In a previous post, I had described how we use photons to map the material in a detector. Here I will mention a complementary way using particles such protons, pions, neutrons, etc. (these particles are collectively known as hadrons).

Hadrons interact with matter differently than photons; the latter interact purely via the electromagnetic force, whereas the former do so mainly via the strong force. The likelihood of hadrons interacting in matter is quantified by a property called the “interaction length; more about this later.

Just as a photon can convert when it travels through material, a hadron can interact and produce what we call a “secondary interaction”. In a way, this is the same idea as when the two proton beams at the LHC collide. Let’s say I have a proton that was created in the primary collision. As it travels out through the detector, it can interact with another proton in a nucleus in, say, the silicon detector. At times, this secondary interaction will have two or more charged particles emerging from it; at other times, one may have only one charged particle coming, e.g., one pion and two neutrons, or, the initial proton may just suffer a small deflection, etc.

If the secondary interaction has two or more charged particles coming out of it, we can use our software to check if the daughter particles come from the same spatial point. If they do, we have a vertex describing the location of the secondary interaction. The spatial distribution of these secondary vertices will give us a map of the material in the detector. I am currently working on this project and preliminary results are very promising.

As I wrote in the previous post, the likelihood of photon conversions in a material can be quantified by a property called “radiation length”; this depends on the intrinsic properties of the material such as atomic number, i.e., number of protons in the atom, and also atomic mass, which is proportional to the number of protons and neutrons in the atom. Since photons interact via the electromagnetic force, “radiation length” has to depend on the charge of the nucleus, i.e., the atomic number. In contrast, the strong force makes no distinction between a proton and a neutron, thus, “interaction length” has no dependence on the atomic number, but only on the atomic mass. The latter length also has some dependence on the energy of the incident particle. Although, we can derive from one from the other, it can be tricky. Since every material in our simulation package has to be described with a radiation and an interaction length, material maps made using photons and hadrons serve as very good checks on our understanding.

– Vivek Jain, Indiana University

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Being a member of ATLAS, I’ve spent a fair amount of time in the ATLAS control room. I realized when I was talking with some of my colleagues who work on accelerator operations that I’ve never seen the actual LHC control room.
Yesterday, while at lunch, I asked if my friend if she would give me a tour (since you need  proper access to get in), so I thought I’d share the experience.

Picture taken from Proceedings of ICALEPCS07,Knoxville,Tennessee

The main CERN control room is not just the for LHC, it is the heart and brain of all the accelerators at CERN. It’s brand new facility, completed in 2006 in preparation for the start of the LHC. I had taken an accelerator physics course before, but needless to say, it’s quite an experience to witness it first hand.
Our little proton friends have quite a journey before they make it into our interaction point and get smashed into bits. Here’s how it goes:
There are 4 accelerators that are used to inject the initial beam into the LHC. The magic begins in “Linac 2″ (Linac – Linear Accelerator) which creates the protons and then injects them into the Proton Synchrotron Booster (PSB, or “Booster”). This accelerator provides beam to the ISOLDE (Isotope Separator On-Line) experiment. (There are many physics experiments at CERN other than the ones located on the LHC ring). Every 1.2 seconds a decision is made as to where to send the beam. When ISOLDE doesn’t need it, the Booster can inject into the Proton Synchrotron (PS) where is gets accelerated up to 25 GeV. The PS accelerated it’s first protons in 1959 and continues to work to this day. There is a physics complex called the East Area which utilizes this beam when it’s not being sent elsewhere. Once the protons are up to energy, they are injected into the Super Proton Synchrotron (SPS). Off of this ring, CNGS, a fixed target experiment which sends neutrinos off to Gran Sasso, Italy, and the North Area physics facility are located.
Now for the big one. Once the protons are accelerated to 450 GeV, they can then be injected into the main LHC ring. It will take several injections of the SPS to fill the LHC (~2000) which initially will take around 20 min. All of these injections will have to be in phase, and steered properly because losing the beam at this energy isn’t an option.

The CERN Accelerator Complex

This is my rudimentary understanding of an amazingly complex system, that sometimes as a particle physicist I don’t appreciate enough. So hats off to the accelerator physicists, the next time you run into one buy him or her a drink.

