Why can't the acceleration of the expansion measured in type 1a surveys be a part of the geometry of the large-scale curvature of the universe without needing dark matter or a Cosmological Constant? When I think about the images of raisins in a cake or dots expanding over time on a page, the idea comes to mind that the expansion may be galaxies moving in curved space, just like local gravity but on a universe-scale and in the opposite direction, of course. If this were the case, you might expect an acceleration in the expansion with great distances due to the principle of equivalence.

Could the acceleration in the expansion be a natural part of the large-scale curvature geometry of the universe?

I'm no expert, but my answer would be no. As I understand it, the large-scale curvature of space in the universe is reflective of the gravitational potential of all the mass and energy within the universe. Recent independent observations are supportive of a very nearly flat overall curvature. But if the curvature is "less than flat", that is, if it is saddle-shaped, this just means there is not enough mass and energy to gravitationally halt the expansion. Such a curvature has no means to effect an acceleration on the expansion. An accelerating expansion must come from some as yet unknown "force," which by coincidence, is (so far) mathematically well described by Einstein's discarded cosmological constant.

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I agree with Cougar, just taking a slightly different approach. If gravity and spacetime curvature are manifestations of the same underlying 'force', it makes sense to me they are indistinguishable. IOW, gravity and spacetime curvature are merely different ways of defining the same effect.

Dark energy is the main problem that your view would eliminate or we could be looking at a cosmological constant.

"But if the principle of equivalence states we cannot discern gravity from accelerating, CONTRACTION then it also means that we cannot discern the Einstein-Perlmutter repulsive force (gravity’s opposite force between all the stars and galaxies), from an accelerating, EXPANDING universe."- Daniel Fitzpatrick

A major conundrum of the Big Bang theory is that the most distant galaxies that are moving away from the Earth with the greatest velocity are simultaneously moving towards us in curved spacetime. Angus Graham said something to that effect.

The following article explains how our use of special relativistic Doppler redshifts can lead to errors in measurement at extreme distances because they don’t consider the gravitational curved space-time geometry of general relativity. You can’t make a flat SR map match the large-scale geometry of curved space.

http://www.astronomycafe.net/cosm/expan.html

Thanks for the replies and thoughts. The article Bob mentions and his notes are very interesting and a good read.

Since we know spacetime curvature makes things accelerate here based on experience, why wouldn't we EXPECT that celestial bodies would accelerate at greater distances in a saddle shaped large-scale curvature?

Sorry, but the two cases are in no way comparable for a variety of reasons. The geometry of spacetime is completely different in these two cases; in the first case, you have a spherically symmetric static spacetime, whereas in the second you have a homogeneous, isotropic, decidedly non-static spacetime. In the first case, there is a clearly defined center towards acceleration happens, in the second, there is no (clearly definable) center at all.

Additionally, you apparently have missed the fact that the acceleration of the expansion of the universe is happening *today*, whereas we see the distant galaxies as they were several billion years ago. Hence an acceleration of these galaxies obviously would have little to do with the observed acceleration today.

A further point is that if you look back even farther in time (i. e. to even more distant galaxies), you see that back then, there was *deceleration*, not acceleration.

Hope this helps.

See the de Sitter effect.

Also, Einstein's cosmological term has nothing to do with dark energy, acceleration. The original cosmological constant was an equillibrium generating manifestation (the physical mechanism of which was unknown).

The new cosmological constant is not the original version on speed or crack cocaine, it is a grotesque (I could think of anything worse to say about it, but don't take it personally Cougar) fudge factor used in an attempt to salvage an outdated hypothesis: the standard canonical hot big bang model.

To answer the question asked in this thread: yes the deviation from linearity observed in the SNe Ia spectrum is due to general relativistic spacetime dilation (curvature). It is not evidence of an accelerated expansion: a far cry from it. In fact, it is evidence that the expansion is not real.

You see, a theory makes predictions, the theory is then tested against those predictions. If the predictions are not satisfied, then the theory is either modified or dumped. In this case, the theory (in this case not just any theory; the standard model) was modified, and the result is catastrophic. The modification, a gross one, certainly, leads to a universe that does not simply contain something strange, kooky and otherworldy, but is dominated by it (whatever IT is, no one knows).

No theory predicted the results of the SN survey, and no standard model should be subjected to this kind of unphysical abuse.

