Underdetermination and the phenomena of physics
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Underdetermination and the Phenomena of Physics. Introduction The Phenomena of Physics How to Determine Particle Phenomena Underdetermination in Astroparticle Physics Conclusions. [email protected]

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Underdetermination and the phenomena of physics

Underdeterminationand the Phenomena of Physics

  • Introduction

  • The Phenomena of Physics

  • How to Determine Particle Phenomena

  • Underdetermination in Astroparticle Physics

  • Conclusions

[email protected]


Underdetermination and the phenomena of physics brigitte falkenburg@tu dortmund de

Underdeterminationand the Phenomena of [email protected]

1. Introduction


1 introduction

1. Introduction

Underdetermination: An Empiricist Story

  • Phenomena  Empirical Structures

    • Same empirical structure many theories

  • Fewexamples 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 )


  • Underdetermination and the phenomena of physics

    1. Introduction

    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 & explanandaof theories

      (Bogen & Woodward; most physicists)

       no unambiguous

      meaning of “phenomenon”


  • 1 introduction1

    1. Introduction

    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 introduction2

    1. Introduction

    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

    Hence:

    The Phenomena of Science

    are Underdetermined, too!


    1 introduction3

    1. Introduction

    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!

    Goal of Physics:

    To Determine the Phenomena

    in terms of Laws of Nature!


    Underdetermination and the phenomena of physics brigitte falkenburg@tu dortmund de1

    Underdetermination and the Phenomena of [email protected]

    2.The Phenomena of Physics


    2 the phenomena of physics

    2. The Phenomena of Physics

    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 physics1

    2. The Phenomena of Physics

    Newton’s “phenomena” ?

    • ambiguous concept:

    • “Principia” : motions of celestial bodies

      • planetary motions described by Kepler’slaws

      • 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 physics2

    2. The Phenomena of Physics

    Newton’s Phenomena:

    Two examples

    • 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 physics3

    2. The Phenomena of Physics

    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 physics4

    2. The Phenomena of Physics

    Niels Bohr (Nobel lecture, 1922):

    Phenomena are: • explanandaof 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 analogiespertaining to other domains [...], where one has presumably to do with simpler phenomena.”

     scientific realism of phenomena

    & weakened account of explanation!


    2 the phenomena of physics5

    2. The Phenomena of Physics

    Niels Bohr (Como lecture, 1927):

    There are noquantum objects,

    only quantum phenomena

    Physical objects are:

    •defined in terms of spatio-temporal & causalproperties

    • these properties can beobserved simultaneously

    For quantum “objects”: definition observation

    Quantum phenomena are:

    • individual (=indivisible)

    • complementary(=mutually exclusive)

    • in correspondence to classical models

    of wave or particle


    2 the phenomena of physics6

    2. The Phenomena of Physics

    Bohr’s Quantum Phenomena:

    Wave-Particle Duality

    • Particle Tracks:

    • Proton tracks in nuclear emulsions

    • 2. Wave interference:

    • Diffraction of (a) electrons & (b) photons at a crystal


    2 the phenomena of physics7

    2. The Phenomena of Physics

    Newton & Bohr: Phenomena are

    • concrete, intuitive facts of Nature

       spatio-temporally individuatedobjects &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

    Phenomena

    can be found at many levels of observation & measurement!


    Underdetermination and the phenomena of physics brigitte falkenburg@tu dortmund de2

    Underdetermination and the Phenomena of [email protected]

    3. How to Determine Particle Phenomena


    3 how to determine particle phenomena

    3. How to Determine Particle Phenomena

    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 phenomena1

    3. How to Determine Particle Phenomena

    The Track of the Positron (Anderson 1932):

    Electron mass, but opposite charge?

    • Experimental device:

    • Bubble chamber:

    •  tracks from cosmic rays

    • Magnetic field:

    •  curvature of charged particle

    • 3. Lead plate as stopping device:

    • direction of particle

    Without the lead plate,

    the phenomenon remained

    underdetermined!


    3 how to determine particle phenomena2

    3. How to Determine Particle Phenomena

    Particle Identification in the 1940s:

    Puzzle of “mesons”

    Later particle accelerator measurement

    of energy loss

    dE/dx

    -

    

    

    p

    • Problem:

    • Particle tracks in bubble chamber

    • melectron < mass < mproton

    • 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”

    e-

    Without safe measurement method,

    the phenomenon remained

    underdetermined!


    3 how to determine particle phenomena3

    3. How to Determine Particle Phenomena

    Particle Identification in the 1940s:

    Puzzle of “mesons”

    • Resolution:

    • 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

    Without safe measurement method,

    the phenomenon remained

    underdetermined!


    3 how to determine particle phenomena4

    3. How to Determine Particle Phenomena

    Particle Identification in the 1930s-1960s:

    Many Puzzles!

    • Problems:

    • 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

    • classifiedin terms of unstable particles

    •  wide range of phenomena

    • at different levels of observation & measurement!

    •  How are they established?

