Wednesday, April 18, 2018

Forum with Congressman and Physicist Bill Foster

This is the talk given by Congressman and the only Physicist left in the US Congress, Bill Foster, at this year's APS March meeting.



I have been in attendance to one of Bill Foster's talk before, at the 2011 TIPP conference in Chicago. You may read my "live" reporting of that talk back then, and also a follow-up post on it.

Zz.

Tuesday, April 17, 2018

The Friedmann Equation

Astrophysicist Ethan Siegal picked the Friedmann equation as the "most important" equation in the universe.

The first Friedmann equation describes how, based on what is in the universe, its expansion rate will change over time. If you want to know where the Universe came from and where it's headed, all you need to measure is how it is expanding today and what is in it. This equation allows you to predict the rest!

I don't have the "most important equation" in the universe for my pick, mainly because I don't know the criteria for picking such a thing. And often times, people confuses "interesting" with "important", which need not be mutually inclusive.

It's still fun to read what other physicists think is the most important equation, even if I don't necessarily agree with their picks.

Zz.

Friday, April 13, 2018

An Overview of CLIC at CERN

This is the lesser known effort at CERN among the general public, and yet, it may have one of the most significant impacts coming out of this high-energy physics lab.

CLIC, or the Compact Linear Collider research project at CERN has been studying accelerator science for many years. This is one of a few prominent research centers on accelerator physics throughout the world. Both they and many other accelerator research centers are making advancements in accelerator science that have a direct benefit and application to the general public.

So my intention in highlighting this article is not simply for you to learn what the people at CLIC do. Some of the description may even be beyond your understanding. What you should focus on is all the applications that are already in use, or can be possible in the near future, on the advancements made in this area of physics/engineering. These applications are not just within physics/engineering.

Unfortunately, as I've stated a few times in this blog, funding for accelerator science is often tied to funding in high energy physics, and for the US, the funding profile in this sector has been abysmal. So while accelerator science is actually independent of HEP, its funding has gone downhill with HEP funding over the last few years, especially after the shutdown of the Tevatron at Fermilab.

Whether you support funding, or increase in funding, of this area of study is a different matter, but you should at least be aware and have the knowledge of what you are supporting or not supporting, and not simply make a decision based on ignorance of what it is and what it's implication can be.

Zz.

Tuesday, April 10, 2018

What Astronomers Wish You Know About Dark Matter And Dark Energy

If you do a search of this blog, you will encounter numerous entries on both "dark matter" and "dark energy". It is something I've covered quite often, mainly because it is still an ongoing and active research area in astrophysics/astronomy/cosmology. Even high-energy physics/elementary particle physics is getting into the picture with particle astronomy.

In this article, Ethan Siegel gives you a condensed version of what "dark matter" and "dark energy" are, and what you need to know about them. But more importantly, if you think that you can discard them, you need to do more than just say that they are not needed.

It wasn't always apparent that this would be the solution, but this one solution works for literally all the observations. When someone puts forth the hypothesis that "dark matter and/or dark energy doesn't exist," the onus is on them to answer the implicit question, "okay, then what replaces General Relativity as your theory of gravity to explain the entire Universe?" As gravitational wave astronomy has further confirmed Einstein's greatest theory even more spectacularly, even many of the fringe alternatives to General Relativity have fallen away. The way it stands now, there are no theories that exist that successfully do away with dark matter and dark energy and still explain everything that we see. Until there are, there are no real alternatives to the modern picture that deserve to be taken seriously

It might not feel right to you, in your gut, that 95% of the Universe would be dark. It might not seem like it's a reasonable possibility when all you'd need to do, in principle, is to replace your underlying laws with new ones. But until those laws are found, and it hasn't even been shown that they could mathematically exist, you absolutely have to go with the description of the Universe that all the evidence points to. Anything else is simply an unscientific conclusion.

Zz.

Monday, April 09, 2018

Another "Unconventional" Superconductor?

This is definitely exciting news, because if verified, this will truly open up a whole new phase space for superconductivity.

An advanced publication has appeared reporting the discovery of high-spin state quasiparticles that are involved in superconducitivty.[1] This occurs in a topological semimetal YPtBi.

Previously, superconductivity occurs due to quasiparticles of spin 1/2 forming pairs called Cooper pairs. Now these Cooper pairs can have a total spin of either 0 (singlet state), or 1 (triplet state). This new superconductor seems to be formed by quasiparticles having spin 3/2! The resulting Cooper pairs may have total spin of 3 or 2.

It turns out that based on their measurements, the pairing symmetry appears to be predominantly in the spin state of 3, with a sub-dominant component having 0 (the singlet) state.

