Theory Selection and Discord in Quantum MechanicsNeal RavindraProfessor Don HowardPhilosophical Issues in PhysicsMonday, 29 April 2013Class PresentationCovers chapter 24, “An essential role for historical contingency?” in Philosophical Concepts in Physics

A quick look ahead…Background

Brief review of some early quantum mechanical ideasBell’s theorem, sort of relevant

UnderdeterminationInference to the best explanationPierre DuhemWillard Quine

Relevance to quantum mechanicsHistorical contingency?A hypothetical scenario?

Two different schools of thought…

The completeness of quantum mechanics?Niels Bohr frames contextuality, and complementarityBohr and “the irreducible, ineliminable and uncontrollable minimum disturbance” – Copenhagen interpretation of quantum phenomena1

Dissatisfaction with uncertainty led to the search for an hidden variables theory

Einstein’s belief in an objective physical reality Remarked that the Copenhagen theory is little more than “a highly successful provisional theory.”2

A quick note about Bell’s theorem…

Recall that Bell’s theorem demonstrates and proves that “no determinate, local hidden-variables theory can agree with all of the predictions of quantum mechanics.”3

Fig. 1: Photons released from source, and entanglement measured at various angles

Quantum mechanics as a theory…

The theory of quantum mechanics has two components4

A formalismCopenhagen theory and Bohm theory have equivalent formalism

An interpretationCopenhangen interpretation differs from Bohm interpretationIncompatibility of the two causes a dilemma

Scientific theory functions on three levels:Empirical adequacyFormal explanationunderstanding

Bohm’s 1952 papers, a history

David Bohm’s 1952, a rediscovery of Louis de Broglie’s quantum theory established in 19275

Einstein and the origin of the pilot-wave (as an EM wave)5

Max Born treated the wave equation as a guiding waveDe Broglie’s poor response to an objection raised by Wolfgang Pauli in 1927 shuts many doors

Hilary Putnam, and Heisenberg’s negative reception of Bohmian mechanics5

Leavens, Cushing, and Daumer elaborate on the ease of description of some quantum phenomena by Bohmian mechanics6

“… one purpose of Bohm’s 1952 papers was to show that trajectories are possible and that, therefore, part of the Copenhagen dogma (completeness and, hence, the alleged impossibility of such trajectories) is false. That it certainly did.”7

Not only Copenhagen and Bohmian mechanics…There are actually several highly

developed attempts at alternative interpretations to quantum phenomena

Many worlds8

Consistent histories8

Decoherence9

Modal interpretations10

Fig. 2: a quick graphic explaining the many worlds interpretation of quantum phenomena

An introduction to a problem of choice…

Quantum mechanical formalism (standard orthodox formalism and Bohmian formalism) supports two mutually incompatible ontologiesCushing’s thesis on the resolution of the competition

“… the historical competition between these theories ad the selection of Copenhagen over Bohm illustrate that such an historically contingent process is not meaningfully distinct from the rational reconstruction and logical judgment of the victorious theory”11

Underdetermination of quantum mechanical theory

UnderdeterminationCorrelation does not imply causation12

A simple example

Just because there is a high incidence of violent kids watching cartoons, cartoons don’t necessarily cause violence; therefore, a high correlation underdetermines what we should believe about the causal relationship between the two12 Descartes’ evil demon12

Fig 3: a simple definition of underdetermination is a situation in which there is insufficient evidence to decisively select between beliefs regarding the evidence in consideration

Pierre Duhem on the acceptability of a scientific

theory“The sole purpose of physical theory is to provide a representation and classification of experimental laws; the only test permitting us to judge a physical theory and pronounce it good or bad is the comparison between the consequences of this theory and the experimental laws it has to represent and classify.”13

“The methods [physicists] follow are justifiable only by experiment, and if they both succeed in satisfying the requirements of experiments each is logically permitted to declare himself content with the work that he [or she] has accomplished.”13

‘Experimentum crucis’ – Bacon, Hooke, and Newton and their interpretation of the accpetability of a scientific theory14

Eddington expedition to Africa in 1919 confirming Einstein’s gravitational lensing hypothesis

Fig 4: the French physicist, philosopher, and mathematician, Pierre Duhem (1861-1916)

Duhem – logical justification if experimental phenomena

is saved Duhem argues that it is futile to attempt to discriminate between two plausible theories based on a crucial experiment

