Empiricism and Philosophy of Physics

293 Pages·2021·3.161 MB·English

by  Lars-Göran Johansson

Synthese Library 434
Studies in Epistemology, Logic, Methodology,
and Philosophy of Science
Lars-Göran Johansson
Empiricism
and Philosophy
of Physics
Synthese Library
Studies in Epistemology, Logic, Methodology,
and Philosophy of Science
Volume 434
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¨
Lars-Goran Johansson
Empiricism and Philosophy
of Physics
Lars-Go¨ranJohansson
DepartmentofPhilosophy
UppsalaUniversity
Uppsala,Sweden
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Preface
Praeteracenseometaphysicamessedelendam.
(Furthermore,Iconsiderthatmetaphysicsmustbedestroyed.)
AxelHägerström
Entianonsuntmultiplicandapraeternecessitatem
(Entitiesshouldnotunnecessarilybemultiplied.)
WilliamofOckham
Thepurposeofthisbookistwofold:(i)topresentathoroughlyempiricistposition
inepistemologyand(ii)toapplyittophilosophyofphysics.Mymotiveisthesame
asthatofthelogicalempiricists,viz.,(i)totellwhattocountasempiricalevidence
foratheoryand(ii)topresentaphilosophicalviewonscience,inparticularphysics,
whichdoesnotengageinanysuperfluousmetaphysics.
Empiricists are united in holding that empirical evidence is the only evidence
therecouldbeforanempiricaltheory;thecrucialquestionistosaymoreprecisely
whattocountasempiricalevidence.Regardingmetaphysics,thecrucialquestionis
howtodistinguishbetweensuperfluousandnon-superfluousmetaphysics.
Adherents to logical positivism were hostile to theoretical entities. A common
viewwastodistinguishbetweenobservableandnon-observable,thatis,theoretical
entities, where the latter were viewed with scepticism. Modern empiricists, for
example van Fraassen, hold in a somewhat similar vein that we have no good
reason to believe theoretical sentences being true. (But he accepts that theoretical
sentences are truth-apt.) Scientific realists by contrast believe in the existence of
sometheoreticalentitiesandthatwehavegoodreasontothinkatleastsometheories
are approximately true. In my view, neither the scientific realist’s defence of their
views nor the empiricist’s criticism are well founded. In this book, I will develop
what I hope is a more tenable version of empiricism, not based on the distinction
betweenobservable/non-observable,butinsteadbasedonsemanticconsiderations.
v
vi Preface
A fundamental distinction in semantics is between singular and general terms,
the latter alternatively called predicates.1 The referent of a singular term, if it
exists, is an individual, whereas the referent of a general term, if it exists, is a
universal.(ThiswillbethoroughlydiscussedinChap.3.)Whenweacceptatheory
as (approximately) true, we tentatively accept all its sentences as being true. It
follows that its singular terms must refer to things that exist and the domains of
its first-order variables must be non-empty. But it does not follow that the general
termsdeployedmusthavereferents,northatsecond-orderquantificationisneeded.
Myontologicalpositionisthatweneverhavegoodreasonforassumingproperties
andrelations,thatis,universals,asreferentsofgeneralterms;theyaresuperfluous.
IthusadheretonominalismintheveinofOckhamandGoodman,tobediscussed
inChap.3.
The question of ontology is intimately connected to semantics. The question
‘Whatexists?’maybeviewedasshortfor‘Whatexistsaccordingtoourbesttheory
oftheworld?’andtheansweris:Whenweholdatheorytobetrue,orapproximately
so, we must accept as existing those things which the theory says exist. But an
empirical theory is rarely explicit about the ontological commitments made when
acceptingit.Weneedtoparaphrasephysicaltheoriesintopredicatelogicinorderto
seetheirexistenceassumptions.
The fundamental issue in the semantics of scientific theories is the connec-
tion between theory and reality. When contemplating this issue, I have found
Löwenheim-Skolem’s theorem of utmost importance. This theorem says, roughly,
thatnotheorybyitselfcandeterminewhatitisabout.FromLöwenheim-Skolem’s
theorem it follows that the connection between theory and reality must be estab-
lishedbynon-theoreticalmeans.2 Theseconsistofindexicalwords,suchas‘this’,
‘that’,‘here’and‘now’,usedinconnectionwithpointinggestures;suchcombina-
tionsofindexicalexpressionsandgesturesdeterminethereferencesofcertainterms.
