[Gorjus]

And didn't Einstein originally just assume the speed of light as a constant?

Here's an explanation, take it or leave it as you will.

Two scientists named Michaelson and Morley conducted an experiment to measure the speed of the earth through the 'ether' - a material characteristic to space assumed to exist. After all, 'when light waves, what waves?' In other words, what propogates light through what appears to be a vacuum? The theory said there was something called ether that existed even in a vacuum.

In their experiment, they set up a right-angled apparatus, one leg of which was aligned with the direction of the earth's motion around the sun, and the other perpendicular to it. By measuring the difference in the time it took a light pulse to travel both legs, you could get a measure of the speed of the earth through the ether which is what 'waved' when a light wave went by (since the ether would drag the light along with it).

They didn't find any difference. A host of other similar experiments showed that, regardless of the circumstances, the speed of light (in a vacuum) was always the same to the limits of accuracy of the measurement.

So, Einstein didn't 'assume' the speed of light was constant. That's what the data showed.

Two other guys names Lorentz and Fitsgerald developed a relationship that quantified how much things at very high speed behaved differently than those at normal speeds. This 'Lorentz-Fitgerald contraction' was SQRT(1 - V**2/C**2).

Einstein came along and in his 'Special' theory of relativity showed that the speed of light as measured by an observer is constant regardless of his own velocity if the rate of time passes differently for the observer based on his velocity, using the Lorentz-Fitsgeral contraction to quantify the amount of change in perceived rate of time passage.

Then Einstein extended from the 'Special Theory Relativity' to the 'General Theory of Relativity' by devloping a mathematical expression for the curvature of the universe which related linear dimensions to time, with the units worked out by combining t (time) with c (speed of light). The mathematical expression is called a 'tensor', and it's as good an example of how you can't 'speak' real science without mathematics as I've ever bumped my head up against.

One good thing about the General Theory of Relativity is that it provided an explanation for gravity. It was always a challenge to conventional physics to explain action at at distance without an interaction phenomenon. How does the earth know the sun is over there pulling on us? And how does the sun manage to grab the earth and yank it around without a string between the two? The curvature of space described by solving the Einstein tensor for local conditions offers the prediction that the earth is following an equal-value (in the tensor) line around the sun even as it changes direction. In other words, the earth goes 'straight', but 'straight' is not straight in the Euclidean sense. Instead, the 'straight' travel of a body in motion is actually to follow an equipotential line in the Einstein tensor value for space.

The other good thing about the General Theory (okay, there are lots of them, but this is already a long note) is that it predicts that light itself obeys gravity, despite having no rest mass for the conventional Newtonian model to act upon. This is provable by lots of experimental data, so the General Theory gained a lot of credibility.

Now, to wrap it up, if the speed of light is not a constant, then the Einstein tensor doesn't provide a solution to the motion of bodies in space-time. There's another variable that makes it impossible to solve. There is an awful lot of observable data that would need another explanation. (Obviously, if the speed of light is almost a constant, then the Einstein tensor is almost right, and still very useful for lots of situations.)

I don't know if this data on the natural nuclear reactor proves the speed of light is variable or not, but there are lots of challenges with a totally constant, for all time, speed of light, too (as mentioned in the article), so it'll be interesting to see what happens.

[Southack]

"The other good thing about the General Theory (okay, there are lots of them, but this is already a long note) is that it predicts that light itself obeys gravity, despite having no rest mass for the conventional Newtonian model to act upon. This is provable by lots of experimental data, so the General Theory gained a lot of credibility."

No, no, and no.

Experiments in the last decade have managed to slow light down, in some cases to as little as ten miles per hour...but the light at those slower speeds isn't bent by Gravity.

At all.

[Light Speed]

Article excerpts from:
The Remarkable Slowness of Light

The fact remains that everything we know about electric and magnetic fields requires electric charges, in other words, a medium, as a focus for the fields. If there is to be a wave, there must be something to wave!

We know that the “vacuum” of space is teeming with neutrinos. Countless trillions of the ghostly particles pass through each square centimetre every second. Maybe neutrinos constitute the medium of “empty” space? It makes sense if, as I suggest elsewhere on this site, all particles are composed of orbiting massless electric charges. And neutrinos are the most collapsed form of particle.

This brings us to the speed of light, “c.” We know from experiment that “c” varies depending on the medium. More particularly, “c” varies depending on the electrical characteristics of the medium. The speed of light in a vacuum cannot then be simply declared a universal constant, because a vacuum is not empty space ­ it is filled with vast but varying numbers of neutrinos and some other particles.

It seems more reasonable to suggest that the speed of light is the speed with which an oscillating electrical disturbance is transmitted through a dielectric medium. The speed of light is highest in a medium where the rate of charge polarization in the particles of that medium is greatest. Neutrinos, having the lowest mass, or inertia, of any particle, have the fastest rate of internal charge polarization and response to an electric field. Therefore “c” is a maximum in a vacuum, paradoxically full of neutrinos.

The notion that c was considerably faster in the past has appeal to both cosmologists and creationists. Both camps have severe difficulties in explaining the observed universe, even with their vastly different time frames, unless things happened much faster initially. Cosmologists would like to see a near infinite speed of light immediately following the big bang and creationists about 10^11 times “c.” Both are misled by their misunderstanding of the creation myths. It was no accident that a Belgian priest, Georges LeMaitre, proposed the big bang theory, as it came to be known. Science is as much driven by culture and religion as any other human activity.

Proof that the cosmologists are mistaken both in their speculations about light-speed and the big bang hypothesis comes from the very source referred to in the above report ­ the light from a quasar. The above-quoted article says that the quasar is 10 billion light years distant. That is based on the most peculiar big bang theory that the volume of the universe is increasing. It follows the observation that faint objects have their spectrum shifted towards the red. The discoverer of this phenomenon, Edwin Hubble, was careful to not attribute this “redshift” to the Doppler effect of the velocity of recession of the object, but theorists were not so circumspect. The redshift ­ velocity - distance equation quickly became another of the many dogmatic assumptions of cosmology.

[Doctor Stochastic]

And how does the sun manage to grab the earth and yank it around without a string between the two?

No strings attached? What's all this brouaha about String Theory then? Violin tunings?

[Freesofar]

Thanks for the explanation.(125) I didn't know that.

It stands to reason that light would be subject to the law of entropy also

[ScuzzyTerminator]

So, Einstein didn't 'assume' the speed of light was constant. That's what the data showed.

My understanding is that Einstein insisted that he did not know of the Michaelson-Morley results when he wrote his paper.

Einstein's assumption was that the laws of physics, including Maxwell's theory, are the same in every reference frame. That assumption results in the speed of light being constant in all reference frames.

[<1/1,000,000th%]

Very nice.

[mikegi]

Two other guys names Lorentz and Fitsgerald developed a relationship that quantified how much things at very high speed behaved differently than those at normal speeds. This 'Lorentz-Fitgerald contraction' was SQRT(1 - V**2/C**2).

Actually, it was Heaviside who first calculated the distortion of the electromagnetic fields of a moving charge.

One good thing about the General Theory of Relativity is that it provided an explanation for gravity. It was always a challenge to conventional physics to explain action at at distance without an interaction phenomenon. How does the earth know the sun is over there pulling on us? And how does the sun manage to grab the earth and yank it around without a string between the two?

Heaviside published the first serious post-Newtonian gravitational theory in 1893, his "A Gravitational and Electromagnetic Analogy" in Electromagnetic Theory Vol I. He introduced the concept of mass currents, gravitomagnetic fields, and gravity waves. Not coincidentally, Einstein's GR reduces to Heaviside's theory in the weak field limit.