Richard Feynman: The Two-Slit Experiment Contains the One Mystery in Quantum Mechanics

In his famous Lectures on Physics, some of the lectures repeated in the 1967 Messenger Lectures at Cornell and published as The Character of Physical Law, Feynman famously said that “nobody understands quantum mechanics” and that the two-slit experiment contains the “one mystery” of quantum mechanics.

“I will take just this one experiment, which has been designed to contain all of the mystery of quantum mechanics, to put you up against the paradoxes and mysteries and peculiarities of nature one hundred per cent. Any other situation in quantum mechanics, it turns out, can always be explained by saying, ‘You remember the case of the experiment with the two holes? It’s the same thing’. I am going to tell you about the experiment with the two holes. It does contain the general mystery; I am avoiding nothing; I am baring nature in her most elegant and difficult form.”

Separating #FreeWill from #MoralResponsibility, by separating free from will and moral from responsibility

Four Degrees of Separation:

  1. The Separation of “Free” from “Will”
  2. The Separation of “Responsibility” from “Moral Responsibility”
  3. The Separation of “Free Will” from “Moral Responsibility”
  4. The Separation of “Free Will and Moral Responsibility” from “Punishment” – both Retributive and Consequentialist

We must separate the concept “free” from the concept of “will” in order to better understand “free will,” as John Locke recommended we do to avoid verbal confusion. He said, “I think the question is not proper, whether the will be free, but whether a man be free.”
(Essay Concerning Human Understanding, Book II, Chapter XXI, Of Power, s.21)

We must also separate “moral responsibility” from ordinary “responsibility” or simple accountability. If our intentions and decisions caused an action, we are responsible for it, but moral responsibility requires that the action has moral consequences. Immanuel Kant and the modern free willist Robert Kane think that only moral decisions can be free decisions.

Finally, we should explore the connection between moral responsibility and punishment , both backward-looking retributive punishment (revenge or restitution) and forward-looking consequentialism (re-education and rehabilitation).

See Chapter 20 of Free Will: The Scandal in Philosophy

Best animations on YouTube of the #TwoSlit Experiment

We review the best animations on YouTube of the #TwoSlit Experiment to solve the #WaveParticle Duality Problem.

Let’s look first at the one-slit case. We prepare a slit that is about the same size as the wavelength of the light in order to see the Fraunhofer diffraction effect most clearly. Parallel waves from a distant source fall on the slit from below. The diagram shows that the wave from the left edge of the slit interferes with the one from the right edge. If the slit width is d and the photon wavelength is λ, at an angle α ≈ λ/2d there will be destructive interference. At an angle α ≈ λ/d, there is constructive interference (which shows up as the fan out of lightening patterns in the interfering waves in the illustration).

When both slits are open, the maximum is now at the center between the two slits, there are more interference fringes, and these probabilities apply whichever slit the particle enters. The solution of the Schrödinger equation depends on the boundary conditions – different when two holes are open. The “one mystery” remains – how these “probabilities” can exercise causal control (statistically) over material particles.
Remembering that the double-slit interference appears even if only one particle at a time is incident on the two slits, we see why many say that the particle interferes with itself. But it is the wave function alone that is interfering with itself. Whichever slit the particle goes through, the interference pattern is what it is because the two slits are open.

Einstein Discovered Wave-Particle Duality Decades Before Heisenberg and Schrödinger

Besides quantizing light energy and seeing its interchangeability with matter, E = mc2, Einstein was first to see many of the most fundamental aspects of quantum physics – the quantal derivation of the blackbody radiation law, nonlocality and instantaneous action-at-a-distance (1905), the internal structure of atoms (1906), wave-particle duality and the “collapse” of the wave aspect (1909), transition probabilities for emission and absorption processes that introduce indeterminism whenever matter and radiation interact, making quantum mechanics a statistical theory (1916-17), the indistinguishability of elementary particles with their strange quantum statistics (1925), and the nonseparability and entanglement of interacting identical particles (1935).

