Who Killed Schrodinger’s Cat?

In 1935 Erwin Schrödinger illustrated a hypothetical experiment to show that something is incorrect with the traditional analysis of Quantum Mechanics.

One can even set up quite ridiculous cases. A cat is penned up in a steel chamber, along with the following device (which must be secured against direct interference by the cat): in a Geiger counter there is a tiny bit of radioactive substance, so small that perhaps in the course of the hour one of the atoms decays, but also, with equal probability, perhaps none; if it happens, the counter tube discharges and through a relay releases a hammer which shatters a small flask of hydrocyanic acid. If one has left this entire system to itself for an hour, one would say that the cat still lives if meanwhile no atom has decayed. The [wave-function] of the entire system would express this by having in it the living and dead cat (pardon the expression) mixed or smeared out in equal parts. [1]

Schrödinger’s cat quickly emerged as the most famous example of what is now called the measurement problem, “the most controversial problem in physics today”, [2] with more than 30 youtube video clips devoted to it. (Less well-known is that Einstein suggested a similar bomb experiment to make the same point, stating “a sort of blend of not-yet and already-exploded systems [can not be] a real state of affairs”. [3])

The measurement problem appears because QM does not offer a picture of reality when no one is looking. Instead we have particles that are neither here nor there, states that are in superpositions, and equations that merely provide probabilities. Most physicists strongly believe that these superpositions are real, and several even acknowledge that the cat can be both half dead and half alive. Then there are physicists who opt not to talk about reality.

I am a positivist who believes that physical theories are just mathematical models we construct, and that it is meaningless to ask if they correspond to reality, just whether they predict observations.— Stephen Hawking. [4]

Something was clearly missing.

That something came along later in the form of Quantum Field Theory— a theory that does offer a picture of reality, even when no one is looking. However there are numerous explanations and understandings of Quantum Field Theory, while some physicists reject it completely. For instance, N. David Mermin wrote in Physics Today, “I hope you will agree that you are not a continuous field of operators on an infinite-dimensional Hilbert space, [5] and Meinard Kuhlmann wrote in Scientific American, “quantum field theory … sounds like a theory of fields. Yet the fields supposedly described by the theory are not what physicists classically understand by the term field”. [6]

Among those who accept Quantum Field Theory, most observe Richard Feynman’s method based on particles and virtual particles, while Julian Schwinger’s (and Sin-Itiro Tomonaga’s) version, which is based only on fields, is much less well-known. [7] Surprisingly enough, Frank Wilczek discloses that Feynman later changed his mind:

Feynman told me that when he realized that his theory of photons and electrons is mathematically equivalent to the usual theory, it crushed his deepest hopes … He gave up when, as he worked out the mathematics of his version of quantum electrodynamics, he found the fields, introduced for convenience, taking on a life of their own. He told me he lost confidence in his program of emptying space. [8]

Although both approaches lead to the same equations, the physical pictures are very different. It is Schwinger’s Quantum Field Theory that we refer to in this article, but since this version is so little known, we need to first give a brief description.

Definition of field. A field is a property of space. This idea was proposed by Michael Faraday in 1845 as an explanation for electric and magnetic forces. However the concept that space has properties was not easy to accept, so when James Maxwell predicted the presence of EM waves in 1864, an ether was invented to carry the waves. It took many years before the ether was dispensed with and physicists approved that space itself has properties:

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“SPOOKY ACTION AT A DISTANCE” ISN’T ALL THAT SPOOKY

“Spooky action at a distance”, as Einstein called it, refers to the experimental fact that particles can impact each other instantly, even when separated by sizable distances. For example, if two photons are produced collectively in what is referred to as an entangled state and the angular momentum of one is altered, then the angular momentum of the other one will adjust in a corresponding manner at the same time, no matter how far away from each other the particles are. This “spooky” behavior has been known for almost a hundred years and still is a source of confusion.

Still there is a theory in which the result is not spooky, but rather a natural consequence. I’m referring to Quantum Field Theory, which describes a world constructed only of fields, with no particles. What we call a particle is really a piece, or quantum, of a field. Quanta are not localized like particles, but are spread out through space. For example, photons are pieces of the electromagnetic field and protons are parts of the matter field. These quanta evolve in a deterministic way as per the basic field equations and there is a term in these equations that restrains the speed of propagation to the velocity of light.

