If the Speed of Light changed, would we even notice it.

[Qfwfq]

Essentially, gravity is no more than refraction.

The refractive index is determined by how much energy the region already contains.

 

I think that makes sense

It does make sense qualitatively but it would remain to be worked out in detail.

 

Qualitatively, there's no doubt that, in GR, a suitable coordinate transformation would make the local change in c equivalent to some curvature of space-time. I haven't worked out if or how well it would work for the gravitational fields that we actually observe, i. e. the Schwarzschild solution (at least outside the Schwarzschild radius). This would be the first step before proposing an "optical" alternative to the geometric interpretation.

 

To work it out exactly, I would have to shake a few cobwebs out of my memories of these things.

[paultrr]

You can get an approximation of such out of using a PV(Polorized Vacuum) approach, see Hal Puthoff's work(UT Texas). However, with such a model the changes in C are brought about by changes in vacuum conductance values. I have a friend who redid Hal's idea somewhat since Hal's version does not work well with say a Blackhole state, and found his own model rather tended to match GR when it comes to those states. Hal has a variable when it comes to spacetime curvature. Todd used a strickly flat spacetime case letting the conductance changes alter spacetime from flat which I think is why his tended to work better in extremal cases.

[Qfwfq]

Interesting stuff Paul. With a bit of googling I found that VSL, mentioned by you here, is Variable Speed of Light which seems to mean this idea. The other day, googling just VSL gave me a mass of unrelated results but googling "Variable Speed of Light" as a phrase, gives plenty of stuff on the topic.

 

I even found a ref to a pubblication by a certain Fernando de Felice. I'm not quite sure if it's the professor F. de Felice that I know of, who used to hold the GR course at Padova. Although I followed the course and passed the exam with others, I'm sure he is nobody's fool. Funny, yesterday I had even thought that, if I were around the department when it's open, I could ask his opinion about the idea! I'm not there during the week but it's not necessary, if he's the one!

[paultrr]

I do not know him personally. However, I think they are one and the same if memory serves me.

 

There are a few different parties in the VSL camp. Guys like myself think C varied only at the start of creation. Some see C as varying slowly over time. Some see other positions. There is also an argument about weither or not this implies other constants have varied. A lot of more recent articles argue that the process by which C could vary works in a fashion where those constants, with the exception of perhaps say vacuum conductance are not variables. I've tended to find myself in that camp simply because I still see no strong evidence out there for Lorentz symmetry breaking. However, I've read a few discussions on this of late that have me questioning that position a bit. Nothing of a clear cut case. Just some minor observations on old experiments and some of the probe data we get back from time to time. They are not as Null as we tend to think or suppose they are, at least on first look. I think most honest VSL proponents agree with the main of Einstein's relativity. Its more the fine points we sometimes argue on a bit.

 

Now the guy who started all this view(Jose) I sometimes wonder just where he stands on the subject and how Smolin, his friend, has not come out stronger one way or another.

 

You might find it funny with all the God/evolution debates that arise on this forum that the Creationists are some of the first to point to such findings and say they now have scientific proof our models are all wrong. Personally, I could do without their nods of agreement. It does nothing for the theory or the idea that's good in my book any more than Jose's cutdowns on the mainline establishment do.

 

Basically, the VSL camp could be wrong and it could be right. The idea is to push and test what we think we know to discover new things about this universe and to improve our best theories as much as we can. It was never ment to create the kind of diversion into different camps that some like Jose favor. I know old mainline thought makes it hard to accept such on first review and I understand Jose's position that if you cannot argue within then argue the case without. But to me that serves no lasting purpose and only tends to turn people off. To me real scientific research will find the answer one way or another.

 

I had avoided this conversation for the most part because actually I agreed for the most part in what you where answering this with. The PV modeling is just a suggestion because I found it in a related case to help somewhat see things a bit different. Some of us who have researched a bit along simular lines to the NASA BPP program found that version of modeling one way to study ideas like wormholes and say Alcubierre's warp drive idea. I still perfer the GR way of doing things because I'm not certain any of the current versions of PV out there really have the correct picture. But as something to get a grasp on how things could change and everything still look the same it does work. I've used that model myself even in a few articles I did. I know one researcher who's more into math who favors such also. He's even gone so far as to get an article or two actually published in regular Journals using that modeling. I'm not that far out on the limb yet to say its a fully correct model.

