Friday, March 28, 2014

10 Things That Can Tangle Your Brain?

A blog on the Huffington Post listed 10 things in physics that can "tangle" one's brain. Normally, I would read this and shrug. But there's a bit of misleading and incorrect information here that should be corrected. Let's go through the list:

1. Space ripples

OK, this one was on the news a lot the past couple of weeks. Nothing much to say here since the coverage is appropriately on the superficial level, which is fine this this is meant for the masses.

2. Quark-gluon plasma

I'm not going to nitpick this one since the description doesn't say much more than some generalization of what it is.

3. Time is slowing down

This is where the trouble begins. The argument for "time slowing down" is given by "Tidal friction caused by the Moon's gravitational pull is causing Earth's rotation to slow so that a day on Earth gets 1.4 milliseconds longer about every 100 years. " Sorry, but this is NOT time slowing down. It is the earth's rotation that is slowing down. The rate of oscillation of cesium atom in an atomic clock remains the same.

4. Light can be stopped completely

This is not new, but it might appear to be if you read it here: "Last year scientists in Germany successfully stopped light from traveling for an entire minute, by trapping it in a crystal." Light has been stopped in atomic gasses since way back in 2001, especially from Lene Hau's group at Harvard.. That's more than a decade! They may not have done it as long as the German group, but they have stopped it, completely!

5. Teleportation

6. Quantum entanglement

I'm grouping these two together because they are basically the same thing. The claim that a photon has been "teleported" is false, because what is teleported is not the photo, but rather a particular property of the photon, and that is tightly connected to quantum entanglement. If you read the article, you'd think this is your "teleportation" that one sees in Star Trek. It isn't.

7. Quantum foam

OK, so this is vacuum fluctuation.

8. Light bends matter

On one hand, this may be unusual to most people. But if one learns a little bit about physics, is this really new and unexpected? Compton scattering, anyone? That old and well-known phenomenon alone shows that light of a certain wavelength can change the trajectory of matter (electrons, for example). And let's not forget, particle accelerators around the world use RF sources to accelerate, bend, and manipulate charged particle trajectories.

9. Invisibility cloak?

10. The "God particle"

Nothing much to comment on there.

Anyhow, I guess it should be commended that a mainstream news source is covering something in physics. I just wish that they would at least find an expert FIRST to clean up the article, rather than just use "an education research assistant" as the other contributing author. I'm always surprised that people without the proper background seem think that they can write an accurate description of something which clearly is way over their heads.


Wednesday, March 26, 2014

"Brief history for the search and discovery of the Higgs particle - A personal perspective"

I find this "personal perspective" on the search for the Higgs to be extremely enjoyable. Don't be deceived by the title. This article has a lot of tabulated values and information that one can easily refer. It also explained why physicists were looking for the Higgs and why there was such a huge range of mass that had to be explored before it could be narrowed down during the final years before its discovery at the LHC.

Highly recommended.


One Of The Most Common Practice That Students Make

Over the years, I've seen several things that students make repeatedly that had to be "corrected". I know I've made some of these things myself when I was a student. I've talked to a number of professors, and they too have commented that these things that students do are quite common before they learned not to do it.

One of the most common ones happen when they have to plot a graph. Inevitably, physics students will have to produce a report that includes graphs. This often continues into graduate school where they either will have to produce graphs for publication, or for presentation.

Inevitably, when they first do this, the most common thing they failed to do is to resize the labels and the axis titles. What they typically will do is simply to use the default setting of whatever data plotting/analysis software that they were using. For example, the graph below was done using Origin, and I simply used whatever the default settings that the software had:

Now, here's the problem. The labels are just too small! These may be fine at "normal" size, but they present a problem when (i) one is submitting this for publication where graphs are often required to fit inside a 2-column paper, and (ii) you are presenting this on the screen and expect everyone, especially in the back row, to see this.

My graduate students meet with me and a couple of other faculty members weekly to discuss the work being done. During these meetings, the students often present their results and whatever else that they did, and inevitably, there will be a few graphs. The new students ALWAYS, never fail, did what I had just described. Most of the time, we could hardly see the axis labels and values on the screen because they were so small. It is almost a right of passage that one of us will have to tell them that they have to resize these things and make them bigger. If they forget to do this when they're submitting a manuscript for publication, then they will encounter a comment from the editor of the journal about resizing the labels.

