Tuesday, August 14, 2018

MinutePhysics Special Relativity Chapter 8

If you missed Chapter 7 of this series, check it out here.

This time, the topic is on the ever-popular Twin Paradox (which really isn't a paradox since there is a logical explanation for it).



You can compare this explanation with that given by Don Lincoln a while back. I think Don's video is clearer to me, since I can comprehend the math.

Zz.

Thursday, August 09, 2018

Is Online Education Just As Good And Effective?

Rhett Allain is tackling a topic that I've been dealing with for a while. It isn't about learning things online, but rather is an online education and degree just as good and effective as brick-and-mortar education? Here, he approached this from the point of view that an "education" involves more than just the subject matter. It involves human and social interaction, and learning about things that are not related to your area. He used the analogy of chocolate chips and chocolate chip cookies:

The cookie is the on-campus experience. College is not just about the chocolate chips. It's about all of that stuff that holds the chips together. College is more than a collection of classes. It's the experience of living away from home. It's the cookie dough of relationships with other humans and even faculty. College can be about clubs and other student groups. It's about studying with your peers. College is the whole cookie.
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But wait! While we are talking about learning stuff, I have one more point to make. Don't think that you should acquire all of the skills and knowledge you need for your whole career during your time at school. You will always be learning new things, and there will always be new stuff to learn (no one learned about smartphones in the '80s). In fact, a college degree is not about job training. It's not. Really, it's not about that.

Then what is the whole chocolate chip cookie about? It's about exploring who you are and learning things that might not directly relate to a particular field. College is about taking classes that might not have anything to do with work. Art history is a great class—even if you aren't going to work in a museum. Algebra should be taken by all students—even though you probably won't need it (most humans get by just fine without a solid math background). So really, the whole cookie is about becoming more mature as a human. It's about leveling up in the human race—and that is something that is difficult to do online (but surely not impossible).

I have no issue with these points. However, we can even go right down to the jugular with this one instead of invoking some esoteric plea for a well-rounded education and social skills. There are compelling evidence that online-only lessons are not as effective and efficient as in-person, in-class lessons, if the latter is done properly.

I will use the example of the effectiveness of peer-instruction method as introduced by Harvard's Eric Mazur. Here, he showed how active learning, instead of passive learning, can be significantly more effective for the students. In such cases, student-to-student interactions are a vital part of learning, with the instructor serving as a "guidance counselor".

This is not the only example where active learning is more favorable than passive learning. There have been other students that have show significant improvement in students' understanding and grasp of the material when they are actively engaged in the learning process. Active learning is something that hasn't been done and maybe can't be easily done with online lessons, and certainly not from simply watching or reading the material online.

So forget about honing your social skills or learning about art history. Even the subject matter that you wish to understand may be more difficult to comprehend when you do this by yourself in an online course. There are enough evidence to support this, and it is why you shouldn't be surprised if you struggle to understand the material that you are trying to learn by yourself.

Zz.

Wednesday, August 08, 2018

Loop Quantum Gravity

This is one of those still-unverified theory that tries to reconcile quantum mechanics with General Relativity. I'm not in this field, so I have no expertise in it. But I know that for many people who have read about it, they are aware of String theory and it's competition, Loop Quantum Gravity.

In this video, Fermilab's Don Lincoln tries to explain LQG to the masses.



Keep in mind that this idea is still lacking in experimental support. The gamma ray burst observation that he mentioned in the video has been highlighted here quite a while back.

Without experimental verification, both String theory and LQG continue to have issues with their credibility as a science.

Zz.

Tuesday, August 07, 2018

Ban Cellphone Use In Classrooms?

First of all, let me state my policy on the use of electronic devices (mobile phones, tablets, laptop computers, etc.) in my classrooms. I do not have an outright ban (other than during exams and quizzes) during class, but they can't be use in an intrusive manner that disrupts the running of the class. So no making phone calls, etc. So far, I haven't had any issues to change that policy. Many of my colleagues do have an outright ban on the use of these devices during class.

Now, a few weeks ago, I came across this paper. They studied students who used these devices for non-class related purposes during class. They found that the distraction of these devices, in the end, affects the average class grade that the student received at the end of the course (they were psychology courses). The distracted students, on average, scored half a grade lower than those that are in classes that ban the use of these devices for non-class related purposes.

But what is also surprising is that there was a collateral damage done onto students who were in the same class as these distracted students, but they themselves did not use these devices during class.

Furthermore, when the use of electronic devices was allowed in class, performance on the unit exams and final exams was poorer for students who did not use electronic devices during the class as well as for the students who did use an electronic device. This is the first-ever finding in an actual classroom of the social effect of classroom distraction on subsequent exam performance. The effect of classroom distraction on  exam performance confirms the laboratory finding of the social effect of distraction (Sana et al.,2013). 
 So this is like second-hand smoking.

The good thing about this is that, I can now tell my students that, while I allow their use in the class during lessons, there is evidence that if they choose to use them, their grades may suffer. I may even upload this paper to the Learning Management System. However, because of the collateral damage that might be done to other students who do not use these devices during class, I am seriously rethinking my policy, and am considering imposing an outright ban on the non-class related use of these devices during my lessons.

If you teach, what is your experience with this?

Zz.

Sunday, August 05, 2018

APS's Don't Drink And Derive T-Shirt

I was cleaning my closet (I do that now and then) and came across this old shirt from way back when. This was bought during the 1999 APS March Meeting in Atlanta, GA, which celebrated the 100th anniversary of the APS.

When I first saw it, I said to the person at the counter that all the formulae are wrong. And then, duh, it suddenly hit me why and I got it. So of course, I had to buy it.



I haven't worn it in ages, because of a small tear on the front. But I'll probably start wearing it around the house, especially if I'm working on the yard.

This t-shirt is the opposite of the one I bought while I was at the Kennedy Space Center in Cape Canaveral, FL. That t-shirt had all the correct formulae and shows my nerdy self whenever I wear it.

😁

Zz.

Sunday, July 29, 2018

Looking for Psychics To Teach Physics

I know, I know, this is trivial, but it is so hysterically funny!

Someone pointed this out to me and I couldn't stop giggling. So of course I have to share it with all of you! This is a jobs ad from Kennedy-King College, one of the City Colleges of Chicago. They are looking for someone to be an adjunct physics faculty member to, presumably, teach physics.

I'm doing a screen capture here, because I expect someone there will see this and make corrections to it soon... or maybe not!


I am guessing that two different people did this, because the category for the job is correct (circled in green), and the required qualification is also spelled correctly, but then it goes hysterically wrong in the job description. It says:

ADJUNCT FACULTY PSYCHICS/ PART-TIME
CITY COLLEGES OF CHICAGO, KENNEDY-KING COLLEGE

Kennedy-King College is currently seeking a part-time Faculty to teach Psychics during the Fall  2018 semester. 

Well of course they're looking for Psychics. This is because they want a part-time Faculty to teach it during this upcoming Fall semester!

Dear Kennedy-King College, you may want to have someone proof-read your ad. The spell-check would not have flagged you for this hilarious error. And for an academic institution, this is an embarrassing boo-boo. Having psychics to teach physics is like having heretics coming in to teach Sunday School.

Zz.

Friday, July 27, 2018

Gravitational Red Shift Shows That Einstein Is Right Once More!

Albert Einstein's General Relativity is 3-for-3 this year so far! We already had GR passing its first galactic-scale test, and then we had the verification of the strong equivalence principle. This time, observation of light from a star in our Milky Way passing near a supermassive black hole has shown the predicted gravitational red shift. Holy Cow, Batman!

The team compared the position and velocity measurements from GRAVITY and SINFONI respectively, along with previous observations of S2 using other instruments, with the predictions of Newtonian gravity, general relativity and other theories of gravity. The new results are inconsistent with Newtonian predictions and in excellent agreement with the predictions of general relativity.
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The new measurements clearly reveal an effect called gravitational redshift. Light from the star is stretched to longer wavelengths by the very strong gravitational field of the black hole. And the change in the wavelength of light from S2 agrees precisely with that predicted by Einstein’s theory of general relativity. This is the first time that this deviation from the predictions of the simpler Newtonian theory of gravity has been observed in the motion of a star around a supermassive black hole.

