Saturday, April 22, 2017

Earth Day 2017 - March For Science Day

Today is the March for Science day to coincide with Earth Day 2017.

Unfortunately, I will not be participating in it, because I'm flying off to start my vacation. However, I have the March for Science t-shirt, and will be wearing it all day. So I may not be with all of you who will be participating it in today, but I'll be there in spirit.

And yes, I have written to my elected officials in Washington DC to let them know how devastating the Trump budget proposal is to science and the economic future of this country. Unfortunately, I may be preaching to the choir, because all 3 of them (2 Senators and 1 Representative of my district) are all Democrats who I expect to oppose the Trump budget as it is anyway.

Anyhow, to those of you who will be marching, YOU GO, BOYS AND GIRLS!


Friday, April 21, 2017

"Physics For Poets" And "Poetry For Physicists"?

Chad Orzel has a very interesting and thought-provoking article that you should read.

What he is arguing is that scientists should learn the mindset of the arts and literature, while those in the humanities and the arts should learn the mindset of science. College courses should not be tailored in such a way that the mindset of the home department is lost, and that a course in math, let's say, has been devolved into something palatable to an arts major.

I especially like his summary at the end:

One of the few good reasons is that a mindset that embraces ambiguity is something useful for scientists to see and explore a bit. By the same token, though, the more rigorous and abstract scientific mindset is something that is equally worthy of being experienced and explored by the more literarily inclined. A world in which physics majors are more comfortable embracing divergent perspectives, and English majors are more comfortable with systematic problem solving would be a better world for everyone.

I think we need to differentiate between changing the mindset versus tailoring a course for a specific need. I've taught a physics class for mainly life science majors. The topics that we covered is almost identical to that offered to engineering/physics majors, with the exception that they do not contain any calculus. But other than that, it has the same rigor and coverage. The thing that made it specific to the group of students is that many of the examples that I used came out of biology and medicine. These were what I used to keep the students' interest, and to show them the relevance of what they were studying to their major area. But the systematic and analytical approach to the subject are still there. In fact, I consciously emphasized the technique and skills in analyzing and solving a problem, and made them as important as the material itself. In other words, this is the "mindset" that Chad Orzel was referring to that we should not lose when the subject is being taught to non-STEM majors.


Wednesday, April 19, 2017

The Mystery Of The Proton Spin

If you are not familiar with the issues surrounding the origin of the proton's spin quantum number, then this article might help.

It explains the reason why we don't believe that the proton spin is due just to the 3 quarks that make up the proton, and in the process, you get an idea how complicated things can be inside a proton.

There are three good reasons that these three components might not add up so simply.
  1. The quarks aren't free, but are bound together inside a small structure: the proton. Confining an object can shift its spin, and all three quarks are very much confined.
  2. There are gluons inside, and gluons spin, too. The gluon spin can effectively "screen" the quark spin over the span of the proton, reducing its effects.
  3. And finally, there are quantum effects that delocalize the quarks, preventing them from being in exactly one place like particles and requiring a more wave-like analysis. These effects can also reduce or alter the proton's overall spin.
Expect the same with a neutron.


Tuesday, April 18, 2017

Testing For The Unruh Effect

A new paper that is to appear in Phys. Rev. Lett. is already getting quite a bit of advanced publicity. In it, the authors proposed a rather simple way to test for the existence of the long-proposed Unruh effect.

Things get even weirder if one observer accelerates. Any observer traveling at a constant speed will measure the temperature of empty space as absolute zero. But an accelerated observer will find the vacuum hotter. At least that's what William Unruh, a theorist at the University British Columbia in Vancouver, Canada, argued in 1976. To a nonaccelerating observer, the vacuum is devoid of particles—so that if he holds a particle detector it will register no clicks. In contrast, Unruh argued, an accelerated observer will detect a fog of photons and other particles, as the number of quantum particles flitting about depends on an observer's motion. The greater the acceleration, the higher the temperature of that fog or "bath."

So obviously, this is a very difficult effect to detect, which explains why we haven't had any evidence for it since it was first proposed in 1976. That is why this new paper is causing heads to turn, because the authors are proposing a test using our existing technology. You may read the two links above to see what they are proposing using our current particle accelerators.

