Auto Mechancis to Quantum Mechanics: Any Questions?

It's been a while since we've done this and I've been meaning to get back to it for about a month or so, so let's have at it.

For those new to the Playground, I have a schtick I do at the beginning of each class where I let the students ask absolutely any question they have, any question at all, from auto mechanics to quantum mechanics. Some former students asked me to revive it on-line when this blog first started, so every once in a while I open it up. So, if you've ever had a question you always wanted to ask or something that's just been stumping you, here's your chance. Ask away and I'll get to as many as possible in this week's posts.