What Evidence is Needed to Confirm Dark Energy's Existence?

[Garth]

http://arxiv.org/abs/0705.0165" may be of interest: Is Modified Gravity Required by Observations? An Empirical Consistency Test of Dark Energy Models

Hmmm..

assuming a flat universe,

I have previously made the observation that as the WMAP data is angular in nature, and conformal transformations are angle preserving, then the statement that the WMAP data is consistent with the universe being 'spatially flat' should actually be 'conformally spatially flat'. Am I mistaken in this assertion?

If I am not mistaken then the constraint of a flat universe may be too restrictive.

Garth

 

[George Jones]

In other words that there really is only matter in the Universe, but that the way gravity works gives us the appearance of DE if we interpret the results in terms of GR?

... for interpreting \Lambda as a geometric term

I am not completely sold on this idea, but I do think that this is a possibility that doesn't get taken as seriously as it should. When we examine the world on levels far removed from our everyday experience, we find often find that our expectations are wrong. We could be seeing an aspect of gravity with which we were previously unfamiliar, i.e., at "close" range gravity is attractive, but, over cosmological distances and times, gravity might be repulsive. In this scenario, nothing is needed to counteract gravity, as it's gravity itself that's causing the acceleration of the expansion. I wouldn't call this a modification of GR, I would call it GR.

But I hope for a profound solution, not a mundane one! I would love to "take a bow for the new revolution" in physics, and I hope "we don't get fooled again."

Possibilities:

1) vacuum energy (without introducing a new field) on the right side of Einstein's equation;

2) new (scalar?) field energy on the right side of Einstein's equation;

3) geometry/cosmological constant on the left side of Einstein's equation;

4) Combinations of 1), 2), and 3).

Both 1) and 3) act like w = -1, which is consistent with observations, and I don't think we can talk sensibly about 1) without a quantum theory of gravity. I think we need this to set a zero for energy, which will tell us what to include on the right of Einstein's equation (or whatever reduces to Einstein's equation in the new theory). Without this, I don't see how it's possible to distinguish between 1) and 3).

Robust cosmological observations that show w =/= -1 would convince me that some type of dark energy 2) exists, but in order to say that this is soley responsible for the acceleration, i.e, in order to rule out 4), I think that quantum gravity is needed.

 

[Garth]

I am not completely sold on this idea, but I do think that this is a possibility that doesn't get taken as seriously as it should. When we examine the world on levels far removed from our everyday experience, we find often find that our expectations are wrong. We could be seeing an aspect of gravity with which we were previously unfamiliar, i.e., at "close" range gravity is attractive, but, over cosmological distances and times, gravity might be repulsive. In this scenario, nothing is needed to counteract gravity, as it's gravity itself that's causing the acceleration of the expansion. I wouldn't call this a modification of GR, I would call it GR.

But I hope for a profound solution, not a mundane one! I would love to "take a bow for the new revolution" in physics, and I hope "we don't get fooled again."

Possibilities:

1) vacuum energy (without introducing a new field) on the right side of Einstein's equation;

2) new (scalar?) field energy on the right side of Einstein's equation;

3) geometry/cosmological constant on the left side of Einstein's equation;

4) Combinations of 1), 2), and 3).

Both 1) and 3) act like w = -1, which is consistent with observations, and I don't think we can talk sensibly about 1) without a quantum theory of gravity. I think we need this to set a zero for energy, which will tell us what to include on the right of Einstein's equation (or whatever reduces to Einstein's equation in the new theory). Without this, I don't see how it's possible to distinguish between 1) and 3).

Robust cosmological observations that show w =/= -1 would convince me that some type of dark energy 2) exists, but in order to say that this is soley responsible for the acceleration, i.e, in order to rule out 4), I think that quantum gravity is needed.

George:

You are right to distinguish between 1) and 3), which others tend to roll together because they behave identically as far as long range gravitation is concerned.

If we have 1), a non-zero-vacuum energy, then that ought to be discoverable in 'the laboratory'. (Where anywhere inside the trajectory of the Pioneer spacecraft could be 'the laboratory'.)

If it is simply 3), the cosmological constant, then as you say it is simply gravity, which attracts at short ranges but repels over cosmological distances.

I favour 2) personally, which should also be discoverable in the laboratory, and I am particularly interested in theories that are conformally equivalent to GR in vacuo (the scalar field coupling parameter \omega = -3/2), which reduce down to canonical GR. So the geodesics and null-geodesics of the theory through vacuum are identical with those of GR.

But as you say we might have to live with a combination of all three!

Garth

 

[Chronos]

I'm not a fan of distance dependent gravity - how do it know when to turn back upon itself?

 

[jal]

It will be detected in the lab.

I want to understand how the universe is made and how it works.
I reserve the right to change my mind on what I extrapolated from what I have learned if new information contradict what I have already learned.

