The Antirealist’s Reality

Ultimate reality

The Invisible Hand
Chapter seven of Bernard d’Espagnat’s On Physics and Philosophy is a kind of grab bag, entitled: “Antirealism and Physics; the Einstein-Podolsky-Rosen Problem; Methodological Operationalism.”

D’Espagnat’s points in this chapter seem to boil down to this:

  1. Physics (and science in general) is about predicting observations not describing some kind of reality
  2. Operationalism (which concentrates on methodology) increases the reliability of science as it counters critics who complain scientific theories (which they say should describe and explain reality) keep changing, and
  3. Although measurements (of “empirical” reality) depend on the observer, physical laws seem to be constrained in various ways (by the structure of an “ultimate” reality that’s scientifically indescribable).

This chapter feels a little scattered as d’Espagnat pre-emptively defends himself against a bevy of incoming realist missiles.

In the end, though, he’s an antirealist in terms of empirical reality, and a realist in his belief there’s an ultimate reality that’s (probably) beyond our direct knowledge but nonetheless influences the shape of our everyday reality.

Here’s some more detail…

Unconscious vs Conscious Antirealism
D’Espagnat says modern physicists (ever since Galileo) generally use an antirealist approach in their methods even if they don’t explicitly embrace antirealism as a philosophy.

Mind-independent Realism vs Pythagorean Ontology
Objectivist realism claims there’s a mind-independent reality whose contents resemble our observations.

A Pythagorean Ontology (capital “O”) claims there’s a mind-independent reality that is reachable through deeper mathematical truths.

Unlike either of these approaches, modern physics emphasizes instruments and measurements. It’s not very interested in saying what’s “really” out there in the “world,” whether physical or mathematical.

Meaningful Statements in Classical vs Quantum Physics
While done more intuitively in the past, physicists nowadays can more formally apply “meaningfulness conditions” to statements.

Also, quantum systems are so peculiar that certain distinctions need to be made. Antirealist statements have to be expressed and tested in special ways.

Facts vs Contingent Statements
D’Espagnat is concerned here not with general “factual” statements such as “Protons bear an electric charge” but rather with satements about physical quantities. A value is assigned to the speed of a particular object, for instance.

True/False Statements vs Meaningless Statements
Based on Dummett’s approach a statement about an object’s speed would be meaningful only if we can measure (at least in principle) that physical quantity at some specified time and place.

Necessary vs Sufficient Grounds for Meaningfulness
D’Espagnat says Dummett’s criterion is necessary, but that doesn’t mean it’s sufficient. Other conditions may need to be fulfilled.

Imagining vs Measuring a Quantity
It’s possible that we can conceive of a physical quantity that has no meaning. However, if we can measure it then that quantity will definitely have meaning.

Classical vs Quantum Measurements
In classical physics it’s intuitive to think a measurement reflects the “true” values of an object, but in quantum systems the measurement of a particle (depending on your model) either creates or changes the values that you’re trying to measure.

In quantum physics we’re not simply “registering” some pre-existing value when we take a measurement. So the “truth value” criteria will need to include more than just measurability.

Disturbing vs Non-disturbing Measurements
In the spirit of antirealism D’Espagnat introduces a test: for a statement to have a truth value “it should be possible” (at least in theory) to measure the required physical quantity without disturbing the system.

The Einstein–Podolsky–Rosen trio claimed in 1935 that in some cases there are indirect ways to make non-disturbing measurements, admittedly only on correlated systems.

Correlated Darts vs Photons
If you throw a pair of correlated darts (see chapter three) they originally have some identical orientation. Measuring one dart’s value after they become separated will tell us the other dart’s value. As a bonus, the measurement won’t even change that other dart’s orientation.

If instead of darts you use correlated photons, and instead of measuring orientation you measure the polarization vector’s component at some angle, then you run into a problem.

Consistent vs Broken Correlations
If you measure one photon’s component at a certain angle then you can be sure if you measure the other photon’s component at the same angle you’ll get the same value (which will simply be “plus” or “minus”).

Because we are capable of making this measurement then by our meaningfulness test we can tell if a statement about those values is true or false.

But quantum formalism says the system of these two photons can have just one value at a time. We can’t measure one photon at a particular angle, then measure the other photon to measure another angle’s polarization component.

Multiple Values vs Bell’s Inequalities
At least we can’t then claim the second photon has simultaneous values at two different angles. The first measurement destroys the original correlation.

Because Bell’s inequalities have been disproved experimentally, we know that these multiple values don’t exist simultaneously.

And because our original meaningfulness test implied such a simultaneity we know that test is flawed.

Actual vs Possible Measurements
If we instead require that measurements are available rather than merely could be available then we get a stricter test. By phrasing our requirements in the indicative not the conditional we end up with a sufficient condition, not just a necessary one.

Possible Measurements vs Observational Predictions
Dummett’s meaningfulness test is a very general antirealist approach. It doesn’t look at the factual data actually available in a microscopic situation. It just considers our ability to make measurements in principle.

D’Espagnat says the tighter requirements he’d impose take an approach even further along the antirealist path as they speak of observational predictions not measurements. This also takes us further down the path of instrumentalism.

Operationalism vs the Value of Science
D’Espagnat says if you understand operationalism properly then you’ll realize operationalism confirms the value of science and makes its statements more reliable.

