A joint Fermilab/SLAC publication

may 2014dimensionsofparticlephysicssymmetry

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Table of contents

Application: Building artificial body parts with particle beams

Breaking: Planck reveals galactic fingerprint

Signal to background: Saving the Feynman van

Signal to background: Science fiction or science fact?

Essay: The twin paradox

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applicationMay 13, 2014

Building artificial body parts withparticle beamsCompanies are using an electron-beam 3-D printing process tomanufacture medical implants.By Glenn Roberts Jr.

Each year in the United States, millions of people receive medical implantsfrom hipjoints to heart and brain stents to spinal devices. In 2010 alone, patients in the UnitedStates received an estimated 721,000 knee replacements, 463,000 spinal fusions and454,000 hip replacements. These numbers are projected to multiply in the years ahead,and particle accelerator technologies are playing an increasing role in the manufacture ofmedical implants.

The key to a successful implant is in convincing the body that it belongs there. Evensome previously popular implant devices have had significant rates of infections andother complications that have cause them to fail, leading to removal andreplacement. Implant materialsgenerally corrosion-resistant metals, plastics andpolymerscan make a big difference in the bodys reaction.

Medical researchers seeking to make implant materials safer and more reliablesearch for ways to minimize common causes of failure while promoting bonding betweenthe implant and bone or healthy tissue and reducing potential scar tissue and clotformation.

Researchers have discovered that the microscopic composition and texture of animplanteven features just tens of atoms deepcan make a big difference in implantbiocompatibility.

3-D printing

Particle accelerators allow for the manufacture of medical devices with precise,customized features at even these small scales. Arcam, a Swedish company founded in

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1997, pioneered an electron beam melting process that functions as a 3-D printingplatform for superstrong metals.

In Arcams preprogrammed machine, a series of mirrors narrow the electron beam,which is aimed into a vacuum-sealed chamber. Powdered titanium is fed, layer by layer,into the chamber, and the electron beam melts each new layer of powder according tothe specified design. The layers quickly cool and harden after the beam moves away,leaving behind a precisely formed implant.

Creating the electron beam was the easy part of the technology, says Jim Robinson,who serves as Arcam sales director for North America. If you look at the math andphysics of what were doing, its 20 percent physics and from that part on its all math:developing the algorithms, the software, he says. The electron beam moves at a rate ofabout 10 kilometers a second, he says, so fast that it gives the illusion that there aremultiple beams moving in the build chamber.

Its possible to build more than 100 medical implants in an Arcam machine in a singlebuild cycle, which lasts about two days, Robinson says.

A growing industry

Companies around the world use this process to fabricate medical implants on a largescale. Adler Ortho Group in Italy, for example, has produced more than 30,000 cup-shaped devices used for hip and shoulder replacements since 2007, when the processwas formally certified for use in the European Union. Florida-based Exactech in 2011became the first US company to offer hip replacement components fabricated withArcams electron beam melting process.

We researched a variety of different processes, says Xavier Sarabia, Exactechsvice president of engineering for large joints. The material has to be biocompatible, firstand foremost; it has got to grip real well when its inserted; and it has to have theappropriate mechanical strength. The company also sought tiny, porous features thatencouraged bone cells to grow and bond with the material. Beam-built implants check allthose boxes and also offer the potential to develop other types of implants using thesame process, Sarabia says. A similar process was used to fabricate skull plates forwounded soldiers treated at Walter Reed Army Medical Center in Maryland.

More particle-beam technologies

In addition to 3-D printing a full implant, particle-beam processes can be tuned in avariety of ways to alter non-3-D-printed implants to create rough or polished surfaces,embed specific elements or add a coating.

Our tissues and cells are nanostructured, and we have used plasma processes andother processes to mimic nanostructures in these natural materials, says ThomasWebster, a professor and the chairman of the Department of Chemical Engineering atNortheastern University who researches the use of plasma-beam and other particle-beamtechnologies to alter the surfaces of medical implants and prosthetics. We can changethe way cells behave: We see increased tissue growth, and also for bone and forcartilageeven increased activity for brain cells in neurons. The porous features can helpstomp out bacteria, too, he says.

Although the cost of particle-beam fabrication systems is high, it can be the bestoption in specialized cases, he says.

Massachusetts-based Exogenesis offers systems that accelerate clusters of argongas atoms before pummeling them into a material, changing surface features at a depth

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between 1 and 10 nanometers. The technology was spun out of similar particle-beamprocesses used to change the electrical properties of silicon wafers for the semiconductorindustry, and can be used with a wide range of materials, including polymers that havebecome widely used in spinal implants, for example.

What were finding here is that the modification of surfaces by these charged particlebeams results in all kinds of very useful, functional changes in those surfaces, saysAllen Kirkpatrick, Exogenesis technical director.