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I was recently underground on a tour of the LHCb detector. It was the last one of the four main LHC detectors I hadn’t seen in person. I also got to see the old DELPHI detector which is still down there. I will post some pictures soon.
On my way down, I took a picture of one of the infamous iris scanners mentioned in Angels and Demons. In the book, someone at CERN is murdered and their eye taken in order to get through this security feature. In reality, a dead eye cannot be used with this technology.
Everyone who visits the underground areas at CERN is fascinated by this technology. I think CERN should put one of these scanners in the visitor’s center just for tourists.

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I have returned to the San Francisco Bay Area for two weeks for a friend’s wedding.  Fortuitously, that means I can visit other friends and also see my parents — it’s nice to have things in one place!  Oh, and one other thing is here: Lawrence Berkeley National Laboratory, where my group is based, where I work when I’m not working at CERN.  Yesterday, I got up at 5 AM to make the train trip from my parents’ house to Berkeley in time for an 8 AM meeting with my advisor, and I ended up working the whole day.  Yes, I’m on vacation, but I didn’t have any friends who were free during the day, and I thought it would be useful to work with and talk to the various group members who I don’t see so much of because we work on separate continents.  I like my job; I don’t take vacations to get away from it, but because there are other things I want to do.  So, if I have a free moment, well, why not get a few things done for work?

For the Facebook crowd: I’m Seth, my page is http://blogs.uslhc.us/?author=9

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Some time ago I had a discussion originally got interested in particle physics and I traced it all back to a book I read in 7th grade, The Physics of Star Trek by Lawrence Krauss. (The book not only turned me into a physicist, but also a trekkie.)

It’s a little late to put out a summer reading list, but for those of you who are still looking around for something to tickle your particle physics fancy, here are a few other personal recommendations.

First of all, let’s start with just about anything that Richard Feynman has written. Perhaps the most enjoyable and playful volume for a general audience is his auto-biographical Surely You’re Joking, Mr. Feynman, a collection of anecdotes about his life. There isn’t much physics in this book, but you’ll see why Feynman is a hero to generation after generation of physicists and laypeople alike. If you’re looking for something with more physics intuition (accessible to ambitious high school students), check out QED, a surprisingly accurate description of the work for which Feynman was awarded the Nobel prize in physics.

To the best of my knowledge, Brian Greene’s The Elegant Universe is still one of the most successful popular introductions to theoretical physics, focusing on string theory. The NOVA documentary is also available free online. While I haven’t read it, I’ve heard that Lisa Randall’s Warped Passages is also an excellent read with more of a particle physics emphasis.

For those interested in extra dimensions (one of my current projects), I would also strongly recommend Edwin Abbott’s 19th century novel, Flatland. It’s available free online, but I’d recommend an annotated version to fill in some of the background. The book is, in some sense, a social commentary on Victorian life; but more importantly it is a remarkable lesson in how to think about higher dimensions by analogy to the two-dimensional flat land. (And it was written more than a century ago!)

These are all great popular-level books, but what about something for people who want to get their hands dirty? I remember the summer before starting college I was itching to start learning ‘real physics.’ For the autodidactically inclined, I would recommend starting with any fairly recent college physics textbook. Ugh! So dry, right? Don’t worry, I suggest skipping to the last few chapters that discuss modern physics. Most textbooks I’ve seen have some neat things to say about special relativity, quantum physics, and even the Standard Model. So to all you eager college freshmen, I suggest taking a skim through these chapters now because it’s unlikely your intro-level courses will ever get to the ‘good stuff.’

For more specific suggestions, I’ve recently found a wonderful exposition on special relativity called Very Special Relativity by Sander Bais. The book is accessible to anyone with a high-school physics background and a good grasp of algebra. It is remarkably adept at conveying a real working understanding of special relativity through illustrations. I would even recommend this book as a model of excellent pedagogy to graduate students who will be teaching courses in modern physics.

For advanced undergrads or beginning grad students who are interested in particle physics, an excellent first book in quantum field theory is Zee’s Quantum Field Theory in a Nutshell, which illuminates the concepts behind the equations with expert clarity. Don’t rush out to buy it just yet, though, as I’ve been informed that a new expanded edition is right around the corner. For those rising graduate students who want a lighter summer, get acquainted with PhD Comics… you’ll laugh now, and then realize it’s all spot-on.

