Dark Matter Biggest Challenge

A very nice article on Forbes' website on the latest challenge in understanding Dark Matter.

It boils down to on why in some cases, Dark Matter dominates, while in others, it seems that everything can be satisfactorily explained without using it. It is why we continue to study this and why we look for possible Dark Matter candidates.  There is still a lot of physics to be done here.

Zz.

10 Years Of Not Even Wrong

Physics World has a provocative article and podcast to commemorate the 10-year anniversary of Peter Woit's devastating criticism of String Theory in his book "Not Even Wrong".

Not Even Wrong coincided with the publication of another book – The Trouble with Physics – that had a similar theme and tone, penned by Woit’s friend and renowned physicist Lee Smolin. Together, the two books put the theory and its practitioners under a critical spotlight and took string theory’s supposed inadequacies to task. The books sparked a sensation both in the string-theory community and in the wider media, which until then had heard only glowing reports of the theory’s successes. 

Interestingly enough, the few students that I've encountered who told me that they want to go into String Theory have never heard or were not aware of Woit's book. I can understand NOT WANTING to read it, but to not even be aware of it and what it is about sounds rather .... naive. This is a prominent physicist who produced a series of undeniable criticism of a particular field of study that you want to go into. Not only should you be aware of it, but you need to read it and figure it out.

It is still a great book to read even if it is 10 years old now.

Zz.

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.

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.

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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.

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.

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).

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.

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:

• ¹⁄₂ butter
• 1 sugar
• 2 eggs, beaten
• 4 bananas, finely crushed
• 1 ¹⁄₂ flour
• 1 baking soda
• ¹⁄₂ salt
• ¹⁄₂ 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.

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.

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.

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 contend with.

Zz.

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.

CP Violation in Neutrino Oscillation

It is always nice when non-science media carries physics news. Unfortunately, often times, the accuracy is lacking and, in many cases, gives misleading ideas. This is one such case.

It is reporting on the news about CP violation in neutrino oscillation from muon neutrinos and muon antineutrinos that was reported in last week's 2016 ICHEP.

At the T2K experiment, researchers looked for a difference between neutrinos and antineutrinos oscillations. Their findings, announced at the International Conference on High Energy Physics in Chicago, suggest that there are — more muon neutrinos were found changing into electron neutrinos than muon antineutrinos changing into electron antineutrinos.

The researchers, who had expected to detect 23 electron neutrinos and seven electron antineutrinos, observed 32 electron neutrinos and 4 electron antineutrinos.
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If confirmed with a greater level of certainty, this would point to a violation of charge-parity (CP) symmetry in neutrinos. CP symmetry tells us that a system remains unchanged even if two fundamental properties — charge and parity, which refers to a 180-degree flip in spatial configuration — are reversed. If a violation of CP symmetry is confirmed, it would not only hint at the existence of physics beyond the Standard Model — a theory of almost everything — it would also help us understand why the universe is completely devoid of antimatter.

There's nothing wrong with the report. However, it is inaccurate with regards to what it left out. If you don't know any better, you'd think that this is something new, and that this is the first instance of CP violation. This is not true. CP violation has been seen in other particle systems. So there is no longer a question on whether such violation exists. What is new here is that it is the first time it is observed in neutrino oscillation.

This is why science reporting is difficult. You need someone who has a wide breadth of knowledge in many fields to be able to not only report things accurately, but also give a full view of it. There's nothing inaccurate here in what was included. But the inaccuracy occurs on what was omitted, and therefore, not giving a general reader a more complete state of knowledge of the field.

Zz.

The 750-GeV Blip At LHC - It Came And Went

A lot of HEP were in a tizzy since last year over the unexpected peak in the data at 750 GeV. And now, early reports from the current meeting going on in Chicago are indicating that this might be just a statistical anomaly.

Sadly, it seems that the 750 GeV particle wasn’t meant to be. Physicists at the International Conference on High Energy Physics (ICHEP) in Chicago were due to reveal the latest data on the excess of photon pairs at 750 GeV later today, but a paper accidentally posted online last night by the CMS collaboration states that their new round of data found no extra photons. This suggests the earlier hints were just a statistical fluke.

