In this episode of Rationally Speaking, Caltech physicist Sean Carroll describes an "embarrassing" state of affairs in modern physics: that we still don't know how to interpret quantum mechanics, almost a century after its discovery. Sean explains why he thinks the "Many Worlds Interpretation" (MWI) is the most plausible one we've got, and Julia explores his thoughts on questions like: Can MWI be tested? Is it "simpler" than other interpretations, and why? And does MWI threaten to destroy our systems of ethics?

Sean Michael Carroll is a research professor in the Department of Physics at the California Institute of Technology. He is a theoretical cosmologist specializing in dark energy and general relativity.