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

[paultrr]

I will mention one major exception on this. Some of the different string based possible lorentz symmetry breaking predictions might if ever detected constitute something is very missing in the SR interpretation. But generally speaking SR and VSL can coexist very well as far as modeling goes. They really do not exclude each other as much as some think they do. The first example about the inflation period is one example where they actually complement each other well. Then it simply translate to a very expanded lightcone shrinking over a very short period of time to the lightcones we have today. The second point of view(C has varied over time) is a picture of many different seperate lightcone states all eventually narrowing down due to changes to the one we observe at present. Casuality has remained the same in either case. Its just the speed of casuality that has altered with time. No odd boil time traveling effects to worry about. We're not talking tachyons here in any of this. It's the frame of reference itself that has altered in all these cases.

 

Also as mentioned, outside of the inflationary period the rest is still very subject to debate at present. The only part I personally hold to is the inflation period. As for the C has varied with time. There is some minor evidence for it and a lot of ongoing argument of that evidence at present. I also find no solid evidence out there yet for any Lorentz symmetry breaking at all. If anything a lot of modern research has placed some very hard constraints on such.

[WebFeet]

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.

There is a third alternative to VSL and GR.

 

The Speed of Light is in direct relationship to the refractive index of the medium that it

is travelling through. When light moves to a region of space that has a lower refractive

index, its velocity will increase. The refractive index is directly related to the permeability

of space, in PV, which is taken from Maxwell's work on electromangetic fields.

The refractive index varies dependant on the amount of energy present in any particular

region of space.

 

So what happened during inflation? At the outer edges at least, there would not have been

energy present. The effective refractive index beyond the leading edge would have been zero - absolute permeability. This would put the velocity of light at that point as infinite.

 

That scenario still applies in our frame of reference.

 

We accept through GR that Space is compressed in a strong gravitational field. Through PV

the view is that the energy density has increased.

Both these views point to a reduction in the distance between chunks of energy. The

distance between these chunks is precisely the same scenario as the leading edge

during inflation.

 

So, the third alternative is that the Speed of Light is infinite. Its velocity is only tempered

when encountering a region of space with a higher refractive index than zero, ie a region where energy is present.

 

This alternative would still be in line with both GR and PV, but also provides a very simple mechanism by which the velocity of light is determined.

[paultrr]

One PV model that I did a short series of Cern articles on starts with a near infinite condition for C and slows down, depending upon which side of the argument on is on here to either its current known value or something slightly higher than present. As to the outer edge personally my own article did not address such. If one followed the general PV type modeling of inflationary events the outer boundary/no-boundary might not be the way you are thinking simply because with such a model its spacetime as we understanding it that is expanding. As such, even though the vacuum conducatance is varying swiftly over time its the whole birthing universe that would be undergoing this change. In general, there is no real boundary to the universe at all. At least for those of us who subscribe to the finite and unbounded view point. So actually to my knowledge no one has ever considered the model with an actual boundary.

 

To get a bit clearer idea on this. At T=0 we have hyperspace, which for all intents is near infinite in expanse. Our spacetime arose inside of hyperspace under this idea. As it expanded hyperspace collapsed till eventually it was smaller than the Planck scale. Inside of hyperspace the value of C is different than here. This has never changed with hyperspace and it still applies. But in our spacetime as the vacuum decayed from a false vacuum state into a stable one the value of C slowed down drastically in fractions of a second. What was changing was the stress energy tensor itself. This, when you take the CMB evidence into account, shows us that the transition at least during those few brief fractions of a second was nearly uniform across the whole expanding universe. That does not rule out small local differences. It simply says that as a whole the medium was all undergoing the same general change at the same time. In this case, unless you count the Planck scale as a boundry of sorts between our spacetime and hyperspace the normal aspects of conventional BB theory tend to apply. The Universe was what was expanding and as such there really is no outside the universe to have a boundry with. If there was a boundry then its possible that such a region would have an infinite speed of light. However, speed there or velocity does not actually apply given that such a state would have no energy begin with which to have travel or transfer from one point to another given that such a space would be empty and devoid of points of reference to begin with. Being that the case then what's the use in the first place with an outside region to have a boundry with?

 

But remember something here all of this is theory. Its just as simply to think in terms of the stress energy tensor as changing during inflation in the first place. Either way one gets C having varied at some point in the history of this universe. The reason I employed that hyperspace model was based upon an equation proposed by some Dutch researchers which after looking such over lended itself not only well to a PV perspective, but also to account a bit for the whole inflationary period under such a model and it lends itself well to the idea of compacted regions smaller than the Planck scale right out of string theory. Actually, I could well term that model a toy model since there are a lot of details that one would have to work out before anything concise could be established. I'm still looking into that model as time allows to see if there might be certain signatures of such a model one could test the idea with.