“As data comes in, excesses tend to come and go,” says CMS researcher Nadja Strobbe at Fermilab, near Batavia, Illinois. Researchers from ATLAS are due to present their results later today, but rumours suggest they will announce that the 750 GeV bump is gone.

But the fun part is all the theory papers that came gushing out as soon as the possibility of this being real.

A week after the announcement, theorists had written over 100 possible explanations; today, there are over 500. Nearly all of these papers posit the existence of a particle with a mass of 750 GeV or higher whose decay created the extra photons. Because this particle would have been outside the standard model of particle physics, it could have forced a reconsideration of how particles and forces interact.

I've always been curious to ask many of the people who did similar things on what they have to say for themselves. They had just created an explanation for the existence of the unicorn.

This is not new. When the OPERA collaboration indicated a faster-than-light neutrino detection a few years ago, numerous theory papers came out for that as well, proposing a myriad of particles and new physics. This is all before this result was confirmed. And of course, we all know what happened with that one as well.

I guess that people would rather be FIRST to be correct rather than be cautious and not appear foolish. After all, how many of us would remember that such-and-such wrote a paper to explain something that never existed in the first place?

Zz.

Combining QM, SR, and HEP is "New"?

Often times, when science news is reported in the mass media, while the reporting might be somewhat accurate, the implications that it leaves behind, especially when read by someone not trained in that area, may lead to a horribly wrong idea. This might be the case here.

This news report is covering a paper out of the Princeton's Plasma Physics Lab (PPPL) on a new theoretical model to explain a plasma physics phenomenon. Nothing wrong there. However, I have a lot of issues with this part of the report very early on:

Researchers at the Princeton Plasma Physics Laboratory (PPPL) have developed a new way to explore some of the most extreme environments in the universe by combining three separate branches of physics: High energy physics (which describes charged particles traveling at or close to the speed of light), quantum mechanics (which describes the motion of subatomic particles), and Einstein’s theory of special relativity (which describes the propagation of matter and light at high speeds).

“People haven’t done this before,” Yuan Shi, a graduate student in the PPPL and lead author of a paper published July 29 in the journal Physical Review A, told Business Insider. “Nobody really wanted to cross the boundaries between the disciplines to see what other scientists are doing. The difficulty was mostly that there’s no communication between these fields.” 

Now, I'm sure that if you are a physics, or even a graduate student in physics, you can already spot something odd here. The existence of quantum field theory (QFT) is already evidence that Special Relativity (SR) has already been incorporated inside quantum mechanics (QM). And high energy physics (HEP) is a field that makes use of QFT!

But if you don't know that, then reading this news report will give you the impression that this isn't known till now, and that this is all new!

And the statement made that "People haven't done this before" with regards to crossing boundaries between disciplines in physics is blatantly false, especially with all the brouhaha surrounding the discovery of the Higgs within the the past couple of years. Anyone following the history of the Higgs field will have seen how the idea originated out of a condensed matter system, and how Phil Anderson, a condensed matter physicist and a Nobel laureate, was himself a strong candidate to be considered for the Nobel prize when the Higgs was finally discovered.

I know that press releases can sometime over-glorified the importance and significance of something. But there really is an important mission here to make sure that one is conveying a message that is clear and unambiguous to the audience that can easily be misled. What you mean may not be exactly what they understand!

Zz.

Photoemission Spectroscopy - Fundamental Aspects

I don't know if this is a chapter out of a book, or if this is a lecture material, or what, but it has a rather comprehensive coverage of photoionization, Auger, and photoemission in solids. I also don't know how long the document will be available (web links come and go, it seems). So if this is something you're interested in, it might be something you want to download.

At the very least, it has an extensive collection of references, ranging from Hertz's discovery of the photoelectric effect, to Einstein's photoelectric effect paper of 1905, all the way to Spicer's 3-step model and recent progress in ARPES.

Zz.