Game Development Reference
Albert Einstein is that he had the foresight to abandon time as a constant. Instead he
postulated that light travels at the same speed regardless of the motion of the source.
That is to say, if you shine a flashlight in a vacuum, the electromagnetic radiation it emits
in the form of visible light travels at a set velocity of c (299,792,458 m/s). Now, if you
take that same flashlight and put it on the nose of a rocket traveling at half that speed
directly at you, you might expect that light is traveling at you with a velocity of 1.5 c . Yet,
the rocket-powered flashlight would still be observed as emitting light at a velocity of
c . As Einstein's theory of special relativity matured, the postulate has been reformulated
to state that there is a maximum speed at which information can be transferred in the
space-time continuum, a principal called locality . As electromagnetic radiation has no
mass, 4 it travels at this maximum speed in a vacuum.
The most startling consequence of the theory is that time is no longer absolute. The
postulate that the speed of light is constant for all frames of reference requires that time
slow down, or dilate , as velocity increases. It is actually fairly easy to demonstrate this
The following example depicts a conceptual clock. A beam of light is bouncing between
two mirrors. The time it takes for the beam of light to start from one mirror, bounce off
the second, and return to the first constitutes one “tick” of this clock. That tick can be
Δt = 2L/c
Where L is the distance between the mirrors and c is the speed of light. Figure 1-12
shows what the clock would look like if you were above it traveling at its velocity.
Figure 1-12. Traveling with the clock
4. Photons, the particle form of electromagnetic radiation, can have relativistic mass but are hypothesized to
have no “rest mass.” To avoid getting into quantum electrodynamics, here we'll just consider them without