Simple Electric Motor Experiment

This was the last lab that my students managed to do before all in-person classes were cancelled due to the coronavirus. They had to build a simple electric motor, making use of the concept of magnetic field created by a loop of wire, the concept of magnetic moment, and magnetic torque.

The final "proof" that they had successfully built the motor is to show that it will spin continuously, which looks like this:

It's a common experiment done in many General Physics labs, but it is still a cool exercise. The students certainly had fun doing it and they felt a sense of accomplishment when they see the spinning coil in motion.

I was just glad we managed to do it just before the shutdown.

Zz.

First Hint of CP Violation in the Neutrino Sector

The latest report on T2K results has been published[1], and it looks good for the upcoming long neutrino baseline experiment at DUNE and T2HK. The result may suggest that these two upcoming experiments may finally nail down CP violation in neutrinos, which will be a substantial advancement in our understanding on why there are more mater than antimatter in our universe.

The discovery of substantial leptonic CP violation would be groundbreaking. Its observation, together with evidence that a quantity known as lepton number has been violated (that is, not conserved), would provide strong circumstantial evidence for leptogenesis as the origin of the matter–antimatter imbalance.

Zz.

[1] T2K collaboration, Nature v.580, p.339 (2020).

Making Physics Funny

Although Tom Gauld's cartoons do not actually focus on physics, he has included topics related to physics before. This NY Times article gives a brief interview and background on him, someone you would know if you read New Scientist frequently.

I decided to mention it here because the article included one of his cartoons that made me chuckle. I decided to include it here and make sure everyone is aware that this is credited to him. If he or his publisher object to this, I'll remove it.

It's pretty funny, though, because if you are involved in any kind of science forum or discussion online, this happens more often than you think.

And considering that our current President of the US thinks he's an expert in many different fields as well, I feel that I'm living in that Science Hell right now.

Zz.

More Geeky T-Shirts

Before all this mess with the coronavirus came up, I got the chance to wear these two t-shirts to my class when I was teaching resistance/circuits, and when I was teaching magnetic fields. These two are in addition to the other geeky t-shirt that I mentioned last time.

I'm thinking of buying more for a couple of different topics that I will be covering, but who knows when I'll get to wear them again in a class setting. I suppose I can wear them when I run my Zoom class session, but who gets to see the full effect of it when all you want to show is your face.

Zz.

Busy With Online Course Conversion

I'm sure everyone involved in course instruction is facing the same issue. The past 2 weeks have been rather hectic as I rush to reform the course and adapt it to a purely online course. It is certainly more daunting and more of challenge for science courses that have lab components.

I find myself not struggling as much as a few of the other faculty members that had never taught anything remotely or online. I've had some experience in teaching blended or hybrid courses, so I have had experience with conducting either asynchronous courses, synchronous courses via video-conferencing app such as WebEx. So for me, the work involves adapting my material that was meant for an on-site course into something more suitable for an online course.

As for the labs, I already have a collection of "virtual labs" that I had written previously that make use of the various online experiments such as the ones fro PhET, etc. So those actually require only minor rewrites and tweaks and they are good to go.

My main struggle and something that I still find a bit dubious, are the exams. I still do not believe that students will not cheat if they can when doing online tests and exams, no matter how much one tries. This is my main issue with any online courses, the ability to determine if the work was truly done by the student him/herself. I have heard many anecdotal cases where for the same course and same exam, students who took the online version scored significantly higher exam scores than the students who took the exam in class. So make your own conclusion there. I've written my exams in such a way that the questions are somewhat "unique" and can't be easily "googled". But there is no way to prevent the student from having someone else helping or even outright doing the exam for him/her. At the end, there is only so much one can do given the circumstances.

As of now, all I'm trying to do is survive the remainder of the semester with the new workload, and to stay healthy. I wish the same for all of you as well.

Zz.

RIP Freeman Dyson

Freeman Dyson has died at the age of 96.

