To understand relativity, one must first understand reference frames.

All measurements in physics are taken from the origin. 3D Cartesian coordinate space has x, y, z axes at right angles to each other.

Coordinates x, y, z and t.
Any event can be represented by observer with x, y, z, t (time)

There are many possible reference frames, and all measurements are made from a frame of reference.

 Coordinates x, y, z and t for some even.
Reference frames S and S^{\prime} relate to each other by x^{\prime}=x-{\Delta}x

Inertial reference frames (IRF) are defined as having no acceleration. Though Earth is not a true IRF, its acceleration is so small that it can be ignored.

Galileo and Einstein agree that all IRFs and their laws of physics are identical.

Reference frames can differ from the origin via rotation or translation. Alternatively, one frame of reference can be moving relative to another.

Reference frames do not have to line up. However, for our study we consider one dimension only where the two coordinate systems run parallel along an x-axis.
Various different reference frames. In the bottom right diagram, S^{\prime} is moving at a speed v with respect to S.

Leave a comment