The Quantum World: Your Ultimate Guide to Reality’s True Strangeness

132 Pages·2016·22.45 MB·English

by  New Scientist

VOL THREE / ISSUE THREE
Y O U R
U L T I M A T E G U I D E
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THE COLLECTION
Welcome to the weird
VOL3/ISSUE3 IT IS something of a tragedy that Lewis Carroll What can we infer from all of this? Is reality a
THE QUANTUM
died just as quantum theory was being born. mathematical illusion? Are there such things
WORLD The author of Alice’s Adventures in as space and time? Are we, as non-quantum
Wonderland had a wonderful eye for the beings, limited in our perception?
absurd, and learning about quantum oddities Of course, that assumes we really are
would have given him enormous pleasure. non-quantum. In chapter 3 we explore the role
It was Carroll, after all, who gave us strange quantum physics may play in biology, from
NEWSCIENTIST
THECOLLECTION shrunken worlds that require one to believe birds’ navigation skills to the extraordinary
110HighHolborn, six impossible things before breakfast. He capabilities of the human mind. None of this
LondonWC1V6EU
[phone] came up with a cat that disappeared, leaving is quite as hard-set as physicists would like,
[email protected] its grin hanging in the air. His world is one but it has moved beyond the realms of
Editor-in-chiefGrahamLawton where the unfolding of events is always speculation. Our experiments are now
EditorMichaelBrooks “curiouser and curiouser”, a phrase that fits probing the idea that evolution really has
ArteditorCraigMackie
PicturesNewScientist the quantum world of atoms, electrons and taken advantage of the weirdness.
picturedesk photons of light perfectly. And if nature has given itself quantum
SubeditorHannahJoshua
GraphicsDaveJohnston Shrink down to these scales, and you will superpowers, maybe we can follow suit.
ProductioneditorMickO’Hare find objects that exist in two places at once, Chapter 4 details our quantum creations:
ProjectmanagerHenryGomm
PublisherJohnMacFarlane share seemingly telepathic links and even technologies that exploit the strange rules of
change their properties if they think they are the very small. We now have computers that
©2016ReedBusiness
InformationLtd,England being watched. Physicists have laboured for a carry out all possible calculations at once,
NewScientistTheCollectionis century to make sense of all this, though it has government secrets protected by the laws of
publishedfourtimesperyearby
ReedBusinessInformationLtd been a labour of love. We revel in quantum nature and tiny machines that investigate
ISSN2054-6386 weirdness in the same way Carroll’s readers those laws in an attempt to make sense of it all.
PrintedinEnglandbyPrecision revel in the world Alice found by following the A complete understanding of the quantum
ColourPrinting,Telford, White Rabbit. world may be beyond us, however – at least
SMharrokpestfhoirrece,aUnKdLdtisdtributedby This issue of New Scientist: The Collection until we have a way to mesh quantum theory
[phone] goes down the rabbit hole, through the with our understanding of what happens on
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[phone] looking glass and beyond – a mesmerising cosmic scales. Chapter 5 is all about this search
[email protected] journey through the quantum world. for a quantum universe, a quest that involves
We open with a survey of quantum theory’s diving into black holes, creating quantum
Cover image strangest phenomena. Here you will meet a time machines and exploring the role
Christopher Stevenson/Getty
field that isn’t there, see liquids that climb out quantum laws played in bringing the universe
of their containers, encounter telepathic into existence. Our end goal, it turns out, may
electrons and particles that live a separate be reached by going back to the beginning of
existence from their properties, like the everything. Carroll would be delighted: it
Cheshire cat and its smile. For the most part surely doesn’t get curiouser than that.
there is no way to explain them, but we can
state what we see, and make attempts to Michael Brooks, Editor
understand what the observations mean.
Chapter 2 goes deeper in search of meaning.
