Sunday, September 16, 2018

Want To Located The Accelerometer In Your Smartphone?

Rhett Allain has a simple, fun rotational physics experiment that you can perform on your smartphone to locate the position of the accelerometer in that device, all without opening it.

Your smart phone has a bunch of sensors in it. One of the most common is the accelerometer. It's basically a super tiny mass connected with springs (not actual springs). When the phone accelerates in a particular direction, some of these springs will get compressed in order to make the tiny test mass also accelerate. The accelerometer measures this spring compression and uses that to determine the acceleration of the phone. With that, it will know if it is facing up or down. It also can estimate how far you move and use this along with the camera to find out where real world objects are, using ARKit.

So, we know there is a sensor in the phone—but where is it located? I'm not going to take apart my phone; everyone knows I'll never get it back together after that. Instead, I will find out the location by moving the phone in a circular path. Yes, moving in a circle is a type of acceleration.

I'll let you read the article to know what he did, and what you can do yourself. 

Now, the only thing left is to verify the result. Someone needs to open an iPhone 7 and confirm the location of the accelerometer (do we even know what it looks like in such a device?). Any volunteers? :)


Friday, September 14, 2018

Bismuthates Superconductors Appear To Be Conventional

A lot of people overlooked the fact that during the early days of the discovery of high-Tc superconductors, there was another "family" of superconductors beyond just the cuprates (i.e. those compounds having copper-oxide layers). These compounds are called bismuthates, where instead of having copper-oxide layers, they have bismuth-oxide layers. Otherwise, their crystal structures are similar to the cuprates.

They didn't make that much of a noise at that time because Tc for this family of material tends to be lower than the cuprates. And, even back then, there were already evidence that the bismuthates superconductors might be "boring", i.e. the results that they have produced looked like they might be a conventional superconductor. This is supported by several experiments, including a tunneling experiment[1] that showed that the phonon density of states obtained from tunneling data matches that of the density of states obtained from neutron scattering.

Now it seems that there is more evidence that the bismuthates are conventional BCS superconductors, and it comes from ARPES experiment[2]. There have been no ARPES measurement done on bismuthates before this because it had been a serious challenge to get a single-crystal of this compound large enough to perform such an experiment. But obviously, large-enough single-crystals have been synthesized.

In this latest experiment, they look at the band structure of this compound, and extract, among others, the strong electron-phonon coupling that matches the superconducting gap. This strongly indicates that phonons are the "glue" in the superconducting mechanism for this compound.

So this adds another piece of the puzzle for the whole mystery of the origin of superconductivity in the cuprates. Certainly, having similar layered crystal structure does not discount being a conventional superconductor. Yet, the cuprates have very different behavior when we perform tunneling and ARPES experiments, and they certainly have higher Tc's.

The mystery continues.


[1] Q. Huang et al. Nature v347, p369 (1990).
[2] CHP. Wen et al. PRL  121, 117002 (2018).

Thursday, September 13, 2018

Human Eye Can Detect Cosmic Radiation

Well, not in the way you think.

I recently found this video of an appearance of astronaut Scott Kelly on The Late Show with Stephen Colbert. During this segment, he talked about the fact that when he went to sleep on the Space Station and closed his eyes, he occasionally detected flashes of light. He attributed it to the cosmic radiation  passing through his body, and his eyes in particular.

Check out the video at minute 3:30

My first inclination is to say that this is similar to how we detect neutrinos, i.e. the radiation particles interact with the medium in his yes, either the vitreous or the medium that makes up the lens, and this interaction causes the ejection of relativistic electron and subsequently, a Cerenkov radiation. The Cerenkov radiation is then detected by the eye.

Of course, there are other possibilities, such as the cosmic particle causes an excitation of an atom or molecules when they collided, and this then caused a light emission. But Scott Kelly mentioned that these flashes appeared like fireworks. So my guess here is that it is more of a very short cascade of events, and probably the Cerenkov light scenario.

This, BTW, is almost how we detect neutrinos, especially at Super Kamiokande and all the neutrino detectors around the world. Neutrinos come into the detector, and those that interact with the medium inside the detector (water, for example), cause the emission of relativistic electrons that move faster than the speed of light inside the medium. This creates the Cerenkov radiation, and typically, the light is blueish white. It's the same glow that you see if you look in a pool of fuel rods in a nuclear reactor.

