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PHYSICS Massachusetts

“A student will never do all that he iscapable of doing if he is never required to dothat which he cannot do.”

—Herbert Spencer

Boone & Rines:Fifth force– 2

Kerrigan:Future physics– 4

O’Donnell:The electron: a dipole?– 5

Fischetti & Pierce:Dark cosmology– 6

Parker:Universe expanding– 8

Bingham & Mirigian:God particle– 9

Deegan & MacLellan:Atom smasher– 10

Hughes & Rogers:Gravity waves– 12

Fratus & Lund:Neutrino oscillations– 14

Drake: Complexity– 16

Emma: Food nanotech– 17

Cervo: Cell imaging– 18

Mortsolf:Molecule flashlight– 20

Kiriakopoulos:Single molecules– 19

Herbert: New matter– 22

Lally: Thin-film buckling– 24

LIGO AND BOREXINO

Making Waves at UMassLaura Cadonati brings a revolutionary perspective on the cosmosto Amherst

Laura Cadonati

Paul Hughes & Daniel Rogers, AmherstAlbert Einstein is a household name. Most peo-

ple know that E = mc2, and that funny things hap-pen to space and time at speeds near that of light.A less commonly known prediction of relativity,however, is the existence of gravitational waves,which have yet to be directly observed.

Since the cornerstone of scientific progressis the verification of such predictions, this is aproblem for Einstein and his theory. Fortunatelyfor him, there is LIGO (the Laser InterferometerGravitational-Wave Observatory), which hopes tofinally detect gravitational waves. The project is acollaborative effort of about 500 scientists from across the country. One of them,Dr. Laura Cadonati, has helped to start a gravitational waves research group in theUMass Amherst Physics department. [ . 12]

DARK ENERGY AND MATTER

Where Did (Just About) Everything Go?Lorenzo Sorbo, our local cosmologist

Sebastian Fischetti and Rob Pierce, AmherstA couple walking down a street late

at night notice a man, obviously drunk,searching for something under a street-light. When asked about his behavior, theman replies, “I lost my keys.” “Where?”the couple ask. “In the park.” “Then whyare you looking for them here?” “Be-cause here I can see.”

This story describes the manner ofresearch of a cosmologist like LorenzoSorbo, a Professor of Physics at UMassAmherst. Because many ideas in cos-mology, like dark energy, are still veryobscure, sometimes cosmologists canonly research within the known realm ofphysics before making progress on moremysterious topics. [ . 6]

Sam Bingham and Matthew Mirigian, AmherstSome people are concerned that new experiments atthe world’s largest particle physics laboratory couldhave some disastrous consequences. Perhaps it isdue to the talk of high energy collisions possibly re-sulting in black holes. The Large Hadron Collider(LHC) will be capable of smashing protons at thehighest energies seen in a laboratory setting. Thecollider’s major ring, where the protons will zoomaround at 99.999999 percent of the speed of light, isa circular track 17 miles in circumference and is lo-cated underground straddling the Franco-Swiss bor-der near Geneva. [ . 9]

ATLAS: LORDOF THE RING

A titan under construction

UMass DEPARTMENT OF PHYSICS, UNIVERSITY OF MASSACHUSETTS

PHYSICS December 19, 2008

UMass PHYSICS December 19, 2008 2 / 24

THE FIFTH FORCE

Rules of AttractionHow a simple experiment challenged centuries of physical theory

Sam Boone and Rich Rines, Amherst

In Northfield, Massachusetts, 935feet above sea level on Northfield Moun-tain, engineers in the 1970s created amassive lake (pictured). The mountainand area surrounding the lake serves as apublic recreational area for the surround-ing towns. At first glance, the lake maynot seem unusual (save for its artificialcement edges), but with an extended stay,visitors would notice an overwhelmingpeculiarity: the height of the water in thelake is in dramatic constant fluctuation.Deep underground and below the surfaceof the lake, water turbines are responsi-ble for continuously draining and refill-ing of the lake. When there is an excessof electricity in the area, the pumps useit to fill the reservoir with water from theConnecticut River. This water is then re-leased from the lake through large gener-ators in times of electrical demand. Andwhat is most peculiar about this lake isnot its intrinsically unusual nature, but

a single physical experiment completedthere in 1991.

Physicists have long characterized in-teraction in terms of four fundamen-tal forces. Gravity keeps us on theground. Electromagnetism, being muchstronger than gravity, keeps atomic struc-tures rigid, so that we don’t fall throughthat ground. The strong nuclear force,stronger still, holds those atoms them-selves together. The weak nuclear force,though less obvious in everyday experi-ence, is responsible for the nuclear ac-tivity that makes the sun burn. With-out these forces the infrastructure of ouruniverse would collapse leaving us witha completely chaotic and intangible uni-verse that we cannot begin to imagine.

Each of these forces are defined bytheir particular “sources,” or propertiesof matter which are attracted or re-pelled. Electromagnetism, for exam-ple, is a product of the “electric charge.”Gravity, by contrast, is solely a function

of an object’s mass. In this way, allobjects (including ourselves) experiencea small attraction toward one another,which is greater the closer together theobjects are. This is the cause of Galileo’sinfamous 17th-century claim: that all ob-jects, without the effects of wind resis-tance, fall to the Earth with the same ac-celeration. This principle is known as“weak equivalence,” and has been testedwith high precision many, many times.Years later, Sir Isaac Newton used this asthe basis for his gravitational explanationof planetary orbits.

But late in the 1970s, three centuriesafter the times of Galileo and Newton,physicists began questioning their fun-damental assertions. Motivated by cer-tain sub-atomic phenomena that couldnot be explained by any existing phys-ical law, they were beginning to sus-pect yet another, fifth fundamental force,with its own unique “source.” As thissource would presumably be different for

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different kinds of materials, they wouldfall to Earth with slightly different ac-celerations. This would mean an endfor weak equivalence. And being muchweaker and less prevalent than even grav-ity, this force could have gone undetectedthrough any previous experiment.

It was the existence of this new forcethat Paul A. Nakroshis, as part of hisPHD thesis, for the University of Mas-sachusetts under the direction of Profes-sor Bob Krotkov, began to experimen-tally search for on the side of NorthfieldMountain, in the Metropolitan DistrictCommission (MDC) Building.

Nakroshis saw that the NorthfieldReservoir provided a perfect testing sightfor a possible fifth force. All objects are,to some small extent, attracted to eachother via gravity. A fifth force would,presumably, provide this same univer-sal interaction between objects. How-ever, unlike gravity, different objectsof the same mass could be either at-tracted or repelled from one another. Thestrength of this attraction or repulsionwould also vary between different mate-rials. Nakroshis used this as the basis forhis experiment.

The changing volume of water in thereservoir provided a constantly changingsource of attraction for nearby objects.When the reservoir is full, objects sus-pended nearby should have a measurable,however miniscule, attraction toward the

great water mass. This attraction dimin-ishes as the water is emptied from thelake.

Under just the effects of gravity, thisattraction would be identical for all ob-jects of the same mass. However, withthe addition of a fifth force that is de-pendent on some other property of thematerial, the attraction of different kindsof materials toward the lake would beslightly different. This difference is read-ily tested: by hanging two different ma-terials of equal mass in balance once thelake has been drained and then allowingthe lake to refill, the balance would “tip”so that the object most attracted to thewater could get closer.

Nakroshis used a variant of this pro-cedure in his experiment. He assumed, asdid most fifth-force research at the time,that the source of the force was an atomicproperty known as baryon number. Thisis a property which varies slightly be-tween different kinds of atoms, and there-fore between different kinds of materi-als. The two materials he comparedwere copper and polyethylene, whichare known to have very different baryonnumbers. He balanced these materials ona metal rod which was allowed to oscil-late, much like a horizontal version ofa clock’s pendulum, known as a torsionpendulum. Just as the speed at which aclock’s pendulum swings changes whenthe pendulum is made heavier or lighter,

the attraction between each material andthe changing amount of water would the-oretically alter how fast the torsion pen-dulum oscillates.

Nakroshis’ experiment was one ofmany in search for a violation of the weakequivalence principle at the time. Thephysics community at the time was cap-tivated by the possibility of a new, undis-covered fundamental force. Nakroshis’test differed, however, from the majorityof fifth force experiments, in his utiliza-tion of such a large amount of fluctuatingmaterial. The unique Northfield Reser-voir provided this huge fluctuating body.

Like the other fifth-force experimentsat the time, Nakroshis’ results were in-conclusive. As these results came in,physicists more and more began to fleefrom the idea of the existence of a fifthforce. A little more than a decade af-ter its proposal, the fifth-force proposalwas beginning to flounder. Eventually,as no positive, reproducible experimen-tal results were being reported, the forcewas largely considered dead. In this way,weak equivalence and the ideas of New-ton and Galileo were once again consid-ered accurate. It was not until the rise andfall of the fifth force, three centuries andthousands of experiments after their con-ception, that these laws had been testedand confirmed with such high meticu-lousness.

Left to Right: Nakroshis, Sakai and Krotkov with the experimental apparatus.



CONTEMPORARY THEORY

A Ripening RealityExploring two controversial new physical theories

Chris Kerrigan, AmherstA chapter in contemporary physical theory may be drawing

to a close. Physicists have long made the comparison of realityto an onion, having layers of truth to be explored and later dis-carded when further research reveals a “deeper” or more funda-mental existence. Right now, many of the world’s top physicistshave thoroughly explored current theories sufficiently enoughto decide that it’s time to peel back a new layer.

The current description of reality agreed upon by mostphysicists is called the Standard Model. This theory dependson an idea everyone has heard, that of the “fundamental build-ing blocks” of existence. The Standard Model describes a fewfundamental interactions, or forces, that occur in nature, and theelementary particles that take part in these interactions. Whenall is said and done, this theory gives us 26 constants (unchang-ing numbers that describe various quantities) which describereality; the mass of the electron is one of these, for example.Physicists are now ready to take the theory a step further anddiscover what created these particles and what determines theseconstants.

I was recently able to sit down with Professor of Physics atthe University of Massachussetts at Amherst John Donoghue,who quite literally wrote the book on the Standard Model (itis entitled The Dynamics of the Standard Model), and discussthe future of physics. His recent claim to fame is a theory ofthe “multiverse.” The theory is as surprising as the name sug-gests. The idea is that the 26 constants brought forth by theStandard Model could have been assigned at random by nature.Not only that, but in different “domains” of our universe, whichis perhaps larger than we expect, there exist places where the 26constants were assigned differently. This means that our entireuniverse consists of separated, smaller universes that each havetheir own set of constants and therefore behave very differently.Perhaps in one universe the mass of the electron turned out tobe very great and so gravity made it collapse very quickly. Per-haps in another the constants worked in such a way that therewas only one type of particle, and so nothing ever happened.The implications of this theory are that we live in one of thefew possible universes that could exist as something other thana clump of particles, and that this universe only came aboutthrough the trial and error process of nature playing with 26constants. It is a lot to stomach to hear this about the universewe have come to know and love, but it may also be a step closerto the truth.

A different theory suggested by Donoghue is even more ab-stract, but pushes further toward the center of the onion. Itinvolves the concept of “emergence,” the way patterns arise out

of simple interactions, and has been called the opposite of thepopular String Theory. Though easy to define, the idea of emer-gence is hard to properly conceptualize. The classic example isto look at the notion of a wave. We can have waves in water,sound waves in the air, electromagnetic waves, etc., yet thereis no such thing as a “water-wave particle,” or a “sound par-ticle,” or an “electromagnetic particle.” The idea of the waveis nothing more than a convenient way to describe what hap-pens on a larger scale when small particles interact with eachother. Regular water molecules rub against each other in a waythat creates “wave” motion. Regular particles in the air bounceoff of one another to create alternating regions of high and lowpressure that we call a “sound wave.” Emergence, then, is theconcept that embodies this. It is the means by which our con-cepts to describe macroscopic phenomena come about.