A copy of the paper (or maybe a preprint) can be found here.

It bears repeating: the more they test it, the more convincing it becomes!

Zz.

Thursday, July 26, 2018

The Physics Of Baking Pizza

For those who are purist and prefer the thin-crust, Neopolitano-style pizza, this one might be right up your alley.

This preprint on ArXiv tackles the question on whether baking such pizza is better done in a stone over rather than the standard metal ovens. Which one do you think will win?

Stone ovens heat up to very high temperatures, higher than typical home ovens. But ceramic or stone surface also has low thermal conductivity while having a high specific heat. It means that it retains heat longer and does not cause the dough to burn. It is why this is also the preferred way to bake rustic, crusty bread.

I guess we all just have to build a brick pizza oven in our backyards! :)

Zz.

Saturday, July 21, 2018

University Research Made Your Smartphone

A lot of people are ignorant of the fact that a smartphone, or any device, for that matter, is a result of research work done by many people and organization and over a very long time. The iPhone was not solely the work of Apple. Apple benefited from all the scientific and technological progress and accumulation of knowledge to be able to produce such a device. These knowledge and progress are often done many years ago by researchers who work on a particular topic that eventually found an application in a smartphone.

I found this interesting website that highlights how research that originated out of universities under various funding agencies, resulted in the smartphone that we currently have. It lists one aspect of each of the major component of a smartphone that had it initial incubation in university research. A lot of these research work is physics-related. It is why I continue to say that physics isn't just the LHC or the Higgs or the blackhole. It is also your MRI, your iPhone, your GPS, etc...

If you need more background info on this, check out this page.

Zz.

Friday, July 20, 2018

Feynman's Lost Lecture

If you didn't buy the book or didn't read about it, here's a take on Feynman's Lost Lecture, presented by a guest on Minute Physics video.



Zz.

Burton Richter Dies at 87

Another giant in our field, especially in elementary  particle physics, has passed away. Burton Richter, Nobel Laureate in physics, died on July 18, 2018.

Richter’s Nobel Prize-winning discovery of the J/psi subatomic particle, shared with MIT’s Samuel Ting, confirmed the existence of the charm quark. That discovery upended existing theories and forced a recalibration in theoretical physics that reverberated for years. It became known as the “November Revolution.” One Nobel committee member at the time described it as “the greatest discovery ever in the field of elementary particles.”

He would be shortchanged if all the public ever remembers him is for his Nobel Prize discovery, because he did a whole lot more in his lifetime.

Zz.

Thursday, July 19, 2018

MinutePhysics Special Relativity Chapter 7

If you missed Chapter 6 of this series, check it out here.

In this chapter, the concept of spacetime intervals is presented. This is where we have "proper time" and "proper length".



Zz.

Wednesday, July 18, 2018

Khan Academy's Photoelectric Effect Video Lesson

A lot of people use Khan Academy's video lessons. I know that they are quite popular, and I often time get asked about some of the material in the video, both by my students and also in online discussions. Generally, I have no problems with their videos, but I often wonder who exactly design the content of the videos, because I often find subtle issues and problems. It is not unusual for me to find that they were inaccurate in some things, and these are usually not the type of errors that say, an expert in such subjects would make.

I was asked about this photoelectric effect lesson by someone about a month ago. I've seen it before but never paid much attention to it till now. And now I think I should have looked at it closer, because there are a couple of misleading and inaccurate information about this.

Here is the video:



First, let's tackled the title here, because it is perpetuating a misconception.

Photoelectric effect | Electronic structure of atoms
First of all, the photoelectric effect doesn't have anything to do with "structure of atoms". It has, however, something to do with the structure of the solid metal! The work function, for example, is not part of an atom's energy level. Rather, it is due to the combination of all the atoms of the metal, forming this BANDS of energy. Such bands do not occur in individual atoms. This is why metals have conduction band and atoms do not.

We need to get people to understand that solid state physics is not identical to atomic/molecular physics. When many atoms get together to form a solid, their behavior as a conglomerate is different than their behavior as individual atoms. For many practical purpose, the atoms lose their individuality and instead, form a collective property. This is the most important message that you can learn from this.

And now, the content of the video. I guess the video is trying to tackle a very narrow topic on how to use Einstein's equation, but they are very sloppy on the language that they use. First of all, if you don't know anything else, from the video, you'd get the impression that a photon is an ordinary type of "particle", much like an electron. The illustration of a photon reinforced this erroneous picture. So let's be clear here. A "photon" is not a typical "particle" that we think of. It isn't defined by its "size" or shape. Rather, it is an entity that carries a specific amount of energy and momentum (and angular momentum). That's almost all that we can say without getting into further complications of QED.

But the most serious inaccuracy in the video is when it tackled the energy needed to liberate an electron from the metal. This energy was labelled as E_0. This was then equate to the work function of the metal.

E_0 is equal to the work function of the metal ONLY for the most energetic photoelectrons. It is not the work function for all the other photoelectrons. Photoelectrons are emitted with a range of energies. This is because they came from conduction electrons that are at the Fermi energy or below it. If they came from the Fermi energy, then they only have to overcome the work function. These will correspond to the most energetic photoelectrons. However, if they come from below the Fermi energy, then they have to overcome not only the work function, but also the binding energy. So the kinetic energy of these photoelectrons are not as high as the most energetic ones. So their "E_0" is NOT equal to the work function.

This is why when we have students do the photoelectric effect experiments in General Physics courses, we ask them to find the stopping potential, which is the potential that will stop the most energetic photoelectrons from reaching the anode. Only the info given by these most energetic photoelectrons will give you directly the work function.

Certainly, I don't think that this will affect the viewers ability to use the Einstein equation, which was probably the main purpose of the video. But there is an opportunity here to not mislead the viewers and make the video tighter and more accurate. It also might save many of us from having to explain to other people when they tried to go into this deeper (especially students of physics). For a video that is viewed by such a wide audience, this is not the type of inaccuracies that I expect for them to have missed.

Zz.

Multiverse

In this article, Ethan Siegel valiantly tried to explain, in simple language, what "multiverse" is within the astrophysical/cosmological context:

Inflation doesn't end everywhere at once, but rather in select, disconnected locations at any given time, while the space between those locations continues to inflate. There should be multiple, enormous regions of space where inflation ends and a hot Big Bang begins, but they can never encounter one another, as they're separated by regions of inflating space. Wherever inflation begins, it is all but guaranteed to continue for an eternity, at least in places.

Where inflation ends for us, we get a hot Big Bang. The part of the Universe we observe is just one part of this region where inflation ended, with more unobservable Universe beyond that. But there are countlessly many regions, all disconnected from one another, with the same exact story.

Unfortunately, as is the problem with String theory, none of these have testable prediction that can push it out of the realm of speculation and into being a true science.

Zz.

Tuesday, July 17, 2018

94 Aluminum Pie Pans On A Van de Graaf

What happens when you put 94 aluminum pie pans on a Van de Graaf? Sometime you do things just because it is darn fun!



Now let's see if you can offer your own explanation for this silly thing! :) Happy 10th Anniversary on YouTube, Frostbite Theater!

Zz.

Monday, July 16, 2018

Neutrinos Come Knocking For Astronomy

I feel as if these are the golden years for astronomy and astrophysics.

First there was the discovery of gravitational waves. Then a major astronomical event occurred, and we were able to detect it using the "old" standard technique via EM radiation, and via the detection of gravitational waves from it. So now astronomy has two different types of "messengers" to tell us about such events.

Well now, make way for a third messenger, and that is ubiquitous neutrinos. Two papers published in Science last week detected neutrinos (along with the accompanying EM radiation) from a "blazer". The neutrino detection part was made predominantly at IceCube detector located in the Antarctica.

Both papers are available as open access here and here. A summary of this discovery can be found at PhysicsWorld (may require free registration).

Zz.

Friday, July 13, 2018

The Most Significant Genius

No, not Einstein, or Feynman, or Newton. Fermilab's Don Lincoln celebrates the hugely-important contribution of Emmy Noether.



