

[pmb_phy]

Another one of the physics teacher working at the college I attended (see my previous post) wrote a book on basic http://universite.deboeck.com/Resources/Titles/28011100266200/Images/28011100266200L.gif . In this book it says that the expansion of the Universe is due to the expansion of space itself and that this expansion of space is entirely predicted by Einstein's theory of GR. Now, if this is so, where does the DARK ENERGY (suposedly a MYSTICAL force of repulsion between matter) fit it ?!

The term Dark Energy is given to that matter which is causing the universe to expand at an accelerating rate. This is what some call "anti-gravity" since this is clearly gravity acting in a repulsive manner.

Back in Einstein's day nobody knew of any kind of matter which could produce such an effect. since Einstein assumed that the universe was static he added a term to his field equations to allow for this repulsive effect. Einstein's equations changed from

G^{\alpha\beta} = -\frac{8\pi G}{c^4}T^{\alpha\beta}

to

G^{\alpha\beta} + \Lambda g^{\alpha\beta} = -\frac{8\pi G}{c^4}T^{\alpha\beta}

\Lambda is called the cosmological constant. In modern terms the cosmological constant is also called "Dark Energy." This is the term which, for normal matter, allows for anti-gravity when \Lambda > 0. However this was before the concept of negative pressure was around. It is now conceivable that pressure terms in the T^{\alpha\beta} can be negative. This would also give rise to resulsive gravitational effects. For weak gravitational fields Einstein's equations, for \Lambda = 0, can be expressed as

\nabla^2 \Phi = 4\pi G(\rho + 3p/c^2)

Let \rho_A = 4\pi G(\rho + 3p/c^2) = effective active gravitational mass. If the pressure is negative enough then \rho_A < 0. Therefore when there is a large negative pressure the matter acts like a negative active gravitational mass (defined as that which generates a gravitational field).

Pete

 

[Chronos]

Some modern phlogiston?

Hehe. The visible universe is merely dephlogisticated Chaplygin gas.

 

[Garth]

The term Dark Energy is given to that matter which is causing the universe to expand at an accelerating rate. This is what some call "anti-gravity" since this is clearly gravity acting in a repulsive manner.

Only it is Dark Energy that is the subject of this thread!
Pete everything you went on the say was true of Matter, however the matter density has been constrained by WMAP, using the GR paradigm to interpret the data, to be only 4 % baryonic matter (from BB nuclei-synthesis) and 23 % other unknown matter (Dark Matter). (All %'s are that of the critical density)

As the total density is assumed to be unity because of spatial flatness therefore 73 % is assumed to be something else called Dark Energy.

As I have said before these Dark entities may be a case of just adding "extra epicycles" to make the paradigm work, as Inflation, Dark matter and Dark Energy have not been demonstrated in over thirty years of active laboratory experimentation.
Garth

 

[Olias]

Try thus:http://arxiv.org/abs/math.DS/0409019

 

[meteor]

It seems that there's perhaps some preference within the physics community to a dark energy with constant energy density (e.g. cosmological constant). NASA scientists declared months ago that they bet for a cosmological constant
But I prefer a model with dependence on time. Examples of such models are quintessence, phantom energy and k-essence
Phantom energy (aka superquintessence) postulates an increase of dark energy density over time. So the universe will end violently tearing all apart in the Big Rip, aka Big Smash
Quintessence is a scalar field that varies over time and also has dependence on space ( so it will be more dense in some localizations than in others). It actually exercises negative pressure, but exercised positive pressure in the past! So, it can perhaps exercise positive pressure in the future (leading to a Big Crunch?)
K-essence also varies in space and time, its equation of state varies over time but its always w>(-1)
I prefer the model of quintessence because I think that the acceleration is not going to be eternal. Since I'm also a fan of Loop Quantum Cosmology and this theory has recently forecasted the possibility of the universe undergoing a Big Crunch, it's a model perfect for me

 

[turbo]

I too expect that there will be time-dependant variation at the fundamental level (structure and coarseness of space-time, for instance) and I also expect that the Einsteinian space-time "curvature" caused by embedded mass will be better visualized as gradients in the properties of the basic units of space-time (density, orientation, energy states...). These space-time gradients will be found to cause "gravitational lensing" redshifting, and other effects, not gravity itself.

