==== Light Speed! ====


DESCRIPTION

     This is a simulator designed to illustrate relativistic effects on
the appearance of objects moving at ultra-high velocities.

     It simulates a geometrical lattice object traveling at a given speed
in a straight line through space. Specifically, the object moves along the
x-axis of this space, in the positive-x direction; at time t=0, the object
is precisely centered on the origin.

     The simulator displays, in essence, a still image of the vicinity of
the origin snapped at the exact moment that the object is *seen* to be at
the origin; i.e. the moment that light reflected off the object, when the
object was exactly at the origin (at t=0), eventually reaches the camera.
This moment will usually be a few billionths of a second after t=0,
accounting for the time needed for the light to traverse this distance.
(The camera's info display will explicitly indicate the time of the
snapshot, to 0.001 microsecond accuracy).

     Light Speed! will allow you to move around and see interactively how
the object appears to change with observer position. At low velocities,
this isn't much the case, but up in the several-million-meters-per-second
range, the object as viewed from one angle to another can vary
significantly.

     To get started, drag the slider at the right of the window upward.
Relativistic effects will immediately become noticeable. Click and drag
in the graphics window to move around. Have fun!



THEORY

Light Speed! takes into account the following consequences of special
relativity:

  1. Lorentz contraction     (fast objects appear shorter)
  2. Doppler red/blue shift  (the Doppler effect on light/color)
  3. Headlight effect        (redistribution of reflected light)
  4. Optical aberration      (warping due to the finite speed of light)

A lengthier treatment of the above phenomena, complete with the formulae
used (really, they're not that bad!) may be found in the file MATH.



LIMITATIONS

The only major weakness of this simulator is color. The Doppler shifts
produced are only approximations, and in certain cases may be wildly
inaccurate. If color fidelity is a must, Antony Searle's BACKLIGHT
raytracer program may be a better choice. (See the Acknowledgements
section below for details).



REQUIREMENTS

Light Speed! requires the X Window System with OpenGL or Mesa3D support,
as well as the GTK+ libraries to function. Compilation will additionally
need Janne Lof's GtkGLArea widget. See the file INSTALL for more.



ACKNOWLEDGEMENTS

I would like to thank Antony Searle, of the Australian National
University, for allowing me to make use of the Doppler-shift code from his
well-received relativistic raytracer, BACKLIGHT. This program illustrates
relativistic effects via a four-dimensional raytracing engine, and I
highly recommend it in case greater scientific rigor or creative
flexibility is desired. You may find it at:
http://www.anu.edu.au/Physics/Searle/



====================================
Daniel Richard G. // <skunk@mit.edu>
