On Wednesday May 16, the day before the Rutgers-Columbia QFT Workshop, MAPS will host a pre-workshop workshop at the NYU philosophy department, in room 202 (5 Washington Place, New York, NY). See the schedule below for more details.
J. Brian Pitts (Cambridge).
Title: Even Observables Change in Hamiltonian General Relativity.
Abstract: The Hamiltonian formulation of Einstein’s General Relativity is the one most readily suited for merger with quantum mechanics. But since the 1950s there has been a worry that change has disappeared, especially from the physically real “observables”. The freedom to change time coordinates, already important in Special Relativity and greatly amplified in General Relativity, also seems to disappear from the Hamiltonian formulation. These issues yielded a memorable 2002 exchange between Earman and Maudlin.
This talk, building on a reforming literature from the 1980s onward, discusses how the radical relativity of simultaneity, change, and even change in observables are to be found. Key moves include recognizing that the Hamiltonian formulation is a special case of the more familiar and fundamental Lagrangian formulation (implying that radical conceptual novelty cannot arise) and redefining observables such that equivalent theory formulations have equivalent observables.
Jeremy Butterfield (Cambridge).
Title: On Dualities and Equivalences Between Physical Theories.
Abstract: my main aim is to make a remark about the relation between (i) dualities between theories, as `duality’ is understood in physics and (ii) equivalence of theories, as `equivalence’ is understood in logic and philosophy. The remark is that in physics, two theories can be dual, and accordingly get called `the same theory’, though we interpret them as disagreeing—so that they are certainly equivalent, as `equivalent’ is normally understood. So the remark is simple: but, I shall argue, worth stressing—since often neglected.
My argument for this is based on the account of duality by De Haro and myself: which is illustrated here with several examples, from both elementary physics and string theory. Thus I argue that in some examples, including in string theory, two dual theories disagree in their claims about the world.
I also spell out how this remark implies a limitation of proposals (both traditional and recent) to understand theoretical equivalence as either logical equivalence or a weakening of it.
Chip Sebens (UCSD).
Title: How Electrons Spin.
Abstract: There are a number of reasons to think that the electron cannot truly be spinning. Given how small the electron is generally taken to be, it would have to rotate superluminally to have the right angular momentum and magnetic moment. Also, the electron’s gyromagnetic ratio is twice the value one would expect for an ordinary classical rotating charged body. These obstacles can be overcome by examining the flow of mass and charge in the Dirac field (interpreted as giving the classical state of the electron). Superluminal velocities are avoided because the electron’s mass and charge are spread over sufficiently large distances that neither the velocity of mass flow nor the velocity of charge flow need to exceed the speed of light. The electron’s gyromagnetic ratio is twice the expected value because its charge rotates twice as fast as its mass.