Monday, December 30, 2013

Highlights Of The Year

APS Physics lists the highlights of the year from papers published in the APS family of journals. I'm glad to say that I mentioned many of them on this blog when they first appeared.


Q&A With John Pendry

This is a quick question and answer with John Pendry, the person responsible for many of the physics behind metamaterials. I can totally understand why he gets tired of having being repeatedly asked about the "invisibility cloak".



Monday, December 23, 2013

More Update On Feynman Lectures Online

I've been posting updates on the availability of the infamous Feynman Lectures online. Mike Gottlieb has posted a new update on Vol. 2 at Physics Forums.

I have just posted FLP Volume II at The Feynman Lectures Website and at it's speedy Caltech mirror. This more or less completes the online edition of the book, though there are still some improvements to be made that I will be working on as time allows. For example: in Volume II you will notice under the title of many chapters (linked) recommendations for review of chapters or sections in Volumes I or II, references to other books and papers, and helpful reminders such as, "In this chapter c=1." Though this kind of supplementary information was never present in Volume I, it is present in (the printed and PDF editions of) Volume III but is currently missing from the HTML edition, and I intend to add it. I also plan to improve the tables, and the typography of the text and mathematics in Volume I, and to improve figure and table placements throughout all volumes.

In addition to posting Volume II, I have made some systemic style changes. Previously the pages had margins 70 pixels wide on each side. I have reduced that to 10 pixels (max) on the left, and 65 on the right to make room for the floating menu, which is slightly narrower and now also includes a "style changer," implemented mostly for the sake of iOS users who wrote to inform us that our text was un-readable on their devices: too small. The default font sizes are the same as before (12 pt body text), but now you have a choice: you can scale the size of all fonts up by 125% or 150%, and when you do so the left margin becomes narrower and the text is no-longer justified, which saves screen space. You're style preference is remembered between pages and between sessions, so you should only have to choose once on each device you use to read FLP. (There was another problem too on tablets: our pages were sometimes not opening zoomed to fit the device width: now they should.)

I would also like to inform you that Dr. Rudi Pfeiffer and I have (finally!) completed the manuscript for our edition of "Exercises for The Feynman Lectures on Physics," which was started in 2008. It's 306 8.5"x11" pages include approximately 1000 exercises covering the main sequence material in all three volumes of FLP, with 28 pages of answers/solutions in the back. According to our Executive Editor at Basic Books, the exercise book will be available in paperback online and in stores in the summer of 2014. We will also offer a PDF edition in our "Desktop" format (the same as the printed book, but with margins all on the right). My next project will be to produce a "Tablet" edition of the new exercise book to go with our recently released Tablet Edition of FLP.

In closing, I would like to thank all those people who have written to us. You're appreciation and interest in FLP is very rewarding and encouraging. I wish to particularly thank those who informed us of _problems_ with our web interface, or errors in the text or equations of the online edition of FLP; you're input helps make FLP more accessible, and more comprehensible. So, please keep those emails coming!

Best regards,
Mike Gottlieb
Editor, The Feynman Lectures on Physics New Millennium Edition
There ya go!


Thursday, December 19, 2013

Phil Anderson 90th Birthday Symposium

A symposium in honor of Nobel Laureate Phil Anderson's 90th birthday was held at Princeton this week.

The workshop to honor Anderson, the Joseph Henry Professor of Physics, Emeritus, and a senior physicist, was held Dec. 14 and 15 at the Frick Chemistry Laboratory on campus. About 150 colleagues and former students from as far away as India and Japan attended, as well as five fellow Nobel Prize winners and one Fields Medal recipient. The gathering was organized by N. Phuan Ong, the Eugene Higgins Professor of Physics at Princeton, and Piers Coleman, professor of physics at Rutgers University.
Anyone who has followed this blog for a while would have seen me mentioned Anderson's name a few times. He, of course, had a huge role to play in the formulation of the Higgs mechanism. And the discovery that bears his name, the Anderson Localization, has been a ubiquitous presence in condensed matter physics. But of course, he also championed the notion that More Is Different, an influential essay that started other physicists to question the reductionism philosophy.

