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

[coldcreation]

Indeed, the idea that there is some sort of finely tuned stability or balance in the solar system or the galaxy is pure fantasy. You can find this idea in much of coldcreation's writings, if you care to look. It is an integral part in his fantasy about the cosmological constant and Lagrange points...

 

OK, this discussion is become increasingly off-topic.

 

I will retaliate first though. I am not saying that the solar system has been stable for 5 Gyr. I wrote a few Gyr. The sun, if I recall, has only existed for 4.5 Gyr (whether there was a first generation progenitor I do not know). So Littlebang is obviously correct (the straw man in his argument was the 5 Gyr). However, he did not answer my question. How the fine tuning (like a pencil balancing, or oscillating rather on its point), observed in the solar system (as well as other observed gravitationally bounded stable systems) is possible.

 

Of course, the solar system is chaotic in a sense: it has instabilities associated with it and its constituents, and the trajectories of its constituents (say, the Earth) cannot be predicted for time periods exceeding 100 Myrs.

 

However,

...it is structurally stable' date=' since small variations of the parameters of the planets, comparable with the accuracy of their measurements, lead to different but [b']similar orbits[/b] – it is thus unlikely that the Solar System will fall apart during the next billion years. However, this structural stability is limited and the Solar System is fragile: if variations of the parameters were of the order of ten percents, the configuration of the system might suffer crucial qualitative changes. For instance, decreasing the mass of the Sun by half would strongly destabilize dynamics of the System

My bold.

 

I doubt the mass of the Sun will be decreasing by half any time soon. So it is structurally stable (probably, I would guess, for another 5 Gyr, give or take a Gyr or two). Hmm, sounds like a pencil on its point to me. What gives?

 

See On the stability of the solar system

 

 

 

Note this too:

Abstract**Large scale chaos is present everywhere in the solar system. It plays a major role in the sculpting of the asteroid belt and in the diffusion of comets from the outer region of the solar system. All the inner planets probably experienced large scale chaotic behavior for their obliquities during their history. The Earth obliquity is presently stable only because of the presence of the Moon' date=' and the tilt of Mars undergoes large chaotic variations from 0° to about 60°. On billion years time scale, the orbits of the planets themselves present strong chaotic variations which can lead to the escape of Mercury or collision with Venus in less than 3.5 Gyr. The organization of the planets in the solar system thus seems to be strongly related to this chaotic evolution, [b']reaching at all time a state of marginal stability, that is practical stability on a time-scale comparable to its age.[/b]

Source, Large scale chaos and marginal stability in the solar system My bold.

 

The large chaotic variations from 0° to about 60° in the tilt of Mars, is not what I am talking about. It is the structure and its long term stability of the solar system in general, and its constituents specifically, that is of interest, not the tilt of the Earth or its ice ages (at least for the purpose of this off-topic discussion). The latter type of marginal stability (or marginal instability) is evident, since small gravitational perturbations and mean motion resonance (etc.) interactions occur all the time. But again, there "is practical stability on a time-scale comparable to its age." (see above).

 

If you wish to continue this discussion on the stability and/or instability of gravitationally bounded systems, celestial mechanics - a truly fascinating field, tie it in with SNe Ia, lambda, dark, energy, the critical model and its finely tuned one to one expansion relation (the galaxies separate at a critical rate that prevents gravitational attraction from over-powering the expansion: also referred to as the the Einstein-de Sitter model), the fine tuning problem, the flatness problem, coasting expansion vs. accelerating expansion, i.e., cosmology.

 

Or, begin a new thread on the topic: I will most definitely be there.

 

Recall, the subject of the stability of the solar system began with a discussion on the fine-tuning problem related to expansion (the favored Friedmann model, now defunct, in light of the SNe Ia data). Indeed, the fine tuning problem was more ubiquitous than appeared at first glance (not to mention thermodynamic or quantum states that appear also either stable, chaotic or both to one extent or the other.

 

 

 

A note on fantasies...

 

The demarcation between behavioral history and fantasy are clearly distinguishable: by observation. (DVDjHex)

 

The fascination with the twilight zone has opened a creative space between dream and fantasy, between mythical and historical realities of society: believe whatever you like. I believe observations first. (Coldcreation)

 

The fantasy I am selling has nothing to do with self-achievement or with first-love passion and vicarious romance. It is a shadier, hot-and-heavy, shocking yet commercial, a set-up: it is based on observations at the telescope - nothing less. (Coldcreation)

 

Global curvature as a cause for time dilation (e.g., as seen in the High-z SNe Ia data) doesn’t sound like a wildly improbable or unrealistic fantasy to me. It certainly isn’t radical, chimeric, or non-conventional. It’s not even really new. (Coldcreation)

 

