Gravity and developments in GR after WMAP 5 year data

[Wallace]

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?

 

[MeJennifer]

My vote

GR is incorrect if it needs any kind of fudge factor such as the cosmological constant.

 

[marcus]

...
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...



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

You know what I'm going to say. Classic GR has to be wrong because it has singularities (and other reasons, like one Jenny suggested.)
GR will inevitably be replaced by a quantized version. It is a good bet that the renovation will affect predictions at large scale and low curvature---as collateral byproduct to resolving singularities.

There will be a new understanding of space time and matter. That will bring about a new perspective on things that are rather ad hoc at the moment, like inflation, acceleration etc. When we have a better understanding of geometry and matter---the fundamental DOF they emerge from---we will be able to say more clearly what DM and DE are. When we can say what they are, it will be a better time to ask whether they "really exist."

As observed effects that need to be explained, they exist (is my feeling). I don't buy Wiltshire-ian dismissal, as just some happenstance unevenness. There is something that needs deeper physics to explain. But the customary way of explaining things by developing some new particle field might not be the requisite new physics this time.
That way of explaining stuff may be getting a bit old.

 

[Wallace]

Edit: As far as I can see there haven't been votes from either of you guys registered? Is this a bug in the poll or do none of the options suit?

GR is incorrect if it needs any kind of fudge factor such as the cosmological constant.

The cosmological constant arises quite naturally in the derivation of the Einstein Field Equations, it has to be manually set to zero in order for it to not appear. It is also a very specific quantity that makes very specific predictions, not infinitely tuneable in the way that say a more generic dark energy term might arguably be. I think it's a bit much to suggest that it is merely a fudge factor. GR with a cosmological constant as a geometric effect (i.e. 'just how gravity is') is a perfectly reasonable and readily falsifiable model of gravity.

Thanks also for your input marcus.

 

[MeJennifer]

The cosmological constant arises quite naturally in the derivation of the Einstein Field Equations, it has to be manually set to zero in order for it to not appear.

You mentioned this before and you failed to convince me how it arises naturally in the derivation of the Einstein Field Equations.

For those interested here is Wallace's explanation why he thinks it arises naturally, or in this case he claims it is actually suggested:
https://www.physicsforums.com/showthread.php?t=163702

Sorry Wallace but I see nothing in your explanation how, where, or why it would arise naturally or is in any way suggested.

 

[Wallace]

I'll leave what I posted previously (as linked to above) as my explanation for now. I'll leave it to another day (and thread) to say anything more detailed. Let's not get too OT in this thread by discussing this point at length. If you consider that GR with a CC is not really GR but actually a different theory of gravity (containing an additional fudge factor) it looks like option 3 would be more to your taste perhaps? That's of course if the CC turns out to be the correct fudge!

 

[my_wan]

I was forced to vote "GR is correct but DE and/or DM are not real". Sure it merely a bet and not a statement of empirical knowledge but it's the one I arrived at very carefully.

Wrt GR being "correct" requires some qualifiers. The "extended descriptions" didn't allow a really good match to what I would have liked to choose. I think GR as presently interpreted fails to account for the full range or interactions of symmetries involves. Like the Cosmological Constant debate, issues remain in which the assumptions are not fully defined. This does not mean GR is wrong in the sense that that it must be replaced, only constrained properly. It might, however, be that an equivalent but mathematically different version is needed to help explore the assumptions. In fact such an equivalence is required if GR and QM are to be brought under the same framework.

ETA: Oh yeah. I find the idea that observations will never decide too alien a concept for my taste.

 

[MeJennifer]

If you consider that GR with a CC is not really GR but actually a different theory of gravity (containing an additional fudge factor) it looks like option 3 would be more to your taste perhaps? That's of course if the CC turns out to be the correct fudge!

A theory to me needs to be able to predict things. Plugging in constants to fit current observations is not predicting anything. Every time we discover something new the constants are adjusted accordingly. Now that should give some a clue as what they are actually doing instead of creating a theory wouldn't you agree? Dark energy, dark matter, cosmological constants, dynamic parameters, perhaps to some these things sounds very impressive, but to me it is similar to medieval angels, invisible pink unicorns or tiny green turtles. Old wine in new bags!

 

[sysreset]

I just voted. I think GR is wrong, but only insofar as it breaks down at the the extremes of event horizons and it also breaks down for extremely large scales. It is still remarkable how well it predicts observations between these extremes over so many magnitudes of order, just as it is remarkable how well Newtonian gravity makes predictions within its scope. For me, both DM and DE are fudge factors for a failing theory rather than true derivatives of observational science. In a sense, finally discovering the limits of GR is a triumph of science and a testament to our abilities to push the boundaries of our observations so far outward. The theory that will eventually supplant GR may or may not be developed in our lifetimes, but given enough time and patient observation, it will be developed by humankind.