Even so the QFT equations don’t tell the whole story. There are events that are not explained by the field equations– for example, when a field quantum moves energy or momentum to a different object. This event is non-local in the sense that the change in, or even disappearance of, the quantum happens immediately, no matter how spread-out the field may be. It can even happen with two entangled quanta– no matter how much they are separated. In QFT, this is essential if each quanta is to act as a unit, as per the fundamental basis of QFT.

There is a big difference between quantum collapse in QFT and wave-function collapse in QM. The former is a real physical change in the fields while the latter is a change in our knowledge. Even though we don’t have a theory to describe quantum collapse, there is nothing inconsistent about it. To quote from Fields of Color: The theory that escaped Einstein:

In QFT the photon is a spread-out field, and the particle-like behavior takes place because each photon, or quantum of field, is consumed as a unit … It is a spread-out field quantum, but when it is taken in by an atom, the entire field disappears altogether, no matter how spread-out it is, and all its energy is placed into the atom. There is a big “whoosh” and the quantum is gone, like an elephant disappearing from a magician’s stage.

Quantum collapse is not a very simple concept to accept– perhaps more difficult than the concept of a field. Here I have been working hard, trying to persuade you that fields are a real property of space– indeed, the only reality– and now I am seeking you to consider that a quantum of field, spread out as it may be, quickly disappears into a tiny absorbing atom. But still it is a process that can be visualized without inconsistency. In fact, if a quantum is an entity that lives and dies as a unit, which is the very meaning of quantized fields, then quantum collapse must occur. A quantum can not divide and put half its energy in one area and half in another; that would violate the fundamental quantum principle. While QFT does not provide an explanation for when or why collapse occurs, some day we may have a theory that does. In any case, quantum collapse is important and has been confirmed experimentally.

Some physicists, including Einstein, have been bothered by the non-locality of quantum collapse, professing that it goes against a fundamental postulate of Relativity: that nothing can be transferred more quickly than the speed of light. Now Einstein’s postulate (which we must remember was only a guess) is certainly valid in relation to the evolution and propagation of fields as illustrated by the field equations. Having said that quantum collapse is not described by the field equations, so there is no reason to assume or to insist that it falls in the domain of Einstein’s postulate.

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Dear New York Times

In the write-up (“With faint chirp, scientists prove Einstein correct”, p. A1, 2/12/16) we study that black holes were part of Einstein’s theory. The reality is quite different. “Einstein argued vigorously against black holes [as] incompatible with reality” (see “Black Holes” by R. Anderson) and his rivals held back their acceptance for many years.

Einstein was also mistaken when he rejected Quantum Field Theory. According to his biographer A. Pais,” QFT was repugnant to him”. This is ironic because QFT, and only QFT, reveals and resolves the paradoxes of Relativity and Quantum Mechanics that most people struggle with (see “Fields of Color: The theory that escaped Einstein” by this writer).

Quite possibly the most significant irony is the statement, “according to Einstein’s theory, gravity is caused by objects warping space and time”. While that is what everybody accepts today, the truth is that Einstein recognized gravity as a force field, similar to electromagnetic fields, except that it is produced by mass, not charge. That an oscillating mass generates gravitational waves is no more incomprehensible or unexpected than that electromagnetic waves are produced when electrons move back and forth in an antenna. To Einstein, curvature was actually a consequential result, similar to the changes in space and time produced by motion according to his Special theory of Relativity.

Black holes. Contrary to many studies, black holes were actually not part of Einstein’s supposition. In fact Einstein argued strongly against black holes [as] incompatible with reality, and his opposition held back their approval for many years.

Synopsis. Gravitational waves are easy to understand if you accept gravity as a force field, similar to the electromagnetic field (QFT). And while the contraction effect is more subtle, it is not that much different from the F-L contraction that has been accepted for over a hundred years.

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Recent Physics Theory Solves Paradoxes

By Rodney Brooks

For one hundred years, most people have found it impossible to understand physics. Examples include Joseph Heller (“writhing in an exasperating quandary over quantum mechanics”), Bill Clinton (“I hope I can finally understand physics before I leave the earth”, Richard Feynman (“One had to lose one’s common sense”), and even Albert Einstein (“fifty years of pondering have not brought me any closer to answering the question, what are light quanta?).

Julian Schwinger’s Insight to Physics

And yet, there is a theory that makes perfect sense and can be understood by any person. This concept, with roots in the 1930s, was ultimately developed by Julian Schwinger, who once had been called “the heir-apparent to Einstein’s mantle”. This accomplishment happened a number of years after Schwinger had already achieved physics fame for solving the “renormalization” problem, defined by the NY Times as “the most important development in the last 20 years” and was duly awarded the Nobel prize.

