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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Looking at the Principle of Relativity the Easier Way

In the entire history of physics there is no equation more famous than e = mc2. This partnership amongst mass (m) and energy (e) was derived in 1905 by Albert Einstein from his Principle of Relativity. The derivation wasn't easy and warranted a paper by itself, referred to as "Does the inertia of a body depend upon its energy content?". The equation continues to baffle and dumbfound lay people, since in the usual particle picture of nature, it is difficult to see exactly why there is an equivalence between mass and energy.

In the meantime, a new theory called Quantum Field Theory was created. QFT was perfected in the 1950s by Julian Schwinger in 5 papers called "Theory of Quantized Fields". In QFT there are no particles, there are only fields-- quantized fields. Schwinger succeeded in placing matter fields (leptons and hadrons) on an equal footing with force fields (gravity, electromagnetic, strong and weak), despite the obvious differences among them. Moreover, Schwinger established the theory from fundamental axioms, as opposed to Richard Feynman's particle picture, which he justified because "it works". Regrettably it was Feynman who won the battle, and today Schwinger's method (and Schwinger himself) are mainly forgotten.

Yet QFT has lots of benefits. It has a stronger basis than the particle picture. It describes lots of things that the particle picture does not, including the numerous paradoxes connected with Relativity Theory and Quantum Mechanics, that have puzzled so many people. Philosophically, lots of people can accept fields as basic properties of space, instead of particles, whose composition is unknow. Or if there visualized as point particles, one can only ask "points of what?" And above all, QFT offers an easy derivation and understanding of e = mc2, as follows.

Mass. In classical physics, mass is a measure of the inertia of a body. In QFT some of the field equations contain a mass term that impacts the rate at which quanta of these fields evolve and propagate, slowing it down. Thus mass takes on the same inertial role in QFT that it does in classical physics. But this is not all it does; this exact same phrase causes the fields to oscillate, and the greater the mass, the higher the frequency of oscillation. The result, if you're imagining these fields as a color in space (as in my book "Fields of Color"), is a kind of glimmer, and the greater the mass, the quicker the glimmer. It might appear unusual that the same term that slows the spatial development of a field also provokes it to oscillate, but it is actually straightforward mathematics to show from the field equations that the frequency of oscillation is given by f = mc2/h, where h is Planck's constant.

Energy. In classical physics, energy means the capability to perform work, which is specified as applying a force over a distance. This definition, however, does not offer much of an image, so in classical physics, energy is a rather abstract idea. In QFT, on the other hand, the energy of a quantum is established by the oscillations in the field that comprises the quantum. In fact, Planck's famous relationship e = hf, where h is Planck's constant and f is frequency, found in the centennial year of 1900, follows directly from the equations of QFT.

Well, since both mass and energy are associated with oscillations in the field, it does not take an Einstein to see that there must be a connection between the two. In fact, any schoolboy can combine the two equations and find (big drum roll, please) e = mc2. Not only does the formula tumble right out of QFT, its significance can be imagined in the oscillation or "shimmer" of the fields. Nobel laureate Frank Wilczek calls these oscillations "a marvelous bit of poetry" that produce a "Music of the Grid" (Wilczek's phrase for space viewed as a lattice of points):.

"Instead of plucking a string, blowing through a reed, banging on a drumhead, or clanging a gong, we play the instrument that is empty space by plunking down different combos of quarks, gluons, electrons, photons, ... and let them settle till they get to balance with the spontaneous activity of Grid ... These resonances represent particles of different mass m. The masses of particles sound the Music of the Grid.".

This QFT derivation of e = mc2 is not typically known. In fact, I have never seen it in the books I've read. And still I consider it just one of the great accomplishments of QFT.

Find more information about the Principle of Relativity on the Fields of Color Blog!!

Mass in Quantum Field Theory

The tale of exactly how the gravitational field entered into physics and quantum field theory is a remarkable one, entailing apples and moons, predictions and confirmations, problem-plagued expeditions, and the two greatest scientific geniuses of all time. And it might not have happened if not for the Great Plague.  Read more, Fields of Color - The Theory That Escaped Einstein