What is a superselection rule?
A superselection rule is a special limitation on what is observable in the quantum world. For example, we can never seem to observe interference from the relative phases between a…
Read moreWriting a book on time reversal
So, I’m writing a book on the foundations of time reversal. I’ve decided to bring back the Soul Physics blog to talk about the book as it’s being written, and…
Read moreCPT: The ‘Intuitive’ Approach
Khriplovich and Lamoreaux (1997, §2) suggest a very interesting argument that CPT provides the correct notion of “complete reversal” in physics. The background assumption is that “complete reversal” should have…
Read moreWigner’s elegant characterization of time reversal
There’s a nice post at The Eternal Universe illustrating discrete symmetries like time reversal. The father of this idea, Eugene Wigner, actually gave a very elegant characterization in his 1931…
Read moreDavid Albert on symmetries of motion in quantum mechanics
In Time and Chance, David Albert writes that since the Schrödinger equation involves a first (instead of a second) derivative, “the dynamical laws that govern the evolutions of quantum states in…
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