A common goal of all of these implant technologies is to minimize inflammation,rejection and failure while improving surgical outcomes, extending lives, improvingmobility and reducing pain. Research and industry interest in new implant technologiesappears to be on the upswing, Webster says.

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breakingMay 12, 2014

Planck reveals galactic fingerprintThe Planck mission released a first glimpse of data that, later thisyear, will test BICEP2s discovery of gravitational waves.By Kathryn Jepsen

One of the most anticipated experimental results this year is scheduled to come from theEuropean Space Agencys Planck missionand theyve released a teaser of what itmight look like.

The Planck mission was designed to study the early universe by measuring theCosmic Microwave Background, or CMB, a low-frequency hum of energy leftover fromthe big bang. In doing so, it has also measured several other kinds of radiation, includingthe heat released by dust in our galaxy.

Planck scientists are studying how much of this local radiation is polarized, somethingthat occurs when the dust becomes aligned along a magnetic field. If the dust emitsenough polarized radiation, it makes it difficult to measure the polarization of the muchfainter CMB.

Scientists are searching for a certain pattern in the CMB, called B-mode polarization,which could tell them about how the universe first formed.

Its so fundamental, says Jan Tauber, ESA project scientist for Planck. Weretrying to understand our universe and how it began. Its amazing to think we can evendare to make this kind of model.

Seeing B-mode polarization would serve as supporting evidence for the existence ofprimordial gravitational waves, ripples generated in the rapid expansion of the universethat initiated the big bang.

Theorists first posited the idea of cosmic inflation in the late 1970s, but until this Marchexperimentalists had no evidence to support it. All of that changed when scientists on theBICEP2 experiment declared that they had seen a clear signal of B-mode polarization in

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the CMBa landmark discovery, if it proves to be true.

Although a handful of experiments are now investigating or preparing to investigatethe CMB, the next one to have a say on the matter is likely to be Planck, which haspromised new results by October.

On May 7, Planck released a map showing the polarization of the heat emitted byinterstellar dust.

Space-based Planck has a view of the entire sky, but the South Pole-based BICEP2detector focuses on just one region. In the image Planck released, that region is leftblank.

In this map we are only showing the regions with the most intense radiation, Taubersays. Part of the sky is so dominated by this polarized radiation from our galaxy that wecould never see the CMB through it. But a good fraction can be cleaned well enough thatwe will be able to use our data to measure the polarized CMB.

Anyone with money on the March result hopes that Planck scientists will see whatBICEP2 saw: a clear portion of the sky with a fairly unobstructed view of the polarizedCMB. Anyone betting against it expects Planck to see something else: a mask of dustradiation, or a CMB signal too weak for the BICEP2 result to be correct.

If the strength of the CMB signal is as high as BICEP2 says it is, then we should beable to see it as well, Tauber says.

The completed parts of the Planck map form a beautiful, swirling fingerprint of ourgalaxy. Were still waiting to find out what lies underneath.

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signal to backgroundMay 08, 2014

Saving the Feynman vanA team of Richard Feynmans friends and fans banded together torestore the Nobel laureates most famous vehicle.By Kathryn Jepsen

The game I play is a very interesting one, says Nobel Laureate Richard Feynman in alow-resolution video posted to YouTube. Its imagination in a tight straitjacket.

Feynman is describing his job as a theoretical physicist: to lay out what humanityknows about how the world works, and to search the spaces in between for what wemight have missed.

The video shows more than Feynman's way with words. It shows his approachability.One of the greatest minds that particle physics has ever known stands barefoot, lecturingin a distinct Queens, New York, accent for an audience lounging casually on the floor atthe new-age Esalen Institute in Big Sur, California.

In a way, Feynman remains approachable to this day for all of the snippets of hispersonality left behind in books, letters and recordings of formal and informal lectures andinterviews.

Recently, a more concrete bit of Feynman history came out of retirement: A smallteam has brought back to life the so-called Feynman van.

One camper, special order

In 1975, Feynman and his wife, Gweneth Howarth, bought a Dodge Tradesman Maxivanand had it painted with Feynman diagrams, symbols Feynman had invented to expresscomplicated particle interactions through simple lines and loops.

It might seem arrogant to drive around in a van covered in reminders of ones ownintellectual prowess. But Feynman's daughter, Michelle, thinks the decorationsrepresented something else: a love of physics.

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My dad was pretty low-key about himself, she says. I think decorating the van wasmore to celebrate the diagrams than to celebrate himself.

Michelle's parents put a lot of thought into the design of the vehicle, which theyprimarily used for camping, Michelle says. It was outfitted with a small hammock forMichelle to use in case the family of four needed to sleep inside during inclementweather.