[paultrr]

I noticed in one post you did how you mentioned you still had hope there might be a way around C when it comes to space travel. When I first turned over to the VSL camp I actually did a lot of the articles I did to help people try and think outside the box a bit in the hope that perhaps one day someone would find that kind of solution. I've actually never thought we have the knowledge or the tech yet to achieve such. But it would be nice to know that someday we will since I'd like to see my own children's children go out there an explore this universe more fully. I also suspect that there is an answer in all this debate that will help us come to a better understanding of nature and the processes by which all came together in the first place.

 

I got a complement a bit back that a lot of us where there pushing the early boundries which to me was far better than any Nobel prize. I've seen simular thoughts and ideas showing up more and more out there which to me is a good thing. Unlike a few of my friends I'm at that age when I enjoy the research and yet, have no lofty dreams of some big invite either. One friend I know thinks the invite is the best way to get things done. Perhaps he's right. Personally if I got the invite, actually did get one and turned it down, I'd more enjoy working at some astronomy observatory or perhaps being on the research crews at NASA than anything else. Both places push the boundries of our knowledge of the universe which is what I think is the most important aspect.

[WebFeet]

Paultrr & Qfwfq,

I'd just like to say how informative I found your posts.

 

Thanks for the pointer to PV, a very interesting read, although somewhat over my head.

 

I've actually never thought we have the knowledge or the tech yet to achieve such. But it would be nice to know that someday we will since I'd like to see my own children's children go out there an explore this universe more fully.

 

I like to think that we have all, or most, of the pieces to this jigsaw, we just don't know what the final picture should look like. Unfortunately this is complicated by additional pieces that are for a different jigsaw, but that we are still trying to use to complete ours.

[Qfwfq]

I tried a brilliant idea and I found that it's him, but this topic doesn't seem to be in his current research interests. I wouldn't email him or phone him about this topic. http://www.pd.infn.it/~defelice/

 

I think most honest VSL proponents agree with the main of Einstein's relativity.

Actually, I would see it as an alternative to the geometrical interpretation, not to the whole of GR at all. As we know, the geometric interpretation is considered verifiable only by knowing the global topology of the space-time manifold. The distinction between it and the optical interpretation could of course be made if there is a measurable difference not yet detected. I wonder just how the two would compare.

[WebFeet]

This optical interpretation is not just restricted to GR.

 

The same principles can also be applied to SR.

[paultrr]

That's a good question in itself. Generally they predict about the same. But some recent data and ideas made me suggest to a friend who uses it a lot to try seeing if some of those new data findings and ideas would be supported by the PV model.

 

And yes, it has implications to SR itself.

[WebFeet]

Gravitational lensing should cause differences, albeit very small ones, in the refraction index at specific positions around a large mass.

 

This, as far as I'm aware, is not considered by GR.

[paultrr]

http://socrates.berkeley.edu/~tatebe/sl/Strong%20Gravitational%20LensingB_files/frame.htm#slide0008.htm

 

Magnetic Lensing near Ultramagnetized Neutron Stars (Make Corrections)

Mon. Not. R. Astron. Soc. 000, 1-12 (1998) Printed 15 January 1999 (MN L T E...)

 

http://arxiv.org/abs/physics/0409124

 

http://arxiv.org/abs/astro-ph/9901376

 

http://www.spacedaily.com/news/blackhole-05m.html

 

http://www.aas.org/publications/baas/v31n2/head99/98.htm

[WebFeet]

There would appear to be number of alternative theories as to the mechanics behind the refraction, ranging from polarization to extended atmospheres.

 

That the results of VSL/PV agree with those produced by GR is a big step forward, even though the two should be mutually exclusive - GR's basic postulate that VSL is a non starter. But then again, is VSL a viable alternative only because the numbers come out right?