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As August rolls around and most of the locals head out of town on vacation… some place sandier, sunnier, and less full of computers, I’m going to remain at my post (working hard posting ). This isn’t to say that I’m spending all my time slaving away in front of a computer. The past 3 weeks the world’s premiere cycling race was going on in my backyard. The Sunday before last some friends and I decided we were going to wake up insanely early, camp out on a mountain top, and cheer on these elite athletes participating in The Tour de France. Now before you think that professional sports are way to cool for the likes of us, I’d like to make you aware of its true geekiness. Really anyone who can appreciate aerodynamics, dry British humor, and grown men wearing polka-dots should be excited about the world of professional cycling. And this year, arguably the most famous cyclist of our time, Lance Armstrong staged his 2nd comeback (the first being after his bout with cancer) and placed an impressive third behind teammate Alberto Contador who won overall. I was lucky enough to witness these guys for a few seconds as they flew by while climbing up to the mountain top town of Verbier.

Cyclists at the Tour

Other than enjoying the Tour, I’ve been busy wrapping up and continuing to work on a couple of studies – one I’ve already blogged about (the one involving cosmic rays) and the other maybe once I’ve gotten a little farther. In a week the Department of Energy is reviewing our group, so everyone is trying to pull together their analyses to present. But, I’d be lying if I didn’t have other things on my mind. At the end of August, I return to the United States. One month to go and I’m filled with a mixture of emotions. I was supposed to come out for the first year of running: last September to this September. Unfortunately things don’t always work out as we planned. My first thought was to extend my stay, but with news that the accelerator wouldn’t start until first the summer, then September and now mid-November. I decided it was probably best to wait in New York, where my husband is, for the machine to start. Luckily, with the power of the internet, I can do most of the same work there as I can here (like blogging ), but I’m always going to feel like there’s work to do on site. I’m just very lucky that I have supportive friends, family, and colleagues.

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What hiking and mountain biking has to do with physics? Well, a lot, as it turns out! For one, try climbing 2000 feet and then tell me if you still think that gravity is a very weak force!

Aspen, Colorado is a tiny gem tucked away in the Rockies, some 200 miles from Denver. Most famous for its top-notch skiing resorts and a record number of private jets per capita, it is also a home for Aspen Center for Physics. Founded in 1962, the Center is a warm and welcoming place hosting a number of workshops and conferences in all areas of physics. Founded by physicists and for physicists, the Center offers very informal and productive atmosphere for work and collaboration with other physicists. There are about 50 people visiting the Center at any given time – usually from two or more different disciplines. The days are full of discussions, informal seminars, trips up the mountains, lunches and picnics, where new ideas are being exchanged, papers are discussed, and new collaborations formed. Want to talk about Supersymmetry? – Just cross the corridor and walk in the office of Howie Haber. Feel that four dimensions are not enough? – Cross the little meadow to an adjacent building and chat with Lisa Randall.

For the past couple of weeks I have been attending a workshop on Physics Beyond the Standard Model in Aspen, run by the leading theorists in the field. I was one of the only two experimenters invited to the workshop to offer expertise on LHC detectors and to discuss with theorists our plans for the first year of the LHC running. Michael Schmitt from Northwestern, my CMS colleague, was the other invitee.

Michael and I gave seminars for theorists about the LHC schedule and our preparations to exciting discoveries the new energy frontier is expected to offer. We also had many informal discussions on various new theoretical ideas and possible ways of testing them experimentally. Some of these ideas would require certain modifications to the way we look at the LHC data, perhaps even changes to the trigger – the fast system that decides, which few out of millions of collisions happening every second to keep for further analysis. Many of these discussions started at the Center, where continued on hiking trips, in the Alpine meadows and aspen groves, on the shores of mountain lakes and on rocky ridges leading to them. All in all, it was very productive and a lot of fun.

I’ll write more about the hikes and the biking trips we took and the discussions we had in this blog.

On top of the Ute trail on the Aspen Mountain

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Hello, all.  This week my code finally went into production at CMS, and
it seems to work.  Hooray!  My little piece of the puzzle is some
monitoring code which tells the shifter whose job it is to guard the
pixel subdetector if a certain specific piece of the experiment is
malfunctioning in real time.  My boss, Dr. Karl Ecklund, wants me to
eventually add functionality to monitor other things, but for now, life
is good!

In other news, I've done some exploration of the surrounding area.
Lausanne and Montreux were very pretty, and I got to go hiking at a ski
resort called Les Diaberets, which was cool until it started raining, at
which point it became quite cold!  I also spent a weekend in Lyon, but
it was hot and not very interesting.