Description vs Prediction
D’Espagnat says critics of science believe scientific knowledge is easily influenced by social and cultural factors, and is frequently throwing out old theories for the sake of very different new ones.

Superficially this makes sense. Einstein’s curved space-time replaced Newton’s gravitational force. They’re radically different approaches.

But science isn’t trying to describe reality. It’s trying to make predictions about observations. Newton’s approach makes good predictions in its own domain, but in other domains Einstein’s predictions are the only ones that work out.

Sometimes the predictions and domains can be identical. Fresnel’s and Maxwell’s theories of light make the same predictions. D’Espagnat says the value of Fresnel’s theory was independent of whether the ether was really out there.

If you drop the naïve realism and its concern for description, then science as a method for synthesizing and predicting experience is not so inconsistent.

Now we can see steady progress as science gets better and better in its power of prediction.

Scientific Knowledge vs Practicality
D’Espagnat says science is mainly knowledge. Even if science is  concerned with prediction and not description, don’t confuse science with the various practical uses it’s put to (such as technology).

Descriptive vs Instrumentalist Knowledge
Science brings together an account of human experience that can be communicated: “If we do this, then we observe that.” Just because it’s not trying to describe “reality” doesn’t mean it’s not imparting some kind of knowledge.

Instrumentalist vs Theoretical Knowledge
These methods of making observational predictions are at the core of science. Coming up with a theory to define certain terms and describe certain entities can be useful, but that’s something added onto this predictive foundation.

Operationalism vs Instrumentalism
D’Espagnat doesn’t try to distinguish the two terms. He says the most important aspect of any theory that conforms to this approach is that it’s an instrument of making observational predictions. He says mathematical physics is a prime example.

Open Realism vs Endless Possibilities
In chapter five D’Espagnat talked of his preferred approach of “open realism.” Certainly our view of “reality” (specifically its physical laws) depends on us, including our ability to make observations. But there seem to be “constraints” on what kinds of theories are valid.

Describing vs Acknowledging Constraints
This “something else” that lies beyond our observations but somehow constrains them may not be directly accessible by us, but D’Espagnat says our inability to describe the constraints does not mean they don’t exist.

Ultimate vs Empirical Reality
An elusive, indescribable “ultimate reality” may still shape the physical laws that we describe. In turn the laws we infer are shaped from our observations that contribute to our sense of “empirical reality.”

Explanations vs Theories
D’Espagnat quotes one critic of operationalism, Mario Bunge, who says that the main role of a theory is to provide an explanation. Therefore a theory must provide at least a “rough sketch” of reality as it is.

D’Espagnat replies that the explanation would actually lie in the ultimate reality that constrains our physical laws, but this ultimate reality is not scientifically describable. Therefore what Bunge desires is impossible.

Unless we grant that “miracles” happen all the time there appear to be constraints on our physical laws. But the ultimate reality producing these constraints can’t be scientifically described because of the problems with objectivist realism noted before.

Physics vs Physical Objects
D’Espagnat says that Bunge considers a value in physics attached to something that is not physical is meaningless. If the value doesn’t refer to something “real” then it’s pointless.

D’Espagnat points out that many physical laws refer to values that are not attached to existing physical objects. Probability is a concept referring to either imaginary objects or is a thought not subject to physics.

Particles vs Waves
Also, wave functions are useful, in fact, essential for quantum physics. So are wave functions real? If so, then particles would have to be real too. If waves and particles exist simultaneously then we’d have to accept the Broglie–Bohm model with all its problems (see chapter nine).

Also, a ground-state electron in a hydrogen atom would seem to have zero momentum because it’s not changing state (quantum potential is balanced by Coulomb force). But the Compton effect shows momentum is non-zero. We have two different versions of momentum. If they were both “real” then we get into pointless difficulties, says d’Espagnat.

Other possibilities: waves change into particles (but the collapse of the wave function has lots of problems attached to it) or only waves exist (but then nonseparability and measurements cause problems).

So D’Espagnat says Bunge’s objections seem pretty “dogmatic.”

Circular vs Practical Definitions
Another objection notes (correctly, d’Espagnat acknowledges) that operationalists place a lot of emphasis on precise definitions, but Bunge says some concepts will remain undefined (just like a dictionary uses some undefined words to define other words).

D’Espagnat replies that operationalism is a methodology, not an “a priori” philosophical system. We want efficiency. Dictionaries are useful despite their undefined terms. Some concepts we just seem to naturally know (whether they’re born with us or not).

These undefined concepts (though neither certain nor absolute) let us operate a measuring instrument, for instance, which then lets us define other concepts.

Sometimes concepts considered “primary” in the past get defined explicitly, such as Einstein’s replacement of “absolute time” with a time that’s partly relative to the observer.

Measurement vs Change
The act of measurement seems to change the quantum system. If, as Bunge’s approach would suggest, this change is “real” then we’d have the difficult problem of explaining this change.

But the quantum approach is “weakly objective” so it refers only to measurement. In the end theoretical entities are useful for helping to make predictions in modern physics. Just don’t regard them as self-contained and “real.”

Einsteinian Hope vs Descriptive Failure
Einstein and those of a similar optimistic bent believed reality would be increasingly describable. This view does not seem consistent with the reality that the quantum framework paints.


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