 

Although PV provides comparable results to GR, it does so at the expense of adding a level of complexity by regarding the vacuum as a polarizable medium. That whatever this medium consists of can be polarized, I don't dispute, but is it a necessity?

[paultrr]

It takes far more than numbers coming out for something to be valid. Any theory has to be backed up with observational/experimental evidence for support. At the present time there are very strong constraints from observational evidence on Lorentz Symmetry breaking, as proposed by certain String models, by some VSL modeling, etc. As such a lot of these basic, sometimes termed "Toy models", tend to be ruled out at the present. Its sometimes raised that there is still a debate going on over weither C might have varied in the past after the period of inflation. This is true. However, the observational evidence for such is rather highly debated still. Its also sometimes debated based upon that same evidence weither the Fine Structure Constant might not have varied.

 

I can only say this much. GR has no actual built in velocity of light. SR does have one. But GR was designed to supplement and complement SR. Generally we always use a value of 1 for the speed of light. What we look for in observations is certain signatures that do not fit the 1 case. Looking for these, especially if say PV was correct, is a lot harder than one would think. Simply put, PV generally with the exception of say Blackholes, yields the same answers as GR. The curvature like effect is a product under PV of changes in vacuum conductance. Those changes can exactly match curvature differences out of GR. So there would be no major observational evidence of such.

 

There is something we call a cutoff on energy levels thats derived using relativity. You might have heard of it before. If we found hard evidence that there are photons out there showing energy way above that cutoff then we'd know something about C is a variable. That's the kind of observational evidence at the present that is the center of all the debate. Most of the research at the present relies upon SR/GR. The other somewhat equal to GR models are mostly used to get a better idea on how our universe could possible work and revolve more closer to the whole search for quantum gravity than anything else.

 

One other model being considered and articles being done on is Double Special Relativity(DSR). In this there are two fundamental limits. One at large scale with C and one at the Planck scale. In someways DSR is very much simular to the proposed ideas of two different frames of reference. There would be some small scale markers that we could possible observe on this as far as the standard DSR modeling goes. The dual frames of reference(Model I perfer) signature would be exactly the type of quantum information exchange that one witnesses with quantum entanglement. So here there are again no major observational evidence difference to search for except in the area of perhaps playing with entanglement more and testing its limits of quantum information exchange. By quantum information I refer to particle state qualities versus say sending a direct message of normal information through. I still keep an open mind to that second form of information exchange. But at the current time the experimental evidence seems to suggest otherwise.

 

Basically, a dual frames of reference model is simply a quantum interpretational model that incoporates SR/GR into it. Thus, why one ends up with the same spacetime as GR. Some Authors have assumed this external frame with a higher value of C would allow for superluminal travel. But when one considers the two frames together one discovers the timeline of the second frame is no different than our own. Its just a very small compressed version of time here. As such, even if we could figure a way into that spacetime one cannot beat light in relation to here simply because even though one moves faster there you are still going into the future here. At the best case situation such travel might allow one to equal C here and it could allow one to contruct say a warp field or something akin to such ahead of a craft's path if such jumping over tech existed. But the general idea of a hyperspace or alternative frame travel as some like to picture it simply will not work to get around C. The reason is such models have that limit already built into them.

 

Now, none of this means a No go for other possible universes where such may be possible. Biggest problem about all of this is other universes really is a big unknown at the present. By theory they could exist. But at the present we really do not have any solid observational/experimental evidence that says they do. Its mostly just theory at this time and theory we think we might could begin to find evidence either for or against in the future.

 

The best safest position at this time is there is no solid evidence out there at the present that Einstein was wrong in any way. There is some minor evidence from observations that has raised the question of how constant C is. If this minor evidence proves out and if we find further evidence it still would not translate to Einstein being wrong. It would simply mean we need to modify a bit of the theory on such almost the same as Einstein modified Newton. At that point I think myself and a few other VSL proponents tend to differ a lot from Jose and his camp.

[Qfwfq]

That the results of VSL/PV agree with those produced by GR is a big step forward, even though the two should be mutually exclusive - GR's basic postulate that VSL is a non starter.