 

[Wallace]

A theory to me needs to be able to predict things. Plugging in constants to fit current observations is not predicting anything. Every time we discover something new the constants are adjusted accordingly. Now that should give some a clue as what they are actually doing instead of creating a theory wouldn't you agree? Dark energy, dark matter, cosmological constants, dynamic parameters, perhaps to some these things sounds very impressive, but to me it is similar to medieval angels, invisible pink unicorns or tiny green turtles. Old wine in new bags!

Are Maxwells equations like medieval angels since they need you to fit \epsilon_0 and \mu_0 to data? Likewise what about particle physics? There are more free parameters set by data alone in the standard model than you can poke a Feynman diagram at! What about that charlatan Newton, sure gravity goes as 1/r^2 but you can fit that to any old G that you couldn't predict before you do the measurement.

I agree, as I stated in previous posts, that allowing dark energy to have arbitrary properties gives it too much freedom, the point about the CC is that a model with this non-zero has a very particular form that does not have infinite freedom. Sure you don't know the value of one parameter, but changing this value, like changing G in Newtonian gravity doesn't give you infinite freedom. The data could very easily suggest that there is no value of the CC that fits, in the same way as say non-keplarian orbits would tell you that Newtonian gravity didn't work, regardless of the value of G.

To turn the tables though, what do you think people should be doing if the current method doesn't suit your taste? Even if dark energy is a complete furphy, by measuring carefully what its properties are that gives us a way of frameworking new data. If a new theory comes that says 'if you you thought dark energy existed, it would look like this' and that matches the measurements then the new theory looks a goer. If you hadn't gone after the dark energy properties in the first place though, you'd never have progressed the theory.

There were plenty of very good astronomers carefully calculating the periods of epicycles that allowed Copernicus to realize a better model. Without the data, which was taken with the motivation of a different model, we would never have improved the theory.

 

[rbj]

A theory ... green turtles. Old wine in new bags!

(doesn't matter)

Jennifer, i thought you dropped off of the edge of our flat world!

it's good to see your presence again.

bestest,

 

[Garth]

Classic GR has to be wrong because it has singularities

I really do not have a problem with singularities in GR, we may not like the idea but that doesn't make their existence impossible.The standard \LambdaCBM theory fits the WMAP etc CMB data very well. I make just one comment; the theory has at least six free parameters that are adjusted to fit the data. If you have enough free parameters you can make anything fit. The evaluation of these parameters is theory dependent, change the theory and their evaluations change as well. A modified theory with a different set of parameters might also be made to fit.

On the other hand there is the question of a quantum gravity theory. When such is discovered and tested I cannot imagine that GR will be not be modified in the non-quantum regime in some way.

Anomalies such as the Pioneer Anomaly and Flyby Anomalies may already be indicating our present understanding of gravity needs such modification.

Also there may be an age problem at high z, where there seem to be some evolved structures...
This may indicate that we do not understand the early expansion history of the universe very well, possibly DE acts in the BBN epoch thus elongating the time of nuclearsynthesis. This would lift the restriction on baryonic density.

Once the hypothetical non-baryonic particle is discovered in the laboratory, its properties measured and found to be concordant with cosmological constraints then we will know what we are talking about. Until then an open mind must be kept.

There seems to be evidence of the existence of something out there, MOND type theories keep getting more complicated to fit new data, which is the sure sign of an epicycle. However the same can be said for the old FWL cosmology with is invocation of Inflation, DM and now DE, all at present undiscovered in the laboratory.

DE is more difficult to pin down. I agree with Wallace that it could be the cosmological constant. Note in this case there is no actual DE, no quintessence or whatever, it is just the way gravity behaves, attractive at short ranges and repulsive at cosmological distances. And yes, MeJennifer, GR is such a woolly theory that it cannot predict what value the CC ought to take! It was this inadequacy of the theory that led relativists over many decades to set the constant at zero to save our embarrassment.

Unfortunately you cannot distinguish observationally between the CC and false vacuum energy, which has the same effective equation of state. The problem with false vacuum energy density of course is that quantum expectations are ~~10¹²⁰ times too large!

So my vote? I do not have an option in the poll.

I say GR will be modified by a future quantum gravity, the local predictions of which would also explain DM and DE at galactic and cosmological ranges.

Just my two pennyworth...