I dont think that they had ever done anything like that with a car purchase before,Michelle says. It was always: Go to the dealer and find somethingit doesnt reallymatter what color it isand youll have it for a million years.

The Feynman family took the van to Canada, Mexico and dozens of US campsites inbetween, often traveling with a couple of other families, often leaving the paved road forthe unknown.

Michelle began driving the van to school after she turned 16.

I thought it was kind of embarrassing, she says. But at a certain point I kind of gotover it. If you want to drive at that age, youll drive anything.

After Michelles first couple of years in college, one of her fathers friends, filmproducer Ralph LeightonFeynmans drumming partner in another famous fuzzyYouTube clipbought the van and put it into storage, where it began to rust and fade.

Saving the Feynman van

When video game designer Seamus Blackley, known as the father of the Xbox, got aholdof the van in 2012, it was just about too late, Blackley says.

Blackley has a history with particle physics. He was in his early 20s, working on hisPhD thesis at Tufts University and Fermi National Accelerator Laboratory, when he sawhis plans for the future disintegrate with the defunding of the planned SuperconductingSuper Collider.

I found out on CNN, he says.

He changed course and wound up taking a job working on some of the first computergames with 3D graphics. He designed the physics of the game environments, keepingthings from going into other things. He has helped shape the world of video games in avariety of different roles since.

Game design takes the same type of thinking Feynman described in his talk at theEsalen Institute, Blackley says. A designer must creatively solve problems withoutbreaking the rules that keep the environment realisticand then you have to have a lot ofintuition about how to make it fun.

In 2005, Blackley moved to Pasadena, California, just miles from where Leighton waskeeping Feynmans van. Oblivious to his proximity to the famous camper, Blackleynonetheless began to make a hobby of restoring classic Italian cars.

It was fellow Pasadena resident Michael Shermer, founder of the Skeptics Society,who told him about the van in 2012. Blackley knew right away that he had to help save it.

The universe is telling me Ive gotta do this, he says.

With the help of Leighton and Shermer, along with a donation from Feynman fan and

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world-class designer Edward Tufte, Blackley registered the van as a historic vehicle andbrought it to his preferred restoration specialists in Los Angeles.

The vans Feynman diagrams, which were painted poorly in the first place, turned outto be too degraded for restoration. So a pinstriper re-painted them, taking care toreplicate the quality of the original work.

It looks like this crappy job again, Blackley says with a smile. You see the brushmarks and everything.

After the restoration, Blackley prepared to ship the van across the country for aFeynman-themed exhibit by Tufte, held at Fermilab.

Keeping the Feynman spirit alive

The test of whether the specialists had stayed true to the original came when Blackleyinvited Michelle to come see the van before its next big trip. She came with her 11- and13-year-old children.

It didnt look brand new, Michelle says, but it was as if it had been rewound 30 years,back to the days when her father was still in the drivers seat. She told Blackley and herkids about the times her father slept on the floor below her hammock.

As a father now, you appreciate what that means, says Blackley, who has an11-year-old son.

A camping van incongruously covered in physics notations seems to be a fittingsymbol for a man who couldnt seem to help thinking about particle physics, Michellesays.

I think it was impossible for him to turn it off, she says. I remember in the car therewas a Kleenex box, and the back of it had been used for equations. Every little piece ofpaper and every waking moment was fair game.

Richard Feynman died of cancer in 1988 at the age of 69. But projects like the vanrestoration keep his memory alive, Michelle says.

He wouldve been an amazing grandfather, and he never had the opportunity, shesays. So Im thrilled that there are so many people around who want to share his spiritand his life so my kids can get a sense of who he is.

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signal to backgroundMay 09, 2014

Science fiction or science fact?In a new class at Duke University, professors from different realmsexplore the intersection of literature and physics.By Sarah Charley

Duke University professor Mark Kruse grew up reading science fiction, but his fascinationwith dystopian futures and quantum jumping waned once he started studying particlephysics.

I think reality is always more bizarre than anything we can come up with, Krusesays. Even gifted authors and writers can't imagine how crazy reality is beyond ourcurrent understanding. Real science gives us greater surprises by taking ourunderstanding even further.

But when he was asked to co-advise a Duke graduate student whose dissertationspanned both the literature and physics departments, Kruse decided to give sciencefiction a second look. He teamed up with Duke literary professor and science fictionspecialist Katherine Hayles to design a class that is the first of its kind at theuniversityone that explores the intersection of science fiction and science fact.

Hayles and Kruse originally structured the class to play to their separate realms ofexpertise. Hayles discussed the literary elements of science fiction stories and theirsocial, political and philosophical implications, while Kruse, who is a member of theATLAS experiment at the Large Hadron Collider, examined and evaluated their scientificaccuracy. But as the class progressed, these roles started to blur.