So what does emergence have to do with reality as we knowit? Donoghue is beginning to lean toward the answer “every-thing.” The idea is that many of the things we describe areemergent properties of more fundamental interactions (for ex-ample, waves happen even though, in a sense, there are noreal waves), so why not take it a step further (as is often thephysicist’s wont)? Knowing that phenomena occur based onthe interactions between the particles described by the Stan-dard Model, we may riskily say that the Standard Model itselfis nothing more than an emergent phenomenon of somethingeven more fundamental. That is, elementary particles may seemto exist, but are in fact just a convenient way to describe some“deeper” interactions. When asked about the nature of theseinteractions, Donoghue replied, “We can’t go there yet.”

Indeed the idea of the Standard Model as an emergent phe-nomenon rather than a foundation is controversial and only dis-cussed by a narrow range of physicists: those who are bothwell-versed enough to explore it and willing to perhaps sac-rifice credibility within the more conservative scientific com-munity to explore an avenue so novel and abstract. One suchphysicist is 1999 Nobel Prize in Physics winner Gerardus ’tHooft, who is beginning to publish papers which attempt toshed light on this bold concept. Clearly some of the top physicsminds in the world are starting to take the idea of emergencevery seriously.

Although Donoghue admits that the few who consider thistheory are “further along thinking of ways to test the theorythan thinking of the theory itself,” it is clear that physics as weknow it is on the verge of change. Which direction it will gois up in the air, but one thing seems true: reality as we know itnow is ripe to be peeled away.



PARTICLE PHYSICS

Something Smaller than an Electron?Answering a Fundamental Question of Physics

David Kawall

Andrew O’Donnell, AmherstScience is always trying to push the frontiers of our knowl-

edge about the world. One of those questions that has alwaysbeen pursued is what is the world made up of? We alreadyknow there is a lot beyond just protons and electrons that ev-eryone learns about in chemistry class, but for the electron, noone currently knows for certain if there is anything beyond it.Here at UMass, Professor David Kawall is trying to answer thisquestion.

The general experiment that Professor Kawall is trying todo is called the Electron Electric Dipole Moment or EDM ex-periment. There are about a dozen of these experiments be-ing setup across the United States and they are all racing to tryand improve sensitivities. An electric dipole moment is formedwhen there is a separation of positive and negative charges. If adipole is found for the electron, it would be evidence that thereis something smaller than it. EDM experiments have been go-ing on for the past 50 years, but the sensitivities are not goodenough yet and Professor Kawall is trying to improve these sen-sitivities. Surprisingly, no improvements have been made tomeasurements in the past 5 years.

For sub atomic physics we have a theory called The Stan-dard Model that is used to describe the world below protonsand electrons. Evidence of an electron dipole moment wouldimply that there is physics beyond Standard Model. One of thecurrent theories of physics beyond the Standard Model is calledSuperSymmetry and that is the key theory used in many StringTheory models. Professor Kawall is hoping that within the nextyear or two he will complete upgrade to the experiment and willincrease sensitivities of the EDM.

Professor Kawall joined the Physics Department in the Fallof 2005 and has been working on this experiment for over 3.5years now searching for the Electron Dipole Moment. With

some startup money from UMass, Professor Kawall hopes thathis proposed changes to past methods for the experiment wouldincrease sensitivities by 100.

The experimental setup of the EDM goes as follows; a pow-erful laser evaporates a lead oxide sample that is inside a vac-uum with a buffer of Neon Gas at 14 Kelvin (or −437◦ F).Then, magnetic and electric fields are applied to the chamberand the energy shifts of the system are measured. Lead oxide isused in this experiment instead of electrons because lead oxidehas a big dipole moment and allows for a more sensitive mea-surement. If certain energy shifts are found, that would giveevidence for an Electron Dipole Moment. Even if no dipolemoment is found, increased sensitivities of the dipole momentmight prove or disprove theories beyond the Standard Model.

The setup of this experiment has been a long and difficultprocess, but a very rewarding one. Despite this experimenthaving the potential to answer some fundamental questions ofphysics, funding has been a little tight with this experiment. In-stead of being able to order state of the art equipment, bargainsand upgrades to used equipment is needed to create the levelsof sensitivities for this experiment. Professor Kawall says ”Oneinteresting thing is that a lot of used equipment can be foundonline for a lot cheaper. For instance, some of the lasers usedin this experiment were once used in cosmetic surgery to helpfix people’s vanes.” The whole process of setting up the systemto measure the energy has been quite challenging. ProfessorKawall says that ”The wave meters used to measure energy forthis experiment are just as good as a state of the art system,espite the fact that it has been created from old parts.” Evenwith all the hard work being put into this experiment, ProfessorKawall has found it quite rewarding. ”One of the best parts ofexperimental physics is trying out new things, planning themout, executing the plans, and seeing them work out.”

In the Spring of 2008, Professor Kawall made yield mea-surements for the ablation of lead oxide. This was a landmarkof his experimental setup and has left Professor Kawall opti-mistic that improved sensitivities will be found once the setup isfinished. One of Professor Kawall’s proposed ways to improvethe sensitivity of the EDM experiment is to increase the amountlead oxide molecules in the vacuum chamber. This was doneby using a laser that has bigger pulse duration over a larger sur-face area, thus allowing for a large flux of lead oxide moleculesto be ablated. As a result, 100 to 1000 times more lead ox-ide molecules have been placed into the vacuum chamber thanprevious experiment.

The final step for Professor Kawall is to setup the refrig-eration system. When Professor Kawall was a post doctorateat Yale, lead oxide molecules were ablated and then measure-ments were taken. His proposed improvement to the exper-iment is to put a buffer gas of Neon to cool down the leadoxide molecules. This will allow for enhanced resolution ofthe energy shifts during data taking. If all goes according toplans, this experiment will have a large impact on the field ofphysics.



COSMOLOGY

Looking Were We Can SeeLorenzo Sorbo: Our Local Cosmologist

Lorenzo Sorbo

Sebastian Fischetti and Rob Pierce, AmherstA couple walking down a street late

at night notice a man, obviously drunk,searching for something under a street-light. When asked about his behavior, theman replies, “I lost my keys.” “Where?”the couple ask. “In the park.” “Then whyare you looking for them here?” “Be-cause here I can see.”

This story describes the manner ofresearch of a cosmologist like LorenzoSorbo, a Professor of Physics at the Uni-versity of Massachusetts Amherst. Be-cause many ideas in cosmology, like darkenergy, are still very obscure, sometimescosmologists can only research withinthe known realm of physics before mak-ing progress on more mysterious topics.

Cosmology, from the Greek wordkosmos, meaning beauty and order, seeksto develop an understanding of the entireuniverse: its origins, its current structure,and its future. Most of the revolutions incosmology have only occurred over thelast decade or so: the discovery of the ef-fects of dark energy and dark matter, andthe observation of fluctuations in the cos-mic microwave background (CMB). The-ory has failed to keep up with these ob-servations, so the most pressing goal forcosmologists is to come up with explana-tions of these mysterious phenomena.

Sorbo’s interest in cosmology beganwith a fascination of the stars and heav-ens as a 15-year-old boy in his hometownof Bologna, Italy. He wanted to pursuethese interests in his professional careerby studying astronomy, but his mother,concerned with his future employment,suggested that he steer towards a morepractical subject: engineering. Compro-mising, Sorbo decided on a middle route,

physics. Sorbo, like many college-boundItalian students, attended his hometownuniversity, the University of Bologna, forhis undergraduate career. His love of the-ory prompted him to work on his under-graduate thesis with the strongest theorygroup in the university. He was askedto study the unwrapping of scotch tape.Not utterly enthralled with his assignedresearch, and having discovered a lovefor quantum field theory during a courseon the subject, Sorbo decided to move onto graduate school.

After receiving his Laurea (the Ital-ian equivalent of a Bachelor’s Degree) in1997, Sorbo, unlike the majority of Ital-ian students, applied to schools outside ofhis hometown. He was accepted to andthen attended the International School ofAdvanced Studies in Trieste, Italy. Whenasked about his decision to go againstthe majority (“You go to High Schoolin Bologna; then you go to college atthe University of Bologna; then you goto graduate school at the University ofBologna; then you work for a profes-sor at the University of Bologna with thehope that it will eventually lead to a goodposition at the University of Bologna”),Sorbo says that he does not regret it, de-spite the lifestyle that his friends main-tain today: they live at home with theirparents, eat dinner at 8:00 with their par-ents, go out on dates with their girlfriendsand come home to their parents, and,most importantly, don’t pay rent to theirparents. All in all, his current lifestyle isnot so bad.

At Trieste, he immediately found outthat a professor there was doing researchin cosmology, his old love. Since theprofessor’s main focus was not on Cos-mology at the time, Sorbo’s research wasmainly his own. When Sorbo lost ayear of school because of mandatory civilservice, he ended up doing most of hiswork with a fellow student. After get-ting his Ph.D. in 2001, Sorbo was offereda postdoctoral position in Paris, France,where he continued to work on cosmol-ogy. He was then offered another post-doctoral position at the University of Cal-ifornia Davis, where he began his workon dark energy, and, in 2005, Sorbo cameto UMass Amherst as an assistant profes-sor, where he teaches today.

Here at UMass professor Sorbo’smain focus is looking for candidates fordark energy. Experimental observationshave shown that the expansion rate ofthe universe is, in fact, increasing: darkenergy is the term given to (the yet un-known) agent responsible for this accel-erating expansion. Unlike dark matter, ofwhose nature we have some understand-ing but no direct observation, there is noagreement on what exactly dark energyis: it could actually be something, a newand (we hope) one-day observable formof matter, or it could simply be an arti-fact of a mistake in Einstein’s equations.All we know is that, unlike dark matter,which “clumps” into halos around galax-ies, dark energy’s distribution is uniformeverywhere, and although it makes up themajority of the mass of the universe (nor-mal stuff makes up 5 percent of the uni-verse, dark matter makes up 20 percent,and dark energy a whopping 70 percent!),its density is incredibly small.

An initial theory consisted of reintro-ducing what was once thought to be amistake: the cosmological constant. Inhis formulation of general relativity, Ein-stein initially included a constant in or-der to keep the universe static. The staticuniverse was eventually disproved, andEinstein removed this cosmological con-stant from his equations. Now cosmolo-gists have found a reason to reinstate it:mathematically, it can be used to producethe same effect as dark energy. Roughlyspeaking, the cosmological constant is ameasure of how much energy is asso-ciated with empty space: the “cost ofspace.”

Almost three-quarters of the universe isunexplained!



Initial theories for the origin of thecosmological constant tried to explain itas quantum fluctuations of the vacuum:in accordance with the Heisenberg un-certainty principle for energy and time,energy can be “borrowed” from the vac-uum to create a particle and its antipar-ticle, provided they annihilate each otherwithin a short enough period of time. Be-cause of their fleeting nature, these parti-cle pairs are called virtual particles, andtheir existence has been confirmed exper-imentally. Unfortunately, the total masscontribution of these particles to the uni-verse is gigantic (1 with 120 zeros fol-lowing it times larger than the observedvalue!), so naturally, physicists decidedto set this huge number equal to zero.However, attempts to explain dark en-ergy as consisting of these vacuum fluc-tuations need to reconcile the incrediblylarge value that emerges with the fact thatthe density of dark energy is very small.