So there! You can detect something with your eyes closed!


Thursday, August 30, 2018

Where Do Elementary Particle Names Come From?

In this video, Fermilab's Don Lincoln tackles less about physics, but more about history and classification of our current Standard Model of elementary particles.


Wednesday, August 29, 2018

Monday, August 27, 2018

US National Academies Endorse Building Electron-Ion Collider

The US National Academy of Sciences, Engineering, and Medicine have endorsed the building of an electron-ion collider in the US as the top priority for the nuclear physics community. The detailed report on the building and science of such facility can be found here.

An EIC slams electrons into protons or heavier ions to investigate the quarks and gluons inside the nucleons. A collider with high energy and luminosity—a measure of the rate at which particle collisions occur—would have the fine resolution needed to answer some of the big-picture questions cited by the committee. Those include elucidating the origin of the mass and spin of nucleons, learning how gluons hold nuclei together, and determining whether emergent forms of matter made of dense gluons exist.

Beyond nuclear science, an EIC would benefit astrophysics, high-energy physics, accelerator physics, and theoretical and computational modeling, the committee writes. Further, it is the only high-energy accelerator (excluding light sources) being considered for construction in the nation, and building it would help to maintain US expertise in accelerator and collider science. “An EIC would be a unique facility in the world and would maintain US leadership in nuclear physics,” the report states. Although there is no existing EIC, China is also considering building one.

While this facility has the word "collider" attached to it, this is not a high-energy physics facility nor will it be funded out of the high-energy physics directorate of the DOE and NSF. It will be a nuclear physics facility, just like RHIC, CEBAF, and the upcoming FRIB.

Now, if only the politicians in Washington can be convinced of the need to build such a thing... y'know, make America "great" again, even though we no longer have any high-energy physics collider on US soil.


Saturday, August 25, 2018

Don't Go To The Movies With A Physicist?

OK, no one tell any of my friends that, or I'll be going to the movie alone from now on.

This article interviews professors Maxim Sukharev and Michael Dugger of the Applied Physics Lab at Arizona State University on the physics that they noticed in the movies. The article focuses on light, as in lasers, since these scientists are experts on them.

“Lightsabers? I don’t know what those are supposed to be,” said Dugger in puzzlement, as the two settled into Siskel and Ebert mode. “If that’s a laser, particles of light would never just stop abruptly like that."

“Of course, if you see somebody on the big screen with a Russian accent doing science, that person will turn out to be a bad character,” Sukharev said with a chuckle. He completed a doctorate in the Department of High-Power Lasers in the General Physics Institute of the Russian Academy of Sciences in Moscow. “But what’s really laughable to me is when a spacecraft is shown speeding through the vacuum of deep space and yet we hear, ‘Zoom, zoom.’ 

I'm not that critical of the scientific mistakes or outrageous applications of science in the movies. They are, after all, fiction. But I can suspend my disbelief only so much, and if a movie takes too many liberties and transgression against science, then the movie is not longer that credible, because one can just make things up without regards to anything.

I can't wait for Avengers 4!


Tuesday, August 21, 2018

Preaching Not To The Choir

I attended a faculty meeting last week and got to chat with faculty members from various departments. This had always been a fun occasion, especially getting to know people that I've never met before.

One of the topics of conversation inevitably was on the students that we get in our classes. As a physics instructor (and I'm sure it is relevant to other subjects as well), we get a wide range of spectrum of students, especially in courses not aimed for physical sciences/engineering students. I was then asked which group of students I prefer to teach to: the physics/chemistry/engineering students, or the life sciences/biology/pre-med/non-science students?

I actually surprised myself when, without hesitation, I replied that I prefer to teach the latter, i.e. the students who are not physical science majors. In fact, if I think about it more carefully, I prefer to teach a physics class to non-science students.

We had a lively discussion on this topic, and I have boiled it down to a simple reason. Maybe I'm a glutton for punishment, but I find it to be a challenge to run a physics class for students who do not really want to take that class, and who are there because they have to.

