SNe Ia, Implications, Interpretations, Lambda-CDM...

[PhysBang]

Originally Posted by coldcreation

It's the other way around. The CMB data is supported by dark energy.

Do you have a source for this claim? Every WMAP publication indicates a determination for the energy density of the cosmological constant. Later publications give a determination for the possible range of the equation of state for a variable energy field that acts as a cosmological constant.

I await your source.

Here's some: http://www.sdss.org/news/releases/20...rspectrum.html

Unfortunately, quantum field theory predicts a very large value for the vacuum energy: greater than 120 orders of magnitude off the mark. Recall, that was the largest error (the biggest blunder) of all scientific history.

In another way, calculations have shown that the energy output exceeds predictions by 122 orders of magnitude (that’s enormous by any standards). The huge imbalance is worse than the gloomiest expectations. Ok, so maybe the acceleration bubble comes in two different flavors: one driven by irrational exuberance and the other by bunk, whether rational or irrational.

I can't recall that discrepancy in value, since I don't accept the derivation. Perhaps you'd like to review the original source for that prediction? The standard derivation uses an arbitrary high-frequency cut-off point for the vacuum energy in order to return a finite result. This is fine for a calculation of the Casimir effect, which depends only on the low-frequency modes of the vacuum energy, but needs to be justified for the calculation of vacuum energy density.

A convincing model has yet to emerge that could explain why the cosmological constant is so small.

A convincing model has yet to show why mass density or baryon density is so small. Should we not believe in these energy densities? All we have is measurements of these densities. Why should the demand for a law-like explanation trump actual measurements?

But a totally crazy thing about ‘dark energy’ is that it’s not diluted or thinned with expansion like any normal forms of matter and radiation would be. And, totally insane is that something like 73% of the universe must be made up of dark energy, 23% of dark matter, and 4% of known material (protons, neutrons, electrons).

This division is accurate if dark energy is actually an energy density and not simply a constant of the Einstein Field Equation. It may be that the vacuum energy of quantum mechanics has not gravitational effect. The cosmological constant still acts as an effective energy density, but that is because of the algebra of the Einstein Field Equation.

In other words, 96% of the energy-density in the universe is in a form that has never been directly detected in the laboratory or anywhere else that human-kind has stepped foot, or sent probes.

Given the strength of the effect as measured, we could not expect to detect the impact of dark energy in a lab.

Even more peculiar, if at all possible, is the prospect that lambda or quintessence must have been an insignificant fraction of the mass-density of the universe just a short time ago. The self-repulsive ogre is growing fast and out of control. And it’s so ugly it repels itself.

Given that the expansion of the universe dilutes other energy densities, we can only expect that the dark energy density was not always the dominant energy density of the universe.

[modest]

Originally Posted by coldcreation

No one knows for sure, but it would seem the large-scale structures require a much longer time-scale to form than permitted by the lambda-CDM model. I will try to find the reference(s) for that.

I await your source.

The Sloan Digital Sky Survey has provided evidence:
Physical Evidence for Dark Energy
the results were repeated by:
Afshordi (2004); Boughn (2004); and Nolta (2004)

Originally Posted by coldcreation

Unfortunately, quantum field theory predicts a very large value for the vacuum energy: greater than 120 orders of magnitude off the mark. Recall, that was the largest error (the biggest blunder) of all scientific history.

In another way, calculations have shown that the energy output exceeds predictions by 122 orders of magnitude (that’s enormous by any standards).

Yes, I agree. Like I said, we're a ways off from quantitizing the effect. Especially without a quantum gravity field.

Originally Posted by coldcreation

But a totally crazy thing about ‘dark energy’ is that it’s not diluted or thinned with expansion like any normal forms of matter and radiation would be. And, totally insane is that something like 73% of the universe must be made up of dark energy, 23% of dark matter, and 4% of known material (protons, neutrons, electrons). In other words, 96% of the energy-density in the universe is in a form that has never been directly detected in the laboratory or anywhere else that human-kind has stepped foot, or sent probes.

I think this could easily follow from quantum field theory. As you point out above, the cosmological constant by way of vacuum energy is already predicted to be way too large. The idea that dark energy is so substantial seems natural to me.