Because of this disagreement be-tween the quantum-mechanical predic-tion and observations, cosmologists havecome up with other theories of dark en-ergy. One theory that Sorbo has workedon is the quintessence theory. In this the-ory, the empty parts of space are viewedas being comprised of a “quintessence

field.” In contrast with the cosmolog-ical constant, which cannot be excited(i.e. it’s infinitely rigid) and is a constantproperty of the universe, the quintessencecan be excited and change as the uni-verse evolves. The major support forthis theory comes from this very feature:the time-dependence of the quintessencefield allows it to be used to explain in-flation, the period of accelerated expan-sion of the early universe, which is an-other important field of study in cosmol-ogy. After the quintessence field helpedwith the formation of large-scale struc-tures during the inflationary period, it be-gan to behave like the dark energy we seetoday, causing the accelerating expansionof the universe.

Yet another theory dares to ask thequestion: What if Einstein’s equationsare downright wrong? Although gen-eral relativity has been proven in a num-ber of relatively small-scale experimentsand observations (around the size of agalaxy), no experiments have been doneto test it at scales around the size of theuniverse. This question has led some cos-mologists to attempt to modify Einstein’sequations so that the accelerating expan-sion of the universe emerges simply as amathematical artifact when general rela-

tivity is applied at large distances, remov-ing the need for mysterious dark energyaltogether. Unfortunately, general rela-tivity is a very rigid and symmetric the-ory, and even extremely small changes inits equations meant only to affect largedistances trickle down to dramatically al-ter the effects of gravity at smaller scales.Many cosmologists, including Sorbo, donot like this approach because of thesemodification problems, and others preferto explore alternative theories.

So what’s Sorbo’s take on all of this?He believes that one of the major draw-backs to the quintessence theory is thefact that it introduces a number of newparameters, each of which will in turnneed to be explained. Similarly, Sorboalso finds the idea of modifying Ein-stein’s equations less compelling due tothe “trickle down effect.” Despite thesedrawbacks, however, Sorbo still thinksthat we should continue working on anyideas that haven’t yet been disproven: aslong as a theory is a logical possibility, hesays, it’s just one more chance of gettingit right. Like the drunken man searchingfor his keys, we should work on what wecurrently know and understand, howeverunlikely that it is correct, in the hopes ofone day reaching the correct answer.

The growth of the universe from the Big Bang to the present day. The initial spurt of rapid growth is the inflationary period.



COSMOLOGICAL CONSTANT

Einstein Right Again: Universe ExpandingHe just can’t help it

David Parker, AmherstWhen Einstein formulated the equa-

tions of General Relativity they showedthat the universe was expanding, know-ing that this would be viewed as ridicu-lous by the scientific community, whichon this point Einstein was, for some rea-son, not willing to go to bat as he didfor the rest of his “ridiculous” ideas, triedto include a “cosmological constant” thatwould allow the universe to remain non-expanding without collapsing to a singlepoint.

The necessity for some sort of agentto prevent the collapse of the universe isapparent when you think about the natureof gravity. Imagine that all of the stars,planets, gas clouds, and everything werecompletely evenly distributed throughoutthe entire universe, in this case gravitywould be perfectly balanced in all direc-tions and the universe would remain sta-ble, i.e. non-collapsing. However, assoon as a slight change occurred, no mat-ter how small, the universe would beginto collapse towards the point that had aslightly higher mass than the rest of theuniverse.

Einstein’s cosmological constant wasa repulsive force that would allow aheterogeneous universe to remain static.However, Einstein didn’t have to supportthis idea for long because in the 1920’sEdwin Hubble discovered, through care-ful monitoring of the motion of stars atdifferent distances from the Earth, thatthe universe actually is expanding. Notonly that, but the expansion of the uni-verse is accelerating.

In fact, it is this acceleration of theexpansion of the universe that is neces-sary to support a non-collapsing universe,otherwise, since gravity does not makematter move at a constant velocity, butinstead accelerates it, a constant veloc-ity expansion would eventually be over-come by gravity and cause a collapse.So, given this new discovery by Hubble,Einstein threw the cosmological constantout, later calling it “the worst mistake ofmy career”.

The expansion of the universe isslightly more complicated than every-thing moving out from a single point,as most would naturally assume. It is

actually, in the words of Dr. LorenzoSorbo, assistant professor at Universityof Massachusetts Amherst, “like a raisincake as it bakes, all of the raisins moveaway from each other, and those far-thest away move away fastest”. The uni-verse, as Hubble discovered, behaves inexactly this way, everything is movingaway from every other thing, and thestars that are farther away from us aremoving away faster.

Therefore, the universe is currently ina phase of accelerated expansion, this isknown as the current phase of acceler-ated expansion. However, there was an-other accelerated phase in the very earlyuniverse known as the primordial phaseof accelerated expansion in which theuniverse expanded at a phenomenal rate.Now, the major question surrounding allof this is what is causing this expansion?An acceleration must be fueled by someenergy, and there is most certainly accel-eration, so what is this energy? The an-swer, sort of, is Dark Energy. Dark En-ergy is the name given to whatever en-ergy it is that is fueling the accelerationof the expansion of the universe, its prop-erties are basically unknown other thanit doesn’t react with anything other thangravity, and with that very weakly.

The vertical lines separated by roughly 1billion years, the separation of the hori-zontal lines represents the expansion of theuniverse

Enter the cosmological constant.Welcome back. However, this time, in-stead of being the agent for a static uni-verse it is in fact the agent for an ex-panding universe. At the moment thereis no hard evidence for the existence ofthe cosmological constant other than thefact that the universe goes through peri-ods of accelerated expansion and theremust be something causing these phases.

Current theories speculate that the cos-mological constant has some very smallbut non-zero energy, it permeates evenlythroughout the universe, it doesn’t dissi-pate or dilute with the expansion of theuniverse, and it almost doesn’t interactat all with anything. These things allcombined make for an extremely stickyscientific problem. If it barely interacts,how can we observe it, if it does not di-lute, why the changes in acceleration, andwhat about conservation of energy?

To be inclusive I must admit thatthere are other possibilities that could ex-plain the expansion of the universe suchas Quintessence, an energy similar to thecosmological constant except that it canbe interacted with a little more, or per-haps General Relativity is flawed andgravity actually has a repulsive compo-nent at very large distances. Neither ofthese are any less proven than the cosmo-logical constant, however, at least in theeyes of Dr. Sorbo, “[Other explanationsof the expansion of the universe] are toospecific, if it can be changed, then why?And by what? And there is almost noevidence that show General Relativity aswrong”.

The types of experiments being doneright now to find evidence for or againstthe cosmological constant are basicallyrecreations of Hubble’s original experi-ment, mapping out the relative veloci-ties and accelerations of the surround-ing universe, at much higher precisionswith a more thorough process. Scien-tists are looking for changes in the rate ofexpansion throughout the history of theuniverse in order to see when and whychanges might occur.

Basically, we are still being stumpedby the elegance introduced into our pic-ture of the universe that was painted forus by a dreaming relativist in a Swisspatent office. There are very few whothink seriously about the nature of theuniverse without a nod, and in most casesa lot more than that, to Einstein. Withinthe next 50 years we may have figuredout that “if it’s not the cosmological con-stant, it is certainly very close, and at thislevel of precision we might as well callit the cosmological constant.” Thank youagain, Einstein.



PARTICLE PHYSICS

Physicists Search for God ParticleProfessor Carlo Dallapiccola and ATLAS

Sam Bingham and Matthew Mirigian, Amherst

Some people are concerned that newexperiments at the world’s largest particlephysics laboratory could have some dis-astrous consequences. Perhaps it is dueto the talk of high energy collisions pos-sibly resulting in black holes. The LargeHadron Collider (LHC) will be capableof smashing protons at the highest ener-gies seen in a laboratory setting. The col-lider’s major ring, where the protons willzoom around at 99.999999 percent of thespeed of light, consists of a circular track17 miles in circumference and is locatedunderground straddling the Franco-Swissborder near Geneva. In September thefirst proton beams circulated in the mainring. As some of the kinks are workedout physicists hope to use the data col-lected to explore and test theoretical con-cepts about the most fundamental build-ing blocks of the universe–and yes, pos-sibly produce black holes.

The LHC will be used for many dif-ferent collaborative experiments to takeadvantage of the large amount of ground-breaking data. University of Mas-sachusetts Professor Carlo Dallapiccolais part of the effort to make sense of whatwill be seen in these high energy colli-sions through his involvement in the AT-LAS experiment. ATLAS (A ToroidalLHC ApparatuS) is one of six particle de-tector experiments at the LHC. The AT-LAS detector weighs over 7000 tons andwill be used to collect data from protonsthat will collide with an energy of 14 TeV,about the same energy as a collison ofcars moving at about 2700 mph. One ofits main goals is to search for the theoret-ical Higgs boson, or as it is affectionatelyknown, “the God particle.” In the presentStandard Model of particle physics theHiggs boson accounts for a hole in thetheory, allowing for the explanation ofthe origins of the mass of the other el-ementary particles. The Higgs boson isthe only particle in the standard modelthat has yet to be observed. The predictedenergy necessary for a Higgs boson ob-servation is just outside that of the sec-ond largest particle accelerator, Fermilab

in Chicago, but well within the range at

The ATLAS detector.

the LHC. Dallapiccola suggests that withsensible data definitive answers for theHigg’s boson would be provided by theLHC rather quickly.

Another possible result of the col-lisions is that black holes will be pro-duced. But rest assured that the LHC willnot produce a planet-eating black hole,as these black holes would be micro-scopic and evaporate immediately. Dal-lapiccola points out that cosmic rays havebeen colliding with energies greater thanthose produced at the LHC for billionsof years and have not caused the endof the universe yet. If black holes arein fact produced during collisions theyshould decay by means of radiation asStephen Hawking predicted, and in theprocess produce all the particles in theStandard Model, including the Higgs bo-son. The production of black holes wouldalso support the existence of extra dimen-sions in our universe. These extra di-mensions would explain why gravity isso weak compared to the other physicalforces. The theory says that the force ofgravity as we know it is only a part ofthe full force, as much of it is dispersedin other dimensions outside our currentspace. But if we smash protons togetherat high enough energy, they could getclose enough together where the disper-sion is negligible and the full force ofgravity is perceived in our space, produc-ing a black hole. Dallapiccola says, “Ifwe don’t produce black holes it would in-validate some of the current models.” Soeither way, physicists are excited for theadvances that will inevitably occur as aresult of the collisions.

Like a head on car crash, the high en-

ergy collisions of protons will producea lot of “stuff” flying every which way.The ATLAS detector is designed to makesense of the “stuff” and connect it to the-ory. The detector itself is massive, heav-ier than the Eiffel Tower, and consists ofmany super precise parts. To give a senseof the precision, some specifications re-quire accuracy on the order of a micronfor distances on the scale of a footballfield. Part of what Professor Dallapic-cola does is write software to analyze thedata the detector collects. The amount ofdata is overwhelming, so it is imperativethat the software can recognize the essen-tial parts of the data, like the evidence ofblack holes and of the Higgs boson.

The ATLAS team has been opera-tional and taking cosmic ray data sinceSeptember 2008, and high-energy colli-sions are scheduled to resume in sum-mer 2009. The experiments were delayedwhen on September 19, 2008 an inci-dent in the LHC tunnel, far from ATLASand the other experiments, did substan-tial damage to portions of the LHC. Afaulty electrical connection between twomagnets lead to a massive leak of liquidhelium and delays in the LHC’s sched-ule. Professor Dallapiccola spoke on thetime table of his groups works and pre-dicted that it would be around the fallof 2010 before the LHC yielded sensiblehigh quality data with results.