I have highlighted this genius previously, especially in connection to her insight relating symmetry to conservation laws (read here, here, and here).

Zz.

Wednesday, July 11, 2018

First Human Scanned By Spectral X-Ray Scanner

Chalk this up to an application of high-energy physics in the medical diagnostic field. The first human has been scanned by a new type of x-ray scanner (registration required to read article at this moment).

The MARS scanner uses Medipix3 technology developed at CERN to produce multi-energy images with high spatial resolution and low noise. Medipix is a family of read-out chips originally developed for the Large Hadron Collider and modified for medical applications.

The Medipix3 detector measures the energy of each X-ray photon as it is detected. This spectral information is used to produce 3D images that show the individual constituents of the imaged tissue, providing significantly improved diagnostic information.

I'll repeat this, maybe to those not in the choir, that many of the esoteric experiments that you think have no relevance to your everyday lives, may turn out to be the ones that might save your lives, or the lives of your loved ones, down the road. So think about this when you talk to your elected political representatives when it comes to funding basic science.

Zz.

Thursday, July 05, 2018

Einstein Is Right Again!

... or rather, General Relativity passed another test.

This is on the heels of the first ever verification of GR at the galactic scale. This time it is a test of GR's strong equivalence principle involving a neutron star and two white dwarfs (no, not the kind from that Snow White movie).[1]

Archibald and colleagues’ study breaks new ground because the gravitational energy inside a neutron star can account for as much as 20% of the body’s mass. The authors’ results therefore imply that the accelerations of gravitational energy and matter differ by no more than a few parts per 105 — a tenfold improvement over the bound from lunar laser ranging.

More importantly, the authors have provided what is known as a strong-field test of general relativity. Unlike the Solar System, for which Einstein’s theory predicts only small deviations from Newton’s theory of gravity, the motion of a neutron star in a gravitational field invokes full general relativity in all its complex glory. Einstein’s theory passes this strong-field test with flying colours.

The more they test it, the more convincing it becomes.

Zz.

[1] A.M. Archibald et al., Nature, 559p73 (2018).

Tuesday, July 03, 2018

What Type of Physicist Are You?

... leader, successor, or toiler?

A new bibliometric study has found that authors can be roughly grouped into three categories: lead scientists who are already prominent in their fields, successors who are early career scientists, and toilers, which are those who do a lot of the dirty work but aren't going anywhere.

When looking at the citation data for mathematicians, psychologists and physicists, the authors identified three broad clusters that are “loosely based” on how the citations per year changes over time. Leaders tend to be experienced scientists who are widely recognized in their fields, which results in an annual citation increase. The successors tend to be early-career scientists who have had a surge in their citations in recent years. Toilers, meanwhile, may have a high citation count, but this stays mostly constant and may even drop slightly.

Not sure of the significance of this study, but hey, it's another criteria to classify people!

Zz.

Saturday, June 23, 2018

Super Kamiokande and Extremly Pure Water

This is a rather nice overview of Super Kamiokande, a neutrino detector in Japan. It has produced numerous ground-breaking discoveries, including the confirmation of neutrino oscillation many years ago. Unfortunately, the article omitted an important incident at Super-K several years ago when there was a massive implosion of the phototubes.

The article has an interesting information that many people might not know about extremely pure water, the type that is used to fill up the detector tank.

In order for the light from these shockwaves to reach the sensors, the water has to be cleaner than you can possibly imagine. Super-K is constantly filtering and re-purifying it, and even blasts it with UV light to kill off any bacteria.

Which actually makes it pretty creepy.

"Water that's ultra-pure is waiting to dissolve stuff into it," said Dr Uchida. "Pure water is very, very nasty stuff. It has the features of an acid and an alkaline."
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Another tale comes from Dr Wascko, who heard that in 2000 when the tank had been fully drained, researchers found the outline of a wrench at the bottom of it. "Apparently somebody had left a wrench there when they filled it in 1995," he said. "When they drained it in 2000 the wrench had dissolved." 

In other words, such pure, deionized water is not something that you want to drink.

And this leads me to comment on this silly commercial of PUR drinking water filter. It showed an ignorant public complaining about lead in the drinking water, even though he was told that the amount is below the safety level.



A drinking water contains a lot of other dissolved minerals, any one of which, above a certain limit, can be dangerous. Even that PUR commercial can only claim that it can REDUCE the amount of lead in the drinking water, not completely removed it. It will not be zero. So that guy should continue complaining about lead even with PUR filter.

If this person in the commercial is representing the general public, then the general public needs to be told that (i) you'll never be able to get rid completely of all contaminants in drinking water and (ii) pure water will dissolve your guts! This is why we set safety levels in many things (360 mrem of radiation per year, for example, is our acceptable, normal background radiation that we receive).

Zz.

Friday, June 22, 2018

General Relativity Passes Its First Galactic Test

Ethan Siegel is reporting the latest result of a test of General Relativity at the galactic scale.[1]

This effect of gravitational lensing, which occurs in both strong and weak variants, represents the greatest hope we have of testing General Relativity on scales larger than the Solar System. For the first time, a team of scientists led by Tom Collett performed a precise extragalactic test of General Relativity, and Einstein's theory passed with flying colors.

This new result also puts a strong damper on alternative theories of gravity, such as MOND.

For the first time, we've been able to perform a direct test of General Relativity outside of our Solar System and get solid, informative results. The ratio of the Newtonian potential to the curvature potential, which relativity demands be equal to one but where alternatives differ, confirms what General Relativity predicts. Large deviations from Einstein's gravity, therefore, cannot happen on scales smaller than a few thousand light years, or for masses the scale of an individual galaxy. If you want to explain the accelerated expansion of the Universe, you can't simply say you don't like dark energy and throw Einstein's gravity away. For the first time, if we want to modify Einstein's gravity on galactic-or-larger scales, we have an important constraint to reckon with.

This is definitely a big deal of a result.

Zz.

[1] T.E. Collett et al., Science v.360, p.1342 (2018).

Friday, June 15, 2018

Is Theoretical Physics Wasting Our Best Minds?

Before you continue reading this, let me be very clear right off the bat that there are TWO separate issues here that I will be discussing, and they are thinly connected simply by the over-general reference of "theoretical physics" made by the author of the article that I will be citing.

In this Forbes article, Ethan Siegel highlights the main point made by Sabine Hossenfelder in her book "Lost In Math". Siegel not only pointed this out, but also did an in-depth description leading up to the "naturalness" philosophy that is prevalent in the esoteric fields of physics such as string, etc.

If you are a theoretical particle physicist, a string theorist, or a phenomenologist — particularly if you suffer from cognitive dissonance — you will not like this book. If you are a true believer in naturalness as the guiding light of theoretical physics, this book will irritate you tremendously. But if you're someone who isn't afraid to ask that big question of "are we doing it all wrong," the answer might be a big, uncomfortable "yes." Those of us who are intellectually honest physicists have been living with this discomfort for many decades now. In Sabine's book, Lost In Math, this discomfort is now made accessible to the rest of us.

Certainly this is thought-provoking, and it isn't something I disagree about. For science to give up on empirical evidence, and simply pursue something that looks "natural" or "beautiful" is dangerous and verging on being a religion. So my feelings are consistent with what has been said in the article.

Now comes the other part of the issue. It has always been my pet peeve when someone over-generalize physics as being predominantly being "high-energy physics, astrophysics, string theory, etc...", i.e. the esoteric fields of study. In this case, "theoretical physics" certainly is NOT dominated by those fields. There are theoretical studies in condensed matter physics, atomic/molecular physics, medical physics, accelerator physics, etc... etc., i.e. fields of studies that are certainly not esoteric, have lots of practical applications, etc.

In fact, I would argue that the esoteric fields of physics represents the MINORITY in terms of the number of practicing physicists that we have around the world. As a zeroth-order approximation of this claim, I decided to look at the members of the APS. The APS Divisions correspond to the number of members who declared themselves to be in a certain field within physics. Note that not all members made the declaration, and it is also not uncommon for a member to declare more than one division.