One incorrect assumption and everything that follows may be meaningless, untrue, false, fallacious, erroneous, wrong, invalid, inaccurate, fantasy, misleading, erroneous, empty, hollow, pointless, futile, worthless, unfounded, fictional, fictitious, fabricated, deceitful, illusory, imaginary, untrustworthy, untruthful, bogus, mythical, fraudulent, phony, baseless, day-dream, to be regarded with suspicion, deceiving, deceptive, not to be trusted, unrepresentative, unreliable, inauthentic, specious, fairy-tale, spurious, and chimerical. (Coldcreation)

 

That which may be unrivaled in popularity, created by human intellect, discovered and proved not at the telescope but sitting behind a desk at the tip of a pencil, has the potential to be nothing but fantasy. (Coldcreation)

 

Cosmology demonstrates the illimitable impulses of the imagination: sandwiched between fantasy and hope. (DVDjHex)

 

"If one is lucky, a solitary fantasy can totally transform one million realities." (Maya Angelou)

 

"We live in a fantasy world, a world of illusion. The great task in life is to find reality." (Iris Murdoch)

 

"I like nonsense, it wakes up the brain cells. Fantasy is a necessary ingredient in living." (Dr. Seuss)

 

"Abandon the search for Truth; settle for a good fantasy" (Dr. Seuss) LOL

 

 

 

 

Don’t fight the chill.

 

 

 

 

 

CC

[modest]

OK, this discussion is become increasingly off-topic.

 

I will retaliated first though. I am not saying that the solar system has been stable for 5 Gyr. I wrote a few Gyr. The sun, if I recall, has only existed for 4.5 Gyr (whether there was a first generation progenitor I do not know). So littlebang is obviously correct (the straw man was 5 Gyr). However, he did not answer my question. How the fine tuning (like a pencil balancing, or oscillating rather on its point), observed in the solar system is possible.

 

I also wanted to respond and did so in this thread:

Dynamic Equilibrium of the Universe and Subsystems

 

-modest

[coldcreation]

I also wanted to respond and did so in this thread:

Dynamic Equilibrium of the Universe and Subsystems

 

-modest

 

What follows seems more related to the lack of equilibrium related to the new standard model, as opposed to a stable regime. So I will write it below rather than in the new off-shoot thread cited above (though it could have gone in either). Sorry if there is an overlap.

 

 

 

Lambda and the Creation of Empty Space

 

In a standard expanding universe, every newly created cubic centimeter of space emerges with an equal quantity of energy. On the other hand, a universe dominated by some mysterious form of energy (whether it be quintessence or lambda) has the capability of continually producing new energy from literally nothing (Goldsmith 2000). Each new cubic centimeter emerges with more energy than the preceding. Donald Goldsmith, in his ouvrage The Runaway Universe, writes:

 

• “Only when we have satisfied ourselves that a nonzero cosmological constant offers by far the most coherent way to interpret the observational facts should we embrace the concept of the runaway universe. Even then, we must remain aware that new data and new interpretations may soon appear, causing us once again to question the framework within which we conceive the cosmos.” (Goldsmith, 2000, p. 5-6)
  

 

After a hawkish explanation of how a universe with a cosmological constant gives birth to “new space” (and new energy) from “literally nothing,” Goldsmith adds, without reinventing the wheelchair himself:

 

• “It seems clear from his later discussions, however, that for several years Einstein believed in a nonzero cosmological constant, a hitherto-unknown aspect of space with the near-magical property of hiding energy, capable of explaining why the universe is neither expanding nor contracting. How utterly wrong he was, and yet how right—in a way—he nevertheless proved to be!” (p. 12)
  

 

He draws a firm line between the major modes of automatism played by the cosmological constant in an expanding frame and decisively rejects lambda in the stationary frame. Is it not—in a way—more magical to create new energy in new space, than it is to balance the pre-existing gravitational energy—just as the energy levels of electrons in atoms can remain in ‘stationary’ states, basically forever? Are not both concepts equivalent to a free lunch?

 

Isn’t it archaic to suggest, today, as Newton had centuries ago that “all parts of the cosmos attract one another gravitationally?” (Goldsmith 2000 p. 11) Or, in the words of Krauss: “Gravity sucks. The gravitational attraction of matter is universally attractive. Gravity only pulls, it never pushes.” (Goldsmith 2000 p. 103).

 

 

 

If gravity sucks, the cosmological constant blows.

(Coldcreation)

 

 

 

 

 

CC

[PhysBang]

More factual errors, quote mining, and pithy sayings. Creationists the world over marvel.

[coldcreation]

More factual errors, quote mining, and pithy sayings. Creationists the world over marvel.

 

lol.

 

I'm still waiting for you to find something in the following text that was not published in the references given.

