Velocity and absurdity in modern physics

Abstract

When physicists write the variable v, they usually mean the velocity of an object in an inertial coordinate system, otherwise known as a reference frame. This is the most common velocity concept in modern physics. The velocity of an object in this sense depends on which inertial coordinate system one is working with. For example, an airplane in flight has a velocity of about 500 miles per hour in a coordinate system anchored in a nearby mountain, a velocity of more than 60 000 miles per hour in a coordinate system anchored in the sun, and a velocity of 0 in a coordinate system anchored in the airplane itself. The widely accepted idea that the ticking rate of a clock is a function of this type of clock velocity is absurd. It implies that a human analyst can control the ticking rates of physical clocks through the mental act of selecting a coordinate system. This is a nonsensical mingling of imagination with reality that is akin to believing that a movie character can jump out of your television set and take a seat in your living room. Despite this absurdity, the idea that a clock’s ticking rate depends on its velocity in an inertial coordinate system is a staple of modern physics. It is a pillar of Einstein’s special theory of relativity. It is central to the standard analysis of the so-called twin paradox. It underlies the predictions of Hafele and Keating concerning the ticking rates of clocks that travel in airplanes. Velocity absurdity of this sort flourishes today, and it may well continue to flourish for many years to come.