Still for Schwinger this was not good enough. He believed that Quantum Field Theory, as it stood then, was still lacking. His objective was to feature matter fields and force fields on an equivalent basis. After several years of hard work, he distributed a collection of five papers called “The theory of quantized fields” in 1951-54.

Physicists have been combating a particles-vs.-fields battle for over 100 years. There have been 3 “rounds”, starting when Einstein’s concept of light as a particle (called photon) triumphed over Maxwell’s belief that light is a field. Round 2 happened when Schrödinger’s hope for a field theory of matter was overcome by the particle-like behavior that physicists could not ignore. And round 3 took place when Schwinger’s field-based solution of renormalization was usurped by Feynman’s easier-to-use particle based approach.

For that reason, and others, Schwinger’s final development of Quantum Field Theory, which he regarded as far more noteworthy than his Nobel prize work, has been sadly ignored, and is indeed not known to most physicists– and to all of the general public.

Fortunately there are signs that QFT, in the true Schwingerian sense is reemerging, so in this sense it is a “new” theory There have been numerous books and articles, such as “The Lightness of Being” by Nobel laureate Frank Wilczek, “There are no particles, there are only fields” by Art Hobson, and “Fields of Color- The theory that escaped Einstein” by Rodney Brooks. The last one explains QFT to a lay reader, without any equations, and shows how this terrific “new” theory” resolves the paradoxes of Relativity, Quantum Mechanics and physics that have confused so many people.

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GRAVITATIONAL WAVES REVEALED

By Rodney A. Brooks
author of “Fields of Color: The Theory That Escaped Einstein”.

The recent discovery of gravitational waves at LIGO (Laser Interferometer Gravitational-Wave Observatory) has captured the mind of the public. It will stand as one of the great accomplishments of experimental physics, in addition to the famous Michelson-Morley experiment of 1887 which it resembles. In fact by comparing these two experiments, you will see that understanding gravitational waves is not as difficult as you believe.

Contraction. Michaelson and Morley measured the speed of light at different times as the earth moved around its orbit. To their – and everyone’s – surprise, the speed turned out to be continuous, separate of the earth’s motion. This breakthrough caused great consternation until George FitzGerald and Hendrick Lorentz came up with the sole feasible explanation: objects in motion compress. Einstein then showed that this contraction is a consequence of his Principles of Relativity, but without saying why they contract (other than a need to conform to his Principles). In fact Lorentz had previously provided a partial explanation by showing that motion affects the way the electromagnetic field interacts with charges, causing objects to contract. However it wasn’t until Quantum Field Theory came along that a full explanation was found. In QFT, at least in Julian Schwinger’s model, everything is made of fields, even space itself, and motion affects the way all fields interact.

Waves. Electromagnetic waves, e.g., radio waves, have long been recognized and accepted as a natural phenomenon of fields. Now in QFT gravity is a field and, just as an oscillating electron in an antenna sends out radio waves, so a substantial mass moving back and forth will send out gravitational waves. But it didn’t take QFT to show this. Einstein also believed that gravity is a field that obeys his equations, just as the EM field obeys the equations of James Maxwell. In fact gravitational waves have been accepted by many physicists, from Einstein on down, who see gravity as a field.

Curvature. But what about “curvature of space-time”, which many people today say is what produces gravity? You may be shocked to learn that’s not how Einstein saw it. He believed that the gravitational field triggers things, even space itself, to contract, comparable to the way motion causes contraction. In fact Einstein used this analogy to show the correlation between motion-induced and gravity-induced contraction: they both affect the way fields work together. It is this gravity-induced contraction that is sometimes knowned as “curvature”.

Evidence. The first detection of gravitational waves was done at LIGO, using an apparatus similar to Michelson’s and Morley’s. In both experiments the time for light to travel along two perpendicular paths was examined, but because the gravitational field is much weaker than the EM field, the distances in the LIGO apparatus are much greater (miles instead of inches). Another difference is that while Michelson, not knowing about motion-induced contraction, anticipated to see a shift (and found none), the LIGO staff used the known gravity-induced contraction to view an alteration when a gravitational wave passed through.

Fields of Color: The theory that escaped Einstein explains Quantum Field Theory to a lay audience, without any math. If you want to learn more about gravitational waves or about how QFT resolves the paradoxes of Relativity and Quantum Mechanics, read Chapters 1 and 2, which can be seen free at http://quantum-field-theory.net.