The technical difficulties will not bethe only obstacle in the way of the AT-LAS team as over 2500 physicists worktogether on the project. Collaborationwill be essential to the success of theproject as it is one of the largest col-laborative efforts ever attempted in thephysics world. The ATLAS team is likea virtual United Nations with physicistscoming from 37 different countries and139 different universities. The groupis involved in what Dallapiccola calls a“friendly competition” with one of theother detector experiments called CMS(Compact Muon Solenoid). The two de-tectors are designed to complement eachother and to provide further corrobora-tion of findings.



THE LARGE HADRON COLLIDER

Atom SmasherUMass professors help in search for Higgs Boson, dark matter, and extra dimensions

Chris MacLellan and Robert Deegan, AmherstHalfway across the world, near the

shores of Lake Geneva, lies the LargeHadron Collider (LHC), the largest par-ticle accelerator ever built. This massivemachine is buried dozens of meters be-low the ground and forms a ring of cir-cumference 17 miles that straddles theborder between Switzerland and France.

The LHC project is part of an interna-tional effort led by The European Centerfor Nuclear Research (CERN) to unlockthe secrets of one of the most mystify-ing areas of science, particle physics. Itis hoped that a better understanding ofthe fundamental particles that make upthe universe will be achieved by collid-ing beams of protons that circulate in op-posite directions through the massive cir-cular tunnels.

The protons in the LHC will collideat 99.999999% of the speed of light ata rate of 600 million collisions per sec-ond. Each of the collisions is recorded by

one of the LHC’s six particle detectors.However because of the overwhelmingamount of data this would create, onlyone out of every two million collisions isactually recorded. Despite this reduction,the data recorded by each of the major ex-periments at the LHC will be able to fillaround 100,000 dual layer DVDs everyyear.

Although this massive undertakingmay seem to be only taking place in Eu-rope, it turns out that the project is a col-laboration of over 10,000 scientists andengineers representing over 100 coun-tries, three of which are faculty right hereat UMass.

Professors Stephane Willocq, CarloDalipicolla, and Benjamin Brau are allcurrently concentrating their research ef-forts on one of the two largest particle de-tectors at the LHC: ATLAS. The Umassprofessors are also joined by three post-doctoral research associates and one gradstudent. Over 2500 physicists work on

this massive detector which is about 150feet long, 80 feet high, and weighs about7,000 tons. ATLAS is made up of fourmajor components: the inner tracker andmagnet system which both measure thespeed of charged particles; the calorime-ter, which measures the energy of parti-cles; and the muon spectrometer whichidentifies and measures muons.

This immensely large and complexmachine is maintained by hierarchy ofphysicists that work in highly special-ized groups. For example, the group atUMass concentrates solely on the muonspectrometer portion of the detector. Al-though group members can be separatedby thousands of miles, they work to-gether using the internet. Face to face in-teraction is still needed, as the membersof the UMass team travel to Switzerlanda few times a year to attend large meet-ings.

Many may wonder what the LHCis meant to discover. The most publi-



cized potential discovery is a new parti-cle called the Higgs Boson, which is sup-posed to be responsible for giving parti-cles their mass. In fact, the Higgs Bosonis so important to particle physics that itsdiscovery would easily warrant a NobelPrize.

Everything we know about particlephysics is encapsulated in a theory calledthe Standard Model which is used to ex-plain the nature of all subatomic parti-cles. To date, theory has outpaced experi-ment as the Standard Model can only pre-dict the existence of the Higgs Boson, butwe have not been able to detect it due totechnical limitation. Specifically no otherparticle detector can produce collisionswith enough energy to create the HiggsBoson. If it exists the LHC will have theability to create the Higgs Boson.

The collisions at the LHC may alsobe able to identify and describe dark mat-ter, which has never been directly ob-served. This mysterious form of matteralong with its counterpart, dark energy,are predicted to make up over 90% of theuniverse. The high energies of the LHCmay also make it possible to confirm theexistence of extra dimensions. These ex-tra dimensions are predicted by and nec-essary for string theory, which has the po-

tential to reconcile quantum mechanicsand general relativity, which are two ma-jor branches of physics that don’t alwaysagree.

The six detectors that are attachedto the LHC are the measuring devicesneeded to make these discoveries. Whenthe proton beams collide at such high en-ergies they either combine or decay intoentirely new particles. These new parti-cles continue to decay until they form aset of stable particles. There are manydifferent combinations of these particledecays which are known as decay modes.Each of the major parts of the detectorsworks to find the identity, trajectory, andspeed of the particles.

Computer programs then work back-ward to determine each particular decaymode. For example, since the Higgs Bo-son will exist for such a short time beforedecaying, it can’t be directly detected.Therefore its existence will be proved byidentifying decay modes that are consis-tent with having originated from a HiggsBoson. Because the probability of pro-ducing a Higgs Boson is very small thephysiscists at the LHC will analyze mas-sive amounts of collisions in hopes offinding these characteristic decay modes.Further analysis of this data may confirm

or deny the existence of the dark matterand extra dimensions.

One of the possible consequencesof these extra dimensions could be theformation of microscopic black holes.This possibility has raised a considerableamount of concern about the safety ofthe LHC and has led to multiple law-suits hoping to halt its operation. How-ever these black holes would most likelydecay instantaneously and thus pose noactual threat to mankind. If they wereany real danger we would have alreadyfelt their effects since cosmic rays thatconstantly bombard our atmosphere cre-ate similar conditions to those in the LHCand would produce these black holes.

Despite the excitement generated inthe science community by this massiveexperiment, nobody will be able to makegroundbreaking discoveries in the nearfuture. Although the first beams were cir-culated through the collider on Septem-ber 10th, overheating in superconductingmagnets caused a serious malfunction inthe collider. The cause for the problemhas since been diagnosed and is currentlybeing fixed. Because of this malfunctionwe will likely have to wait until the sum-mer of 2009 before the collider will beworking again.

The ATLAS Collider while under construction



GRAVITATIONAL WAVE ASTRONOMY

Making Waves at UMassDr. Laura Cadonati brings a revolutionary perspective on the cosmos to Amherst

Laura Cadonati

Paul Hughes & Daniel Rogers, AmherstAlbert Einstein is a household name.

Most people know that E = mc2, andthat funny things happen to space andtime at speeds near that of light. A lesscommonly known prediction of relativ-ity, however, is the existence of gravita-tional waves, which have yet to be di-rectly observed. Since the cornerstoneof scientific progress is the verificationof such predictions, this is a problemfor Einstein and his theory. Fortunatelyfor him, there is LIGO (the Laser Inter-ferometer Gravitational-Wave Observa-tory), which hopes to finally detect grav-itational waves. The project is a col-laborative effort of about 500 scientistsfrom across the country. One of them,Dr. Laura Cadonati, has helped to start agravitational waves research group in theUMass Amherst Physics department.

“In high school,” admits Cadonati, “Ihated physics. I did. I was very goodat math, I loved science of all types, andI hated physics. I just didn’t understandit. When we were first exposed to it inhigh school, we didn’t have calculus.” Inher senior year, however, calculus shedsome light on physics. She also realizedthat she needed something more concretethan a degree in mathematics. “I’m notgoing to be doing calculus only, or differ-ential equations for the rest of my career.”

Dr. Cadonati went on to be trained inexperimental particle and nuclear physicsin Milan, Italy. When she came to theUnited States to undertake her graduatestudies at Princeton, she was involvedin Borexino, a project studying solarneutrinos. On moving to MIT for herpost-doctorate work in 2002, her inter-est shifted to gravitational waves and she

became involved in LIGO. “In my previ-ous work,” she said, “I was doing a lotmore hands on lab work—hardware de-sign, installation—and I wanted to... pullscience out of data, kind of the oppo-site.” When she was looking for a profes-sorship in 2005, the opportunity to starta new gravitational wave research groupwas a factor in her decision to come toUMass.

Gravitational waves are theorized tobe propagating ripples in space-time thatcause relative distances to change. Forexample, a gravitational wave passingthrough a circular section of space-timewould warp into an oval as it went by.This effect is predicted to be extremelysmall: a circle with a diameter of 27 tril-lion miles would only see a compressionof about the width of a human hair. De-tecting the small effects of these waveson a terrestrial scale raises monumentalchallenges in both engineering and dataanalysis.

“If you think about your perception ofreality, you see and you hear. We’ve got

electromagnetic waves which we’ve beenseeing, and then we’re going to be

listening using gravitational waves.”

LIGO overcomes these challenges byusing very sensitive laser interferometers.An interferometer splits an infrared laserbeam down two perpendicular tubes ofequal length; the two beams are thenreflected by mirrors at the ends of thetubes, and are recombined and directedinto a detector. If there is no distortionby a gravitational wave, then both beamsshould be “in phase”, which means thatthe peaks and troughs of the waves matchup. If a gravitational wave happens tobe passing through, however, then onetube stretches while the other contracts;the tubes are no longer of equal length,and the beams are no longer in phase.Interferometers with tube lengths on thescale of a few kilometers would only seedistortions smaller than the radius of aproton—about a billionth of the width ofa human hair.

LIGO uses one four-kilometer inter-ferometer in Louisiana, and a second in-stallation in Washington state that com-bines one four-kilometer and one two-

kilometer interferometer. This cross-country separation allows LIGO to tellwhether a signal is coherent—that is,whether both sites are detecting the samesignal from an individual source. Thishelps to distinguish gravitational wavesfrom background noise.

Major intrinsic sources of noise (thescientific equivalent of static on a radio)include stray gas particles inside the vac-uum tubes, thermal vibrations in the mir-rors and their supports, and the “shotnoise” from individual photons (smallpackets of light) slipping through to thedetector. The experiment has to dealwith a range of external noise sources, aswell. In the initial stages of LIGO, therewas a logging operation taking place justoutside the Louisiana installation, whichmade it practically impossible to takeuseful data during the day. “If a tree fellin the forest,” Dr. Cadonati said, “LIGOheard it.”

mirror

half-silveredmirror

lasersource

detector

mirror

Diagram of a simple interferometer

“But not anymore!” she clarified.Since the early days of the project, LIGOhas made a wide range of improvementsin vibration isolation, vacuum technol-ogy, and laser power output to drown outtroublesome shot noise. Over the last sixyears, the system’s noise reduction hasbeen upgraded to meet and even exceedthe projected design specifications. Moreimprovements are yet to come in the nextstage of LIGO’s development: new in-terferometers with ten times the sensitiv-ity of the current ones, planned to be-come operational in 2014. At present,LIGO should be able to detect gravita-tional waves emitted from two neutronstars (with a combined mass of about



three times our Sun’s) coalescing in theVirgo cluster; that’s about 60 millionlight years away. In 2014, LIGO scien-tists can expect to pick up signals froman additional 1,000 galaxies.

Dr. Cadonati’s particular role in thecollaboration is in the search for ‘burst’-type gravitational wave sources, such assupernovae (the explosive deaths of starsmuch larger than our Sun) and other suchcataclysmic astronomical events. Assuch, she also does a great deal of work—especially in the present, developmentalphase of LIGO—in tracking down un-wanted noise sources and working withthe engineers and commissioners to findways to eliminate them.

Part of what makes this search forburst signals so interesting is that so littleis known about the gravitational wavesmade by supernovae. “Based on the cur-rent understanding,” Cadonati explained,“we could see a supernova in our galaxy;it’s not clear we could see supernovaein Andromeda,” our closest neighboringgalaxy at two and a half million light

years’ distance. “But that’s based on sim-ulations based on ‘axis-symmetric’ evo-lution,” meaning they assume that thesupernova distorts space-time equally inall directions. “But if it’s not axis-symmetric we could see farther out.”This means that combining LIGO’s datawith more traditional astronomical obser-vation, we may be able to learn muchmore about what goes on in very massivestars as they die.