The general public may not know him, but he has inserted his influence into our modern world.


Wednesday, December 18, 2013

Making Better Fog With Dry Ice

In case you are ever in a school play that requires a lot of fog.....


Tuesday, December 17, 2013

The Physics, And Metaphysics, Of Santa

We get this kind of articles popping up at this time of the year. So why not another one. This one has a bit more detailed description of what Santa has to do to accomplish what is said that he does (for a living). For example:

• How long would it take Santa to deliver presents to every child in the world?

Considering the 3.5 billion children on Earth (without regard to religion) and 500 million square kilometers of the Earth’s surface, Santa would need 14 years if he traveled at the speed of our fastest jets (Mach 10). Santa could finish the job in about 80 minutes assuming he travels at light speed — a timeline that even Amazon’s Jeff Bezos with his experimental army of delivery drones would find difficult to match.
Now, the more important message in this article is not really about Santa, or his reindeer, or even the problem being tackled. Rather, it is one aspect of science that is often neglected and what many in the general public aren't able to do. It was described as the "Fermi problem".

For non-geeks: Enrico Fermi was the landmark Italian-American physicist of the 20th century who discovered nuclear fission. “Fermi problems” are (in the succinct words of Wikipedia) “justified guesses about quantities that seem impossible to compute given limited available information.”

In other words, this is the wacky trivia that physicists love to debate after a couple of glasses of spiked eggnog. Santos calls them “back-of-the-envelope questions” and scratches out a typical solution within 5 or 10 minutes. He loves “the idea of being able to come up with something using as little information as possible.”

“It doesn’t tell you what the answer is,” he clarified of this more stringent estimation game. “But it tells you what the answer can’t be.”
This is often a crucial step whenever we think of something, especially when it is new. We make gross estimate of what the result should be, so that we know that at the very least, it can't be either bigger, or smaller, than such-and-such a number. But this requires, as you can see, a QUANTITATIVE understanding of it. You make an estimate and produce a value, rather than just a qualitative idea. It tells you of the SCALE of things.

For many people, this is what they do not have a feel for.


Sunday, December 15, 2013

"I Don't Know Where/How To Start!"

I get that type of plea often on physics forums and when students used to come and see me for help with homework-type problems. Often, the person asking the question simply typed in the problem, and showed nothing else other than the claim that he/she just simply didn't know how to tackle the problem. This was despite my explicit requirement that required students to show their attempts.

Not only that, this policy of forcing the person asking the question to actually show attempts, or at least, what they know, has also been criticized. Somehow, this requirement was deemed to be unusually harsh by some people

There are three separate issues here that will require a bit of explanation on why this policy is in place. And this policy is especially applicable homework problem in physics/engineering/chemistry/biology, etc.

1. In order to assist, help, and teach you how to solve a problem, we must know (i) what you know and (ii) what you don't know. We need to know what you have already understood, and then build from that. It is useless to simply tell you something that has no connection to what you've already understood, because if we do that, you will end up MEMORIZING it without understanding it, which is a recipe for disaster and failure in physics. When we can connect it to something you already know, then you can see a connection and a logical progression of your knowledge. The information isn't just hanging there in mid air. It has some logical connection with what you've learned and already know.

This is why we always need to know what you have attempted. It is not because we want to force you to do it, but a good teacher will be able to figure out what you already know and where you got stuck! We can point it out to you where you made the wrong turn. You, in turn, should also find this highly useful, because you learn more from your errors than from what you did right. You can do your own self-diagnosis on why you did something wrong, and why such-and-such is correct. This is the essence of learning!

If you simply say "I don't know where to start!", it tells us absolutely nothing. You simply must know SOMETHING in order to be given homework problems. Did you sleep through the class? Did you not even read the chapter in the book? You must know something! Can you even make a sketch of the problem? If it is a simple kinematic problem, can't you even show us a free-body diagram? At the very least, we can tell if you know what the relevant forces are! You must know something!

