What is energy anyway?

Physics, while absolutely fascinating, can be impenetrable. And it isn't just cutting-edge ideas that can melt our brains, often we accept basic principles and ideas without really knowing how they work or even what they are. This week, Jonathan is joined by Sean Carroll, physicist, and author of 'The Biggest Ideas in the Universe: Space, Time, and Motion', to explain some of the fundamental aspects of science we thought we knew.