Friday, September 23, 2016

Without Direction, or Has No Prefered Direction?

This is why popular news coverage of science can often make subtle mistakes that might change the meaning of something.

This UPI news coverage talks about a recent publication in PRL that studied the CMB and found no large-scale anisotropy in our universe. What this means is that our universe, based on the CMB, is isotropic, i.e. the same in all direction, and that our universe has no detectable rotation.

However, instead of saying that, it keeps harping on the idea that the universe "has no direction". It has directions. In fact, it has infinite directions. It is just that it looks the same in all of these directions. Not having a preferred direction, or being isotropic, is not exactly the same as "having no direction".

If you read the APS Physics article accompanying this paper, you'll notice that such a phrase was never used.

I don't know. As a layperson, if you read that UPI news article, what impression does that leave you? Or am I making a mountain out of a mole hill here?

Zz.

Wednesday, September 21, 2016

Recap of ICHEP 2016

If you missed the recent brouhaha about the missing 750 GeV bump, here is the recap of ICHEP conference held recently in Chicago.

Zz.

Tuesday, September 20, 2016

We Lost Deborah Jin

Wow! I didn't see this one coming.

I just read the news that Deborah Jin, someone who I consider to be a leading candidate to win the Nobel Prize, has passed away on Sept. 15 after a battle with cancer. Her work on the ultra-cold Fermionic gasses was groundbreaking, and she should have been awarded the Nobel Prize a long time ago!

Nearly two decades ago, Jin and her then PhD student Brian DeMarco were the first researchers to observe quantum degeneracy in a sufficiently cooled gas of fermionic atoms. They were the first to demonstrate the creation and control of such an ultracold "Fermi gas", which has since provided us with new insights into superconductivity and other electronic effects in materials. You can read this 2002 feature written by Jin on "A Fermi gas of atoms"

CRAP! We have lost another good one, and well before her time! Deepest condolences to her family and friends.

Edit: Here's the press release from JILA about this.

Zz.

Monday, September 19, 2016

What Happen When A Law Professor Tries To Use The Physics Of Climate Change

Usually, something like this doesn't have a happy ending. This happened in a congressional hearing by Ronald Rotunda of Chapman University’s Fowler School of La.

But during the hearing, Rotunda picked an odd example of such a dissenter — Jerry Mitrovica, a Harvard geoscientist whose work has shown that when, in a warming world, you lose massive amounts of ice from Greenland or Antarctica, sea level actually plunges near these great ice sheets, but rises farther away from them. The reason is gravity: Ice sheets are so massive that they pull the ocean towards them, but as they lose mass, some of the ocean surges back across the globe.

We have covered this idea extensively in the past, including by interviewing Mitrovica. He has found, for instance, that if the West Antarctic ice sheet collapses, the United States would experience much worse sea level rise than many other parts of the world, simply because it is so distant from West Antarctica. “The peak areas are 30 to 35 percent higher,” Mitrovica told me last year.

But if Greenland melts, pretty much the opposite happens — the Southern hemisphere gets worse sea level rise. And if both melt together, they might partially offset one another.

Rotunda appears to have misinterpreted Mitrovica’s important insight as reflecting a contrarian perspective on climate change.

It is always a bad idea when a person, testifying as an "expert", does not understand the source that person is using, and then had the gall to tell a physicist questioning the conclusion to "read his article".

Zz.

Friday, September 16, 2016

Another Case Where Electrons "Attract" Each Other

This is from a couple of months ago (hey, I'm kinda slow nowadays!), but what the hey....

So we all know (at least, I hope we all do) that the basic mechanism in conventional superconductors is the formation of Cooper Pairs. This is where two electrons in the material form an attractive coupling, which simply means that two electrons attraction each other. Despite the Coulomb repulsion between the two electrons, this attraction is due to the fact that the electrons live in a sea of phonons (lattice vibrations) that are formed by the positive ions of the material (or crystal lattice). So these phonons are the "glue" that bind these electrons together. Without them, two isolated electrons do not attract one another, obviously.

Now it seems that a long-proposed alternative mechanism of electron attraction has been confirmed. This time, two electrons attract each other not due to phonons, but due  to the repulsion of other electrons surrounding them. This is significant, and different than the phononic mechanism because this time, it is purely electronic in nature.

