Frame of Reference vs. Observer: Where Relativity's Pedagogy Goes Wrong

(Technically, all that's required to understand this post is high school physics, but a prior familiarity with special relativity is very helpful)

The following statement is WRONG: The speed of light travels at the speed C (in vacuum) relative to all inertial (non-accelerating) OBSERVERS. 

The CORRECT statement is: The speed of light travels at speed C (in vacuum) relative to all inertial (non-accelerating) FRAMES OF REFERENCE. 

Though lost to popular history, Einstein was not the only contender for the discovery of special relativity. Henri Pointcare and H.A. Lorenz also made relevant discoveries. Einstein succeeded where his contemporaries failed by discarding the luminiferous ether and embracing the true universality of C and the equality of all frames of reference. Given the apparent importance of frames of reference, one would think physicists wouldn’t be sloppy about how they define the term—and would distinguish between them and OBSERVERS.   

One of the first things a beginning relativist must learn is the difference between relativistic PERCEPTIONS and relativistic MEASUREMENTS, especially if he/she wants to understand the relativistic doppler effect. The field’s sloppiness is especially unfortunate because the relativistic doppler effect is key to understanding the twin paradox--the very reason many people study relativistic kinematics in the first place. 

Frames measure; observers perceive. If all observers in the same frame of reference (all those at rest with respect to each other) take light delays into account, they will all MEASURE the same thing, but what they actually SEE—e.g., time between events--depends on where they are with respect to the object(s) in motion.

A beam of light takes a certain amount of time to arrive from Mars and vis versa. If you shoot a beam of light there, you don’t see it until 2D/C later—D/C there, D/C back. This is NOT a relativistic effect; it’s simply a delay due to light’s finite speed. Speed-of-light weapons, like lasers*, are zero-warning weapons. If a man across the Universe pulled a trigger just below the barrel of a laser, it would appear to travel at infinite speed, even if delayed by billions of years. The photons that reflect off the man’s fingers, trigger, and barrel travel at the same speed as the laser's photons--and, therefore, arrive at you simultaneously. 

 *In movies, such as “Star Wars,” what are called lasers usually fire plasma, or electrified gas, at far lower speeds. Properly, they’re called plasma guns, blasters, or ray guns. 

If a ship traveled at the sub-relativistic speed of 100,000 MPH to a space station one parsec away, it would arrive, according to Earth observers, D/V + D/C later, the latter due to the 3.26 years it takes light from the traveler at the space station to reach Earth. If you broke up the distance between Earth and the space station with a million markers, the light from the ship's arrival at a marker travels a parsec/million more distance than its predecessor to reach Earth. Multiply that by a million and you got your 3.26-year delay time. The distance and, therefore, the delay time between intervals are equal regardless of the ship speed since the distance between pulses, 1 parsec/million, and the light pulses' speed, C, are the same in both cases. The first half of the journey, and the apparent velocity, will be a hair slower because of the movement. The opposite is the case on the way back. And the situation will be viewed almost exactly the same from the point of view of the traveler, since he’ll see the Earth moving at the same (sub-relativistic) speed. Thus, no “chronological irreversibility” or asymmetry between the frames and observers.     

In the relativistic doppler-shift version of the twin paradox, the stay-at-home twin will perceive the traveler’s blueshifted journey home occur, or appear to occur, faster than C and the redshifted voyage to the star much slower (recall the laser fired across the Universe--the very fact that the ship doesn't arrive instantly from the point of view of an observer in front of the clock means it doesn't actually travel faster than C). Blueshifted clocks will also move FASTER than the observer at rest with the clock, not just the blueshifted observer's frame of reference. All this results from successive light signals having to travel more or less distance to Earth than their predecessors, and are more or less delayed, not that the light is actually MEASURED at a speed other than C. 

The difficulty in observing light is that the photons have to first reach the observer in order for it to be processed (usually electrically) by a brain, antenna, etc.; there isn't a viable means of observing it en route.   

Relativistic effects occur when the universality of C leads to the breakdown of the Galilean (classical) velocity addition equations (or Galilean closing speed), resulting in the slowing of clocks in motion.

Classically, speed is altered by other motion rather straightforwardly. When a ball is tossed from the back to the front seats of a speeding car, the speeds simply add. The ball moves faster in relativity, too (for that, you need the Lorenz velocity equations), but if the ball was replaced with a beam of light, it would not.   

Imagine a vertically-oriented light pulse clock inside a ship moving close to C. As viewed by the passenger next to it, a pulse travels straight down a foot-long channel and returns, representing a single unit of time. An observer standing on the ground perpendicular to the ship will see the pulse move diagonally in order to reach the bottom, and diagonally again to return. Speed of light is measured the same while the total distance traveled can vary a great deal depending on the speed of the moving frame.   

The observer on the ground is what I call a "Frame Measurer," an "idealized" observer standing perpendicular to the moving frame whose calculations are unencumbered by net light delays. This observer presumably stands equal distance between the events of interest--in this case, just below wherever the clock is at the instant the pulse reaches the bottom of the channel (since the diagonals are equal in length and angle, the event of the pulse's projection at the top of the channel and the event of its return will be equal distance to him). More specifically, calculations are the SUM of the measurements of a series of Frame Measurers placed along the path of the moving frame. This is the "observer"/"observers" relativists generally use for making measurements (along with an equivalent one for the frame moving with respect to the ground).

 

The accepted interchangeability of the words allows relativists to communicate more easily--but not more effectively. This is the definition of slovenly expression: pursuing the ease of execution, or expression, at the undue cost of efficacy, communication. The result is cultivated misconceptions, especially lingering misconceptions. The misconceptions may be mostly dormant while students take a relativity class, as students generally work with the idealized observer, but as they forget things over time, lingering confusion can manifest upon the student's return to the subject. 

Although there isn't a problem with the nomenclature in this case, something similar happens with contact force and net force. Students become so accustomed to calculating net force they forget about contact force, which is just as important. The fact that students deal so much with the Frame Measurer temporarily negates the subtle confusion while simultaneously reinforcing it.   

It's possible, however, that one could turn the introductory paragraph on its head and argue that the use of observer reinforces the need for students to abandon the notion of objective space and time, since it’s more absolute than frame of reference. Even still, given that a mainstream physicist hasn't believed in an etheric frame since before the second World war, I think it's clear that such a need is antiquated at best.  

Whereas the texts are merely sloppy, the documentaries get it (and Einstein only knows what else) flat-out wrong. One with Brian Green actually showed clocks moving slower when they should have been moving faster.To his credit, Alan Guth of MIT (who shops at my supermarket) pointed this out to him before it was released, and Green went ahead with it anyway (Here is Guth on relativity documentary). This is a textbook example of what the Nobel laureate physicist Hans Alfen called "pseudo-pedological": An explanation designed to create the illusion of understanding. 

Being offended by such things should be a rite of passage for young intellectuals. 

Even under the best of circumstances, it's next to impossible to acquire understanding without at least a certain degree of misunderstanding, especially in the months or years taking a course. The least people could do is not encourage it. 

Knowledge is only power if it's supported by wisdom and understanding; without them, it's dangerous. Increasing one's knowledge of the parts without a proportional increase in how it all fits together leads to a self-inconsistent understanding, making it vulnerable to misuse (especially if someone doesn't know what knowledge and understanding are in the first place). Modern science is four centuries old; it's high-time scholars realized this--and did something about it.