Everywhere and Everywhen: Adventures in Physics and Philosophy

234 Pages·2010·1.73 MB·English

by  Nick Huggett

Everywhere and Everywhen
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Everywhere and Everywhen
Adventures in Physics and Philosophy
Nick Huggett
1
2010
3
OxfordUniversityPress,Inc.,publishesworksthatfurther
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LibraryofCongressCataloging-in-PublicationData
Huggett,Nick.
Everywhereandeverywhen:adventuresinphysicsandphilosophy/NickHuggett.
p. cm.
ISBN 978-0-19-537951-8;978-0-19-537950-1(pbk.)
1. Physics—Philosophy. I. Title.
QC6.H824 2009
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For my paradoxical twins, Kai and Ivor
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Preface
IrememberwhenIdiscoveredthatyoucouldbeaphilosopherofphysics.
Iwasinthelibraryofmyschoolstudyingbrochuresforuniversityadmis-
sionswhenIcameacrossthePhysicsandPhilosophyprogramatOxford.
It made perfect sense to me at the time; physics was my best subject
and I’d developed an interest in philosophy in a fairly typical teenage
intellectualway.SoIappliedandgotin.
Inhindsight,though,I’mnotquitesurewhatIthoughtthephilosoph-
ical study of physics was. I certainly didn’t give a very good answer to
that question in my admission interview! That was something I learned
later, during my studies. (In fact, according to Rom Harré, a founder of
the program at Oxford, the intention was not to produce philosophers
ofphysics,butfutureleaders,wellgroundedinreasoning,ethics,andthe
sciences.) Still, I found that my youthful intuition was reliable, and after
I completed my undergraduate studies I went on to Rutgers University
in New Jersey, where I was lucky enough to work with some of the best
and most generous philosophers of physics I have ever met. Best of all,
afterward I found a job where I could research and teach my subject, at
theUniversityofIllinoisinChicago.
So now my only problem is explaining to people—parents, friends,
neighbors on planes and at dinner parties, and especially physicists and
philosophers—what it is that I do. Something to do with the ethics of
science? That’s an important topic, but generally not part of philosophy
ofphysics.OrperhapstheconnectionsbetweenBuddhismandquantum
physics? That idea was popularized in the 1970s by Fritjof Capra and
GaryZukav,butit’snotwhatmostphilosophersofphysicsareinterested
in. Or is it an attempt to tell physicists what must be the case by pure
speculation, regardless of the facts of experiment? Or perhaps to show
that physics is nothing but a social fabrication, that truth about the
physical world is not objective but whatever physicists decide. Well, the
sociological dimensions of science are interesting, and some people do
takeaveryhardline,butmostphilosophersofphysicstakeveryseriously
physics’ ability to get at objective truth—and they think that it is the
ultimatestandard,notpurespeculation.
Sothisbookistoexplaintoallthosepeoplesomeofthewaysinwhich
physicsandphilosophycanbeinfruitfuldialogue—itisthatdialoguethat
viii Preface
engages philosophers of physics (and, as we’ll see, many physicists). We
shall see that indeed the traffic is two-way: while physics has important
lessons for philosophy, the kind of investigations at which philosophers
excelarenecessaryinscience,andsomeofthemostimportantadvancesin
physics have required philosophical contemplation. To be more specific,
wewillseethreemainkindsofinteraction.
First, there are cases in which philosophical questions can be for-
mulated in a precise way in physics and then addressed with resources
of physics. For instance, could space have an edge? Second, there are
cases in which ideas used in physics turn out to be conceptually unclear
or incompatible with new knowledge in physics. What physics requires
here is a careful analysis of the concepts and an understanding of how
they are used. That kind of work is philosophical, though it is often
done by physicists—‘philosopher-scientists’, as Einstein was described.
For instance, what is it for events to be “simultaneous”? And third and
finally,thefactthatwearephysicalbeingslivinginaphysicalworldofa
specific type has profound consequences for the way we experience the
world. Having an understanding of these consequences is crucial for a
clear philosophical view of a variety of problems. How, for instance, do
weperceiveleftversusrighthandedness?