The original theoretical idea of such mechanism was first proposed by William Little[1], and the first experiment indicating its validity has been shown by Hamo et al,[2]. Certainly, there is an impetus to show if such electronic coupling could be a mechanism that leads to superconductivity. So far, none has been found. The Hamo et al., experiment decided to not deal with such complexity and just try to investigate first if such coupling would occur in the first place. So they did a nano-scale engineering design to show such a thing.

Very, very clever!

The big hurdle next is to find a material that can exhibit a similar effect.

Zz.

[1] W.A. Little, Phys. Rev. 134, 1416 (1964),
[2] A. Hamo et al., Nature 535, 395 (2016).

Tuesday, September 13, 2016

The Difference Between Ghosts And Dark Matter

A rather interesting piece that I stumbled upon on the NPR website. The author is trying to explain why, since both ghosts and dark matter can't be "seen", why wouldn't scientists believe in ghosts while a large percentage of physicists believe in the existence of dark matter.

So how do physicists and astronomers get away with claiming the existence of cosmic ghosts (dark matter and dark energy) when they would probably roll their eyes at descriptions of the more terrestrial haunted-house kind?

The answer is data, its prevalence and its stability.

There are literally thousands of studies now of those rotating-too-fast galaxies out there — and they all get the same, quite noticeable result. In other words, data for the existence of dark matter is prevalent. It's not like you see the effect once in a while but then it disappears. The magnitude of the result — meaning its strength — also stays pretty consistent from one study to the next. The same holds true for studies of dark energy.
We need to make something VERY CLEAR here, especially for non-scientists. While we do not know exactly what this dark matter is made of, or we don't know what it is, we have already a very clear set of parameters of its CHARACTERISTICS. Based on what we have already observed and measured, there are QUANTITATIVE properties of these so-called dark matter.

This is important because of two reasons: (i) there are no such definitive behavior, characteristics, and quantitative description of "ghosts", and (ii) these quantitative properties allow us to make measurements and rule out unsuitable candidates that to not fit into what we already know.

This article is similar to the public science event that I attended several years ago in which Dan Hooper of Fermilab/UofC described the science of ghosts. Back then, he too included the possibility on whether ghosts can be made up of dark matter, and based on what we know about dark matter and what people have described what ghosts can do, he concluded that ghosts cannot be made up of dark matter.

So no. Ghosts and Dark Matter are not in the same league.

Zz.

Direct Measurement of the Density Matrix

It is often a source of irony. We teach, or learn, something by dealing with the simplest case first, devoid of complexities. Only after that do we start learning more complex situations.

Yet, in many cases, it is extremely difficult to duplicate, in practice, this simplest case. Quantum mechanics is one such example. While we learn about QM at the intro level by looking at the case of an infinite potential well, a finite potential well, 1-electron central force, etc... trying to actually get a clear experiment on this is actually quite difficult. This is because we have to isolate the system that we want to measure from the rest of the world, so that only the simplest, most fundamental parameters are involved in the experiment.

This is one such case. The experimenters claims to finally being able to directly measure the elements of a density matrix. Yet, if you have done any amount of QM, you would have seen this density matrix in your QM classes. I remember encountering it when I was using Merzbacher's text. So this is a classic, text-book item that we are all taught in school. Yet, it is not an easy thing to measure directly, till now. This is possible due to advancements in the so-called "weak measurement" that have previously produced Bohn's Pilot-Wave-like results.

Still, it is nice to know that what you learn in those textbooks are actually correct! :)

Zz.

Thursday, September 08, 2016

Drilling In The Importance Of Units, Via A Banana Bread

For some odd reasons, intro physics students somehow can't get it into their heads the importance of having units in their answers whenever they are called for. And they also don't tend to see why carrying their units during a calculation can help them check if they are doing things correctly.

I've had constant issues with students not including units in their solutions. Even after I emphasize its importance, and even after I explain why it is important, I still constantly get answers, even in exams, of just a number without any units for length, speed, etc...

So one day, at the beginning of a new session, I decided to try something that I hope would be memorable to the students. I normally have between 10 to 20 students in a class. So on the first day of class, I baked a loaf of banana bread (I am actually a decent baker) and brought it to class. I cut the up into enough pieces for all the students, warning them that it has nuts and not gluten free, in case there are students with such allergies.

