Ivan Seeking said:
Yes, this is confusing. The best answer that I can manage at the moment is that he describes a model that avoids the wave function by introducing other magic, like "smelling the neighborhood".
This is incorrect. He does away with the need for a concept of wave function by calculating
probability amplitudes. Look back at the paragraph that footnote #8 refers to. The opposite of "similar magic" is
probablility amplitudes, not "smells" the neighborhood.
The "smells" remark was just a colorful metaphor that he, himself, put in quotes: it's an amusing anthropomorphisation. It's the way he talks. Look on page 57, second paragraph from the bottom:
'Now, let's have some fun. Let's `fool the light,' so that
all paths take exactly the same amount of time."
In case there's any doubt in your mind, Feynman is not suggesting that photons are sentient beings that can be fooled, or that can smell. Don't get all Aspergery and start taking amusing remarks like that literally.
I haven't read this for a long time so the context is no longer clear, but I think you are reading too much into what he says. I will try to come up with a better explanation when time allows.
I am positive Feynman is saying there is no need for a wave function.
I should add that the proper interpretation of the wave function and collapse is still hotly debated.
This is clear from everything I've dug up for this conversation.
In fact, some Cosmologists now propose that a measurement collapses the wave function of the observer and not that observed. So in a sense, since Feynman, the problem has only gotten worse. Some scientists think that collapse has been explained via Von Neumann's wave function collapse postulate, but other scientists disagree.
The double slit has obviously created a mystery. When you can't tell what something is, you start speculating, then hypothesizing. I am kind of amazed at how mystical a lot of these trains of thought become. The double slit is one thing for certain: a rohrschach test.
Ivan Seeking said:
I think his last sentence accounts for the confusion with Feynman's comments.
The last sentence being:
If someone could figure out a testable implication, that would make a big difference; but right now most of the argument is about "interpretation" of the existing theory, with no hint that different interpretations affect anything except the way individuals visualize things.
This is a statement I agree with to the very small extent I am aware of and can follow all the competeing theories, but it actually has nothing to do with any confusion on my part about what Feynman said. I don't believe I am confused in asserting he did away with the need for a collapsable wave function. In QED no such thing has to be accounted for or calculated:
"This strange phenomenon of partial reflection by two surfaces can be explained for intense light by a theory of waves, but
the wave theory cannot explain how the detector makes equally loud clicks as the light gets dimmer. Quantum electrodynamics "resolves" this wave-particle duality by saying that light is made of particles (as Newton originally thought), but the price of this great advancement of science is a retreat by physics to a position of being able to calculate only the
probability that a photon will hit a detector, without offering good model of how it actually happens."
He shoves the collapsable wave function to the side and says in effect, "I'm going to approach the whole thing from a completely different angle."
He does the same thing to the HUP. Look at the footnote on pages 55 & 56:
3This is an example of the "uncertainty principle": there is a kind of "complementarity" between knowledge of where the light goes between the blocks and where it goe afterward-precise knowledge of both is impossible. I would like to put the uncertainty principle in ts historical place: When the revolutionary ideas of quantum physics were first coming out, people still tried to understand them in terms of old-fashioned ideas (such as, light goes in straight lines). But at a certain point the old-fashioned ideas would begin to fail, so a warning system was developed that said, in effect, "your old-fashioned ideas are no damn good when..." If you get rid of all the old-fashioned ideas and instead use the ideas that I'm explaining in these lectures - adding
arrows for all the ways an event can happen - there is no need for an uncertainty principle!
If you happen to have a copy of
Genius by James Gleick you will remember the story of Niels Bohr's uncomprehending reaction to Feynman's
diagrams:
"The chicken-wire diagrams that Feynman had etched on the blackboard seemed, by contrast, quite definite. Those trajectories looked classical in their precision. Niels Bohr stood up. He knew this young physicist from Los Alamos-Feynman had argued freely and vehemently with Bohr. Bohr had sought Feynman's private council there, valuing his frankness, but now he was disturbed by the evident implications of those crisp lines. Feynman's particles seemed to be following paths neatly fixed in space and time. This they could not do. The uncertainty principle said so.
"Already we know that the classical idea of the trajectory in a path is not a legitimate idea in quantum mechanics," he said, or so Feynman thought-Bohr's soft voice and notoriously vague Danish tones kept his listeners straining to understand. He stepped forward and for many minutes with Feynman standing unhappily to the side, delivered a huniliating lecture on the uncertainty principle. Afterward Feynman kept his despair to himself.
Genius, p.8
Feynman was no respector of the "well-established" wave-particle duality, and found the most useful means of approaching the problem was to analyze light as particles. I say "most useful" not "most accurate" because in Six Easy Pieces he says that the true naure of a photon is not particle
or wave, nor is it
both wave and particle, it is
neither wave nor particle: a thing unto itself that has no comprehensible analogy on a macro scale, but which is most usefully analyzed as a particle.