 

Cosmologists Ponder Missing Energy “Cosmologists gather at Fermi National Laboratory in effort to explain compelling new evidence that the universe is expanding at an accelerating rate and to understand what appears to be an unknown form of energy associated with vacuum of space' date=' the so-called ‘missing energy’ of the universe; if both current theory and new observations are correct, this energy must be acting as repulsive force to counteract gravity’s restraining influence and thus speed up cosmic expansion” (New York Times, May 5, 1998 Sec: F Science Desk p. 1). Wary Astronomers Ponder An Accelerating Universe (New York Times, March 3, 1998 Sec: F Science Desk p. 1)

 

Revolution in Cosmology …something is amiss. At the very least, the expansion is not decelerating as rapidly as once though. Either scientists must reconcile themselves to kooky energy, or they must modify or abandon inflation. (Scientific American, Jan. 1999 Vol. 280, 1

 

Accelerating the Cosmos “The cosmological constant, also called lambda...is a uniform, background energy permeating all of space. This energy gives space itself a sort of springiness, counteracting gravity on large scales…It came as a shock…the universe appeared to contain twice as much energy in the cosmological constant as it did in matter. POW…Thunderstruck astronomers…particle physicists are studying the structure of space to determine just what lambda might be…funny energy…gravity that bends space…slightly illicit…cosmological constant was mentioned as a possible culprit, but that reasoning still seemed to strange to take seriously…a huge cosmological constant…some form of energy we don’t understand…weird, fluid-like substance called quintessence, a squishy possibility…“This led me to reconsider my theoretical prejudices. I now think it is very reasonable that there should be a cosmological constant” [the latter is a quote from S. Hawking'] (Astronomy, Oct. 1999 Vol. 27, 10, p. 44-51)

 

Brave New Cosmos: Making Sense of Modern Cosmology: Plan B for the Cosmos: “New discoveries have challenged long-held theories about the evolution of the universe…cosmic expansion is accelerating…an idea once considered laughable, even after a few beers…an odd kind of energy known as quintessence…we have been missing most of the story…The bulk is a ubiquitous “dark energy” with a strange and remarkable feature: its gravity does not attract. It repels. Whereas gravity pulls… The universe is a battleground between two tendencies, and repulsive gravity is winning… Where does the energy come from? Such energy is a venerable notion that dates back to Albert Einstein and his attempt in 1917 to construct a static model of the universe…he had to introduce vacuum energy…These concepts may sound strange…a serious flaw…That seems bizarre… Extrapolating back in time, vacuum energy gets even more paradoxical…our universe was the size of a grapefruit…that seems ludicrous to expect from the real world. This need for almost supernatural fine-tuning is the principle motivation for considering alternatives to the cosmological constant… Over the long term, all of us will be left to ponder the profound implications of these revolutionary discoveries. They lead to a sobering new interpretation of our place in cosmic history… Most researchers, however, had a real distaste for the cosmological constant. Now the majority accept it, or its allied concept, quintessence… Could the enthusiasm generated by inflation and its offshoots conceal a monstrous error?” (Scientific American Jan. 2001 Vol. 284 p. 37, 54, 58)

see original posts here, and here.

 

 

I apologize for my zeal. It is just that science is too often misrepresented as merely the success of the predicted as if theories spring from the mind like Athena. Coldcreation couples this presentation with the false claim that the cosmological constant was entirely unprecedented (though this also contradicts his claims that it was discussed and rejected).

 

His cutting and pasting of that article together is very dishonest, as there are phrases in his quote that do not appear anywhere in the document.

 

Which phrases in the quotes do not appear anywhere in the original referenced document(s)?

 

I'm sure I'll be waiting a long time before you come up with anything, so I won't hold my breath. Nor will I be holding my breath waiting for an apology for yet another unsupported ad hom attack.

 

 

 

 

 

CC

[modest]

After a hawkish explanation of how a universe with a cosmological constant gives birth to “new space” (and new energy) from “literally nothing,” Goldsmith adds, without reinventing the wheelchair himself:

 

• “It seems clear from his later discussions, however, that for several years Einstein believed in a nonzero cosmological constant, a hitherto-unknown aspect of space with the near-magical property of hiding energy, capable of explaining why the universe is neither expanding nor contracting. How utterly wrong he was, and yet how right—in a way—he nevertheless proved to be!” (p. 12)
  

 

He draws a firm line between the major modes of automatism played by the cosmological constant in an expanding frame and decisively rejects lambda in the stationary frame.

 

He draws no such line. He makes no such distinction. I couldn’t believe Goldsmith would do that so I found the book you’re quoting and discovered in context what you’ve said here to be in error.

 

As I continually point out there is no qualitative difference between Einstein’s cosmological constant and current application of the cosmological constant. The only difference is the value. Goldsmith knows this and writes accordingly. The only other difference he points out is Einstein’s motivation for setting Lambda to the value he set it.