When you teach a physics class for physics/chemistry/engineering students, you do not need to sell the importance of the material. These students, whether they like physics or not, realize that the subject matter is relevant to their major. There is a clearer connection to their area of study to the various topics that we cover in a typical General Physics course. So stressing the importance and relevance of physics to these students is preaching to the choir.

This connection is not as apparent for life science/pre-med/non-science majors. More often than not, they take the class to fill their required electives, and given a choice, they'd rather take a different class. It also does not help that, among the students, a physics class is often touted to be one of the more difficult subjects. So for these students, there are already a lot of negative vibes towards a physics class. These students are not in the choir.

My philosophy in teaching physics to these students comprises of two factors
  1. I don't need to make then love, or even like, physics. However, I want to give them an appreciation of the importance of the subject matter. You do not have to like something to know that it is still important. I find the subject of Accounting to be a bore and something I can't see myself doing. However, it doesn't mean that I do not realize the importance of accountants, especially during tax time! The students to not have to like physics, but they need to be aware of its importance, and how it has affected their lives in a very significant way.
  2. I appeal to things that they already know, and show them that, whether they realize it or not, they already know a lot of physics. I ask them what will happen if I toss a ball vertically up in the air; ask then which one will boil faster: a kettle with a cup of water or a kettle with a gallon of water; query them of what will happen if I take a corner too fast while driving, especially if the road is wet or icy;, etc. Inevitably, many of the students will know what will happen next, because these are all part of their everyday experience, and this is what physics is.
When I teach a physics class for non-physical science students, I very seldom start with teaching the topic. I usually begin with either a demo, or an example of an application. If this is a class for biology/pre-med students, then the example will be from biology or medicine. It is in my experience that this type of motivation and relevancy are more effective and needed for non-physical science students to get them to pay closer attention to the physics topic being presented.

For non-science students, this, and the conceptual understanding of the physics come ahead of the mathematical description. Often, these students have very weak mathematics, and a few even have math/science phobia. So I resort to using mathematics only in the latter half of the class session after the students are comfortable with the concept being presented.

But the one important reason why my preference is to teach physics to these non-physical science students is because these are group of people who make up the majority of the population, and the group of people who may be in deciding the future of science funding, the public policy on science education, scientific results, etc. This group of people should not leave school with a distaste for physics, and for science in general. They may not want to do science, but they should be aware and appreciate why science is important, and how science plays a hugely significant role in their lives.

They may not be in the choir, but they should not be neglected and not preached to.


Monday, August 20, 2018

Another Superconductor Scandal Brewing?

I heard about this preprint and the reported result towards the end of July, and my reaction to this type of "discovery" is "wait-and-see". In the history of superconductivity, we have had MANY of such similar claims, and many of them amounted to nothing.

However, this one seems to have taken a life and a drama of its own. SciAm has a report on what has transpired so far.

I heard about the identical background noise in the data more than a week ago when Brian Skinner posted his ArXiv comment. The first thing that came to my mind was "Oh no, this is Hendrik Schon all over again!" Turns out, I'm not the only one based on what was written in the SciAm article.

The only way this will be determined is an independent verification. That is how science works, and this is how experimental discovery works. We simply do not accept something just because someone says so.


Friday, August 17, 2018

The Quantum Form of General Relativity's Equivalence Principle?

This is an interesting approach to one of the dilemma being faced in physics, which is trying to reconcile General Relativity, or gravity in particular, with the quantum mechanical picture. We have had String Theory and Loop Quantum Gravity, etc. going through this effort. But in this paper that just got published in Nature[1], the authors tackled it in a different way, by examining the Einstein's equivalence principle and formulating the QM's version of it, which is different than the classical version.

The ArXiv version of the paper can be found here. However, I have not verified if it is identical to the published version. The ArXiv manuscript was submitted in 2015, while the version in Nature Physics has only been published recently (2018). There doesn't appear to be any updates to this version since its submission to ArXiv.

The best part about this is that the predictions are testable (gives dirty look at String Theory).

I'll let you explore this and see what you think.


[1] Magdalena Zych, Caslav Brukner, Nature Physics,

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.