“If a tree fell in the forest, LIGO heardit... but not anymore!”

LIGO scientists hope not only to lookfurther out into space, but also fartherback in time. In 1964, radio astronomersdiscovered the cosmic microwave back-ground radiation: the leftover electro-magnetic energy from the big bang. IfLIGO can achieve great enough sensitiv-ity, it may be possible to measure the cos-mic gravitational background radiation.As Dr. Cadonati explains it, the grav-itational force decoupled from the other

forces within a tiny fraction of a secondafter the big bang; by contrast, it took al-most another half a million years beforethe universe became transparent to elec-tromagnetic radiation—the radiation as-tronomers currently rely on for observa-tions. This means that gravitational waveastronomy may give us a much earlierpicture of the structure of our universe,answering many questions about why ittook on the shape it has today.

All in all, LIGO promises to open“a new window on the universe” by pro-viding a completely new way of observ-ing cosmic events. “If you think aboutyour perception of reality,” says Cado-nati, “you see and you hear. They arevery different. One is pressure waves,the other is electromagnetic waves. Andthe two combined gives you a better per-ception of the reality around you. Thisis kind of the same: we’ve got electro-magnetic waves which we’ve been see-ing, and then we’re going to be listeningusing gravitational waves... it’s really anew way to explore the universe.”

The LIGO facility in Livingston, Louisiana



NEUTRINO PHYSICS

Searching for GhostsThe Borexino Solar Neutrino Detector

An inside view of the Borexino detector

Keith Fratus and Amanda Lund, AmherstHow do you catch a practically massless, nearly light-

speed, charge-free particle that flies straight through the earthand across entire galaxies without interacting with a singlething? Physicists have been trying to accomplish this tricky featsince the elusive neutrino was first hypothesized in 1930, build-ing cunningly elaborate detection facilities to trap the “ghostparticle.”

The Borexino solar neutrino detector is a large sphericaltank located in a tunnel below Gran Sasso mountain in theAbruzzo region of Italy. It is one of the most recent of theseexperiments, having been collecting data for only a year andhalf. Borexino is the first detector to measure in real-time thelow energy neutrinos that make up 99% of the solar neutrinosemitted from the Sun, which are produced in large numbers asa result of nuclear fusion.

Laura Cadonati, an assistant professor of physics at the Uni-versity of Massachusetts Amherst, has been with Borexino forits entire lifetime, since she was an undergraduate in Milan. Inan interview last week she spoke about her research on Borex-ino and what to expect from the experiment. “I think the goodresults will come in a year, that’s my guess,” she said.

The detector tracks down neutrinos using 300 tons of liquidscintillator (a material that emits light when struck by a parti-cle) contained in a thin, spherical nylon vessel that could holdabout four SUVs. A layer of buffer fluid and a layer of wateralso encompass the sphere and help reduce background noise,and the entire detector is enclosed in a steel water tank. Whenneutrinos interact with electrons in the scintillator, a set of 2000light detectors surrounding the vessel record the flashes of lightthey produce.

But what exactly is a neutrino, and what is the point ofstudying a particle that seems so indifferent to the rest of theuniverse?

Nuclear fusion inside the sun produces huge quantities ofneutrinos, which because of their low interaction rate are rela-tively unchanged by the time they reach Earth. Studying theseneutrinos could provide us with an inside look at the Sun andhow it works.

It turns out that to the best of our knowledge, the world aswe know it can be described in terms of a few fundamental par-

ticles, grouped together into three “families” in something re-ferred to as the Standard Model. The first family contains fourparticles: two quarks (which can combine to form protons andneutrons, which in turn make up atomic nuclei), the electron,and the neutrino.

The next two families of particles are almost exactly thesame as the first; in fact, everything about them is identicalexcept for their mass. Each family is composed of heavier par-ticles than the one before it. Neutrinos from different familiesare said to be different “flavors.”

Each of the particles in the standard model interacts withthe others through one or more of the four fundamental forces.Gravity (which affects all matter, and actually even light it-self to a small extent) and electromagnetism (which mediatesthe interactions between particles with electric charge) are themost familiar of these. The remaining two forces are namedthe “strong” and “weak” forces–the strong force helps hold to-gether the nuclei of atoms, while the weak force is responsiblefor radioactive decay.

What is challenging about neutrino detection is that the onlyforces that neutrinos are capable of interacting with are gravityand the weak force. Contradictory to our everyday experience,on the scale of fundamental physics, gravity is so weak thatit has almost no effect on particle interactions. While the weakforce is many times stronger than gravity, compared to the elec-tromagnetic and strong forces it is still quite feeble. Saying aforce is “weak” implies that interactions involving that forcehappen very rarely; so neutrinos interact with other particlesincredibly infrequently, and as a result studying them becomesa very complicated process, requiring the use of large under-ground detectors.

The Sun gives scientists a free source of neutrinos to study,which helps them refine their theories about the standard modeland its various components. As the Standard Model is currentlythe best theory we have for explaining the world, studying so-lar neutrinos is a very real way to expand our knowledge of thefundamental laws of the universe.

When Austrian physicist Wolfgang Pauli first postulated theexistence of the neutrino, he feared he had cooked up a particlethat could never be detected. Every second, 100 billion neutri-nos born from nuclear reactions in the Sun pass through yourthumbnail, but they interact with matter so rarely you wouldnever know it.

The first successful detection of solar neutrinos was in 1960at the Homestake mine in South Dakota, where Ray Davis, achemist at the Brookhaven National Laboratory, developed aninnovative detector using a 100,000 gallon underground tankfilled with cleaning fluid. Despite the trillions of neutrinos con-stantly bombarding the detector, Homestake was predicted todetect only 10 each week.

In fact, Davis found even fewer. Though the experimentsucceeded in observing the “ghost particle,” it detected onlya third of the anticipated number, generating a new problem:where were the missing solar neutrinos? The answer lay inneutrino oscillations, a theory proposed by Italian-born atomicphysicist Bruno Pontecorvo within a year of Homestake’s ini-



tial results but not proven for another 30.Homestake could only trap electron neutrinos (from the first

family of the Standard Model), letting the other two flavorssneak through unrecognized. Following Homestake’s neutrinodeficiency, it was proposed that on their journey from the Sunto Earth, neutrinos could oscillate, or change flavor; so Davis’missing neutrinos had not vanished, but switched from electronto a flavor that was not observable. That is, a neutrino from onefamily of matter had turned into a neutrino from another familyof matter.

The Sudbury Neutrino Observatory (SNO), another detec-tor located in the deepest part of Canada’s Creighton mine,verified neutrino oscillation in 2001 with measurements of allneutrino flavors relatively close to the predicted solar neutrinolevel.

The neutrino’s ability to change flavor had enormous im-plications for physics. The existence of neutrino oscillationsproves that neutrinos have mass. Though intuitively it mightseem like a particle that makes up matter should have mass it-self, this was an open question; it could have been possible forneutrinos to make up ordinary matter, interact with gravity, andbe massless. Because there are so many neutrinos flying aroundthe universe, how much mass they have has a huge impact onhow much “stuff” is in the universe–which affects everythingfrom particle physics to astronomy.

It has also been theorized that the sister particles of theneutrinos–the electron, muon, and tau–should be able to trans-form into each other. However, the predicted rate at which thisshould happen is remarkably low, and to this day has never beenobserved (the odds that a muon will decay into an electron areabout the same as the odds you have of winning the Mega Mil-lions five years in a row).

Because muons and taus are much heavier than electrons,they generally decay into lighter particles. This tendency ofmuons and taus to decay, combined with the fact that trans-formations amongst the sister particles are unimaginably rare,means that we see very many electrons and very few taus andmuons.

Deep in a mine or under a mountain may sound like astrange place to search for particles coming from the Sun, butthe layers of rock and earth actually insulate the detector fromdistracting background radiation and cosmogenic events, whichcannot penetrate as much material as the slippery neutrinos. Tominimize this noise, almost all neutrino detectors are locatedin mines, under the ocean, or beneath mountain ranges (likeBorexino).

Almost a mile of rock shields the tunnel containing theBorexino detector from cosmic rays and neutrons, creating arelatively low-background environment. This is especially im-portant for this particular experiment, as the low energy of theneutrinos it is trying to detect imposes strict requirements onthe amount of radioactivity around the detector.

“The trick was, can we really have purity at this level–it wasnever measured or achieved before,” Cadonati said.

Before Borexino was built, Cadonati worked on a mini-Borexino prototype called the Counting Test Facility (CTF), adetector to measure the impurity in the scintillator and provideinsight on the best design for Borexino.

“There was no proof that this could be done on a ton scale,and so that’s why the counting test facility was required. You

start from a smaller scale, somethings that’s cheaper...you cantry things out to prove that you can actually reach a biggergoal.”

The CTF was one meter in radius, had only water for shield-ing, and had a thicker membrane than Borexino, so it was notan ideal design for finding neutrinos.

“It’s a different set of problems,” said Cadonati. ”It’s reallydesigned to measure the possible radiopurity of the scintillatoritself.”

As an undergraduate working on the CTF, Cadonati studiedthe water purification system; from this her research morphedinto analyzing radon diffusion and radon propagation in the wa-ter. She was there when the CTF was filled and began collectingdata, and remembers the excitement seeing it come to life.

“We had this bottle of champagne, we smacked it againstthe tank,” she said. “When we got the first data, for me it wasthis new thing of realizing you learn in books...and then if youlook for events with given cuts you actually find what the bookssay. It was like, “Oh wow, that’s real!”

After the CTF came online, Cadonati took a short breakfrom Borexino, working temporary employment, teaching inhigh school, and applying to grad school. In 1996 she cameto the U.S. to start graduate school at Princeton. She contin-ued working for Borexino intermittently until 2002, when theexperiment experienced a major setback.

“[There] was this spill of liquid scintillator. That was in thesummer of 2002,” said Cadonati. “The hope was to come out ata comparable time to SNO, Kamland. The leak put in a setbackof 3 or 4 years.”

The delay from the accident was long not just because ofproblems with the detector, but due to the political, legal, andsecurity issues that it sparked. “That accident was like a Pan-dora Box,” Cadonati said.

Other experiments have faced hurdles too–in 2001, a sparkand a chain reaction caused most of the light detectors in theJapanese neutrino detector Super-Kamiokande to explode. For-tunately, Super-K had already turned out its important results;Borexino was not as lucky with its own glitch, as it had noteven become live when the spill halted progress.

However, thanks to support from funding agencies and ded-ication from its members, Borexino got back on track and be-gan taking data in May 2007. The first results came out afteronly 100 days, in the ballpark of what was expected.

“The real job to do now is to reduce the systematic [error],”said Cadonati. “We need to get rid of the noise and track thestability of the detector...the lower energy threshold, that’s alsogoing to be an important result once we understand the sys-tematic.” The detector’s ability to look at low energies meansit could be useful for other things such as searching for geo-physical neutrinos (produced in radioactive decay), for whichits location is particularly good.

Cadonati believes Borexino can produce significant datawithin two years. But what will become of Borexino after that?“There are now talks to morph the neutrino detector into a newkind of experiment,” she said. “You could do beta decay mea-surements with it, or now there are some talks to make it into adark matter experiment.”

So after more than a decade, it seems that Borexino is justreaching the peak of its career–and that its future may even holdmore than solar neutrinos.



STATISTICAL PHYSICS

A New Definition of ComplexityJust how much can we know?

