Ah.. the speed of lite (light)

[paultrr]

The short answer is one could look at it that way if one fully accepts C as constant. Basically, Einstein's SR simply says that C is constant in a vacuum. That vacuum state has certain properties. If those properties have changed over time in any way then C is no longer a constant. Its well known that during inflation those properties of the vacuum where not the same as today. C was not a constant during inflation period. For one the stress energy tensor was changing then which is basically what happens when a false vacuum decays to a more stable state. The real question is did the vacuum continue to change after inflation? Those who subscribe to an answer of yes general fit under the subject of Variable Speed of Light Cosmology. Those who do not take the standard line approach. I personally subscribe to VSL as being possible. However, I also agree with the most up to date evidence that the variance is only slight. So slight, in fact, that saying it has remained constant is not a problem actually.

 

Now, the question that stems from this is C constant across all of space-time globally? The only evidence we possible have to date on that comes from the Pioneer missions with the slowdown that has been observed that points back towards the sun. With PV type models and certain dark matter models such is easy to account for. But that would also imply that C varies somewhat across space-time itself and that the vacuum has a varying local stress energy tensor. However, the slowdown difference is like some 8 meters per second. At such a small difference a lot of things could be at play here. So at the present its anyone's guess who is correct. My own stance is I believe it does vary. But I also believe that no matter the local stress energy tensor that within that local frame one can safely state that lorentz invariance is not broken. At that point I hold to something different than a lot of VSL Cosmoligists hold to. I also tend to take a stance different than most String Theorists do because of such. I think Einstein was correct in his general assumptions. The problem is in defining local frames when it comes to the stress energy tensor. There are a lot of unknowns under GR within the equations themselves. If any of those unknows varies then C should also vary somewhat.

[DivineNathicana]

But what if they don't vary? Einstein's theory is way too smooth and perfect for weird variations. The whole theory is built on a c limit. Wouldn't rejecting this limit basically mean rejecting its founder?

 

- Alisa

[paultrr]

Depends again on what version of VSL one follows. The variance during the inflation period poses no problem simply because Invariance depends upon the stress energy tensor to begin with. Einstein's exact wording in his papers was that the speed of light was constant in a vacuum. That specific vacuum state is defined via GR itself. So in essence if its the vacuum state that varies and C varies because of that then nothing being derived from that violates the spirit and intent of Einstein himself. The speed of light for example in air is slower. The local stress energy tensor for air is different than for a vacuum. If by the strict logic any variance of C would mean Eistein was wrong then he'd be wrong. But in the context of what Einstein stated in his original theory he was not wrong at all. We can create certain mediums in our labs where C can nearly be slowed down to a stand still. Do those different mediums imply Einstein was wrong? The answer is no. They are not the vacuum condition that Einstein refered to.

 

One of the major center issues of Einstein's theory is the invariance of C. Now some VSL models and some String based models seem to imply its broken. Now that would imply that Einstein was wrong. But to date there is no evidence that is true.

[Tormod]

Originally posted by: DivineNathicana

Like, as I understand it, the Big Bang model says that galaxies are not so much moving away from a central point, but are rather staying fixed on a stretching space-time (which is considered vacuum).

 

Alisa, this assumption is mostly correct. The reason the Big Bang model does not describe the universe as a balloon is that our universe (on a macroscopic scale) consists of a four-dimensional space-time. There is no "center", as the entire universe sprung out of the Big Bang. Thus there is no such place as "the center of the universe".

 

So our universe is more comparable to a section of the surface of the balloon, rather than the inside of it.

 

We have discussed this before in older threads.

[paultrr]

Yes, as far as observation goes and as far as the expansion itself goes the assumption or picture of cosmic evolution is correct.

[DivineNathicana]

Yeah, I read that in Hawking's book. But the real question was, is it correct to assume that space-time itself (and therefore the "fabric" of vacuum) is stretching? Wouldn't that logically slow c down?