“the physicist is never sure he has exhausted all the imaginable assumptions”15

Holist underdeterminationInability to test hypotheses in isolation leaves us underdetermined in our response to a failed prediction12

Contrastive underdeterminationOccurs when a theory in which the evidence confirming the given theory also confirms another, different theory12

This is the philosophical classification of the underdetermination resulting from the Copenhagen school and Bohmian mechanics

Use good sense to discern between approaches to the modification of a set of hypothesis (or to a theory) that produced an underdetermination

The problem with the employment of nonevidential and nonlogical criteria (aka good sense) to eliminate

underdetermination“But these reasons of good sense do not impose themselves with the same implacable rigor that the prescriptions of logic do. There is something vague and uncertain about them; they do not reveal themselves at the same time with the same degree of clarity to all minds.”13

Willard Quine and universal

underdeterminationThe role of good sense:

“nothing more than a loose association reflecting the relative likelihood, in practice, of our choosing one statement rather than another for revision in the event of recalcitrant experience”16

“Much latitude of choice as to what statements to reevaluate in light of any single contrary experience”16

Quine suggested that underdetermination challenges applied to all knowledge claims13

The only test of a belief is whether it fits into a web of connected beliefs that accords well with our experience on the whole13

Fig 5: Willard van Orman Quine (1908-2000), an American philosopher , professor at Harvard

Inference to the best explanation: another

criterion for theory selectionA.k.a. abduction or hypothesis selection criterionCharles Sander Peirce on IBE17:

An inference that a certain hypothesis that adequately explains phenomena represents the truthThere may be equally plausible phenomena, but experimentation and repetition should reinforce the validity of the inductionAbductive validation – one explanation is validated, or a theory is chosen over others, because it is considered the best explanation of the set of empirical data

Best explanation often chosen based on aesthetic qualities (simplicity, elegance, etc)Difference between underdetermination and IBE?

Underdetermination as a tool for leveling the playing field IBE as a method of raising one theory to the top of the hill

Back to quantum mechanics…

Copenhagen school and Bohmian mechanics: two theories that are empirically adequate

Not a problem if differences between ontologies is insignificantThe ontologies entailed by these two interpretations are radically different and incompatible with one another

Inherent indeterminacy is incompatible with absolute determinism

Observational indistuingishability between the two interpretations coupled with conflicting ontology makes a complete, clear picture of the underlying physical structure of the universe impossible

A more complete picture of the process of the selection of

accepted theoriesSince there is no evidential criteria employed to discern the credibility of the Copenhagen interpretation, nonevidential criteria must have employed to accept the theorySociological factors often breaches the realm of the scientific enterprise to influence the scientific body of knowledge Theory acceptance is not entirely subjective

Fashion selective criteria (coherence, beauty, simplicity)Political expedience factors, and professional development influences

Cushing’s worryPopular acceptance of empirically adequate theories may exclude an equally empirically successful theory that entails a more accurate world view“For instance, Einstein allowed the theoretical (or logical) possibility of more than one empirically adequate theory, but then went on to declare that at any given time the ‘world of phenomena’ (that sounds pretty objective) uniquely determines one theory as superior to all others.”18

Dilemma for the realistRealism

The object of perception has real existence – it has n objective or absolute existence and isn’t reducible or dependent on a perceiving agent

The two-fold dilemma:Accept the Copenhagen interpretation and suffer from the measurement problem, contextuality, and fuzzily defined complementarityRealize the underdetermination of interpretation in quantum mechanics and fail to choose one theory over the other using logical principles, resulting in despair between the simultaneous existence of viable theories that propose indeterminacy and absolute determinism

An argument between the antirealist and the

realistAntirealist begins with the Copenhagen interpretation of quantum mechanics, finds no coherence in microrealm and finds it impossible to explain the macrorealm with a coherent ontologyRealist develops a coherent ontology in the macrorealm but struggles to explain the microrealm

Bohmian mechanics looks pretty good to her (or him) because Bohm is able to determine a time evolution path for a particle in a space-time background, preserving classical sensibilities and relativistic invariance

Fig 6: a graphic that scales across small scale phenomena and the macroscopic realm of the entire earth