Many anti-academia often used him as an example of being able to do physics without a PhD. But really, how many people are as gifted and as brilliant as he is? He was part of academia, because that was where he worked, and using him as an example is like planning your life as if you'll win a lottery.

Dyson's legacy will go on long after he is gone.

Zz.

2020 APS March Meeting Cancelled

By now, I'm sure those of you involved would have heard the news of the cancellation of the APS March meeting this year due to the coronavirus issue. For those of you who don't know, the APS March meeting is the LARGEST yearly physics conference in the world, attracting more than 10,000 physicists from around the world over a week of intellectual discussion and presentations.

This cancellation is quite unprecedented, because I do not remember the last time this has happened, if it has ever happened. So this is quite a big deal. I'm sure there's a lot of people impacted by this, especially in terms of travel and accommodation cancellations and fees.

No news yet on what will happen to the APS April meeting, which is looming in the very near future.

If you are affected by it, I'd like to hear it. Luckily (or unluckily), I wasn't going this year, so I don't have to deal with the mess.

Zz.

Quantum Entanglement

I made a post quite a while back on "Quantum Entanglement for Dummies" that tried to describe what it is. I emphasized the fact that this phenomenon is different than classical physics because of one every important characteristics of quantum mechanics, which is the superposition principle that is built into the quantum wavefunction. So to be able to understand why quantum entanglement exists and why it is so "spooky", one must first understand the superposition concept.

Don Lincoln has produced a video on quantum entanglement, and if you pay attention closely, he starts off with describing the superposition concept and how that made a quantum system not "predetermined" before a measurement. He also give a good overview on a Bell-type measurement that shows how experiments agree with QM description but not the hidden variables scenario.



A good video to start you off on understanding this phenomenon.

Zz.

State of the Art of MRI

This is a very good article from Physics Today on the history and development of Magnetic Resonance Imaging, which has become ubiquitous in medical diagnostics. Of course, this came out of the discovery of the nuclear magnetic resonance phenomenon, a technique that itself came out of our understanding of quantum mechanics.

When you read this article, pay attention to how it is continuing to be developed, to evolve, and its continuing improvement. Medical physicists are still actively improving this, and other aspect of the medical field by incorporating things that physicists already know and use. Without advancement in physics, both theoretically and experimentally, there is nothing to trickle down from to the medical field.

Zz.

Charge Fluctuation at a Quantum Critical Point.

This is a fascinating paper[1] (which I'll be reading more of in the next several weeks). But for now, I'll just highlight it here.

The authors found that charge fluctuation in a "strange metal" antiferromagnetic compound exhibit a scaling of f/T (frequency over temperature) in the optical conductivity, which often indicates the presence of a quantum critical point.

If anyone has done MBE before, you'll know how tedious and difficult it is to synthesize a material such as this, and have it be pristine enough to produce these effects that can be measured, at a THz level, no less!

There are many implications here, not the least of which is that the cuprate high-Tc superconductors share the same "parent" or undoped state, being antiferromagnetic perovskites themselves. There have been experiments indicating that the cuprates superconductors are also influenced by their proximity to a quantum critical point.

This is another example where some of the most fundamental aspects of quantum mechanics, in this case the concept of quantum criticality, can often be clearly manifested in a condensed matter system, not in elementary particle physics experiment.

Zz.

[1] L. Prochaska et al., "Singular charge fluctuations at a magnetic quantum critical point." Science v.367, p.285 (2020). ArXiv version of the paper can be found here.

What Really Happened At The Big Bang?

Don't you want to know?

Here is a simplified explanation of what the Big Bang is, and what the Big Bang is NOT!



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Thirteen tips for engaging with physicists, as told by a biologist

This is a rather fun reading, and it has a bit of truth if we (physicists) do a bit of self-reflecting on how we operate.

I think I'm going to post the link to the LMS for the general physics course I'll be teaching this Spring for Life Science/Pre-Med majors. 😄

And then there's a reverse flow, where you get 12 tips for engaging with biologist, as told by a physicist. Even a lot more self-reflection there!

In the end, biologists and physicists gain a lot from talking to each other.