The Quantum World | NewScientist: The Collection | 1
CONTENTS
THE COLLECTION 2
CONTRIBUTORS VOL3/ISSUE3
AnilAnanthaswamy
isaconsultantforNewScientist
THE
StephenBattersby
isaconsultantforNewScientist
MichaelBrooks QUANTUM
isaconsultantforNewScientist
MarkBuchanan
isaconsultantforNewScientist WORLD
JonCartwright
isawriterbasedinBristol,UK
MatthewChalmers In search
isawriterbasedinBristol,UK
MarcusChown
isaconsultantforNewScientist of reality
StuartClark
isaconsultantforNewScientist
SophieHebden
isattheUniversityofLeicester,UK
RowanHooper
ismanagingeditoratNewScientist
JustinMullins
isaconsultantforNewScientist
Richard Webb
is features editor at New Scientist
1
42 Mindthegap
48 Whatliesbeneath
54 Realitycheck
58 Ghost in the atom
What does
it mean?
6 Weirdestoftheweird
13 Quantumshadows
16 Matterofinterpretation
The articles here were first published
in New Scientist between May 2010 20 Themultiverseand me
and January 2016. They have been
updated and revised. 26 Lostandfound
30 Uncertaintyentangled
34 Stateofmind
38 The secret life of reality
2 | NewScientist: The Collection | The Quantum World
3 4 5
Quantum life Practical magic Our quantum
cosmos
62 Theweirdnessinsideus 74 Riseofthequantummachines 104Whereworldscollide
66 Abitintwominds 78 Honey,Ishrunktheproton 108Zombieuniverse
71 Quantum sense 82 Thequantumsims 112 Thequantumtimemachine
87 Quantumcomputingbestbuys 116Entangleduniverse
92 Howweirddo you want it? 120Quantumbounce
96 Theflash 124Ring of fire
100Trust no one
The Quantum World | NewScientist: The Collection | 3
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C H A P T E R O N E
THE QUANTUM WORLD
Weirdest of
the weird
From undead cats to particles popping up out of
nowhere, from watched pots not boiling – sometimes –
to ghostly inluences at a distance, quantum physics
delights in demolishing our intuitions about how the
world works. Michael Brooks tours the quantum efects
that are guaranteed to boggle our minds
Both and neither
Wave-particle duality
I
T DOES not require any knowledge of electron can diffract and interfere with itself
quantum physics to recognise quantum as if it were a wave, and believe it or not, an
weirdness. The oldest and grandest of the object as large as a car has a secondary wave
quantum mysteries relates to a question that character as it trundles along the road.
has exercised great minds at least since the That revelation came in a barnstorming
time of the ancient Greek philosopher Euclid: doctoral thesis submitted by the pioneering
what is light made of? quantum physicist Louis de Broglie in 1924.
History has flip-flopped on the issue. He showed that by describing moving
Isaac Newton thought light was tiny particles as waves, you could explain why
particles – “corpuscles” in the argot of the day. they had discrete, quantised energy levels
Not all his contemporaries were impressed, rather than the continuum predicted by
and in classic experiments in the early 1800s classical physics.
the polymath Thomas Young showed how a De Broglie first assumed that this was just
beam of light diffracted, or spread out, as it a mathematical abstraction, but wave-particle
passed through two narrow slits placed close duality seems to be all too real. Young’s classic
together, producing an interference pattern wave interference experiment has been
on a screen behind just as if it were a wave. reproduced with electrons and all manner
So which is it, particle or wave? Keen to of other particles (see diagram, page 8).
