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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Underdeterminationand the Phenomena of Physics

  • Introduction

  • The Phenomena of Physics

  • How to Determine Particle Phenomena

  • Underdetermination in Astroparticle Physics

  • Conclusions

[email protected]


Underdeterminationand the Phenomena of [email protected]

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 )


  • 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. 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. 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. 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 [email protected]

    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 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 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 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 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 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 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 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 [email protected]

    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 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 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 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 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 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 [email protected]

    4. Underdetermination

    in Astroparticle Physics


    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

    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 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 Physics

    Phenomena of APP

    All Particle Spectrum

    particle content of

    primary CRs:

    charged particles:

    90 % protons

    9 % -particles

    1 % electrons

    (uncharged particles:

    photons & neutrinos)


    • 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?


    • 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?


    • 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?


    • 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)


    • 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!


    • 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!


    • 4. Underdetermination in Astroparticle Physics

    Explanations

    Extragalactic sources

    Sources & their activities

    astrophysical data:

    luminosity & spectra & temporal evolutionof

    AGNs,

    GRBs,

    SNRs


    • 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?


    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


    Underdeterminationand the Phenomena of [email protected]

    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. 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

    • 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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