First of all, 79% of APS members are accounted for in this chart for the 2018 membership. Now, what is the percentage of members within the so-called esoteric fields of Astrophysics, Gravitation, and Particles and Fields? 14.9%. Even if you include Nuclear Physics into this, it will come up to 19.8%

Now, forget about theoretical or experimental. Can 19.8% represents ALL of physics? The fields of studies that a lot of people associate physics with are done by ONLY 19.8% of physicists! Using them, one will get a severely inaccurate representation of physics and physicists.

In fact, if you look at the fields more commonly associated with the physics of materials (condensed matter physics and Materials Physics), we get 18.2%, almost as big as Astrophysics, Gravitation, Particles and Fields, and Nuclear Physics combined! Condensed matter physics alone dwarfs other fields, being almost twice as big as the next division, which is Particles and Fields.

But what is more important here is that outside of the 19.8% of physicists in these esoteric fields, an overwhelming percentage of physicists (59.2%) are in fields of studies that are associated with practical applications of physics. So if you were to bump randomly into a physicist, chances are, you will find someone who works in a field related to something of practical importance and NOT a high-energy physicist, a nuclear physicist, etc.

This is my round-about way of complaining that Ethan Siegel article should not be a damnation of "theoretical physics" in general, because the overwhelming percentage of theoretical physics is NOT about these esoteric topics that have been mentioned in his article. Rather, theories in other parts of physics rely very heavily on empirical observations and verification, i.e. the good and tested way of doing science. In those areas, we are definitely NOT wasting our best minds!

A while back, I said that physics is not just the LHC. It is also your iPhone. Even that requires modification. We should say that physics is predominantly your iPhone, with only a smidgen of LHC added as garnishing. That is a more accurate representation of the field as a whole.

Zz.

Wednesday, June 13, 2018

MinutePhysics Special Relativity Chapter 6

If you missed Chapter 5 of this series, check it out here.

Here's Chapter 6 of the Minute Physics series on Special Relativity. This time, they are tackling a topic that I see being asked numerous times : velocity addition. ("If I'm traveling close to the speed of light and I turn on my flashlight.....").

I know that this topic has been covered here many times, but it is worth repeating, especially since someone may have missed the earlier ones.



Zz.

Tuesday, June 12, 2018

Work Begins On FACET II at SLAC

The upgrade to FACET facility at SLAC promises to improve the beam electron beam quality at the accelerator facility. One of the direct benefits of this upgrade is further advancement in the plasma wakefield accelerator technique. This technique has previously shown to be capable of producing very high accelerating gradient and thus, has the potential to produce accelerating structures that can accelerate charged particles to higher energies over shorter distances.

Now, when you read the press release that I linked above, make sure you are very clear on what it said. The FACET II facility is NOT a facility that operates using this "plasma wakefield" technique. It is a facility that produces an improved electron beam quality, both in energy and emittance, among other things. This electron beam (which is produced via conventional means) is THEN will be used in the study of this wakefield accelerator technique.

The project is an upgrade to the Facility for Advanced Accelerator Experimental Tests (FACET), a DOE Office of Science user facility that operated from 2011 to 2016. FACET-II will produce beams of highly energetic electrons like its predecessor, but with even better quality. These beams will primarily be used to develop plasma acceleration techniques, which could lead to next-generation particle colliders that enhance our understanding of nature’s fundamental particles and forces and novel X-ray lasers that provide us with unparalleled views of ultrafast processes in the atomic world around us.

So read carefully the "sequence of events" here and not get too highly distracted by thinking that FACET II is a "novel X-ray laser, etc..." facility. It isn't. It is a facility, an important facility, to develop the machines that will give us more knowledge to make all these other capabilities.

Consider this as my public service to you to clarify a press release! :)

Zz.

Wednesday, May 30, 2018

What Is A Plasma?

I love the Chicago's Museum of Science and Industry (MSI). In fact, I am a member and a donor to the museum. So let's get that out of the way first.

Secondly, I know how difficult it is to explain scientific concepts to the public. The need to use simple words and terminology, AND, make it accurate can be a daunting task.

Still, I can't help but be a bit disappointed by this sign that I saw at MSI this past week. Granted, this was in the gift store, but still, for an institution promoting science, this falls a bit short.

The sign accompanies one of those "plasma arc ball" thingy that they were selling:

Here's what the sign says:

A plasma is a gas that has been heated to extremely high temperatures. At these high temperatures, the atoms are moving so fast that they lose their electrons, creating ionized particles. The electrons and ionized particles jump from one place to another to try and get as far away from each other as possible, creating a "lightening" effect.

There are problems with this description.

1. A plasma need NOT be only a gas that has been heated to high temperatures. I can create a plasma by blasting gas atoms with energetic electrons. In fact, when you have an electrical discharge, that is essentially what happens. The gas has not been heated by any means. So there are other means of creating a plasma beyond just heating. So a plasma is NOT defined as ".... a gas that has been heated to high temperatures...."

2. At high temperatures, the atoms lose their electrons not because they are moving "so fast". They lose their electrons because when they move "so fast", they also collide harder against other atoms, and collide more frequently. This tend to give each atom the energy to knock off one or more electrons, thus causing it to be ionized. Atoms do not lose electrons simply because they are moving "so fast".

3. The description that "... The electrons and ionized particles jump from one place to another to try and get as far away from each other as possible, creating a "lightening" effect.... " is extremely puzzling and, frankly, irrelevant to the description of what a plasma is. In fact, if you think about it, when an atom is ionized, it has a net positive charge. An electron, having a negative charge, would tend to want to go back to the positively-charged ion. So why would they want to "... get as far way from each other as possible..."?

4. The last part is trying to describe the creation of an electric discharge or an arc. This is superfluous, and is not part of the definition of a plasma. An electric discharge is a form of a plasma, but a plasma is not JUST an electrical discharge.

So what is a plasma? If, say, someone at MSI who isn't a physicist needed to make this sign, and Googled it, he/she will see several definitions. I'll pick one (the bold is mine).

Plasma is the fourth state of matter. Many places teach that there are three states of matter; solid, liquid and gas, but there are actually four. The fourth is plasma. To put it very simply, a plasma is an ionized gas, a gas into which sufficient energy is provided to free electrons from atoms or molecules and to allow both species, ions and electrons, to coexist. The funny thing about that is, that as far as we know, plasmas are the most common state of matter in the universe. They are even common here on earth. A plasma is a gas that has been energized to the point that some of the electrons break free from, but travel with, their nucleus. Gases can become plasmas in several ways, but all include pumping the gas with energy. A spark in a gas will create a plasma. A hot gas passing through a big spark will turn the gas stream into a plasma that can be useful. Plasma torches like that are used in industry to cut metals. The biggest chunk of plasma you will see is that dear friend to all of us, the sun. The sun's enormous heat rips electrons off the hydrogen and helium molecules that make up the sun. Essentially, the sun, like most stars, is a great big ball of plasma.

The bold sentence, to me, is a sufficient definition of a plasma to be given to the general public. An ionized gas can be made up of equal parts of positive ions and electrons, unequal parts of positive ions and electrons, all ions, or all electrons, i.e. there are free charges floating around at a given time. This, to me, is a more accurate definition than what the MSI sign says.

I'm not sure how many of MSI guests paid attention to the sign or learned what a plasma is from that sign. But I hope those responsible for such signs pay closer attention to the accuracy of the info that they put out.

Zz.

Tuesday, May 29, 2018

MinutePhysics Special Relativity Chapter 5

If you missed Chapter 4 of this series, check it out here.

In this chapter, the topic of "time dilation" and "length contraction" is tackled.



Zz.

Wednesday, May 23, 2018

That Impossible EM Drive Might Be ..... Impossible After All!

Crackpots were just having a field day when NASA announced several years ago of an EM propulsion that somehow violates momentum conservation laws. Now comes a more careful experiment from a group that tried to reproduce this result, and the outcome is rather hysterical.

The team built their EM drive with the same dimensions as the one that NASA tested, and placed it in a vacuum chamber. Then, they piped microwaves into the cavity and measured its tiny movements using lasers. As in previous tests, they found it produced thrust, as measured by a spring. But when positioned so that the microwaves could not possibly produce thrust in the direction of the spring, the drive seemed to push just as hard.