If you want to know how a quasiparticle here could have a spin 3/2 state, then you need to learn about spin-orbit coupling that we all learned in intro QM classes, and read the article.

This is utterly fascinating. Just when you think you can't be surprised anymore by the phenomenon of superconductivity, along comes one!

Zz.

[1] H. Kim et al., Sci. Adv.2018;4

Wednesday, April 04, 2018

Twin Paradox - The "Real" Explanation, But With No Math

Don Lincoln made a video a while back explaining the apparent twin paradox, explaining that it isn't due to acceleration. It seems that his audience wanted an explanation, but without using math. He has graciously agreed and this video is his attempt at providing the same explanation, but without all that math in the earlier video.



Is this clearer for people who didn't quite get the first video?

Zz.

Tuesday, April 03, 2018

MinutePhysics Special Relativity Chapter 3

If you missed Chapter 2 of this series, you can check it out here.

Here is Chapter 3, and this is where he uses that thing-ma-jiggy to illustrate Lorentz transformation.



Zz.

Sunday, April 01, 2018

Do A Search On "Physics" and "Physicist"

.. which, btw, is almost the title of this physics blog! :)

Chad Orzel must have been bored when he decided to do a search on the words "physics" and then "physicist". Hilarity ensues.

I'm not surprised that some of these search engines confuse "physicist" and "physician", since many people think people who work in physics are "physician". But a few of those stock photos that he found from Shutterstock are just hilarious. Of course, stereotype abounds, but some of these are so far out in left field, they are hardly relevant.

I guess, subconsciously, this was partly the reason why I did that superficial poll on the most attractive male and female physicist a while back. We all don't look like Albert Einstein, even for our women physicists!

Zz.

Friday, March 30, 2018

Revamping Introductory Physics Laboratory - Part 8

If you are not aware of my own pet project, this post will get you up to speed.

It has been a while since I updated this series, but better late than never. For this one, I'm going a bit against my own philosophy that physics just doesn't say what goes up must come down, but also when and where it comes down. For this exercise, I'm sticking with just the "what goes up must come down" part, i.e. only the qualitative aspect, not the quantitative aspect. But I have a good reason for it. It is because, in my experience, students often have a tough time understanding the concept itself, and I often found myself having to spend a considerable amount of time on this before I could proceed to the quantitative aspect of it. So in this exercise, the main idea is to make the students understand the concept and not worry about the "numbers" yet.

The topic of this exercise is Lenz's Law. This "lab" can actually be done either with real equipment in a laboratory setting, or done using a virtual setup. The PhET virtual setup for Faraday's Law is perfectly suited for this:

https://phet.colorado.edu/sims/html/faradays-law/latest/faradays-law_en.html

If you are doing this as a real experiment, you will need a solenoid, a bar magnet, a galvanometer with the "zero" position at the center of the scale, and some connecting wires. I've used a tightly-wound homemade solenoid, and it works fine. Note that you will need to know the direction of how the solenoid is wound (i.e. you need to be able to see the windings) so that you can figure out the sense of rotation of any current flow in the solenoid.

For this exercise, I will use the PhET simulation. I have used this as part of my in-class lecture on this topic, since every student in my class has a laptop or tablet and can access the PhET website during class. And yes, they were reminded to bring those devices to class for this topic.



Let's start with the aim of this exercise: It is to let students figure for themselves a "general rule" on when there is current in the circuit, and the direction of this current.

Keep in mind that the whole principle of this revamped lab idea is that the instruction is kept to a minimum, the students do not need to know the actual physics concept or principle, and we let them discover or learn about the phenomenon for themselves. So with that in mind, my only instruction to the students is this:

By using the magnet and moving it in and out of the solenoid, find a GENERAL RULE on when there is current in the circuit, and the direction of this current. Your rule must be able to tell  me that by doing an action, it will or will not result in a current in the circuit, and the direction that this current flows.

I give them a bit of a guideline, especially for those who are a bit clueless on what to do.

