Tuesday, November 13, 2018

Muons And Special Relativity

For those of us who studied physics or have taken a course involving Special Relativity, this is nothing new. The case of a lot of muons being detected on the earth's surface has been used as an example of the direct result of SR's time dilation and length contraction.

Still, it bears repeating, and presenting to those who are not aware of this, and this is what this MinutePhysics video has done.


Friday, November 09, 2018

Comparing Understanding of Graphs Between Physics and Psychology Students

I ran across this paper a while back, but didn't get to reading it carefully till now.

If you have followed this blog for any considerable period of time, you would have seen several posts where I emphasized the importance of physics education, NOT just for the physics knowledge, but also for the intangible skills that comes along with it. Skills such as analytical ability and deciding on the validity of what causes what are all skills that transcends the subject of physics. These are skills that are important no matter what the students end up doing in life.

While I had mentioned such things to my students during our first day of class each semester, it is always nice when there are EVIDENCE (remember that?) to back such claim. In this particular study, the researchers compare how students handle and understand the information that they can acquire from graphs on topics outside of their area of study.

The students involved are physics and psychology students in Zagreb, Croatia. They were tested on their understanding of the concept of slope and area under the graph, their qualitative and quantitative understanding of graphs, and comparing their understanding of graphs in the context of physics and finance. For the latter area (finance), both groups of students did not receive kind of lessons in that subject area and thus, are presumably unfamiliar with both groups.

Before we proceed, I found that in Croatia, physics is a compulsory subject in pre-college education there, which is quite heartening.

Physics is taught as a compulsory subject in the last two grades of all elementary schools and throughout four years of most of high schools in Croatia. Pupils are taught kinematics graphs at the age 15 and 16 (last grade of elementary school and first year of high school). Psychology students were not exposed to the teaching on kinematics graphs after high school, while physics students learned about kinematics graphs also in several university courses. Physics and psychology students had not encountered graphs related to prices, money, etc., in their formal education.
So the psychology students in college are already familiar with basic kinematics and graphs, but did not go further into it once they are in college, unlike physics students. I'd say that this is more than what most high school students in the US have gone through, since Physics is typically not required in high schools here.

In any case, the first part of the study wasn't too surprising, that physics students did better overall at physics questions related to the slope and area under the graph. But it was interesting that the understanding of what "area under the graph" tends to be problematic for both groups. And when we got to the graphs related to finance, it seems clear that physics students were able to extract the necessary information better than psychology students. This is especially true when it comes to the quantitative aspect of it.

You should read the in-depth analysis and discussion of the result. I'll quote part of their conclusion here:

All students solved the questions about graph slope better than the questions about the area under a graph. Psychology students had rather low scores on the questions about area under a graph, and physics students spent more time than psychology students on questions about area under a graph. These results indicate that area under a graph is quite a difficult concept that is unlikely to be developed without formal teaching and learning, and that more attention should be given to this topic in physics courses.

Physics and psychology students had comparable scores on the qualitative questions on slope which indicates that the idea of slope is rather intuitive. However, many psychology students were not able to calculate the slope, thus indicating that their idea of slope was rather vague. This suggests that the intuitive idea of slope, probably held by most students, should be further developed in physics courses and strongly linked to the mathematical concept of slope that enables students to quantify slope.

Generally, physics students solved the qualitative and the quantitative questions equally well, whereas psychology students solved qualitative questions much better than the quantitative questions. This is further evidence that learning physics helps students to develop deeper understanding of concepts and the ability to quantitatively express relationships between quantities.

The key point here is the "transfer" of knowledge that they have into an area that they are not familiar with. It is clear that physics students were able to extract the information in the area of finance better than psychology students. This is an important point that should be highlighted, because it shows how skills learned from a physics course can transfer to other areas, and that a student need not be a physics major to gain something important and relevant from a physics class.


Thursday, November 08, 2018

The Origin Of Matter's Mass

I can't believe it. I'm reporting on Ethan Siegel's article two days in a row! The last one yesterday was a doozy, wasn't it? :)

This one is a bit different and interesting. The first part of the article describes our understanding of where mass comes from for matter. I want to highlight this because it clarify one very important misconception that many people have, especially the general public. After all the brouhaha surrounding the Higgs and its discovery, a lot of people seem to think that all the masses of every particle and entity can be explained using the Higgs. This is clearly false as stated in the article.