Eventually, they learn, as with other things, as part of their process of becoming a scientist. In the scheme of things, this is not a big issue, but I find it amusing that almost every single student that I've encountered started out by doing this identical habit.


Tuesday, March 25, 2014

Walter Kohn and The Creation Of DFT

You all know that I try to highlight the lives and contribution of physicists that many in the general public are not aware of. This is another such example.

I cannot vouch for the accuracy of the article, since I haven't read any other biography on him, but this one describes the life of Walter Kohn, the person most responsible for the creation of Density Functional Theory (DFT), which has become a ubiquitous method in computing band structure and other properties of atoms, molecules, and solids.

Abstract: The theoretical solid-state physicist Walter Kohn was awarded one-half of the 1998 Nobel Prize in Chemistry for his mid-1960's creation of an approach to the many-particle problem in quantum mechanics called density functional theory (DFT). In its exact form, DFT establishes that the total charge density of any system of electrons and nuclei provides all the information needed for a complete description of that system. This was a breakthrough for the study of atoms, molecules, gases, liquids, and solids. Before DFT, it was thought that only the vastly more complicated many-electron wave function was needed for a complete description of such systems. Today, fifty years after its introduction, DFT (in one of its approximate forms) is the method of choice used by most scientists to calculate the physical properties of materials of all kinds. In this paper, I present a biographical essay of Kohn's educational experiences and professional career up to and including the creation of DFT.

The purpose of all my effort in pointing out the stories of these various physicists is not for us to worship and idolize these figures. I see people quoting many of these famous scientists as if they are word of god, and using those as if they are a sufficient counter argument. Far from it. I highlight them because we need to know that many of the things we accept and use and take for granted came from many of these nameless folks. It is trying to instill a sense of gratitude that the intelligence, creativity, and hard work of many of these people gave us the numerous convenience and advances that we enjoy today. You may not know before how much they had affected your lives, but you should now. You've gained another piece of knowledge/information that you didn't have before about someone who mattered.


Wednesday, March 19, 2014

Flex Your BICEP

... or in this case, BICEP2.

The recent BICEP2 results seem to have caught a lot of media attention. News coverage ranges from NY Times to CNN, etc. And let's face it, this isn't easy to understand even if the news media coverage glosses over the physics on why this is such an important discovery.

To add to the body of "explanation" given out there, here's MinutePhysics version of it.

With all the euphoria surrounding this, Neil Turok voice his caution to all the brouhaha surrounding this result.

"If...and it's a big if...this is true, it would be spectacular evidence for what happened at the Big Bang," Turok told While he agreed that at first glance, the BICEP2 observations are in keeping with inflation "as suggested over 30 years ago, wherein space–time would resonate with the aftershocks of inflation and would ring like a bell", a closer look at the discrepancy between the new results and previous data from the Planck and WMAP telescopes is what worries Turok. Indeed, the tensor-to-scalar ratio of 0.20 that BICEP2 measured is considered to be significantly larger than that expected from previous analyses of data. But the BICEP2 researchers said in their press conference yesterday that they believe certain tweaks could be made to an extension of the ΛCDM cosmological model that could make the two results agree. 

As with ALL experimental observations and discovery, there has to be reproducibility, and agreement with other types of experiments that point to one single, consistent picture. This is what makes science different than other areas of human endeavor. We NEVER confirm something with just one single experiment or with just one single type of experiment. Superconductivity is confirmed with resistivity measurement and magnetic susceptibility measurement.

So while this is certainly a major discovery, there's a lot of hard work left to be done to confirm this observation.


Tuesday, March 18, 2014

Single-Photon Detectors

This topic came up a few times during the past month in online discussions and with a few people that I've met. Most of these were in context with the photon detectors used in the EPR-type experiments, but a few came up due to the photon detectors used in detecting Cerenkov light from neutrino experiments.