  • To simplify things, first figure out the direction of current flow in the solenoid if the galvanometer deflects to the right, and the direction of current flow if the galvanometer deflects to the left. Let's define the point of view by looking at the solenoid from the right, i.e. from where the magnet is in the figure above. The galvanometer will deflect to the right if current flows into it via the positive terminal, while it will deflect to the left if current flows into it via the negative terminal. So if one were to trace this path carefully, one can see that when viewed from the right, the current goes clockwise for positive deflection, and counter-clockwise for negative deflection. Armed with this info, we don't need to figure out anymore the sense of rotation of current in the solenoid, since by looking at the galvanometer deflection alone, we can tell the direction immediately.
  • Next, since we only care about when there is current in the circuit, and the direction of this current, and not its magnitude (yet), we can simplify the relevant magnetic field coming out of the bar magnet. For this exercise, we can just consider the magnetic field along the pole of the magnet, i.e. the direction of the magnetic field at the two pole ends. So a student must be given the information (if he/she doesn't know it already), that the magnetic field points straight out from the N-pole of the magnet, while at the other end, the magnetic field points straight in into the S-pole of the magnet. This is defined via convention.
  • A few students will simply not know what to do or how to start, so I give them a list of things for them to check out: (i) move the N-pole of the magnet into the solenoid while watching the galvanometer. (ii) stop moving the magnet and leave the N-pole inside the solenoid. (iii) move the N-pole of the magnet out of the solenoid while watching the galvanometer. (iv) repeat the same thing steps with the S-pole of the magnet.
  • Remind the students that they need to be able to describe clearly and succinctly a general rule for what they see. This means that they are required to convey, in writing, what they understand (communication skills). I tell the students that once they think they have written their general rule down, TEST it. See if their general rule explains everything that they observe in this exercise. For example, does their general rule explains why the galvanometer shows no deflection (i.e. no current) when the magnet is not moving inside the coil?
If this were done as a real experiment, I required the students to write exactly what they did and what they observed at every step.

What this exercise does is (i) to force students to think analytically on how to understand and make sense of what they observe and (ii) to get the students to communicate clearly what they understand in their heads into written form. Both of these are invaluable skills, and not just in physics. The second part is not as trivial as you think, because I find that a lot of students still have not mastered the art of conveying something in their heads via written communication (students who are not native English speakers will have a tougher time with this part so they may need extra assistance).

In my lessons, I introduce Lenz's law as the "qualitative" description, and then follow it up with Faraday's Law as the "quantitative" description of the same phenomenon. In addition to showing how Faraday's law "explains" Lenz's law, it will also allow you to explain why the galvanometer deflects with different amplitudes depending on how fast you move the magnet in or out of the solenoid. But this is one as part of the class lesson rather than as part of the lab exercise.

I toyed with the idea of putting the "answer" here (it is not as if one can't google for it), but I'm going to leave it out for now and let any interested party try it out. I will update this post at a future date to include my version of the "general rule" that reflects what Lenz's law says.

Zz.

Monday, March 26, 2018

Newton's Gravitational Law Still Valid At Sub-Nanometer Scale

A new experiment using neutron scattering off noble gasses has shown no deviation from Newton's gravitational law at 0.1 nm scale.

The team fired pulses of neutrons at a chamber filled with either helium or xenon gas and monitored both the travel time of the neutrons through the gas and the neutrons’ scattering angles. From these measurements, they reconstructed the scattering process with the aid of simulations. They found that the scattering-angle distribution fit the predictions—based only on known laws of physics—for neutrons bouncing off gas nuclei. This result indicates that, within the sensitivity of the experiment, no unexplained force—be it modified gravity or another type of interaction—acts on length scales below 0.1 nm.

This one may not be as transparent, since it required quite a bit of reconstruction to simulate the interaction. So while the length scale being probed has improved considerably, I'm not so sure on how convincing this result is.

Still, where are those curled-up extra dimensions anyway?

Zz.

Thursday, March 22, 2018

Fermilab Accelerator Complex

This is a neat animation video of the Fermilab Accelerator Complex as it is now, and all the various experiments and capabilities that it has.



Of course, the "big ring", which was the Tevatron, is no longer running now, and thus, no high-energy particle collider experiments being conducted anymore.

Zz.

An Astrophysicist Describes Stephen Hawking's Last Paper

The astrophysicist in this case is, of course, Ethan Siegel, who I've cited here a few times.

In this article, he describes what Hawking's last paper is all about, if you want simple description of it. The link to the preprint (we'll update this post if and when it is published) is also given if you don't have it already.

Here is, in a nutshell, what they do. They create a (deformed) conformal field theory that is mathematically equivalent (or dual) to an eternally inflating spacetime, and investigate some mathematical properties of that field theory. They look, in particular, at where the border of a spacetime that inflates for an eternity (forward in time) versus one that doesn't, and choose that as the interesting problem to consider. They then look at the geometries that arise from this field theory, try to map that back onto our physically inflating Universe, and draw a conclusion from that. Based on what they find, they contend that the exit from inflation doesn't give you something eternally inflating into the future, with disconnected pockets where hot Big Bangs occur, but rather that the exit is finite and smooth. In other words, it gives you a single Universe, not a series of disconnected Universes embedded in a larger multiverse.

There! Do you even need to read the actual paper after that?

😁

BTW, let's also give some love to his co-author, Thomas Hertog, who seems to be left out in many of this discussion and news articles.

Zz.