1. Most “paradoxes” result from poorly-posed questions.
2. All observers must agree!
3. Special relativity changes our understanding of matter.

Estimated Time: 20 minutes, including wrap-up

• Warmup: Have the class as a whole discuss the first two paradoxes on the handout.
• Have each group select one of the next two paradoxes.
• Half the group should draw a spacetime diagram of what is observed from one reference frame; the other half from the other reference frame.
• Each group should reconcile their two diagrams.
• If time permits, repeat with one of the other paradoxes on the handout.

• basic understanding of spacetime diagrams
• the ability to calibrate spacetime diagrams using hyperbolas would be helpful

• Table top whiteboards and markers
• Handout

• Compare the spacetime diagrams from different groups, and for different paradoxes.
• Discuss the rules for drawing spacetime diagrams, along the lines of §6.5 of the text.
• See also the discussion of spacetime diagrams for the pole and barn paradox, which can be found here.