Gravity and developments in GR after WMAP 5 year data

[jonmtkisco]

But while Hamilton's river models work in static and even stationary spacetimes they do not work in non stationary spacetimes.

MeJennifer, why doesn't the theory work in expanding space? Has someone demonstrated that it doesn't work, or is it just a case that no one has come up with an equation yet? I don't see any obvious reason why an inflow theory of gravity shouldn't work in expanding space. As I suggested before, the instantaneous total inflow volume (constant over time) just acts as a direct offset to the instantaneous expansion volume (which unlike the expansion scale factor is actually increasing slowly over time even in an Einstein-de Sitter model without Lambda).

Tom Martin shows in his paper that the spatial inflow model is consistent with a deSitter exponential expansion.

Jon

 

[MeJennifer]

MeJennifer, why doesn't the theory work in expanding space? Has someone demonstrated that it doesn't work, or is it just a case that no one has come up with an equation yet? I don't see any obvious reason why an inflow theory of gravity shouldn't work in expanding space. As I suggested before, the instantaneous total inflow volume (constant over time) just acts as a direct offset to the instantaneous expansion volume (which unlike the expansion scale factor is actually increasing slowly over time even in an Einstein-de Sitter model without Lambda).

I said it did not work for non stationary spacetimes, which is something different.

Tom Martin shows in his paper that the spatial inflow model is consistent with a deSitter exponential expansion.

I looked at the document you referenced.
Where does he demonstrate that the spatial inflow model is consistent with a deSitter exponential expansion?

 

[turbo]

Einstein believed that gravitational and inertial effects arise from matter's interaction with the local vacuum in which it is embedded, and that the presence of matter conditions the physical characteristics of the space in which it is embedded. Rather than describing this vacuum polarization as "curvature", we might more constructively consider that the fine-scale structure of space is conditioned by the matter embedded in it. I highly recommend Saunders and Brown's book "The Philosophy of Vacuum" to the people interested in the intersection of classical physics and quantum physics because it contains so much wonderful material. Chapter One is Einstein's "On the Ether" and Chapter Two is Penrose's "The Mass of the Classical Vacuum". How can you go wrong?

 

[jonmtkisco]

I said it did not work for non stationary spacetimes, which is something different.

I don't understand what you mean by that distinction.

Where does he state that?

Sorry, my mistake. I thought it was in Martin's paper but instead it's in http://http://arxiv.org/PS_cache/gr-qc/pdf/0309/0309072v3.pdf" which describes applications of the Painleve-Gullstrand coordinates to develop Newtonian analogues to GR. These applications seem very close to the spatial inflow model, but he does not use that terminology or adopt such a physical description. So I overstated the point I was making.

Jon

 

[jonmtkisco]

than describing this vacuum polarization as "curvature", we might more constructively consider that the fine-scale structure of space is conditioned by the matter embedded in it. I highly recommend Saunders and Brown's book "The Philosophy of Vacuum"

Thanks Turbo-1 for the book recommendation.

Your suggested terminology, that "the fine-scale structure of space is conditioned by the matter embedded in it" helps create wiggle room for broader physical explanations, but did you intend it to be broad enough to encompass the idea of physical space flowing dynamically into matter's "gravitational sink" and being absorbed?

Jon

 

[turbo]

Thanks Turbo-1 for the book recommendation.

Your suggested terminology, that "the fine-scale structure of space is conditioned by the matter embedded in it" helps create wiggle room for broader physical explanations, but did you intend it to be broad enough to encompass the idea of physical space flowing dynamically into matter's "gravitational sink" and being absorbed?

Jon

I do not think that the concept of space flowing into a gravitational "sink"is at all helpful. You may remember that Fotini Markopoulou (of the Perimeter Institute) predicted a number of years back that EM waves of very high energy (high frequency) should be slowed more than those of lower energy as they propagate through "empty" space because they would interact with the medium through which they propagate more frequently. She hoped that GLAST (which has not yet launched) might demonstrate this. Last year, the consortium operating the MAGIC Cherenkov air-shower telescope determined that a particular gamma-ray burst showed that the high-energy gamma rays showed up 4 minutes later than the lower-energy gamma rays. This is a single observation, and it could be due to conditions at the source of the GRB, but it is intriguing. If MAGIC and eventually GLAST can confirm such delays, we have a revolution in physics in our hands. If the delays are proportional to the redshifts of the sources, then the BB is dead and all of cosmology is up for grabs. If redshift is due to light's interaction with the medium through which it propagates, the Hubble redshift/distance relationship cannot be laid on the doorstep of Doppler-shift/cosmological expansion.

 

[jonmtkisco]

If redshift is due to light's interaction with the medium through which it propagates, the Hubble redshift/distance relationship cannot be laid on the doorstep of Doppler-shift/cosmological expansion.

OK Turbo-1, I think I understand what you're saying. The concept that light might interact with the "aether" is a very interesting one, which as you say is fundamentally important to cosmology. You are correct that the spatial inflow concept says nothing about interaction with the aether. Spatial inflow postulates that spatial coordinates move as a result of physical space being locally sucked into matter, but that is independent of the question whether that moving space interacts with light in interesting ways.

