Archive for June, 2011

So Say We All

28 June 2011

Quantum States of Confusion
The weeks or months between entries do not reflect a lack of desire to post, or to read, or to learn. I’ve just found Bernard d’Espagnat’s On Physics and Philosophy a tough slog.

His rather involved prose and the often bewildering translation combine to produce some very indecipherable moments, and my merely rudimentary understanding of quantum theory doesn’t help much either.

Here’s the latest of my chapter summaries, presented in the black-and-white dichotomous style that seems to match my thinking. Things are looking up, though, as he’s now getting into more philosophical territory.

Up to now he’s spent a lot of time justifying his interpretations by reviewing the experimental evidence and pointing out flaws in other approaches to the physics. It’s all perfectly legitimate, but as a lay reader I don’t always feel competent to judge who’s right.

So here’s a look at chapter ten of Bernard d’Espagnat’s On Physics and Philosophy.

Laws of Classical Physics vs Quantum Physics
D’Espagnat says that the laws of classical physics were “objectively interpretable” while in quantum physics the laws merely predict observations and the mutual agreement of observers.

Prediction vs Justification
D’Espagnat says modern physics prefers to come up with laws to explain patterns of observation rather than explain what’s “objectively” going on. Even so, can we justify why we choose these rules and why they work?

Quantum Laws vs Macroscopic Predictions
Quantum laws lead to paradoxes such as the Schrödinger cat, not observed in real life. Can we justify the laws behind these paradoxes?

Quantum Laws vs The Alternatives
But more generally, how do we justify (as in “explain”) that these laws work better than any others we might invent?

Ensembles vs Individual Observations
In chapter eight d’Espagnat tackled the “and-or” problem: quantum laws seem to suggest the mixing of two quantum states (aA + bB) whereas our world looks classical (either we detect aA or we detect bB).

Decoherence theory shows how observing a whole ensemble of cats will show each one is either dead or alive in the proportions quantum mechanics predicts. Quantum laws are thus reconciled with observation—except that we generally observe individual cats not ensembles of them.

Mere Predictions vs Hidden Variables
If quantum mechanics merely predicts observations rather than says anything about the “reality” behind what we see then simultaneous states are just a way of calculating probabilities.

On the other hand, Broglie-Bohm’s pilot wave (see chapter two) has a particular probability of being in one of two regions—really being in one of two regions (equivalent to aA or bB).

Standard quantum mechanics says whatever the “Real” happens to be is what produces results that match quantum predictions. The pilot wave approach gets more ontological and suggests what the “Real” must look like to produce those observations.

The two approaches are compatible, though that doesn’t solve various problems with the hidden variable approach (as d’Espagnat has already pointed out).

Outside vs Inside Observations
D’Espagnat then moves beyond our vaguely disembodied, collective observations of instrument pointers, which is what decoherence theory can explain.

He ponders conscious beings that can make predictions about themselves—making observations from within.

Consciousness vs Matter
D’Espagnat says both scientists and “the enlightened general public” look upon states of consciousness as states of matter.

Matter vs Sense Data
D’Espagnat says equating consciousness and matter is hasty, as the argument depends not on the concept of matter but rather on the concept of awareness, as in “registering sense data.”

Sense Data vs Reality
D’Espagnat says Berkeley, Kant, and the neo-Kantians followed the “great principle” that things take place “as if” our senses and classical physics give a true picture of reality.

In other words, the belief was that our sense data give us “an access to ontology.” However, quantum mechanics makes it clear that this principle is a faulty assumption.

Schrödinger’s Cat vs Wigner’s Friend
D’Espagnat says Schrödinger’s cat presumably has a viewpoint on whether it’s alive or not.

Furthermore, Wigner suggested substituting a human. Can we still justify quantum predictions?

Can quantum mechanics agree that an outside observer and “Wigner’s friend” have states of consciousness at the same time?

Improper vs Proper Mixtures
A “proper” mixture of quantum states would be just like a classical sum of states, typically seen in the ordinary macroscopic world.

An “improper” mixture (or “pure case”) is typically seen in entangled quantum systems more or less undisturbed by the outside environment.

The kind of mixture can be determined by measuring a large number (“ensemble”) of identical systems and seeing which states are observed.

Pointers vs Bacteria
Let’s imagine an electron is in the state c = a+b. Some bacteria come along, creating a large number of electron-bacteria quantum systems.

This microscopic electron-bacteria ensemble should be an improper mixture of states aA and bB.

But a problem arises if definite states of consciousness imply definite states of matter.

If the bacteria have states of consciousness then they would be aware if they’re in state A or state B.

The bacteria’s (supposed) self-awareness implies a proper mixture of quantum states, but orthodox quantum theory says there should be an improper mixture.