 

I’d like to quote the entire context of the quote above, but because of copyright concerns I’ll just add this quote from Einstein which Goldsmith also quotes:

 

“The postulate of general relativity requires the introduction of the [cosmological constant] into the field equations. It will be our factual knowledge of the composition of the starry heavens, of the apparent motions of the stars, and of the state of spectral lines as a function of conditions far from us that will allow us empirically to answer the question whether the [cosmological constant] equals zero or not. Conviction is a good mainspring, but a bad judge!"

 

added to that which you quoted:

 

Here Einstein was quite correct. It seems clear from his later discussions, however, that for several years Einstein believed in a nonzero cosmological constant, a hitherto-unknown aspect of space with the near-magical property of hiding energy, capable of explaining why the universe is neither expanding nor contracting.

 

How utterly wrong Einstein was, and yet how right - in a way - he nevertheless proved to be! The motivation for his introduction of the cosmological constant turned out to be fallacious, for space in the universe actually is expanding.

 

and a bit from the top of page 13:

 

Thus when new observations during the final years of the twentieth century once again called for a nonzero cosmological constant, the astronomical community displayed a predictable reaction... Unlike the earlier news of a nonzero constant, the cosmological constant now appears here to stay, with a nonzero value once again different from the number that Einstein had deduced on different grounds.

 

This new value has implications just as shocking as the one that Einstein suggested. As always in science, we would do well not to accept it as validated without new sets of observations that confirm today's conclusions.

 

From:

Google Book; The Runaway Universe: The Race to Find the Future of the Cosmos

…which looks to be a good popularization-of-science book.

 

Goldsmith is correctly characterizing the cosmological constant. He is not rejecting ‘Einstein’s’ cosmological constant because it is in a stationary frame while accepting the ‘current’ cosmological constant because it is in an expanding frame as you state. When he says "a hitherto-unknown aspect of space with the near-magical property of hiding energy" (from your quote) he is talking about the cosmological constant in any frame or any relativistic model (including the standard model).

 

It occurs to me that the claims you made toward the beginning of the thread:

 

1. The cosmological constant has been somehow altered from its original design
   
2. The cosmological constant is not vacuum energy or negative pressure in GR
   

 

…you continue to make despite sources to the contrary as well as Will demonstrating a proof against both. This seems to be the source of misconceptions like misunderstanding Goldsmith above. The problem I have is not that you reject the standard model or dislike the cosmological constant. There are after all good reasons to be suspicious of both (as all good scientist should be). However, you mischaracterize and misrepresent the field equations and Lambda by making claims one and two above. This is not a matter of how a person believes the universe has evolved or different interpretations of evidence. This is an incorrect assessment of general relativity. Posts 63 and 67 as well as sources given throughout this thread show conclusively that according to GR your claims are wrong. I believe you are left with the logical choice of rejecting GR (at least Lambda’s place in it) or amending your claims. If you are unwilling to do either I wonder if you can show a source.

 

Please understand, I am always interested in exploring alternate theories to explain evidence, but, altering relativity through improper interpretation is something different.

 

-modest

[coldcreation]

It occurs to me that the claims you made toward the beginning of the thread:

 

1. The cosmological constant has been somehow altered from its original design
   
2. The cosmological constant is not vacuum energy or negative pressure in GR
   

 

…you continue to make despite sources to the contrary as well as Will demonstrating a proof against both. This seems to be the source of misconceptions like misunderstanding Goldsmith above. The problem I have is not that you reject the standard model or dislike the cosmological constant. There are after all good reasons to be suspicious of both (as all good scientist should be). However, you mischaracterize and misrepresent the field equations and Lambda by making claims one and two above. This is not a matter of how a person believes the universe has evolved or different interpretations of evidence. This is an incorrect assessment of general relativity. Posts 63 and 67 as well as sources given throughout this thread show conclusively that according to GR your claims are wrong. I believe you are left with the logical choice of rejecting GR (at least Lambda’s place in it) or amending your claims. If you are unwilling to do either I wonder if you can show a source.

 

Please understand, I am always interested in exploring alternate theories to explain evidence, but, altering relativity through improper interpretation is something different.

 

-modest

 

Obviously our interpretation of the text above differs.

 

My point for reiterating some of my early pre-Will-post arguments is that the case is by no means closed. I voiced my objections to Will already in posts entitled Part I and Part II above.

 

My further point is that no one really knows what lambda is, despite its inclusion in the Einstein field equations, despite its recent resurrection back into the field equations, and despite Will's proofs.

 

I am not saying we need to change the field equations.

 

What I am saying, this time without the fanfare, is that we need to change our actual interpretation of lambda.

 

If that changes GR then it can only be for the better. If that changes the new standard model (LCDM) then it can only lead to an improved understanding of nature.

 

As long as there exists an alternative explanation for lambda, that does concord with observations, then it should not be taken for granted that we know what lambda (or dark energy) is.

