2008 SEED Reality Tests

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programming life errol morris ON morality russian nukesp.25 p.43

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BY JOSHUA ROEBKE PHOTOGRAPHY BY MARK MAHANEY

A team of physicists in Vienna has devisedexperiments that may answer one of

the enduring riddles of science: DO WE CREATE THEWORLD JUST BY LOOKING AT IT?

ANTON ZEILINGER (opposite) heads up the IQOQI lab in Vienna.


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world around us. Do we create what we observe through the acto our observations?

most of us would agree that there exists a world outsideour minds. At the classical level o our perceptions, this belie isalmost certainly correct. I your couch is blue, you will observeit as such whether drunk, in high spirits, or depressed; the coloris surely independent o the majority o your mental states. I youdiscovered your couch were suddenly red, you could be sure therewas a cause. The classical world is real, and not only in your head.Solipsism hasnt really been a viable philosophical doctrine ordecades, i not centuries.

But none o us perceives the world as it exists fundamentally .We do not observe the tiniest bits o matter, nor the orces thatmove them, individually through our senses. We evolved to expe -rience the world in bulk, our aculties registering the net e ect o

o enter the somewhat ormidable Neo-Renaissance building at Boltzmanngasse 3in Vienna, you must pass through a smalldoor sawed rom the original cathedral-like entrance. When I rst visited this pastMarch, it was chilly and overcast in thelate a ternoon. Atop several tall stories o sca olding there were two men who wouldhardly have been visible rom the street

were it not or their sunrise-orange jumpsuits. As I was aboutto pass through the nested entrance, I heard a sudden rush o wind and elt a mist o winter drizzle. I glanced up. The veiledworkers were power-washing away the buildings aade, downto the century-old brick underneath.

In 1908 Karl Kupelwieser, Ludwig Wittgenstei ns uncle,donated the money to construct this building and turn Austria-Hungary into the principal de stination or the study o radium.Above the doorway the edi ice still bears the name o thisounding purpose. But since 2005 this has been home o theInstitut r Quantenoptik und Quantenin ormation (IQOQI,pronounced ee-ko-kee), a center devoted to the oundationso quantum mechanics. The IQOQI, which includes a sisteracility to the southwest in the valley town o Innsbruck, wasinitially realized in 2003 at the behest o the Austrian Academyo Sciences. However, the institutes conception several yearsearlier was predominantly due to one man: Anton Zeilinger.

This past January, Zeilinger became the rst ever recipiento the Isaac Newton Medal or his pioneering contributionsto physics as the head o one o the most success ul quantumoptics groups in the world. Over the past two decades, heand his colleagues have done as much as a nyone else to test

quantum mechanics. And since its inception more than 80years ago, quantum mechanics has possibly weathered morescrutiny than any theory ever devised. Quantum mechanicsappears correct, and now Zeilinger and his group have startedexperimenting with what the theory means.

Some physicists still nd quantum mechanics unpalatable,i not unbelievable, because o what it implies about the worldbeyond our senses. The theorys mathematics is simple enoughto be taught to undergraduates, but the physical implicationso that mathematics give rise to deep philosophical questionsthat remain unresolved. Quantum mechanics undamentallyconcerns the way in which we observers connect to the universewe observe. The theory implies that when we measure particlesand atoms, at least one o two long-held physical principles isuntenable: Distant events do not a ect one other, and proper-ties we wish to observe exist be ore our measurements. One o these, locality or realism, must be undamentally incorrect.

For more than 70 years, innumerable physicists have triedto disentangle the meaning o quantum mechan ics throughdebate. Now Zeilinger and his collaborators have per ormeda series o experiments that, while neatly agreeing with thetheorys predictions, are reinvigorating these historical dia-logues. In Vienna experiments are testing whether quantummechanics permits a undamental physical reality. A new wayo understanding an already power ul theory is beginning totake shape, one that could change the way we understand the

trillions upon trillions o particles or atoms moving in concert.We are crude measurers. So divorced are we rom the activitybeneath our experience that physicists became relatively assuredo the existence o atoms only about a century ago.

Physicists attribute a undamental reality to what they do notdirectly perceive. Particles and atoms have observable e ects thatare well described by theories like quantum mechanics. Singleatoms have been seen in measurements and presumably existwhether or not we observe them individually. The properties

that de ne particlesexist be ore we measde ned; particles andexist prior to measurblue couch.