If orthodox quantum theory holds true then our “conscious” bacterium will lack any power to make predictions.

Pilot Waves vs Schrödinger Wave Function
In the Broglie-Bohm model the “total wave function” doesn’t “collapse” or get “reduced.”

The Schrödinger wave function just gives the probability that the (unorthodox) pilot wave is in some region of the system. No contradiction.

But in orthodox quantum theory the quantum state of the bacterium is an improper mixture of various states, so we get an apparent contradiction.

Microscopic vs Macroscopic Subjects
Bacteria are microscopic but humans are macroscopic. Decoherence theory kicks in, so in practice we can consider electron-human systems to be a proper mixture of two reduced wave functions. Therefore in practice their state of consciousness has predictive power.

Predictive Consciousness vs Predictive Science
D’Espagnat says he’ll explore notions of consciousness in chapter 18, but says the “scientific” definition of consciousness is limited to one of predictive power, and that’s because science itself limits itself to predictive power.

Predictive vs Non-predictive Consciousness
The bacterium or Schrödinger’s cat who thinks it’s alive cannot influence the outside observer if this state of consciousness is non-predictive, says d’Espagnat.

If you could somehow ask the bacteria what their state had been you’d find the results were the same as for a proper mixture.

But we’d assumed the quantum ensemble was initially a pure case (in other words, in an improper mixture).

Asking a question is like taking a measurement. It disturbs the system. Hence no contradiction.

Group vs Individual Observations
D’Espagnat says the generalized Born rule is “impersonal.” It makes predictions about the correlations among observers not what a particular individual observer will see.

So “Aspect-type” experiments measure correlations among observers, whose states of consciousness are correlated (because they’re observing correlated readings).

But if the Born rule is applied to individual observers this correlation would be cut.

D’Espagnat is not comfortable with the “quite inordinate strangeness” that private states of consciousness would differ in this situation, and hence be deprived of some of their predictive power.

He does not, however, rule out this possibility.

Individual vs Group Observations
Although in theory the overall wave function must be the basis for predictions, in practice decoherence lets macroscopic observers rely on their own states of consciousness to make predictions.

Can this reliability of individual predictions be extended to group predictions?

Two friends are looking at the same pointer. By the conventional Born rule they will get the same “impression” of the pointer and hence build up the same kind of wave function to make future predictions.

The different waves that correspond to different impressions of the pointer mostly don’t overlap. That fact and decoherence assure us that the two friends’ predictions will coincide too.

Physics vs Philosophy
D’Espagnat notes a “turning point” in the book. He feels he’s shown the amazing predictive powers of quantum mechanics and its universality. Now he wants to explain why these rules work and where they came from. This takes him further into philosophical territory.

Instrumentalists vs the Kantians
D’Espagnat says the “diehard instrumentalists” think such questions are meaningless, while those sympathetic to a Kantian viewpoint think some explanations are in order but would be found “within the human realm.”

Naive Realism vs Open Realism
D’Espagnat looks for an explanation he calls “open realism.” He believes an explanation can acknowledge “what truly exists” without descending into a simplistic “naive realism.”

Paying attention to the physics dissuades one’s outlook from becoming too naive, he says.

Scientists vs Philosophers
D’Espagnat says most scientists point to the obvious, common-sense appeal of some kind of objective reality.

Philosophers who lean to Kantianism or radical idealism feel there are no “objects-per-se.” We build up a representation of the world using our senses and intellect.

Most scientists say our body of knowledge has increased immensely since Kant’s time, which they say makes obsolete his reasons for doubting human knowledge as a reliable account of what’s out there.

Most philosophers would say Kant wasn’t daring enough. They say he should have rejected the very idea of a “reality-per-se.”

Kant vs d’Espagnat
D’Espagnat agrees that Kant’s arguments were faulty, though justified at the time considering he knew nothing of evolution or mathematical physics.

However, updated arguments lead to a conclusion roughly similar: science doesn’t seek knowledge of “the Real” but rather just of phenomena.

This is not a rejection of some human-independent reality. In this d’Espagnat agrees with Plato and Kant.

Empirical vs Objective Reality
D’Espagnat does not believe physics describes an objective reality. Rather, it describes at most some kind of “empirical reality.”

He is, though, impressed by the consistent nature of Maxwell’s equations and other major laws, leading him to think physics provides “some not altogether misleading glimpses” of the underlying structure of reality.

“The Real” vs Phenomena
D’Espagnat puts out there the idea of an “extended causality” in which “the Real” imparts some kind of non-quantitative influence on phenomena. He adds that this is just a supposition of his.