The convenience of interpretation -

Schrodinger on the absence of a dilemma for quantum mechanical theory:The description of the universe as deterministic or indeterministic is a matter of convenience, “The most that can be decided is whether the one or the other concept leads to the simpler and clearer survey of all the observed facts.”3

The 1927 Solvay Conference

The 1927 Solvay Conference in Brussels considered the Copenhagen interpretation as the only serious and plausible quantum mechanical theoryProponents stifle opposition to Copehnagen interpretationCopenhagen interpretation becomes the norm in physicsProfessions depend on furthering the Copenhagen interpretation

Fig 7: the 1927 Solvay Conference in Brussels in which 17 of the 29 attendees had won or would eventually win the Nobel prize. Attendees include Marie Curie, Bohr, Einstein, Henriot, Ehrenfest, Herzen, Schrodinger, Pauli, Hesienberg, Dirac, de Broglie, Planck, Lorentz, and Compton

An alternative historical scenario?

Einstein’s three core commitmentsEvent-by-event causalityThe preservation of locality and subluminal information travelRationality and objectivity of the physical world

A lack of encouragement and support for alternative interpretations to the well backed and less flawed Copenhagen interpretation19

The problems of Einstein’s electromagnetic pilot waveDe Broglie’s weak defense of guiding wave equations, and poor response to Pauli’s objectionErwin Madelung’s inconsistencies in hidden variables theory

With the flip of a coin…….?

In summaryScientists today accept the Copenhagen interpretation of quantum phenomena

Rejection of Bohmian interpretationNo point in dislodging the Copenhagen interpretation

Thus, a hugely influential scientific theory that dominates our body of physical scientific knowledge…

…is affirmed in part because of societal, political, and historical situations characteristic of the developmental period of quantum mechanics… lacks resolute and complete objective, empirical, and logical support

Food for thoughtIn light of this chapter, it seems impossible to divorce the scientific enterprise from societal pressure and humanity’s nonlogical inclinations. In the words of Cushing, “Science, even in its products or laws remains historical or contingent in an essential manner.”20 Do you agree?Does the reality that things went a certain way at certain crucial junctures instead of a different, equally viable way imply that non-objective, nonlogical reasons are just as important factors as empirical success and other objective criterion in determining the correct theory to be incorporated into the body of scientific knowledge?

More food…Do you agree with the historian Comer vann Woodward’s statement that, “Inevitability is an attribute that historical events take on after the passage of sufficient time,” especially considering that if Bohm’s interpretation of quantum mechanics was given some legitimacy, research and study into the consequences of the theory could have yielded more powerful branches of science and more successful predictions than those that the Copenhagen interpretation provided? Isn’t there an opportunity cost in choosing to support the Copenhagen interpretation over Bohm’s interpretation regardless of whether or not you think the Copenhagen interpretation was correctly chosen (was it?)?

And more food… “The human understanding, when any proposition has been once laid down (either from general admission and belief, or from the pleasure it affords), forces everything else to add fresh support and confirmation; and although most cogent and abundant instances may exist to the contrary, yet either does not observe or despises them, or gets rid of and rejects them by some distinction, with violent and injurious prejudice, rather than sacrifice the authority of the first conclusions”20 How guilty are we of this?What does this imply for the inherent weakness in the construction of a scientific body of knowledge as one subjected to folklore and subjective intuitions and societal inclinations rather than pure, hard, cold, objective calculation?What do you think serves as sufficient criteria in the selection of one theory over another? Any criteria for selecting one theory over another when both theories adequately explain the same phenomena?

References Cited1Cushing, Philosophical Concepts in Physics, pp. 3062Cushing, pp. 3073Cushing, pp. 3244Cushing, pp. 3325Goldstein, Sheldon, “Bohmian Mechanics” 20016Cushing 1994, Quantum Mechanics: Historical Contingency and the Copenhagen Dominancy7Cushing, pp. 338

References Cited, continued

8Vaidman 20029Bacciagaluppi 200310Lombardi and Dieks 200211Cushing, Philosophical Concepts in Physics, pp. 34512Stanford and Zalta 200913Cushing, pp. 346, excerpt of Duhem 1974, 217. 14Lakatos 1974

References cited, continued

15Cushing, pp. 345, excerpt of Duhem 197416Cushing, pp. 346, excerpt of Quine17Igor Douven 201118Cushing, pp. 34819Cushing Quantum Mechanics 199420Cushing excerpts, section 24.4