I was sent this 14-minute audio recorded during the original "Feynman lectures in physics".
With a somewhat combative common-sense voice, Feynman talked about the generalized "philosophical lessons" that people extract from quantum mechanics, or at least they claim to do so.
Well, almost all this stuff is just junk. The actual physical content is almost always distorted beyond recognition and the resulting essence is just silly.
Feynman mentioned several examples of ideas that follow from quantum mechanics that are being distorted in this way.
One topic is about the inevitable influence of the measuring apparatus on the system. The true idea says that it is not possible to "arbitrarily minimize" this influence by rearranging the apparatus – there is no objective or classical underlying state (point in the phase space) that would describe how the physical system really "is" independently of any measurements. Instead, we may predict the probabilities of different outcomes of various measurements and the dependence on the question we ask – on the measurement we make – cannot be eliminated.
If you like Feynman's audio above, you may buy a CD with 6 hours from his lectures for $21. See the link below.But that doesn't imply, as some people think, that everything is fuzzy and uncertain. He describes the actual answer using the example of the popular question whether the wind makes any noise in the forest if there's no one to hear it. Well, it does because the noise still leaves some small scratches, some minor traces that may later be observed and used to prove that there was noise. Feynman chose to be "explicitly silent" about the question whether the trees had consciousness.
I would say that people love to err on both sides here. Sometimes, they incorrectly say that some phenomenon's existence becomes "forever undetermined" just because this phenomenon is not being perceived "when it is occurring". That's wrong because one can observe it later. Sometimes, people want to deny that our knowledge about the process ultimately comes from some observations and it can't exist without them.
But I really enjoyed the crisp comments about Feynman's attitude to "concepts that can't be measured", around 4:00.
People love to say that quantum mechanics (and relativity) taught us that the idea that
you cannot speak about the things you cannot measure. If you can't define something by a measurement, it has no place in the theory.This is almost exactly what the Šmoity stinky scumbags and the crackpot sect around them loves to say every day. April 1st was no exception so a bunch of morons has submitted a would-be witty astro-ph preprint named A Farewell to Falsifiability yesterday.
This opinion is a "false position", Feynman says, a result of an "uncareful analysis of the situation". The inequality \[
\Delta x \cdot \Delta p \geq \frac\hbar 2
\] doesn't a priori mean that you can't talk about these observables. Instead, it just means that you don't need to talk about them! The situation in science is as follows:
A concept or an idea which cannot be measured or cannot be directly referred to an experiment may or may not be useful. It need not exist in the theory.I have never heard this Feynman audio before but I am sure that you may find TRF blog posts (look e.g. for the word "auxiliary" here) where I wrote this principle in an almost identical way. This guy has scooped my articulate, original idea and recorded it a decade before I was born. ;-)
He revisits how the principle was actually used by Heisenberg et al. Everyone else was a classical physicist so they were asking questions about the precise position and momentum, and so forth. Heisenberg's answer was that I don't need to answer such questions. But it doesn't mean that you and your theories mustn't use ideas that can't be measured. We just don't have to do so.
It is not necessary to remove all the components that can't be measured. It is not true that a theory which uses no such unmeasurable concepts is preferred over a theory that does use some. The existence of phenomena in the theory that haven't been observed is really necessary for the theory's nonzero predictive power. The theory must be able to make predictions independently of the experiment i.e. say something about regions that haven't been experimentally probed.
So it wasn't an obvious stupidity for the classical physicists to keep on assuming that a position of the electron objectively exists in the same sense as it does for the baseball. Similarly, we still do assume today that the laws of relativity hold at all energies even though we couldn't have verified that. Maybe, someone else in the future will tell us that "we were stupid". But to do science, one has to stick his neck out. And it's not a stupidity to do so. An assumption may be shown to be wrong but it wasn't stupid that it was made.
After 9:00, he talked about the indeterminacy of quantum mechanics.
This has led to interpretations such as weird comments about the freedom of will (in the human sense) and the innocence of criminals. People have said that the indeterminacy opens the room for the supernatural agents to work. Well, feel free to work, supernatural agents, but then the physicists' task is to calculate the probabilities that govern the behavior of the supernatural agents as a function of the circumstances.
One may talk about "supernatural things" but physics remains equally analyzable and there's no evidence that it shouldn't be.
Feynman says that the ideas that the quantum indeterminacy radically changes the character of the free will of the human mind go to far. If the world were classical, it seems plausible that the mind would feel pretty much the same! After all, the brain isn't a coherent quantum computer. It's so warm for that. Except that the elementary building blocks "internally" rely on quantum mechanics to function (even atoms need quantum mechanics to exist, be stable, and have other basic properties), their mutual relationships are pretty much compatible with the basic framework of classical physics.
The people claiming that quantum mechanics is absolutely needed for an aspect of the human mind should do a careful analysis, and if they still believe in their opinion, they should present a solid argument or proof that classical physics makes incorrect predictions about this feature of the mind.
Feynman mentions that even in classical physics, the dependence on the inaccuracy of initial conditions exists – chaos theory – and this unpredictability affects the "free will" of the human mind in pretty much the same way as the (unavoidable) uncertainty dictated by the laws of quantum mechanics. He describes the "butterfly effect" using the words "given a small but nonzero \(\varepsilon\), there exists a long enough time \(T(\varepsilon)\) so that you can't predict it for this long future at the 10% accuracy". The students obviously didn't like the \(\varepsilon\)-\(\delta\) gymnastics, as their roaring revealed. ;-)
The required time only grows logarithmically, \(T\sim |\log \varepsilon|\).
Applause. I would have joined it, too.
Remarks on the template:
The readers who prefer this new experimental universally "dark on light" color template should fix the problem with this corner_main.gif image that seems to have wrong colors that look disturbing in the right upper corner of the "nearly white" left strip of the blog. Please create a better corner_main.gif image for me. It may be a transparent GIF so if you don't know how to deal with these things, give it up. ;-)