-modest

[coldcreation]

Originally Posted by PhysBang

Do you have a source for this claim? Every WMAP publication indicates a determination for the energy density of the cosmological constant. Later publications give a determination for the possible range of the equation of state for a variable energy field that acts as a cosmological constant.

First, the notion that the CMB data requires the existence of dark energy and dark matter is founded on the assumption that the primordial power spectrum is a power-law spectrum. In order to better mimic the lambda-CDM model, which was primarily based on the SNe Ia data, and which required dark energy (amongst other parameters - viz nonbaryonic cold dark matter, DM) to justify an accelerating expansion, the same parameters were applied to the CMB data. It followed, in order to fit the available cosmic microwave background data - particularly regarding the amplitude of the large scale perturbations, or the late-time integrated Sachs Wolfe effect - that flatness, along with the primordial power-law spectrum and dark energy, had to be built into the assumptions.

Therefore the conclusion that the CMB somehow proves (or provides evidence for) the existence of dark energy is not sound logic.

I wrote above, rather, that the CMB data is supported by dark energy, but even that is debatable.

The CMB data (WMAP observational data) alone (pre-1998 SNe Ia data) did not demand the existence of quintessence, tensor modes, modified neutrino properties, dark energy. Interestingly, the inclusion of these parameters does not unambiguously improve the fit to the post-1998 standard flat vacuum-dominated power-law lambda-CDM model cosmology with accelerating expansion.


See for example Wilkinson Microwave Anisotropy Probe (WMAP) Three Year Results: Implications for Cosmology.


Dark energy effects in the Cosmic Microwave Background Radiation Here you will read that much work still needs to be done before the CMB-dark energy problem is solved.



Recall that one of the most generic predictions of the pre-1998 standard model - along with inflation theory - was that the overall density of the cosmos should be extremely close to the critical value, i.e., the universe should be very close to flat (for a variety of reasons).

Indeed, the SNe Ia showed a universe openly curved, i.e., not flat, far from it. (Note: this is not the non-accelerating open Friedmann model). The best fit to the data had to include a substantial dark energy component. That was the only way to keep the geometry of the universe flat (or nearly so) and match the low matter density galaxy cluster measurements, and simultaneously resolve the horizon problem, flatness problem, the age problem, etc.


In short, tweaking (to put it mildly) the DE and DM parameters (amongst others) was the only way to keep the BBT alive.



CC

[coldcreation]

Originally Posted by Mike C

So you accept the BBT as a viable one for our universe?

.

No.

CC

[PhysBang]

Originally Posted by coldcreation

First, the notion that the CMB data requires the existence of dark energy and dark matter is founded on the assumption that the primordial power spectrum is a power-law spectrum. In order to better mimic the lambda-CDM model, which was primarily based on the SNe Ia data, and which required dark energy (amongst other parameters - viz nonbaryonic cold dark matter, DM) to justify an accelerating expansion, the same parameters were applied to the CMB data. It followed, in order to fit the available cosmic microwave background data - particularly regarding the amplitude of the large scale perturbations, or the late-time integrated Sachs Wolfe effect - that flatness, along with the primordial power-law spectrum and dark energy, had to be built into the assumptions.

Therefore the conclusion that the CMB somehow proves (or provides evidence for) the existence of dark energy is not sound logic.

What about the extent to which the model fits the data? Indeed, the WMAP year three report you provided a link to reports better data and better parameter constraints from the data.

What about the fit to the data of models that do not make those assumptions, as reported in the document you linked to?

Dark energy effects in the Cosmic Microwave Background Radiation Here you will read that much work still needs to be done before the CMB-dark energy problem is solved.

Did you read that paper? That paper is about distinguishing between an unchanginc cosmological contant and a dark energy with a differnt equation of state such that the energy density that varies over time. This is a paper about distinguishing between types of dark energy, not about dark energy in general.

Recall that one of the most generic predictions of the pre-1998 standard model - along with inflation theory - was that the overall density of the cosmos should be extremely close to the critical value, i.e., the universe should be very close to flat (for a variety of reasons).

Indeed, the SNe Ia showed a universe openly curved, i.e., not flat, far from it. (Note: this is not the non-accelerating open Friedmann model). The best fit to the data had to include a substantial dark energy component. That was the only way to keep the geometry of the universe flat (or nearly so) and match the low matter density galaxy cluster measurements, and simultaneously resolve the horizon problem, flatness problem, the age problem, etc.

