As a material object makes its flight through the air (molecules / medium), it is a substantially different thing from a sound wave traveling through air. The principle of relativity holds the pair in a tension of physics contrariness. A material object making a straight line flight at constant velocity through space (air / medium), is seen to have two different velocities, when viewed by two different observers, in two different frames. One frame is considered as being at rest, and the other frame is considered as being in motion with constant velocity. Transfer of momentum and addition of velocities mask the velocity of the reference frame considered in motion, and the principle of relativity as a scientific concept prevents the detection of this motion.

The foundational propositions of Einstein’s Special Theory of Relativity (STR): the Lorentz transformation, time dilation, length contraction, etc., are based on a particular interpretation of the nature of the relationship between two inertial reference frames. Given two reference frames moving relatively to each other, the observer within the moving frame is considered at rest, though the reference frame is moving. An observer in another reference frame that is at rest or stationary, views the motion of the first frame. The observer in the first reference frame can not by any mechanical experiment detect his or her own reference frame’s motion.

By STR, though the train is in motion, it is regarded as being at rest in the reference frame attached to the train. In the frame attached to the platform, the observer can clearly see the train’s motion. Nonetheless, the observer on the train is assumed to be unable to do any mechanical experiment that can detect his or her motion. The transfer of momentum of material objects cloaks any motions that might disclose any strange forces at work; through the addition of velocities, substantial speeds are kept hidden. The property of waves (sound, EM, etc.), to not accept this transfer of momentum from its source, leads to the violation of Galilean invariance. In other words, the wave speed remains fixed across reference frames, regardless of their relative velocity.

For example, a ball thrown rearward from the engine of the moving train has the velocity of the train subtracted from the ball’s velocity. This maintains the appearance of the same distance of travel, and the same time for the journey; unbeknownst to the observer within the reference frame of the thrown ball. However, a sound wave directed rearward will not have any velocity subtracted, so that the wave will appear to travel a decreased distance, over a decreased duration of time, as the train moves forward. This would hint at a possibly deeper reality. For a material object, the influences of forces are somewhat hidden; for a sound wave they are not, they are just dodged and evaded.

In this thought experiment, I have shown that it is possible by the properties of sound waves, to lift this veil; to pull aside the curtain from the aforementioned proposition of the STR postulate. That is, it is possible to pass through the wall between reference frames like a subatomic particle; to measure the same velocity value of a sound wave, by observers in separate reference frames that are moving with a constant velocity relative to one another. It may become possible to overcome the static that jams any two-way communications between reference frames.