Assumptions of Physics - Reading the Book

I've been following along these sessions. I don't understand most of the maths, but it's still thought-provoking. They're reading the book Assumptions of Physics by Gabriele Carcassi and Christine A. Aidala.

Today we got to a specially good bit, about Langrangian mechanics with multiple degrees of freedom. (Towards the end of page 51.) 

My comments: 

46:24 Bells and bright lights and sparkles. What "velocity is a derived unit from position and time" means is that in order to make a measurement of velocity, you must have in hand a means to measure time intervals, and a means to measure position, and to these are associated some units, so you have some clocks and measuring rods, but in addition you need an actual observer to make a judgement and that judgement itself constitutes a space-time event. Then your physical theory needs to be based on the coherence of the descriptions that a collection of such actual observers make and which they describe to each other via whatever effective means they have for communication. So whatever mathematical apparatus it is that we need to deal with these initial relationships, it has to include representations of the communications between observers of the judgements they actually make. E.T. Jaynes started this programme in  statistical physics and it's been taken up by Chris Fuchs and others as QBism. Recently (2022) there was a paper by Carlo Rovelli and Emily Adlam "Information is Physical: Cross-Perspective Links in Relational Quantum Mechanics" on the arxiv. [See also Quantum theory cannot consistently describe the use of itself by Daniela Frauchiger & Renato Renner and the response Quantum mechanical rules for observed observers and the consistency of quantum theory by Alexios P. Polychronakos.]

53:16 I only heard that distinction between active and passive gravitational mass a few months ago. I assumed it was just a way to linearise the theory for local observations, but when you consider the issue of derived units and observer-dependence then that distinction might become important.

The talk by Chris Fuchs Christopher A. Fuchs on the Day QBism Shot Itself in the Foot has a quote by Wolfgang Pauli asking for something similar in the 1950s. In that same plenary session there is also an interesting look at measurement presented by Thomas Filk where he talks about units as they relate to experimental measurement.

See also Gabriele Carcassi on The Correspondence Between Quantum and Classical Mechanics and Another Curt Jaimungal Interview With Roger Penrose.

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