CERN in general is surrounded by beautiful scenery and filled with mad
scientists, but the infrastructure leaves something to be desired.  The
buildings look suspiciously like no architects were disturbed in their
construction, and the power grid needs some work!  Other than that
things seem cool.

More later,

Robert

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Growing in the middle of adversities!

This week has been specially difficult in different aspects of my life. There are times where everything just breaks down at once, and you wonder whats is going on! After many trials in my life, I learned that my attitude in the middle of difficult circumstances play a fundamental role. There have been times where I behaved like I didn’t care about what was happening to me, that was a big lie because internally I was suffering. Other times I have felt sorry for myself and complained why life is so hard! This attitude is understandable but It didn’t solve anything and in the end, I added my depression and self compassion to my problems, and believe me it didn’t help! Latterly, I have being trying to  assume a different attitude and recognize that I am going through difficult times, and that although it hurts, I can use those situations to learn something, to become better somehow.

Being a graduate student in high energy physics has taught me valuable things for my personal life. Things to fix, difficult programs to write (specially the ones that never compile and when they do, they don’t do what you expected ) and tons of physics concepts to learn, have been in my daily life for the last three years and a half. When something doesn’t work, I can not  just sit down and cry feeling sorry because my code doesn’t work. I have to fix it somehow. Sometimes I have to get help from other people, or just look in google read about it and try to give it another shot. In the end, when I fix the problem (that usually is just couple lines of code that I didn’t know) I realize that digging around trying to solve the problem, I learned so much about other things, that it impresses me. So, I thought why do not try to have the same attitude in my personal life? I realized, and I know that for many readers this is not something new, that difficult times are just an opportunity to grow, to challenge ourselves, to become better. There are things that probably we’ll never forget, for example when you lose someone you love, it is hard but we have to keep moving and give our best in honor of those who loved us and can’t never be again with us.

Let me finish with a phrase that I know it might be controversial, but that so far, has been very true in my life: That which doesn’t kill me, makes me stronger. -Nietzsche.

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I just returned from a vacation to the United States. It was nice to see my family and friends and get out of the CERN bubble for a little while. Of course, I got the usual questions:

• 1) Did that accelerator start yet/when will it start?
• 2) What good will it do us?

My answer to #1 was that I have no idea, hopefully in 2009.

My answer to #2 changes, probably depending on who I am talking to, or maybe just my mood. Sometimes I say something about Higgs bosons and supersymmetry (I try to avoid black holes since then I have to talk about the end-of-the-world fearmongering). Sometimes I say something about the practical benefits of past projects and that this project will also have as-yet-unknown benefits. And sometimes I say that there probably will be no direct benefit to the average person from the LHC.  Each of these is partially true, but whatever answer I give, I usually feel like I could have done better.  After being asked this question so many times over the years, I should have settled on an answer by now.

From now on, I think the answer should just be my personal reason and not have anything to do with the benefits to society overall.  For me and I think most people that work on LHC physics, I think the answer is the same: curiosity. Humans are curious, and science is the systematic way of satisfying curiosity. And I think that anyone that takes the time to learn about LHC physics would be curious to know more.  70,000 people showed up at CERN for the open day last year which makes me sure that people are curious about the things we study here.

To really answer questions about whether the LHC is worth the cost from a practical point of view, it would probably be necessary to put a dollar amount on the knowledge and other benefits we gain from it, and on the things that we then don’t do because the money is spent on the LHC. I have no idea how to do this, it probably isn’t even possible, but if you try to say whether the LHC is worth its cost any other way, you are just guessing or justifying your own beliefs.

So I think the reason to build the LHC (and to do it now as opposed to later, after we solve the problems of world hunger and disease and all the other things some people say the money would be better spent on) is that the LHC project is right now the next logical step in a series of questions and answers that started a long time ago. Scientists asked some questions and got answers through experimentation, which raised more questions, which led to more experiments, and machines got bigger and bigger until we ended up with a 17 mile long machine. Nothing else on Earth but human civilization could express its defining trait, curiosity, as the LHC. And what other point is there to civilization than coming together to collectively do what we cannot do individually, and what is more important than our defining characteristic, curiosity?