2. There is a misunderstanding of what a "starting" point is. When we ask you to show what you have attempted, we don't just mean "equations" or "calculations". In fact, in my personal approach, when you tell me that you don't know where to start, I will quiz you if you even know the relevant physics concepts that are applicable in the problem. Let me give you an example.

Say that I give you this problem: After a completely inelastic collision between two objects of equal mass, each having initial speed v, the two move off together with speed v/3.  What was the angle between their initial directions?

If you come to me and tell me you don't know where or how to start, I will ask you what is the relevant concept here.

If you tell me that it is the conservation of momentum, then I will at least know that you are aware of the physics being tested here. That is a big plus! And that, by itself, IS THE STARTING POINT! If I'm grading this problem, if the student simply did nothing else but indicated that this a conservation of momentum problem, he/she would have already received partial credit from me.

So now that I've already determined that the student is aware of the relevant concept, I want to see if the student can actually APPLY the concept. I will then ask "So if this is the conservation of momentum problem, what can you tell me about the momentum before and after the collision?"

If the student says that the momentum before the collision from both objects must be the same as the momentum of the two objects sticking together after the collision, then there is another indication that the student simply just didn't memorize the concept, but has some understanding of how that concept works.

Next, I will ask the student to sketch out the problem. Often, for this question, this is where the student gets stuck. The question doesn't say how they collided. Did they hit each other head on? At an angle? Via simple physics, we can rule out the former, because head on collision of identical objects with equal and opposite velocity will not result in a net velocity of a final object AFTER the collision. Furthermore, making them collide at an angle is a more "general" problem that we can solve. So if this is where the student got stuck, then we have found the source of the problem. As an instructor, I can make a mental note to make sure I emphasize on this aspect of problem solving. As a student, you learn where you got stuck, and how to get unstuck.

Note that the ability to make this sketch is crucial! By making use of the symmetry of the problem, the student will simplify this problem because the final velocity will only occur along the x-direction. This means that the momentum before and after along the y-direction will be zero! This ability requires insight, understanding, and repeated practice.

Next, I will ask the student to proceed to actually write down the mathematical form of the conservation of momentum. This will tell me if the student has the ability to translate "word concepts" into "mathematical equation", which is necessary to solve this problem. If the student gets stuck here, then I know where the problem is. This is also another common issue with many students, trying to translate conceptual ideas into mathematics. If the student realizes that this is where he/she often gets stuck, he/she can make a conscious effort to pay closer attention to when the instructor makes such a connection. I, on the other hand, as the instructor, will try to make a clearer emphasis during lecture, or when helping a student, that this is where we formulate our understanding into mathematics.

For this problem, we can write the momentum before and the momentum after, based on the sketch that we had drawn:

p1_x + p2_x = pf_x = pf
p1_y + p2_y = 0.

Notice the simple form for the y-component of the momentum as mentioned before.

From now on, it is just a matter of solving the math by substituting what we know and given from the problem. There is no more physics involved here.

2mv*cosθ = 2mv/3
cosθ = 1/3
θ = 70.5 deg.

So the angle between their initial directions is

2θ = 141 deg.

This demonstration and example is an illustration where there is a step-by-step progression in solving the problem. Every step is distinct, and as someone who wants to help the student trying to solve this problem, it must be clear if the student either understands, or is able to make each of the step. When he/she can't, then we have diagnosed the problem, and that is extremely important. One has to figure out where the source of the problem is, where the student got stuck. This is because it is a symptom of a bigger problem where there is a lack of understanding or knowledge in that particular area. Knowing where the problem is is beneficial not just to the instructor, but also to the student! He/she at least will know where to pay closer attention to and try to overcome that hurdle.

I've lost count how many times I hear students complaining that they find physics very difficult, and they can't solve physics problems. Upon undergoing a similar diagnosis such as this, more often than not, the most common problem that the students have was their lack of mathematical skills! In other words, I could have set up the problem for them and ask them to write down the vector components of the momenta, and they can't because of their lack of ability to do algebra and trigonometry. So here, we have also diagnosed the problem, and hopefully, the students realize that they have issues, not with physics, but rather with mathematics. Again, knowing this, the student has the ability to take the necessary actions to correct this.