As a physical exaphotons that each hasuring polarization iproperty can be thouon a clock. For unpodirection as with a nwill ace in only onbroken. That photonsome sunglasses to polarizations and let o light is also being

For a ew monthstarted his PhD notrealism. Time in theing the week other underway. Zeilingertoo worried that thisThey were content spare time.

It was a ter 2 pm just woken up; they he works nights. Hethe IQOQI building granite steps, and on topen door. There waWhen Grblacher sa

The lab where Grrealism is on the secdepartment, which foor bridge. The origbut, Grblacher tells

In the middle o ace, about the size oA orest o black oppoles, seems to growexact, glass die. In tvisible, and on the en

Grblacher walkeThe laser light passehits the crystal, and spDetectors in both bphoton, which are ragainst two theoriesstrange e ects romquantum mechanics

The whole experoom, and as I lookmy rst instinctual qtested realism? I awere. It had taken a or Zeilingers grouprealism. Be ore tha

OLD SCHOOL

The nested entrance tothe IQOQI building. A

century-old blackboardin Anton Zeilingers

o ce once owned byanother amous

Viennese physicist,Ludwig Boltzmann.

SOME PHYSICISTS ST ILL FIND QUANTUMMECHANICS UNPALATABLE, IF NOT UNBELIEVABLE,

BECAUSE OF WHAT IT IMPLIES ABOUT THE WORLD.


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versus the classical. While the distinction appeared physical,many, like Bohr, thought it philosophical; the theory lacked aproper interpretation.

According to Bohr every measuring device a ects what itis used to observe. The quantum world is discrete and so therecan never be absolute precision during a measurement. To knowabout quantum mechanics, we rely on classical devices. To Bohrthis implied that the hierarchy between observer and observedhad no meaning; they were nonseparable. Concepts once thoughtto be mutually exclusive, such as waves and particles, were alsocomplements. The di erence was only language.

By contrast Einstein was a realist who believed in a worldindependent o the way it is measured. During a set o con er-ences at the Hotel Metropole in Brussels, he and Bohr arguedamously over the validity o quantum mechanics and Einsteinpresented a number o thought experiments intended to showthe theory incorrect. But when Bohr used Einsteins own theoryo relativity to evade one o these thought experiments, Einsteinwas so stung he never tried to disprove quantum mechanicsagain, though he continued to criticize it.

In 1935, rom an idyllic corner o New Jersey, Einstein andtwo young collaborators began a di erent assault on quantummechanics. Einstein, Podolsky, and Rosen (EPR) did not questionthe theorys correctness, but rather its completeness. More thanthe notion that god might play dice, what most bothered Einsteinwere quantum mechanics implications or reality. As Einsteinprosaically inquired once o a walking companion, Do youreally believe that the moon exists only when you look at it?

The EPR paper begins by asserting that theres a real worldoutside theories. Any serious consideration o a physical theorymust take into account the distinction between the objective

reality, which is independent o any theory, and the physicalconcepts with which the theory operates. I quantum mechan-ics is complete, then every element o physical re ality must havea counterpart in the physical theory. EPR argued that objectsmust have preexisting values or measurable quantities and thatthis implied that certain elements o reality could not be deter-mined by quantum mechanics.

Einstein and his colleagues imagined two electrons thatcollide and fy apart. A ter the collision the electrons exist in astate o superposition o the possible values or their momenta.Mathematically and physically, it makes no sense to say thateither electron has a de nite momentum independent o theother be ore measurement; they are entangled. But whenone electrons momentum is measured, the value o the others

physicists began to argue about what quantum mechanicshad to do with reality at all.

n the summer of 1925 , Werner Heisenberg wasstricken with hay ever and having trouble withmath. He asked his advisor or two weeks o and le t or a barren island in the North Sea.He spent his mornings swimming and hiking,but every evening Heisenberg tried to describeatoms in a theory that included only what couldbe measured. One night, everish with insight, hecalculated until dawn. A ter Heisenberg put down

his pencil as the sun began to rise, he walked to the tip o theisland, con dent he had discovered quantum mechanics.

By this time a quarter century had passed since Max Planckrst described energy as whole-number multiples o a basicunit, which he called the quantu m. When two o the quantumsother leading progenitors, Niels Bohr and Albert Einstein,heard about Heisenbergs completion o the work they began,their reactions were almost immediate; Bohr was impressed,Einstein was not. Heisenbergs theory emphasized the discrete,particle-like nature o matter, and Einstein, who tended tothink in images, could not picture it in his head.

