underdetermination and the phenomena of physics

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Underdetermination and the Phenomena of

Physicsbrigitte.falkenburg@tu-dortmund.de

1. Introduction2. The Phenomena of Physics3. How to Determine Particle Phenomena4. Underdetermination in Astroparticle

Physics5. Conclusions

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1. Introduction

Underdetermination and the Phenomena of Physics

brigitte.falkenburg@tu-dortmund.de

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Underdetermination: An Empiricist Story Phenomena Empirical Structures

Same empirical structure many theories Few examples from “real physics”

Classical Mechanics: With/without Absolute Space? (van Fraassen’s example) Continuous particle trajectories (given up in QM)Quantum Mechanics (probabilistic view of ): Bohm’s QM (hidden variables & particle trajectories) Many Worlds (splitting wave functions )

1. Introduction

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But, what are the Phenomena? philosophical tradition (phenomena noumena):

phenomena = appearances (Leibniz, Kant) phenomenology = logic of what seems to be (Lambert)

tradition of physics (“saving the phenomena”): motions of celestial bodies (Ptolemy – Kepler - Newton) law-like, non-miraculous appearances (Hacking) events predicted by a theory & explananda of theories

(Bogen & Woodward; most physicists) no unambiguous meaning of “phenomenon”

1. Introduction

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Tradition of Physics: motions of celestial bodies:

description of apparent motions? (Ptolemy) explanation of true motions? (Kepler & Newton)

observation of the appearances: by sensory experience only? (Aristotle & empiricism) by technological devices? (Galileo & scientific realism)

events predicted by a theory: sense data only? (Mach, Carnap, van Fraassen) physical effects? (physicists & principle of causality)

“phenomena” debated since Galileo!

1. Introduction

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Phenomena of Physics = Theory-Laden theory phenomena: fuzzy distinction

Phenomena of physics have always been theory-laden To talk of “empirical substructure” is naïve! Example: Particle tracks of subatomic physics

phenomenon of CM = full-fledged trajectory of QM = sequence of measurement

points

1. Introduction

Hence: The Phenomena of Science

are Underdetermined, too!

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Phenomena of Physics: Underdetermined

No Problem - Only for Empiricists! “Myth of the Given”

Underdetermination of Phenomena: Not strong, but weak = transient Demarcation theory/phenomena: time-dependent Evidence depends on well-established knowledge!

1. Introduction

Goal of Physics: To Determine the Phenomena

in terms of Laws of Nature!

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2.The Phenomena of Physics

Underdetermination and the Phenomena of Physics

brigitte.falkenburg@tu-dortmund.de

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Two prominent examples: Newton’s “Phenomena” ?

Principia: motions of celestial bodies Opticks: observations in experiments

Bohr‘s “quantum phenomena” Claim: there are no quantum objects Quantum Phenomena are “individual” (=indivisible) They correspond to classical pictures of physical reality

Current physics/science: phenomena

“evidence”

2. The Phenomena of Physics

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Newton’s “phenomena” ? ambiguous concept: “Principia” : motions of celestial bodies

planetary motions described by Kepler’s laws phenomenological laws

Optics: observations in experiments light propagation light colors light diffraction

but common features: regularity, predictability, law-likeness phenomena are typical & connected

2. The Phenomena of Physics

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Newton’s Phenomena:Two examples

1. Connection of the Phenomena:from Galileo‘s to Kepler‘s motions

2. Analysis & Synthesis of Phenomena:spectral decomposition & re-composition of light Principia: connection between

Galileo‘s and Kepler‘s motions

Opticks: spectral decomposition & re-composition of light

2. The Phenomena of Physics

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Newton’s Phenomena: phenomena = what is given

at any stage of research : appearances, phenomenological laws, experimental results, measurement outcomes

phenomena = subject to causal analysis mathematical analysis forces & universal laws experimental analysis atoms of matter & light

phenomena = connected by laws trust in law-likeness & unity of nature

“Nature will be very conformable to herself and very simple.” (Newton 1704)

2. The Phenomena of Physics

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Niels Bohr (Nobel lecture, 1922):Phenomena are: • explananda of theories • observations Explanation is: • classification in terms of analogies

“By a theoretical explanation of natural phenomena we understand in general a classification of the observations of a certain domain with the help of analogies pertaining to other domains [...], where one has presumably to do with simpler phenomena.”

scientific realism of phenomena & weakened account of explanation!

