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.


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.


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.


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.


[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.


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.


[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.


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.


Wednesday, February 28, 2018

MinutePhysics Special Relativity Chapter 2

If you missed Chapter 1, check it out here.

Here's Chapter 2.


Tuesday, February 27, 2018

How People Got Time Dilation Wrong

While we are still waiting for Minute Physics to continue with its Special Relativity series, Fermilab's Don Lincoln has a nice video on the things that many people got wrong with SR's time dilation concepts. I see these misconception often, so this might be quite beneficial to those who do not have a formal lesson in SR. Heck, I think even physics students might benefit watching this.


Monday, February 26, 2018

Lawrence Krauss Hit By Sexual Misconduct Allegations

Oh dear. I knew it was going to happen that someone from within the physics community will be hit by such allegations (hey, we are all still human after all and not immune to doing such nasty actions). But it is still a bit surprising and disappointing when such allegations happens to someone whose writings I've enjoyed over the years.

I'm sure this will work through the legal system, and I'm not going to comment anymore than that. I think most, if not, all of us here in the US who work either in the academic settings or at a govt. lab had gone through training or classes on sexual harassment. In my case, I've had gone through several of these, including training on Title IX, etc.. etc.

This is an issue we all have to face, and we are now starting to see how pervasive it really is.


Saturday, February 24, 2018

New Measurement of Hubble Constant Brings New Puzzle

The most extensive measurement of the Hubble constant based on observations made by the Hubble telescope (how appropriate) has revealed a discrepancy between its value and those made earlier by ESA's Planck satellite.

Planck’s result predicted that the Hubble constant value should now be 67 kilometers per second per megaparsec (3.3 million light-years), and could be no higher than 69 kilometers per second per megaparsec. This means that for every 3.3 million light-years farther away a galaxy is from us, it is moving 67 kilometers per second faster. But Riess’s team measured a value of 73 kilometers per second per megaparsec, indicating galaxies are moving at a faster rate than implied by observations of the early universe.

The Hubble data are so precise that astronomers cannot dismiss the gap between the two results as errors in any single measurement or method. “Both results have been tested multiple ways, so barring a series of unrelated mistakes,” Riess explained, “it is increasingly likely that this is not a bug but a feature of the universe.”

The arXiv version of the paper can be found here.