 

- Alisa

[paultrr]

Not in and of itself. Space can move, spreading objects further apart. But if the vacuum state itself remains constant during that movement then no. C would still be normal irrespective of the spread. Movement of space-time itself does not induce any real local change in the velocity of objects within that. From one object to the other they would appear to be moving apart faster and faster. But their own local velocity is unchanged. Now, if the mechanism causing space-time to spread out somehow also effects the local vacuum state then C changes also. This was the case during inflation when the vacuum state was changing. But weither its the case now also will depend upon the observational and experimental evidence in the long run.

[DivineNathicana]

How can we know whether or not the vacuum state is changing? How could it change? Doesn't it fluctuate anyway already? And what kind of effect might a change of the vacuum state have on us?

 

Sorry for all the annoying questions. = )

 

- Alisa

[paultrr]

Our current vacuum state is considered generally as stable. During inflation the universe had a false vacuum state. Minor flux in the vacuum has little if any effects on us. And yes, the vacuum always is generally in flux due to quantum uncertanity itself. However, it has a general average energy or stress energy tensor. In Casimir setups for example one can find the local stress energy tensor between those plates showing a lower energy condition than one would find globally. With the universe at large we have not only normal energy to account for. We also have based upon observation exotic energy to account for also. It that exotic energy that can lead to local conditions were C could be different and perhaps globally have C slowing down over time.

[BlameTheEx]

paultrr

 

This all very confusing. What ia a vacuum state? How can it be false? References for "Casimir setups" please. Where, and how, do plates get involved?

[paultrr]

Run a search under the subject inflation to get a good discription of a false vacuum state. Basically, the false vacuum was an overly high energy vacuum that was unstable and decayed down to a stable one. It was the energy of that decay that formed all the particles we now have in this universe. The Casimir effect is a well documented lab eperiment that a simple search online will give one many links to. Basically, if two conductive plates are space at microscopic distances apart the energy within the plates shows to be less than the energy outside the plates. This works in vacuum and in air. What the plates do is cancel out certain quantum modes of the zero point field itself. Since only certain modes or wavelengths can exist between the plates the energy there is less than outside the plates. This was one of the first experiments every conductd that backed up quantum theory that the vacuum is filled with energy.

[paultrr]

A false vacuum is a classically stable excited state which is quantum mechanically unstable. Inflation Theory relies on a proposal, originating in modern particle physics, that extraordinarily high densities can lead to a form of matter that would turn gravity on its head, causing it to become repulsive rather than attractive. This form of matter is called a false vacuum. Inflation is the proposal that the expansion of the universe that we see today is the result of the gravitational repulsion of a false vacuum that filled the universe during a small fraction of a second of its early history. During this time the energy of the vacuum drives inflation.

 

As tempature increases we see a succession of phase transitions for water in which its properties change dramatically: the solid phase - ice - melts to the liquid phase - water - and then eventually boils to the gaseous phase - steam. You should notice that steam is `more symmetric' than water, which is in turn more symmetric than ice. This pattern is repeated in the universe at large as we move backwards towards T=0. The basic premise of grand unification is that the known symmetries of the elementary particles resulted from a larger (and so far un known) symmetry group G.

 

Phase transitions can be either dramatic - first order - or smooth - second order: When cosmologist refer to inflation, they are speaking of the first order type. They are also discribing an era before the current vacuum structure of the universe became fixed. Since the vacuum isn’t the same in value as our’s at present it would not have the same value of C as our vacuum does. Basically this is because the fine structure constant wouldn’t have evolved yet, to its present state. During a first-order phase transition, the matter fields get trapped in a `false vacuum' state from which they can only escape by nucleating bubbles of the new phase, that is, the `true vacuum' state. The above is the primary premise of inflation theory and the same premise backs VSL versions of inflation.

