Re:Relative to what? (Score 1)

First, your parenthetical has it backwards. Special relativity is a subset of general relativity. Specifically, special relativity ignores the effect of gravity.

I'm afraid that acceleration isn't the magic bullet that breaks through the paradoxes of relativistic velocities, though intuitively it seems to. Acceleration changes velocity, yes, but the same acceleration that raises my velocity with respect to one object decreases it with respect to another. To use your example of the space shuttle, it is better to consider the shuttle in relationship to the space station. When it is ready to leave the station and return to earth, it points away from the station and accelerates, increasing its velocity relative to the station, and experiencing all the effects of acceleration. Except that, the whole manuver is vectored specifically to decrease its orbital velocity, dropping it out of orbit.

So which is it? Does acceleration increase or decrease velocity? Earthly intuition tells me that the answer is obvious: if I'm hitting the accelerator, I'm increasing my velocity; if I'm hitting the brakes, I'm decreasing velocity.

But earthly intuition learned at the bottom of a massive gravity well isn't much help in understanding relativistic velocities. In a universe filled with an infinite number of objects, any acceleration changes my vector with all of those objects, increasing my velocity relative to some and decreasing it relative to others.

What the special theory of reletivity describes is not what objectively happens to me as I accelerate, but how two objects manifest themselves to each other at different shared velocities, regardless of which one is assumed to have "accelerated" (because what from one perspective may seem obviously to be acceleration may seem just as obviously to be deceleration from another perspective).

Intuition is a powerful prison. Given two objects in space converging at a shared velocity of .9 c, one a planet sized object and the other a subatomic particle, I will invariably assume that the massive object is at rest (or nearly at rest) and the subatomic particle is in a "high energy" state. Particularly if I am familiar with the special theory of relativity, I will "know" that it would be impossible to accelerate the planet to .9 c. So, it must be the subatomic particle that has been accelerated.

Except that, to the special theory, it doesn't matter how velocity is achieved. An observation made from either object would show an object approaching at .9 c, and the relativistic changes in mass, time, length, whatever, would be perceived accordingly. Which means, of course, that the observation of the planet by the particle would indicate an incredible energy state.

But then, isn't that the problem with cosmic rays? Given their velocity at even such a miniscule mass, their energy state is too high to be credible. So, relativistically speaking, cosmic rays are just as problematic as space ships or even planets traveling at near light speed.

Except that the special theory of relativity doesn't really directly address the acceleration of objects. What it addresses is the observation of objects that share a high velocity. Indirectly, it may tell you that, if you boost an object with a quantity of energy that would seem sufficient to take it over light speed, you will nonetheless measure its velocity as being less that c. Yet, the boost energy is still there, not lost to friction. Your object will hit with a force out of proportion to its measured speed, which we take to mean that it must be more massive than it was before you accelerated it.

But the special theory doesn't care what gets accelerated. For all the special theory cares, two objects blinking into existence with a shared velocity of .9 c isn't a problem. The special theory will predict how they will observe each other and what their impact on each other would be, but it doesn't really care how their relative velocity comes about, or which one is "really" in motion.