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Quantum Field Theory– A Solution to the “Measurement Problem”.

Definition of the “Measurement Problem”.

A significant question in physics these days is “the measurement problem”, likewise known as “collapse of the “wave-function”. The issue developed in the early days of Quantum Mechanics as a result of the probabilistic nature of the equations. Because the QM wave-function describes merely probabilities, the outcome of a physical measurement can only be calculated as a probability. This naturally brings about the question: When a measurement is made, at exactly what point is the ultimate result “decided upon”. Some folks believed that the role of the observer was critical, and that the “decision” was generated when someone looked. This led Schrödinger to design his well-known cat experiment to demonstrate how ludicrous such an idea was. It is not usually known, but Einstein also proposed a bomb experiment for the same reason, saying that “a sort of blend of not-yet and already-exploded systems. can not be a real state of affairs, for in reality there is just no intermediary between exploded and not-exploded.” At a later time, Einstein remarked, “Does the moon exist only when I look at it?”.

The controversy continues to this day, with a few individuals still thinking that Schrödingers cat remains in a superposition of dead and alive until somebody looks. On the other hand most people believe that the QM wave-function “collapses” at some earlier point, before the uncertainty achieves a macroscopic level– with the definition of “macroscopic” being the primary question (e.g., GRW theory, Penrose Interpretation, Physics forum). A few people take the “many worlds” perspective, in which there is no “collapse”, but a splitting into various worlds that include every possible histories and futures. There have been a lot of experiments designed to address this question, e.g., “Towards quantum superposition of a mirror”.

We will now find that an unequivocal solution to this question is supplied by Quantum Field theory. But because this theory has been neglected or misunderstood by many physicists, we need to initially specify what we mean by QFT.

Definition of Quantum Field Theory.
The Quantum Field Theaory referred to within this post is the Schwinger version where there are no particles, there are only fields, not the Feynman version which is based on particles. * The two versions are mathematically equivalent, but the concepts backing them are very different, and it is the Feynman model that is chosen by the majority of Quantum Field Theory physicists.

* According to Frank Wilczek, Feynman ultimately changed his mind: “Feynman told me that when he realized that his theory of photons and electrons is mathematically equivalent to the usual theory, it crushed his deepest hopes … He gave up when … he found the fields introduced for convenience, taking on a life of their own.”.

In Quantum Field Theory, as we will make use of the term henceforward, the world is comprised of fields and only fields. Fields are defined as characteristics of space or, to put it in a different way, space is comprised of fields. The field concept was introduced by Michael Faraday in 1845 as an illustration for electric and magnetic forces. Even so the idea was not easy for folks to accept and so when Maxwell showed that these particular equations predicted the existence of EM waves, the concept of an ether was introduced to carry the waves. These days, however, it is normally accepted that space can possess properties:.

To deny the ether is essentially to presume that empty space has no physical qualities whatsoever. The key realities of mechanics do not harmonize with this view.– A. Einstein (R2003, p. 75).

Moreover space-time on its own had emerged as a dynamical medium– an ether, if there ever was one.– F. Wilczek (“The persistence of ether”, Physics Today, Jan. 1999, p. 11).

Although the Schrödinger equation is the non-relativistic limit of the Dirac equation for matter fields, there is an important and fundamental difference between Quantum Field Theory and Quantum Mechanics. One illustrates the strength of fields at a given point, the other describes the probability that particles could be found at that point, or that a given state exists…..

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How Quantum Field Theory Solves the “Measurement Problem”.

It is not usually recognized that Quantum Field Theory gives a simple answer to the “measurement problem” which was discussed on the September letters page of Physics Today. But by QFT I do not mean Feynman’s particle-based theory; I imply Schwinger’s QFT where “there are no particles, there are only fields”.1.

The fields exist in the form of quanta, i.e., chunks or units of field, as Planck pictured over a century ago. Field quanta evolve in a deterministic way defined by the field equations of QFT, aside from when a quantum abruptly deposits some or all of its energy or momentum into an absorbing atom. This is called “quantum collapse” and it is not defined by the field equations. As a matter of fact there is no principle that describes it. Everything we understand is that the likelihood of it occurring depends upon the field strength at a given location. Or, if it is an interior collapse, like a shift in angular momentum, the likelihood depends on the component of angular momentum in the given direction. In QFT this collapse is a physical event, not a mere shift in probabilities as in Quantum Mechanics.

