I'm not so good on Heisenberg, but the (non-physicists') deal with Schroedinger's cat is that observing something changes its state -- unobserved, things could be doing pretty much anything, but when we observe them, we "fix" their state. If a cat's in a box either alive or dead, until we look in and see, then the cat exists in both states. Once we look, then we're the ones who really create the situation in which the cat is in only one state, alive or dead.
The Heisenberg joke is basically you can know how fast you're going or where you are (position and momentum according to Wikipedia) but not both at once, in a nutshell. Hence the response to the cop. occhiblu has the cat thing pretty well. Neither one of them make "sense" they're just riffing off the two scientific examples in a sort of wink-nudge way.
Schrodinger's cat is an idea put out by Schrodinger to illustrate the problem of the "Copenhagen" interpretation of quantum mechanics being applied to real objects. Einstein and friends felt that a quantum view of something includes all the possible states a thing can be at once. That means something only has a definite state at the moment of observation. Schrodinger felt that a cat in a box, unobserved, would be dead or alive without observation and used that to show that quantum mechanics can't be used to explain an object in real space.
The Heisenberg joke is very funny. The Schrodinger one not so much.
A few weeks ago I would never have gotten the Schrodinger's cat joke, but I just saw it referenced on a way cool episode of Nova.
Incidentally, I'd highly recommend that Nova special if you get a chance to see it. It's called Parallel Worlds, Parallel Lives and follows Mark Everett (the main guy from the Eels) as he learns more about his father, Hugh Everett, a legend in quantum physics and the founder of the parallel universe theory.
I knew the foundation of both those jokes, and didn't find them to be very funny. Sort of like, "Newton was pulled over by the Carriage Police and they asked if he knew how fast he was traveling. Newton said, 'No, but you can calculate it based on the time it has taken me to travel this distance.'"
Unless the humor comes from applying quantum laws to macro situations?
Thanks so much everyone for the interesting info and links. Jokes like these would have been right up my science teacher's alley, but I was likely not paying attention. Now of course I'm fascinated by it and wish I knew more. I think I'll start with the Nova site (thanks Slack-a-gogo!).