What actually happened is we started to discuss some of the ideas that are pushingthe very frontier at which Mark is working, Hayles says. At some points, Mark had toadmit that he didnt know the answer, which led into some very interesting discussions.

John Un, a literature major at Duke, took the class because he has always beenfascinated with quantum mechanics. He says learning about scientific research made himthink critically about how he approaches the humanities.

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From a literary perspective, I am inclined to take the position there is alwayssubjectivity in everything, Un says. But Kruses explanations of the scientific methodmade him rethink his approach to evaluating fiction.

What am I basing my points on? he says. Is it just theory and jargon, or can Iground my arguments in evidence?

Stefan Cafaro, an engineering major at Duke, was drawn to the class because he hadspent a summer working with Kruse on a project to upgrade the ATLAS detector. For him,the best part of it was being able to branch out from the typical engineering track whileremaining within the realm of the sciences.

If you take just pure engineering classes, you miss out on developing important skillslike critical reading, discussion and presentation, Cafaro says. Especially as anengineer, you will be doing that sort of thing throughout your entire career. If you donthave any social or verbal skills, it is going to hurt you.

Kruse and Hayles were both impressed with the performance of their students andtheir willingness to step outside their comfort zones.

We had amazing questions from the humanities students that really probed thescientific concepts we were discussing, Kruse says. I was really impressed that theywere taking the science so seriously.

For their final projects, the students wrote short science fiction stories based on thescientific concepts discussed in class. These stories explore topics like quantummechanics, black holes, the Large Hadron Collider and the Higgs field. You can read theirwork on the class website.

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essayMay 07, 2014

The twin paradoxFermilab physicist Don Lincoln explains a well-known thoughtexperiment examining the consequences of special relativity.By Don Lincoln, Fermi National Accelerator Laboratory

Time waits for no man goes the saying, and it appears to be true. Inexorably themoments of our lives tick away until we have none left and slip into the darkness.However, as painful as that truth is, we have some comfort in the fact that time marcheson equally for all of uspauper and prince. Time plays no favorites.

Einstein turned this comforting truism on its head in 1905 when he published histheory of special relativity. In one of the most nonintuitive consequences of his theory,time does not march at the same pace for us allit depends on a persons velocity. Slow-moving objects age more quickly than their speedy brethren.

But how can that be, if the question of who is moving is a matter of opinion?

If you are standing on a train platform and a train whizzes by, you would say that aperson on the train is moving. On the other hand, a person sitting on the train would saythat he is stationary and that you are moving.

This longstanding question about special relativity is called the twin paradox. Supposeone in a set of twins sets off in a spaceship, travels to a distant star and then returns. Onboth legs of the trip, he accelerates to high velocity and then coasts for most of thejourney. If the passage of time depends on velocity, the twin who stays on Earth will haveexperienced one duration, while the traveling twin will have experienced another, slowerduration. The spacefaring twin will return to Earth younger than his homebody brother.

But wait, says the traveling twin, according to my definition, I was just sitting thereon my stationary spaceship while the Earth zoomed away from me and then zoomedback. By all rights, the Earth twin should be younger!

The solution to this seeming paradox has to do with the idea of a reference frame,

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which is central to special relativity. Reference frame is just a fancy term that meansthe world according to me, putting each person at the center of his or her universe. Allinertial observersthose who dont experience any accelerationwill agree that thehomebody never changed his reference frame. He just sat there. Similarly, all observerswill agree that the traveler lived in two reference frames, one moving away from Earthand one returning. Any third observer coasting through space will see that thehomebodys velocity doesnt change while the travelers velocity does.

The law of relativity takes the travelers two reference frames into account. Thus theso-called paradox isnt really a paradox. While the question of who is moving is a matterof opinion, the question of who has experienced two reference frames is not.

Some readers, probably including some readers who hold doctorates in physics, willclaim that the difference between the two twins is that one of the two has experienced anacceleration. (After all, thats how he slowed down and reversed direction.) However, therelativistic equations dont include that acceleration phase; they include just the coastingtime at high velocity. For the professional (or the brave), I work out the predictions ofrelativity. That one twin inhabits two frames is the only thing that matters.

The twin paradox is one of those mind-bending questions you encounter as you firstbegin to explore the predictions of relativity, but dont be fooled: It really isnt a paradoxat all. Keep that in mind as you explore other explanations that may resonate withyouthe well-known ones posted by physicist John Baez, a video by Neil deGrasseTyson, the idea of acceleration, or my own description here of one twin being in oneframe.

Embracing the twin paradox is an important first step as you dip your toe into thenonintuitive world of special relativity. If you dig a little deeper (and show a littledetermination), hopefully youll begin to be more comfortable that Einstein really wasright.

A version of this article was first published in Fermilab Today.You can follow DonLincoln on Facebook.

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