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ntributions to the theories of quantum gravity and nuclear fission, but is best known for coining the term 'black holes'. A keen teacher and mentor, he was also a key figure in the Manhattan Project. [Listener: Ken Ford] TRANSCRIPT: In particle physics when we have particles collide, we may have strangeness, we may have parity, we may have charge, we may have a Baryon number, a Lepton number - we have a variety of numbers which serve to characterize particles and help keep track of what can happen in a collision, to find the commonality between the particles that come out and the particles that went in by saying the strangeness is conserved, or parity is conserved or not conserved and so on. But mutability is the argument that there is nothing that can't be 'un-conserved' if we look hard enough at processes that are extreme enough. Well somebody might very well say "What about electric charge?" Yes, we don't know any process that violates the Law of Conservation of Electric Charge, so if one believes in the principle of mutability, you'll keep looking for a process where electric charge is not conserved. I'm not immediately animated to go on a raging tearing search for such a process because I don't envisage it right now.