This page contains an interactive applet, which will only be run if your browser supports the Java programming language.

The *Null Chamber* is a cavern in the Splinter that contains a part of the *Null Line*, the line traced out by the orbit of
the Splinter, where objects are perfectly weightless. Using the applet above, you can re-create the experiments that Zak and Roi conduct in
the Null Chamber, and try out new ones of your own. The directions within the Splinter are:

**garm**= closer to the Hub (the unknown object that the Splinter orbits) /**sard**= further from the Hub;**rarb**= the direction that the Splinter orbits /**sharq**= opposite the direction that the Splinter orbits;**shomal**= above the plane of the orbit /**junub**= below the plane of the orbit.

The applet shows three simultaneous views of the chamber: from “shomal/above” (top left) and two orthogonal side views. The small black square with an arrow protruding from it represents a machine for firing stones; you can drag this machine to any coordinates you like, and drag the tip of the arrow to choose a velocity for the stones it fires. (You can also use the ARROW KEYS on your keyboard to move the machine, or to change the velocity by holding down the SHIFT KEY; you need to click on one of the view panels first.)

If you click the FIRE button, a stone will be ejected from the machine with the chosen velocity.
You can fire as many stones as you wish; if the chamber becomes cluttered, use the CLEAR button. Also, you can release a stone
from the machine with zero initial velocity using the DROP button. Hitting the *F*, *C* and *D* keys respectively will have the same effect
(though you need to have clicked on some part of the applet first). If the “Show trails” checkbox is ticked, the path each stone
follows is drawn on to all the views; these trails are cleared when you hit the CLEAR button. The *S* key toggles this checkbox.

The panel in the top right lets you choose the size of the Splinter’s orbit (*r*/*M*) and the amount of angular momentum the Hub possesses (*a*/*M*);
just click or drag the white cross to the desired choice of parameters. The curves here are lines of constant “weight ratios”:
the ratio between the weight of a given object at a certain distance garm or sard of the Null Line to its weight at the same distance
shomal or junub of the Null Line.
The ratios from –1 to –2 (grey curves) represent unstable orbits. Note that when you change these parameters, all the current stones (and their trails)
are cleared from the chamber.

You can learn more about the interpretation of these experiments from the Orbits and Tidal Accelerations overview, and the accompanying mathematical details.

Greg Egan
science fiction writer

Incandescence / The Null Chamber / created Thursday, 3 January 2008 / revised Saturday, 12 January 2008