A Lucky Day On The Train
The first science article of the year described the straight lines of "special" relativity, the simplest form of relativity that there is, the relativity of space and time, distances and angles, for 'uniform' motion, motion that does not change speed or direction. It explained how relativity can be readily understood by using a simpler reality of flat, rising two-dimensional surfaces inhabited by two-dimensional creatures in a three-dimensional universe (adding the third dimension of time) with room enough to rise forever. Flat surfaces were "stacked" upon each other, across time, as a series of consecutive moments, creating stacks of momentary surfaces 'in' – or rather 'across' – a third dimension, time. This simpler universe was used to make the concept of relativity easier to grasp. In our universe, instead of stacks of two-dimensional surfaces tilting with respect to each other, stacks of three-dimensional 'spaces' tilt with respect to each other across time, in a universe with an additional 'fourth' dimension, instead of just three.
The next science article complicated this simple picture of flat, tilting surfaces (and spaces) by recognizing that not all motion is uniform, but instead, is non-uniform, because so much motion changes in a "non-uniform," changing either speed or direction or both. This complicated the image of "straight" stacks of flat surfaces (or spaces) into curved stacks of curved surfaces (or spaces), because bending is really never anything more than a progression of tilts. Then, because the effects of non-uniform motion are absolutely "indistinguishable" from the effects of gravity, the two being wholly 'equivalent,' its description works perfectly for gravity. The outcome of this more "generalized" form of relativity is General relativity. General Relativity is, unquestionably, a brilliantly stunning example of natural truth's expression and of the marvels that such an expression can accurately reveal about nature's amazing phenomena.
The preceding two articles explained the 'how' of relativity. Although they touched upon the idea, neither of the two articles explained the 'whys' behind this brilliant idea. This article does, by describing the straight-forward, simple-minded, yet monumentally insightful thinking that led to the best working description of gravity ever conceived by anyone.
We begin with what were at the time relativity was first imagined, the "laws of physics" for energy, which were a set of statements called Maxwell’s equations. These equations "unified" electricity and magnetism into a single description, into a single force, "electromagnetism." Amazingly, these equations ultimately led to the discovery of relativity and the best description of gravity ever conceived, and this is how. It is remarkably straight-forward.
Today, physics recognizes that there are four forces: electromagnetism, gravity, the strong force and the weak force. At the time of Maxwell's equations however, the last two were unknown (they simply were accommodated by means of a measure called 'mass'). The atom had yet to be discovered as an element of nature, so these last two forces (the strong and weak forces), restricted to the internal structure of atoms, were completely unknown at the time. This left only Maxwell’s equations for electromagnetism and Newton's equations for gravity and motion as the extent of the "laws" for describing nature.
Maxwell's equations for electromagnetism and Newton's laws for gravity and motion were, again at the time, what could be termed, the 'laws of physics'. Notwithstanding errors predicting the orbit of the planet Mercury, these 'laws' worked "well enough," except for a single, slight, insurmountable detail. According to the equations of Maxwell, the speed of light never changed, which was a stark contradiction to conventional thinking – or looking at it another way, an absolutely stunning opportunity for the proper insight to discover.
In those days, science, along with everyone else, was convinced that space and time measures were absolute; that is, that space and time, distances and angles never changed for any reason ever. In those days, science was mistakenly incorrect in so assuming, the absoluteness of space and time measures being one of its most fundamental assumptions in science. Light’s speed never changing was a direct contradiction to this notion, as an insightful young thinker recognized.
Enter Albert Einstein, an inquisitive young man who happened to be sitting on a train one day, contemplating the speed of light never changing. For what was very probably the first time in human history, someone recognized just what this meant.
Sitting in the seat located at the very center point of the train (the same distance from the caboose as from the engine), a passenger looks at a light that flashes just outside their window. Naturally, the light from this flash, traveling at the same speed in every direction, reaches the caboose at the exact same moment that it reaches the engine.
Next, let us imagine the same set of events, same passenger seated at the same location with respect to the engine and caboose, same flash of light just outside passenger’s window, only this time the train is 'moving' instead of 'stationary'. At this point it is important to recognize that with the train, and in particular, with the engine and caboose 'moving', instead of the light from the flash hitting the engine and caboose at the same time (the light moving at the same speed in both directions), this light strikes the caboose BEFORE it strikes the engine. This is because while the light travels, the caboose moves toward it, reducing the distance that it must travel and hence reducing the time that must be spent to do so, thus the light strikes the caboose sooner than it would strike the engine. Meanwhile, the engine, racing away from the light, increases the distance that the light must travel to strike it and hence increases the time required for the light to reach the engine, thus the light strikes the engine later than it strikes the caboose. BUT, this is all assuming that it is the train that moves and that the surroundings do not. This is what our innate, intuitive construction of reality automatically imagines, without giving it a second thought. Automatically, it fails to imagine differently, or to imagine more complexly – unless, of course, we decide to choose truth over tradition, as a young Mister Einstein once did.
Now remember, these two different moments for the observer watching the train pass are the exact same moment for the seated passenger riding on the train. Stating the same fact another way, 'when' varies according to whether you are on the train 'moving' or 'stationary', just as the 'unmoving' surroundings are. The 'truth', however, is that 'stationary' and 'moving' are flatly NOT absolute, but always a matter of perspective, because were the ride smooth enough, it would seem to the seated passenger that the train remained stationary while the surroundings moved (prov1ded speed or direction remains unchanging: uniform).
For the laws of physics of the passenger to provide the same results for a different set of 'whens' (likewise, a different set of 'wheres' are correspondingly required), either the laws of physics must change, or the measures for the elements subject to those laws must. Because the laws of physics clearly do not change with motion, then, to make the 'whens' (and again, not to mention 'wheres' also) for the passenger and observer to correspond to measures appropriate for the same physical laws, the distances, angles, and the pace of time itself had to be adjusted, in order to make the erroneous context (again, the tradition of the day) of an all-encompassing present-moment 'now' for the universe "work." To make an erroneous idea 'work', instead of changing the laws of physics, science (specifically, physics) changed the measures, remarkably, in a way that really did work, by corresponding to observation. They did this by means of a set of adjustments termed the Lorentz transformations. Until Einstein explained otherwise, science itself perpetuated a long-standing yet completely inaccurate cultural tradition.
Einstein saw the folly of this point of view, explaining the changes in space and time measures in a logically consistent way (tilting and bending spaces), impeccably. He did so using the Lorentz transformations in a way that worked and still continues to work today.
Relativity is true, a stunning of example of nature's truth, as true as time, space, and gravity are, as true as our individual existence is. Moreover, it is a clear example of just how much richer nature actually is, than our stark and simple cultural constructions of it could ever provide and proof positive that a little luck in the most common of places can lead to great discoveries.