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

[WebFeet]

One thing of note, using EM formula there is a solid reason the vacuum has the speed of C it does.

 

Can you expand on this.

[Qfwfq]

I can see in one respect that Webfeet's idea could work -- a restricted example.

Maybe not what he is thinking. It would work like this. We the universe to have

a mystical phase transition for the speed of C instantaneously to C/2 say.

This is an example of a gauge choice that isn't local but wouldn't equate to a physical effect, except for the 'instantaneously'. I have misgivings about that discontinuity, I would speak of a gradual variation over time. I don't see it though as just a matter of remembering. Especially with an instantaneous discontinuity, Lorentz covariance would break your argument anyway.

 

I myself am still baffled by the what the point of all this is.

I'm a lot less baffled, I see WebFeet's point quite well, I wouldn't even consider it a novelty. It's an epistemological matter, a subtle one too. Unfortunately WF doesn't understand my discussion of the matter, apparently for lack of differential geometry which is the basis of GR.

 

Here's an example of what I'm on about:

 

Consider a delta c(x) which is a smooth function having a compact support. Consider a coordinate tranformation that will bring c to unity at every point. What does this mean physically?

 

In mentioning GR, you are implying that C does not have local variations

It is a basic postulate of the theory of relativity that the speed of light is constant.

Not really WebFeet, not in GR, it's a bit more subtle.

 

GR is all about extending covariance from global SO(1, 3) (Lorentz) to local GL(1, 3) (genaral) and the assumption is that for each point we can find a coordinate map that's locally inertial, meaning that SR will hold around that point.

 

I hope that makes sense.

It does. That isn't something I'm arguing against.

 

These are no different from global values. After all global values are only the average taken over a series of local values.

No, a global symmetry is one concerning a change identical for all points. Nothing to do with an average.

 

The real point is: What does it mean to measure the velocity of light? Or to change it?

[Qfwfq]

Maddog, how do you produce a valid value for the Speed of Light, before factorization, that does not rely on a method of measurement which is itself dependant on the speed of light ?

 

I'm saying to ignore factorization because you will have had to measure it in the first place before you can then apply factorization.

Actually, this factorization isn't necessary.

[WebFeet]

The real point is: What does it mean to measure the velocity of light? Or to change it?

It is generally accepted that the speed of light is the universal constant. I wanted to pose the question as to whether we could actually prove it, even in our own backyard.

 

It would appear that there is no valid method to determine the speed of light. Every measurement relies in some way on the speed of light to produce a result.

 

If our measurement of its velocity is entirely dependant on its value, then the speed of light ceases to be a fixed velocity, but instead becomes a natural number similar to pi.

Essentially the speed of light becomes a ratio, maybe between the properties of free space.

 

If the speed of light is no longer viewed as a constant, then where does this leave current theories.

Relativity relies on the invariance of the speed of light and curves space around it. Maybe the invariant is space with light being curved around it.

[Qfwfq]

It is generally accepted that the speed of light is the universal constant. I wanted to pose the question as to whether we could actually prove it, even in our own backyard.

 

It would appear that there is no valid method to determine the speed of light. Every measurement relies in some way on the speed of light to produce a result.

First of all, it depends on what you mean by constant. I'm beginning to think you're not distinguishing the meanings of 'constant' and 'invariant' which are not the same thing.

 

Invariance of c is considered proven by interferometry, supporting SR, which in turn makes it unnecessary to measure c as it is equal to 1.

 

...becomes a natural number similar to pi.

It becomes even more similar to 1.

 

Essentially the speed of light becomes a ratio, maybe between the properties of free space.

It does, according to SR and as I have been saying.

 

What does it mean to say that a measurement of c gives it as being around 10^8 m/s?

 

What would it mean to say that the value of c has changed?

[Tormod]

It is generally accepted that the speed of light is the universal constant

 

Just want to pop in here: The speed of light (in vaccum) is not the only natural constant. There are others, like the alpha constant, that are not dependant on the speed of light.

[Qfwfq]

Planck's constant!

[WebFeet]

What does it mean to say that a measurement of c gives it as being around 10^8 m/s?

C would never be measured at anything other than it s current value due to the need to use units of measurement and their their dependance on c.

Catch 22.

 

What would it mean to say that the value of c has changed?

If the speed of light is not constant, with reference to space and not using our units of measurement, then I think there are a number of significant consequences.

 

As previously posted, the concept of the curvature of space is called into question. Rather than light maintaining its velocity into a curve region of space, and that space being compressed, it simply slows down. Time then becomes an attribute of light rather than a property of space time.

The reason for its slowing down is due to the properties of free space. A higher concentration of mass/energy in the region would result in an increase in permittivity and a reduction is permeability. These values will suffer from that same catch 22 as when measuring light, they are dependant on it for its units of measurement.

 

The result would be a more straightforward explanation for the apparent curvature of spacetime.

[WebFeet]

There are others, like the alpha constant, that are not dependant on the speed of light.

Isn't the alpha constant a ratio between physical constants, one being the speed of light. (googled)

 

Planck's constant!

Planck's constant is measured in terms of metres, kilograms and time. Take your pick.

 

Planck's constant would measure exactly the same near a black hole as it does here.

[Tormod]

The planck constant is *measured* using constants like c, yes. Not defined by them. Big difference. Your original question was would we notice a change in the speed of light? Yes. About 6 billion years ago the speed of light appears to have slowed down slightly. This study (Paul Davies et al - homepage ) was a remarkable breakthrough in the understanding of cosmological constants. They may not be so constant after all.

 

fine structure constant, usually denoted as the lower case Greek alpha, is the dimensionless ratio e2/(hbar*c) = 1/137.03599976... [in cgs units, or e2/(4*pi*epsilono*hbar*c) in MKS units], which gives the strength of the electromagnetic interaction. Here e is the electron charge, hbar is Planck's constant divided by 2*pi, and c is the speed of light.