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I was recently preparing a “Physics of Angels & Demons” talk for a group of high school physics teachers who were visiting Cornell for a “Contemporary Physics for Teachers” workshop. While researching ‘natural sources of antimatter,’ I discovered a curious article about a naturally occurring potassium isotope that, some fraction of the time, decays via positron emission. The conclusion was that:

Tthe average banana (rich in potassium) produces a positron roughly once every 75 minutes.

Now any time you find something like this you have to remember that not everything on the Internet is true — not even Wikipedia, but I checked it out (e.g. the LBNL/Lunds table of isotopes) and indeed this seems to be correct!

Potassium-40 (⁴⁰K) is a naturally occurring isotope that is unstable and decays, but it has a huge half life, about a billion years. These days only a small fraction (100 parts per million) of potassium atoms are actually ⁴⁰K, but objects that are dense in potassium — such as bananas — are likely to have tens of micrograms of the stuff. If one crunches the numbers (as they do in the original article), it turns out that bananas pop out a positron every 75 minutes or so.

These positrons quickly annihilate with ambient electrons, perhaps undergoing some other interactions and releasing some photons beforehand. I’m sure the bloggers here who work on LHC calorimetry would have a better description of what happens to it! Advanced readers can read the “Passage of particles through matter” section of the PDG.

Potassium plays a necessary role in our biology, so yes, even you produce positrons every once in a while.

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News of delays are always a little disheartening but it doesn’t mean that we at CERN will be twiddling our thumbs until the machine starts. For the past year we’ve been working on preparing software and understanding the detector as best we can. Mostly people are looking at Monte Carlo Simulations. These are our best guesses as to what will or could possibly be seen at the experiments of the LHC. We use them to make predictions and set up analyses. We have models of the detector and the collisions; and combined they paint a picture of what we may find. Then once the machine turns on, we can check our predictions.

In addition to Monte Carlo Simulations, others, like me, are looking at the current data we’re getting — real data. Every second Atlas gets bombarded by cosmic ray muons.  Since we are a particle detector and cosmic rays just so happen to be particles, we can see these speedy critters as they travel through the different layers of our detector.

Muon showering process

Cosmic ray muons occur when particles (mostly protons) from outer space collide with our atmosphere. This interaction causes bunches of mesons – a meson shower – to occur. (Note: a meson is a particle comprised of a quark-antiquark pair, as opposed to a baryon which is a 3 quark particle – like a proton). The mesons, which are mostly pions (up and down quark pairs), then decay into muons and muon neutrinos (muons are like heavier electrons). Muons have a relatively long lifetime, depending on their energy and the material that they have to travel through, so usually they are what makes it to the detectors. (It’s also possible to see electrons if the muon decays inside the detector). For the most part muons travel through relatively unaffected. As the muons travel through the detector material, they ionize a small number of atoms and deposit a minimum amount of energy. Thus we call them Minimum Ionizing Particles (MIPs).

Muon going through the ATLAS detector as seen from beam pipe perspective

We see these ionized parts of the detector as a signal and can predict the energy deposition as it travels through. Then we can check to see if what we predict is what we actually measure.  Things like the detector response, how uniform the material is, and how well we know the timing can all be observed using this type of data.  Studies with cosmic rays will hopefully make the process of calibrating the detector that much easier once the LHC turns on. Until then I’ll be looking at cosmics.

(Regina Caputo, Stony Brook University)

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Are you dumb or what?

As part of my research, I have been getting involved with several projects: Tau trigger, Pixel DCS (Detector Control System) and Tau physics analysis. I have been doing what we call service work for CMS for almost 3 and a half years. It has been an interesting experience, but at the same time I was feeling frustrated for not being able to get involved with a physics analysis. Fortunately, my advisor is a very supportive person and he gave me the degree of freedom to go and start a physics analysis, he just told me go for it!

After two classes of quantum field theory and one class of particle physics, I found that I didn’t know what kind of physics that I wanted to do! So, that made me realize: man, I am freaking lost! After doing some research about what I could do in physics, I found an interesting group to work with. To make the long history short, I will just say that I will be working on the study of a Z’ decaying into an electron plus a tau. This is part of the Lepton Flavor Violation (LFV) studies that some people have been working on for some time. When I talked to the leader of the group that studies the Z’ and Neutralino decays that imply LFV, he explained the basic motivations for this study. Soon after that, I was talking to a friend about this (who by the way is very smart but a little bit proud about himself some times) and his first words were: Are you dumb or what?  I don’t think that that analysis is possible. Of course these words coming from him made me feel like an idiot! As any other human being, I have strengths and weaknesses. One of my weaknesses is that I am very sensitive (yeah, I know, I am a girl ), but one of my strengths is that I take situations that hurt me and try to learn from them to become better. The words of my friend motivated me to put my service work for couple days on the side and just spend some time to read papers about the subject. It was so cool to find out so many interesting things about this topic (LVF) and the experiments and theories that people have been working on for long time. A good example of it is the MEG experiment, a search experiment, currently being prepared at the Paul Scherrer Institute (PSI) in Switzerland, which is going to start running soon.