 

In general, I started playing with that model in trying to answer an old friend's proposal on hyperspace travel. To get a real picture of what he was trying to show was possible one needed to picture how this type of hyperspace could come about. What I discovered was that even if we assume that C is nearly infinite there it still did not provide a way around C as far as travel times here once one returned where taken into account. But his idea, one he borrowed from some others, did seem to solve some quantum effects hard to fully interpret. There are actually two choices on the C in hyperspace issue. It may have slowed itself or it may have stayed nearly infinite.

[paultrr]

.

 

We accept through GR that Space is compressed in a strong gravitational field. Through PV

the view is that the energy density has increased.

Both these views point to a reduction in the distance between chunks of energy. The

distance between these chunks is precisely the same scenario as the leading edge

during inflation.

 

So, the third alternative is that the Speed of Light is infinite. Its velocity is only tempered

when encountering a region of space with a higher refractive index than zero, ie a region where energy is present.

 

.

 

Yes and no. Gravity simply is curvature under GR. Its not that things do not get compressed in say high gravity fields. They do. But boil it all down matter/energy bends or curves spacetime and the curvature of spacetime tells matter/energy how to move.

 

Outside of our spacetime may or may not exist. There really is nothing little beyond human perspective on things at the present in the way of support for anything outside of the universe. What the speed of light if any would be outside of the universe is a matter of conjecture at best. In some ways, at least as far as science goes the universe is what there is to study. Anything outside of the universe is beyond our ability to really study. The hyperspace my own model dwelt with is actually part of this universe. As such, while there would be a boundry there and both regions would make for dual frames of reference you are still talking about our own spacetime as a whole. As such small scale effects concerning that region could be studied, at least eventually. In short, most scientific modeling on this has no explination or need for one to explain what spacetime expands into. Spacetime is all there is to begin with.

[paultrr]

I might add that with the general multiverse idea there are multiple spacetimes existing all at once. All these seperate universes compose what one might term a superspace with many subspace manifolds. In some models, they all float in a hyperspace of sorts. As with the sometimes mentioned idea of bubble universes colliding, etc. This type of hyperspace is a seldom defined kind of spacetime different from the one my own model was using. What actually changes in the model I used was the Planck scale itself. This type of model does not involve real mutiple universe at all afloat in some undefined hyperspace region.

 

However, the multiverse idea has its own support and supporters. I generally tend to think that model may actually be correct. Let's say that with best case my toy model was mostly correct about the early on period here. One could then speculate that other universes evolved this way also. The simplest way to understand the hyperspace then that exists between bubbles of spacetime would be something like an anti-de Sitter spacetime. But each universe would then have a domain wall between that hyperspace and their own spacetime. Yes, a domain wall could be termed a boundry. For conditions at the boundry there are actually plenty of explinations out there on domain walls to go by. Some can be repulsive and some can be attractive to each other. But the picture is still one of a larger superspace composed of smaller subspaces with that type of hyperspace being its own subspace within that composite picture. One still can only speculate at present on the conditions inside of that type of hyperspace region. Within each domain wall, say with our own, the rest on the start of the universe would still apply.

[WebFeet]

Yes and no. Gravity simply is curvature under GR. Its not that things do not get compressed in say high gravity fields. They do. But boil it all down matter/energy bends or curves spacetime and the curvature of spacetime tells matter/energy how to move.

GR has no causal mechanism to generate the curvature of spacetime other than a divine command. As you've said, boil it all down matter/energy bends or curves spacetime.

And the Speed of Light it is taken as a fundemental property of spacetime, for the same reasons.

 

If the speed of light is infinite, then the mechanism that defines how we perceive the speed of light can be determined. The energy in the universe does not need to rely on a third party mechanism, it is the mechanism.

[paultrr]

First off, devine commands are outside of science and are not scientific. I also would say that when scientists refer to the stress energy tensor of spacetime there are more than one aspect to that tensor. But, third party mechanisms rather implies the idea of an external force or cause which is again not scientific at all, unless that external cause is something that results from other natural effects say like those encountered under the Randall-Sundrum model where gravity is weak here because its stronger in other dimensions. In that case, its still gravity being weak here because its source is not local. Even there there is no third party mechanism implied or some devine act.

[WebFeet]

First off, devine commands are outside of science and are not scientific. I also would say that when scientists refer to the stress energy tensor of spacetime there are more than one aspect to that tensor. But, third party mechanisms rather implies the idea of an external force or cause which is again not scientific at all, unless that external cause is something that results from other natural effects say like those encountered under the Randall-Sundrum model where gravity is weak here because its stronger in other dimensions. In that case, its still gravity being weak here because its source is not local. Even there there is no third party mechanism implied or some devine act.