 

The Universe, because of properties of elementary particles not accounted for in the standard big bang models is conjectured to have expanded for a fleeting instant at its beginning at a much higher rate than that expected for the big bang. This period, which is called the inflationary epoch, is a consequence of the nuclear force breaking away from the weak and electromagnetic forces that it was unified with at higher temperatures in what is called a phase transition. This phase transition is thought to have happened about 10-35 seconds after the creation of the Universe in the standard version.

 

Basically, the universe cooled down during this transition period after a short heating phase and our present vacuum state is sometimes termed a frozen vacuum state.

[paultrr]

Casimir effect

 

http://physicsweb.org/articles/world/15/9/6 and

 

http://math.ucr.edu/home/baez/physics/Quantum/casimir.html and

[paultrr]

The issue about weither C has slowed down all centers around what is the overall effect of this exotic energy that seems to be causing the current observed accelerated expansion of the cosmos. The question being asked is does this extra negative type energy alter the ground state of the vacuum overall. If it does then C would not be a constant. Most current theory proposes that this extra energy is the same energy that drove inflation in the first place. That being the case then C should be a variable. Its then a debate on what is changing exactly that effects C. Some propose its the fine structure constant that changes, some propose that the Planck scale changes with time, some propose other accounts.

 

Part of the logic behind this goes back to Casimir effects. By theory C should be faster between those plates in those experiments simply because the vacuum energy is less there. If simular lower energy regions exist within our universe then C would not be an absolute constant from region to region. The logic here gets interesting. For one, a high energy region should have a slower value for C. During inflation one would think C was slower. But, the stress energy tensor of a false vacuum is different and it was that which controled C. So, C was higher during the false vacuum stage than at present. After inflation the cosmos may have regions where it is slower and regions where it is a bit higher. What seems to control that value is the local energy density itself. One theory, first popularized by Hal Puthoff, commonly called Polorized Vacuum or PV, thinks the difference stems from the local dielectric values of the vacuum itself.

[paultrr]

The speed of EM radiation through a substance such as cables or any other medium is defined by the following formula:

V = c / (u r e r)^ 1/2

Where: u r = relative permeability and e r = relative permittivity

The real component of e r = dielectric constant of medium.

EM propagation speed in a typical cable might be 65-90% of the speed of light in a vacuum. In air its less than C. In Casimir vacuum state it should be less. However, oweing to the small area involved that part of theory has never been tested to date. The general dielectric values of a normal vacuum state are both 1. But this value by experimental measurment is actually based upon an average and is not really a constant to begin with. The simple presence of more or less particles in a vacuum region alters that value. With high or lower quantum virtual particles numbers the same would also hold. Certain mediums used in experiments where C is slowed down or speeded up all have different values from a normal average vacuum state.

 

Basically, part of Eistein's stress energy tensor incoporates that property of the vacuum into it. If that property changes locally then C is not a constant. Its only by SR/GR a constant is a specific vacuum state that was defined by the theory itself. Alter any value from that theory and C can not be seen as a constant. What a lot of us think is that globally C has a certain value that generally fits what we measure locally. Based upon that we tend to consider C a constant. However, by the same logic it is possible that different regions have a slightly different value and that what we tend to observe is the average value of all regions.

[paultrr]

It is also possible that globally that average has changed over time which by the few observations to date would imply that C has slowed down over time. However, the observational evidence on this is still being argued out and no hard conclusion has been determined at present. That leaves one with the two general choices as far as theory goes:

 

1.) It stays generally stable.

 

2.) It varies with time.

[paultrr]

I take the first stance with an open mind on the second. I think C can vary a bit locally, but, that all those different regions give us what we observe normally across the cosmos. The only observation to date that best fits a locally variable approach is the one from the Pioneer mission. But even here that is a small variance based upon observation of signals from the edge of our solar system. Experiment and observation wise we'd need a lot of repeats of this effect to come to any real hard conclusions. Untill that time its just as safe to consider it constant than any other position.