A Mysterious Trajectory

Mysterious Trajectories

Construction vs Deconstruction
Continuing on with my binary (but gentle) deconstruction of Bernard d’Espagnat’s On Physics and Philosophy, we can now proceed to chapter two, entitled “Overstepping the Limits of the Framework of Familiar Concepts.”

Here are some points I’ve gleaned, which I’ve repackaged into the black-and-white dichotomies I love so much.

Aristotle vs Galileo (Reprise)
Although Galileo believed in a priori mathematical concepts, d’Espagnat says Galileo’s two main scientific contributions — inertia and the relativity of motion — were based on sensory data derived from inclined planes and moving ships.

Primary vs Secondary Qualities
Galileo believed he could make observations of “primary” qualities to find out what “really is.” He could then reject the supposedly illusory “secondary” qualities.

Galileo vs Descartes
Descartes was the other “founding father of modern science,” but more of a philosopher than Galileo. He justified his realism from “cogito ergo sum” (I think therefore I am), an ontological argument for an infinite Being that could deceive us, self-evident truths, and finally fundamental notions of form, size, and motion, which are true because they’re clear.

He believed in “near realism”: nature can be described through basic notions of figure, size, and motion. Natural and manmade objects are similar but differ in size.

D’Espagnat says Galileo, Aristotle, and Descartes were all objectivist realists, even multitudinist ones. However, Descartes was more concerned with metaphysics and his system of thought could hardly have led to Galilean relativity, says d’Espagnat.

Petitot vs d’Espagnat
D’Espagnat rejects Jean Petitot’s view that Galilean relativity’s space and time are “desubjectized mental forms.” Galileo, responds d’Espagnat, kept the number of intrinsic properties to a few, but he still believed in their reality. Relative positions and motions are normally said to be real, and neither Galilean relativity nor Newtonian mechanics are inconsistent with absolute space.

Forces vs Fields
Galilean ontology led to the notion of forces, which could produce action at a distance. However, forces were still properties of objects. No object? No force. In the 19th century the notion of fields was introduced. For instance, an electromagnetic field can exist “in vacuum” devoid of electric “sources.”

Physics vs Realism of the Accidents
As physics joined with mathematics to overcome the old familiar concepts the other sciences looked for simpler notions allowed through a belief in the realism of the accidents.

A quantum wave is a function of many variables: the number of particles times three (for each particle’s x,y,z coordinates). So the wave has no value at a particular three-dimensional point. Unlike a field one can compare to gelatin, the wave is hardly realism-friendly.

Relativity vs “Universal Thing-ism”
Although relativity replaced objects with events, it didn’t reject realism. Realism of the events is allowed. Naïve realism of “universal thing-ism” is not.

Objects are sequences of events but the events (and geometry of space and time) still supposedly exist, even if they’re perceived differently by different observers.

Useful Notions vs Actual Existence
Physicists explain complex features that are visible by simple invisible ideas that work well. The temptation is then to think these “clear, distinct ideas” (as Descartes might say) also “exist.”

The notion of “electrons” is great for explaining things, but when you start to think of an electron as localized, one per orbit, the picture gets misleading.

To say each electron exists simultaneously on all “allowed” orbits is much less misleading.

Trajectories vs Quantum Probabilities
Put a bubble chamber where it can capture cosmic rays. Soon tracks will appear that we will be tempted to call “trajectories.” We imagine a particle started out in space along some trajectory and reached the bubble chamber, leaving a trail.

Quantum mechanics says there are no such trajectories. The liquid in the bubble chamber reacts with radiation, and the quantum probability that two adjacent atoms will get excited is essentially zero unless they’re almost exactly aligned with the direction of the radiation.

Quantum Field Theory vs Dirac’s Virtual Sea
Quantum pioneer Paul Dirac correctly predicted that every time a fermion (such as an electron) is created so should its opposite partner, an anti-fermion (such as a positron).

He visualized a sea of invisible and nonlocalized fermions. A particle is created when it escapes this sea, leaving a “hole” in the sea with opposite properties. It wasn’t a very credible theory.

Quantum field theory says the existence of a particle is just a state. Existence is a property of “something” — but everyday physicists are reluctant to commit to whether this “something” actually exists.

Hidden Variables vs Quantum Completeness
Einstein and others disliked that quantum theory doesn’t describe the world as it “really” is. Instead of the quantum wave only predicting probabilities people like Louis de Broglie and David Bohm theorized about specific particles on specific paths moving in a way that produced the same predictions.

These specific paths are determined through invisible factors not included in quantum theory.

Such “hidden variable” theories run into problems when paired particles grow distant and one particle ends up experimentally detected. Assuming a specific trajectory doesn’t eliminate nonlocality, as Bell’s Theorem shows.

Ontology vs Pseudo-ontology
Physicists avoid espousing “near realism” or “realism of the accidents.” They try to remain “open” about the concepts they use. Instead they’ve developed a pseudo-ontology using diagrams.

Feynman Formalism vs “Something’s” State
Feynman diagrams help physicists navigate through complicated formulas. An “H” diagram will show one particle on the move, emitting a virtual particle, absorbed by the second incident particle, and they continue on their way.

In this system there is no state of “something” that’s changed. If pressed, a physicist may say the elements of such a diagram are just a “way of speaking.” But the danger is we think they’re actual names of actual things.

Description of Experience vs “Reality Out There”
While some physicists feel empirical evidence gives us only a description of experience, other physicists feel some reality is “obviously” out there. These two positions are distinguished by three factors.

Experiential vs Realist Objectivity
In chapter four d’Espagnat will explore objectivity. For now he says the realist has more stringent standards for objectivity than the experiential proponent.

General Laws vs Specific Entities
A realist looks for specific objects with specific properties, and likely relies on counterfactuality (inferring that unobserved objects still retain their properties).

An experientialist may believe in an explanation of the world compatible with the realist’s, but works from general laws to account for specific observations.

Quantum Completeness vs Incompleteness
A realist may look for hidden factors to preserve the belief that localized particles and trajectories “really” exist. Founders of quantum theory retorted that quantum theory is a complete description of reality. Additional factors just don’t exist.

Strong Completeness vs Weak Completeness
Slight problem with saying hidden variables “don’t exist.” It makes definite statements about nonexistence in a similar way to a realist’s pronouncements on existence. This early position might be called “strong completeness.”

“Weak completeness” just says that no competing theory can make predictions about atomic phenomena that aren’t also correctly predicted by quantum theory (as Henry Stapp puts it).

Compatible vs Incompatible with Quantum Theory
D’Espagnat says weak completeness is compatible with his approach in the book. If another theory imagines reality’s structure with additional parameters or variables — but has no “false consequences” — then he’ll say it’s “compatible with truth.”

He says his approach will be one of “enlightened agnosticism.”


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