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Tuesday, December 18, 2018

Killing The Schrodinger's Cat, at last and for good: part II


This post is one of the series of posts 
listed in Appendix below
Killing The Schrodinger's Cat, at last and for good: part II
After writing my first reflection on the first two chapter so the book (Part I), I continued reading the book and keeping my notes while reading.
In general, I enjoyed the reading, especially the parts about personal history of various people. In that part my expectation turned out to be correct, Adam Becker offers a good account of the history. 
Once in a while the reading initiated an argument, and those I present below.
Page 39
“When an electron is shot out into the tube, its wave function obeys the Schrödinger equation, undulating and propagating outward like a wave”
This statement makes us think that a wave function describes an actual physical field, like an electric field. This is simply wrong, because a wave function describes a number distribution ("an amplitude") in space and time (related to the probability distribution).
“So sometimes the electron behaves like a wave, and sometimes it behaves like a particle”.
This statement is wrong, because an electron never behaves like a wave and always behaves like a particle. However, that particle demonstrates different macroscopic behavior under the same macroscopic conditions – which is different from the behavior of macroscopic particles, those always demonstrate the same macroscopic behavior under the same macroscopic conditions. Specifically, an electron hits a screen at different locations. Electronspluralmany electrons under the same macroscopic conditions demonstrate behavior visually similar to the behavior demonstrated by a macroscopic waves. For example, when many electrons hit a screen at different locations, the resulting picture may look similar to the picture formed by waves traveling on a surface of water through two narrow slits. The difference between the waves in water and electrons is that every electron actually travel in space from a source to a screen, but water waves happen do to water molecules slowly moving about their equilibrium position and pushing on each other.
The whole idea of “wave-particle duality” was developed as an attempt to make sense of the theoretical concepts which could not fit into a well-developed classical picture. But since then physics has grown and today, almost hundred years later, we do not need to hold on this mental bridge anymore. At the dawn of the quantum mechanics the fact that a particle cannot demonstrate its location and velocity at the same time was a shock. Today, we just accept it as a fact; yes, a quantum object cannot demonstrate (note: I am not saying “have” – that is a different conversation about possible interpretations of quantum mechanics), so, a quantum object cannot demonstrate its location and velocity at the same time. The real “mystery” is why macroscopic objects, which are made of quantum objects, do demonstrate their location and velocity at the same time; how does that ability of the whole comes from an inability of its parts?
About a hundred years ago, when physicists would say something like “an incomplete description”, “incompatible variables”, “complementary”, they simply meant “different from classical”.
Page 59
“For any entangled system, Einstein’s choice applied: either the system is nonlocal, or quantum physics can’t fully describe all the features of that system”.
There is the third choice. The parts of a system interact via a physical interaction of some sort which has speed high enough to explain the behavior of the system – assuming the experiment is feasible at least in principle. The “high enough speed” condition may include interaction via agents which travel above the speed of light.
Page 100
“How do … the photons … know you’re watching them at all?” (in a double-slit experiment).
Answer – because “watching” means having photons interacting with  device which has one state in the absence of a photon and changes its state in the presence of a photon, and that inter-action changes the photon as well. Placing a detector by each slit makes the necessity for including those detectors in the mathematical description of the experiment.
The much more intriguing question is how does a photon “know” – after traveling through one of the slits (and we don’t know which) – where to hit a screen, or more importantly, where NOT to hit it? It seems like a photon “knows” that well before reaching a screen. A photon “knows” must mean that there is an interaction between a photon and the environment which affects its motion toward a screen. But the Schrödinger equation gives NO information about such interaction.
Here is where Bohm’s theory steps in.
Page 124
“Everett … insisted that a single universal wave function was aa there was”.
The idea of the existence of a single universal wave function for the whole existing universe is no different from the idea of a single universal Lagrangian for the whole world. It should be natural to every physicists who believes that our understanding of the universe should reflect the existence of the universe. However, the idea of the “many-worlds” logically is not connected with the idea of a single universal wave function; these two ideas do not demand each other.
Term “many-worlds” implies the existence of many different worlds – at the same time at the same place – (however one may see it). However, the passage (page 126) “universal wave function splits into more and more noninteracting parts” shows that those many worlds just represent different parts of the whole world, parts which exists at the same time at different locations. This picture is no different from any classical view on the world.
The notion that every single event in the universe creates new universes which correspond to all possible outcomes of the event, and an observer in each universe observes his own outcome may be seen as an innovation, but it has nothing to do with science, because does not help making predictions does not lead to new insights, and instead of making things easier and clearer, make them harder.
This is a situation when a treatment is worse than a disease.
Page 145
Bell’s quote “The great von Neuman … made assumptions in his proof that were entirely unwarranted”.
Many though experiments about entanglement make the same mistake. Human mind can imagine things which may seem natural, but physically “unwarranted”. It is not enough just to say “let’s assume these particles are entangled”, there has to be a specific physical mechanism in place for that to happen. If that specific mechanism of entanglement does not exist, the whole thought experiment makes no sense.
Page 149
“Bell used … Bohm’s version of EPR involving photons with entangled polarization. … When a photon hits a polarizer, it either passes through or gets blocked”
This is an example of a very commonly used interaction between a photon and an optical device (a polarizer, a mirror, a lens, etc.). And it is an example of a very common misunderstanding of the physical phenomenon happening during this interaction. Every author bases his/her logic on the options what may happen with a photon during this interaction, for example, a photon maybe be reflected, deflected, transmitted, blocked. And then the same photon keeps traveling (and something else is happening to it). The fact of the matter is that the photon traveling away from a device is simply not the same photon which was approaching a device. When a photon starts interacting with a device, it means it collides with an atom inside the device (at least one), it most probably gets absorbed, then – after some microscopic time interval – a new photon is emitted, which may be again absorbed, emitted, absorbed, emoted, etc., and such a process eventually leads to a photon – a new one! – leaving a device. Any conclusion on what property that final photon has is probabilistic and has to be derived based on quantum electrodynamics (in general). Until this description is provided, any conclusions on the results of an experiment involving a photon-device interaction may be plausible, but not necessarily definite.
A polarization axis (a transmission axis) of a polarizer is a macroscopic property of a device. When one photon encounters a polarizer, it encounter the existence of one atom or molecule. How would a photon “know” the direction of a transmission axis when it meets with only one atom? That atom absorbs a photon, emits a new one, etc. The final result is probabilistic. Hence, when a single photon interacts with a polarizer, there is always non-zero probability for a new photon be emitted by the polarizer on another side (what we call “passing through”). The phrase “a photon is polarized perpendicularly to the transmission axis” simply makes no sense. Hence, statement that (page 150) “the two [entangled] photons will always pass through together or be blocked together” is just wrong. Even if one polarizer completely absorbs one photon, there is a non-zero probability to see a photon on another side of a second polarizer. And that ruins the whole idea of the experiment, of any experiment with entangled photons (and also of the example with the casino).
Page 153
“That suggests a need for a radical revision of our conception of space and time, far beyond Einstein’s relativity”
Bell’s theorem may have pointed in that direction, but today “a need for a radical revision” is nothing but obvious, because, clearly, that seems the only way toward quantum gravitation – nothing else has been working.
Page 198
“further work on the subject would extinguish his academic career”.
The book provides many insights into the world of science, but it also provide many insights into the world of scientists. Those two worlds are not identical. The world of scientists is actually not much different from the world of actors, or politicians. “You are wrong” does not mean “you made a logical mistake here and there” (as it should be in the world of science), but “you think different from me, and that is wrong” (as it often in the world of scientists). And if you are not a member of “a pack”, you have a slim chance to find a good position.
Page 231
“What causes the collapse of the system-apparatus-environment combined wave function?”
The answer is – instability of immeasurable states (e.g. those states in a Hydrogen atom that would have energy NOT equal to the energy of the Bohr's energy levels).

