Fundamental bounds on transport
There is a long history to the idea that transport may be subject to fundamental constraints. I will argue that a variant of these ideas offers promising ways to think about transport in unconventional metals such as high temperature superconductors. I will discuss both proposed lower and upper bounds on transport, and I will suggest that such bounds may address long-standing transport puzzles in unconventional metals. I will discuss recent experimental probes of these ideas as well as theoretical connections to questions in quantum statistical mechanics.