A lot of people are confused with, and misinterpret, the meaning of "single-photon detectors". Most of them who are not familiar with it think that such detectors can detect every single photons that the detector comes in contact with, i.e. if there's a photon hitting a detector, it will detect it.

This is false. A single-photon detector is sensitive down to detecting single photons. So this is a sensitivity issue. However, it doesn't mean that it has a 100% efficiency. It doesn't detect every single photons that it encounters.

A photodetector such as a photomultiplier tube used in many photon detector is often made up of a photocathode (it converts the incoming photon into a photoelectron), an electron amplifier (something that multiply that single photoelectron into many electrons), and a signal generator/converter that converts the many electrons into an electrical signal. This is what we eventually detect in our electrical signal.

The problem here is that the photocathode does not have a 100% quantum efficiency. In fact, most photocathodes used in photodetector tubes have quantum efficiency less than 50%. What this means that if 100 photons hit the photocathode, less than 50 of them will be successful in generating a photoelectron each. The rest of the photons that hit the photocathode will generate no photoelectron and are lost.

So while the detector is sensitive down to the single-photon level, it is not 100% efficient. Single-photon detectors refer to the sensitivity, not the efficiency, of the detectors.


Snapshot of 2014 APS March Meeting

If you didn't get to attend this year's APS March Meeting, or didn't get to the highlights they listed here, APS Physics has a summary of 4 of the major presentations at the recently-ended meeting. They range from "no-photon laser" to hyperbolic metamaterial.

Don't miss it.


Tuesday, March 11, 2014

Oh, You Poor LHC Blackholes. You Were So Much Fun When You Almost Existed!

Remember all the brouhaha when the LHC was about to fire up and the whackos were out in force trying to stop it because they thought it will create blackholes that will destroy our planet? Wonder what happened to them now that the LHC has been in operation, and we are all still here. Hey, there's always the next apocalyptic event to get busy for, I suppose.

The latest analysis out of the ATLAS collaboration at the LHC has published a paper in search of these quantum blackholes at the LHC. Their conclusion? None has been found.

Had such QBHs been created, they would have decayed into various particles that could be seen with the ATLAS detectors. ATLAS looked for a specific set of predicted decay products: an electron or a muon and a quark jet. While the search came up empty, the analysis set a lower bound of 5 TeV on the mass of QBHs, which may help guide future searches.

Now, let's be clear about this, since there might be people out there reading this and automatically assume that (i) if we do detect these blackholes, then (ii) it will automatically mean we'll be dead. There is a HUGE series of logical step that needs to connect from (i) to (ii), and so far, all our physics point to the knowledge that these quantum blackholes, if they get created, will be extremely fleeting, will decay very fast (that's why they're looking for the decay signals at ATLAS), and they are not these gravitational blackholes swallow galaxies! I often wish that many of these reports and news article clarify that, rather than simply go for the sensational, headline news that skip over important details.

So we haven't found it at 8 TeV yet, and the LHC will run at a much higher energy soon enough. There's no guarantee that they'll find it at these higher energies, but even if they do (and I hope they do), this has nothing to do with ending our existence on this earth here! There is a higher probability that we will kill each other first before we get killed by some stray blackhole!


Monday, March 10, 2014

PhysicsWorld Special Edition On Physics Education

The March 2014 issue of Physics World focuses on physics education. It can be downloaded for free (with registration). The blurb on this says:

In the March 2014 issue of Physics World a PDF copy of which you can download free of charge – we offer a snapshot of just some of the many innovative ideas that exist for learning and teaching physics. It’s not an exhaustive selection, but includes topics that we felt were interesting or novel.

Friday, March 07, 2014

Physics Talk With No Powerpoint Slides?

Oh, say it isn't so!

In an effort to get a better interaction between speaker and audience, organizers at a biweekly forum on the LHC at Fermilab banned the use of any Powerpoint presentation by the speaker.

“Without slides, the participants go further off-script, with more interaction and curiosity,” says Andrew Askew, an assistant professor of physics at Florida State University and a co-organizer of the forum. “We wanted to draw out the importance of the audience.”