And oh, Happy New Decade, btw!

Zz.

Tesla Coil at MSI

I was at the Chicago Museum of Science and Industry this past weekend, and got to see the Tesla Coil presentation. I've seen this several times, but it is always a hoot, so we never miss it every time we are there.

Strangely enough, this is the first time I've recorded a video of it, so here it is.



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What Is Quantum Mechanics Really All About?

Don Lincoln tries to explain what QM is to non-expert. Do you understand, and buy it?



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Non-Newtonian Fluids On America's Test Kitchen Show

I've seen this episode of America's Test Kitchen before. It is Ep. 1 of Season 19. However, during a recent rerun of the show, I did a double take when I read the description of the show being displayed on my TV menu guide:

There as an entry that said "non-Newtonian fluids".

Like I said, I've seen this show before, at least twice, and I don't quite remember them mentioning this type of phenomenon.

When I saw the show again, I realized what it was. They had a "Science" segment on "fluids" such as ketchup and liquid thickened by corn starch. These two are common examples of..... you guessed it ... non-Newtonian fluids.

But interestingly enough, no where in the show or during this segment, did any mention of the phrase "non-Newtonian fluids" ever appeared. It was odd that they would discuss the phenomenon, but not mention the name given to it. Yet, it appears on the description for this episode. At the very least, giving the phenomenon a name not only allows someone who wants to know more about it something to Google on, but also relates known physics to a common observation.

Or maybe they don't want to mention it so as not to scare away their audience?

Zz.

Electron Neutrino Losses It's Mass By Almost Half

A new experimental result out of KATRIN has cut the upper limit of the mass of electron neutrino by half, to 1.1 eV. This was reported at the recent conference and in a recent preprint.

I suppose if I want to be accurate, I should say it is the electron antineutrino, since they measured this from beta decays, but nowadays, we don't have a clear cut idea of the difference between the neutrino and its antiparticle. For all we know, they can possibly also be a Majorana particle.

I'll be giving this report to my students in the general physics class, and see if they can convert the 1.1 eV into "kg". :)

Zz.

Big Bang Disproved?!

Of course not! But this is still a fun video for you to watch, especially if you are not up to speed on (i) how we know that the universe is expanding and (ii) the current discrepancy in the measurement of the Hubble constant via two different methods.



But unlike politics or social interactions, discrepancies and disagreement in science are actually welcomed and a fundamental aspects of scientific progress. It is how we refine and polish our knowledge into a more accurate form. As Don Lincoln says at the end of the video, scientists love discrepancies. It means that there are more things that we don't know, and more opportunities to learn and discover something new.

Zz.

Relativisitic Length Contraction Is Not So Simple To See

OK, I actually had fun reading this article, mainly because it opened up a topic that I was only barely aware of. This Physics World article describes the simple issue of length contraction, but then delves into why OBSERVING this effect, such as with our own eyes, is not so simple.

If the Starship Enterprise dipped into the Earth’s atmosphere at a sub-warp speed, would we see it? And if the craft were visible, would it look like the object we’re familiar with from TV, with its saucer section and two nacelles? Well, if the Enterprise were travelling fast enough, then – bright physicists that we are – we’d expect the craft to experience the length contraction dictated by special relativity.

According to this famous principle, a body moving relative to an observer will appear slightly shorter in the direction the body’s travelling in. Specifically, its observed length will have been reduced by the Lorentz factor (1–v²/c²)^1/2, where v is the relative velocity of the moving object and c is the speed of light in a vacuum. However, the Enterprise won’t be seen as shorter despite zipping along so fast. In fact, it will appear to be the same length, but rotated.

You might not have heard of this phenomenon before, but it’s often called the “Terrell effect” or “Terrell rotation”. It’s named after James Terrell – a physicist at the Los Alamos National Laboratory in the US, who first came up with the idea in 1957. The apparent rotation of an object moving near the speed of light is, in essence, a consequence of the time it takes light rays to travel from various points on the moving body to an observer’s eyes.

