There's an interesting tidbit in The Economists' article: Einstein originally wanted to call what we now know as "Theory of Relativity" the "Theory of Invariants" instead, but was eventually convinced otherwise.

Good thing, since it does vary and is relative.

No, Orrin. It is the observations of different observers which vary, i.e. they are relative to their states of motion. Einstein's single, contravariant tensor field equation is invariant, i.e. it is the same for all observers. This enables any observer to calculate what any other observer would 'see', even though it differs from what he 'sees'. The field equation contains the relativized form of Newton's laws of motion (Special Relativity), the relativized form of Maxwell's equations (Relativistic electrodynamics), and the curvature of space-time due to mass-energy (Relativistic Gravitation), all in one equation.

Our individual observations are epiphenomena, simply manisfestations of the phenomena of events described by the tensor field equation. As a conservative, you should appreciate this viewpoint: that our subjective perceptions stem from an objective reality obeying a single law, which is the same for everyone.

Except that it's variable itself.

You do though stumble into a genuine insight--people believe in scientific theories for exclusively political/philosophical reasons, not because they describe reality.

My question, which I don't have nearly enough physics to begin to figure out, is whether c^2 defined as the speed of light in vacuum is simply a convenient constant in the equation, or if it really mediates the relationship between mass and energy.

If it does control the relationship (if the equation is true for any value of c), and if the speed of light was nearly infinate in the baby universe, then the conversion of any matter at all would release an almost infinate amount of energy. That would actually explain a lot.

"I'll let go of my dogma when you pry it from my cold, dead hand!" - generic scientist

Didn't Kuhn describe paradigm shifts as occuring when the majority of the holders of the old paradigms die?

David:

It has been some years since my physics class covering this, but I'll give it a go.

What E=mc^2 really means is that energy is proportional to mass, and that c is the constant of proportionality. So c changing over time doesn't effect the validity of the equation at all; only the amount of E a given mass defect will produce.

Your last para is extremely insightful (sure never occurred to me before you mentioned it). Going way out on a limb speculative limb here, c could be inversely proportional to the radius of the universe (c/Ru).

14 Billion years on, the percentage rate of change in the universe's volume is so small that c appears locally constant, but increases looking far enough out (far enough back in time, hence to a smaller universe with a higher rate of change).

Speculatively speaking, of course.

IIRC, none of this would invalidate Relativity as it stands, but might point to some incompleteness.

Robert - that was Kuhn quoting Max Planck.

"A new scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die, and a new generation grows up that is familiar with it" - Max Planck, translated I'm sure.

OJ - Personally, I would wait for more evidence before saying things have or have not changed with time. Because of its high profile, a large portion of what gets published in Nature turns out to be controversial - if not misconstrued or wrong. Besides which, relativity always attracks the most crackpots.

Actually, of all of this stuff, I think the anomalous acceleration of the Pioneer craft leaving the solar system is most interesting. Time will tell if there really is anything going on there.

David: I believe that 'c' ...really mediates the relationship between mass and energy because it is, at any time, the velocity of massless particles (photons) and therefore the upper limit of velocity for any particle with mass (in agreement with Jeff). As to your speculation, current big-bang mythology holds that there was no matter before the strong force decoupled and the hadrons precipitated out of the energy flield -- everything prior was pure energy, with the massive particles appearing as things cooled off. Besides, it is still assumed that mass-energy is conserved, so no additional energy could ever be produced.

Jeff: In electromagnetic field theory the velocity of light is a derived quantity, being the inverse of the square root of the product of the electric permittivity and magnetic permeability. There is no reason these should depend simply on the size of the universe -- rather perhaps the energy density affected these quantities, which would give the appearance of a dependence on the size.

JD:

You are quite right--I'm glad I caveated the heck out of that.

The speed of light could not have been infinite in a vacuum in the very earliest Universe, because there wasn't any vacuum.

The vacuum is an emergent phenomenon, not a basic parameter of the Universe, and Orrin is slightly (very slightly) right to say there is no vacuum.

Considering the arc subtended by a quasar at 10 billion years distance, the vacuum is pretty complete, on average, by now, though imperfect on some scale -- a very big one now, very small at the earliest.

It's really great being a materialist, because you don't have to worry your head about stuff that drives Orrin nuts. And our solutions work, and his don't.

A bonus.

Harry:

Mine works--the speed of light is whatever intelligent beings want it to be at any given moment.

So OJ have you joined the Po-Mos as an extreme social contructionist now? I thought you would at least let the Almighty have the perogative of setting the fundimental physical constants. Or have Harry and Jeff argued you out of your faith?