But what is a bit amusing is that there are already skeptics about this methodology of testing, but each camp is arguing it for different reasons.

Skeptics say the experiment won’t work, but they disagree on why. If the situation isproperly analyzed, there is no fog of photons in the accelerated frame, says Detlev Buchholz, a theorist at the University of Göttingen in Germany. "The Unruh gas does not exist!" he says. Nevertheless, Buchholz says, the vacuum will appear hot to an accelerated observer, but because of a kind of friction that arises through the interplay of quantum uncertainty and acceleration. So,the experiment might show the desired effect, but that wouldn't reveal the supposed fog of photons in the accelerating frame.

In contrast, Robert O'Connell, a theorist at Louisiana State University in Baton Rouge, insists that in the accelerated frame there is a fog of photons. However, he contends, it is not possible to draw energy out of that fog to produce extra radiation in the lab frame. O'Connell cites a basic bit of physics called the fluctuation-dissipation theorem, which states that a particle interacting with a heat bath will pump as much energy into the bath as it pulls out. Thus, he argues, Unruh's fog of photons exists, but the experiment should not produce the supposed signal anyway.

If there's one thing that experimenters like, it is to prove theorists wrong! :) So which ever way an experiment on this turns out, it will bound to disprove one group of theorists or another. It's a win-win situation! :)


Monday, April 17, 2017

Hot Atoms Interferometer

This work will not catch media attention because it isn't "sexy", but damn, it is astonishing nevertheless.

Quantum behavior are clearly seen at the macroscopic level because of the problem in maintaining coherence over a substantial length and time scales. One of the ways one can extend such scales is by cooling things down to extremely low temperatures so that decoherence due to thermal scattering is minimized.

So it is with great interest that I read this new paper on atoms interferometer that has been accomplished with "warm" atomic vapor[1]! You also have access to the actual paper from that link.

While the sensitivity of this technique is significantly and unsurprisingly low when compared to cold atoms, it has 2 major advantages:

However, sensitivity is not the only parameter of relevance for applications, and the new scheme offers two important advantages over cold schemes. The first is that it can acquire data at a rate of 10 kHz, in contrast to the typical 1-Hz rate of cold-atom LPAIs. The second advantage is the broader range of accelerations that can be measured with the same setup. This vapor-cell sensor remains operational over an acceleration range of 88g, several times larger than the typical range of cold LPAIs.

The large bandwidth and dynamic range of the instrument built by Biedermann and co-workers may enable applications like inertial navigation in highly vibrating environments, such as spacecraft or airplanes. What’s more, the new scheme, like all LPAIs, has an important advantage over devices like laser or electromechanical gyroscopes: it delivers acceleration measurements that are absolute, without requiring a reference signal. This opens new possibilities for drift-free inertial navigation devices that work even when signals provided by global satellite positioning systems are not available, such as in underwater navigation.

And again, let me highlight the direct and clear application of something that started out as simply appearing to be a purely academic and knowledge-driven curiosity. This really is an application of the principle of superposition in quantum mechanics, i.e. the Schrodinger Cat.

This is an amazing experimental accomplishment.


[1] G. W. Biedermann et al., Phys. Rev. Lett. 118, 163601 (2017).

Sunday, April 16, 2017

Why Is The Weak Force Weak?

Fermilab's Don Lincoln has another fun and informative video on our elementary particles and interactions.


Saturday, April 15, 2017

To Draw Or Not To Draw?

OK, this is a rather lengthy paper, and I thought I would have gotten through it by now, but I just don't have the time. So instead, I'm just going to mention it here and let you people read for yourself.

This paper seems to argue that in cases of supporting diagram that accompanies a physics question (not diagram that actually is essential to the question), this diagram can often be useless, or even a hindrance to the students' ability to solve the problem.

This isn't the same as the student having to draw a diagram in solving a problem. That is not the subject of the paper here. I'm still trying to understand what is actually categorized as "supporting diagram" that accompanies a physics question. Maybe once I have a hang of that, the rest of the paper might be more relevant.

Still, if you're bored, you might have a go at it first ahead of me.


Tuesday, April 11, 2017

Dark Energy Is Not An Illusion

This is a good intro to Dark Energy if you want to know more about it. Even if you don't buy into Ethan Siegel's argument, you at least have a good description of what we know of about Dark Energy at the moment, and why certain explanations for what have been observed have been ruled out.