Yet if we take a look at the proton (made of two up and one down quark) and the neutron (made of one up and two down quarks), a puzzle emerges. The three quarks within a proton or neutron, even when you add them all up, comprise less than 0.2% of the known masses of these composite particles. The gluons themselves are massless, while the electrons are less than 0.06% of a proton's mass. The whole of matter, somehow, weighs much, much more than the sum of its parts.

The Higgs may be responsible for the rest mass of these fundamental constituents of matter, but the whole of a single atom is nearly 100 times heavier than the sum of everything known to make it up. The reason has to do with a force that's very counterintuitive to us: the strong nuclear force. Instead of one type of charge (like gravity, which is always attractive) or two types (the "+" and "-" charges of electromagnetism), the strong force has three color charges (red, green and blue), where the sum of all three charges is colorless.

So while we may use the Higgs to point to the origin of  mass in, say, leptons, for hadrons/partons, this is not sufficient. The strong force itself contributes a significant amount to the origin of mass for these particles. The so-called "God Particles" are not that godly, because it can't do and explain everything.

The other interesting part of the article is that he included a "live blog" of the talk by Phiala Shanahan at occurred yesterday at the Perimeter Institute, related to this topic. So you may want to read through the transcript and see if you get anything new.


Wednesday, November 07, 2018

US No Longer Attracts The Best Physics Minds

So much for making America great again.

Ethan Siegel summarizes the recent data on the severe drop in the number of international students seeking advanced physics degree in the US, and the drop in the number of applicants to US schools.

You need to read the article and the history of US advancement in physics, and science in general, to realize why this is a troubling trend. Whether you realize it or not, what you are enjoying now is the result of many such immigrants who came to the US and made extraordinary discoveries and contribution to science. This may no longer be true soon enough.

Yet, according to the American Physical Society, the past year has seen an alarming, unprecedented drop in the number of international applications to physics PhD programs in the United States. In an extremely large survey of 49 of the largest physics departments in the country, representing 41% of all enrolled physics graduate students in the United States, an overall decrease of almost 12% in the number of international applicants was observed from 2017 to 2018.

Graduate students in physics, if you are not aware of it, are the workhorse in advanced physics research. While senior researchers often think of the project, find the funding, and form the group, it is the graduate students and postdoc that often are the ones doing the actual work and executing the plan. And many of us not only rely on their skills and knowledge, but also their creativity in solving the myriads of problems that we often did not anticipate during the research work.

Without graduate students, many research programs would either come to a halt, or will be severely impacted. Period!

And the reality here is that the overwhelming majority of US institutions, both universities and US National Labs, have come to depend on a lot of international graduate students for these research projects. The ability to attract not just the best talent in the US, but also the best talent from all over the world, was a luxury that was the envy of many other countries. But that is no longer the case now, and the gloomy prediction of the beginning of the decline isn't that outrageous.

We find ourselves, today, at the very beginning of what could be the end of America's greatness in the realm of scientific research and education. Science has always been touted as the great equalizer: the scientific truths underlying our Universe know no borders and do not discriminate based on race, gender, or religion. We still have time to reverse this trend, and to welcome the brightest minds the world has to offer into our country.

But if we fail to do so, that intellectual capital will thrive elsewhere, leaving America behind. If we do not change course, "America First" will be the downfall of scientific greatness in our country.

I said as much way back in 2012 when I started noticing for the first time of many established Chinese researchers and college professors starting to migrate back to China and to Chinese institutions, something that was unheard of several years before. So now, compounding the budget constraints, we now have clear data on US no longer attracting as many international students as before.

There are no "greatness" in any of these here.


Thursday, November 01, 2018

Cerenkov Radiation

Don Lincoln tackles the origin of Cerenkov radiation this time. This is the case where a body travels faster than light in a medium.

This is not purely academic. This is how we detect certain particles, such as neutrinos. Those photodetectors in, say, SuperKamiokande, are detecting these Cerenkov radiation. In fact, if you look in a pool of water of nuclear fuel rods, the blue light is the result of Cerenkov radiation.

So here's a chance for you to learn about Cerenkov radiation.