Real Time Relativity User Guide Real Time Relativity User Guide Version 0.8, August 2007 (updated 27 August 2007) Web site: www.anu.edu.au/Physics/Savage/RTR Contents 1. Overview 2. Installation 3. Basics 4. Controls 5. Customization 6. Exploring relativity 7. Physics 8. The Code 9. References 1. Overview RTR is a simulation of a world which obeys the physics of special relativity. It allows users to learn by exploring. Some of the physics can be turned off to allow easier study of specific effects. 2. Installation RTR is installed using the Windows Installer which may be downloaded from the RTR web site. All RTR files are installed in the "Program Files" directory in the directory "Australian National University". The executable is called "RTR.exe". A link is placed in the start menu under "Real Time Relativity". Earlier versions must be uninstalled using the "Add or Remove programs" Windows control panel. If it doesn’t work The most likely reason for RTR to display an error message when starting up is that your Video card does not have a programmable Graphics Processing Unit (GPU). All modern cards should have one. We believe the following are compatible cards: nVidia GeForce FX Series, 6xxx Series, or 7xxx Series; ATI Radeon 9500-9800 Series, or X Series. Apparently, RTR does not run on some systems which do have GPUs. If it does not run on your system and you would like to work with us to figure out why, contact us through the RTR web site. You can try running in Safe Mode: see under “Parameters” in the Customization section. This turns off some features, such as the clocks, and uses safer Direct X files. If all else fails, you can try version 0.2a, available from the versions page on the RTR web site. 3. Basics Starting up. Start up using the Start menu or the desktop alias. You will appear in the world, looking down a path lined with stone columns. Press W to accelerate. The default window size may be changed as described in the Customisation section below. Message boxes may announce errors. They can be dismissed by pressing Enter. The most common errors are due to older graphics cards that do not support features required by RTR. Exiting. To end RTR press the Escape key (ESC). The RTR window. Your current velocity is expressed as a fraction of the speed of light (c) in the top left corner. Also shown are the pointing angles of your camera. The bottom left hand corner gives some key mappings. Note that if the Desktop colour quality is set below 24 bits the 3D will not work properly -- behind and in front may become confused – set it as high as possible. 1 of 9 Real Time Relativity User Guide The RTR window may be captured to the clipboard with Alt-PrintScreen. Switch to full screen mode with ALT+ENTER. Repeat to toggle back to a window. Note that if your screen resolution is too high for your graphics card (e.g. >1024 pixels in width or height) the frame rate will drop, perhaps dramatically, so that RTR appears to freeze. The World. The world in the simulation is big, because the speed of light is fast. It is denoted by “c”, and c = 300,000 km/s. The Earth and Sun are to scale, respectively about 0.043 and 4.7 light- seconds in diameter. A light-second is the distance light travels in a second: 300,000 km. The square on which the world sits is 35 light-seconds on a side, the colored cubes are 2.5 light- seconds on a side, the distant bar is 25 light-seconds long, and the two clocks are 10 light- seconds apart. In the RTR world it is useful to use light-seconds as the unit of distance, and seconds as the unit of time. The speed of light is then 1 light-second per second. The object in the “sky”, the skybox, are moved every frame to stay centred on the camera, so their absolute sizes are undefined. The clocks in the world show world time in seconds since RTR started, or since the timers were reset with the zero key. However, the time you see is delayed by the time it takes the light to travel from the clock to you. For example, if the clock is reading 50s, and you are 10 light- seconds away from the clock in the world frame, you will see the clock reading 40s. The clocks can be used to observe time dilation and the relativity of simultaneity. 4. Controls The mouse controls where you are looking, but not the direction your ship is pointing. Try looking around a bit with the mouse. You'll notice that the red cross always points in the same direction- this tells you which way your ship is facing. Placing the red cross in the centre means you are looking in the direction of travel (F key). The keyboard controls the ship's direction of motion. The arrow keys control pitch and yaw (pitch is tilting the nose up and down, yaw is rotating it side to side). Try moving around a little with the keys. You'll notice that the red cross remains fixed in the centre of the screen. If you get lost you can reset to the starting configuration by using the O (Oh) key. To accelerate and decelerate, use the W and S keys. Accelerate up to about 0.2c and practice flying around and looking with the mouse, until you are familiar with the controls. To stop use the 1 key. To instantly accelerate to 0.866c use the 2 key, and to 0.9682 use the 4 key. These give gamma factors of 2 and 4 respectively and hence length contraction and time dilation by these factors. Keys 3 and 5 accelerate “backwards” to -0.866c and -0.9682c. To help measure lengths a grid can be toggled on the screen with the G key. When travelling toward an object, the Doppler Effect causes the wavelength of the incoming light to change. By default, this effect is turned off in the simulation, but you can toggle it on/off with the K key. An indicator at the top left of the screen tells you its status. When travelling at relativistic speeds, the world appears to brighten in the direction of travel, and darken away from the direction of travel. This is called the headlight effect. This effect is disabled in the simulation by default, but can be toggled with the H key. An indicator at the top left of the screen tells you its status. All relativistic effects, Doppler, headlight and aberration, may be toggled on and off with the M key. This may make it easy to navigate the world. 2 of 9 Real Time Relativity User Guide The time you actually experience flying around the world is called "proper time". The time that would be experienced by hypothetical observers in the world frame is called "world time". By default RTR works in proper time. Sometimes it is useful to work in world time, even though it is unphysical, because it is "slower". These two times can be switched between with the T key. When you are in proper time, timers are displayed at the top left of the screen. When you are in world time they are not displayed. You can zero the timers using the 0 (zero) key. By default RTR uses constant proper acceleration when the acceleration and deceleration keys are pressed. Constant world frame acceleration can be toggled with the P key. Constant proper acceleration is physically realistic, but takes longer to reach speeds above about 0.95c. Hence it is sometimes convenient to use the physically unrealistic constant world frame acceleration. By default RTR uses game type yaw and pitch control, with increasing angular speed while the arrow keys are depressed. This is convenient but unrealistic. The Y key toggles a more relativistically correct control, approximating constant proper acceleration perpendicular to the velocity. This makes turning slow at high speed. Controls summary Mouse: look direction. Left click or L: look 90 degrees to left of direction of motion. Right click or R: look 90 degrees to right of direction of motion. Middle click or B: look behind direction of motion. Keyboard. Navigation Up & Down arrows: Pitch direction of motion. If Game Navigation is on (N to toggle): W: Accelerate.Default: 0.2 light-seconds / second2. (Customise as below). S: Decelerate. Default: -0.2 light-seconds / second2. A & D: Yaw direction of motion. If Game Navigation is off (N to toggle): A: Accelerate. Default: 0.2 light-seconds / second2. (Customise as below). Z: Decelerate. Default: -0.2 light-seconds / second2. Left & Right Arrows: Yaw direction of motion. Speed presets 1: Set speed to zero. 2: Set speed to +0.8660c, for a gamma (time dilation) factor of 2. 3: Set speed to -0.8660c. 4: Set speed to +0.9682c, for a gamma (time dilation) factor of 4. 5: Set speed to -0.9682c. Position presets O (Oh): Reset to the initial camera setup: (x=0,y=0,z=0). Do this if you get lost. C: Looking at the clocks: (x=-10,y=0,z=-17). v=0.5c.Looking left. Used for relativity of simultaneity. I: Looking at the clocks: (x=-10,y=0,z=-40). v=0. Looking left. Used for relativity of simultaneity. Look directions F: Look in the direction of motion. B: Look behind the direction of motion.