 

Indeed it is my contention that we haven't an inkling of an idea as to the true nature of the cosmological constant.

 

And so I will continue to argue in favor of the naturalist stance, where the artificial is removed from GR (and thus from the concordance model) and replaced with something that is palpable, with something that is physical, with something that illuminates the nature of the physical universe and the dynamics of its constituents (not with 97% bunk), with something that provides answers rather than more questions.

 

Regarding the points 1 and 2 above:

 

My points remains (restated): (1) the original cosmological term was introduced into the field equations to justify a stable regime. The new lambda was introduced to explain a catastrophic accelerating expansion. Clearly that is what I have been saying (perhaps not in so few words). And (2) because gravity is a curved spacetime phenomenon, it seems quite natural to assume lambda is also a geometric spacetime phenomenon (as opposed to yet another field, negative pressure, dark energy, or another layer of reality, to be added to the others: electromagnetic field, the gravitational field, strong and weak atomic forces).

 

Indeed, for now, it is assumed that lambda is a geometric property of spacetime directly related to, and inextricable from, gravity. And it can be shown that this is indeed the case. So the concept that lambda is vacuum energy or negative pressure in GR (or even in physics generally) is easily amendable to a more meaningful, and yes, all-encompassing solution. And, one more time, GR does not change in essence, but rather, the new definition of lambda describes a boundary condition inherent in nature, and thus, something the function or mechanism of which is missing from both GR and Newtonian gravitation, yet observationally has been present all along, and without the need for artificial fine tuning (or Devine intervention, or dark energy).

 

 

In other words, what I propose is not a test of the field equations (or even an extension of the type loop-quatum gravity, branes or sting theory), but rather, a test of the boundary conditions of GR, pure and simple. The problem with GR (if one could call it a problem) is that it is too general, in that just about anything can be interpreted from it when pushed to extremes. What interests me is not the high energy, high density regime of GR, but the low energy, low density regime., when the field is all but equal to zero, or very nearly so (gravity-free spacetime: the pristine vacuum). What interest me are the peaks and troughs in the gravitational field, where the trough is the potential well surrounding massive bodies, and the peaks are particular points (Lagrangian points, e.g., L1, L2 and L3) that all carry the same value of the field, equal to zero.

 

 

I would even go so far as to state (without justification for now):

 

 

• For all interacting systems (e.g., planets, stars, galaxies, clusters of galaxies) that are bound under the sole influence of gravity, and which may be all at different elevations in the gravity field (inside their potential wells), there exists an equal and opposite reaction provided by the cosmological constant, corresponding to zero force and zero acceleration.
  

 

 

 

 

 

CC

[Erasmus00]

What I am saying, this time without the fanfare, is that we need to change our actual interpretation of lambda.

 

Changing an interpretation of lambda will not change the PHYSICS of the Einstein equations. The SNe Ia data will still indicate that our universe is slightly accelerating. Hence, lambda will still be necessarily non-zero. Its how it was measured.

 

As long as there exists an alternative explanation for lambda, that does concord with observations, then it should not be taken for granted that we know what lambda (or dark energy) is.

 

Knowing what it is, and measuring its effects are two different things. I doubt anyone has claimed to know what it is- this is why scientists are building dark energy surveys to learn more.

 

And so I will continue to argue in favor of the naturalist stance, where the artificial is removed from GR

 

It has been explained many times that lambda enters GR in the same way the Einstein field tensor does. It is no less "artificial" then a Ricci tensor or a curvature scalar.

 

and replaced with something that is palpable.... (not with 97% bunk), with something that provides answers rather than more questions.

 

First, astronomers are actively seeking the answers to the questions raised (what is dark matter, is expansion caused by a cosmological constant or some other form of matter?).

 

Second, IF GR is correct you cannot get away from dark matter, and "dark enery" just from experimental measurements. Your options are 1. get rid of GR, 2. deal with the dark matter/dark energy.

 

(1) the original cosmological term was introduced into the field equations to justify a stable regime. The new lambda was introduced to explain a catastrophic accelerating expansion.

 

Regardless of the MOTIVATION, the PHYSICS is the same! It doesn't matter WHY it was put in, what matter is the physics of the term.

 

(2) because gravity is a curved spacetime phenomenon, it seems quite natural to assume lambda is also a geometric spacetime phenomenon

 

Thats fine and dandy- and further tests may reveal what it is. Regardless- its responsible for a large portion of the "energy density" we measure.

 

And it can be shown that this is indeed the case.

 

Not without further measurement!

 

the new definition of lambda describes a boundary condition inherent in nature,

 

The cosmological constant is not at all a boundary condition in form! You can't just take an equation and call a random piece of it a boundary condition.

-Will

[Southtown]

More factual errors, quote mining, and pithy sayings. Creationists the world over marvel.

