4. The Development of the Theory of Relativity
I will now outline how Relativity developed, and what the things were which originally prompted people to embrace the theory. I will leave a few things open which I will link to when I show what is wrong with relativity, but I will in the main be aiming at something which an advocate of relativity would agree with (at least, if they were in a good mood).
Relativity tells us about exotic things like mass increase and time dilation. However, it is a theory which was first used to explain more mundane phenomena such as the propagation of light and the way charges and electromagnets interact. It explained these phenomena, but had as its consequences mass increase and time dilation.
In order to see how charges, magnets and the propagation of light are important, it is necessary to go back and review how theories of charges and magnetic fields developed.
One of the first electrical discoveries was Coulomb's law. This explained such things as how bits of paper are attracted to a charged comb, and other phenomena such as static electricity. It was simply the notion that two oppositely charged bodies would attract, and that the force of attraction would diminish with increasing distance.
A related phenomena was the attraction and repulsion of magnets. Intuitively, you might expect there was a "field" involved, but the explanation of how magnets behaved was not well developed.
But then it was discovered that charges could be set in motion, causing what was called electricity. Electricity meant that there were a whole new set of phenomena to explain.
Four newly discovered effects were particularly important :
The first thing to explain was the force between two wires carrying current. This could be thought of as explaining the force between two electromagnets in terms of the current and dimensions of the windings.
The force between the two wires was found to be mathematically derivable from the total current and current direction in the two wires and the distance between them. This was called Ampere's law. Ampere himself only saw it as mathematical link between characteristics of the wire and the resultant force. He did not imagine that one wire generated a "field" which acted on the other.
Another effect was the fact that a changing current in a wire would generate a voltage between two points (Induced EMF). This effect was behind the operation of transformers (and related to the operation of generators).
The radiation of energy from an oscillating charge was another puzzle. This was the generation of "radio waves", and was discovered by Hertz in the 1880's.
One last thing needed explaining; the effect of current in a wire on a single electric charge.
If we have a gap between the two poles of an electromagnet, and we fire an electron through the poles, the electron is not attracted to either pole; instead, it is pushed to the left or right. This is the odd thing about how "magnetic fields" operate. It is called the "Lorentz force".
(I don't like "magnetic fields" for reasons which I'll get to later. But I must use these terms because to describe them properly would mean very clumsy expression).
Maxwell came up with a theory which explained all the above results. It relied on the idea that an electrical current generated a magnetic field. This magnetic field could then act on "magnets" of the conventional variety, or other currents moving in wire (Ampere's law). It could also act on individual charges, explaining the Lorentz force.
However, a changing magnetic field could also generate an electrical field (of the same type as the one which attracts paper to a comb). This electrical field could then move charges, causing electricity. In this way, Maxwell's theory explained transformers and generators.
Mawell's theory also explained the operation of radio waves. Just as a changing current generated a changing magnetic field, so too a changing electrical field could generate a changing magnetic field. But a changing magnetic field could generate a electrical field.
So a changing electrical and a changing magnetic field could generate each other, moving along like a pair of coiled snakes. This was how radio waves propagated.
In time, light was recognised as merely a form of radio waves, and it was realised that you could understand both light and radio waves from within the same framework.
Maxwell's theory explained all the four important experiments. It also made predictions about how light would propagate through an ether, the material that light waves were in, just as waves in the ocean are waves in water.
Experimenters set up experiments to look for the ether, the material through which light propagated. One such important experiment which was set up was the Michelson-Morley experiment. Its results could not be explained on the basis of a fixed ether. However, they could also be explained by means of a "dragged ether" and a ballistic theory of light (light is "fired off" from the source, and its velocity varies with motion relative to the source of the light.)
However, light had been observed to have a fixed velocity, regardless of the velocity of the source, in binary stars. Together with another pair of experiments (Fizeau light convection and Stellar Abberation), it was found that no theory really seemed to explain everything - not a fixed ether, a dragged ether or the ballistic emission of light.
One thing was found which could "explain" the situation : the Lorentz transforms. These were essentially a "fudge" to make the predicted results fit the observations. They later formed part of the theory of relativity.
However, Maxwell's theory was found to have problems with the fields it postulated. It was found that the force between magnetic fields and charges was not always reciprocal.
According to Newton's third law, forces must be reciprocal. When we have two electrical charges, this is always the case. If one object exerts a force on another, that other object must exert the same amount of force on the original object.
(Newton's third law may or may not have anything to do with sex and waterbeds. But that is not important to the present discussion. :-) )
However, for wires carrying current and isolated charges, this is not always the case. An electromagnet will exert a force on a moving charge. The moving charge will generate a magnetic field. This magnetic field will exert a force on the electromagnet. Recoprocality.
However, imagine we have a moving electromagnet and a stationary charge. The changing magnetic field exerts a force on the charge. But the charge does not move, and does not generate a field. So there is no force on the elecromagnet.
An experiment was set up to resolve the situation, the Trouton-Noble experiment. According to this experiment, we would conclude that a stationary charge next to a moving electromagnet * does * generate a magnetic field which acts on the electromagnet.
When we apply the Lorentz transformations to the electric field generated by the charge, we find that they generate the appropriate magnetic field which explains what happens to the electromagnet.
A modified theory of electromagnetism, the Maxwell-Lorentz theory, applying the Lorentz transforms to Maxwell's original theory would then be said to explain all of the observed electromagnetic effects.
At this stage, however, the Lorentz transforms were an ad hoc "fudge". People knew that you needed to add them to Maxwell's theory to explain everything which happened to electromagnets and charges. But they "came from nowhere". It wasn't what physics was about.
Then, Einstein found that by assuming that the speed of light was constant no matter of how you were moving, and that (metaphorically) forces were reciprocal, you could derive the Lorentz transforms.
>From this assumption about the speed of light, you could explain what light did and all of what electric and magnetic fields did. This was what physics was about.
However, it did not end there. If you took Einstein's theory and its equations, you found that if you were moving with respect to something, its size diminished. Its mass increased.
Time slowed down.
These were the exotic effects that the theory is most known for.
(OK, I'm being a bit loose with language. I should be saying "as seen by a particular observer". Slap me on the wrists).
Of course, the mass increase * did * end up explaining a diminishing acceleration in certain conditions. Time dilation * did * end up explaining the observed decline in populations of high speed sub atomic particles.
But, of course, these were not the only possible explanations.
Next : 5. A brief illustration of how Ritzian theory explains observations supposedly explained by Relativity.