Many physicists are bothered by the non-locality of quantum collapse in which a spread-out field (or perhaps two correlated quanta) unexpectedly vanishes or transforms its internal state. Yet non-locality is needed if quanta are to work as a unit, and it has been experimentally proven. It does not result in inconsistencies or paradoxes. It may not be what we anticipated, but just as we accepted that the world is round, that the planet orbits the sun, that matter is built from atoms, we ought to be able to acknowledge that quanta can collapse.

In some cases quantum collapse can bring about a macroscopic change or “measurement”. Yet the measurement outcome, i.e., the “decision”, was determined at the quantum level. Everything after the collapse follows without doubt. There is no “superposition” or “environment-driven process of decoherence.”.

Take Schrödinger’s cat as an example. If a radiated quantum collapses and transfers its energy into 1 or more atoms of the Geiger counter, that starts a Townsend discharge that leads inexorably to the demise of the cat. In Schrödinger’s words, “the counter tube discharges and through a relay releases a hammer which shatters a little flask of hydrocyanic acid” and the cat dies. On the other hand, if it does not collapse in the Geiger counter then the cat lives.

Obviously we don’t know the outcome until we look, but we never know anything until we look, no matter if it’s throwing dice or picking a sock blindfolded. The fate of the cat was determined at the time of quantum collapse, just like the result of throwing dice is determined when they hit the table and the color of the sock is determined when it is taken out of the drawer. After the quantum collapse there is no entanglement, no superposition, no decoherence, only ignorance. What could be easier?

Along with delivering a simple solution to the measurement problem, Quantum Field Theory offers a reasonable explanation for the paradoxes of Relativity (Lorentz contraction, time dilation, etc.) and Quantum Mechanics (wave-particle duality, etc.). It is regrettable that so few physicists have accepted QFT in the Schwinger sense.

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The Uncertainty Principle

The probabilistic translation of Schrödinger’s formula ultimately brought about the uncertainty principle of Quantum Mechanics, formulated in 1926 by Werner Heisenberg. This principle specifies that an electron, or any other particle, can not have its specific position known, or even pointed out. More exactly, Heisenberg derived a formula that relates the uncertainty in position of a particle to the uncertainty of its momentum. So not only do we have wave-particle duality to take care of, we must take care of particles that might be here or may be there, but we just can’t say where. If the electron is actually a particle, then it only stands to reason that it must be someplace.

Resolution. In Quantum Field Theory there are no particles (stop me if you have indeed heard this before) and hence no position– certain or uncertain. Alternatively there are blobs of field that are spread over space. As opposed to a particle that is either here or here or perhaps there, we have a field that is here and here and there. Extending out is one thing that only a field can do; a particle cannot do this. Actually Heinsenberg’s Uncertainty Principle is not very different from Fourier’s Theorem (found in 1807) that relates the spatial spread of any wave to the spread of its wave length.

This does not mean that there is no uncertainty in Quantum Field Theory. There is uncertainty in relation to field collapse, but field collapse is not explained by the equations of QFT; Quantum Field Theory can just predict probabilities of when it happens. Nevertheless there is a significant distinction between field collapse in QFT and the corresponding wave-function collapse in QM. The former is an actual physical change in the fields; the latter is only a change in our understanding of precisely where the particle is….

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Scientific American, EINSTEIN DIDN’T SAY THAT!

In the September “Einstein” issue of Scientific American, readers are granted the impression that gravity is caused by curvature of space-time. As an example, on the 1st page of that section, we read “gravity … is the by-product of a curving universe”, on p. 43 we find that “the Einstein tensor G describes how the geometry of space-time is warped and curved by massive objects”, and on p. 56 there is a reference to “Albert Einstein’s explanation of how gravity emerges from the bending of space and time”.

In reality, lots of physicist today emphasize “curvature” as the definition for gravity. As Stephen Hawking penned in A Brief History of Time, “Einstein made the revolutionary suggestion that gravity is not a force like other forces, but is a consequence of the fact that space-time is not flat, as had been previously assumed: it is curved, or warped.”.

The issue is, that’s NOT what Einstein said. Einstein made it quite clear that gravity is a force just like other forces, along with (of course) specific distinctions. In the actual paper cited by Scientific American (“The foundation of the general theory of relativity”, 1916) he wrote,” [there is] a field of force, namely the gravitational field, which possesses the remarkable property of imparting the same acceleration to all bodies”. The G tensor, said Einstein “describes the gravitational field.” The term “gravitational field” or just “field” occurs 58 times in this article, while the term “curvature” does not appear whatsoever (besides in relation to “curvature of a ray of light”). And Einstein is not the only physicist who thinks that. For instance Sean Carroll, a prominent physicist of today, wrote:.