Someone has to.

[Southtown]

...science is too often misrepresented as merely the success of the predicted as if theories spring from the mind like Athena.

Ahh but they do. The pudding is in the proof.

[modest]

I believe you are left with the logical choice of rejecting GR (at least Lambda’s place in it) or amending your claims.

I am not saying we need to change the field equations.

 

I know. You are saying they are correct yet give the wrong answer. Your claims are mutually exclusive.

 

I think it stems from this:

 

The problem with GR (if one could call it a problem) is that it is too general, in that just about anything can be interpreted from it when pushed to extremes.

 

When, in fact, all you can do in GR is set the values and solve.

 

A positive cosmological constant causes accelerated expansion of empty space. That is the result of the term in the equation. If the constant is zero then it neither decelerates nor accelerates expansion. This is the solution to the field equations. If you think the field equations are spot-on then how can you disagree with the result?

 

It's the same as someone saying they like the equation pi=c/d but they don't necessarily think a circumference of pi means a diameter of 1.

 

-modest

[coldcreation]

Changing an interpretation of lambda will not change the PHYSICS of the Einstein equations.

 

Perhaps not, but it could change the cosmology associated with it.

 

 

The SNe Ia data will still indicate that our universe is slightly accelerating. Hence, lambda will still be necessarily non-zero. Its how it was measured.

 

This is true, but only according to the standard model. Other models have different interpretations for the SNe Ia data, and thus, of lambda. It is possible to formulate a model, say, a nonexpanding model, that fixes the value of lambda—with an alternative interpretation based on measurements—to zero for all time (rather than determining its value through measurements based on an expanding model).

 

 

Knowing what it is, and measuring its effects are two different things. I doubt anyone has claimed to know what it is- this is why scientists are building dark energy surveys to learn more.

 

Once we know what lambda is, it will be possible to measure its value directly, based on its effects. But again, the interpretation will be model dependent. It would then have to be determined which model best fits the data. BTW, I claim to know what lambda is (but then again, I could be wrong).

 

 

 

And so I will continue to argue in favor of the naturalist stance, where the artificial is removed from GR

 

It has been explained many times that lambda enters GR in the same way the Einstein field tensor does. It is no less "artificial" then a Ricci tensor or a curvature scalar.

 

Maybe 'artificial' was not the best word to use. I should have written: And so I will continue to argue in favor of the physical stance, where the fudge factor is removed from GR (or modified).

 

 

First, astronomers are actively seeking the answers to the questions raised (what is dark matter, is expansion caused by a cosmological constant or some other form of matter?).

 

My point is that lambda only acts as if it were negative pressure, without actually being negative pressure, that counters gravity. The real problem aside from lambda, is gravity. There is a major discrepancies between the current picture of gravity together with the cosmological constant and the one hinted at in my prose above. I feel a new physical law is required that describes the 4-dimensional spacetime manifold both in the absence of gravity (curvature) and in the presence of massive bodies where curvature is generated.

 

It could even be surmised (again without proof for the time being):

 

• The cosmological constant is an equilibrium state that does not change as a function of time. It is an ideal vacuum state: the invariant substratum in which all systems and their constituent elementary building blocks, properties and nest of forces manifest themselves.
  

 

 

Second, IF GR is correct you cannot get away from dark matter, and "dark energy" just from experimental measurements. Your options are 1. get rid of GR, 2. deal with the dark matter/dark energy.

 

This is the kind of vicious circle I prefer to avoid. There is a way around it that saves GR (albeit introducing a slight modification by doing away with at least part of the instability associated with it) and gets rid of dark energy. I argue that experimental measurements are not solely indicative of one interpretation, or one model. So your solutions are: get rid of LCDM with its huge dark energy content (as well as its non-negligable dark matter component), save GR by deriving a new world-model.

 

 

(1) the original cosmological term was introduced into the field equations to justify a stable regime. The new lambda was introduced to explain a catastrophic accelerating expansion.

 

Regardless of the MOTIVATION, the PHYSICS is the same! It doesn't matter WHY it was put in, what matter is the physics of the term.

 

It is the physics of the cosmological term that I question. By changing the physics of lambda, Einstein's original motivation can be reconciled.

 

 

(2) because gravity is a curved spacetime phenomenon, it seems quite natural to assume lambda is also a geometric spacetime phenomenon.

 

Thats fine and dandy- and further tests may reveal what it is. Regardless- it[']s responsible for a large portion of the "energy density" we measure.

 

It may turn out that lambda actually describes a state of zero energy density, i.e., a state of zero spacetime curvature, thus related to geometry (not a new form of pressure with a negative sign). That is the point I will argue and defend on empirical grounds (either here or in another thread).