To see these things in more detail, naturally we’ll need to introduce
some physics and philosophy. You’ll notice some difference between the
two here. The physics will be presented largely as the materials for our
discussion, while I will be showing you how to think about the physics
like a philosopher. When you read a popular book on physics, the goal
usually is to explain recent developments in terms that are accessible to
the layperson; the details themselves take years of study even for very
smartpeople.Thebestbooksofthiskinddoagreatjobofexplicatingthe
fundamental ideas and implications, but of course they don’t make you
a physicist. I have a rather different ambition for this book. This is not
a book that just seeks to explain recent developments in philosophy of
physics—though we will talk about some of them—but one that aims
to help the reader really think philosophically about physics and the
physical world. Having taken ten years in higher education to become
a philosopher, I hesitate to say that this book will make the reader a
philosopherofphysics,butIdohopeitwillshowthewayandallowafirst
stepinthatdirection.Toputitanotherway,thebookdoesn’tjustreport
onphilosophy,itdoesittoo,andIhopethatexamplewillbeuseful.
Asaresultthisbookwillbedemandinginplaces.Philosophyinvolves
patient reasoning, canvassing of different possible positions, step-by-step
argument, and to-and-fro. Sometimes it takes effort to keep the logic of
thetopicclear.However,I’vepickedpiecesofphysicsandofphilosophy
thataresuitableforageneralaudience(I’vetaughtthesetopicstoalotof
undergraduatesofverydifferentabilities,soIhaveaprettygoodsenseof
whatisdigestible).ThebottomlineisthatI’vepickedtopicsthatshould
Preface ix
befullycomprehensibletoanyonewhoispreparedtoapplysomecareful
thought.
Iofferthefollowingdeal:inreturnforcarefullythinkingthroughsome
sometimes challenging (but always interesting, I hope!) arguments, the
readerwillstarttolearntobeaphilosopherofphysics.
Here’stheplanofaction.InthefirstchapterIwillgiveanexampleof
aphilosophicalproblemsothatthereadercanseerightawaywhatkinds
of concerns and what kinds of approaches drive the book. We’ll also fill
in some of the physics background that we need, and some important
philosophical concepts (just what is a ‘law’ of physics?). Chapters2–3
discuss Zeno’s paradoxes, which challenge the very idea of motion. For
instance,anarrowcannotmoveduringanyinstantbecauseaninstanthas
noduration.Butifitdoesn’tmoveatanytimethenhowdoesitmoveat
all?
Chapters4–6concerntheoverall‘shape’ofspace,forinstancewhether
it has an edge, whether it is ‘closed up’ on itself, and whether it has
more than three dimensions, and if not why? Chapters7–8 continue the
discussion of the shape of space in a different direction, investigating its
geometry.Isitflat?Whatwoulditmeanifitweren’t?Howcouldwetell?
Andgenerally,whatdoesitmeantosayspaceiscurved?Chapter9com-
pletes the discussionof spaceby askingthe obvious remaining question–
whatisit?
Chapters10–11takeuptheissueoftime.Timeseemssodifferentfrom
space: for instance, we certainly experience time differently than we do
space, as something ‘moving’. How could physics account for this fact?
Chapters12–13 are devoted to another puzzling aspect of time: is time
travel possible? We’ll see possibilities and restrictions, and see ultimately
howitisacoherentpossibility.
Chapters14–15explainandinvestigateEinstein’srelativity,whichcru-
cially changes our understanding of space and time. The presentation is
a little more rigorous than most popular presentations, but all that is
involved is a simple, if unfamiliar, geometry. We will be able to show
why moving bodies contract and why moving clocks slow down, and
understandwhatthismeans.
Chapters16–18aredevotedtosomeissuesthathavebeenofparticular
interest to me. First is the question of what it is for an object to be left
rather than right; what is it about a left hand, or left-handed glove, or
left-handed screw that makes it left rather than right? After all, all these
thingsarevery,verysimilartotheirmirrorimages.Andthenthereisthe
question of identity and indistinguishability in physics. The particles of
physicsareexactlyalike,sodoesitmakeanydifferenceiftheyswaptheir
locations,say?Aretheylikemoneyinthebankoraretheylikepeople?
A note on citations. To maintain an informal style I have gathered
annotated references at the end of each chapter instead of inserting
citations in the main text. I have also omitted certain more technical