Unreachable vs Veiled Reality
D’Espagnat does not believe “the Real” is “radically unreachable.” Rather, it is “merely veiled.”

He emphasizes that this doesn’t mean there’s even a “vague similarity” between our perceptions of reality and what’s behind the veil.

“The Real” vs Space-time
Bell’s theorem and Aspect’s experiments (among others) connect space-time with nonlocality. D’Espagnat hence doesn’t think “the Real” lies in space-time.

Mirroring Kant, d’Espagnat believes space-time is not “noumenal.” It’s just a “reality-for-us,” hence “phenomenal.”

D’Espagnat vs Mohrhoff
Another approach comes from Ulrich Mohrhoff. He thinks some aspects of phenomenal space may be considered strongly objective as long as other aspects are discarded. He suggests that physical space does not intrinsically exist independent of the objects that are in them.

In a footnote d’Espagnat says the suggestion “is certainly worth studying.”

D’Espagnat vs Modern Philosophers
Compared to his disagreement with science’s “physical realists,” d’Espagnat says there’s a “high degree of convergence” between his views and many philosophers.

There’s still some difference of opinion. D’Espagnat believes in a veiled reality while many philosophers think reality is “radically unreachable.”

He also notes that many philosophers feel his “open realism” postulate is arbitrary. D’Espagnat admits it’s unprovable (he does call it a postulate, after all) but feels there are serious arguments to support it.

Existence vs Knowledge
D’Espagnat’s first argument for his postulate is that “existence” comes before “knowledge.”

He admits that the existence of a particular something may logically depend on the possibility of our knowing it.

However, he agrees with Plato and Kant that the very notion of existence can’t depend on our possible knowledge of this existence.

Beautiful Theories vs Falsifiability
D’Espagnat’s second argument for his postulate is that beautiful, consistent theories can be struck down by experiment. Theories predict consequences that can be contradicted by observations.

We can’t be totally in control of what we perceive or not.  In d’Espagnat’s words: Something says “no.”

Realism of the Accidents vs External Influence
D’Espagnat’s third argument for his postulate refers back to chapter five’s “no-miracle” and “intersubjective agreement” arguments.

He says they do not support realism of the accidents or anything close to it. However, they do show, in his opinion, that physical laws depend at least partly on something that is not “us.”

Present vs Past Building Blocks of Knowledge
D’Espagnat’s fourth argument for his postulate is that a priori concepts of human knowledge change over time. Kant could rely on Euclidean space, universal time, and determinism to reject reality-per-se as the source of such concepts.

Nowadays science’s building blocks include curved space, space-time, and indeterminism. It’s hard to believe that we can rely on these basic concepts of human knowledge when they keep changing.

Also, Kant’s building blocks were very intuitive. Physics today uses unintuitive concepts that are so unintuitive it’s hard to believe they sprung from some innate concepts we hold.

So we’re left with either physical realism or contenting ourselves with science as prediction.

Physical realism has (in d’Espagnat’s view) been thoroughly demolished, leaving just the empirical/predictive option—with the caveat that there’s something out there that prevents us from being entirely arbitrary in our perception of reality.

Partial Knowledge vs Veiled Reality
D’Espagnat also mentions some misunderstandings he feels others have of his work.

He says Roland Omnès takes his concept of veiled reality and calls it some kind of “weak realism” in which only partial knowledge of reality is possible.

D’Espagnat says he never uses the term “weak realism,” and thinks Omnès doesn’t appreciate the huge jump from “independent reality” to “empirical reality.”

Veiled reality is no more partially knowable than Kant’s phenomena “are knowable bits of noumena.”

D’Espagnat repeats, though, that the mathematics of some physical laws may “vaguely resemble” some of the “great structures of ‘the Real.’”

D’Espagnat vs Esotericism
Although d’Espagnat says he’s mostly disappointed with the “esoteric visions” that have pointed to his writings, although there are some “intermediate cases.”

D’Espagnat appreciates Thierry Magnin’s approach to “levels of reality” but feels he got it wrong when he sees veiled reality related to “unpredictability and chaos,” the “constructive role” of time, and science as a social construct.

D’Espagnat does note that he’ll explore the objectivity of science in the next chapter, but his concept of veiled reality does not spring from that issue.

Veiled Reality vs Anomalous Phenomena
D’Espagnat says it’s understandable that the views of anyone not agreeing with a “mechanistic conception of nature” would be used to explain various “phenomena seemingly defying the laws of science.”

However, d’Espagnat believes nonlocality in no way explains supposed influences at a distance.

Neither does d’Espagnat doubt the “robustness of the physical laws,” but rather believes them likely to be “correct and universal.”

Finally, the concept of veiled reality addresses a philosophical understanding of reality, not the particulars of observed phenomena.