The SNe Ia results support a closed model far more than they support an open model. If you look only at the 1999 paper of the Supernova Cosmology Porject, you will see that the total energy density skews above the critical density. Because of the mathematics of the cosmological constant (or another kind of dark energy), it contributes to the overall geometry of the universe. In a purely Friedmann model, the mass-erergy density of matter is about the only thing to consider for closure, so it is used interchangably for referring to closure. However, it is important to include all energy densities when considering the overall curvature of the universe, because they all play a role.

In short, tweaking (to put it mildly) the DE and DM parameters (amongst others) was the only way to keep the BBT alive.

Luckily, the big bang theory had a built in way to tweak its parameters through measurement.

[coldcreation]

Originally Posted by PhysBang

What about the extent to which the model fits the data?

The model (Lambda-CDM) was made to fit the data thanks to the free-parameters. No matter what (practically) the SNe Ia data showed, the parameters would be adjusted, tweaked, stretched, exploited, abused [did I miss anything?] until a fit was made. On that score the results so far are far-from-impressive.

Originally Posted by PhysBang

What about the fit to the data of models that do not make those assumptions, as reported in the document you linked to?

Here you present a good point. None of the other models were a good match. So, yes, for now, the lambda-CDM model is the best fit. But that by no means excludes the possibility that a better model, preferably without dark energy and CDM, will surface in the near future (the sooner the better). I believe it is possible to construct such a model, if it does not already exist. The ramification would obviously be enormous, and probably not at all what you would expect. Then again, I could be mistaken. Perhaps the concordance model is on target.

Originally Posted by PhysBang

The SNe Ia results support a closed model far more than they support an open model. If you look only at the 1999 paper of the Supernova Cosmology Porject, you will see that the total energy density skews above the critical density. Because of the mathematics of the cosmological constant (or another kind of dark energy), it contributes to the overall geometry of the universe. In a purely Friedmann model, the mass-erergy density of matter is about the only thing to consider for closure, so it is used interchangably for referring to closure. However, it is important to include all energy densities when considering the overall curvature of the universe, because they all play a role.

True (almost) that the best fit was found for a marginally closed universe. However, considerable theoretical prejudices were involved in the variable set of parameters that were chosen (see Melchiorri et al, astro-ph, 1999 for example). With a little (a lot of) tweaking, the flat geometry of the universe had been confirmed. This and other balloon-borne experiments that measured the fluctuations in the cosmic microwave background would find similar results. But there is absolutely no guarantee that thermal fluctuations of CMB are at all useful for testing spacetime curvature (geometry). An enormous assumption has to be made first about the origin and evolution of the blackbody radiation.

The geometry then depends on the model, not on the differences in temperature from one region to the next. In this particular case, the theory determined the outcome of the experiment, just as the theory determined its own laws.

“What the new measurements tell us,” Turner thinks, “is that the universe is in fact flat.” He’s flat wrong. Draw a triangle from Earth that reaches the distant SN and any other point in the cosmos, and the sum of the angles will always be less than 180 degrees. That is a hyperbolic spacetime signature. The observational evidence that shows hyperbolicity also means inflation theory has flunked a key test.

A consistent impartial approach to determine the geometry is through the measurement of distances.

Dark energy is used as a parameter that can be adjusted according to will or necessity. Models aside, the supernovae results show that the universe is openly curved, hyperbolic, not that the universe is in a mode of wretched-excess expansion, propulsive style. Stay tuned.

Originally Posted by PhysBang

Luckily, the big bang theory had a built in way to tweak its parameters through measurement.

Recall that Einstein formally abandoned the lambda in 1932 after having reviewed the theoretical work of Friedmann and the experimental discoveries of Hubble (see Pais 1982 p. 288). This was when the idea of an initial explosion began raising its ugly head. It is a sweet paradox that today the blunder (lambda) resurfaces with a new pretext: to explain why the expansion appears to be accelerating. The SNe Ia data indicates that the universe is open, hyperbolic: also called negative curvature, as opposed to spherical space (called positive curvature, a closed universe).

Einstein’s only failure had been not to capitalize on his discovery - his achievement had been to open the way, first!