Gravity (as expressed as force acting over a distance) is very weak and should not be invoked as a force capable of bending the paths of photons passing nearby. The amount of mass needed to provided such refraction might overstate the mass of a galaxy or galactic cluster by quite a large amount (a pretty common problem these days, with about 96% of the mass of the universe tied up in invisible undetectable "dark matter").

 

[Nereid]

I too expect that there will be time-dependant variation at the fundamental level (structure and coarseness of space-time, for instance) and I also expect that the Einsteinian space-time "curvature" caused by embedded mass will be better visualized as gradients in the properties of the basic units of space-time (density, orientation, energy states...). These space-time gradients will be found to cause "gravitational lensing" redshifting, and other effects, not gravity itself.

Gravity (as expressed as force acting over a distance) is very weak and should not be invoked as a force capable of bending the paths of photons passing nearby. The amount of mass needed to provided such refraction might overstate the mass of a galaxy or galactic cluster by quite a large amount (a pretty common problem these days, with about 96% of the mass of the universe tied up in invisible undetectable "dark matter").

Something like dark matter, which can't be accounted for within the Standard Model, and which we can't get into the lab to zap and prod, surely causes many folk heartburn.

However, to call it 'undetectable' does a considerable disservice to the ingenuity of observational astronomers. In particular, there is a consistency in the observations which is a challenge for alternative views - estimates of the mass of dark matter in rich clusters are consistent across three independent types of observation - X-ray data on IGM gas temperature (assume equilibrium, derive mass), redshift data on galaxy velocity dispersion (apply virial theorem, derive mass), and gravitational lensing (both weak and strong; assume Einstein, derive mass).

For at least one cluster, the distribution of dark matter has been derived (not just the mass), and a nice piccie made - if it ain't DM, what is it a piccie of? http://www.astro.caltech.edu/~tt/0024/CL0024II.pdf

 

[Garth]

For at least one cluster, the distribution of dark matter has been derived (not just the mass), and a nice piccie made - if it ain't DM, what is it a piccie of? http://www.astro.caltech.edu/~tt/0024/CL0024II.pdf

Thank you for a nice reference; "what is it a 'piccie' of?" How about dark baryonic matter?

In my post #12 on this thread I referred to two papers from an Indian team that show in the "Freely Coasting Universe", which is expanding strictly linearly, the mass density of ordinary baryonic matter is aboput 20% and not a maximum of 4% as in the standard paradigm.

Therefore this stuff does not have to be re-invented, we know it already and are made of it!
Garth

 

[turbo]

Something like dark matter, which can't be accounted for within the Standard Model, and which we can't get into the lab to zap and prod, surely causes many folk heartburn.

However, to call it 'undetectable' does a considerable disservice to the ingenuity of observational astronomers. In particular, there is a consistency in the observations which is a challenge for alternative views - estimates of the mass of dark matter in rich clusters are consistent across three independent types of observation - X-ray data on IGM gas temperature (assume equilibrium, derive mass), redshift data on galaxy velocity dispersion (apply virial theorem, derive mass), and gravitational lensing (both weak and strong; assume Einstein, derive mass).

For at least one cluster, the distribution of dark matter has been derived (not just the mass), and a nice piccie made - if it ain't DM, what is it a piccie of? http://www.astro.caltech.edu/~tt/0024/CL0024II.pdf

Well, we have fundamentally different views of this, so I'll try to state mine succinctly. First of all the picture of dark matter is not real in any sense - it is only a guess at how this invisible stuff "might" be distributed to explain the amount of "gravitational lensing" (a misnomer) observed through that cluster. I would like to see this same group show us how the dark matter needs to be distributed around a typical spiral galaxy in "just" such a way as to cause the differential rotations they exhibit. I'm afraid that dark matter gets very messy in that area.

As an optician, I am very interested in the behavior of light and other electromagnetic waves. Since detecting and measuring these radiations are the primary means by which we explore our universe, I am sensitive to quandries and puzzles regarding our understanding of light. You already know about some of my struggles with discordant redshift.

