Hi Ken, here are the passages from your essay to keep in mind for the comments below:
If one wants to place quantum theory into the spacetime of GR,
one must use the Lagrangian Schema, solving the
problem "all at once". Only then can the solution
take into account the actual future measurement
which, recall, is imposed as a boundary constraint
on L. So an LSU-minded physicist, when encountering
entanglement, would have no reason to add new
dimensions. The "spooky" link between entangled
particles would merely be joint correlations enforced
by virtue of both particles contributing to the same
global action.[12]
We can treat the universe as a global, four dimensional
boundary-value problem, where each subset of the universe can be solved in exactly the
same manner, with exactly the same rules. Stories
can be told about what happens between quantum
measurements, and those very measurements can be
enfolded in a bigger region, to simultaneously tell
a bigger story.
Beautiful essay, and as you know, we are with you on: rejecting Hilbert space realism and realism about Schrodinger dynamics, block universe, and the use of future boundary conditions ( see http://fqxi.org/community/forum/topic/1393 for example). But we want to explore the logic of your essay as a stalking horse. As you know, both the NM formalism and the LM formalism are compatible with either a block universe or say presentism. And as you know, both the LM and NM formalism can be done with or without a future boundary condition. So nothing ontological follows from the use or dis-use of these formalisms, which is to say they must be interpreted to get out ontological conclusions such as block universe. So you have not given us any argument for a block universe apart from the claim that it would allow us to get rid of Hilbert space. But even if you had argued for a block universe, is block universe either necessary or sufficient for the non-existence of Hilbert space? Is a block universe either necessary or sufficient for a time-symmetric account of QM which provides a local account of entanglement? None of these conclusions are established in your essay. So you have not argued for a block universe directly and you have not established its necessity to your ONTOLOGICAL conclusion about LSU over NSU. We already knew that a psi-epistemic account makes the measurement problem go away and we already knew that future boundary conditions could be used to tell a local story about entanglement, nothing new there. But from this it doesn't follow that the future is equally real or 'already there'. What you need is an argument to the effect that if NSU is true and block universe false then getting rid of Hilbert space, use future boundary conditions, etc., becomes much harder, but there is no such argument in your essay. As far as we can see, someone could (and they do) still believe in NSU/reject block universe and adopt all your other suggestions. In your defense you do suggest the possibility of finding a formalism that demands the use of future boundary conditions, that would certainly be a good start.
Second, your essay doesn't provide us with any positive alternative interpretation of either NRQM or QFT. The only thing we can conclude is that you want a psi-epistemic account and to preserve locality. So we would like to see your interpretation of QM, hear how it helps with larger problems about unification, how it explains presumably unique QM phenomena like discrete outcomes, etc. It is clear that you want "QM systems" to have definite position values with worldlines and continuous mediation "between measurements". In other words, in spite of all your NSU bashing, you still insist on that type of explanation for the QM so long as it's in spacetime and not Hilbert space; so for you, even if you found your new formalism that demanded the use of future boundary conditions, you still assume there would always be a 3+1 type explanation of a NM sort between the measurements, you just have to work backwards to get it. So in fact, the only thing non-NSU-like about your universe is that it's a block universe, but as we suggested above, it isn't clear that is much of a difference maker by itself. Also notice that the use of future boundary conditions doesn't require that QM systems have definite worldlines and the only reason to assume they must is some sort of NSU prejudice.
Ken says the following at the end of his essay:
We can treat the universe as a global, four-dimensional
boundary-value problem, where each
subset of the universe can be solved in exactly the
same manner, with exactly the same rules. Stories
can be told about what happens between quantum
measurements, and those very measurements can be
enfolded in a bigger region, to simultaneously tell
a bigger story. And most importantly, such models
will suggest further models, with alterations that
only make sense in a Lagrangian framework { perhaps
a local constraint like L=0, or treating the
Euler-Lagrange equations as just an approximation
to a fundamentally underdetermined problem.
So for anyone in the audience listening, our post to Ken here is one shot in a long series of exchanges where we try to convince him that he simply doesn't go far enough down the rabbit hole in his rejection of NSU. If you want to see what a complete rejection of NSU-type thinking (we call it dynamism) really looks like and what it can do well beyond just interpreting QM, read our essay. We don't write as well as Ken unfortunately, but we do paint a more detailed picture. In our essay you will find that our fundamental equation (or toy model of it anyway) might be the sort of new fundamental explanation that Ken is looking for. But our account requires giving up much more of the NSU-type picture than Ken's does. The pay-off however, is much greater across the board.