Forexample,thereferenceofthesingularterm‘thisdetector’usedinthesentence
‘Thisdetectornowshows50counts’isdeterminedastheveryobjectpointedatin
aparticularsituationwhereatokenofthissentenceisused.Löwenheim-Skolem’s
theoremtellsusthatsuchconcreteusesareneededforconnectingatheorytoreality.
Thisfitsnicelyintoanempiricistoutlook.
This book is thus based on three foundations: empiricism in epistemology,
nominalisminontologyandLöwenheim-Skolem’stheoreminsemantics.Thiswill
beelaboratedinsomedetailinChap.3.
A great part of philosophy of science is philosophy of physics. This is easy to
understand: since physics is the most basic and general of all empirical sciences,
1Onemayholdthatgeneraltermsandpredicatesarestrictlyspeakingnotthesamekindsofthings,
butforthisdiscussionthedifferencedoesn’tmatter.
2Ifweuseanauxiliarytheoryforrelatingaparticulartheorytoreality,wecanviewthisauxiliary
theoryasanextensionoftheoriginaltheoryandLöwenheim-Skolem’stheoremappliesalsotothis
extendedtheory.
Preface vii
philosophical discussions concerning fundamental issues in philosophy of physics
implicitlycoveralsosomefundamentalissuesinallsciences.
Alargeproportionofphilosophyofscience,inparticularphilosophyofphysics,
isdevotedtologicalandformalaspectsoftheories,suchastheirformalsemantics
and axiomatisation. For certain purposes this is interesting, but I will not discuss
such matters. My focus of interest in this book is epistemological and ontological
questions, both in relation to physics. Therefore, I see no need to say anything
about formal semantics, axiomatisation, consistency or set theoretical foundations
of science. With only little exaggeration, one may say that these topics are about
relationsbetweenwordsonly;theyrarelyhavemuchbearingonhowwordsrelate
totheworld.NordoIneedmodallogic,whichmayastonishmostreaders,forhow
could one give an account of natural laws without talking about their necessity?
Well,Icertainlyaccept thatlaws,properlysocalled,arenecessaryinsomesense,
butIneednomodallogicformyaccountoftheirnecessity,aswillbeexplainedin
Chap.10.
The first two chapters give a background for the rest of the book. Chapter 1
listsanumberofphilosophicalproblemsinphysics,whichareinterestingfroman
empiricist point of view, and Chap.2 presents very briefly the development from
Aristotle’sphysicstoquantumtheory.Itisnotreallyanythingthatcanbecalleda
historyofphysics;itcontainsonlysomeaspectswhicharerelevantfortheensuing
chaptersonissuesinphilosophyofphysicswhichIhavefoundinteresting.
Chapter3isanoverviewoftheempiricisttraditionanditendswithwhatIbelieve
is a tenable version of empiricism. Chapter 4, about mathematics, may seem a bit
odd in this context, but I have come to the conclusion that it should be included:
physics and mathematics are so intimately related that it is almost impossible to
avoidtakingastanceonquestionsaboutmathematicalknowledgeandmathematical
objectswhendiscussingontologyandsemanticsofphysicaltheories.Inparticular,
Ihavearrivedattheconclusionthatevenforanempiricist,thereisgoodreasonto
acceptmathematicalobjects,forexample,vectors,intheontology.Butwehaveno
goodreasontoassumethattherearephysicalentities,suchasforces,corresponding
to vectors in the mathematical sense. And similar reflections apply to spacetime:
Just because a Lorenzian manifold with a metric, a mathematical entity, is very
usefulinrelativitytheory,itdoesnotfollowthatthatthismathematicalobjecthas
acounterpartinthephysicalworld.Wecandowithoutassumingaphysicalentity
spacetime.
Chapters5to8discuss topics ingeneral philosophy ofscience and Chaps.9to
17narrowdowntosomespecificissuesinphilosophyofphysics.