I suggest that we be parsimonious and NOT invoke the existence of dark matter to explain lensing. Right now, we know that massive objects exist, we know that massive objects distort space-time, and we know that light propogates through space-time. We have all the ingredients we need for lensing. The simplest explanation for "gravitational lensing" is that masses distort space-time and the distorted space-time refracts light passing through it, resulting in lensing. There is no need for dark matter, nor should we call this "gravitational" lensing. The lensing is cause by refraction of light passing through a space-time domain that is distorted by the presence of mass. The refraction is not caused by gravity (in the Newtonian sense). Newtonian gravity is an extremely weak force of attraction between massive bodies, and photons are not massive in any real sense. Their paths can be deflected however by density differences in the medium through which they travel - Space-Time.

How does mass distort space-time? Does it cause gradients in the distribution, orientation and/or energy state of the basic units of space-time? These are the questions that will have to be answered (probably by the LQG or String people) before quantum physics and relativity can be united. The optical qualities of clusters might hold clues as to how we can expect the distortion of space-time to manifest itself. The LQG people are modeling space-time as if it comes in discrete units with lengths, areas, and volumes quantized at the Planck level. What do these basic units of space-time do in the presence of mass? That's the tough part.

 

[Nereid]

Well, we have fundamentally different views of this, so I'll try to state mine succinctly. First of all the picture of dark matter is not real in any sense - it is only a guess at how this invisible stuff "might" be distributed to explain the amount of "gravitational lensing" (a misnomer) observed through that cluster. I would like to see this same group show us how the dark matter needs to be distributed around a typical spiral galaxy in "just" such a way as to cause the differential rotations they exhibit. I'm afraid that dark matter gets very messy in that area.

As an optician, I am very interested in the behavior of light and other electromagnetic waves. Since detecting and measuring these radiations are the primary means by which we explore our universe, I am sensitive to quandries and puzzles regarding our understanding of light. You already know about some of my struggles with discordant redshift.

I suggest that we be parsimonious and NOT invoke the existence of dark matter to explain lensing. Right now, we know that massive objects exist, we know that massive objects distort space-time, and we know that light propogates through space-time. We have all the ingredients we need for lensing. The simplest explanation for "gravitational lensing" is that masses distort space-time and the distorted space-time refracts light passing through it, resulting in lensing. There is no need for dark matter, nor should we call this "gravitational" lensing. The lensing is cause by refraction of light passing through a space-time domain that is distorted by the presence of mass. The refraction is not caused by gravity (in the Newtonian sense). Newtonian gravity is an extremely weak force of attraction between massive bodies, and photons are not massive in any real sense. Their paths can be deflected however by differences density in the medium through which they travel - Space-Time.

How does mass distort space-time? Does it cause gradients in the distribution, orientation and/or energy state of the basic units of space-time? These are the questions that will have to be answered (probably by the LQG or String people) before quantum physics and relativity can be united.

First let's clear up our terminology ... observational astronomers use the phrase 'gravitational lensing' rather loosely, referring to both 'true gravitational lensing' (what you expect from a straight-forward application of GR to the EM images of a distant object seen 'through' a closer, massive one - arcs, multiple images, magnification, etc), and image distortion as EM is deflected by passing 'near' a massive body (sometimes called 'weak lensing', or 'gravitational shear'; it's also the (in)famous 1919 eclipse photos through to Cassini, the Sun being the massive object).

Next, let's see if we agree on 'nearby' examples of 'lensing'. AFAIK, deflection of EM has been observed in our solar system, by both the Sun and Jupiter, and the most accurate data are consistent with GR to 1 part in ~10⁴; in these cases, the mass of the Sun (and Jupiter) are obtained independently of the deflection, and those mass estimates are consistent with a great deal of physics. Does either turbo-1 or Garth have an alternative theory to account for these solar system observations?

Within the Milky Way, a number of programs have detected transient gravitational lens events - a massive object passes into the line of sight from Earth to a distant star, the star appears to brighten, then fade. This is usually interpreted as the lensing object being a closer star. Again, the observations are consistent with GR, and include caustic crossing events as well as later, direct observations of the lensing star. (If any reader is unfamiliar with this work, please say so and I'll post links). Does either turbo-1 or Garth have an alternative theory to account for these Milky Way (and LMC/SMC?) observations?