Professor Machta shows off some of his work

Matthew Drake, AmherstSince the beginning of the universe, many systems that can

be analyzed have had an ever-increasing amount of complexity.From biology to astronomy, the world as we know it constantlychanges, generating more and more complex systems. What doI mean by “complex?” Professor Jon Machta of the Universityof Massachusetts Amherst says that it’s related to what we cansimulate. “The evolution of life is often considered the mostcomplex systems. Even using a computer with millions of pro-cessors, I believe it’d still take hundreds of millions of years tosimulate the evolution of life on Earth.”

Machta has been researching how to define the concept ofcomplexity and its implications for some time now. The mostimportant implication that comes from Machta’s definition ofcomplexity is that it will limit which problems we can reason-ably understand through computer simulations. Of course com-puter simulations become very useful for many physics prob-lems, but some systems can be too complex for a computer tohandle. A definition of complexity, based around computation,can create limits on what would be appropriate to use simula-tions for and also guide physicists on how to research variousphysical systems.

Although Machta shies away from fully defining complex-ity itself, he argues that we can make some requirements forcomplexity that will fit our intuition. “The emergence of com-plexity requires a long history,” argues Machta. It seems likea natural requirement if we think that the passage of time willmake a system more complex. However, the common concep-tion of time is insufficient. Instead, we want to think about timein terms of depth, or how many computational steps a simula-tion on a parallel computer would need. A parallel computeris a specific type of computer with multiple processing units,meaning it can do multiple mathematical operations in one step.

Time gives trouble to complexity if we think about sys-tems that seem comparably complex and occur over differenttime periods. Think about comparing a hurricane and a spi-ral galaxy. Both of these systems are self-organizing rotatingstructures with about the same difficulty in terms of mathemat-

ics, but it takes millions of years longer to make a galaxy than ahurricane. The amount of time that a system takes going from“point a” to “point b” is unnecessary during simulation of asystem, so it would make sense that these are both similarlycomplex systems. If we use the common conception of time,a galaxy is millions of times more complex than the hurricane.As an example, the depth of a galaxy would be the number ofsteps between a beginning where stardust is floating around andan end where the galaxy has formed.

Knowing that computation is a more effective measure, it isimportant to simulate systems appropriately. Since we’re usinga parallel computer, we can make it have as many processingunits as we want it to have. We can do as many mathematicaloperations at one time as we have processors, so we want toknow how many parts our system has, then we can allow ourcomputer to have a number of processors proportional to num-ber of parts. Essentially, we want to have enough processors toreach the next state of the system in one step. “Just because asystem is big and has many parts doesn’t mean it’s complex”says Machta. “It’s the evolution of the system that causes asystem to have depth.”

The actual method that we use to simulate the system is alsovery important. We wouldn’t want a system to seem any morecomplex than it needs to be, so it is important that we use thefastest method possible. Not only fast, but the method must beaccurate and understandable by defining the properties that wewant to know about the system. Without an accurate and un-derstandable answer, the simulation becomes useless anyway.The best possible method can take us from the beginning of thesystem to the end of the system as fast as possible while alsoaccurately defining properties we need to know along the way.

It can be interesting to think about systems which are notcomplex according to this definition. A system with a high en-tropy might seem like an ideal candidate for a complex system,but that is not the case. Entropy is often used as a measure forchaos and randomness of a system. Picture a gas at a constanthigh temperature. We can think of it as a large number of par-ticles moving around very fast and in random directions. Therewould be little to no order to the system and so it would havea lot of entropy, but it would actually be a very low complex-ity system. Statistical Physicists have been able to solve thisproblem for a long time. In fact, Albert Einstein won the 1921Nobel Prize in part because of a 1905 paper that he wrote de-scribing exactly this system, proving that it is simple enough tosimulate properly without a computer.

So what is complexity exactly? Well, there is no accepteddefinition of complexity yet, so Justice Potter Stewart’s famousdefinition of pornography may be applicable here, “I shall nottoday attempt to define the kinds of material I understand to beembraced with that shorthand description...But I know it whenI see it.” However, Professor Machta’s concept of a complexsystem having substantial depth may well prove to be a veryhelpful guide on how to simulate complex systems appropri-ately.



Hurricane Andrew (left) and the spiral galaxy M51 (right). Courtesy of NOAA and NASA, respectively

CHEMISTRY

UMass makes big discoveries with small scienceNanotechnology in food science

Christopher Emma, AmherstIf someone were to throw out the

word nanotechnology, it would instantlyevoke futuristic themes of technologybased self-improvement. Things liketiny robots, invisible to the human eye,swimming around in our bodies, act-ing as things like white blood cells andartery de-cloggers. Professor D. Ju-lian McClements, an associate profes-sor studying food physio-chemistry atUMass Amherst, would be the first todebunk that thought process. Throughan interview with Professor McClements,we are able to shed some light on the con-cept of food-based nanotechnology, theprogress made so far, and how it couldcome to affect the everyday American.

Research teams are currently work-ing on issues pertaining to microencap-sulation, emulsion, and ultrasonic sens-ing. The end goal of all of this re-search is to find better ways of distribut-ing medicines and nutrients into the hu-man body. McClements’ first point of in-terest was that of microencapsulation; inessence the storing of medicine and nutri-ents into capsules made to be taken orallyand the ways in which they are processedin the body on a molecular level.

Functional agents such as vitaminsand antioxidants tend to interact poorlywith water solubility, food matrices, etc.As such, it is pertinent to develop newdelivery systems with which to make theagents more soluble and stable, with theend goal of maximizing the intake of saidagents. In order to do this, the team at

Umass has focused its research on differ-ent food-grade ingredients as substitutesfor traditional means of distribution.

Proteins and lipids, or fat, have beenthe center of attention thus far. Foods inthe aqueous, or water soluble, phase havethese proteins and lipids, both biopoly-mers, which can make them viscous andmore rigid. He also applies this thoughtprocess to Micellar Technology. Oneof the many things found inside a cellare vesicles. These small blobs of wa-ter act as the cells way of transportingdi erent substances to different parts ofthe cell, much like a capsule is usedto transport vitamins or medicine to thebody. Even smaller than vesicles aremicelles, which are currently being re-searched to absorb and move non-polarsin water. Theoretically, the application ofthis could be used to control such thingsas flavor release. The research teamat Umass is currently working on ab-sorption rates and solubility for micelles.Through the studying of molecular inter-action of biopolymers and their solubilityin the human body, McClements hopesto improve the distribution methods ofmedicine and nutrients.

One of McClements’ less relevant butslightly more interesting projects is thatof food emulsion. Emulsion is the mix-ture of unmixable liquids such as milk,butter, ice cream, salad dressing, etc.Again his research tends to culminate ona molecular level and focuses on how un-mixable ingredients, such as oil and wa-ter, blend in things like salad dressing.

Research is currently being done on whatmachines can be used to create this fauxbonding and how it can be kept stable.The purpose of all of this is to one daybe able to better blend these currentlyresistant components. McClements cur-rently does consultation work for out-side research groups on the subject, whilethe university research team is dele-gated to microencapsulation and anotherinteresting research subject, UltrasonicSensing. While ultrasonic sensing maysound complex, it actually is quite self-explanatory.

Through the firing of sound wavesinto various types of food, scientists areable to sense the di erent components thatmake up said food. Though such a con-cept seems futuristic, it actually has beendeveloped and is being applied by scien-tists today. The purpose of such sensingis to create a fast, non-invasive detectorfor various types of food.

McClements and his team have usedthis process on things such as dairy basedcreamers. It allows them to test thefat percentage of the mixture as well asfind the most e cient mixture (which canbe applied to the microencapsulation re-search). They are also currently workingon a hand held sensor for use with live an-imals, most notably fish. This would al-low them to describe the full compositionof a live fish, fat content included, with-out ever causing harm to the fish. Whilethe principal research on this has beencompleted, the technology needs com-mercial development.



BIOPHYSICS

When Physics and Biology CollideUMass Professor Plans to Improve Cell Imaging

Photo taken by Ross using TIRF.

Morgan-Elise Cervo, AmherstImagine if you had the ability to give an MRI or PET scan

to the smallest component of our bodies; cells. Being able totake a closer look at our bodies cells could greatly improve ourunderstanding of disease prevention and even bring us closerto find a cure for HIV. Recent addition to the UMass Physicsdepartment, Jennifer Ross, is working on a new method of mi-croscopic imaging that bring us a great deal closer to under-standing the inner workings of cells.

Ross, who completed her postdoctoral work at UPenn inPhiladelphia, has brought a a great opportunity for expan-sion in the newly developing biophysics department at UMassAmherst. She began her postdoctoral work studying the move-ment of dynein, a motor protein that can be found in eucary-otic cells (cells found in animals). Dynein’s job is to transportcargo necessary for cells to function. Dynein is able to transportthings by converting chemical energy into mechanical energyand moving along the cell microtubules towards the negativeend. Kinesin, a more studied and well understood motor pro-tein, moves towards the positive end of the microtubules. Mi-crotubules are important to study because they are involved inmany of the processes that take place within cells. For example,certain drugs taken by cancer patients are used for stabilizingGDP-bound tubulin in microtubules.

Until recently, Biologists believed that both kinesin, anddynein only had the ability to move in one direction along themicrotubule. Therefore if they hit an obstruction, such as a mi-crotubule associated proteins or MAP, while carrying the cellcargo they become either be permanently stuck in one place orsimply fall of the microtubule. However, Ross created a newtechnique for observing the movement of kinesin and dyneinby placing two microtubules in such a way that they are crossedone over the other. This setup creates a known obstruction forher to observe how dynein and kinesin react to MAPs. By run-ning experiments in which the progress of dynein is tracked

along the microtubule, Ross observed that dynein had a greatersuccess rate for passing the obstruction than kinesin. She dis-covered that when dynein bumps into MAPs it is able to eitherside step or back step to get around the MAP. Kinesin how-ever, continues to bump into the MAP and either remains thereforever or falls off of the microtubule.

Why is it useful to have biophysicists studying cells as op-posed to biologists who have a far greater knowledge or cellsand other living things? Ross describes biologist study of cellsas a“top down” method. “[Biologists] are studying and mak-ing observations of an entire cell,” says Ross. Ross and otherbiophysicists tend to have a ”bottom up” approach. For exam-ple with microtubules, Ross’s team of researchers go throughstrenuous laboratory procedures in order to eliminate parts ofthe cell that they are not interested in looking at. In otherwords, she studies specific parts of the cell in specific condi-tions. Ross’ hope is that biologists and physicists will be ableto meet somewhere in the middle and produce an effective un-derstanding of what is happening inside cells.

Physicists who concentrate in biological studies can also beuseful in improving the means for how we can look at cells.More recently Ross has been moving in the direction of creat-ing a new method for looking at cells on microscopic levels.Currently the best available method for observation of cells forbiologist and biophysicists is Total Internal Reflection Flores-cence (TIRF) microscopy, which won the Nobel Prize in 1986.TIRF imaging allows Ross to be able to view movement of mi-crotubules in multiple directions. TIRF microscopy works byusing an evanescent wave to excited an illuminate fluorophoresbound to a specimen. The evanescent wave is generate by hav-ing the incident light (usually a laser) pass through of series oflenses to achieve total internal reflection.

In the picture the squiggle on the right side is the micro-tubule (which on average have a diameter of only twenty-fivenanometers). The brighter areas represent movement towardsand away from the microscope. Microscopic imaging withoutTIRF would lack these lighter areas because only side to sidemovement (wiggling) can be detected.

