
Richard Healey replied to the topic Is there an inconsistent friend? in the forum Workshop on Wigner’s Friend 2018 8 months, 1 week ago
Hi Mark,
No, I don’t agree. I regard retrocausation here as a desperate and unnecessary response to the situation you present. (Though I’m happy to entertain this as a conceptual possibility in other contexts and for other reasons.)
Equation (13) and its equivalents represent probabilistic correlations between the outcomes of possible m…[Read more]

Richard Healey replied to the topic Is there an inconsistent friend? in the forum Workshop on Wigner’s Friend 2018 8 months, 2 weeks ago
Dear Ruth,
Let me comment on something you said in your last post:
Richard noted earlier (if I understand correctly) his assumption that the existence of a measurement result in the world has no relation to whether anyone knows what it is, nor to any particular physical condition of the system under study. So it seems that when one party engages…[Read more]

Richard Healey replied to the topic Is there an inconsistent friend? in the forum Workshop on Wigner’s Friend 2018 8 months, 2 weeks ago
Dear Shan,
I quote two sentences from your draft paper:
In Bob’s frame, since after the superobserver’s reset measurement the states of Alice and the particles are the same as their initial states, the result of Bob’s measurement has no correlation with the result of Alice’s measurement. Then we have E(a,b)=0 for any a, b.
I think these two…[Read more]

Richard Healey replied to the topic Is there an inconsistent friend? in the forum Workshop on Wigner’s Friend 2018 8 months, 2 weeks ago
Mark,
Wbar measures an observable z on a quantum system composed of everything in Fbar’s lab (including the quantum coin, Fbar herself, her measurement apparatus and recording devices, …). z is a twovalued observable with orthonormal eigenstates okbar, failbar. Noone, including Frauchiger and Renner, has any idea of how to measure this…[Read more]

Richard Healey replied to the topic Is there an inconsistent friend? in the forum Workshop on Wigner’s Friend 2018 8 months, 2 weeks ago
Shan,
Re 3. I think your derivation of $E(b,c)=4sin^2[(ab)/2]cos^2[(ab)/2]1$ is incorrect. The derivation proceeds by separately considering two possible outcomes of Carol’s measurement and then summing over the associated probabilities, treated as exclusive and exhaustive. In effect, this is to treat Carol’s measurement as inducing a physical…[Read more]

Richard Healey replied to the topic Is there an inconsistent friend? in the forum Workshop on Wigner’s Friend 2018 8 months, 3 weeks ago
Shan,
1. It is important to notice that a quantum state assignment on a fixed spacelike hyperplane (like the hyperplane t*^3) may itself be made with respect to different inertial frames (say, Alice’s and Bob’s). Quantum states on different spacelike hyperplanes (like t^3 and t*^3) are not related by a boost transformation. So a derivation of…[Read more]

Richard Healey replied to the topic Is there an inconsistent friend? in the forum Workshop on Wigner’s Friend 2018 8 months, 3 weeks ago
Ruth,
A modern version of the SternGerlach experiment uses a hotwire detector (see, for example, http://web.mit.edu/8.13/www/JLExperiments/JLExp18.pdf ).
In this case, potassium atoms pass through an SG magnet, thereby entangling their spin and translational quantum states (not collapsing the spin state)! Interaction with the hot wire likely…[Read more] 
Richard Healey replied to the topic Is there an inconsistent friend? in the forum Workshop on Wigner’s Friend 2018 8 months, 3 weeks ago
Ruth,
In my view quantum theory may be applied to predict probabilities for certain magnitude claims, each restricting a dynamical variable to a Borel subset of real numbers. When quantum theory is targeted on a quantum system, a quantum state is assigned to that system in order to apply the Born rule to yield these probabilities. The magnitude…[Read more]

Richard Healey replied to the topic Is there an inconsistent friend? in the forum Workshop on Wigner’s Friend 2018 8 months, 3 weeks ago
Shan,
You focus on an important part of the third argument.
In my paper I first considered the use of QM to predict the probabilistic correlation E(a,d) in equation (29), and then appealed to Lorentz symmetry to justify the analogous equation for E(b,c). So let’s consider the argument for equation (29).If Carol had performed no measurement (C…[Read more]

Richard Healey replied to the topic Is there an inconsistent friend? in the forum Workshop on Wigner’s Friend 2018 8 months, 3 weeks ago
The third argument makes no assumption of hidden variables. In particular, it makes no assumption concerning the actual spin values of the measured particles, either before or after the spin measurements. It assumes only that each measurement has a definite physical outcome, which may correspond to a light flashing red rather than green (for…[Read more]

Richard Healey replied to the topic Is there an inconsistent friend? in the forum Workshop on Wigner’s Friend 2018 8 months, 3 weeks ago
As stated in the first sentence of the paragraph in which equation (31) appears, it is a central assumption of this third argument that every spin measurement performed by A,B,C and D has a definite, physical outcome. Consistent with that assumption, the measurements by A, B destroy all
 records
of C’s and D’s definite, physical outcomes. So none…[Read more]

Richard Healey replied to the topic Is there an inconsistent friend? in the forum Workshop on Wigner’s Friend 2018 8 months, 3 weeks ago
Shan,
You say
” it seems to me that Richard’s result about the Limits of Objectivity is not valid. This result is derived from the third argument in his paper. I think the argument is based on the implicit assumption of locality, like Bell’s theorem, and one should drop this locality assumption, not the objectivity of outcomes.”Where do you thi…[Read more]

Richard Healey joined the group Workshop on Wigner’s Friend 2018 9 months ago



Richard Healey replied to the topic Why Bohmian theory? in the forum Bohm’s theory 4 years ago
I think we have arrived back at the starting point of my first post on Bohmian mechanics (under a different thread—the one I emailed to you originally). There I compared the Bohmian research program after quantum theory to a Lorentzian research program after special and general relativity.
Bohm and GRW are not quantum theories but nonquantum…[Read more] 
Richard Healey replied to the topic Why Bohmian theory? in the forum Bohm’s theory 4 years ago
Everything is fair except the last sentence. The existence of atoms is strongly supported by the evidence. The existence of a Higgs boson is also supported by the evidence, though not nearly as strongly. By contrast, the existence of Bohmian trajectories, a preferred spacetime foliation, etc. is not.

Richard Healey replied to the topic Why Bohmian theory? in the forum Bohm’s theory 4 years ago
I don’t want to permanently and irrevocably give up on the goal of describing the world as accurately and completely as possible. But I think that goal is at least (probably) humanly unachievable, and possibly even incoherent, since it presupposes that there is some set of concepts rich enough to permit such a complete description. Pragmatism i…[Read more]

Richard Healey replied to the topic Why Bohmian theory? in the forum Bohm’s theory 4 years ago
I started to compose a short reply to your last post, Travis, but decided that your pointed questions required a more extended response. So instead I’ve attached a piece I wrote a few years ago on what quantum theory teaches us about the concept of physical reality.
In brief, like Einstein I think of the “real” in physics as a a type of program…[Read more]

Richard Healey replied to the topic Why Bohmian theory? in the forum Bohm’s theory 4 years ago
At the end of your first paragraph you ask “Am I at least close to right so far?”
No. In formulating or understanding quantum theory it is not necessary to appeal to a microscopic/macroscopic distinction. As a fundamental theory, quantum theory may be applied to systems of arbitrary size.
Quantum mechanics may be applied to systems of particles,…[Read more]  Load More