It took the physics community eighteen years to accept Einstein’s light-quantum hypothesis. He saw wave-particle duality fifteen years before deBroglie, Schrödinger, Heisenberg, and Bohr. He saw indeterminism a decade before the Heisenberg uncertainty principle. He saw nonlocality as early as 1905, presenting it formally in 1927, but was ignored. In the 1935 Einstein-Podolsky-Rosen paper, he added nonseparability, which was dubbed “entanglement” by Schrödinger.

We show that there was a glimpse of wave-particle duality even in Einstein’s “very revolutionary” 1905 light-quantum hypothesis paper.

Quantum Particles Are Matter/Energy. Quantum Waves are Immaterial Information.

Of all the mysteries, puzzles, and paradoxes associated with
modern physics, none is more profoundly metaphysical than
the strange connection between waves and particles in quantum
mechanics. And no philosophical method is better positioned to
provide a metaphysical explanation than information philosophy,
with an information analysis of the physics and the fundamental
nature of physical reality, the so-called “quantum reality.”

Most surprisingly, the solution to this most modern of scientific
problems throws new light on perhaps the oldest philosophical
problem, the ancient question about the existential status of ideas,
and the relation between the ideal and the material.

Put most simply, the quantum wave function is an idea, pure
information about the possible places that matter may be found.
And perhaps most shocking, we can show that this abstract idea
has causal power over the paths of the concrete particles, even as we
can only learn about their paths statistically and not individually.

David Layzer: The Origin of Information

David Layzer is a Harvard cosmologist who in the 1960’s made it clear that in an expanding universe entropy would increase, as required by the second law of thermodynamics, but that the maximum possible entropy of the universe might increase faster than the actual entropy increase, making room for the growth of order or information at the same time entropy is increasing.

He pointed out that if the equilibration rate of the matter was slower than the rate of expansion, then the “negative entropy” (defined as the difference between the maximum possible entropy and the actual entropy) would increase. Claude Shannon identified this negative entropy with information, though visible structural information in the universe may be less than this “potential” information.

In a 1975 article for Scientific American called The Arrow of Time, Layzer wrote on what is the fundamental question of information philosophy , what was the origin of information?

“the complexity of the astronomical universe seems puzzling.
Isolated systems inevitably evolve toward the featureless state of thermodynamic equilibrium. Since the universe is in some sense an isolated system, why has it not settled into equilibrium? One answer, favored by many cosmologists, is that the cosmological trend is in fact toward equilibrium but that too little time has elapsed for the process to have reached completion. Fred Hoyle and J. V. Narlikar have written: “In the ‘big bang’ cosmology the universe must start with a marked degree of thermodynamic disequilibrium [information] and must eventually run down.” I shall argue that this view is fundamentally incorrect. The universe is not running down, and it need not have started with a marked degree of disequilibrium; the initial state may indeed have been wholly lacking in macroscopic as well as microscopic information.”

Many Forms of Determinism: Only One Indeterminism

Determinism is the idea that everything that happens, including all human actions, is completely determined by prior events. There is only one possible future, and it is completely predictable in principle, most famously by Laplace’s Supreme Intelligent Demon, assuming perfect knowledge of the positions and velocities of all the atoms in the void.

More strictly, determinism should be distinguished from pre-determinism, the idea that the entire past (as well as the future) was determined at the origin of the universe, and from pre-destination, the idea that the will of an omniscient supreme being has determined the one possible future.

Determinism is sometimes confused with causality, the idea that all events have causes. But some events may be undetermined by prior events. Such an event is indeterminate, sometimes known as a “causa sui” or self-caused event. But it may in turn be the cause for following events that would therefore not be predictable from conditions before the uncaused event.

Uncaused events are said to break the “causal chain” of events back to a primordial cause or “unmoved mover.” Aristotle‘s “accidents” and Epicurus‘ “swerve” are such uncaused causes.

Although there is only one basic form of indeterminism, there are many determinisms, depending on what pre-conditions are considered to be determinative of an event or action. We identify more than a dozen distinguishable determinisms.