Edited to add: Look at...

http://antwrp.gsfc.nasa.gov/diamond_.../hub_1929.html

...Of which here is a well known quote:

The outstanding feature, however, is the possibility that the velocity-distance relation may represent the de Sitter effect, and hence that numerical data may be introduced into discussions of the general curvature of space. In the de Sitter cosmology, displacements of the spectra arise from two sources, an apparent slowing down of atomic vibrations and a general tendency of material particles to scatter. The latter involves an acceleration and hence introduces the element of time. The relative importance of these two effects should determine the form of the relation between distances and observed velocities; and in this connection it may be emphasized that the linear relation found in the present discussion is a first approximation representing a restricted range in distance.

From the Proceedings of the National Academy of Sciences
Volume 15 : March 15, 1929 : Number 3

A RELATION BETWEEN DISTANCE AND RADIAL VELOCITY
AMONG EXTRA-GALACTIC NEBULAE

By Edwin Hubble

Mount Wilson Observatory, Carnegie Institution of Washington
Communicated January 17, 1929

Note: 1929 is the supposed year Hubble discovered or proved the universe was expanding.


Don't loose your mittens.

Coldcreation

See too in addition to 'de Sitter effect,' 'de Sitter redshift.'

Quite wrong here. Both Einstein's cosmological term and the Lambda CDM model use exactly the same math. The only difference is in the value of one specific parameter - the cosmological constant. Einstein set this constant to the very specific value which would lead to equilibrium (well, in fact it wouldn't, since this situation is unstable against perturbations), for long decades it was assumed that the value is zero (for simplicity, and because there were no observations availabe showing otherwise), and some years ago we have discovered that it is non-zero, but different from Einstein's value.

So you want to claim that simply using another value for a parameter turns this parameter from being "an equilibrium generating manifestation" to "a grotesque fudge factor"? Doesn't sound very sensible.


Feel free to come up with a quantitative description of the data obtained from that idea.

You make no sense. Accelerated expansion explains the data, hence the data is evidence for accelerated expansion. It's that simple. Why do you think otherwise?


Indeed, the universe is dominated by dark energy, and indeed, we so far don't know what that is. But why do you call that result "catastropic"?

Hint: the energy density of dark energy grows with time, hence obviously there has to come a time where it dominates! The time when it didn't dominate was in fact quite short (well, on a cosmological time scale): only a few billion years. So it's no big miracle (or "catastrophe") that it dominates today.

Well, models with a non-zero cosmological constant were used in cosmology already before the SN results (for example, in simulations of structure formation). But before the SN results, obviously no one knew the value of the cosmological constant - so how could anyone have predicted that?

You fault a theory for not predicting something which it was simply not able to do - because the value for a crucial parameter was not known before, and was essentially determined by these observations which you claim should have been predicted! That makes little sense.


What is unphysical about doing observations which determine the value of a parameter in a theory?

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For sure there is a zero value for lambda, only, there are no negative values, it is no parameter (yes it is being erroneously used as one, a grave error). There are no positive values.

The problem, both with respect to Einstein's and the new cosmological term, is that neither concept is backed by a physical definition that enlightens the mechanism behind lambda, for the simple reason that there is no such illumination for the mechanism behind the gravitational interaction. Only when light is shed on the latter will lambda take on its trus physical form. For now, dark matter means nothing, save the tweakable parameter to patch up a theory destined for the same place the cosmological constant was recently pulled.

The concept differences are enormous. One lambda was a stabilizing term, the other, the brute fury of Chi. The concept, the value and the physical definition make all the difference



I will leave the adaptation of the math (to the data) to those more qualified to do the dirty work. I will negotiate the conceptual aspects. The math, by the way, has already been written. See the original de Sitter metric (1916-1918), his interpretation of GR to the "Kosmos."



I understand all too well the train of thought leading to the idea of acceleration. The general relativistic curavture of the large-scale structure of spacetime explains the observations equally well (it is my contention that the GR approach is even more elegant) and without the artificial flavor of dark energy (something with which many sound quite compfortable, but it just isn't physics). It is that simple!


The first part of your question answers the second.

What is growing with time, what dominates the universe?
Negative pressure, antigravity, a dark force? No one can answer these questions. Just as no one can explain what miraculous force could possibly cause the ocean to spread open to allow the passage of a chimerical convoy...



No theory predicted the results of the SN survey because most physicists had trashed lambda decades ago and did not care to see it return. Not because it was distastful, or because it was a fudge factor, but because if it returned then no one could exclude the possibility that it exactly balanced gravity, thus leading to stable, nonexpanding universe, as Einstein had originally suspected. This is exactly what I suspect today. Though the word "balance" used above is not entierly appropriate. The explanation may be beyond the scope of the present thread.


There is nothing physical to be said of dark energy. The observations are sound, it is the interpretation of those that is lacking, to say the least.

