A Century of Quantum Mechanics

CERN Courier has a special issue this month celebrating what they consider as the 100th anniversary of Quantum Mechanics.

Of course, the focus here is predominantly on elementary/particle physics. And yet, many of the most obvious demonstration and manifestation of quantum mechanics can be found not in particle physics, but in condensed matter physics. The Schrodinger-Cat type demonstration using SQUIDs, and the clearest manifestation of the effect of coherence can be seen in condensed matter experiment. To quote Carver Mead's article[1]:

Although superconductivity was discovered in 1911, the recognition that superconductors manifest quantum phenomena on a macroscopic scale (4) came too late to play a role in the formulation of quantum mechanics. Through modern experimental methods, however, superconducting structures give us direct access to the quantum nature of matter. The superconducting state is a coherent state formed by the collective interaction of a large fraction of the free electrons in a material. Its properties are dominated by known and controllable interactions within the collective ensemble. The dominant interaction is collective because the properties of each electron depend on the state of the entire ensemble, and it is electromagnetic because it couples to the charges of the electrons. Nowhere in natural phenomena do the basic laws of physics manifest themselves with more crystalline clarity.

Zz 

 [1] C.A. Mead, PNAS v.94, p.6013 (1997); or you may be able to access it here.

Another Sighting of a Possible Fifth Force?

First of all, I'm old! I started being in a student in physics since the early 1980's (do your own math). During all of that time when I have paid attention to physics, I've seen a lot of major milestones, including the discovery of High-Tc superconductors, discovery of exoplanets, the cold-fusion debacle, etc...etc.

The one thing that pops up every now and then is the claim of the possible discovery of this "fifth force". Honestly, even back in the 1980's, there were already such claims being made. None of the have amounted to anything as far as I can tell. Therefore, you can understand my "Oh no, this again?" reaction when I read the latest claim of the possible detection of the Yukawa particle as an indication of the existence of this fifth force (that article contains a link to the actual PRL paper that you can download).

This is not a knock on this work, heavens no. But the publicity surrounding this makes it sound as if this has not happened before. I guess it is not surprising that people have short memory, which is why mistakes are often repeated.

I'm going to wait a year and revisit this post and see if we have gone beyond first based on this discovery.

Zz. 

A Century of Bose-Einstein Condensation

Nature has published a wonderful review of the discovery and progress that we have made in understanding BE condensation since its discovery. It is an open access article and you can download the full article. I definitely like the figure that shows the major milestone in its development, but it would be nice if that is expanded even more to include references, or at least citation numbers so that I don't have to go hunting for them. 

Scanning through the article, I actually did a quick headcount on how many of the names mentioned in the article that I had met personally: Schrieffer, Leggett, Anderson, and Abrikosov. I believe Leggett is the only one still around as of this writing.

I didn't get too much into BE condensation even though I was working in superconductivity at that time. I was transitioning out of that field of study when the big BEC-BCS connection was experimentally established. Still, it was, and still, an exciting field to follow even on the peripheral.

Zz. 

Did I Expect Too Much?

In one of my exam questions, I gave the students the average radius of Earth's orbit around the Sun at 150 million km. I told them that we can assume that the orbit is circular. I even gave them the formula for the circumference of a circle.

The question then asked them to find the speed of the Earth as it moves around the Sun.

After the exam and after the results were published, a number of students told me that I did not give them enough information to solve the problem. They said that they could figure out the circumference of the circle to correspond with the distance that the Earth has traveled, but they don't have any information on the time of travel and thus, can't find the speed.

I argued that they should know this because it is common knowledge.

Did I expect too much? Did I make the wrong assumption that everyone (especially 1st and 2nd year university students) knows that it takes the Earth one year to make one complete orbit around the Sun? Was this something I should have given them?

Zz.

100 Years of Quantum Mechanics

I mentioned earlier of an article on the Davisson-Germer's experiment as part of the commemoration of 100 anniversary of Quantum Mechanics (QM). This is an article describing a bit more of the celebration and the importance of QM. Hint: without QM, none of your modern electronics (computers, smartphones, etc.) will work.

Zz.

The Davisson-Germer Experiment

As we continue to celebrate 100 years of Quantum Physics, this is a fun account of the famous Davisson-Germer experiment that was the first to demonstrate the wave-like nature of electrons.

It's interesting that, at the end of the article, it was pointed out that this experiment did not originally was set out to seek the experimental evidence for the wave-like nature of electrons. They were intended to do something else, and then learned about something, and adapted it later. This is not really that unusual. The first thing that popped into my head was the discovery of the cosmic microwave background (CMB) by Wilson and Penzias. They certainly were not looking for the CMB with their microwave antenna. It was a serendipitous discovery. In fact, one can even say that the discovery of superconductivity also came out of an experiment that was not designed to look for it, because no one knew at that time that such a thing could exist.

One could say that this is another one of those "Who Ordered That" scenario.

Zz.

5 Physics Equations Everyone Should Know

Rhett Allain posted this article on Wired on the 5 physics equation that "everyone" should know. They are, in the order that was presented:

1. Newton's 2nd Law of motion
2. The wave equation
3. Maxwell's equations (he cheated a bit because this is a set of 4 equations)
4. Schrodinger's equation (natch!)
5. Einsten's energy-mass equivalence equation
   

You can read the article to see what he has to say about each. I'm going to show this article to my students and see what they think, or maybe ask the how many of these do they think we will encounter in the course.

Zz.