    •  Independent measurement methods


    3 how to determine particle phenomena5

    3. How to Determine Particle Phenomena

    Particle Identification in the 1930s-1960s:

     Particle phenomenaare identified in terms of

    particle types (mass, charge, spin, parity, …)

     ifindependent measurement methods available

    Identification

    of the Particle Phenomena

    aims at their Theoretical Explanation!

    stage 1: classif. in terms of particle types

    stage 2: classif. in terms of symmetries

    stage 3: quantum dynamics


    Underdetermination and the phenomena of physics brigitte falkenburg@tu dortmund de3

    Underdetermination and the Phenomena of [email protected]

    4. Underdetermination

    in Astroparticle Physics


    4 underdetermination in app

    4. Underdetermination in APP

    Phenomena of APP: Cosmic Rays (CRs)

    • Discovered in 1912 (ViktorHess, Vienna)

    • (Institutfür Radiumforschung)

    • Extraterrestrial Origin

    • „primary“ & „secondary“ CRs

    • scattering in the atmosphere


    4 underdetermination in astroparticle physics

    4. Underdetermination in Astroparticle Physics

    Primary CRs:

    Satellites &

    Space telescopes

    Phenomena of APP: Cosmic Rays (CRs)

    Secondary CRs:

    Earthbound experiments

    neutrino  muon

    detected: Cherenkov light

    high-energy photon  e+e-

    detected: Cherenkov light

    MAGIC

    Cherenkov

    neutrino&gamma ray

    telescopes

    ICECUBE


    4 underdetermination in astroparticle physics1

    4. Underdetermination in Astroparticle Physics

    Phenomena 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!


    4 underdetermination in astroparticle physics2

    4. Underdetermination in Astroparticle Physics

    Phenomena of APP

    All Particle Spectrum

    particle content of

    primary CRs:

    charged particles:

    90 % protons

    9 % -particles

    1 % electrons

    (uncharged particles:

    photons & neutrinos)


    Concepts of app

    • 4. Underdeterminationin Astroparticle Physics

    Concepts of APP

    Messenger particles

    CRs

    carry

    Information from Cosmic Sources

    Where do they come from? What did happen to them?


    Concepts of app1

    • 4. Underdetermination in Astroparticle Physics

    Concepts of APP

    Messenger particles

    Information

    = signal transmisson

    from emitter

    to receiver

    to read it out, you

    must know 2 of:

    • cosmic source

    • nature of signal

    • interactions

    • during transfer

  • Explanatory Model

    • Determined?


  • Concepts of app2

    • 4. Underdetermination in Astroparticle Physics

    Concepts of APP

    Messenger particles

    Information

    =particle propagation

    from source

    to detector

    reading it out, you will

    learn about 1 of:

    • cosmic source

    • messenger particles

    • interactions

    • during propagation

  • Explanatory Model

    • Determined?


  • Concepts of app3

    • 4. Underdetermination in Astroparticle Physics

    Concepts of APP

    Messenger particles

    Only

    uncharged particles

    point to

    their source!

    They allow

    „direct observation“

    of source,

    (if !) no interactions during transfer

    (D.Shapere 1982)


    Concepts of app4

    • 4. Underdetermination in Astroparticle Physics

    Concepts of APP

    Messenger particles

    Photon & neutrino telescopes

    observe

    extragalactic sources,

    like

    Galileo observed Jupiter moons

    Proton detection does not!


    Concepts of app5

    • 4. Underdetermination in Astroparticle Physics

    Concepts of APP

    Messenger particles

    But, be cautious!

    Shapere‘s example: Observation of sunwith solar neutrinos

    Solar neutrino experiments

     neutrino oszillations

    (information about

    messenger particles,

    notsource!)

    Observation of cosmic sources depends

    on knowledge of messenger particles

    & their interactions !

    „theory-ladenness“

     underdetermination!


    Explanations

    • 4. Underdetermination in Astroparticle Physics

    Explanations

    Extragalactic sources

    Sources & their activities

    astrophysical data:

    luminosity & spectra & temporal evolutionof

    AGNs,

    GRBs,

    SNRs


    Explanations1

    • 4. Underdetermination in Astroparticle Physics

    Explanations

    Extragalactic sources

    • But, what goes on in between?

      astrophysical data:

      Dark matter

      & gravitational lensing

      & other effects

      How reliable are the models?


    Underdetermination and the phenomena of physics

    4. Underdetermination in Astroparticle Physics

    Phenomena & Concepts & Models of APP:

     Cosmic Ray phenomenaare identified in terms of

    messenger particles

     andinterpreted in terms of extragalactic sources

    Goal of APP:

    Investigation of Cosmic Rays

    in order to Identify their Sources!

    stage 1: measurement of messenger particles

    stage 2: identification of cosmic origin

    stage 3: dynamics of source


    Underdetermination and the phenomena of physics brigitte falkenburg@tu dortmund de4

    Underdeterminationand the Phenomena of [email protected]

    5. Conclusions


    5 conclusions

    5. Conclusions

    1. Goal of Physics: ToDeterminethePhenomena interms of Laws of Nature

    2. Concrete & stablePhenomena can be found at Many Levels of Observation &Measurement

    3. To Identifythe Particle Phenomena aims at their Theoretical Explanation.

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

    Typical for physics: Transient Underdetermination of Phenomena &

    Explanatory Models


    5 conclusions1

    5. Conclusions

    1. Goal of Physics: ToDeterminethePhenomena interms of Laws of Nature

    2. Concrete & stablePhenomena can be found at Many Levels of Observation &Measurement

    3. To Identifythe Particle Phenomena aims at their Theoretical Explanation.

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

    So: All the Worse for Scientific Realism?

    No: Physicists are struggling very hard for independent measurement methods.


    Literature

    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.


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