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", additionally known as "collapse of the "wave-function". The problem arose in the early days of Quantum Mechanics due to the probabilistic nature of the equations. Because the QM wave-function explains only probabilities, the outcome of a physical measurement can only be determined as a probability. This obviously brings about the question: When a measurement is made, at exactly what point is the ultimate result "decided upon". Some folks believed that the duty of the observer was critical, and that the "decision" was generated when someone looked. This led Schrödinger to propose his well-known cat experiment to demonstrate how ridiculous such an idea was. It is not typically 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 dispute carries on to this day, with several individuals still thinking that Schrödingers cat remains in a superposition of dead and alive until someone looks. However the majority of people believe that the QM wave-function "collapses" at some earlier point, before the uncertainty reaches a macroscopic level-- with the definition of "macroscopic" being the primary question (e.g., GRW theory, Penrose Interpretation, Physics forum). Several individuals take the "many worlds" view, in which there is no "collapse", but a splitting into various worlds which contain all possible histories and futures. There have been a lot of experiments created to address this issue, e.g., "Towards quantum superposition of a mirror".

We will now find that an unequivocal answer to this issue is offered by Quantum Field theory. However since this theory has been neglected or misunderstood by many physicists, we have to initially specify what we suggest by QFT.

Definition of Quantum Field Theory.
The Quantum Field Theory described here in this article is the Schwinger version in which there are absolutely no particles, there are only fields, not the Feynman version which is based on particles. * The 2 versions are mathematically equivalent, but the concepts backing them are quite different, and it is the Feynman version that is chosen by most Quantum Field Theory physicists.

* According to Frank Wilczek, Feynman ultimately changed his mind: "Feynman informed 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 use the term henceforward, the world is composed of fields and only fields. Fields are defined as properties of space or, to express it in a different way, space is made of fields. The field concept was presented by Michael Faraday in 1845 as an explanation for electric and magnetic forces. However the principle was not easy for folks to accept and so when Maxwell demonstrated that these particular equations forecasted the existence of EM waves, the concept of an ether was presented to carry the waves. Today, however, it is commonly accepted that space can have properties:.

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

Moreover space-time itself had come to be 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 a crucial and fundamental distinction between Quantum Field Theory and Quantum Mechanics. One explains the strength of fields at a given point, the other explains 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 generally understood that Quantum Field Theory gives an easy solution to the "measurement problem" that was examined on the September letters page of Physics Today. But by QFT I do not mean Feynman's particle-based theory; I mean Schwinger's QFT where "there are no particles, there are only fields".1.

The fields are present in the form of quanta, i.e., chunks or units of field, as Planck envisioned over a century ago. Field quanta evolve in a deterministic way specified by the field equations of QFT, except when a quantum suddenly 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. In fact there is no theory that describes it. Everything we understand is that the probability of it happening depends upon the field strength at a given position. Or, if it is an interior collapse, like a shift in angular momentum, the likelihood depends on the element of angular momentum in the given direction. In QFT this collapse is a physical event, not a mere change in probabilities as in Quantum Mechanics.

Many physicists are troubled by the non-locality of quantum collapse where a spread-out field (or perhaps 2 correlated quanta) unexpectedly disappears or changes its interior condition. Yet non-locality is required if quanta are to serve as a unit, and it has been experimentally proven. It does not result in inconsistencies or paradoxes. It might not be just 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.

Sometimes quantum collapse can cause a macroscopic change or "measurement". However the measurement outcome, i.e., the "decision", was determined at the quantum level. Everything after the collapse follows inevitably. There is no "superposition" or "environment-driven process of decoherence.".

Take Schrödinger's cat as an illustration. If a radiated quantum collapses and transfers its energy into 1 or more atoms of the Geiger counter, that initiates 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 smashes a little flask of hydrocyanic acid" and the cat dies. Alternatively, if it does not collapse in the Geiger counter then the cat lives.

Of course we don't know the result until we look, but we certainly never know anything until we look, no matter if it's throwing dice or choosing a sock blindfolded. The fate of the cat was actually determined at the moment of quantum collapse, just like the outcome of throwing dice is identified when they hit the table and the color of the sock is figured out when it is taken out of the drawer. After the quantum collapse there is no entanglement, no superposition, no decoherence, only lack of knowledge. What could be easier?

In addition to offering an easy solution to the measurement problem, Quantum Field Theory provides a logical 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 acknowledged QFT in the Schwinger sense.

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