In one recent meeting, physics professor John Paul Chou of Rutgers University (pictured above) presented to a full room holding a single page of handwritten notes and a marker. The talk became more dialogue than monologue as members of the audience, freed from their usual need to follow a series of information-stuffed slides flying by at top speed, managed to interrupt with questions and comments.
It is definitely a development and a change that I find interesting and support... so some extent. You see, something like this will be amazingly fun and useful IF the speaker is engaging and actually pays attention to the audience. I'm sure you've been in seminars (or even a class) where the speaker simply rambled on and on looking at the screen, without even looking behind him/her to see if the audience was even there! So how well something like this goes depends very much on the speaker.

Still, not having the powerpoint slides will force these speakers to be more creative and inevitably, will create a less formal atmosphere during such a presentation. And from the report, having more of a dialog than a monolog is exactly what the organizers were trying to accomplish.

It is interesting to note that while these physicists are going back to the "primitive" form of communication, others in the education field are trying various technologies and techniques to get away from the primitive form of teaching. It is now almost common that college lecturers use Powerpoint in their lectures, and other forms of teaching techniques and technologies are being used in the classrooms. Yet, at the top, we go back to chalkboard/whiteboard to communicate.


Thursday, March 06, 2014

What Happens When You Cross A Bicycle With A Tricycle

Is this another case against cross-breeding and genetic modification? :)

Those crazy folks at Cornell produced a hybrid between a bicycle and a tricycle, and ended up with a vehicle that has a very weird steering capability.
Similarly, he wanted to see if the bike/trike dichotomy was really true in practice: A vehicle perfectly balanced between tricycle and bicycle would negate the effect of gravity by both preventing it from exerting force with its rear wheels like a trike, and by allowing the rider to lean the bike at any angle without shifting her center of mass.

Ruina’s “bricycle,” as he calls it, is a bike equipped with two training wheels attached by means of a spring. When the spring is stiff, the bricycle turns like a trike. When the spring is loose, the bricycle turns like a bike. But at a certain point when the spring is just stiff enough, the training wheels and rear wheel offset the force of gravity on each other. At that stiffness, the bike becomes unsteerable and falls over if the rider tries to turn, Ruina reported today at the American Physical Society meeting in Denver.
More info on this can be found at the YouTube page where they have uploaded a video of this device.
The bricycle is really the same as the gravity-free pendulum. Assuming friction and so on are negligible, if we start from an upright position, the lean and the sideways displacement of the ground contact point are always in proportion to each other. So changing direction would cause both an ever-growing distance for the original line of travel, and an ever-growing lean angle. The riders don't tolerate this. Instead, they maintain balance and thus are stuck going about straight.

So gravity, superficially the thing that makes it hard to balance a bicycle, is the thing that allows you to steer it.
Here's the video:


Monday, March 03, 2014

Checking On Antimatter

This is a rather nice, short summary on the study of anti-atoms, and in particular, CERN's effort to study the properties of anti-hydrogen and why it is so important.

With a big enough sample of anti-hydrogen, one can make detailed studies of the energy levels that the positron can occupy in its journey around the antiproton. These energy levels have been measured very precisely for hydrogen, and the expectation is that they should be identical in antihydrogen. But we won’t know until we look.
The symmetry principle which these experiments are designed to test is whether physics, and therefore the whole universe, would look the same if we simultaneously swapped all matter for antimatter, left for right, and backwards in time for forwards in time. This is called a CPT (Charge/Parity/Time) inversion. The Standard Model of physics, and almost all variants on it, require that indeed the universe would be identical after such an inversion.
Now pay attention, kids. In physics, even when some of our most cherished theories have been used, and known to be valid, we STILL go out and test out many of its predictions. Here, the Standard Model says that antihydrogen should behave the same way as hydrogen. While the Standard Model certainly has been useful, and has been correct in many aspects, we do not simply accept its predictions for the behavior of antihydrogen. We still want to test it! In fact, many physicists are hoping that we see something the Standard Model can't explain, that something "weird" is going on that might give hints of new physics. This is what many of us in this field look gleefully for!

This is how science works. We verify an idea, a theory, etc., but we continue to test its RANGE OF VALIDITY, i.e. how far out does this thing work? It works here, but does it work there? It works when you do this, but does it work when you do that? This is how we expand the boundaries of our knowledge.