What is the source of SpaceTime ? Where did it originate ?

[C1ay]

What is the source of SpaceTime ? Where did it originate ?

 

That seems a bit off topic for this thread. It sounds more like a question for one of the ID vs Evolution vs God vs Darwin threads.

[WebFeet]

That seems a bit off topic for this thread. It sounds more like a question for one of the ID vs Evolution vs God vs Darwin threads.

Hopefully we wont be going down that route.

 

For SpaceTime to be a valid scientific construct it must be devoid of divine intervention.

 

There must be a valid method for the construction of SpaceTime and if so, where did the components originate? What are they/it ?

[paultrr]

Lee Smolin in his book, "Three Roads to Quantum Gravity" rather outlines the three major paths being looked at today. One of the reasons about the interest in weither C is constant or not is that certain physical properties could well be effected by a change in C, especially if other constants like the fine structure constant or planck energy are involved. Also, part of those three roads tends to make predictions that imply C should change at least at certain scales. So what's actually being sought is a better understanding of those natural processes that brought about this universe in the first place, irrespective of the actual changes themselves.

 

One equation that would tend to vary if C is not a constant is E=MC^2. The velocity of light in the equation if it is a variable would then signal that energy itself has varied over time and possible from place to place.

[WebFeet]

Lee Smolin in his book, "Three Roads to Quantum Gravity" rather outlines the three major paths being looked at today. One of the reasons about the interest in weither C is constant or not is that certain physical properties could well be effected by a change in C, especially if other constants like the fine structure constant or planck energy are involved. Also, part of those three roads tends to make predictions that imply C should change at least at certain scales. So what's actually being sought is a better understanding of those natural processes that brought about this universe in the first place, irrespective of the actual changes themselves.

But does it explain where spacetime came from and what it is constructed of ?

 

One equation that would tend to vary if C is not a constant is E=MC^2. The velocity of light in the equation if it is a variable would then signal that energy itself has varied over time and possible from place to place.

If you substitute Maxwell's equation for the speed of light into e=mc^2, then the amount of energy in a mass is dependant on the properties of the space it occupies. Brings us back to PV and does not imply that energy will have varied.

 

For the speed of light to be constant, then there must have been a medium in place prior to whatever was the initial event of our Universe. This tends to suggest that there would have had to have been something there before, otherwise how else would a perfect constraint be put on something that permeates our entire Universe.

 

Surely, to build a model of the Universe you have to start off with a completely blank space. From there add a little energy (Big Bang or whatever was the primary event) and then build everything out of that.

[paultrr]

Actually, one of Smolin's own goals with LQFT, is to create a picture devoid of spacetime to begin with at the start even though I'd personally see a minimual space/time unit as rather implying some form of basic geometry itself. Hawking used the idea of an Instanton to try and allow one to picture how time itself could have no beginning in one sence and an initial beginning in another.

[WebFeet]

Actually, one of Smolin's own goals with LQFT, is to create a picture devoid of spacetime to begin with at the start even though I'd personally see a minimual space/time unit as rather implying some form of basic geometry itself.

If there was no requirement for geometry, there would be no need for spacetime.

 

What is a minimal spacetime? This implies that it can be constructued. Or is it a case of having a little spacetime allows for it to manipulated by mass which in turn generates more spacetime?

[paultrr]

What Smolin's loops are is simply units of space and time smaller than the Planck scale. By Minimual what is being implied is that everything is not a continum where things get infinitely small. While some of Tony Smith's original 24 dimensional bosonic string ideas have a simular geometry, the best way to understand Smolin's idea is by reading his own book on the subject.

[WebFeet]

What Smolin's loops are is simply units of space and time smaller than the Planck scale. By Minimual what is being implied is that everything is not a continum where things get infinitely small.

 

I'm familiar with the concept of Granular Space, but this doesn't explain where it came from.

 

I'd personally see a minimual space/time unit as rather implying some form of basic geometry itself.

Is this not divine intervention in providing the tools to allow one particular method of explanation.

 

First off, devine commands are outside of science and are not scientific.

But then again that would be unscientific.

 

I don't dispute that the use of spacetime in GR is of paramount importance. Without it there is no GR. Surely before you use such a construct, you should first explain its origin to satisfy the sceptics that it is not divine.

[maddog]

Surely before you use such a construct, you should first explain its origin to satisfy the sceptics that it is not divine.

Theories or things are not assumed to be DEVINE until "proven"

otherwise !?!?! :) :xx: :eek:

 

Scientific method is based on evidence. Hypotheses are made and logic is used to

produce a valid conclusion or not. Also a counter-example may be found to refute

a claim. The notion "Devine" is theology. :friday: ;) :)

 

Maddog