ABSTRACT
Special relativity involves comparing what different observers see. But
we need to be careful about what these words mean.
A reference frame is a way of labeling each event with its location in
space and the time at which it occurs. Making a measurement corresponds
to recording these labels for a particular event. When we say that an ob-
server “sees” something, what we really mean is that a particular event
is recorded in the reference frame associated with the observer. This has
nothing to do with actually seeing anything-a much more complicated
process that would involve keeping track of the light reflected into the ob-
server’s eyes. Rather, an “observer” is really an entire army of observers
who record any interesting events, and an “observation” consists of recon-
structing from their journals what took place.