For relatively nearby galaxies, SDSS researchers have published papers showing the average radial distribution of mass around the galaxies, from the 'shear' distortions in images of more distant galaxies. This work is statistical; the 'shear signal' is quite weak, but shows up clearly when many galaxies are analysed (and there's no shear signal around bright stars - as expected). It's here that DM becomes evident - the mass required to produce the observed shear (and its distribution) are larger than that inferred from the light observed from these galaxies. Does either turbo-1 or Garth have an alternative theory to account for these relatively local galaxy observations?

 

[Nereid]

Thank you for a nice reference; "what is it a 'piccie' of?" How about dark baryonic matter?

In my post #12 on this thread I referred to two papers from an Indian team that show in the "Freely Coasting Universe", which is expanding strictly linearly, the mass density of ordinary baryonic matter is aboput 20% and not a maximum of 4% as in the standard paradigm.

Therefore this stuff does not have to be re-invented, we know it already and are made of it!
Garth

Well I finally got around to downloading and reading these papers (they are essentially the same; the more recent one is longer and has more details). There was one refence that I couldn't find on the internet: "A study of consistency of linear coasting with gravitational lensing statistics has recently been reported". I think this 'freely coasting universe' idea is quite interesting; it'd be great to hear what marcus, pmb_phy, Chronos, and others think of it!

Although it's a bit OT (DM, not DE), I was left quite puzzled by the Gehlaut et al papers and their account of DM; maybe Garth can help me out.

It seems that Gehlaut et al claim to have a cosmology that is consistent with the WMAP (and other CMBR) observations (most of their paper is devoted to this), nuclide abundance data (though they discuss only element abundance, plus deuterium), the expansion rate observations (including the recent, distant Type Ia SN data), inferred age of the universe vs oldest object observations (though this is not examined in much detail), and multiple quasar images ('true' gravitational lensing, though it is apparently discussed elsewhere).

As Garth says, the DM 'seen' in large galaxies and clusters is 'cold, baryonic matter' in Gehlaut et al. But what baryons? And what about the DM in dwarf galaxies? It seems to me Gehlaut et al still have the same challenge as that which generations of astronomers faced, right back to Zwicky: the DM isn't gas (it doesn't show up as either emission or absorption), dust (ditto), dim or failed stars (MACHO, OGLE etc would have seen that), old stars such as faint white dwarfs or neutron stars (ditto) ... so it is exotic baryons? or pebbles rocks and comets?

Lastly, for this post, Gehlaut et al say "there would just be enough neutrons produced, after nucleosynthesis commences, to give [...] and metallicity some 10⁸ times the metallicity produced in the early universe in the standard scenario. This metallicity is of the same order of magnitude as seen in lowest metallicity objects." But they don't state a) what primordial metallicity they predict, nor b) what the metallicity of the lowest metallicity objects actually is!

 

[meteor]

A pair of models that can interest to someone...
http://xxx.lanl.gov/abs/astro-ph/0409033
"On the Accelerated Expansion of the Universe"
this model postulates the acceleration of the expansion is due to fermion degeneracy pressure of neutrinos of the intergalactic medium

Also, Trans-Planckian Dark energy
http://arxiv.org/abs/hep-th/0212027

 

[Garth]

Neried asks whether I have another explanation for the DM observations and gravitational lensing at different scales. I do not, I am quite happy with the idea that a) gravitaitonal lensing occurs and is as predicted by GR (it is the same in SCC) and b) that Dark Matter exists. My argument is though it is Dark in the sense of being non-luminous, not in the sense of being some unknown new type, or state, of matter. In a freely coasting universe (as in SCC) it is just ordinary baryonic matter as the baryonic cosmological density is about 20 % and not restricted to 4% as in the standard model. If there is a problem in identifying exactly what form it takes then that problem is no greater than in the standard paradigm. It could be bricks, or Jupiters or a population of black holes or whatever, I do not claim to be able to solve all the mysteries at once, just that it should not necessary to multiply mysteries by adding these extra 'epicycles' (Inflation, DM, DE) to keep the old paradigm afloat.
Garth

 

[Chronos]

It is certainly true the Standard Model has evolved over time. I don't think it is accurate to characterize that process as being ad-hoc. I am also reluctant to discard the model in favor of a more radical approach, such as 'free coasting'. Not that other models don't have their attractive features. That is why they are still being kicked about. The more relevant issue is the Standard Model has an imposing mountain of observational and theoretical support. The others do not. Fortunately, different researchers have different opinions and all the viable options will continue to be explored. At present, the Standard Model is the reigning heavy weight champ and any challenger will have to deliver a knockout punch to claim the title.