And, when the team cut the power by half, it barely affected the thrust. So, it seems there’s something else at work. The researchers say the thrust may be produced by an interaction between Earth’s magnetic field and the cables that power the microwave amplifier.

So far, this has only been reported in a conference proceeding, which is linked in the New Scientist article (you will need ResearchGate access).

I'm sure there will be many more tests of this thing soon, but I can't help but chuckle at the apparent conclusion here.

Zz.

Monday, May 21, 2018

Graphene Might Could Kill Off Cancer Cells

Here's another example of how something that came out of physics is now finding an application in other fields, namely the medical field. Graphene, which was discovered quite a while back and won its two discoverers the Nobel Prize in Physics, has now found a possible application at fighting cancer.

It began with a theory -- scientists at the University of California knew graphene could convert light into electricity, and wondered whether that electricity had the capacity to stimulate human cells. Graphene is extremely sensitive to light (1,000 times more than traditional digital cameras and smartphones) and after experimenting with different light intensities, Alex Savchenko and his team discovered that cells could indeed be stimulated via optical graphene stimulation."

I was looking at the microscope's computer screen and I'm turning the knob for light intensity and I see the cells start beating faster," he said. "I showed that to our grad students and they were yelling and jumping and asking if they could turn the knob. We had never seen this possibility of controlling cell contraction."

The source paper can be found here, and it is open-access.

Again, this is why it is vital that funding in basic physics continues at a healthy pace. Even if you do not see the immediate application or benefit from many of these seemingly esoteric research, you just never know when any of the discovery and knowledge that are gained from such areas will turn into something that could save people's lives. We have seen such examples NUMEROUS times throughout history. Unfortunately, people are often ignorant at the origin of many of the benefits that they now take for granted.

Zz.

Thursday, May 17, 2018

Noether Theorem And Symmetries

This is not something new that I'm highlighting on this blog. I've mentioned a link to Emmy Noether theorem before in this post, and also highlighted a history of her work here. However, I think that there is no such thing as too much publicity on Emmy Noether, because she deserves to be remembered and admired through eternity for her accomplishments and insights.

This video tries to explain the significance of her work connecting conservation laws with symmetry principles.



However, I think that if I were a layperson, I'd miss the important point in this video. So here is the takeaway message if you want one:

Everything that we see and every behavior of our universe can be traced to some conservation laws. Each conservation law is a manifestation of some underlying symmetry of our universe.

This is the insight, and a very important insight, that Noether brought to the table, and it was revolutionary to physics. These symmetries are what we currently have as the most fundamental description of the universe that we live in.

Watch this video, and read the links that I gave above, several times if you must, because you owe it to yourself to know about this person and her immense effect on our understanding of our world.

Zz.

Relativistic Velocity Addition

If I get $1 for every time someone asks me "If I'm moving in a spaceship and I turn on my flash light...."

Here's Don Lincoln's lesson on relativistic velocity addition:



Zz.

Wednesday, May 16, 2018

RIP David Pines

This is another one of the physicist who is a giant in his field, but relatively unknown to the general public.

Renowned condensed matter theorist David Pines passed away on May 3, 2018 at the age of 93. I practically read his text (co-authored by Nozieres) on Fermi Liquid from cover to cover while I was a graduate student. In fact, he was on the cusp of a Nobel Prize when he was working with John Bardeen at UIUC. They published a paper on the electron-phonon interaction in superconductors in 1955, a paper that many thought was the precursor to the subsequent BCS Theory paper in 1957. Unfortunately, he left UIUC, and Bob Schrieffer took over his work on this, which ultimately led to the BCS theory and the Nobel prize.

This did not diminished his body of work throughout his life. He certainly was a main figure during the High-Tc superconductivity craze of the late 80's and 90's. His 1991 PRL paper with Monthoux and Balatsky and the 1992 PRL paper with Monthoux, both on the spin-fluctuation effect as the possible "glue" in the cuprate superconductors, where ground-breaking and highly cited.

His contribution to this body of knowledge will have a lasting impact.

Zz.

Monday, May 14, 2018

Dark Energy Levels Not Too Constrained For Star Formation

I've always had a bit of a problem with the anthropic scenario of our universe, i.e. the idea that we are living in a universe JUST fined-tuned to allow us to exist. My problem isn't with the observations so far, but rather how much people are already thinking that this must be true, the data are set, and that we can run away with it. Certainly many people outside of cosmology have tried to spin this into whatever directions that they want.

So when news like this comes along, I just want to yell "I told you so!". It is not that I agree or disagree with the conclusion, but it is to point out that in our attempt to understand all of this, our knowledge is still in its infancy, and that we really don't know enough yet to be able to say things one way or the other on many of the big issues. We do have a fuzzy idea on what direction it is going, but in a number of things and observations, more is required to understand things even better.

The new studies ran the simulation on the star formation of our universe against the amount of dark energy in our universe. They can, to put it crudely, dial in various level of dark energy in their simulations. They found that there is a wider range than initially expected for our present universe to form, i.e. it is not in a very narrow range that was thought of. So keeping everything relatively the same, we could see this present universe that we're in for a large range of dark energy.

The simulations allowed the researchers to adjust the amount of dark energy in the universe and watch what happened.

The results were a surprise. The research revealed that the amount of dark energy could be increased a couple of hundred times – or reduced equally drastically – without substantially affecting anything else.

So for dark energy, the parameter is not as "fine tuned" as one expected.

Zz.

https://academic.oup.com/mnras/advance-article-abstract/doi/10.1093/mnras/sty846/4963750?redirectedFrom=fulltext

https://academic.oup.com/mnras/advance-article-abstract/doi/10.1093/mnras/sty879/4966995?redirectedFrom=fulltext

Friday, May 11, 2018

Not Insignificant Blunder on John Bardeen by UK's "Express"

OK, so to commemorate Feynman's 100th birthday, the UK's Daily Express decided to do a "Top 10" about physics. I thought this was going to be a fun read when I encountered #8 on the list:


It said "8. The only double winner is John Bardeen: 1956 (transistors) and 1972 (MRI images)"

Nope! The 1972 Nobel Prize in physics to Bardeen was for the theory of superconductivity. He is the "B" in BCS theory!

The Nobel Prize for MRI imaging was given in 2003 to Paul Lauterbur and Peter Mansfield.

How come news organizations don't do fact checking anymore nowadays?

Zz.

Happy 100th Birthday, Richard Feynman!

Today, May 11, 2018, is the 100th birthday of physicist and Nobel Laureate Richard Feynman. He was born on May 11, 1918.

This article covers the important commemoration of Feynman's birthday, ranging from the event at CalTech all the way to Tuva in remote Russia.

Zz.

Thursday, May 10, 2018

The Big Bell Test

Hey, I'm missing all the fun here!

A new paper to be published in Nature appears to have closed the "freedom-of-choice" loophole in the standard Bell-type experiment.

The BIG Bell Test asked human volunteers, known as Bellsters, to choose the measurements, in order to close the so-called "freedom-of-choice loophole" -- the possibility that the particles themselves influence the choice of measurement. Such influence, if it existed, would invalidate the test; it would be like allowing students to write their own exam questions. This loophole cannot be closed by choosing with dice or random number generators, because there is always the possibility that these physical systems are coordinated with the entangled particles. Human choices introduce the element of free will, by which people can choose independently of whatever the particles might be doing.
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Participants contributed with more than 90 million bits, making possible a strong test of local realism, as well as other experiments on realism in quantum mechanics. The obtained results strongly disagree Einstein's worldview, close the freedom-of-choice loophole for the first time, and demonstrate several new methods in the study of entanglement and local realism.

I have not read the actual paper yet, so if you have, I'd like to hear about it.

From my personal point of view, I no longer consider that the loopholes of Bell tests are anything significant anymore. This is due to the NUMEROUS consistent and non-contradictory results that we have obtained so far. In terms of the physics, Mother Nature seems to already let us know what she really is in this regards.

But I guess, until all of the loopholes are closed, we will always have to find a way to close them.

Zz.