The important thing here is that when a student is stuck, one has to figure out WHERE the sticking point is. Simply saying that "I can't do a problem" or "I don't know how to start" provides ZERO information to diagnose this.

3. If you look at the above example that I've given, you'll notice that the physics part actually comes in at the beginning. Being aware that (i) this is a conservation of momentum issue and (ii) being able to write down the mathematical form of the conservation of momentum that is relevant to this problem ARE THE PHYSICS PART! Once those are known and written down, the rest is mathematics. To put it bluntly, any monkey that knows math can, from that point on, solve this problem without knowing any physics!

This is important to realize for those who complain that we must help the student who don't know where to start. By telling them how to start, we are doing the physics for them! This is the most important part of the problem and it is why they are in the class studying it! As an instructor, I am keenly more interested in seeing how the student start and approach the problem. I have very little interest in seeing if they can deal with grinding out the math and spitting out the final answer. The physics here occurs at the very beginning!

So giving a student the starting point is not helping. It is depriving him/her of using the physics to set up the problem. The start IS the physics. You might as well tell the readers who did it at the beginning of a mystery novel. If I tell you how to start, I've practically done the physics part of the problem for you. I then have no clue if you didn't know what physics concepts were applicable, or if you've never heard of the concept, or if you didn't understand how to use it, etc. This deprive both of us in diagnosing the source of your problems, and because of that, there's a good chance that your lack of understanding will continue to perpetuate beyond this problem.

It is why I have such a policy.


Note: The example I took here came from a terrific set of example problems from Prof. Marianne Breinig at U. of Tennessee.

Her examples of worked problems in that link are exactly how I would teach and approach problem solving in physics, where there is a systematic identification of each step. It clearly shows where the "starting point" or how to start tackling a problem is the identification of the relevant physics concepts involved in that problem. This is what I want to see from a student.

Friday, December 13, 2013

Stephen Hawking's Snapshots of the Universe

Just saw this app on Apple's App Store. It's produced by Random House Digital. The description is rather long. The general description is that it teaches "... both adults and students the basic theories that govern our lives on earth as well as the movement of the stars and planets"

It costs $4.99. So far the review has either been good, or it has been complaints that it crashed or can't access certain levels.

Not sure if it is also available on Android.

If anyone has this, or has intention to get this, I'd like to hear what you think.


Would You Hire Peter Higgs Today?

This is a rather thought-provoking piece on how competitive it is now in the physics job market, especially for academic position. Peter Higgs was asked if he thinks that he could get a job in today's environment. His answer was "No".

Low productivity, Higgs believes, would sink his chances for an academic post in today's job market. In the 49 years since he wrote the papers laying out what physicists now call the Higgs model, he has "published fewer than 10 papers," The Guardian notes.

Fortunately for his career, at the time Higgs did his groundbreaking work he had a faculty post at the University of Edinburgh, where he is now a professor emeritus. His scanty publication record made him "an embarrassment to the department when they did research assessment exercises," he says, as quoted in The Guardian. Only a 1980 nomination for the Nobel Prize kept him from being let go, he told the paper.

We need to keep in mind that times have changed. Things that used to work, or things that one can get away with a couple of decades ago, may no longer work now. I cringe every time I hear advices being given to people by using the examples of Einstein and Galileo and Dyson, etc. as indicating that something can be done that way. This totally ignored the reality of today and how things no longer work the way they did back then.


Thursday, December 12, 2013

NOvA: Building a Next Generation Neutrino Experiment

A closer look at the NOvA experiment.


Dark Matter

In case you are still clueless on what we call 'dark matter', this might help.


Monday, December 02, 2013

Genius Materials on the ISS

Advances in material science on the International Space Station.

Pay attention, kids. These are physics applications that have direct impacts on your lives. You are using, at this very moment, things that were first studied as part of physics/material science.