In Switzerland, Erwin Schrdinger had also been repelledby Heisenbergs theory. In the all o 1925, S chrdinger was 38years old and ri e with sel -doubt, but when Einstein sent himan article describing a possible duality between particles andwaves, Schrdinger had an idea. Over a period o six months,he published ve papers outlining a wave theory o the atom.

Though it proved di cult to physical ly interpret what his wavewas, the theory elt amiliar to Schrdinger. Heisenberg, whohad moved to Copenhagen to become Bohrs assistant, thoughtthe theory disgusting.

Schrdinger and Heisenberg independently uncovered dualdescriptions o particles and atoms. Later, the theories provedequivalent. Then in 1926 Heisenbergs previous advisor, MaxBorn, discovered why no one had ound a physical interpreta-tion or Schrdingers wave unction. They a re not physicalwaves at all; rather the wave unction includes all the possiblestates o a system. Be ore a measurement those states exist insuperposition , wherein every possible outcome is described atthe same time. Superposition is one o the de ning qualities o quantum mechanics and implies that individual events cannotbe predicted; only the probability o an experimental outcomecan be derived.

The ollowing year, in 1927, Heisenberg discovered theuncertainty principle, which placed a undamental limit oncertain measurements. Pairs o speci c quantities are incom-patible observables; momentum and position, energy and time,and other measurable pairs cannot be known together withabsolute accuracy. Measuring one restricts knowledge o theother. With this quantum mechanics had become a ull theory.But what physicists ended up with was a world divided. Therewas an inherent distinction between atoms unseen and theircollective motion we witness with our eyesthe quantum

THE YOUNG TURK

PhD student SimonGrblacher sits

behind the foatingtable where he

spends eveningsdoing Schrdingers

cat-style experiments.

WE EVOLVED TO EXPERIENCE THE WORLD IN BULK,OUR FACULTIES REGISTERING THE NET E FFECTOF TRILLIONS UPON TRILL IONS OF PARTICLES ORATOMS MOVING IN CONCERT.


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challenge the theory, Einstein said, I anyone can do it, then itwill be Bohm.

In 1952, during the Red Scare, Bohm moved to Brazil. Therehe discovered a theory in which a particles position was deter-mined by a hidden variable even when its momentum wasabsolutely known. To Bohm reality was important, and so topreserve it, he was willing to abandon locality and accept thatentangled particles infuenced one another over vast distances.However, Bohms hidden variables theory made the same predic-tions as quantum mechanics, which already worked.

In America Bohms theory was ignored. But when the Irish-man John Bell read Bohms idea, he said, I saw the impossibledone. Bell thought hidden variables might show quantummechanics incomplete. Starting rom Bohms work, Bell derivedanother kind o hidden variables theory that could make predic-tions di erent rom those o quantum mechanics. The theoriescould be tested against one another in an EPR-type experiment.But Bell made two assumptions that quantum mechanics doesnot; the world is local (no distant infuences) and real (preexist-ing properties). I quantum mechanics were correct, one or both

is instantly known and the superpositions collapse. Once themomentum is known or a particle, we cannot measure itsposition. This element o reality is denied us by the uncertaintyprinciple. Even stranger is that this occurs even when the elec-trons fy vast distances apart be ore measurement. Quantummechanics still describes the electrons as a single system acrossspace. Einstein could never stomach that an experiment at oneelectron would instantaneously a ect the other.

In Copenhagen Bohr began an i mmediate response. It didntmatter i particles might a ect one another over vast distances,or that particles had no observable properties be ore they areobserved. As Bohr later said, There is no quantum world.There is only an abstract quantum physical description.

Physicists discourse on reality began just as the world slidinexorably toward war. During WWII physicists once inter-ested in philosophy worried about other issues. David Bohm,however, did worry. A ter the war Bohm was a pro essor atPrinceton, where he wrote a amous textbook on quantummechanics. Einstein thought it was the best presentation o quantum mechanics he had read, and when Bohm began to

o these assumptions were alse, though Bells theorem could notdetermine which.