Regards

Coldcreation

A lot of assertions, with not even an attempt to back them up...

How do you know?

Why not?
Why not?

Why not?

What does "physical definition" mean? And how would such a definition "enlighten the mechanism behind lambda"?

Hint: curvature of spacetime.

And what is that supposed to mean?

Ever heard of proposals like neutralinos?

Or do you confuse dark matter with dark energy here? If not, I don't see why you brought dark matter up in this connection.

Both the cosmological constant and the density of dark matter are indeed "tweakable parameters" in the Big Bang Theory. So what? Where is the big problem with that? Do you claim that because we so far don't know what dakr energy and dark matter really are, we aren't allowed to use these parameters, or what?

Physics is about measurements which provide evidence for or refute a theory. Not about "concept differences". Just because one specific value of lambda leads to stabilization (and I already pointed out that in reality, this doesn't work actually), that doesn't imply in the least that all other values have to be treated in another way.


Well, so you admit that you haven't done the math on that so far, and apparently are not even able to do it. What was your basis then for claiming that this would work?

And what makes you think that de Sitter's model can explain the observed SN data? Just above you essentially admitted that you are unable to do the necessary math.




First, even if there would be an alternative explanation possible, that wouldn't negate the fact that the SN data is evidence for an accelerated expansion (hint: one observation can be evidence for several competing models at once). So you original claim that it is no evidence for an accelerated expansion is still wrong.

Second, here again you simply claim that "the general relativistic curvature" can also explain these observation, but again you don't bother to back up that claim. What about showing some math? Show us that this model can explain the data, quantitatively. Oh, wait - you have just admitted yourself that you can't do the math. A pity, isn't it?




Sorry, I still don't see why you call that "catastropic". We don't know what the stuff which dominates the universe is, right - but why do you call that a catastrophe?

Wrong. Just like I said: the density of dark energy grows with time and dominates the universe. Why don't you simply read what I write instead of claiming that no one can answer this?

BTW: what is "a dark force" even supposed to mean?


I have no idea what you are talking about here.




Wrong again.

First, as I have said already some times, such a universe would not actually be stable.

Second, it is absolutely ridiculous to claim that physicists "feared" using the cosmological constant because this might lead to a stable universe. There is precisely one value for which that would be the case, and infinitely many others. So why on earth should anyone fear that if one uses the constant again, precisely this one value would turn up again? This doesn't make any sense at all!

Third, I have already explained the real reason why it was assumed that the constant is zero: because that simplified the models, and because there was no observational evidence against that assumption. This is an absolutely sensible explanation consistent with the historical records. No need to come up with wild fantasies about fear of a stable universe...



Please explain what you mean with "physical" resp. "unphysical".


Feel free to show that another interpretation (e. g. your favored de Sitter model) also matches the data. Simply claiming that the de Sitter model also would work (or even would work better) is not enough. Show that is can also explain the data!



Nevertheless:
a Merry Christmas to you, and all the other readers of this thread!

Bjoern

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Coldcreation,

I tried running the basic idea through here a few weeks ago and didn't have much luck persuading anyone either.

My argument was that while we can take a god's eye view of another galaxy and say it's however many light-years across, if we were to actually shine a light across it, it would fall in the gravity well and we would relativistically say it has infinite radius. We don't have a god's eye view of the space in between galaxies and can only measure the light crossing it, which tells us that the space is expanding. The theory arising from this evidence is that the entire universe is expanding in absolute volume from an initial event, yet it's called relativistic expansion. Gravity relativistically contracts space and curves the path of light crossing it, so if this expansion is relativistic, it would seem the space not affected by gravity would be expanding due to lensing effects similar to gravity, although it wouldn't be curving light toward or away from any particular point. The result would cause the light waves crossing it to expand, creating the impression of a receding source. The more space it crosses, the greater the effect and the faster the source appears to be receding, so that eventually the source appears to be receding at the speed of light and this creates a horizon line. Because the expansion is integral to the relativistic effects of crossing expanding space, not an initial event, it declines at a rate requiring a cosmological constant to explain and thus, dark energy. It also causes light from all directions to be evenly red-shifted, creating the impression we are at the center of this expansion.

The question is what could cause this relativistic expansion of space? Obviously any material lensing would cause distortion that we do not detect.

Gravity causes mass to collapse until density ignites it and the energy radiates back out. As red-shift is a function of the light waves, could the interference from all the other light, of all other frequencies, crossing every point in space, be causing some wave interference, without directly interfering with the light particles. To the extent they would slow, it would an aftereffect of the wave action. Gravity collapses, radiation expands. Could the effect on space be similar.