 

That c is part of the expression of the constant is simply a way for us to communicate the value. It doesn't matter what value c has - the value of the alpha constant will always have the same proportion to it.

[WebFeet]

The planck constant is *measured* using constants like c, yes. Not defined by them. Big difference.

Isn't Planck's constant defined using wavelength/frequency.

 

If SOL is constant then all our units of measurement are valid.

If, on the other hand, SOL is not constant, then our units of measurement are entirely dependant on whatever value the SOL happens to be.

 

Your original question was would we notice a change in the speed of light? Yes. About 6 billion years ago the speed of light appears to have slowed down slightly.

We can determine, indirectly, that SOL may have slowed down in the distant past, yet do we really know what it is doing right now ?

 

That c is part of the expression of the constant is simply a way for us to communicate the value. It doesn't matter what value c has - the value of the alpha constant will always have the same proportion to it.

 

Alpha determines the strength of interactions between charged particles and electromagnetic fields, and, as such, is central to the understanding of electromagnetism - one of the four fundamental forces of nature.

If the Speed of Light varied, then this would directly impact the characteristics of particles and electromagnetic fields.

Yes the proportion would remain constant, but only because when one thing changes, they would all change.

 

There is no constant or unit of measure that would not be effected if the SOL varied.

[Tormod]

WebFeet, this is yet another discussion that I feel is ending up in circles. Please accept my apologies for stepping out of it. Your ideas are of course welcome and do not take this as negative feedback, I simply have problems grasping the issue here and have too many admin tasks to fix right now... B)

[WebFeet]

WebFeet, this is yet another discussion that I feel is ending up in circles. Please accept my apologies for stepping out of it. Your ideas are of course welcome and do not take this as negative feedback, I simply have problems grasping the issue here and have too many admin tasks to fix right now... B)

Thanks for your input.

[bumab]

Just curious- does a changing speed of light neccessarily imply other constants changing, or simply imply it?

 

Another way of putting that- since the speed of light is not a fundamental constant (like pi or e), can it change without a fundamental constant changing (which would be the reason c changed)?

[WebFeet]

Just curious- does a changing speed of light neccessarily imply other constants changing, or simply imply it?

 

Another way of putting that- since the speed of light is not a fundamental constant (like pi or e), can it change without a fundamental constant changing (which would be the reason c changed)?

 

Yes, if the speed of light changed, then other constants would also change.

 

A change in the speed of light would cause a change in, lets say, the length of a metre.

Since we use the metre to help us determine how fast light was travelling, we would not have noticed the initial change in the speed of light.

 

Everything is wrapped up in a package based around the speed of light. Change the speed of light and you change the whole package.

[Qfwfq]

Like Tormod, I must say that I'm a bit on the busy side, I can't take long breaks now. I'd otherwise be willing to continue the discussion because it isn't trivial, actually I'm doing my best despite short time. :)

 

Mass being in the definition of Planck's and not in c makes the two independent: it's possible to choose natural units so that they are both 1. This also means that, like alpha, it couldn't really be used as a rod for measuring c.

 

C would never be measured at anything other than it s current value due to the need to use units of measurement and their their dependance on c.

Catch 22.

In a sense, yes. The value of c is 1. A different choice is just a matter of coordinates/units.

 

Rather than light maintaining its velocity into a curve region of space, and that space being compressed, it simply slows down. Time then becomes an attribute of light rather than a property of space time.

While I don't see the sense of the second sentence, the first is one of the two alternatives in my discussion of local variations. It now seems as if you are thinking what I have been saying but talking in different terms.

 

A higher concentration of mass/energy in the region would result in an increase in permittivity and a reduction is permeability.These values will suffer from that same catch 22 as when measuring light, they are dependant on it for its units of measurement.

I would limit such a statement to index of refraction. It would remain to determine how it is influenced by energy, it is a conjecture as far as I can see. Aside from the cause, this is similar to what I have been getting at.

 

The result would be a more straightforward explanation for the apparent curvature of spacetime.

This is a possibility but, in order to explain gravitation in this manner, you would have to explain the influence of energy on the index of refraction. I would see it as an alternative point of view rather than a better or more straightforward eplanation.

 

Note that it wouldn't be point-by-point dependence, the refractive index would be altered all around the location of the energy. Explain that and you really would have something distinct from GR, it might be worth working on. Without such an eplanation it is really just a point of view that's included within GR. In any case, it's an idea. Not bad! B)

[WebFeet]

I would limit such a statement to index of refraction. It would remain to determine how it is influenced by energy, it is a conjecture as far as I can see. Aside from the cause, this is similar to what I have been getting at.

 

This is a possibility but, in order to explain gravitation in this manner, you would have to explain the influence of energy on the index of refraction. I would see it as an alternative point of view rather than a better or more straightforward eplanation.

 

Note that it wouldn't be point-by-point dependence, the refractive index would be altered all around the location of the energy. Explain that and you really would have something distinct from GR, it might be worth working on. Without such an eplanation it is really just a point of view that's included within GR. In any case, it's an idea. Not bad! B)

 

Qfwfq, thank you for that.

I think you may have provided an important piece to this intriguing jigsaw puzzle.

 

When I mentioned Permeability and Permittivity, I was referring to the properties of Free Space as defined within the Maxwell equations. The Permittivity here is with regards to electromagnetic fields, we are essentially talking about photons. The Permeability is how that region of space will allow the passage of photons through it.

 

Viewing this as the refractive index rather than just a region of space changes things a little.

 

For light to travel from one region into another with a higher refractive index then the angle with the normal is increased by refraction.

 

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