…heorem or something like it? It is widely believe that the CPT may fail in generic extensions of quantum theory. In particular, the requirement of a unitary representation of the Poincaré group is pretty strong, and may not hold in the kind of general context of interest in quantum gravity. Just search for CPT-violation on the arxiv to see what I mean. But there is a sense in which something “like” a CPT theorem probably will hold in physics beyon…
Read more…f spatial regions. However, William and the astronaut will agree about the order in which time-like separated events occur: first Harold is crowned, and then Harold is slain. Figure 1: An observer on Earth and an astronaut traveling away with velocity c/2 will describe two different foliations of spacetime into space-like hypersurfaces of simultaneity. On the other hand, an accelerating observer will not generally agree about the order in which th…
Read more…m the description and explanation of empirical fact, as is the language of prescription and justification. Although Sellars was concerned with the philosophy of mind, there is something important here for philosophers of physics to learn as well. A major activity of physics is the collection of empirical facts. Another is the prediction and justification of these facts. But the activity of investigating meaning is a distinct activity altogether. T…
Read more…lation currently being explored. Each makes use of a symmetry principle in order to establish that the laws of physics are T-violating. And each works even when we don’t have a very clear picture of the laws themselves. T-violation by Curie’s principle. Pierre Curie declared that there is never an asymmetric effect without an asymmetric cause. This idea, together with the CPT theorem, provided the road to the very first detection of T-violation in…
Read more…as a little sloppiness. But it has grown into an error that seems to have spread all over the place. The incorrect mantra The problem comes from a footnote in Wolfgang Pauli’s Quantum Mechanics textbook, where he wrote (pg.63, fn.2): In the older literature on quantum mechanics, we often find the operator equation … . It is generally not possible, however, to construct a Hermitian operator (e.g. as function of and ) which satisfies this equat…
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