Bells work on local hidden variables theory stirred little inter-est until the 1970s, when groups lead by John Clauser, AbnerShimony, and others devised experimental schemes in whichthe idea could be tested with lights polarizations instead o electrons momentum. Then in 1982 a young Frenchman namedAlain Aspect per ormed a rigorous test o Bells theory on whichmost physicists nally agreed. Quantum mechanics was correct,and either locality or realism was undamentally wrong.

During the 1980s and 1990s, the oundations o quantummechanics slowly returned to vogue. The theory had beenshown, with high certainty, to be true, though loopholes inexperiments still le t some small hope or disbelievers. However,even to believers, nagging questions remained: Was the problemwith quantum mechanics locality, realism, or both? Could thetwo be tested?

in may of 2004 Markus Aspelmeyer met Anthony Leggett dur-ing a con erence at the Outing Lodge in Minnesota. Leggett, whohad won the Nobel Prize the yea r be ore, approached Aspelmeyer,who had recently become a research assistant to Zeil inger, abouttesting an idea he rst had almost 30 years be ore.

In 1976 Leggett le t Sussex on teaching exchange to theUniversity o Science and Technology in Kumasi, the secondlargest city in Ghana. For the rst time in many years, he hadree time to really think, but the universitys library was woe-ully out o date. Leggett decided to work on an idea that didntrequire literature because ew had thought about it since DavidBohm: nonlocal hidden variables theories. He ound a result,

led the paper in a drawer, and didnt think about it again untilthe early 2000s.Leggett doesnt believe quantum mechanics is correct, and

there are ew places or a person o such disbelie to now turn.But Leggett decided to ind out what believing in quantummechanics might require. He worked out what would happeni one took the idea o nonlocality in quantum mechanics seri-ously, by allowing or just about any possible outside infuenceson a detector set to register polarizations o light. Any unknownevent might change what is measured. The only assumption Leg-gett made was that a natural orm o realism hold true; photons

should have measurable polarizationsthat exist be ore they are measured.With this he laboriously derived anew set o hidden variables theoremsand inequalities as Bell once had.But whereas Bells work could notdistinguish between realism andlocality, Leggetts did. The two couldbe tested.

When Aspelmeyer returned toVienna, he grabbed the nearest theo-rist he could ind, Tomasz Paterek,whom everyone calls Tomek.Tomek was at the IQOQI on el-lowship rom his native Poland and

together, they enlistdent. With Leggettpain ully checking herror. Then they set aother resident theoriswere done, they wenwouldnt be too di cthem months to reamechanics describedidnt exist be oremechanics would be

ing, Zeilinger bears Kringle. Born in 194mane o hair. He wehands-on kind o guy

As a student inattended a single cohelp to explain the w

zeal o a late convertmany collaborators wcryptography or a bsewers o Vienna), reachieve entanglemenacross the Danube RIslands. Zeilingers wdistinction between

Zeilingers o icbooks lean on a lengZeilinger reclined inred couch. Quantumeven more undamengive up on realism alEinstein, to give up But on the quantum

With eerie precisexperiments had omechanics. The databy three orders o mait, the polarizations tFor so undamentalto test quantum mecbuilding, another Phthe experiment using

Leggetts theory

DOUBLE CHECKING

Alessandro Fedrizzi,another PhD studentat the IQOQI, andthe experimentalsetup he constructedor a secondrigorous test orealism in mid-2007.

IT TOOK THEM MONTHSTO REACH THEIR TENTATIVE

CONCLUSION : IF QUANTUMMECHANICS DESCRIBED

THE DATA, THEN THE LIGHTSPOLARIZATIONS DIDNT

EXIST BEFORE MEASURED.

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HERR PROFESSOR

Anton Zeilinger standsin ront o the doorto his o ce. To hisle t is a glass cabinetthat holds thenumerous medals hehas won or tests oquantum mechanics.

it required that lights polarization be measured not just likethe second hand on a clock ace, but over an entire sphere. Inessence, there were an in nite number o clock aces on whichthe second hand could point. For the experimenters this meantthat they had to account or an in inite number o possiblemeasurement settings. So Zeilingers group rederived Leggettstheory or a nite number o measurements. There were certaindirections the polarization would more likely ace in quantummechanics. This test was more stringent. In mid-2007 Fedrizzi

ound that the new realism model wasviolated by 80 orders o magnitude;the group was even more assured thatquantum mechanics was correct.