Ross is working with others on a new quantum mechani-cal form of microscopic imaging. The idea is to fire a smallnumber of photons at a cell sample. Statistically, some pho-tons will collide and interact with the nucleus of various atoms.When this happens the energy of the photon is converted and anelectron and positron (similar to an electron but with a positivecharge) are formed. Eventually, when an electron and positioncome in close enough proximity of one another they annihilateeach other and two photons are formed (radiation!). Radiationcan easily be detected by various equipment in a process sim-ilar to“position emission tomography”, PET, which is used inhospital everywhere for medical imaging.

Imaging of cells is extremely important because a betterunderstanding of cells could help us learn how cells spread dis-ease. Once we know more about how disease spreads it will beeasier to develop appropriate treatments. The future of scienceand medicine lies greatly in the integration of biological andphysical sciences.



BIOPHYSICS

Single Molecule BiophysicsExploring the Biological Universe of Proteins

Alex Kiriakopoulos, MassachusettsMost people when they hear of pro-

tein think of their favorite rib eye steak orchicken dish. At the University of Mas-sachusetts Amherst, Professor Lori Gold-ner thinks of only scientific experimentsthat can be carried out on them. Pro-fessor Goldner is a recent faculty addi-tion to the physics department and comesfrom the National Insitute of Standardsand Technology. She brings with her herwork on single molecule measurementsusing biophysics. Biophysics is “usingthe tools of physics and the models ofphysics to try to understand biologicalsystems” said Lori Goldner. “I use op-tical microscopy techniques and physicaltechinques to pull on very small objects,to watch them move, and maybe pokethem”

Proteins, from Greek πρωτειoςmeaning “primary”, are large organicmolecules made of amino acids. They arethe building blocks life, whose presentfunctions make life possibly and can bedescribed as the chief actors within thecell. They have an ability to bind othermolecules very specifically and tightlylike a lock and key mechanism.

What first drew Professor Goldnerto this burgeoning field was “the ideaabout being able to mess and see sin-gle molecules. I got interested in it firstthrough optical tweezers. And the ideathat you could manipulate the little ob-jects with light really intrigued me. Iwas looking for a way to make moreof a connection with important applica-tions. When your doing this you find themolecules you work on have some impli-cation in disease or in health or ecology;they have interesting behaviors that actu-ally affect people in real life” said Gold-ner.

Professor Goldner’s and other’s workin this field have wide implication for allus. Anytime we go to the drug store forallergy medications or a diabetic receives

insulin they are taking advantage of whatbiophysics has accomplished or has aidedin the development in. Biophysics canhelp to synthezie proteins like insulin andto develop drugs which will bind withproteins. One of the proteins Profes-sor Goldner’s research has had her comeacross was ”the HIV binding site whichis a drug target and if you can understandhow it functions better you might be ableto design better drugs to inhibit the HIVvirus” said Professor Goldner.

With the aide of a confocal micro-scope Goldner explores the shapes andgeometry of these molecules. “Structureis very important because it often informsor determines function; so alot of whatI do is looking at structure or structuralchanges over time that you could not seeusing x ray crystallography or magneticresonance.” Professor Goldner said.

Professor Goldner’s confocal micro-scope is designed specially to study theseminuscule molecules, and explains that“if you want to see a single molecule youhave to block out all of the light from therest of the world because the moleculedoes not emit alot of light typically atmost million photons per second. So howdo you keep the rest of the light out?The trick is that you build a microscopethat can only see into a very small vol-ume about a femtoliter and that wouldbe a confocal microscope. All the lightis focused into that tiny little area andthat area is again imaged onto a pinholeso that any light that is not coming rightfrom that tiny volume is rejected.”

The fundamental idea behind thisseemingly complex scheme is basicallya simple “trick... we dont shine light oneverything, we don’t get light back fromeverything, we use really good detectorsand really good optics so you don’t loseany photons” Professor Goldner said.

Her objectives for her confocal mi-croscope and single molecule experi-ments will be “to develop, test and use

new techniques that will allow to [what]could not see before, study things youcouldn’t study before and understandthings we couldn’t understand.”

She explains that in her work “Thetechniques that I use are good for look-ing for single moleuculex that are sticky,go boom, and fall apart. So the sortsof techniques that I am developing willhopefully allow for people to look atmolecules... that you couldn’t other-wise look at because around surfaces theydenature, molecular complexes that fallapart, and things that are out of equilib-rium.”

“There are alot of reactions in naturewhere a protein meets a piece of RNAor two proteins come together and somebig confirmational change happens to oneof the proteins which is irreversible ormakes something else happen; these tran-sient interactions out of equilibrium dy-namics are not observable in an easy wayusing single molecule techniques but us-ing the techniques I am developing theymight be”.

Professor Goldner’s work represen-tents a relatively new field of science thatis currently burgeoning. Single moleculetechniques have only been usable andpopular since the 1990s. In past research“measurements were done in bulk whichmeans you make certain assumptions...by looking at the average”. But as Gold-ner explains, “if you have a bimodal dis-tribution... you miss the fact that the dis-tribution is meaningful.” The benefitsof these techinques for single moleculemeasurement that, Professor Goldner’swork is focused on, is as Goldner ex-plains “you are measuring the propertyof each molecule individually. The reallybig advantage to single molecule mea-surements you get the details of the distri-bution and you can to watch the dynam-ics. You can’t do that any other way”.



PHYSICAL CHEMISTRY

Single Molecule SpectroscopyLooking at a Molecule with a Flashlight

Each bright circle is light from a single fluorescent molecule

Tim Mortsolf, Amherst

Almost everything we learn about our environment comesfrom how electromagnetic radiation interacts with matter.Spectroscopy is the branch of science that describes how lightinteracts with atoms and chemical moleulcules. Astronomershave been using the theories of spectroscopy for almost onehundred years to determine the chemical makeup of stars. Per-haps one of the most important discoveries of quantum me-chanics was that atoms emit only certain wavelengths of lightand when we measure these wavelengths, we can use themas a sort of atomic fingerprint that tells us exactly what ele-ment or chemical compound they came from. For example, as-tronomers recently analyzed the light measured from a planetin another solar system and were able to deduce the presence ofcarbon dioxide from its signature in the light spectrum. How-ever, instead of looking at the light coming from large objectslocated thousands of light-years distant, single molecule spec-troscopy utilizes optics that focus light from close molecularobjects — close enough that we can record the light emitted bya single molecule.

When I think about a chemistry laboratory, several imagescome to mind, most of them having to do with the synthesis ofnew chemical compounds. However, when you enter Dr. MikeBarnes chemistry lab and take a mental inventory of the sur-roundings, you would very likely think that you are in a physicslab instead. Dr. Barnes field is physical chemistry — a branchof chemistry that uses applied physics to study chemical com-pounds. The benches in the back of his lab are not coveredwith the bottles and glassware used by synthetic chemists, butinstead are shock absorbent counters, suspended by nitrogengas, that are adorned with lasers, beam splitters, and very sen-sitive digital cameras. His specialty as a physical chemist isa recently unfolding area of research called ”single moleculespectroscopy”. So what does that mean? Dr. Barnes simple

explanation is that the researchers on his team are ”chemicalphotographers”.

The experiments they perform take pictures of the lighttransmitted by individual chemical molecules and individualnanostructure composite species. These are not pictures in aconventional sense because the photographs we look at havecontextual clues that tell us a lot about the scene. For example,when you look at a picture of a famous person in a magazineyou can almost always tell who is in the picture and maybeeven where and when the picture was taken. But individualmolecules cannot be imaged in this way. The information hisresearchers rely on is not in the picture, but in any informationthey can glean from individual photons (particles of light) thatthese molecules transmit.

Prior to single molecule spectroscopy, spectroscopic mea-surements could only be made on a large group, or ensemble,of related molecules; they could not easily be performed on in-dividual molecules. These molecules are similar but not identi-cal even though they have the same chemical structure. Differ-ences between molecules arise from physical properties suchas their orientation in space or energies of motion. An analogyto this is a device that measures the flow of electrical currentthrough a wire. The current that a device records arises fromthe flow of a large number of electrons, but our device also can-not tell us anything about the behavior of any individual elec-tron. With the advent of single molecule spectroscopy, it hasbecame possible to measure some physical properties of indi-vidual molecules, but there are still many significant obstaclesthat restrict what molecules we can look at and just what infor-mation we can learn. According to Dr. Barnes, the ability toanalyze the behavior of individual molecules has only becomepractical during the last 20 years. Prior to this we were able tomeasure average quantities, but could not easily measure spec-troscopic information for single molecules.

Dr. Mike Barnes in his Lab



Flasks of quantum dots that emit light at different wavelengths. Photo courtesy of nanolabweb.com

One of the compunds that Dr. Barnes group is interested inis a family of molecules called ”quantum dots”. When askedwhat a quantum dot is, Dr. Barnes replied ”A quantum dot isoften referred to as an artificial atom. It is the synthetic ana-logue of a sodium atom.” The sodium atom has two signaturewavelegnths that emit light in the visible light spectrum andsodium is used in light bulbs for places like factories and park-ing lots. The advantages our using a quantum dot is that unlikeatoms such as sodium which has energy levels fixed by nature,synthetic chemists can engineer a quantum dots to absorb andemit light at a desired color.

The benefits of the this research have a broad range of ap-plications. Dr. Barnes noted that some discoveries have al-ready yielded benefits in biochemistry with applications forDNA sequencing and proteomics. The Nobel prize for chem-istry in 2008 was awarded for the development of green flu-orescent protein for use in biochemical research. Green fluo-rescent protein, or GFP, is attached by biological scientists tospecific moleucles in a cell. Since this protein is fluorescent,any light emitted at its signature wavelength informs the sci-entist about the presence of the molecule that was tagged withGFP. Dr Barnes also sees future applications for the submini-turization of nanoscale optoelectronic devices that could haveapplications to better display technology and optical comput-

ing. Physical chemistry research labs also train future scientistsfor work in industry. During his four years at the University ofMassachusetts in Amherst, Dr. Barnes has had four graduatestudents, two post-doctoral research assistants, and several un-dergraduate students assist in his research.

When I asked where he thinks this research could lead intofor the next 50 years, his outlook was very optimistic. WhenDr. Barnes worked as a post-doctoral researcher, many of thetools that are used today such as single photon counting devicesthat can count individual photons with precise timing informa-tion were not available. The amount of light we have been ableto collect from a molecule has increased tremendously fromjust a few photons per molecule to more than one million; thisis the key driver that has advanced the field of single moleculespectroscopy. One key limitation that exists today is the rangeof wavelengths has been limited to a narrow spectral range of400-700 nanometers, which corresponds to the visible range oflight for humans. In the coming decades, maybe even sooner,he thinks that we will be able to make single molecule measure-ments at higher frequencies in the X-ray spectrum. This wouldbe an important achievement, because these higher frequenciespermit better resolution maps to be constructed for the structureof single molecules.



A Bose-Einstein condensate produced at Amherst College

LOW TEMPERATURE PHYSICS

What’s the MatterResearchers are using a new form of matter, made of ultra cold gases, to open up new frontiers inphysics.

Douglas Herbert, Amherst

In the early 1920s, Satyendra Nath Bose was studying whatwas then the new idea that light came in little discrete pack-ets that we now call “quanta” or “photons”. Bose assumeda set of rules for deciding when two photons should be con-sidered either identical or different. We now call these rules“Bose statistics” or sometimes “Bose-Einstein statistics”. Ein-stein read and liked Bose’s ideas, and used his influence to helpget them published. Einstein thought that Bose’s rules mightalso apply to atoms, and he worked out a theory for how atomswould behave in a gas if these new rules were applied. Ein-stein’s equations said that there would not be much difference,except at extremely low temperatures. If the atoms were coldenough, something very unusual was supposed to happen, sounusual that he was not sure that it was correct.