Sunday, May 06, 2018

Alternative Theories of Gravity In Deep Doo-Doo

This is a rather nice article on the troubled times facing many alternative theories to Einstein's General Relativity due to the recent results from the colliding neutron stars. It should be especially useful to laymen to read and understand the methodology and the scrutiny that every theory goes through in physics to be considered to be valid. The one "take-home-lesson" that you should see is that my often-repeated manta here is more true than ever:

"Physics just doesn't say what goes up, must come down. It must also say when and where it comes down" - Warren Siegel.

The quantitative aspect is what is able to separate theories from being wrong to being right. One can't just say "oh, gravity gets weaker as we go farther away". It must say how much weaker, how it behaves with distance, etc.. etc.. and make precise predictions (i.e. to what level of uncertainty). These are "numbers" that we can compare with experiments, if there are already results or if new ones are collected.

This was exactly what happened with the merging neutron stars result, where our verification of the speed of gravity matches that to such precision with the speed of light, that a number of alternative gravitational theories died instantly.

The moral of the story here is that you should not fall in such deep love with any theory yet to have substantial verification, and you should not jump too quickly when new theories appear. I still point out to the OPERA debacle a few years ago when the OPERA project thought they measured superluminal neutrinos. As soon as they published their results, a bunch of theoretical explanations appeared on the e-print arXiv website, proposing theories of superluminal neutrinos, without waiting for independent verification of the validity of the result.

Not surprisingly, they all died of a horrible death when the result was attributed to bad optical cable connection! The history of physics is littered with theories that died and disappeared into obscurity when they could not match the experimental results or observations. Any beliefs or ideology, no matter how beautiful, satisfying, or popular, will crumble at the hands of Mother Nature if she says so.

Zz.

Wednesday, May 02, 2018

Hawking's Final Paper Is Published

The late Stephen Hawking's final paper written while he was alive, has been published. You can get the full version of it at that link.

If you missed it, read Ethan Siegel's earlier explanation of the paper.

Zz.

Friday, April 27, 2018

Quantum Entanglement Just Got "Big"

The "big" news of the week so far is the two papers published in nature that increased the size of entities that can be in an quantum entanglement.

It looks like we've approached the size of a human hair, which, by any quantum mechanical standards, is humongous.

This is beginning to approach the the scale size of the Schrodinger Cat. Well, not quite, but it is in the right direction. The Schrodinger Cat-type states, which is more of a demonstration of quantum superposition (and a vital ingredient in quantum entanglement), is also getting to be huge.

Zz.

Thursday, April 26, 2018

MinutePhysics Special Relativity Chapter 4

If you missed Chapter 3, check it out here.

Here's the next chapter in MinutePhysics lessons in Special Relativity.



Zz.

Wednesday, April 18, 2018

Forum with Congressman and Physicist Bill Foster

This is the talk given by Congressman and the only Physicist left in the US Congress, Bill Foster, at this year's APS March meeting.



I have been in attendance to one of Bill Foster's talk before, at the 2011 TIPP conference in Chicago. You may read my "live" reporting of that talk back then, and also a follow-up post on it.

Zz.

Tuesday, April 17, 2018

The Friedmann Equation

Astrophysicist Ethan Siegal picked the Friedmann equation as the "most important" equation in the universe.

The first Friedmann equation describes how, based on what is in the universe, its expansion rate will change over time. If you want to know where the Universe came from and where it's headed, all you need to measure is how it is expanding today and what is in it. This equation allows you to predict the rest!

I don't have the "most important equation" in the universe for my pick, mainly because I don't know the criteria for picking such a thing. And often times, people confuses "interesting" with "important", which need not be mutually inclusive.

It's still fun to read what other physicists think is the most important equation, even if I don't necessarily agree with their picks.

Zz.

Friday, April 13, 2018

An Overview of CLIC at CERN

This is the lesser known effort at CERN among the general public, and yet, it may have one of the most significant impacts coming out of this high-energy physics lab.

CLIC, or the Compact Linear Collider research project at CERN has been studying accelerator science for many years. This is one of a few prominent research centers on accelerator physics throughout the world. Both they and many other accelerator research centers are making advancements in accelerator science that have a direct benefit and application to the general public.

So my intention in highlighting this article is not simply for you to learn what the people at CLIC do. Some of the description may even be beyond your understanding. What you should focus on is all the applications that are already in use, or can be possible in the near future, on the advancements made in this area of physics/engineering. These applications are not just within physics/engineering.

Unfortunately, as I've stated a few times in this blog, funding for accelerator science is often tied to funding in high energy physics, and for the US, the funding profile in this sector has been abysmal. So while accelerator science is actually independent of HEP, its funding has gone downhill with HEP funding over the last few years, especially after the shutdown of the Tevatron at Fermilab.

Whether you support funding, or increase in funding, of this area of study is a different matter, but you should at least be aware and have the knowledge of what you are supporting or not supporting, and not simply make a decision based on ignorance of what it is and what it's implication can be.

Zz.

Tuesday, April 10, 2018

What Astronomers Wish You Know About Dark Matter And Dark Energy

If you do a search of this blog, you will encounter numerous entries on both "dark matter" and "dark energy". It is something I've covered quite often, mainly because it is still an ongoing and active research area in astrophysics/astronomy/cosmology. Even high-energy physics/elementary particle physics is getting into the picture with particle astronomy.

In this article, Ethan Siegel gives you a condensed version of what "dark matter" and "dark energy" are, and what you need to know about them. But more importantly, if you think that you can discard them, you need to do more than just say that they are not needed.

It wasn't always apparent that this would be the solution, but this one solution works for literally all the observations. When someone puts forth the hypothesis that "dark matter and/or dark energy doesn't exist," the onus is on them to answer the implicit question, "okay, then what replaces General Relativity as your theory of gravity to explain the entire Universe?" As gravitational wave astronomy has further confirmed Einstein's greatest theory even more spectacularly, even many of the fringe alternatives to General Relativity have fallen away. The way it stands now, there are no theories that exist that successfully do away with dark matter and dark energy and still explain everything that we see. Until there are, there are no real alternatives to the modern picture that deserve to be taken seriously

It might not feel right to you, in your gut, that 95% of the Universe would be dark. It might not seem like it's a reasonable possibility when all you'd need to do, in principle, is to replace your underlying laws with new ones. But until those laws are found, and it hasn't even been shown that they could mathematically exist, you absolutely have to go with the description of the Universe that all the evidence points to. Anything else is simply an unscientific conclusion.

Zz.

Monday, April 09, 2018

Another "Unconventional" Superconductor?

This is definitely exciting news, because if verified, this will truly open up a whole new phase space for superconductivity.

An advanced publication has appeared reporting the discovery of high-spin state quasiparticles that are involved in superconducitivty.[1] This occurs in a topological semimetal YPtBi.

Previously, superconductivity occurs due to quasiparticles of spin 1/2 forming pairs called Cooper pairs. Now these Cooper pairs can have a total spin of either 0 (singlet state), or 1 (triplet state). This new superconductor seems to be formed by quasiparticles having spin 3/2! The resulting Cooper pairs may have total spin of 3 or 2.

It turns out that based on their measurements, the pairing symmetry appears to be predominantly in the spin state of 3, with a sub-dominant component having 0 (the singlet) state.

If you want to know how a quasiparticle here could have a spin 3/2 state, then you need to learn about spin-orbit coupling that we all learned in intro QM classes, and read the article.

This is utterly fascinating. Just when you think you can't be surprised anymore by the phenomenon of superconductivity, along comes one!

Zz.

[1] H. Kim et al., Sci. Adv.2018;4

Wednesday, April 04, 2018

Twin Paradox - The "Real" Explanation, But With No Math

Don Lincoln made a video a while back explaining the apparent twin paradox, explaining that it isn't due to acceleration. It seems that his audience wanted an explanation, but without using math. He has graciously agreed and this video is his attempt at providing the same explanation, but without all that math in the earlier video.



Is this clearer for people who didn't quite get the first video?

Zz.

Tuesday, April 03, 2018

MinutePhysics Special Relativity Chapter 3

If you missed Chapter 2 of this series, you can check it out here.