Garth

 

[MeJennifer]

To turn the tables though, what do you think people should be doing if the current method doesn't suit your taste? Even if dark energy is a complete furphy, by measuring carefully what its properties are that gives us a way of frameworking new data. If a new theory comes that says 'if you you thought dark energy existed, it would look like this' and that matches the measurements then the new theory looks a goer. If you hadn't gone after the dark energy properties in the first place though, you'd never have progressed the theory.

In the case you might misunderstand me Wallace, I think that cosmologists do excellent, admirable and useful work in the measurements they take, interpreting them, and as you wrote, frameworking them. But do we see any theory development? Don't instead we see GR + various fitting mechanisms presented as new theories?

 

[Wallace]

It could just be a case of different meaning of the term 'theory'. There are many different physical theories that suggest what dark energy might be (far too many to list!), so instead of treating them all individually, dark energy is usually parametrised by some convenient simple function (this is probably not news to you I guess), a common form being to parametrise the DE equation of state as w(a) = w_0 + (1-a)w_a. This is certainly not a 'theory' of dark energy, just a convenient way to get a handle on the basic properties of it. I don't think anyone presents such a thing as a theory as such.

I think the reason that we hear so much about the parametrisations rather than actual micro physical theories (even though plenty of them get suggested in the literature) is simply because there are too many theories that look far too similar. By fitting generic w(a) parametrisations however, we can rule out entire classes of theories, and then examine in more detail those that are left. At least that's how the community is thinking things will turn out in the next few years, but it remains to be seen what the data says and no doubt there may be some surprises.

So I think the problem is not too little theory development but too much, far too much for anyone to be able to consider every new idea individually, hence the focus on parameter fitting, even if those parametrisations are admittedly not actual physical theories.

 

[MeJennifer]

I think the reason that we hear so much about the parametrisations rather than actual micro physical theories (even though plenty of them get suggested in the literature) is simply because there are too many theories that look far too similar. By fitting generic w(a) parametrisations however, we can rule out entire classes of theories, and then examine in more detail those that are left. At least that's how the community is thinking things will turn out in the next few years, but it remains to be seen what the data says and no doubt there may be some surprises.

Good point.

 

[CosmiCarl]

Fudging

A theory to me needs to be able to predict things. Plugging in constants to fit current observations is not predicting anything. Every time we discover something new the constants are adjusted accordingly.

I just voted, and I mostly agree with MeJennifer's words, above. But I do not agree when she says a theory with ANY Fudge Factor is bogus. It is the MAGNITUDE of the fudging that bothers me.

Certainly, GR successfully predicted Gravitational Lensing and Time Dilation, BUT, when observations to date suggest ~70% of the universe is stuff we do not understand at all, I feel very uncomfortable calling the theory "right."

The Methodological limitations that led to DM and DE are what bother me the most of all.

I also agree with Garth: I see no fundamental problem with a theory having Singularities, per se. At least there is an explicit recognition of instances where the theory does not apply.

And the Pioneer Anomaly seems to me to be a VERY important clue. Has anyone explored how that percentage "error" compares with the numerical percentages that observation deviates from theory in other cases?

 

[Jenk]

I just arrived, hello, voted that GR is wrong, and will be replaced by a new theory sooner or later, without DM and/or DE.

I think it'll turn out that DM is real, DE unreal. An interesting question is: if DM was discovered, and it fitted very well with some of our theories but not others, would we abandon the theories it didn't fit with? This is a barometer for whether an idea is a fix up factor or not.

What if DM was discovered but it contradicts big bang theory - would people accept it? Well... it happened in 2002, and was widely ignored. Two Dutch astronomers found HII in an edge-on galaxy, it was difficult to detect, but they did it. it was in the right amount, I think about 10 times the visible mass. 5 - 15 times was needed. But that goes against big bang theory, so out of the window went their excellent work - for many people anyway. I guess that means DM is in some ways a convenient tool only.

 

[Wallace]

it was in the right amount, I think about 10 times the visible mass.

By definition if something is detected in a telescope it is visible!

5 - 15 times was needed. But that goes against big bang theory, so out of the window went their excellent work - for many people anyway. I guess that means DM is in some ways a convenient tool only.

Dark Matter cannot be HII since if would have seen it long ago in many places in the Universe and we would never have arrived at the idea of dark matter in the first place.

 

[Jenk]

HII is invisible and very difficult to detect. It's dark matter, but it doesn't fit with standard big bang theory

 

[Wallace]

HII is indeed difficult to detect in the quantities that it occurs in the Universe. If however, the enormous amount of extra mass needed that lead to the postulation of dark matter was in fact HII, then in such vast quantities and concentrations it would have observable effects that we simply don't see.

