Q: How many Quality managers does it take to change a lightbulb ?
A: We've formed a quality circle to study the problem of why lightbulbs burn out and to determine the best thing we as managers can do to enable lightbulbs to work smarter, not harder.

Q: How many quantum mechanicians does it take to change a light bulb?
A: They can't. When they get the socket to hold still, they can't find it.
A: They can't. If they know where the socket is, they cannot locate the new bulb.

Q: How many quantum physicists does it take to change a lightbulb ?
A: One. Two to do it, and one to renormalise the wave function.