Here is Chapter 3, and this is where he uses that thing-ma-jiggy to illustrate Lorentz transformation.



Zz.

Sunday, April 01, 2018

Do A Search On "Physics" and "Physicist"

.. which, btw, is almost the title of this physics blog! :)

Chad Orzel must have been bored when he decided to do a search on the words "physics" and then "physicist". Hilarity ensues.

I'm not surprised that some of these search engines confuse "physicist" and "physician", since many people think people who work in physics are "physician". But a few of those stock photos that he found from Shutterstock are just hilarious. Of course, stereotype abounds, but some of these are so far out in left field, they are hardly relevant.

I guess, subconsciously, this was partly the reason why I did that superficial poll on the most attractive male and female physicist a while back. We all don't look like Albert Einstein, even for our women physicists!

Zz.

Friday, March 30, 2018

Revamping Introductory Physics Laboratory - Part 8

If you are not aware of my own pet project, this post will get you up to speed.

It has been a while since I updated this series, but better late than never. For this one, I'm going a bit against my own philosophy that physics just doesn't say what goes up must come down, but also when and where it comes down. For this exercise, I'm sticking with just the "what goes up must come down" part, i.e. only the qualitative aspect, not the quantitative aspect. But I have a good reason for it. It is because, in my experience, students often have a tough time understanding the concept itself, and I often found myself having to spend a considerable amount of time on this before I could proceed to the quantitative aspect of it. So in this exercise, the main idea is to make the students understand the concept and not worry about the "numbers" yet.

The topic of this exercise is Lenz's Law. This "lab" can actually be done either with real equipment in a laboratory setting, or done using a virtual setup. The PhET virtual setup for Faraday's Law is perfectly suited for this:

https://phet.colorado.edu/sims/html/faradays-law/latest/faradays-law_en.html

If you are doing this as a real experiment, you will need a solenoid, a bar magnet, a galvanometer with the "zero" position at the center of the scale, and some connecting wires. I've used a tightly-wound homemade solenoid, and it works fine. Note that you will need to know the direction of how the solenoid is wound (i.e. you need to be able to see the windings) so that you can figure out the sense of rotation of any current flow in the solenoid.

For this exercise, I will use the PhET simulation. I have used this as part of my in-class lecture on this topic, since every student in my class has a laptop or tablet and can access the PhET website during class. And yes, they were reminded to bring those devices to class for this topic.



Let's start with the aim of this exercise: It is to let students figure for themselves a "general rule" on when there is current in the circuit, and the direction of this current.

Keep in mind that the whole principle of this revamped lab idea is that the instruction is kept to a minimum, the students do not need to know the actual physics concept or principle, and we let them discover or learn about the phenomenon for themselves. So with that in mind, my only instruction to the students is this:

By using the magnet and moving it in and out of the solenoid, find a GENERAL RULE on when there is current in the circuit, and the direction of this current. Your rule must be able to tell  me that by doing an action, it will or will not result in a current in the circuit, and the direction that this current flows.

I give them a bit of a guideline, especially for those who are a bit clueless on what to do.

  • To simplify things, first figure out the direction of current flow in the solenoid if the galvanometer deflects to the right, and the direction of current flow if the galvanometer deflects to the left. Let's define the point of view by looking at the solenoid from the right, i.e. from where the magnet is in the figure above. The galvanometer will deflect to the right if current flows into it via the positive terminal, while it will deflect to the left if current flows into it via the negative terminal. So if one were to trace this path carefully, one can see that when viewed from the right, the current goes clockwise for positive deflection, and counter-clockwise for negative deflection. Armed with this info, we don't need to figure out anymore the sense of rotation of current in the solenoid, since by looking at the galvanometer deflection alone, we can tell the direction immediately.
  • Next, since we only care about when there is current in the circuit, and the direction of this current, and not its magnitude (yet), we can simplify the relevant magnetic field coming out of the bar magnet. For this exercise, we can just consider the magnetic field along the pole of the magnet, i.e. the direction of the magnetic field at the two pole ends. So a student must be given the information (if he/she doesn't know it already), that the magnetic field points straight out from the N-pole of the magnet, while at the other end, the magnetic field points straight in into the S-pole of the magnet. This is defined via convention.
  • A few students will simply not know what to do or how to start, so I give them a list of things for them to check out: (i) move the N-pole of the magnet into the solenoid while watching the galvanometer. (ii) stop moving the magnet and leave the N-pole inside the solenoid. (iii) move the N-pole of the magnet out of the solenoid while watching the galvanometer. (iv) repeat the same thing steps with the S-pole of the magnet.
  • Remind the students that they need to be able to describe clearly and succinctly a general rule for what they see. This means that they are required to convey, in writing, what they understand (communication skills). I tell the students that once they think they have written their general rule down, TEST it. See if their general rule explains everything that they observe in this exercise. For example, does their general rule explains why the galvanometer shows no deflection (i.e. no current) when the magnet is not moving inside the coil?
If this were done as a real experiment, I required the students to write exactly what they did and what they observed at every step.

What this exercise does is (i) to force students to think analytically on how to understand and make sense of what they observe and (ii) to get the students to communicate clearly what they understand in their heads into written form. Both of these are invaluable skills, and not just in physics. The second part is not as trivial as you think, because I find that a lot of students still have not mastered the art of conveying something in their heads via written communication (students who are not native English speakers will have a tougher time with this part so they may need extra assistance).

In my lessons, I introduce Lenz's law as the "qualitative" description, and then follow it up with Faraday's Law as the "quantitative" description of the same phenomenon. In addition to showing how Faraday's law "explains" Lenz's law, it will also allow you to explain why the galvanometer deflects with different amplitudes depending on how fast you move the magnet in or out of the solenoid. But this is one as part of the class lesson rather than as part of the lab exercise.

I toyed with the idea of putting the "answer" here (it is not as if one can't google for it), but I'm going to leave it out for now and let any interested party try it out. I will update this post at a future date to include my version of the "general rule" that reflects what Lenz's law says.

Zz.

Monday, March 26, 2018

Newton's Gravitational Law Still Valid At Sub-Nanometer Scale

A new experiment using neutron scattering off noble gasses has shown no deviation from Newton's gravitational law at 0.1 nm scale.

The team fired pulses of neutrons at a chamber filled with either helium or xenon gas and monitored both the travel time of the neutrons through the gas and the neutrons’ scattering angles. From these measurements, they reconstructed the scattering process with the aid of simulations. They found that the scattering-angle distribution fit the predictions—based only on known laws of physics—for neutrons bouncing off gas nuclei. This result indicates that, within the sensitivity of the experiment, no unexplained force—be it modified gravity or another type of interaction—acts on length scales below 0.1 nm.

This one may not be as transparent, since it required quite a bit of reconstruction to simulate the interaction. So while the length scale being probed has improved considerably, I'm not so sure on how convincing this result is.

Still, where are those curled-up extra dimensions anyway?

Zz.

Thursday, March 22, 2018

Fermilab Accelerator Complex

This is a neat animation video of the Fermilab Accelerator Complex as it is now, and all the various experiments and capabilities that it has.



Of course, the "big ring", which was the Tevatron, is no longer running now, and thus, no high-energy particle collider experiments being conducted anymore.

Zz.

An Astrophysicist Describes Stephen Hawking's Last Paper

The astrophysicist in this case is, of course, Ethan Siegel, who I've cited here a few times.

In this article, he describes what Hawking's last paper is all about, if you want simple description of it. The link to the preprint (we'll update this post if and when it is published) is also given if you don't have it already.

Here is, in a nutshell, what they do. They create a (deformed) conformal field theory that is mathematically equivalent (or dual) to an eternally inflating spacetime, and investigate some mathematical properties of that field theory. They look, in particular, at where the border of a spacetime that inflates for an eternity (forward in time) versus one that doesn't, and choose that as the interesting problem to consider. They then look at the geometries that arise from this field theory, try to map that back onto our physically inflating Universe, and draw a conclusion from that. Based on what they find, they contend that the exit from inflation doesn't give you something eternally inflating into the future, with disconnected pockets where hot Big Bangs occur, but rather that the exit is finite and smooth. In other words, it gives you a single Universe, not a series of disconnected Universes embedded in a larger multiverse.