 

 

 

[...lambda is a geometric property of spacetime directly related to, and inextricable from, gravity.] And it can be shown that this is indeed the case.

 

Not without further measurement!

 

True. Further measurement are required, some of which can be carried out right here in the solar system.

 

 

The cosmological constant is not at all a boundary condition in form! You can't just take an equation and call a random piece of it a boundary condition.

 

That is a good point. It may turn out, though, that the cosmological constant describes a boundary condition in practice. In that case, lambda would be simply a description of 'empty space' in relation to that which gravitates, i.e., a Minkowski-like spacetime in relation to curved spacetime. No interpretation of lambda could be more simple. And yet, and yet...

 

 

CC

[coldcreation]

Hello all, the party pooper is back... :lol:

 

The latest news on theoretical fronts related to SNe Ia, Implications, Interpretations, Lambda-CDM, dark energy:

 

A few days ago I was browsing through some magazines at Borders and came across the April 2009 issue of Scientific American, entitled, Does Dark Energy Really Exist?

 

On pages 48-55 is an article written by Timothy Clifton and Pedro G. Ferreira.

 

A tiny deviation in the brightness of exploding stars led astronomers to conclude that they had no idea what 70 percent of the cosmos consists of. All they could tell was that space is filled with a substance unlike any other one that pushes along the expansion of the universe rather than holding it back. This substance became known as dark energy.

 

It is now over a decade later' date=' and [b']the existence of dark energy is still so puzzling that some cosmologists are revisiting the fundamental postulates that led them to deduce its existence in the first place[/b]. One of these is the product of that earlier revolution: the Copernican principle, that Earth is not in a central or otherwise special position in the universe. If we discard this basic principle, a surprisingly different picture of what could account for the observations emerges.

 

And...

 

Confronted with something so strange and seemingly so improbable' date=' some researchers are revisiting the reasoning that led them to it [dark energy']. One of the primary assumptions they are questioning is whether we live in a representative part of the universe. Could the evidence for dark energy be accounted for in other ways if we were to do away with the cosmological principle?

 

And...

 

Suppose that the expansion rate is decelerating everywhere' date=' as matter tugs on spacetime and slows it down. Suppose, further, that we live in a gargantuan cosmic void not a completely empty region, but one in which the average density of matter is only a half or maybe a third of the density elsewhere. The emptier a patch of space is, the less matter it contains to slow down the expansion of space; accordingly, the local expansion rate is faster within the void than it is elsewhere. The expansion rate is fastest at the very center of the void and diminishes toward the edge, where the higher-density exterior begins to make itself felt. At any given time different parts of space will expand at different rates, like the unevenly inflated party balloon.[/quote']

 

And still more...

 

Another way to put it is that a variation of expansion rate with position mimics a variation in time. In this way' date=' cosmologists can [b']explain the unexpected supernova observations without invoking dark energy[/b]. For such an alternative explanation to work, we would have to live in a void of truly cosmic proportions. The supernova observations extend out to billions of light-years, a significant fraction of the entire observable universe. A void would have to be of similar size. Enormous by (almost) anyone's standards.

 

And something I've argued on occasion...

 

Another possibility is that dark energy is an artifact of the mathematical approximations that cosmologists routinely use. To calculate the cosmic expansion rate' date=' we typically count up how much matter a region of space contains, divide by the volume of the region and arrive at the average energy density. We then insert this average density into Einstein's equations for gravity and determine the averaged expansion rate of the universe. Although the density varies from place to place, we treat this scatter as small fluctuations about the overall average.[/quote']

 

And finally...

 

Observational tests to distinguish between dark energy and the void models are set to be carried out in the very near future. The Supernova Legacy Survey' date=' led by Pierre Astier of the University of Paris, and the Joint Dark Energy Mission, currently under development, should pin down the expansion history of the universe. The Planck Surveyor satellite and a variety of ground-based and balloon-borne instruments will map out the microwave background in ever greater detail. The Square Kilometer Array, a gigantic radio telescope planned for 2020, will supply us with a survey of all the galaxies within our observable horizon. [b']This revolution in cosmology began a decade ago, and it is far from over.[/b]

My bold

 

 

For further reading see:

 

Geocentrism reexamined, Jeremy Goodman (Princeton University Observatory), Phys.Rev. D52 (1995) 1821-1827

 

 

The State Of The Universe, by Pedro G Ferreira

 

 

Cosmology: Patchy solutions, Ellis,*George, Nature, Volume 452, Issue 7184, pp. 158-161 (2008).

 

 

Living in a Void: Testing the Copernican Principle with Distant Supernovae, Timothy Clifton, Pedro G. Ferreira, Kate Land, Phys. Rev. Lett. 101 (2008) 131302

 

 

 

Something has only just begun

 

 

:eek:

 

 

CC

[modest]

Nice.

