Experiment 2: Mrs. Einstein is standing in a field. Next to her is a light clock. That is, two mirrors that are reflecting a beam of light back and forth, and the journey from one mirror to the other and back again counts as one tick of the clock. Also, Mrs. Einstein is wearing a watch that is synchronized with her light clock.

Standing on a railroad car is Mr. Einstein. He also has a light clock, and his clock is synchronized with Mrs. Einstein's and his own wristwatch. The railroad car is not moving.

Question: What happens?

Answer: Nothing unusual happens. Mr. Einstein's watch and clock stay perfectly synchronized with Mrs. Einstein's.