The 'freely coasting' model proposed by Gehlaut etal is interesting. The paper did put me in full skeptic mode early on when they asserted "First of all, the use of Einsteins equations to describe cosmology has never been justified." The rational for making this rather shocking statement was not very convincing. On the whole, however, it has some nice features. None of those annoying particle or cosmological horizons to address. It also appears to be concordant, although I think some issues were rather thinly supported and others largely ignored. The following papers present some of these issues.
http://adsabs.harvard.edu/cgi-bin/n.....67L&amp;db_key=AST&amp;high=40d9fbf26c22275
http://adsabs.harvard.edu/cgi-bin/n....373L&amp;db_key=AST&amp;high=40d9fbf26c23948
http://adsabs.harvard.edu/cgi-bin/n....543K&amp;db_key=AST&amp;high=40d9fbf26c23948
It seemed pretty obvious the lack of an inflationary epoch in the very early universe posed a problem. Solving it by inserting repulsive gravity without offering a mechanism was a pretty big pill to swallow. You also end up with a universe where recombination did not occur until ~10^7 years as opposed to ~10^5 years after the big bang. The explanation for elemental abundance was not great, but, OK. At least it left room for falsifiable predictions. All in all, I did not feel it solved more problems than it created, but, that's not necessarily a bad thing.

 

[Garth]

It is certainly true the Standard Model has evolved over time. I don't think it is accurate to characterize that process as being ad-hoc. I am also reluctant to discard the model in favor of a more radical approach, such as 'free coasting'. Not that other models don't have their attractive features. That is why they are still being kicked about. The more relevant issue is the Standard Model has an imposing mountain of observational and theoretical support. The others do not. Fortunately, different researchers have different opinions and all the viable options will continue to be explored..

One concern of mine is the absolute confidence placed in the standard model: it is called "precision cosmology", its deductions are presented as facts, it is assumed that it has been robustly established beyond doubt as an intellectual edifice standing on several pillars. Attack one we are told (RAS lecture 2004) and the others will continue to securely support the paradigm. However this confidence ignores the fact that three of these pillars are invisible, Inflation which depend on the Higgs field (we have detected the Higgs boson have we?), Dark Matter (we know what is it do we?) and Dark Energy (we know what we are talking about do we?) In their day the addition of epicycles to the Ptolemaic system was no more "ad hoc" than our addition of these "entities".

”Entia non sunt multiplicand praetor necessitatem” (Entities should not be unnecessarily multiplied) Ockham’s (Occam’s) razor.

The reason "the Standard Model has an imposing mountain of observational and theoretical support" is because it has been so well funded and the alternatives not, yet it is the essence of the scientific method that alternative theories against which the standard model can be tested should be encouraged. As I have pointed out on several posts cosmological observations are all theory dependent, change the theory and those observations change too. The important thing is to have consistency and an economy of "entities".

At present, the Standard Model is the reigning heavy weight champ and any challenger will have to deliver a knockout punch to claim the title.

Maybe, just maybe, Gravity Probe B will deliver this.

Solving it by inserting repulsive gravity without offering a mechanism was a pretty big pill to swallow.

Agreed, but SCC provides the mechanism.

"Cosmologists are often in error but never in doubt"

 

[turbo]

Next, let's see if we agree on 'nearby' examples of 'lensing'. AFAIK, deflection of EM has been observed in our solar system, by both the Sun and Jupiter, and the most accurate data are consistent with GR to 1 part in ~10⁴; in these cases, the mass of the Sun (and Jupiter) are obtained independently of the deflection, and those mass estimates are consistent with a great deal of physics. Does either turbo-1 or Garth have an alternative theory to account for these solar system observations?

Within the Milky Way, a number of programs have detected transient gravitational lens events - a massive object passes into the line of sight from Earth to a distant star, the star appears to brighten, then fade. This is usually interpreted as the lensing object being a closer star. Again, the observations are consistent with GR, and include caustic crossing events as well as later, direct observations of the lensing star. (If any reader is unfamiliar with this work, please say so and I'll post links). Does either turbo-1 or Garth have an alternative theory to account for these Milky Way (and LMC/SMC?) observations?