W. MOOREeqsutaanbtliusmh i tths ereopryu tpartoiovnid feodr aicno annoscwlaesrm so, on obWjeect h sauvcehn a’ts y ae mt doovnine git c warit, had am mitatcerdolsyc. o pic
MATT after it bowled onto the scene in the early Its de Broglie wavelength is something like
ALL ARTWORK 2ae0l wsteah.v A cee s–ni natunglrdey s.m oL,io gfvohirtn tighs pabtao mrtthia catlt epe saru,r itcsihc el avese a ranyndt h ing 1tsh0oim-3n8 gemsth esitunrceghs w, a aisnt dhdi sfmflirtaaskc otin nwg ao i ust ildmdo mi wlaearav snec- aclilreke,ea t ing >
The Quantum World | NewScientist: The Collection | 7
ataskwaybeyondourengineering One in two
capabilities.Theexperimenthasbeen
Updated versions of Thomas Young’s classic double-slit experiment show how particles also look like waves –
performed,though,withabuckyball– depending on how you detect them
asoccer-ball-shapedlatticeof60carbon
Place a detector far behind the slits, and a single electron Place separate detectors close enough behind the
atomsthat,ataboutananometrein will produce a characteristic interference pattern – a slits, and only one registers a click – as if the
diameter,islargeenoughtobeseenunder wave has seemingly passed through both slits at once electron were a single particle
amicroscope.
Allthatleavesafundamentalquestion:
howcanstuffbewavesandparticlesatthe
sametime?Perhapsbecauseitisneither,
saysMarkusArndtoftheUniversityof SLIT
ViennaAustria,whodidthebuckyball ELECTRON DETECTOR
GUN
experimentsin1999.Whatwecallan
electronorabuckyballmightintheend
SLIT
DETECTOR
havenomorerealitythanaclickina
detector,orourbrain’sreconstructionof MOVING
photonshittingourretina.“Waveand DETECTOR
particlearethenjustconstructsofourmind INTERFERENCE NO INTERFERENCE
PATTERN PATTERN
tofacilitateeverydaytalking,”hesays.
Offtheboil
ThequantumZenoeffect
”Bothwavesandparticles “AWATCHEDpotneverboils.”Armedwith revealitselfin,andthewavefunction
commonsenseandclassicalphysics,you “collapses”toasingledeterminedstate.
mightbejustconstructs
mightdisputethatstatement.Quantum Thisisthepicturethatgavebirthto
ofourmindtofacilitate physicswouldslapyoudown.Quantum Schrödinger’sinfamouscat.Supposethe
watchedpotsdorefusetoboil–sometimes. radioactivedecayofanatomtriggersavialof
everydaytalking”
Atothertimes,theyboilfaster.Atyetother poisongastobreak,andacatisintheboxwith
times,observationpitchesthemintoan theatomandthevial.Isthecatbothdeadand
existentialdilemmawhethertoboilornot. aliveaslongaswedon’tknowwhetherthe
Thismadnessisalogicalconsequenceofthe decayhasoccurred?
Schrödingerequation,theformulaconcocted We’renotsure.Allweknowisthattestswith
byAustrianphysicistErwinSchrödingerin largerandlargerobjects–includinga
1926todescribehowquantumobjectsevolve resonatingmetalstripbigenoughtobe
probabilisticallyovertime. seenunderamicroscope–seemtoshow
Imagine,forexample,conductingan thattheyreallycanbeinducedtoadopttwo
experimentwithaninitiallyundecayed statesatonce.
radioactiveatominabox.Accordingtothe Theweirdestthingaboutallthisisthe
Schrödingerequation,atanypointafteryou implicationthatjustlookingatstuffchanges
starttheexperimenttheatomexistsina howitbehaves.Takethedecayingatom:
mixture,or“superposition”,ofdecayedand observingitandfindingitundecayedresets
undecayedstates. thesystemtoadefinitivestate,andthe
Eachstatehasaprobabilityattachedthatis Schrödinger-equationevolutiontowards
encapsulatedinamathematicaldescription “decayed”muststartagainfromscratch.
knownasawavefunction.Overtime,aslong Thecorollaryisthatifyoukeepmeasuring
asyoudon’tlook,thewavefunctionevolvesas oftenenough,thesystemwillneverbeableto
theprobabilityofthedecayedstateslowly decay.Thispossibilityisdubbedthequantum
increases.Assoonasyoudolook,theatom Zenoeffect,aftertheGreekphilosopherZeno
chooses–inamannerinlinewiththewave ofElea,whodevisedafamousparadoxthat
functionprobabilities–whichstateitwill “proved”thatifyoudividedtimeupintoever
8 | NewScientist: The Collection | The Quantum World