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1
Underdetermination and the Phenomena of
1. Introduction
2. The Phenomena of Physics
3. How to Determine Particle Phenomena
4. Underdetermination in Astroparticle Physics
5. Conclusions
3
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
4
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
5
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
6
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!
7
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!
9
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
10
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
11
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
12
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
13
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
14
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 observation
Quantum phenomena are:• individual (=indivisible)
• complementary (=mutually exclusive)• in correspondence to classical models
of wave or particle
2. The Phenomena of Physics
15
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
16
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!
17
3. How to Determine Particle Phenomena
Underdetermination and the Phenomena of Physics
18
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
19
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!
20
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
21
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!
22
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
23
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!
24
4. Underdetermination in Astroparticle Physics
Underdetermination and the Phenomena of Physics
25
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)
26
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)
27
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!
28
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
29
Concepts of APP
CRs
carry
Information from Cosmic SourcesWhere do they come from? What did happen to them?
Messenger particles
4. Underdetermination in Astroparticle Physics
30
Concepts of APP Messenger particles
4. Underdetermination in Astroparticle Physics
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?
31
Concepts of APP Messenger particles
4. Underdetermination in Astroparticle Physics
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?
32
Concepts of APP Messenger particles
4. Underdetermination in Astroparticle Physics
Only
uncharged particles
point to
their source!
They allow
„direct observation“
of source,
(if !) no interactions during
transfer
(D.Shapere 1982)
33
Concepts of APP Messenger particles
4. Underdetermination in Astroparticle Physics
Photon & neutrino telescopes
observe
extragalactic sources,
like
Galileo observed Jupiter moons
Proton detection does not!
34
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!
35
Explanations
4. Underdetermination in Astroparticle Physics
Sources & their activitiesastrophysical data:luminosity & spectra & temporal evolution of
AGNs, GRBs,
SNRs
Extragalactic sources
36
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
37
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
39
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 &
Measurement
3. 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
40
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 &
Measurement
3. 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.
41
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.