I let them enjoy the banana bread and then, I told them I baked it. They were impressed. Then I said that I'll give them the recipe if they want to bake this on their own. This is what I gave them:

  • 12 butter
  • 1 sugar
  • 2 eggs, beaten
  • 4 bananas, finely crushed
  • 1 12 flour
  • 1 baking soda
  • 12 salt
  • 12 vanilla
I then included the rest of the instruction, but that is not relevant here.

Of course, within a minute, I had students telling me that this recipe is not complete and vague. "What is half butter and one sugar?" someone asked.

"Oh, you mean that you need the UNITS of measure for these ingredients to make the banana bread?" I innocently asked. "Does that mean that without knowing if these are 1/2 cup, or 1 teaspoon, or 1 tablespoon, these number really a vague and meaningless?" I continued.

That was when the students realized that they just had a lesson. The lesson here being that the need to know the units of measure is (i) necessary and that (ii) it isn't exclusive only to physics, and that we all have been using these units of measure everyday without realizing it. Without such units, a lot of things won't make sense.

I can't claim that this exercise was effective, but I did notice that I saw a significantly lower occurrences of missing units in the students homework and exams. The few times that this did occur, the only comment that I wrote next to the number with the missing units was "Banana bread!"


:)

Zz.

Wednesday, August 31, 2016

Spherical Tokamaks

Spherical tokamaks - can they beat out ITER to be the first to be a viable fusion generator?

This article describe the two separate efforts at using this technique in building such a facility, and it appears to not cost more than $10 billion and years of delay (yes, I'm looking at you, ITER!).

That's where the spherical tokamaks come in. The delightfully exotic term refers to a kind of device that can contain superheated plasma in powerful magnetic fields. These devices represent our species' best shot at generating those stellar temperatures we need to achieve nuclear fusion.

Right now, the two most advanced spherical tokamaks in the world are the National Spherical Torus Experiment-Upgrade (NSTX-U) at PPPL, and the Mega Ampere Spherical Tokamak (MAST) at the Culham Centre for Fusion Energy in the U.K.

At this stage, we need as many alternatives as we can afford. I'm glad we're not putting all our eggs in ITER, because I'm getting tired of it already.

Zz.

Saturday, August 20, 2016

Brain Region Responsible For Understanding Physics?

A group of researchers seem to think that they have found the region of the brain responsible for "understanding physics".

With both sets of experiments, the researchers found that when the subjects tried predicting physical outcomes, activity was most responsive in the premotor cortex and supplementary motor region of the brain: an area described as the brain’s action-planning region.

“Our findings suggest that physical intuition and action planning are intimately linked in the brain,” said Fischer. “We believe this might be because infants learn physics models of the world as they hone their motor skills, handling objects to learn how they behave. Also, to reach out and grab something in the right place with the right amount of force, we need real-time physical understanding.”

But is this really "understanding physics", though?

Zz.

Who Will Host The Next LHC?

Nature has an interesting article on the issues surrounding the politics, funding, and physics in building the next giant particle collider beyond the LHC.

The Japanese are the front-runner to host the ILC, but the Chinese have their own plans on a circular electron-positron collider that can be upgraded to a future proton-proton collider.

And of course, all of these will require quite a bit of chump change to fund, and will be an international collaboration.

The climate in the US continues to be very sour in building anything like this.

Zz.

Thursday, August 18, 2016

Could You Pass A-Level Physics Now?

This won't tell if you will pass it, since A-Level Physics consists of several papers, including essay questions. But it is still an interesting test, and you might make a careless mistake if you don't read the question carefully.

And yes, I did go through the test, and I got 13 out of 13 correct even though I guessed at one of them (I wasn't sure what "specific charge" meant and was too lazy to look it up). The quiz at the end asked if I was an actual physicist! :)

You're probably an actual physicist, aren't you?

Check it out. This is what those A-level kids had to content with.

Zz.

Friday, August 12, 2016

Proton Radius Problem

John Timmer on Ars Technica has written a wonderful article on the "proton radius problem". The article gives a brief background on an earlier discovery, and then moves on to a new result on a deuterium atom.

This area is definitely a work-in-progress, and almost as exciting as the neutrino mass deficiency mystery from a many years ago.

Zz.

The Science of Sports

With the Olympics in full swing right now, the Perimeter Institute has released a series that discusses the physics behind various sports at the Games. Called The Physics of the Olympics, it covers a wide range of events.

Zz.