I disagree. I continue to see it in terms of a general coordinate transformation between the geometric interpretation and the optical one. Paul appears to be of this opinion too, where he mentions "the most honest" VSL supporters.

 

But then again, is VSL a viable alternative only because the numbers come out right?

Essentially, yes. If they don't give exactly the same predictions in every case they are experimentally distinguishable; sooner or later it would be possible to discriminate between them. Otherwise there is no more reason to "believe" in one than in the other, which of course works both ways.

[paultrr]

The only way I know of to test say PV versus GR is on smaller local scales. PV would predict we may be able to alter the vacuum conductance locally to allow for FTL conditions. In general, using EM theory there are two values that stipulate the velocity of light in a vacuum. The index of refraction, n, is defined as being the ratio of the speed of light in a medium to the speed of light in vacuum. Dielectric displacement = electric field strength * permittivity. These values also control the speed of light in any medium. Under PV it may be possible to change these values so that a region of local vacuum has a higher velocity of light. The how to do just that is actually the biggest question needing to be answered before any tests on this can be done. The problem is how does one alter what is part of the Stress Energy Tensor. Outside of Casmir effects which are artificially induced and very short range there is not much out there yet on how to do this. The whole idea is sometimes called engineering the zero point field. At the present, though based upon theory, we simply do not know enough yet to really achieve such as far as testing PV goes.

 

So that has left the whole subject rather in limbo. And it is correct that in most ways the two really are the same. What a few of us are trying to see is if there are some small differences we could look for observational evidence on.

[WebFeet]

Essentially, yes. If they don't give exactly the same predictions in every case they are experimentally distinguishable; sooner or later it would be possible to discriminate between them. Otherwise there is no more reason to "believe" in one than in the other, which of course works both ways.

 

Is one of the reasons that proponents of VSL accept the results of GR due to the fact that Relativity is a Reference Frame based theory, where as VSL would not be ?

 

VSL should not require a reference frame as all results would be absolute values, as for GR/SR, they are Relative values. There is no reason why the two theories cannot reside alongside each other as they should produce exactly the same results.

 

Relativity vs Absolutivity

[paultrr]

All VSL boils down to is that somewhere in the history and full timeline of this universe that frame of reference has changed. We tend to accept both SR/GR simply because as most decent scientists agree there is strong evidence it is correct as far as the model goes. Einstein never really said or implied that a frame of reference could not have another value for C. In fact, while air itself is not a vacuum, in its frame of reference light travels slower than it does in a vacuum. Its still considered the local speed of light in either case. But the the ruler one uses to measure by has changed with the two different frames or mediums in this case. What Einstein implied was that in the vacuum C is constant. But if the vacuum has ever varied or does vary from one place to another then the constancy of C may or may not hold.

 

One time period the vacuum was not constant or in the same condition it is commonly held to be today was during inflation. What the value of C was during inflation actually depends upon a lot of things only part of which our bests theories to date can begin to answer. But a false vacuum state decaying into a stable one is a different frame of reference decaying into what we tend to observe is the frame of reference today. So in general C did vary if the model of inflation is correct at the very least for the first fractions of a second of creation. After that the evidence either way is still out.

 

Now none of that above violates relativity at all. I've not actually taken the position that an inflating vacuum is the same frame of reference we use at present. So I'm not stating SR is wrong. So the two being exclussive of each other is not the case. Its still not the real case even if C has slowed down over time even after that point. You'd still be discussing an altered frame of reference from the one SR relies on. Still no real argument with SR or Einstein, except perhaps that C is not as constant as we sometimes assume it is. So if SR still generally holds why would one have to abandon SR or GR for that matter. Both would still work either way.

 

Yes, we have on the surface what appears like an issue with hard Lorentz Invariance. But if you break down the timeline I think in each timeline point one would still find that Lorentz Invariance still holds in each period. Its only when you try and compare all the periods together that a problem arises. The problem is actually just a ruler or measuring rod change over periods of time. You can still do a proper comparison and one still has casuality in place. The real problem is little different than comparing travel times for photons in air with those in a vacuum in the first place.