I have known for a long time that there are many people smarter than me, but even if I were the smartest person on earth it doesn’t give me the right to call anybody dumb. I think that there are many different types of intelligence. My dad was a very claver guy for math and science but he was not very smart emotionally and he didn’t succeed much in life. I have met people that are so talented in so many ways. I taught physics for a couple years in a high school and learned that those students that were not very good in physics or math had other talents in music, writing, painting or were natural leaders. For that reason my advice to whosoever is reading this blog is to think twice before you call somebody dumb

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Here in our department at the University of Nebraska-Lincoln, we have a “bridge program” for our incoming graduate students. Students can get a stipend to spend six weeks here during the summer reviewing their undergraduate physics, to make sure that they are ready for our graduate courses and for their qualifying exams. (Want to find out about the other perks of doing graduate work in physics at Nebraska? Contact me!) Every Friday there is lunch with a professor who leads discussion on some topic of value about graduate life.

I am going to be next week’s speaker, and I was given the topic “training your thesis adviser.” I was certainly a bit wary of taking on this topic; after all, I’ve only ever trained one thesis adviser, and although she has done well in life since working with me, I doubt it’s because of any of the training she got from me.

So what to talk about? I was thinking that I would encourage the students to understand just what actually consumes a typical adviser’s time. Unfortunately, the day-to-day work of the student is only a small part of it. Professors spent a lot of time during the school year teaching. There is plenty of administrative work, such as writing and reviewing grant proposals, managing grant money, and participating in the operation of an academic department. In particle physics, with its large collaborative efforts, there are management tasks that count as research but don’t always look like it, such as overseeing the operation of some piece of the experiment or coordinating a group that is focused on some task. We actually have very limited time for what we would honestly call “physics.” The good news is that the “physics” is the most fun part — why we went into the field to begin with — and thus the piece that we always want to get back to. Students have to find a way to break through all of this to make sure that their adviser hears them.

Another way of looking at this is that there is only so much that a student can do to train their adviser. Students ultimately have to take ownership of their own careers and be responsible for seeing themselves through. This isn’t just college++; no one is going to chase after you to make sure you are getting this or that done. A harsh attitude, you say? Perhaps, but that’s why people with PhD’s are ready to go out into the world as independent researchers.

OK, all you graduate students and former graduate students — what do you think I should tell the students next week about this topic?

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Bill Gates has released videos of Richard Feynman’s Messenger Series lectures, “The Character of Physical Law,” the rights of which he purchased from the BBC not too long ago. For those unfamiliar, Richard Feynman was one of the greatest American physicists and most well-known personalities in science. His autobiographical book, Surely You’re Joking, Mr. Feynman!, has been an inspiration to generations of particle physicists.

The lectures, originally filmed at Cornell, are black and white and are of a quality that today’s YouTube-enriched youth would scoff at. But even then, Feynman’s charisma completely transcends the medium and make the recordings a joy to watch for physicists and non-physicists alike. (The lecture were aimed at a general audience.) Even then, Microsoft has tried to enrich the lectures by making them semi-interactive experiences. A transcript of Feynman’s words appears at the bottom of the screen, to the right there is an option to view additional multimedia materials on topics Feynman mentions, and to the left there is a panel to insert notes (like YouTube comments) at different points along the lecture.

Clearly, the “Project Tuva” team at Microsoft has thought carefully about how they might improve the online lecture experience. Many people have already groaned, however, that the format requires Microsoft’s proprietary Silverlight browser plug-in. It appears for the moment that Linux users are largely at a loss for installing the plug-in. (I’ve had more that one colleague refuse to install the plug-in on principle.)

For those with a craving for more public-level Feynman videos, I would also suggest taking a look at his Auckland lectures.

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