There is a missing piece of the puzzle that everyone is trying to find.
I don’t care it they call it a brane, higgs, particle, dark matter, etc.
At the end of the day, it’s going to fit into and be part of a structured spacetime.


http://www.astrobiology.cf.ac.uk/fredhoyle.html
Professor Sir Fred Hoyle [1915-2001]
Fred believed that, as a general rule, solutions to major unsolved problems had to be sought by exploring radical hypotheses, whilst at the same time not deviating from well-attested scientific tools and methods. For if such solutions did indeed lie in the realms of orthodox theory upon which everyone agreed, they would either have been discovered already, or they would be trivial.
==========
We should keep our feet on the ground.
http://www.astro.ucla.edu/~wright/cosmolog.htm
Ned Wright's Cosmology Tutorial
http://www.astro.ucla.edu/~wright/stdystat.htm
Errors in the Steady State and Quasi-SS Models
http://www.aas.org/head/headnews/headnews.nov00.html
3. Robert Michael Hjellming 1938-2000
=============
If matter really vanishes inside black holes, as if they were bottomless pits, where has the matter gone? British Theorist Roger Penrose suggested some time ago that the missing matter may pop out elsewhere in the universe —or even in an entirely different universe.
Picking up where Penrose left off, Robert M. Hjellming says that the point at which the matter re-emerges in the other universe would be a white hole. Even more intriguing, this passage of matter would not be a one-way street. Matter would also leave the other universe through black holes, says Hjellming, and appear in ours through white holes. Thus the flow of matter between the two universes would be kept in balance.
But, he adds, some evidence may already be at hand that white holes do exist. One of the great puzzles of contemporary astrophysics is the huge amount of energy —cosmic rays, X rays, infrared radiation —that is apparently coming from distant quasars and from the centers of galaxies, including the Earth's own Milky Way; the output seems to be greater than can be accounted for by known physical processes, including the conversion of matter into energy by thermonuclear explosions. If it could be shown that matter and energy were coming from another universe, Hjellming says, that problem would be neatly solved.
=============
From J. Baez
http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/universe.html
The big bang is therefore more like a white hole which is the time reversal of a black hole. According to classical general relativity white holes should not exist since they cannot be created for the same (time-reversed) reasons that black holes cannot be destroyed. This might not apply if they always existed.
The possibility that the big bang is actually a white hole remains.
….. we must ask if there is a white hole model for the universe which would be as consistent with observations as the FRW models.
A white hole model which fitted cosmological observation would have to be the time reversal of a star collapsing to form a black hole.
It follows that the time reversal of this model for a collapsing sphere of dust is indistinguishable from the FRW models if the dust sphere is larger than the observable universe. In other words, we cannot rule out the possibility that the universe is a very large white hole.
==============
With minimum length there should be quantum mini black holes then there should also be quantum mini white holes.
Where are the many mini white holes hiding that are still adding to the structural elements into our universe so that we observe expansion, acceleration and dark mater/energy?

============

http://www.citebase.org/fulltext?format=application%2Fpdf&identifier=oai%3AarXiv.org%3Agr-qc%2F9505012
Spectroscopy of the quantum black hole
Jacob D. Bekenstein, V. F. Mukhanov
10 May 1995 (Received April 13, 2006)
One prediction is that there should be no lines with wavelength of order the black hole size or larger. This makes it possible to test quantum gravity with black holes well above Planck scale.
Note: substitute “white” for “black”
===========
Different calculations are being done to find the missing piece of the puzzle but nobody has agreed on the name for the baby elephant.
You will soon see part of this post in my blog (white holes)
jal

 

[dilletante]

If matter from a black hole vanishes into another universe, why are we still able to measure the mass and gravitational effects of black holes in this universe?

dilletante

 

[Wallace]

If matter from a black hole vanishes into another universe, why are we still able to measure the mass and gravitational effects of black holes in this universe?

dilletante

Because matter only travels to other Universes through black holes in science fiction!

 

[zankaon]

Is the smoking gun for dark energy right under our nose?

Is the smoking gun for dark energy right under our nose?
No long range gravity wave propagation?
'The emperor has no clothes'

The gravity wave observatories have no g.w.s.;
in spite of sufficient exquisite sensitivity and a large enough statistical volume. Hence consistent with a stiff pseudo-Riemannian spacetime manifold. Gravity waves would seem to be damped out quickly near sources. Hence the manifold would seem robust to perturbation. Such resistance to deformation would contribute energy to stress energy momentum tensor, and hence to left side of Einstein eq. i.e. Einstein tensor contraction, or curvature tensor. Hence hard qualitative evidence of at least one dark energy candidate (i.e. contributing to critical energy density sufficient for flatness).
zankaon.
See previous more elaborate thread:
09-16-2007 at 12:12 AM. cosmology thread