2. The Phenomena of Physics

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Niels Bohr (Como lecture, 1927):There are no quantum objects,

only quantum phenomena Physical objects are:

• defined in terms of spatio-temporal & causal properties

• these properties can be observed simultaneously For quantum “objects” : definition observationQuantum phenomena are:

• individual (=indivisible)• complementary (=mutually exclusive)

• in correspondence to classical models of wave or particle

2. The Phenomena of Physics

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1. Particle Tracks:Proton tracks in nuclear emulsions

2. Wave interference:Diffraction of (a) electrons & (b) photons at a crystal

2. The Phenomena of Physics

Bohr’s Quantum Phenomena:Wave-Particle Duality

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Newton & Bohr: Phenomena are concrete, intuitive facts of Nature

spatio-temporally individuated objects &events empirical, observable, given

given by some kind of observation or measurement typical, class constructs, connected by laws

explainable in terms of laws & causal stories

2. The Phenomena of Physics

Phenomena can be found at many levels of

observation & measurement!

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3. How to Determine Particle Phenomena

Underdetermination and the Phenomena of Physics

brigitte.falkenburg@tu-dortmund.de

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Phenomena of Particle Physics: Quantum Phenomena

Particle Picture empirical, observable, given

Particle Tracks typical, class constructs, connected by laws

Causal Analysis of Particle Tracks Classified in terms of mass, charge, spin, ... many kinds of particles How are they identified?

3. How to Determine Particle Phenomena

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Experimental device:

1. Bubble chamber: tracks from cosmic rays

2. Magnetic field: curvature of charged particle

3. Lead plate as stopping device: direction of particle

The Track of the Positron (Anderson 1932):Electron mass, but opposite charge?

3. How to Determine Particle Phenomena

Without the lead plate,the phenomenon remained

underdetermined!

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Problem:

1. Particle tracks in bubble chamber melectron < mass < mproton

2. No trust in QED no safe calculation of energy loss no mass measurement from particle range

3. No particle identification possible vague concept of “mesons”

3. How to Determine Particle Phenomena

Without safe measurement method,the phenomenon remained

underdetermined!

Particle Identification in the 1940s:Puzzle of “mesons”

e-

- pLater particle accelerator measurementof energy lossdE/dx

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Resolution:

1. Development of nuclear emulsions better resolution of measurement points

2. mass estimation from density of points QED-independent mass measurement

2. Particle identification possible distinction of - and independent test of QED

Particle Identification in the 1940s:Puzzle of “mesons”

3. How to Determine Particle Phenomena

Without safe measurement method,the phenomenon remained

underdetermined!

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Problems:

1. Many kinds of particle tracks classified in terms of mass & charge

2. Many kinds of particle reactions classified in terms of conserved quantities

3. Many kinds of particle resonances classified in terms of unstable particles

Particle Identification in the 1930s-1960s:Many Puzzles!

3. How to Determine Particle Phenomena

wide range of phenomena at different levels of observation & measurement!

How are they established? Independent measurement

methods

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Particle Identification in the 1930s-1960s: Particle phenomena are identified in terms of particle types (mass, charge, spin, parity, …) if independent measurement methods available

3. How to Determine Particle Phenomena

stage 1: classif. in terms of particle typesstage 2: classif. in terms of

symmetriesstage 3: quantum

dynamics

Identificationof the Particle Phenomena

aims at their Theoretical Explanation!

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4. Underdetermination in Astroparticle Physics

Underdetermination and the Phenomena of Physics

brigitte.falkenburg@tu-dortmund.de

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4. Underdetermination in APP

• Discovered in 1912 (Viktor Hess, Vienna) (Institut für Radiumforschung)

• Extraterrestrial Origin• „primary“ & „secondary“ CRs• scattering in the atmosphere

Phenomena of APP: Cosmic Rays (CRs)

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4. Underdetermination in Astroparticle Physics

MAGIC

ICECUBE

Cherenkovneutrino&gamma raytelescopes

high-energy photon e+e-detected: Cherenkov light

Secondary CRs:Earthbound experiments

Primary CRs:Satellites &

Space telescopes

neutrino muondetected: Cherenkov light

Phenomena of APP: Cosmic Rays (CRs)

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4. Underdetermination in Astroparticle PhysicsPhenomena of APP: Cosmic Rays (CRs)

• Power law decrease• two „kinks“:

„knee“ & „ankle“

Today, the CR phenomena are known! But, what is their explanation?

