# I have a question. Years ago me and two friends got into a debate about a riddle. The riddle goes like this: A train starts from point A and is travelling towards point B. A wasp is travelling in the opposite direction at twice the speed of the train, the wasp touches the tip of the train and goes back to point B. How many times does the wasp touch the train? (this may be one version of many, but this is how it was told that faithful evening) So the "correct" answer was, infinte times. (similar to Zeno's paradox with Achilles and the tortoise). I said, well in theory it's infinte times, but if you were to actually do it, the train would hit point B eventually so it can't be infinte times? For it to be infinite times it would have to stop time (or something) So what would happen if you actually tried this? Say we do an experiment with a model train and instead of a wasp we use a laser (for accuracy). First we measure the railway track and only run the train, let's say it takes 10 seconds to go from point A to point B. Then we add the laser, travelling at twice the speed from point B, hitting the tip of the train back to point B. If the train takes 10 seconds to reach point B, the laser can't have travelled back and forth infinte times? Can it? This "debate" comes up every so often and we argue and never seem to resolve it. Please help us out, what would happen, in real life? Sincerely, Anders K.

Read another response by Stephen Maitzen