 

I'd say this fits my previously formed conclusion:

 

Our cosmic observations do indeed agree with the FLRW metric if the makeup of the universe is currently 74% vacuum energy density and 26% mass density as a ratio to the critical density. Either this is not the makeup of our universe, the universe is not homogeneous and isotropic, or FLRW and by extension GR are wrong.

 

If there is no dark energy and yet cosmic solutions to General Relativity are correct then one possible reason would be an inhomogeneous cosmos.

 

~modest :phones:

[coldcreation]

Nice.

 

I'd say this fits my previously formed conclusion:

 

If there is no dark energy and yet cosmic solutions to General Relativity are correct then one possible reason would be an inhomogeneous cosmos.

 

~modest ;)

 

Hello again,

 

I've been off-line fossil hunting for a while...

 

Yes modest, I remember your sentence. Indeed, the homogeneity assumption is required by the concordance model.

 

Here, interestingly enough, there is an article that does not require spatial inhomogeneity (as in my previous post) to refute the accelerated expansion hypothesis. I have not yet read the entire work but I did notice a few points:

 

Modeling The Expansion Of The Universe By A Steady Flow Of Space-Time, by Juan Casado Giménez Universidad Autónoma de Barcelona

 

Assuming that the Universe is spatially infinite' date=' we depict a

simple model where gravitation does not decelerate the

expansion, which occurs at constant speed for any two distant

galaxies. This Steady Flow model fits the SNe Ia observations

without a repulsive dark energy. [...']

 

 

Conclusions:

In a homogeneous, isotropic and spatially infinite Universe the net gravitational force on any galaxy should be (almost) null for

symmetry reasons. Thus, gravitation does not decelerate the universal

expansion, which follows a steady Hubble flow with constant

recession velocities. The results of SNe Ia are consistent with this

simple model for a commonly accepted value of H0 and without any

free fitting parameters. Neither cosmological constant nor a repulsive

dark energy are required in our model. The horizon problem vanishes

since the Universe should have been always spatially infinite and

homogeneous. The flatness problem is avoided because of the lack of

any spatial curvature (except at local scale) due to the overall

cancellation of the gravitational field. The time evolution of the scale

factor, R ∝ t, is specific of our model and is the same independently

of either radiation or matter dominance in the Universe.

Subsequently, we obtain longer times for the development of

structure seeds observed in CBR and for the formation of the first

galaxies. On the other hand, the steady expansion time coincides with

the age of the Universe obtained from the Concordance model, and

some other features of Big Bang cosmology, such as the evolution of

temperature with the scale factor or the primordial nucleosynthesis of

He, remain unchanged.

 

On a slightly different note, let's consider for a moment the contents of the universe as an ideal expanding gas. The objects (galaxy clusters in this case) within the universe expand adiabatically.

 

Clouds of hydrogen condense under gravitational interactions to form stars (star-clusters, galaxies, galaxy clusters, superclusters). Stars light up and heat the universe. The CMB grows warmer with time. As the undifferentiated matter heats, like gas, expansions occurs.

 

Note that within this latter scenario there is no need to have a big bang at any time in the past, nor any dark energy or CDM...

 

 

 

Just a thought...

 

 

CC

[Pluto]

G'day from the land of ozzzzzzz

 

This paper fits to your discussion

 

Observations of type 1a supernovae are consistent with a static universe

 

Jan-09

 

Observations of type 1a supernovae are consistent with a static universe

http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009

arXiv0901.4172C&link_type=PREPRINT&db_key=PRE

 

Analysis of type 1a supernovae observations out to a redshift of $z$=1.6 shows that there is good agreement between the light-curve widths and $(1+z)$ which is usually interpreted as a strong support for time dilation due to an expanding universe. This paper argues that a strong case can be made for a static universe where the supernovae light-curve-width dependence on redshift is due to selection effects. The analysis is based on the principle that it is the total energy (the fluence) and not the peak magnitude that is the best `standard candle' for type 1a supernovae. A simple model using a static cosmology provides an excellent prediction for the dependence of light curve width on redshift and the luminosity-width relationship for nearby supernovae. The width dependence arises from the assumption of constant absolute magnitude resulting in strong selection of lower luminosity supernovae at higher redshifts due to the use of an incorrect distance modulus. Using a static cosmology, curvature-cosmology, and without fitting any parameters the analysis shows that the total energy is independent of redshift and provides a Hubble constant of $63.1pm2.5$ kms$^{-1}$ Mpc$^{-1}$. There is no indication of any deviation at large redshifts that has been ascribed to the occurrence of dark energy.

[Little Bang]

All of this thread is based on the Hubble redshift. I have what I consider to be proof of tired light. Does the wavelength of light propagating into a gravity well get shorter? Yes, does the wavelength of light propagating out of a gravity well get longer? Yes, can the Universe be considered a gravity well? Yes.