In any case, HII by definition is warm (well pretty hot actually) whereas dark matter must be cold. That is, if there really is stuff out there that really explains the data by being a massive and dark then it must be cold. HII is far too warm to be dark matter in the sense of what is needed to drive structure formation. If you make dark matter too warm it washes out structure and you wouldn't get the agreement in the data that we see for the cold dark matter model.

 

[Jenk]

Those points you make are relevant if standard big bang theory applies. But if it doesn't then of course it could all be very different. But there's still the missing mass needed to make galactic dynamics work, and that can be HII without standard BB theory.

 

[Wallace]

No. Take the Milky Way in isolation. Let's not care about any other galaxies or how the Milky Way formed, so we remove any notion of the Big Bang. In this case, 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! You don't need to include any Big Bang assumptions to come to this conclusion.

 

[jal]

After looking a lot of papers …. I conclude that we need more data and will probably change our theories.
See what I looked at
https://www.physicsforums.com/blogs/jal-58039/a-lambda-dark-energy-vacuum-energy-question-1350/
A LAMBDA, dark energy, vacuum energy question
----------
jal

 

[jonmtkisco]

Hi Wallace,

I am surprised that so many people voted against GR. Maybe it is that spirit of questioning that keeps people interested in this Forum!

I voted against GR reluctantly. It currently provides the most robust and reliable description of gravitation, including the derived Friedmann equations and Schwarzschild solution. On the other hand, it leaves open a can of worms including DE, DM, and matter inhomogeneity, as well relying on as yet unproven but critical concepts such as spatial curvature. GR also strikes me as inordinately complex. Hopefully Occam's Razor can eventually help us derive something simpler.

My current inclination for an alternative to GR leans in the direction of the theories that provide a physical description of gravity as constituting dynamic inflows of space towards matter concentrations. That is, matter acts as a localized "sink" which absorbs space, thus moving nearby objects closer together. These theories posit that localized matter sinks can be adrift in more "global" currents of space representing larger more distant gravitational sources, or perhaps local peculiar movement with respect to a fundamental reference frame. At least with respect to nonrotating masses, these theories posit that the background geometry of space is flat, Minkowski. The math can be derived from GR and is mostly consistent with it, as well as with the observational predictions of GR. But the math is much simpler than GR. I understand that simpler doesn't mean more likely to be correct, but other things equal, simplicity is a virtue.

I expect that many people have seen papers on the subject of spatial inflows. Two in particular that appeal to me are:

http://http://arxiv.org/PS_cache/gr-qc/pdf/0411/0411060v2.pdf" and

http://http://arxiv.org/ftp/gr-qc/papers/0006/0006029.pdf" . (Part II of this paper continues the theme).

I would like to think that spatial inflow models can directly replace the Friedmann equation with a concept that the instantaneous Hubble expansion rate equals the "immediately prior" expansion rate minus the (nearly constant over time) volume of space "absorbed" instantaneously by gravitational matter sinks. Following this road, perhaps a heuristic can be developed to directly connect the causations of cosmic expansion and gravitation.

Perhaps spatial inflow models also can eliminate the need for DE. I note that R.T. Cahill makes such claims, but his methodology has been critisized and does not seem to have drawn support from the mainstream physics community. It's fair to say that the whole concept of spatial inflows hasn't drawn mainstream support.

Jon

 

[MeJennifer]

Note that Hamilton's river models are not in contradiction with GR and are very illustrational. But while Hamilton's river models work in static and even stationary spacetimes they do not work in non stationary spacetimes.

 

[Chronos]

The science [observational evidence] robustly supports GR, dark matter and dark energy. The competitors have the burden of proof.

 

[my_wan]

The science [observational evidence] robustly supports GR, dark matter and dark energy. The competitors have the burden of proof.

I will not attest to robustness but I would certainly agree that competitors have the burden of proof..

Get used to those rules guys, they are your best friend and worst enemy

 

[Jenk]

When you have an unsolved mystery everyone has the burden of proof. Is anyone really saying that GR does not have to prove DM and DE?

 

[Haelfix]

GR has uncountable many experimental successes and correct predictions, so yes the competitors have the burden of proof and not the established theory.

 

[Jenk]

The idea that we can have one established theory contains a hidden assumption. It's the idea that we know enough to do that. A few thousand years ago the Greeks did the same thing - they formed theories far too early, while making the assumption that they were in a position to do so. At that stage it helped them on the way, but we know with hindsight that they needed far more information.

Thirty years ago there was a good argument for making GR the established theory, but not now. Now it should just be the best theory. Decades of searching for DM, and now having to fix things up with DE. Why have an established theory at all? That kind of attitude might hold us back.

 

[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.