The spatial inflow model also can be defined either with or without the concept of fundamental coordinates. Any large region of space which we adopt as a supposedly nonmoving reference frame might in turn be moving with respect to an even larger reference frame beyond our horizon. In theory, a fundamental frame could be identified if the speed of light is eventually demonstrated to be anisotropic due to Earth's movement through the fundamental frame. I'm not sure that's a mandatory prerequisite for the spatial inflow model however. The locally observed speed of light might turn out to be isotropically invariant in every independent comoving observer's frame regardless of the local inflow of space or the local movement of the Earth through a more global spatial background (substratum).

On the other hand, I should also ask, why is it unreasonable to tentatively adopt the CMB rest frame as "the" fundamental frame? Might cosmologists be averse to doing so because they fear being branded as heretics with respect to the entrenched doctrine of relativity (?) Hopefully there's a more sound reason. It would seem to violate the Copernican Principle if eventually the CMB rest frame is discovered to be moving in a specific arbitrary direction relative to some even larger frame. Although of course there could be a perfectly nonarbitrary explanation hiding just over the next horizon.

Jon

 

[Jenk]

Although I voted for the frontrunner, that GR is wrong, can I point out that the 'backrunner', with only two votes, is a better bet than one might think. It's the idea that GR is right, but DM and/or DE are not real.

GR is not a theory of everything, though we want it to be. At present it's the best theory we have, but it doesn't have to do all of cosmology as well - maybe it stops before that. There might be a combination of effects we don't know about, which GR doesn't cover, and which could make things look very different from the DM, DE picture.

 

[jonmtkisco]

Hi Stoonroon,

Benish's "gravitational expansion of matter" theory seems to be manifestly incorrect because it does not explain why a distant observer at rest with respect to a central mass would observe the path of test particles and light passing by the central mass (but not striking it) to be deflected from a straight line.

Interestingly, Tom Martin also sought to test the spatial inflow model by means of a Cavendish hollow spherical shell experiment, and failed to find the gravitational repulsion he had predicted. He claims this puts a dent in the spatial inflow model, but I'm not sure I understand his reasoning why that's so, so I'm going to study it.

http://http://www.gravityresearch.org/pdf/GRI-010515.pdf"

http://http://www.gravityresearch.org/pdf/GRI-011011.pdf"

 

[Jenk]

"Take the Milky Way in isolation… if the missing mass implied by the
rotation curve was actually HII then we would have already detected
that this was the case. You can't surround the galaxy with that much
hot gas and not notice it, the enormous bath of H[alpha] emission
produced would probably have been the first things modern astronomy
would have detected!"

Hello Wallace, I know it's been a while, but was thinking about your point the other day, and wrote to Edwin Valentijn, the astronomer who led the discovery of molecular hydrogen in an edge-on galaxy similar to the Milky way. Cosmology isn't my main field, but I realized that his reply would affect my view of how likely it is that there was a big bang, so it was worth writing to him.
His reply is below:
------
my work is about cold H2 ( T <100K) = molecular and not about hot HII =
atomic hydrogen
regards
Valentijn
----
I should also correct an error in an earlier post of mine - they found the amount of molecular hydrogen was to 5 to 15 times the amount of atomic hydrogen (not times the amount of visible matter). This was the right amount for this dark matter to be the very dark matter you seek, the DM implied in the rotation curve. It was in a very normal, average galaxy.

But the question is, do you still seek it if it contradicts big bang theory? The discovery has largely been swept under carpet. "How many times will a man turn his head, and pretend that he just doesn't see?" Dylan.

 

[Stoonroon]

Questions about dark matter and cosmology are certainly interesting and relevant for any gravity model's large scale properties. But since this thread has long been dormant, I'll chime back in with a different angle on its original question: "What will gravity turn out to be?"

The "angle" concerns a property of GR that has recently been expounded on in the International Journal of Theoretical Physics by C. Schiller (http://arxiv.org/abs/physics/0607090). That is, the existence of a maximum force in nature. The magnitude of the force is c⁴/4G, and Schiller argues that GR can be derived on the basis of the principle of maximum force. He also argues that a key ingredient of the GR/maximum force connection is the existence of gravitational horizons.

This is of interest here because it turns out that the same maximum force (c⁴/4G) can be derived without reference to GR, per se, but by appealing to only Special Relativity (limiting speed, c), the Equivalence Principle and the inverse square law. This latter derivation leads, in turn, to a gravitational model bearing some resemblance to the flow models of gravity referred to by jonmtkisco.

The space-time curvature predicted by this approach is nearly the same (within observational limits) as that of GR--except in the strong field regime. Marcus may be interested because the approach is manifestly singularity-free. And MeJennifer may be interested because, most importantly, the model is testable with a laboratory experiment.

These results are presented in a paper that has been submitted to IJTP and is meanwhile available on Scribd (Google: Scribd Maximum Force).

