A spacetime diagram showing the location of three events.
A spacetime diagram showing the location of three events.
The Simultaneity Spacetime Diagram model uses light-trajectories to show the effect of relative motion when observing (recording) events in special relativity. In the default scenario, an explosion (an event) at the center of a right-moving stick occurs at t=0 and the arrival of the explosion light signal at each end is recorded. The arrival event at the left end occurs before the arrival event at the right end because the stick is moving. How do the location and time of these events change if they are observed in a reference frame (the Other Frame) in which the stick is stationary?
The Simultaneity Spacetime Diagram model was written for the study of special relativity using spacetime diagrams. Initial conditions, such as the locations of the explosion and the detectors, can be adjusted by dragging before the simulation is run. The slider can be used to change the speed of the stick. A third view shows the stick and the wavefront in space. More importantly, a checkbox allows users to compare the predictions of Galilean and special relativity in order to observe how the assumption of a constant speed of light leads to the relativity of simultaneity.
The Simultaneity Spacetime Diagram model is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_sr_SimultaneitySpacetimeDiagram.jar file will run the program if Java is installed. Other special relativity programs are also available. They can be found by searching the OSP Collection for special relativity.
"The Twin Twin Paradox: Exploring Student Approaches to Understanding Relativistic Concepts," Sébastien Cormier and Richard Steinberg, The Physics Teacher, (in press).
Spacetime Physics 2nd ed, Edwin F. Taylor and John Archibald Wheeler, W. H. Freeman (1992).
A Travelers Guide to Spacetime, Thomas Moore, McGraw-Hill Science (1995).
The Simultaneity Spacetime Diagram model was created by Wolfgang Christian using version 4.3 of the Easy Java Simulations (EJS) authoring and modeling tool. You can examine and modify a compiled EJS model if you run the program by double clicking on the model's jar file. Right-click within the running program and select "Open EJS Model" from the pop-up menu to copy the model's XML description into EJS. You must, of course, have EJS installed on your computer.
Information about EJS is available at: <http://www.um.es/fem/Ejs/> and in the OSP ComPADRE collection <http://www.compadre.org/OSP/>.