__________________

There could be no more eloquent testimony to the exquisite flair and vision of a physicist who for the first time introduced a credible formula that would preserve the gravitational stability of planets, stars and galaxies, albeit without explaining how.

Continually changing a theory that ends up being grossly riddled with mystifying matter and kooky dark energy, about which nothing is known, is an ominous misjudgment, a monumental miscalculation, an unsmiling blunder - or worse...

Only now that compelling evidence from the 1998 observational data contradicts every theory (including the radical alternatives) and every law in the textbooks, are cosmologists taking a serious look at the marvelous “fudge factor,” once rejected and ridiculed; the infamous cosmological constant, new nom de plume; quintessence - now rubber stamped with a seal of approval by the new-new relativists. Quintessence and dark energy scenarios both fail miserably: partly because no one knows what dark energy is (so anything can be, and is, claimed) and partly because the data had defied all predictions (a good sign that at least one dramatic error had been made in the theory). What matters is that predictions are verifiable and confirmed.

The circumstance surrounding the new modified interpretation (of dark energy) is repulsive, if not horrendous, but it is the very error itself that points a finger at possible systematic failure of the scientific method regarding theory and predictions thereof.

Cosmologists are expected to be experts in the realm of cosmology. When predictions do not concord with observations, or assertions flow contrary to expectations, dump the bunk.

Dump the bunk.

CC

[modest]

Originally Posted by coldcreation

“What the new measurements tell us,” Turner thinks, “is that the universe is in fact flat.” He’s flat wrong. Draw a triangle from Earth that reaches the distant SN and any other point in the cosmos, and the sum of the angles will always be less than 180%. That is a hyperbolic spacetime signature. The observational evidence that show hyperbolicity also means inflation theory has flunked a key test.

I don't see how you get this.

The standard candle observations are a measure of brightness. Brightness is a measure of distance - or more precisely: light travel time.

Redshift is a direct measure of expansion.

So, if we have both data and many data points we can say (making the least amount of assumptions) how the expansion rate has changed over time.

I don’t see how this implies (without a model or other data) the ‘shape’ of the universe. I would suppose that both a flat and hyperbolic universe could decrease, remain steady, or increase the rate of expansion. Could you explain how the SN 1A data says hyperbolic to you?

- modest

//edit
your method of drawing a triangle is not possible. With one side and no angles - it cannot be done

//second edit
if you mean to measure two SN's and solve side-angel-side... how would you verify your predicted third side? They were only able to do this with the CMB by knowing the distance between peak temp fluctuations. That gave them a number to compare to the side-angle-side result.

[coldcreation]

Originally Posted by modest

I don't see how you get this. The standard candle observations are a measure of brightness. Brightness is a measure of distance - or more precisely: light travel time.

Exactly. Observed is a general relativistic time-dilation. SNe Ia are further than would be expected in a geometrically Euclidean (flat), or spherically closed manifold.

Originally Posted by modest

Redshift is a direct measure of expansion.

Redshift: The shift of spectral lines toward longer (redder) wavelengths in the spectrum of light (or radiation) coming from astronomical objects.

Redshift-distance law: An interpretation of Hubble’s law; stating that an object distance is proportional to the redshift. (Note that the High-z SNe Ia are not proportional to distance, i.e., they are further away than expected).

Originally Posted by modest

So, if we have both data and many data points we can say (making the least amount of assumptions) how the expansion rate has changed over time.

True, according to the standard model. But also, the data points provide an estimate of distance (in accord with the change in scale factor over time, according to redshift z). And it is from the estimated distance that the global geometry of the cosmos can be determined (from our reference frame, or from the position of any observer relative to his/her/its reference frame).

Originally Posted by modest

I don’t see how this implies (without a model or other data) the ‘shape’ of the universe. I would suppose that both a flat and hyperbolic universe could decrease, remain steady, or increase the rate of expansion. Could you explain how the SN 1A data says hyperbolic to you?

Certainly, the SNe Ia project had for aspiration to determine the deceleration parameter, the density parameter omega and its relation to the geometry of the universe (the ratio of energy density to critical density).