Great parts of Chap.5 is taken from my ‘Induction and Epistemological Natu-
ralism’,Philosophies,3,31,2018.Chapters10,11and12arepreviouslypublished
papers,whichherearereprintedwithminorchanges(suchasreplacing‘thispaper’
with‘thischapter’)asadaptionstothecontextofabook.Chapter10waspublished
as‘TheOntologyofElectromagnetism’,StudiaPhilosophicaEstonica,10(1)2017,
25–44, Chap.11 was published as ‘An Empiricist View on Laws, Quantities and
PhysicalNecessity’,Theoria85,2,69–101,April2019,andChap.12waspublished
as‘Propensities’,pp.161–175inLogic,EthicsandallthatJazz.Essaysinhonourof
viii Preface
JordanHowardSobel,editedbyLars-GöranJohansson,JanÖsterbergandRysiek
Sliwinski.Uppsala:DepartmentofPhilosophy,UppsalaUniversity.2009,Uppsala
Philosophical Studies 57. For the papers on electromagnetism, epistemology and
propensities, I have the copyright, whereas Theoria foundation has the copyright
forthepaperonlaws.IherebythankTheoriaforpermissiontoreprintithere.
Anoteontheterms‘concept’and‘predicate’
The word ‘concept’ is one of the most common words in philosophy, but, alas,
it is often not very clear what it is supposed to refer to. In this book, I will use it
asmeaning‘generaltermadjoinedwithrulesforitsapplication’.Inphysics,these
rulesaresometimesexplicitlystated,asisthecasewithquantitiesandunitsdefined
in the SI system. Thus, a concept, in my use of that word, is basically a linguistic
item,notsomethinginourminds.
Use-mentionconfusionisstillcommon,inspiteofQuine’slongfightagainstit.
In order to be absolutely clear about the distinction between talking about a term
andusingit,Iwillusethetextstyle SMALL CAPITAL whenItalkabout ageneral
term(=concept).Thus,observethecontrastbetween‘TIMEisthefourthcoordinate
infour-dimensionalspacetime’and‘Theemissiontimeisfourseconds’.Similarly,
‘The charge of an electron is −1.6 ∗ 10−19 Coulomb’ whereas ‘CHARGE is an
electromagneticquantity’.However,whenIquotesomeoneelse,Ikeeptheoriginal
text style; so, for example, Weyl uses boldface when he talks about concepts, see
thequoteinChap.9.
Concepts,typesandtokens
A token of a term is a physical object, whereas a term in the sense of type is an
abstractobject.Itistemptingtosaythatatypeisthesetofallitstokens.Butthat
isproblematic,forwewouldnotacceptthatanewoccurrenceofatokenofaterm,
whichobviouslychangestheset,entailsthatthetypehaschanged;hence,typesof
termscannotbegivenanextensionalreading.So,wemustacceptthattermsinthe
sense of types must be taken as primitive abstract objects, not reducible to sets of
concreteobjects.
The introduction of abstract objects into discourse is a manifestation of our
general capacity for generalising. We begin teaching our children words for
observable things such as dogs, balls, apples, dolls, etc. When a child masters the
word ‘dog’, she/he usually recognises a new object as being a dog, if it is a dog,
and may say ‘dog’. The inductive generalisation works on both sides, so to say: a
new object is cognised as sufficiently similar to a set of earlier observed objects,
andthetokensoftheword‘dog’heardinassociationwithobservationsofdogsare
cognisedassufficientlysimilartoeachother,andsomethingapproximatelysimilar
isproducedwhenseeingthedog.So,bothcognitionandlanguageuseisbasedon
ourcapacityforgeneralisation.
Thus, even at the most basic level of thinking and language use, we deploy
abstract objects, that is, word types. Since I will argue for nominalism in the vein
of Ockham and Goodman, it might seem inconsistent to accept abstract objects
in the universe of discourse. But it is not. The distinction concrete-abstract is not
Preface ix
the same as the distinction individual-universal. I adopt Aristotle’s notion of an
individualobject,whichAristotlecalledaprimarysubstance,asthatwhichonlycan
bethesubjectofaproposition,neverbeingapredicate,albeitrephrasedinmodern
semantic terms: an individual object is the referent of a singular term, never of a
general term.And there are lots of abstract objects thatare referred to by singular
terms,mostobviouslynumbers,whichwerefertoby,forexample,numerals.That
a natural number may be viewed as constructed as a set of sets is no objection.
The European Commission consists of 27 persons. Still it is an individual, since
‘TheEuropeanCommission’isasingularterm.SomynominalismisGoodman’s;
Iresolutelyrejectuniversalsasreferentsofgeneralterms.So,forexample,thetwo-
placepredicate‘∈’hasextensionbutnoreferent,asallgeneralterms.
UpplandsVäsby Lars-GöranJohansson