The two-way speed of light has been proven to isotropic in all inertial frames, the same in all directions, irrespective of the motion of the inertial frame that measures it. However, the isotropy if the one-way speed of light is somewhat of convention, dependent on the way clocks are synchronized. The Einstein method of clock synchronization can be shown to be the best possible convention, but it is by no means a requirement of physics - other synchronizations are possible and valid. Read More »

The so-called 'speed of gravity' has been the source of some controversy over the years. The anti-relativity fraternity maintains that the speed of gravity must be infinite, i.e., that gravity acts instantaneously over any distance. Relativists, on the other hand, maintain that no influence propagates faster than the speed of light and that gravity is no exception. Read More »

What is gravity? The truth is that at the most fundamental level, no one really knows. This post covers the very basics of Einstein's gravity in terms of the gravitational acceleration that is caused by curved spacetime and velocity.

This old 'enigma' has puzzled scores of people over the last century. There are many so-called 'solutions to the twin paradox', but many are still left confused. Here's how you as engineer should look at it. Read More »

In this opening post, I will start to answer the question: what is relativity? There is obviously a lot more to it than what I describe here, but it's a start...