Friday, February 14, 2020

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.


Monday, February 03, 2020

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.


Monday, January 20, 2020

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.


[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.

Wednesday, January 08, 2020

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!


Monday, January 06, 2020

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!


Wednesday, December 11, 2019

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.


Wednesday, November 20, 2019

What Is Quantum Mechanics Really All About?

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


Friday, October 18, 2019

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?


Tuesday, September 17, 2019

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". :)


Sunday, August 18, 2019

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.


Wednesday, August 14, 2019

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.