There! Do you even need to read the actual paper after that?

😁

BTW, let's also give some love to his co-author, Thomas Hertog, who seems to be left out in many of this discussion and news articles.

Zz.

Tuesday, March 20, 2018

Micro Fusion In Nanowires Array

This is a rather astounding result. The authors have managed to cause deuterons-deuterons fusion in an array of nanowires via igniting it using only joule-level pulsed laser[1], i.e. not using the huge, gigantic lasers such as that as the National Ignition Facility.

This is an open-access paper and you can get the full version at this link.

And no, before you jump all over this one and think that this is the next fusion power generator, you need to think again. The authors are touting this as a viable (and cheaper) ultra-fast pulsed neutron source, which can be useful in many applications and studies.

Zz.

[1] A. Curtis et al., Nature Communnications DOI: 10.1038/s41467-018-03445-

Thursday, March 15, 2018

SQUID: History and Applications

No, this is not the squid that you eat. It is the Superconducting Quantum Interference Device, which is really a very clear application of quantum mechanics via the use of superconductors.

This is a lecture presented by UC-Berkeley's John Clarke at the 2018 APS March Meeting.



Zz.

Wednesday, March 14, 2018

Stephen Hawking: 1942–2018

Of course, the biggest physics news of the day is the passing of Stephen Hawking at the age of 76.

Unfortunately, as popular as he is in the public arena, it also means that he left us without being awarded the highest prize in physics, which is the Nobel prize. This isn't unusual, especially for a theorist, because there are many theorists whose contribution became of utmost importance only many years later after they are gone.

Still, as a scientist who had attained a highly-unusual superstar status among the public, I will not be surprised if he has had a lasting impact of the field, and the perception of the field among the public and aspiring physicists.

RIP, Stephen.

Zz.

Tuesday, March 13, 2018

Twin Paradox - The "Real" Explanation

So this thing doesn't seem to go away. The Twin Paradox is a common question that gets asked in class and online. And of course, the most common answer being given to explain away the paradox is that there is a broken symmetry between the two twins, and thus, they should not experience the same thing. But often, this involves one twin experiencing an acceleration/deceleration, which the other twin did not experience.

However, in this video, Don Lincoln tries to correct the explanation and argues that even without any acceleration/deceleration, one twin will STILL not have the same set of experience (he/she is in two different reference frame, while the "non-moving" twin stays in just one reference frame) when compared to the other twin, and thus, this broken symmetry resolves the twin paradox.



The math is simple algebra, but you do have to keep the notation straight, and the signs.

Zz.

Teaching Intro Physics To Life Science Students

Teaching intro General Physics to Life Science/Bio students is something I do regularly. And it can be quite challenging because, in my case, calculus is not required and isn't used in the lesson. So there are many things that can't be easily derived from scratch.

I've resolved, a long time ago, that the approach to teaching such a class has to be different than the approach to teaching the calculus-based class, which is often populated by physics, chemistry, and engineering majors. In my experience, the average math skill is lower in the non-calc-based general physics class, which isn't too surprising. But more challenging than that, there is less of an interest and inclination towards the physics subject from such students. Most, if not all, of the Life Science/Bio students are in the class because they have to, and some even have an active dislike of the subject matter.

So it is definitely a challenge to not only convey the material in an understandable manner, but also to perk up their interest in the material so that they will do well in the course. It is why I tend to read papers like this one, which studied the correlation between life science students' interest, attitudes, and performance in a general physics class.[1] In particular, I'm always interested in using examples from biology/medicine to illustrate the particular physics topics that we cover in a lecture. As concluded in this paper, tailoring the subject matter to overlap with what the students are majoring in can affect not only the interest in the subject, but also their performance. This is a no-brainer for many of us, but this paper clearly shows the correlation.

BTW, it helps if the text being used is also geared towards the life science students.  The one that I had used before is "College Physics" by Giambattista, Richardson, and Richardson. I like the part where at the beginning of each chapter, it lists out some of the relevant applications in biology, medicine, etc. I just wish that the text has more examples from such areas, and more homework exercises in those areas, the way the paper described the examples and problems that were used in the course.

Zz.

[1] C.H. Crouch et al. Phys. Rev. Phys. Educ. v.14, 010111 (2018).

Friday, March 09, 2018

Fusion Power Is 15 Years Away?

This news article is reporting that "MIT scientists" is predicting that we will have nuclear fusion power in 15 years time.

The project, a collaboration between scientists at MIT and a private company, will take a radically different approach to other efforts to transform fusion from an expensive science experiment into a viable commercial energy source. The team intend to use a new class of high-temperature superconductors they predict will allow them to create the world’s first fusion reactor that produces more energy than needs to be put in to get the fusion reaction going.

Bob Mumgaard, CEO of the private company Commonwealth Fusion Systems, which has attracted $50 million in support of this effort from the Italian energy company Eni, said: “The aspiration is to have a working power plant in time to combat climate change. We think we have the science, speed and scale to put carbon-free fusion power on the grid in 15 years.”

Interestingly, there was no direct quote from any MIT scientists here who is working on the project. The article quoted MIT's vice-president for research, but she's not working on this project.

So essentially, it appears that no one from MIT is making this claim, but everyone else on the peripheral is.

Let's mark this and check back in 15 years. Still, I will not be holding my breath.

Zz.

Wednesday, March 07, 2018

Seeing Anyons With STM?

This is a very intriguing theoretical paper that proposes the detection of anyon using STM (you get free access to the actual paper from the website). The detection involves the measurement of the local density of states (LDOS), and then counting the resonance "rings". This is shown in Fig. 1 and 2 of the paper.[1]

This is quite a fascinating idea, because to get these fractional effects, one has to have a 2D confinement of the charges involved.

Now it becomes a race in seeing who might be able to produce such an experiment to detect these rings. STMs are pretty common, but it is now a matter of having the suitable material to see this.

Zz.


[1] Z. Papic et. al. PRX v.8, 011037 (2018).

Tuesday, March 06, 2018

Magnon Transistors

A number of papers appear almost simultaneously on the invention of "magnon transistors". Instead of a transistor that directs the direction of electronic current flow, these are transistor that direct magnetic spin current flow, i.e. magnon flow.

Magnonic devices run exclusively on spin currents. (Spintronic devices, another electronics alternative, include both charge and spin currents.) To picture a magnon, imagine a row of spins pointing up, representing a magnetic material, and then imagine briefly flipping the spin at one end. This motion leads to a propagating wave that moves through the material as each spin influences its neighbor. Magnons can travel quickly and efficiently over long distances—up to about a centimeter in the best materials—without significantly losing energy or heating up the material, a feat not possible for electrons. But before building fast and efficient magnonic circuits, researchers need components that can regulate magnon currents.

I know I have been repeating this over and over again, but this is another example where basic research in condensed matter/solid state physics is now finding application in modern electronics.

Zz.

Thursday, March 01, 2018

Thermal Footprints of Early Stars

Imagine being able to detect signals coming from the first stars formed in our universe, almost 180 million years after the Big Bang. This is why this astounding feat has been receiving popular media coverage.

A new paper published in Nature this week reports on the measurements of thermal radiation from such events.

A long-standing theory that still awaits testing predicts that absorption of UV radiation from early stars by nearby clouds of hydrogen could have driven TS back down to TG, but not lower. In other words, the cosmic dawn would make the gas seem colder when observed at radio frequencies. This would create an absorption feature in the spectrum of the background radiation left over from the Big Bang.

Bowman et al. now report the possible detection of just such an absorption signal. The authors measured TS , averaged over much of the sky and over a contiguous range of radio frequencies; each frequency provides a window on a different time in the Universe’s past. The measurement is very difficult because it must be performed using an extremely well-calibrated VHF radio antenna and receiver, to enable the weak cosmological signal to be separated from much stronger celestial signals and from those within the electronics systems of the apparatus used. 

For those of you who are not familiar with science, when you read the link, please read how the experimenters made the effort to ensure that their results are not due to their experimental technique or instrumentation.

Zz.