Leggett agrees with Zeilinger thatrealism is wrong in quantum mechan-ics, but when I asked him whetherhe now believes in the theory, heanswered only no be ore demur-ring, Im in a small minority with

that point o view and I wouldntstake my li e on it. For Leggett thereare still enough loopholes to disbe-lieve. I asked him what could nallychange his mind about quantum

Brukner said, There could be other classical worlds completelydi erent rom ours.

Zeilinger and his group have only just begun to consider thegrand implications o all their work or reality and our world.Like others in their eld, they had ocused on entanglement anddecoherence to construct our uture in ormation technology, suchas quantum computers, and not or understanding reality. But thegroups work on these kinds o applications pushed up againstquantum mechanics oundations. To repeat a amous dictum,All in ormation is physical. How we get in ormation romour world depends on how it is encoded. Quantum mechanicsencodes in ormation, and how we obtain this through measure-ment is how we study and construct our world.

I asked Dr. Zeilino ce. In the history distinctions that we space and time It make between in orsaying that everythinwe need a new concZeilinger smiled as hto our philosophy rie

A ew weeks latersite when I noticed a institute. They werewith the group.

mechanics. Without hesitation, he said sending humans intospace as detectors to test the theory. In space there is enoughdistance to exclude communication between the detectors(humans), and the lack o other particles should allow mostentangled photons to reach the detectors unimpeded. Plus, eachperson can decide independently which photon polarizations tomeasure. I Leggetts model were contradicted in space , he mightbelieve. When I mentioned this to Pro . Zeilinger he said, Thatwill happen someday. There is no doubt in my mind. It is just aquestion o technology. Alessandro Fedrizzi had already shownme a prototype o a realism e xperiment he is hoping to send up ina satellite. Its a heavy, metallic slab the size o a dinner plate.

on markus aspelmeyer s desk there are three tall emptyboxes o Veuve Clicquot. Experimentali sts at the IQOQI receivechampagne or exceptional results, and on one o the boxes arewritten congratulations or Markuss initiation o the realismtest. Caslav Brukner, who helped with the theory, keeps a squatbox o Chinese plum wine on his desk acing Markuss. When Iasked about the wine, thinking it the theorists complementarytradition, he laughed and said he just needed a counterbalance.Brukner has an easy manner and has been with Zeilingers groupalmost continuously since arriving in Austria in 1991 a ter leav-ing then Yugoslavia.

Last year Brukner and his student Johannes Kofer decidedto gure out why we do not perceive the quantum phenomenaaround us. I quantum mechanics holds universally or atoms,why do we not see directly its e ects in bulk?

Most physicists believe that quantum e ects get washed outwhen there are a large number o particles around. The particlesare in constant interaction and their environment serves to deco-

here the quantum worldeliminate superpositionsto createthe classical one we observe. Quantum mechanics has within itits own demise, and the process is too rapid to ever see. Zeilingersgroup, which has tested decoherence, does not believe there is aundamental limit on the size o an object to observe superposi-tion. Superpositions should exist even or objects we see, similarto the in amous example o Schrdingers cat. In act, Grblachernow spends his nights testing larger-scale quantum mechan ics inwhich a small mirror is humanely substituted or a cat.

Brukner and Kofer had a simple idea. They wanted to ndout what would happen i they assumed that a reality similar tothe one we experience is trueevery large object has only onevalue or each measurable property that does not change. In otherwords, you know your couch is blue, and you dont expect to beable to alter it just by looking. Th is orm o realism, macroreal-ism, was rst posited by Leggett in the 1980s.

Late last year Brukner and Kofer showed that it does notmatter how many particles are around, or how large an objectis, quantum mechanics always holds true. The reason we seeour world as we do is because o what we use to observe it.The human body is a just barely adequate measuring devic e.

Quantum mechanics does not always wash itsel out, but toobserve its e ects or larger and larger objects we would needmore and more accurate measurement devices. We just do nothave the sensitivity to observe the quantum e ects around us.In essence we do create the classical world we perceive, and as

THE GROUP

Above, Caslav Bruknersits across rom

Markus Aspelmeyer.Below, Brucker stands

between two othertheorists: Johannes

Kofer (le t) andTomasz Paterek (right).

I ASKED LEGGET TWHAT COULD CHANGE HIS

MIND ABOUT QUANTUMMECHANICS.HE SAID

SENDING HUMANS INTOSPACE AS DETECTORS TO

TES T THE THEORY.

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