Recall the three Friedmann models. In brief: A closed universe meant that there was enough mass (gravity) to cause the expansion to slow-down to a halt, then perhaps contract to a big crunch. Observations would have shown objects to be closer than otherwise expected from their redshifts. This is thus ruled out.

See here for example: Ultimate fate of the universe

Closed universe
If ?>1, then the geometry of space is closed like the surface of a sphere. The sum of the angles of a triangle exceeds 180 degrees and there are no parallel lines; all lines eventually meet. The geometry of the universe is, at least on a very large scale, elliptic.

In a closed universe lacking the repulsive effect of dark energy, gravity eventually stops the expansion of the universe, after which it starts to contract until all matter in the universe collapses to a point, a final singularity termed the "Big Crunch," by analogy with Big Bang. However, if the universe has a large amount of dark energy (as suggested by recent findings), then the expansion of the universe can continue forever - even if ?>1.

Open universe
If ?<1, the geometry of space is open, i.e., negatively curved like the surface of a saddle. The angles of a triangle sum to less than 180 degrees, and lines that do not meet are never equidistant; they have a point of least distance and otherwise grow apart. The geometry of the universe is hyperbolic.

Even without dark energy, a negatively curved universe expands forever, with gravity barely slowing the rate of expansion. With dark energy, the expansion not only continues but accelerates. The ultimate fate of an open universe is either universal heat death, the "Big Freeze", or the "Big Rip," where the acceleration caused by dark energy eventually becomes so strong that it completely overwhelms the effects of the gravitational, electromagnetic and weak binding forces.

Conversely, a negative cosmological constant, which would correspond to a negative energy density and positive pressure, would cause even an open universe to recollapse to a big crunch. This option is ruled out by observations, unless the universe undergoes an unexpected phase transition at some point in the future.

Ultimately, Hubble's law is based on observational data. Its relationship - between velocity and distance - was well documented pre-SNe Ia (pre-1998) to at least 3 billion light-years.

But there is no basic physical reason for this relationship. No law of physics demands that all galaxies recede. And no physical law requires distance and velocity to be correlated. Consequently, astronomers are currently unsure if this relationship holds true for cosmic objects beyond several billion light-years. In this sense, then, it's not really a "law" at all. Source

Obviously, the Hubble velocity-distance relation (if indeed redshift is a measure of change in the scale factor), post 1998 SNe Ia, no longer holds, since the data shows objects further than expected (20% further). This is exactly what would be expected in a hyperbolic, open, manifold. So the SNe Ia data is more than just a signature of Lobachevkian geometry, it is the confirmation of hyperbolicity based on empirical evidence.

Originally Posted by modest

your method of drawing a triangle is not possible. With one side and no angles - it cannot be done... if you mean to measure two SN's and solve side-angel-side... how would you verify your predicted third side? They were only able to do this with the CMB by knowing the distance between peak temp fluctuations. That gave them a number to compare to the side-angle-side result.

True. If it could be done the result would be less than 180 degrees, since there is a "stretching" of the beam along the line of sight (a geodesic). The shape of the manifold indicated by the data would resemble a saddle (or a Pringles potato chip) in reduced dimension. Now visualize that "negative curvature" in four dimensions. Distant objects appear further away than on a flat or spherical surface. What you see is what you get.

It is possible to flatten the hyperbolic curvature by adjusting parameters (or even curve space in the opposite direction), but the observations speak louder than words.

For example, if the desired value for omega is 1 (a flat space) and visible matter plus baryonic dark matter (the kind made of real protons, neutrons and electrons) equals only 0.3 to 0.4, then we assume that the cosmological constant vacuum contribution to omega is 0.6 to 0.7: rendering a total of omega = 1, the desired value for a flat universe. It had always been hoped that the matter alone (without lambda) would be sufficient to reach the critical value. But even with the injection of hypothetical (non-baryonic dark matter) or spooky energy, the value of 1 could not be reached.

Therefore, according to the new standard mode (lambda-CDM)l, the universe appears to be dominated by the ubiquitous dark energy with the peculiar feature that its "gravity" does not attract, it repels. No one knows what it is and no one is ever likely to get much beyond a semi-informed guess, no matter how tantalizing it would be for cosmologists to pin point such a phenomenon. A move is afoot to begin unraveling this mystery, but everyone seems to be somewhat panic-stricken by the exotic vocation.