Under the direction of William Mullin, the Laboratory forLow Temperature Physics at the University of Massachusettsat Amherst is among those studying such systems. In quantummechanics, particles can be represented as waves, and whenyou sufficiently cool gaseous particles “a large percentage ofthe particles [...] fall into the lowest [energy] state, and they’re

coherent in the sense of quantum mechanics [...] they all havethe same phase.” says Professor Mullin. When all the atomsfall into a single energy state, their waveforms overlap so thatthe peaks and troughs match up (creating the “phase”), and theyall behave in exactly the same way (they’re coherent).

“ In quantum mechanics we have these non commutingvariables, momentum and position, if you specify the position,you can’t know the momentum [The Heisenberg UncertaintyPrinciple].” explains Mullin. At Absolute Zero atomic motionceases, so the colder an atom gets the slower it travels, and thebetter we know the velocity of the atom. However, the closerwe are to knowing the velocity of the atom, the more uncertainwe are of exactly where it is; its location literally gets fuzzy.

When you collect a lot of atoms in the same ultra low en-ergy state, all of those fuzzy atoms lie on top of each otherand merge together, any one atom could be in the position ofevery other atom at any given time. All of the atoms actuallyoccupy the same space; they coalesce into a single blob calleda Bose-Einstein condensate (BEC), and they all behave in asynchronized fashion (some researchers refer to a BEC as a gi-ant “super atom). The first BEC was created in 1995 by Carl



Wieman, Eric Cornell and their colleagues at the University ofColorado at Boulder, and is an entirely new state of matter; thefifth known state of matter after gas, liquid, solid, and plasma.

An atom’s energy is quantized, which is to say that its en-ergy is limited to a series of discrete values called energy lev-els. The key to forming a BEC is to cool gaseous atoms tovery low temperatures. This is done inside a vacuum cham-ber because any random air molecules would bump the gaseousatoms, transferring kinetic energy (energy of motion), and heat-ing the atoms.

Laser cooling makes use of the force exerted by repeatedphoton impacts to slow the atoms down and push them into themiddle of the chamber. Photons are extremely light comparedto atoms, but if you fire a large enough stream of ping pongballs at a bowling ball you can move the bowling ball. Lasercooling works the same way, battering atoms with photons. Thelasers are aimed from six different directions to keep any atomsfrom wandering off.

A magnetic field is used to form a trap to contain the slowmoving atoms; this is done by allowing a small area within themagnetic field to have no field. The result is a magnetic fieldshaped like a bowl which holds the slowest (coolest) atoms.Evaporative cooling makes use of specially tuned radio waveswhich pass over the magnetic trap and kick the most energetic(hottest) molecules away as they jump above the rim of the“bowl”. Comparable to blowing steam off of a cup of coffeethis leaves the cooler atoms behind.

As the remaining atoms reach very low temperatures, theyslot themselves into the few remaining energy levels above ab-solute zero. Within a billionth of a degree above absolute zero,the BEC forms. “One of the founders of this whole ultra coldstuff was Steve Chu, who was one of the inventors of laser cool-ing, was made energy secretary (by Barack Obama).” says Pro-fessor Mullin.

In an experiment at MIT in 1997, Wolfgang Ketterle andMIT’s Atomic Physics Group showed that a laser like beamcould be formed form a BEC of sodium atoms. This beam issimilar to a laser beam, but it uses matter rather than photons,a “matter laser” as Mullin puts it. This atom beam can be con-trolled by two other lasers, which push the matter and aim thebeam, “if you have a coherent beam you can make it interfere”.

Mullin and his team are conducting research in interferom-etry with BECs. An interferometer is an instrument that usesinterference phenomena between waves to determine wave-lengths, wave velocities, small distances, and thicknesses. Anatomic interferometer would be 100 times more sensitive thana laser interferometer. Since atoms in a BEC move much more

slowly than photons of light, they can be more precisely con-trolled. An atomic interferometer could be used for submarinenavigation systems (GPS cannot pinpoint locations underwa-ter), auto-pilot systems for airplanes, or for countless other ap-plications in which extremely precise displacement measure-ments are necessary.

A plan has been developed for the International Space Sta-tion (ISS) to be equipped with a laser-cooled cesium atomicclock. Cesium atoms move more slowly in the microgravityof space, which would allow for a more precise measurementof the second, 20 times better than anything achieved on earth.This type of clock on the ISS would make the more accuratesecond measurement available on earth, as well as for clockingGPS satellites and testing gravitational theory.

Quantum computing is another promising way to use ultracold atoms. “What we’re thinking about now is using these in-terferometers for making “qbits” for quantum computers” saysMullin. In classical computing, data is represented and storedas “bits”, the binary digits 1 and 0. In quantum computing,an atom can act as a quantum bit, or a qubit, with it’s internalsub-state called “spin” (imagine a marble spinning on a table)functioning as the 0 or 1 of classical computing. It can alsoexist as 0 and 1 simultaneously.

That last state of simultaneity is due to something calledquantum interference, which allows an atom to exist in twospin states at the same time, another oddity of quantum me-chanics. If a classical computer contains three registers (stor-age spaces), it can only store one of eight binary numbers ata time, 000 through 111. A quantum computer could store alleight numbers in a superposition state at the same time, also -in that superposition state - operations can be performed on alleight numbers using a single computational step.

If both computers performed the same operation (usingthree registers), the classical computer would require eightcomputations, while the quantum computer would require onlyone. The classical computer would require a (literally) expo-nential increase in either time or memory in order to matchthe computational power of the quantum computer. If quantumcomputers can be realized, the computing world as we know itwill be revolutionized.

It will be years before BECs see much use outside the labo-ratory, in the meantime, “Just studying Bose condensates them-selves is kind of fun.” says Mullin. Perhaps current researchwill serve to aid the in the application of the laws of quantumphysics to the world of technology. “There are so many peoplethat make condensates now that I’m sure something will comeout of it.” notes Mullin.



SOFT CONDENSED MATTER

Thin Films, Geometry, and 3-D PrintersA doily illustrates an exciting phenomenon

Collin Lally, AmherstCondensed matter physics deals with

things that, so says Professor ChristianSantangelo, “you can hold in your hand.”He can, indeed, hold an analogue of hislatest research project in the palm of hishand; a crocheted doily is not, after all,very big. This doily is not particularlyunusual, but it does illustrate an interest-ing phenomenon: the number of stitchesis not constant along its radius (Prof.Santangelo refers to this as the doily be-ing “radially inhomogeneous”), leadingto a ruffled (or more technically, buckled)shape. There is more “stuff” (yarn) on theouter edge of the doily than in the middle,which causes it to crumple slightly.

The question related to this phe-nomenon is whether the radial inhomo-geneity can be controlled in such a man-ner that the doily buckles into a pre-defined shape. Basically, what Prof. San-tangelo is working on is how to deter-mine when this is possible, and (when itis possible) how to make the doily bucklein the desired manner. While this is inter-esting from a mathematical point of view(it’s an open problem in geometry) thereis also a relevant connection to soft con-densed matter physics.

The phenomenon in question is foundin the case of polymer thin films, undercertain circumstances. Before I say what,exactly, these circumstances are, I shoulddefine what a polymer thin film is. I’ll dothis in two parts.

A polymer is a material composed oflarge molecules (the building blocks ofeveryday matter) that is, in turn, com-posed of some repeating internal struc-ture. The most common example ofa polymer would be plastic, but thereare many other examples as well. Theyhave a specific property that renders themvery useful: the molecules in a polymerstick together very well, forming chains.These chains are the defining character-istic of a polymer, and can give such amaterial great strength on a bulk scale,or flexibility, stickiness (adhesivity), orother useful properties.

A thin film is exactly what itsounds like: a very thin (nearly two-dimensional) layer of the material inquestion. Imagine a slick of oil floatingon top of a pool of water and you have agood picture of a thin film.

Now back to the physics at hand. Ihad mentioned buckling; it turns out thatthis phenomenon happens in thin filmswhen they are made of certain types ofpolymers, and exposed to some agent thatcauses this material to swell. Supposeyou have a polymer thin-film disk, justa round, flat piece of material made of anappropriate polymer. Now add a chemi-cal agent, in reaction to which the poly-mer expands in the plane. So, the diskswells horizontally, but not vertically, inan inhomogeneous manner. Since thedisk wants to stay in one piece, it buck-les, rather than fragment.

How the disk swells can be controlledthrough the application of the “swellingagent” (the chemical introduced above).But, as in the case of the doily, can thedisk be made to buckle into some finalshape? Sometimes, not always, it can.

If the shape of the buckled disk canbe easily and reliably controlled, it mightmean the ready commercial availabilityof so-called 3-D printers. A 3-D printeris not a printer in the traditional sense of acomputer peripheral that transfers ink ortoner onto a piece of paper. Rather, it is adevice for fabricating three-dimensionalobjects. Usually used in computer-aidedmanufacturing for building product pro-totypes, current 3-D printers “print” anobject by building it up, one layer of ma-terial at a time. This technology is expen-sive and relatively slow.

But with the application of Prof. San-tangelo’s research, 3-D printers could bebrought to the masses. The combinationof an inexpensive base polymer and theuse of existing ink-jet technology to ap-ply the swelling agent could easily makea 3-D printer affordable for the averageperson. Why someone would need such adevice is not evident now, but that is al-most certainly because the technology isnot currently accessible on a large scale.Take the example of the personal com-puter: before its commercial advent, no-one knew the impact or use it would have.

However, one thing can be saidfor certain: sufficiently advanced 3-Dprinting technology coupled with user-friendly computer-aided design softwarecould be the real-world equivalent ofthe Star Trek replicator (minus its food-production capability; no-one wouldwant to eat plastic!). One could simply

design a widget, and, with the press of abutton, have it built immediately.

But that is quite enough futurology.An advanced 3-D printer based on thecontrolled buckling of a polymer sub-strate is not anywhere close to reality.Happily, it is not the potential applica-tion that drives Prof. Santangelo’s inter-est in this problem. Prof. Santangelo is atheoretical physicist. He deals with pre-dictions of new phenomena and explana-tions of known phenomena. His interestin physics is not necessarily motivated bydreams of his research leading directlyto a science fiction future. Rather, it ishis enduring fascination with mathemat-ics that has lead him to this problem ofbuckling thin films.

Initially, Prof. Santangelo went tograduate school at the University of Cali-fornia Santa Barbara with the intention ofbecoming a string theorist. When he ar-rived and went to the string theory semi-nars, however, he found it not to be to hisliking. “The seminars were not very in-teresting [to me],” he says. He had beendrawn to string theory by his strong in-terest in geometry and topology, so helooked for another field in which thesetools were heavily used. What he foundwas soft condensed matter theory. Softcondensed matter is essentially that stuff

that is not hard condensed matter; thefield deals with things like liquid crystalsor polymers (but not exclusively) ratherthan with solids and similar hard things.Happily for Prof. Santangelo, UCSB isrenowned for their condensed matter the-ory programs, and geometry is a goodtool for soft condensed matter theory; heeasily found research that meshed withhis mathematical interests.

This was only the beginning: thisfascination with arcane mathematics hassince become a driving principle of hisresearch. The theme, as it were, of hisoverall research program is driven by thequestion “how do geometry and physicsinteract?” In this way, Prof. Santangelofrequently tackles problems that mightseem more common in a mathematics de-partment, the doily problem among them.They all, however, have some direct rela-tion to the physical world.

“There are deep principles hidden inmundane things,” he says. The doilyproves it.


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