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]

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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.

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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.

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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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How Quantum Field Theory Solves the “Measurement Problem”.

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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.

Follow the Fields of Color Blog for more info from Dr. Rodney A. Brooks.