What physical properties of the universe define the speed of light?

[francoisp]

What I mean by this question is why is the speed of light equal to 299,792,458 m/s and not 400,000,000 m/s? What physical property of the universe is imposing this upper limit?

 

Or put in other words: if we consider for a moment the possible existence of parallel universes, it is concievable that c could have different values in different universes. So what properties could cause c to be different?

[freeztar]

What I mean by this question is why is the speed of light equal to 299,792,458 m/s and not 400,000,000 m/s? What physical property of the universe is imposing this upper limit?

 

The speed of light through a vacuum is the upper limit for photons. Nobody can say what is imposing the limit because the limit is limited to theory (although quite sound theory by today's standards).

Or put in other words: if we consider for a moment the possible existence of parallel universes, it is concievable that c could have different values in different universes. So what properties could cause c to be different?

 

That's a loaded question in a way. Lots of properties I have no capability of experiencing COULD be causing multi-dimensional differential events, but I'm still stuck with the unknowing factor.

 

If we postulate for cheese and giggles, then we can run the gambit of Sci-Fi. Light could redshift due to warping effects of other dimensions pulling light in and out of reality (ie this dimension). It could all be a kaleidoscope, or a Spanish windmill...

 

Light is pretty constant though. :)

[Qfwfq]

It is important to realize that c is a property of space-time, although called "speed of light" for historical reasons. The numerical value of c has no significance, c = 1 unless you use different units for spacelike and timelike lengths. When stating the numerical value in m/s you are really stating the ratio between the second, a very large unit of length, and the metre, a very short one.

 

One misconception is that Special Relativity states it to be "constant". No, what it actually postulates is that it's a Lorentz scalar and a limit on propagation of causality (this isn't the way Einstein initially put it). Considering it equal at different locations is related to considering space-time to be straight; in General Relativity this is dependent on choice of coordinates. It would be very subtle to discuss the notion of c changing physically across space and time (IOW not just a choice of coordinates).

[francoisp]

Using the sound wave analogy, if I change the density of the medium the sound wave travels through, I can speed it up or slow it down. Since an electromagnetic wave travels *inside* the universe I would assume it is also subjected to its environment. Can we infer that the propagation speed could be manipulated by changing the medium it travels through? And what would those changes be?

[Qfwfq]

An electromagnetic wave propagates at less than c through glass, water or any transparent material. Even in air it is slightly slower than in vacuo. This however does not amount to a reduction in c which is a more fundamental thing.

[Jay-qu]

[math]c = \frac{1}{\sqrt{\mu_0\epsilon_0}}[/math]

 

permeability of free space: [math]\mu_0[/math]

 

Permittivity of free space: [math]\epsilon_0[/math]

 

I just tried this calculation with the values I have for the two constants and it didnt come out right :( I assume I dont have the right units..

[Qfwfq]

Did you try working it out in natural units?

 

[math]\epsilon_0\mu_0=1[/math]

[Jay-qu]

Did you try working it out in natural units?

 

[math]\epsilon_0\mu_0=1[/math]

:lol:

 

nope.. I had 8.85*10^-12 and 4pi*10^-7 .. which dont work and Im not sure what units these values are in.

[Qfwfq]

Im not sure what units these values are in.

:doh:

 

:(

[Little Bang]

Suppose that the speed of light changes with the expansion of the universe, there would be no experiment that we could perform to show that it did or did not?

[Erasmus00]

[math]c = frac{1}{sqrt{mu_0epsilon_0}}[/math]

 

permeability of free space: [math]mu_0[/math]

 

Permittivity of free space: [math]epsilon_0[/math]

 

These constants aren't "real" in the way c is. Consider, for instance that [math]\mu_0[/math] is DEFINED from c.

 

In the more traditional units for electromagnetism, you don't see these constants, just the physical constant c (which in the case of electromagnetism can be thought of as the ratio of the strength of the electric field to the strength of the magnetic field).

 

It wasn't until the SI system was introduced that these "fundamental constants" were created. The rational was that the equations would look the same both in and out of materials (just drop the 0 subscript on the mu and epsilon). I personally think this hides a bunch of physics (electromagnetic propagation in materials IS different then free space propagation, hence things like cerenkov radiation).

-Will

[Qfwfq]

Suppose that the speed of light changes with the expansion of the universe, there would be no experiment that we could perform to show that it did or did not?

Not likely there would be any real experimental distinction between saying that and it simply being a choice of coordinates. It's an epistemological matter, the modern view is that without any possibility of the distinction it makes no sense to call it an objective, real fact. Prove that there can't be such an experiment and you're proving that it's only a choice of units.

[Farsight]

I'm currently preparing a paper that I hope will shed some light on this. However it is taking me rather longer to complete than I thought it might. I hope to have it ready in about a week.

 

Farsight aka Popular.

[Pyrotex]

This is a touchy question! What determines c? There are many formulas that use c, and if you switcheroo the parameters, you can put c on the left with an equal sign, and some function or other on the right. But this does NOT mean that the speed of light in any way depends on those parameters. Deciding whether c or the permissivity of space or Planck Time is the more "fundemental" constant is not easy. By and large, all the books I have read rely on the speed of light as the "most fundemental".

 

That could change, I suppose. However, if c does "depend" on something, it would have to be found in the bowels of quantum particle physics. Whatever particle (the "mysterion") that gives space is "fabric" qualities and perhaps its dimensionality. Then c would depend on the mysterion's properties. I don't know. Just speculating.

[arkain101]

What

Determines

The

Speed

Of

Light

 

WDTSOL

 

Reversed is of course LOST WD

 

Jokes aside,

 

Lets look at speed.

 

Speed is intimately connected to time and space, those of which are connected to Matter and Energy, of which are equal to each other by the function of C^2

 

Time and Space are relative, thus this plays down the line of connectivity to define that C itself is also a relative proposition.

 

Thus we arrive at locality, our local observation.

 

Matter itself makes no observation. It is we as matter consisting life forms that make observations.

 

We form a kind of stability in the realm of chaotic possibility. We do this through conscious consecutive moments of observation in many forms of intangible personal experience through various forms of senses unique to each individual to some degree (a range of difference to close to note in this discussion).

 

This then lets us make a logical presumption that what determines the speed, units, or way you decide to relate to light, is ones abilities intwined with being alive.

 

It reduces to the experience of a passing moment. Moments are relative. Long and short, yet generally consistent with ones own time measureing device, aka watch/clock.

 

It is simply to vague to state that light is constant and have it express what is going on in the details of this inquiry of the way of reality.

 

The mystery is found in the seeing of things that reality is but unlogical to explain in a singular disconected indivudal way.

 

The way of things is a relationship of interaction with various capabilities of logical reasoning.

 

To futher this statement, The answer of what determines the speed of light is more accurately ansered by asking the question of how light contains a determinable velocity of relative consistency.

 

And thus understanding there is but a web of connectivity of fundamentals as it were that develope a fundamental in itself.

 

Lights constant is a phenomina of then, compounded (many of) individual events.