It seems to me that many Western physicists think of a wave-function as of an actual real physical field, e.g. like electric field. Having this view naturally makes them wonder what happens to the field if just before a measurement it existed in a huge area of space but right after a measurement it exists only at a specific point. that is why they call it a "collapse" and trying to break their heads to understand what happened. However, a wave-function is not an actual physical field, but just a mathematical abstract - like the Dirac Delta-function. Yes, it does have strange behavior, but what is not strange about quantum world?
Page 245
“The idea that the universe as a whole was a suitable subject for scientific investigation was difficult for some physicists to swallow”.
A good example to demonstrate the difference between one who is paid for doing something in the field called “physics”, and a physicist (like not everyone who has a job title “a teacher” is actually a teacher).
Page 291
“But how can the photon “decide” whether to travel down just one path after it’s already passed through the first beam splitter?”
The answer is (again) – the photon does not need to “decide” anything. That photon disappears, being absorbed by the material of the beam splitter. Gone. The rest of the process does not include the original photon anymore.

Appendix I
After writing Part I, but before writing Part II, I also wrote two more piece on the matter, which provide some additional points of view, including on probability, entanglement, “many-words”, philosophy, a “delayed choice experiment”, and more:

I also have short pieces on a scientific method:

Three old pieces on physics:

Appendix II 
The mission (i.e. the reason for existence) of science as a human practice is making reliable predictions.
The mission of a scientists as an agent of that human practice is discovering the truth about the universe and representing it in a testable form (e.g. verifiable, or falsifiable).
When a faculty tells students "Quantum Mechanics is a complete theory, and it means this ..." he or she is simply lying - hence, he or she stops being a scientist. The truth (the fact) is that there are (exist, whether one likes it or not) different views on the state of Quantum Mechanics, and denying that fact is not a scientific action.
A mere fact that someone is involved in a scientific research does not automatically makes that one a scientists.

Appendix III
So many people and so much energy have been focused on a photon traveling through two slits, or two entangled photons or electrons, etc., so no one asks why waves on trillions of strongly interacting atoms behave in a way similar to the behavior of weekly interacting atoms in a dilute  gas? A macroscopic number of strongly interacting microscopic particles does not follow the laws of a macroscopic world. Instead, there is a trick, a recipe – called “quantization” – which works like a charm. Why?
The recipe works, what else do you need? 

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