For relatively nearby galaxies, SDSS researchers have published papers showing the average radial distribution of mass around the galaxies, from the 'shear' distortions in images of more distant galaxies. This work is statistical; the 'shear signal' is quite weak, but shows up clearly when many galaxies are analysed (and there's no shear signal around bright stars - as expected). It's here that DM becomes evident - the mass required to produce the observed shear (and its distribution) are larger than that inferred from the light observed from these galaxies. Does either turbo-1 or Garth have an alternative theory to account for these relatively local galaxy observations?

Relativity predicts the distortions caused by massive spherical objects very well. We should not expect the relationship to hold when the distribution of the mass is non-spherical or diffuse. This is too simplistic.

Let me explain in optical terms: The power of a lens is determined by its refractive index (relative to the surrounding media) and its curvature. You can produce essentially identical optical effects with very different lenses, for example 1) a highly refractive lens with shallow curvature and 2) a lens with lower index of refraction and steeper curvature.

In the example of a roughly spherical or cylindrical cluster of galaxies, the volume of space-time distorted by that mass will likely be similarly curved. This will create a strongly refractive "lens" in space-time.

As for relative refractive index: the cluster is very massive and the space in front of and behind the cluster is relatively free of mass. This will create a very strong relative refractive index, since space-time in the cluster will be highly distorted and space time in front of and in back of the cluster will be relaxed, creating strong gradients through which light must pass. Again, this results in a more refractive lens.

In this model, it is not possible to determine the mass of a galactic cluster by measuring the distortions caused by lensing and simply extrapolating back to the amount of lensing caused by a planet or a star. In fact with these ideal conditions of: 1) strongly-curved lensing region and 2) strong gradients in space-time distortion between the cluster and its relatively mass-free surroundings, we should expect the lensing effect to be very strong. Using relativity to try extrapolate cluster mass in such a situation will lead to a gross overstatement of the mass involved.

For background (for those I have not already bored to tears): The concept of discrete space-time units with dimensions quantized at the Planck scale leads naturally to the question "what does mass do to local space-time, and what is the nature of the distortion that it causes?" Since space-time is the medium through which light propogates, we must then ask "what will the distorted space-time do to light crossing it and what should we expect to observe as a result?" We're probably going to need a dynamical theory of LQG or something similar before we can model the effects of mass on space-time (and vice-versa) and accurately predict the effects of space-time variations on impinging EM. We should expect visible optical effects, however, and strong lensing by mass-dense galactic clusters is appropriate and expected, at least to me.

I approach all of this in purely optical terms because that is the nature of my training and because the primary means by which we observe our universe is the collection and analysis of EM radiation. If we don't understand the effects of the propagating medium on the radiation, our fundamental understanding of EM is flawed and our naive observations will lead us to make wrong conclusions. I believe that measuring the lensing of a galactic cluster and using those measurements to posit a cloud of invisible non-baryonic dark matter to make up the "missing" mass is just such a mistake.

 

[meteor]

Garth, I've reading a bit about your Self creation Cosmology and I'm not sure how you eliminate dark energy. I think that you get rid of General Relativity and create a new Cosmology where the universe is actually not accelerating. Is that correct?
------------------------------------------------------------------------

More models...
Seems that some investigators are playing with the idea of "Solid Dark Energy".For example, a representative of this idea is this model of 1998 by Bucher, where he proposes that dark energy is due to a frustrated network of domain walls. don't be mislead by the title. though the title is "Is the dark matter a solid?", the paper also exposes this idea of dark energy caused by domain walls
http://arxiv.org/abs/astro-ph/9812022

 

[Chronos]

Relativity predicts the distortions caused by massive spherical objects very well. We should not expect the relationship to hold when the distribution of the mass is non-spherical or diffuse. This is too simplistic.

Let me explain in optical terms: The power of a lens is determined by its refractive index (relative to the surrounding media) and its curvature. You can produce essentially identical optical effects with very different lenses, for example 1) a highly refractive lens with shallow curvature and 2) a lens with lower index of refraction and steeper curvature.