The paper brings out the fact that, though we usually regard GR and Newtonian gravity to be thoroughly tested in the weak field and local (laboratory scale) regime, actually, there is a huge gap. Nobody has yet tested interior solutions of either theory. We do not have empirical evidence that demonstrates how test objects move through the centers of gravitating bodies. In terms of GR, this is equivalent to saying we don't have empirical evidence demonstrating that the rates of stationary clocks go to a minimum at the center of a gravitating body.

 

[Laidback]

Since the WMAP 5 year data is now out and contains no nasty new surprises, what does everyone think about the current and future status of gravity? Please read these more detailed descriptions of the poll options before you vote! Note that these options are all basically beyond what we can know with any kind of confidence at present, but what is your gut feeling? It might be interesting to compare the poll results to what we know in 5 years (or more) time!

1) GR is the true theory of gravity and is correct for every situation where it gives a sensible results (i.e. away from singularities). Any future quantum gravity theory might explain in more detail the nature of the centre of black holes and the very very very early Universe but will leave all other GR predictions unchanged. In this case dark matter is real and dark energy is either really some energy source or a true cosmological constant.

2) As above but dark matter and/or dark energy will be shown to be a result of spurious errors either in observation (i.e. for some reason distant SN are intrinsically dimmer for some reason other than acceleration) or a result of the FRW model for GR being a poor approximation and an improved model, using GR only, explains the data without dark energy and/or dark matter.

3) GR turns out to be a poor model for gravity on large scales and a new theory is developed that explains away dark matter and/or dark energy as simply the result of wrongly interpreting the data with GR as the gravity model. This new theory may or may not be a full quantum gravity theory that also explains the centres of black holes and the very very very early Universe without producing singularities.

4) The pessimistic option. We are inherently constrained in terms of what we can ever be able to measure from Earth and therefore we will never be truly able to know whether GR+dark stuff or a new theory of gravity is a better option. Both may be able to explain the data to some degree and we won't be able to say for sure which one is correct.

5) Fence sitter option. At this stage it is impossible to have any gut feeling about the eventual outcome, all or a few of the above options are equally likely.

Note that none of the options mention any direct laboratory detection of dark matter and/or dark energy. If this was to occur that information would feed back into cosmology to support some and reject other options, so if you think this will or won't occur that can guide your choice as well.

Lets not get overly speculative, but what is your leaning at the moment?

I should point out most of my thoughts are based on what I have been educated via Electronic theory, having said that here is my stance..

My gut reasoning, relies heavily on Special Relativity Over General Relativity, and with respects to those who insist Gravity as some attractive force, I feel that is absolutely ludicrous, in fact I simply can't understand how force could ever be casually implied as some magical beckoning, and that includes magnetic and or electromagnetic inferences..

Therefore my reasoning has as "Kinetic energy AKA Photons and or electrons" have to traverse another that originates from the opposite direction, their Kinetic energy and or velocities cancel out..
For example..

let KE=width
let PE=height
let "-" equal to one PE high by one KE wide or an electromagnetic wave and or a Photon being propagated..
let " " equal near vacuum and or near zero PE by one KE wide..

now within the below quotes let's have two photons heading at C towards each other..

"- -" moment one.. Note how we have a model that is four KE wide by one PE high
" -- " moment two.. each photon is propagated towards the other at the speed of light..

" = " moment three.. where we should note our model is now only three KE wide, but it is now two PE high somewhere, I treat this as an exchange of kinetic energy to potential energy, I also treat this as an increase in density and or as a compression point to an area, and this is what also I insist - "what gravity is all about"..

I came to this conclusion by modeling the whole Universe first as a closed system.
And with the following simplistic modeling, I then have defined all the energy of our Universe as per E=Mc^2, Noting - Because the quanta of energy is simply way beyond our accounting for it all so I simply imply E=100%,

From there I divvy up my model with what ever dimensions I need to work with..

So if I portion off the universe to a 3 dimensional model which is divided into 100 cubic sub divisions of energy and all with the same ratio of Potential and Kinetic energy, and then push two cubic divisions together to merge as one, the result is by my repulsion, two or more Opposing velocities are created, to which ends up creating my model ending up as some Klein bottle and or much like a Galaxy with its obligatory Black-Hole at its core, And as we all know our universe consists of many Galaxies, so if I were to model the entire universe correctly, I would treat the Universe as a Multi-necked Klein Bottle..

Also - if I were to refer to some micro area and or what some refer to some macro area, then for each and every area with an increased density - I would refer to it as some part of a Particle from The Standard Model, which would also be treated as part of a mini Klein Bottle and or black hole in its own right by me..

In closing, I fully understand if none of the above makes any sense, as I am omitting far to much data, but its late so I am hoping my main point of opposing velocities is what gravity is all about..

Cheers,

Peter J Schoen..

 

[zankaon]

Cosmological constant, as well as Hubble expansion, are similar in the sense that they are separate additions; they are not part of GR. GR model has a 4-manifold (surface) rendition. Hubble expansion is a 3-manifold, with no constraint of velocity of light as expansion rate. The 2 descriptions giving different perspectives of the same universe. Cosmological constant of course was originally considered in order to balance off gravity, so as to be consistent with a static universe. So GR per se looks pretty good, but says essentially nothing about topology of universe.