You can read the rest of the explanation and graphics in the article. Again, this is not to say that your "pole-in-barn" exercise that you did in relativity lessons is not valid. It is just that in that case, you were not asked what you actually SEE with your eyes when that pole is passing through the barn, and that your pole is long and thin, as opposed to an object with a substantial size and width. The notion that such object will be seen with our eyes flat as a pancake is arguably may not be true here.

Zz.

RIP J. Robert Shrieffer

I'm sad to hear the passing of a giant in our field, and certainly in the field of Condensed Matter Physics. Nobel Laureate J. Robert Schrieffer has passed away at the age of 88. He is the "S" in BCS theory of superconductivity, one of the most monumental theories of the last century, and one of the most cited. So "complete" was the theory that, by early 1986, many people thought that the field of superconductivity has been fully "solved", and that nothing new can come out of it. Of course, that got completely changed after that.

Unfortunately, I wasn't aware of his predicament during the last years of Schrieffer's life. I certainly was not aware that he was incarcerated for a while.

Late in life, Dr. Schrieffer’s love of fast cars ended in tragedy. In September 2004, he was driving from San Francisco to Santa Barbara, Calif., when his car, traveling at more than 100 miles per hour, slammed into a van, killing a man and injuring seven other people.

Dr. Schrieffer, whose Florida driver’s license was suspended, pleaded no contest to felony vehicular manslaughter and apologized to the victims and their families. He was sentenced to two years in prison and released after serving one year.

Florida State placed Dr. Schrieffer on leave after the incident, and he retired in 2006.

I've met him only once while I was a graduate student, and he was already at Florida State/NHML at that time. His book and Michael Tinkham's were the two that I used when I decided to go into superconductivity.

Leon Cooper is the only surviving members left of the BCS trio.

Zz.

Light Drags Electrons Backward?

As someone who was trained in condensed matter physics, and someone who also worked in photoemmission, light detectors, and photoelectron sources, research work on light interaction with solids, and especially with metallic surfaces, is something I tend to follow rather closely.

I've been reading this article for the past few days and it gets fascinating each time. This is a report on a very puzzling photon drag effect in metals, or in this case, on gold, which is the definitive Drude metal if there is any. What is puzzling is not the photon drag on the conduction electron itself. What is puzzling is that the direction of the photon drag appears to be completely reversed between the effect seen in vacuum versus in ambient air.

A review of the paper can be found here. If you don't have access to PRL, the arXiv version of the paper can be found here. So it appears as if that, when done in vacuum, light appears to push the conduction electrons backward, while when done in air, it pushes electrons forward as expected.

As they varied the angle, the team measured a voltage that largely agreed with theoretical expectations based on the simple light-pushing-electrons picture. However, the voltage they measured was the opposite of that expected, implying that the current flow was in the wrong direction. It’s a weird effect," says Strait. “It’s as if the electrons are somehow managing to flow backward when hit by the light.”

Certainly, surface effects may be at play here. And those of us who have done photoemission spectroscopy can tell you all about surface reconstruction, even in vacuum, when a freshly-cleaved surface literally changes characteristics right in front of your eyes as you continually perform a measurement on it. So I am not surprised by the differences detected between vacuum and in-air measurement.

But what is very puzzling is the dramatic difference here, and why light appears to push the conduction electrons one way in air, and in the opposite direction in vacuum. I fully expect more experiments on this, and certainly more theoretical models to explain this puzzling observation.

This is just one more example where, as we apply our knowledge to the edge of what we know, we start finding new mysteries to solve or to explain. Light interaction with matter is one of the most common and understood phenomena. Light interaction with metals is the basis of the photoelectric effect. Yet, as we push the boundaries of our knowledge, and start to look at very minute details due to its application in, say, photonics, we also start to see the new things that we do not expect.

It is why I always laugh whenever someone thinks that there is an "end of physics". Even on the things that we think we know or things that are very common, if we start to make better and more sensitive measurement, I don't doubt that we will start finding something else that we have not anticipated.

Zz.