In the example of a roughly spherical or cylindrical cluster of galaxies, the volume of space-time distorted by that mass will likely be similarly curved. This will create a strongly refractive "lens" in space-time.

As for relative refractive index: the cluster is very massive and the space in front of and behind the cluster is relatively free of mass. This will create a very strong relative refractive index, since space-time in the cluster will be highly distorted and space time in front of and in back of the cluster will be relaxed, creating strong gradients through which light must pass. Again, this results in a more refractive lens.

In this model, it is not possible to determine the mass of a galactic cluster by measuring the distortions caused by lensing and simply extrapolating back to the amount of lensing caused by a planet or a star. In fact with these ideal conditions of: 1) strongly-curved lensing region and 2) strong gradients in space-time distortion between the cluster and its relatively mass-free surroundings, we should expect the lensing effect to be very strong. Using relativity to try extrapolate cluster mass in such a situation will lead to a gross overstatement of the mass involved.

For background (for those I have not already bored to tears): The concept of discrete space-time units with dimensions quantized at the Planck scale leads naturally to the question "what does mass do to local space-time, and what is the nature of the distortion that it causes?" Since space-time is the medium through which light propogates, we must then ask "what will the distorted space-time do to light crossing it and what should we expect to observe as a result?" We're probably going to need a dynamical theory of LQG or something similar before we can model the effects of mass on space-time (and vice-versa) and accurately predict the effects of space-time variations on impinging EM. We should expect visible optical effects, however, and strong lensing by mass-dense galactic clusters is appropriate and expected, at least to me.

I approach all of this in purely optical terms because that is the nature of my training and because the primary means by which we observe our universe is the collection and analysis of EM radiation. If we don't understand the effects of the propagating medium on the radiation, our fundamental understanding of EM is flawed and our naive observations will lead us to make wrong conclusions. I believe that measuring the lensing of a galactic cluster and using those measurements to posit a cloud of invisible non-baryonic dark matter to make up the "missing" mass is just such a mistake.

Crap=crap. Using non-relevatistic reference frames to make your point is... unconvincing. Please explain how the observational evidence takes the stink off your theoretical cow pie.

 

[turbo]

Crap=crap. Using non-relevatistic reference frames to make your point is... unconvincing. Please explain how the observational evidence takes the stink off your theoretical cow pie.

I guess you've had a bad day, Chronos, so I'll let the rudeness slide.

Observational evidence = Galactic clusters exhibit very strong lensing. They lens so strongly that if you try to extrapolate their masses using the simple relativistic model, the calculated mass will be many times larger than that of the observed matter in the cluster.

Conventional astronomers cannot reconcile this with the standard model, but instead of trying to find where the model is broken, they instead claim that the "missing" mass is really there in the form of non-baryonic "dark matter". Of course, it is distributed in just such a manner as to produce the excess lensing. These are the same people who invoke non-baryonic "dark matter" to explain the discordant rotational curves of spiral galaxies. Of course, the "dark matter" again obligingly distributes itself in a very special non-uniform way to fix the rotational problem.

Somehow conventional cosmologists cannot bring themselves to examine these fundamental problems with their models. Instead, they invent "dark matter" that behaves in very special ways in each relevant circumstance. You might as well substitute obedient "fairies" or "angels" for "dark matter". As a very wise man once sang "When you believe in things you don't understand, you will suffer."

 

[Garth]

Garth, I've reading a bit about your Self creation Cosmology and I'm not sure how you eliminate dark energy. I think that you get rid of General Relativity and create a new Cosmology where the universe is actually not accelerating. Is that correct?