Goal: Model determination!

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All Particle Spectrum

particle content of primary CRs:charged particles:90 % protons 9 % -particles 1 % electrons

(uncharged particles: photons & neutrinos)

Phenomena of APP

4. Underdetermination in Astroparticle Physics

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Concepts of APP

CRs carryInformation from Cosmic SourcesWhere do they come from? What did happen to them?

Messenger particles

4. Underdetermination in Astroparticle Physics

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Concepts of APP Messenger particles

4. Underdetermination in Astroparticle Physics

Information= signal transmisson from emitter

to receiverto read it out, you must know 2 of:

• cosmic source• nature of signal• interactions

during transfer Explanatory Model

Determined?

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Concepts of APP Messenger particles

4. Underdetermination in Astroparticle Physics

Information= particle propagation from source

to detectorreading it out, you will learn about 1 of:

• cosmic source• messenger particles• interactions

during propagation Explanatory Model

Determined?

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Concepts of APP Messenger particles

4. Underdetermination in Astroparticle Physics

Only uncharged particles point totheir source!They allow„direct observation“of source, (if !) no interactions

during transfer (D.Shapere 1982)

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Concepts of APP Messenger particles

4. Underdetermination in Astroparticle Physics

Photon & neutrino telescopes observeextragalactic sources, like Galileo observed Jupiter moonsProton detection

does not!

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Concepts of APP Messenger particles

4. Underdetermination in Astroparticle Physics

But, be cautious! Shapere‘s example: Observation of sun with solar neutrinosSolar neutrino experiments neutrino oszillations

(information about messenger particles,

not source!) Observation of cosmic sources dependson knowledge of messenger particles

& their interactions ! „theory-ladenness“

underdetermination!

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Explanations

4. Underdetermination in Astroparticle Physics

Sources & their activitiesastrophysical data:luminosity & spectra & temporal evolution of

AGNs, GRBs,

SNRs

Extragalactic sources

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Explanations

4. Underdetermination in Astroparticle Physics

But, what goes on in between? astrophysical data:Dark matter & gravitational lensing& other effects

How reliable are the models?

Extragalactic sources

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Phenomena & Concepts & Models of APP: Cosmic Ray phenomena are identified in terms of messenger particles and interpreted in terms of extragalactic sources

stage 1: measurement of messenger particles stage 2: identification of cosmic

origin stage 3: dynamics of

source

Goal of APP: Investigation of Cosmic Rays

in order to Identify their Sources!

4. Underdetermination in Astroparticle Physics

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5. Conclusions

Underdetermination and the Phenomena of Physics

brigitte.falkenburg@tu-dortmund.de

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5. Conclusions

1. Goal of Physics: To Determine the Phenomena in terms of Laws of Nature

2. Concrete & stable Phenomena can be found at Many Levels of Observation &

Measurement3. To Identify the Particle Phenomena aims at their

Theoretical Explanation.

4. To Investigate Cosmic Rays now aims at Identifying Galactic & Extragalactic Sources.

Typical for physics: Transient Underdetermination of Phenomena &

Explanatory Models

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5. Conclusions

1. Goal of Physics: To Determine the Phenomena in terms of Laws of Nature

2. Concrete & stable Phenomena can be found at Many Levels of Observation &

Measurement3. To Identify the Particle Phenomena aims at their

Theoretical Explanation.

4. To Investigate Cosmic Rays now aims at Identifying Galactic & Extragalactic Sources.

So: All the Worse for Scientific Realism? No: Physicists are struggling very hard

for independent measurement methods.

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Literature

Brigitte Falkenburg: - Particle Metaphysics. A Critical

Account of Subatomic Reality. Springer 2007.

- What are the Phenomena of Physics? In: Synthese (forthcoming)

- Incommensurability and Measurement. In: Theoria, Vol. 12 Numero 30 (1997), 467-491.