Einstein’s general relativity describes gravity in terms of a field that is defined at every point in space … The world is really made out of fields … deep down it’s really fields … The fields themselves aren’t “made of” anything– fields are what the world is made of … Einstein’s … “metric tensor”… can be thought of as a collection of ten independent numbers at every point.– Sean Carroll.

To suppress the field concept and emphasize “curvature” not only misstates Einstein’s view; it also gives individuals an incorrect or misleading understanding of general relativity.

So where does “curvature” come from? According to Einstein (in the cited paper), the gravitational field causes physical adjustments in the length of measuring rods (just like temperature can cause such changes) and it is these changes that produce a non-Euclidean metric of space. In fact, as Einstein pointed out, these changes can take place even in a space which is devoid of gravitational fields– i.e., a rotating system. He then proved that this non-Euclidean geometry is mathematically equal to the geometry on a curved surface, which had been developed by Gauss and extended (mathematically) to any amount of dimensions by Riemann. That this is a mathematical equivalence is distinctly stated by Einstein in a later paper: “mathematicians long ago solved the formal problems to which we are led by the general postulate of relativity”.

For my complete article on the disparity of Einstein’s theory of relativity visit the blog at Fields of Color.

When Do Fields Collapse?

A main question in physics these days concerns collapse of the “wave-function”: When does this occur? There certainly have been numerous speculations (see, e.g., Ghirardi– Rimini– Weber theory, Penrose Interpretation, Physics forum) and experiments (e.g., “Towards quantum superposition of a mirror”) about this. The most extreme perspective is the view that Schrödinger’s cat is at the same time alive and dead, although Schrödinger proposed this particular thought-experiment (like Einstein’s less-well-known bomb experiment) to demonstrate how absurd such an idea is.

The problem happens because Quantum Mechanics can only calculate probabilities until an observation occurs. Nonetheless Quantum Field Theory, which works in actual field intensities– not probabilities, supplies an uncomplicated unequivocal answer. Sadly, Quantum Field Theory in its authentic sense of “there are no particles, there are only fields” (Art Hobson, Am. J. Phys. 81, 2013) is ignored or misunderstood by most physicists. In QFT the “state” of a system is explained by the field intensities (technically, their expectation value) at each and every point. These fields are real properties of space that act deterministically depending on the field equations– with one exception.

The exemption is field collapse, but in Quantum Field Theory this is a remarkably different thing from “collapse of the wave function” in QM. It is a physical event, not a change in chances. It occurs when a quantum of field, regardless of how spread-out it may be, instantly transfers its energy into a solitary atom and vanishes. (There are also additional kinds of collapse, like scattering, coupled collapse, internal change, etc.) Field collapse is not described by the field equations– it is a different occurrence, but simply because we don’t have a theory for it does not mean it can’t happen. The fact that it is non-local bothers some physicists, but this non-locality has been demonstrated in several experiments, and it does not lead to any inconsistencies or paradoxes.

So whenever field collapse happens, the ultimate “decision”– the defining moment– is reached. This is QFT’s answer to when does collapse occur: when a quantum of field colapses. In the scenario of Schrödinger’s cat, this is when the radiated quantum (perhaps an electron) is captured by an atom in the Geiger counter.

Just before a field quantum finally collapses, it could have interacted or entangled with a lot of other atoms along the way. These interactions are illustrated (deterministically) by the field equations. But the quantum can not have indeed collapsed into any of those atoms, for the reason that collapse can take place just one time, so no matter what you refer to it as– interaction, entanglement, perturbation, or just “diddling”– these initial interactions are reversible and do not bring about macroscopic changes. Then, when the ultimate collapse takes place, those atoms become “undiddled” and return to their unperturbed state.

To sum up, in QFT the “decision” is made when a quantum of field deposits all its energy into an absorbing atom. Besides replying to this question, QFT additionally explains why time dilates in Special Relativity and resolves the wave-particle duality issue of Quantum Mechanics. An individual can simply think about why this particular theory hasn’t already been welcomed and made the basis for our knowledge of nature. I feel it is truly time for physicists to WAKE UP AND SMELL THE QUANTUM FIELDS.

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