O.K. I am not getting rid of GR but modifying it. Einstein had two concerns over GR, the fact that it did not fully include Mach's Principle and the fact that it did not locally conserve energy. The Brans Dicke (BD) theory modified GR to include a Machian scalar field but retained the Equivalence Principle conserving energy-momentum in doing so; SCC modifies BD to include the local conservation of energy.
There are two conformal frames of measurement (of mass, length and time) in the theory. One is the Jordan frame (JF) in which the full theory describing gravitational orbits is formulated, this conserves energy, and the other is the Einstein frame (EF) in which the conservation of energy-momentum and the EEP are recovered, this is canonical GR in vacuo; the trajectories of test particles are the geodesics of GR.
The presence of the scalar field alters the GR cosmological expansion of the universe, the Friedman equations, so that in the EF the universe expands in a strictly linear fashion. When dealing with atoms i.e. in BB nucleo-synthesis it is easier to work in this frame. The Indian team have already done the work for me!
In the JF the universe isn't expanding at all. It is eternal and static with particle masses that increase, clocks that speed up and rulers that shrink, all exponentially according to exp(Ht).
The theory also is highly determined by H - there is no room for manoeuvre. However the values it comes up with are consistent with those that seem to be observed - although the interpretation of those observations is of course open to debate. The theory determines a moderate amount of false vacuum energy - 11% and a reasonable amount of matter - 22%. Hence the density available for gravitational lensing galaxy cluster dynamics etc. is 33%. And that is all that is required.

The EF universe is a hyper-cone and the JF universe is a projection of this, a hyper-cylinder where the long axis of symmetry in both cases is cosmological time. Both the cone and the cylinder are spatially flat; you can slit both time-like up one side and unroll them into a 'sheet'.
The 'Freely Coasting' universe produces about 20% baryons so you don't have to invent any extra Dark Matter, it is all dark baryons in some form or other - I know this poses a problem in identifying exactly what, I don't claim to solve all the mysteries at once! And spatial flatness means the WMAP data can be satisfied without inventing Dark Energy, although the false vacuum might be thought to be such – its effect is observed in the form of the Casimir force.
An economy of "entities"?

 

[turbo]

Chronos, you are quick to insult, and slow to apologize.

I guess you've had a bad day, Chronos, so I'll let the rudeness slide.

Observational evidence = Galactic clusters exhibit very strong lensing. They lens so strongly that if you try to extrapolate their masses using the simple relativistic model, the calculated mass will be many times larger than that of the observed matter in the cluster.

Conventional astronomers cannot reconcile this with the standard model, but instead of trying to find where the model is broken, they instead claim that the "missing" mass is really there in the form of non-baryonic "dark matter". Of course, it is distributed in just such a manner as to produce the excess lensing. These are the same people who invoke non-baryonic "dark matter" to explain the discordant rotational curves of spiral galaxies. Of course, the "dark matter" again obligingly distributes itself in a very special non-uniform way to fix the rotational problem.

Somehow conventional cosmologists cannot bring themselves to examine these fundamental problems with their models. Instead, they invent "dark matter" that behaves in very special ways in each relevant circumstance. You might as well substitute obedient "fairies" or "angels" for "dark matter". As a very wise man once sang "When you believe in things you don't understand, you will suffer."

Chronos, I guess you are really busy. Maybe you would like to post a response next week...or later. You routinely demand all "relevant maths" when you want to embarass other posters, so I'll give you a few days to come up with the goods. You might need the time.

 

[Chronos]

Agreed. Examples include
http://www.earth.uni.edu/~morgan/ajjar/Cosmology/cosmos.html
Turbo and I argue all the time. We have fun with it, most of the time. He is a good guy and very bright.

 

[turbo]

And spatial flatness means the WMAP data can be satisfied without inventing Dark Energy, although the false vacuum might be thought to be such – its effect is observed in the form of the Casimir force.
An economy of "entities"?

For those unfamiliar with Zero Point Energy, here is a link to a primer on the Casimir effect.

http://math.ucr.edu/home/baez/physics/Quantum/casimir.html

One thing not often mentioned in discussions of this effect is that although the virtual particle-antiparticle pairs have opposite spins, charges, timelines etc, and cancel each other in those respects, each particle has mass. The ground state of pure "vacuum" is therefor massive.

 

[Garth]

The ground state of pure "vacuum" is therefor massive.

Which leads to the inconsistency of explaining dark energy by vacuum zero point energy: ZPE is over 120 orders of magnitude too large.

However as a further point of information about SCC; the theory requires and determines a moderate amount of ZPE if space-time suffers curvature. Its density near the Earth is 10^-9 gms/cc, and cosmologically 0.11 of critical density.

One further test of the theory is its prediction that there is an upper limit on the Casimir force which the theory suggests tends to zero as 'curvature' tends to 'flatness'. Therefore, according to SCC, this limit should be detectable in the solar gravitational field between the orbits of Jupiter and Saturn (depending on the sensitivity of the apparatus).