Monday, April 10, 2017

"Genuine" 3-Photon Interference

I continue to be amazed at the creativity and capability of many of these experiments. This is one such example, and there were two groups that achieved this independently.

Two papers in PRL this week are reporting the first genuine observation of 3-photon interference. This is a purely quantum mechanical effect and not explained by any classical light wave description. In case you are not familiar with the background info that is needed here, the "interference" phenomenon that we are familiar with are really single-photon interference, i.e. one photon capable of making multiple paths and taking multiple slits to produce the interference pattern that we know and love. 2-photon interference has been done and is not that commonly observed. 3-photon interference is even more difficult. That is why this is such a spectacular result coming from 2 different groups.

BTW, this is another experiment that can only be described using the photon picture.


Saturday, April 08, 2017

The Search For Neutrinoless Double Beta Decay

This is a nice and simple article on why we are searching for the neutrinoless double-beta decay.

In this new study, physicists are seeking so-called neutrinoless double-beta decay. Normally, some radioactive atoms' unstable nuclei will lose a neutron via beta decay — the neutron transforms into a proton by releasing an electron and a tiny particle called an electron antineutrino. A mirror image can also occur, in which a proton turns into a neutron, releasing a positron and an electron neutrino — the normal-matter counterpart to the antineutrino. Double-beta decay happens when two electrons and two antineutrinos (the antimatter counterparts of neutrinos) are released: basically, the beta decay happens twice. Scientists have long theorized a neutrinoless version of this process — something that would suggest that the two neutrinos annihilated each other before being released from the atom. Essentially, the neutrino behaves as its own antimatter sibling.

A large portion of high-energy physics experiments around the world are done using neutrinos (Daya Bay, MINOS, NOvA, SuperK, etc...).  It won't surprise me one bit that the another major discovery will be made with these particles.


Thursday, April 06, 2017

Developing Skills Versus Developing Concepts In Undergraduate Physics Labs

This is something that is dear to my heart.

If you have followed this blog for any considerable period of time, you might have encountered a project that I started on my own years ago on here titled "Revamping Intro Physics Lab". In a series of posts (there were 7 posts and one follow-up in total), I made suggestions on the type of lab exercises that I would like to do for students in such a class. The lab experiments are more "free form" and more of a discovery-type exercises, where the students make their own self-discovery without the baggage of knowing the underlying physics before hand.

I explained the rational for wanting to do this, and the most important aspect of it is the "skill" that one might develop in trying to systematically discover the connection and correlation between two different quantities. It is the beginning of finding first the correlations, and then proceed to finding the causation. I consider such skill to be of utmost importance, even more important than trying to make the students understand the underlying physics.

Therefore, it was a pleasant bonus when I read this paper. In it, the authors studied the E-CLASS assessment of students who went through a physics lab that (i) focused on developing lab skills; (ii) focused on developing physics concepts; and (iii) focused on both. What they discovered was that the students that went through a physics lab that focused on developing lab skills ".... showed more expert-like postinstruction responses and more favorable shifts than students in either concepts-focused or both-focused course...." And what is even more interesting is the finding that ".... the
ANCOVA demonstrated that the increase in score associated with skills-focused courses was larger for women than for men, and the difference was large enough to eliminate or even reverse the typical gender gap..... "

Of course, while this is very encouraging, I won't jump up and down (yet) because one has to read their caution at the end of the paper. As with anything, this needs to be looked at and studied a lot more to see if there is a true cause-and-effect factor here, especially on why a focus on lab skills could produce such an effect.

As for me, I'm all for this. In a class where the majority of students are not physics majors, or even in a class of non-science majors, having them understand that our knowledge of the physical universe is based on how we know about the relationship between two separate quantities is very important. That is how we make sense of our world. It is why uncorrelated events, such as how one arranges one's furniture in a room somehow affects one's prosperity doesn't make much sense. None science majors do not have a lot of opportunity for a guided study of the physical world. When we get them, we need to impart as much as we can in the most effective manner. A lab when they learn how to find out how one variable affects another, and the skills the employ to do that, can be the most valuable thing they learn in a physics lesson.