My own sense of disorientation seems less colorful, lacking in both amusing anecdotal and charming elocution. After the publications were released and the theories freshly painted, I studied the new décor in a nondescript manner and felt as if cosmology had blown some sort of mental fuse.




CC

[Erasmus00]

Originally Posted by coldcreation

according to the new standard mode (lambda-CDM)l, the universe appears to be dominated by the ubiquitous dark energy with the peculiar feature that its "gravity" does not attract, it repels.

It is interesting to note that first principles (particle physics) based calculations of this "dark energy"/repulsive gravity yield TOO MUCH, not too little.

Also- a general question for Coldcreation/big bang objectors. I'll outline some logic, tell me where it goes wrong.

To 1 part in 1000 (or better), if we look up at the sky we pick up the radiation from a PERFECT blackbody with temperature 2.7 K.

Conclusion: the universe IS a blackbody!

Further conclusion- this means the entire universe MUST have been in thermal contact at some point (otherwise, it wouldn't be a nice blackbody!).

The size of the universe currently makes this impossible, but its observationally true, so at some point in the past, the universe must have been small enough to allow for thermal contact. (this, at least, makes steady state models impossible).
-Will

[modest]

Originally Posted by coldcreation

Redshift: The shift of spectral lines toward longer (redder) wavelengths in the spectrum of light (or radiation) coming from astronomical objects.

Redshift-distance law: An interpretation of Hubble’s law; stating that an object distance is proportional to the redshift. (Note that the High-z SNe Ia are not proportional to distance, i.e., they are further away than expected).

Cosmic redshift is defined as 1 + z = a(now)/a(then) where a is the scale factor. Without getting into a deep discussion on redshift again I'll just reiterate what I said before: "a direct measure of expansion".

Originally Posted by coldcreation

Certainly, the SNe Ia project had for aspiration to determine the deceleration parameter, the density parameter omega and its relation to the geometry of the universe (the ratio of energy density to critical density).

These are just the things it measured. The results though not as expected still fit into the concordance model. It is still the case that the standard model works with all available observations.

Originally Posted by coldcreation

Recall the three Friedmann models.

As long as we are accepting the Friedmann metric then this has already been considered. You posted the link to the plot that invalidates your idea:


image credit

The solid, horizontal line here represents what would be expected in an empty universe. As the paper reports:

In an empty universe the data points would equally likely fall above and below the horizontal line in the middle, but it is obvious that the majority of the points at z ≈ 0.5 and z ≈ 0.8 are above this.

An empty universe with no matter is the most hyperbolic of the Friedmann equations. It would have the most negative curvature. Clearly the dashed line is the only solution to the Friedmann equations that works. And it works well. If the universe is flat with a positive cosmological constant then all observations fit the simplest model.

Originally Posted by coldcreation

Obviously, the Hubble velocity-distance relation (if indeed redshift is a measure of change in the scale factor), post 1998 SNe Ia, no longer holds, since the data shows objects further than expected (20% further). This is exactly what would be expected in a hyperbolic, open, manifold. So the SNe Ia data is more than just a signature of Lobachevkian geometry, it is the confirmation of hyperbolicity based on empirical evidence.

It does still hold - via the ΛCDM model. And no, things are not 20% further than predicted by the FLRW metric if the metric solves for the parameters outlined in the ΛCDM model. They are a fit where no other model can claim a fit. The Hubble velocity-distance relation must take into account the changing parameters of the universe with time. It traditionally did this with the pressure and density parameters - but we have one more to put up with now: the energy of the vacuum.

This is not fine tuning. This is accepting observation. Just because we don’t understand the cause of dark energy does not mean it doesn’t exist. If its effects are measurable and fit into our simplest model with all other observations then why reject something that could easily be very real and significant? I believe one day we will have a theory to explain its origin. When that happens, hopefully it will have been measured accurately enough to compare to the theory.

Originally Posted by coldcreation

So the SNe Ia data is more than just a signature of Lobachevkian geometry, it is the confirmation of hyperbolicity based on empirical evidence.

Obviously not with the FLRW metric. If you think you can solve the friedman equations with significant negative K and no cosmological constant to get a fit with the SNe 1a observations then present it. Otherwise we need to take the word of the people who did the study and their peers.

- modest