How Fundamental Particles Lose Track Of Quantum Mechanical Properties

We have another report on the study on the mechanism of the differences between the quantum world and our classical world. This is another study on the effect of decoherence on a quantum system that couples to an external "bath".

It would be interesting to compare this to an earlier report on the emergence of a classical system from a single-particle state after just one interaction. It is also interesting to see how Roger Penrose would handle this. He seems to think that our classical world emerges due to some coupling or interaction between the quantum systems and gravity, and that eventually destroys the quantum system and out comes the classical system. These two papers above seems to indicate that the mere act of decoherence might be sufficient to produce the classical world.

Zz.

Revamping Intro Physics Laboratory - Part 4

Continuing with this series, here's another experiment that I would propose. This would still be something that can easily be done at the beginning of the semester, which means it doesn't require that the students would have already learned any physics related to it. BTW, in case people think that all the experiments that I'm going to propose are this "simple", that is not going to be the case. These "no physics" experiments are aimed only at the beginning of the semester and where we want to introduce to the students that physics is nothing more than a systematic way of deriving what is valid and how to figure out a way to understand the relationship between things. It reinforces the idea that one doesn't need to abandon all that we already know to understand physics. In fact, we need to bringing in our "common sense" and the sense of "play" to do physics, or at least, these physics experiments. As the semester progresses and, presumably, the students' understanding gets more sophisticated, the experiments should also evolve the same way.

OK, for this experiments, we will deal with springs and masses, so again, it shouldn't be something difficult. The task this time is simple:

You will be given a "mystery" object in which you need to determine its mass. You are given a set of springs, and a set of calibrated masses. In addition, you will also have access to a ruler and a stopwatch if you need them. Figure out how you can determine, as accurately as possible, the mass of this mystery object. You must describe explicitly how you go about doing this determination.

Now, of course, in many intro physics class, this type of experiment typically requires that they find the spring constant by looking at the extension versus force or mass applied to the spring. I'm going about this the other way. Forget about the spring constant for now. The key thing here is that the student learns about the relationship between the spring extension as different masses are added to the spring. This to me would be the most obvious technique that most of the students would do. They would find the extension of the spring with different masses. Then, when given mystery mass, they may have to do some interpolation or extrapolation to estimate the mass of that object.

Now, there's also a possibility that some students may do this differently. They could, instead, let each of the known masses oscillates one at a time and find the relationship between the mass and the period of oscillation. They won't end up with a straight line, but as in the previous suggested experiment, this is OK. While we tell them they need to do this as accurately as possible, in the end, we really don't care as long as they explain what they did and how they did it. So even if they had to extrapolate/interpolate by hand, this is perfectly fine.

Now, what we can do further is this. For the students that did the first method (hanging the mass and finding the spring extension), we can ask them this:

Now, often it is difficult to get the spring to be very still - the mass tends to oscillate up and down. So maybe it might also be a good idea to see if we can make use of this property to see if there's an additional relationship here between the mass on the spring, and the period of oscillation. Can you determine the mass of the mystery object this way? Does it give the same answer? It is always more convincing when two different methods give consistent answers.

For those who did the the second method (oscillating the mass and finding the period), you then say:

Oscillating the spring doesn't allow you to read off the mass very quickly, which is something you need quite often. So is there another way to determine the mass quicker? How about looking at how much the spring extends as you hang different masses? Can this lead you to a different way to measure the mystery mass? Does this value agrees with the one you got earlier? It is always more convincing when two different methods give consistent answers.

.. and voila, you've gotten them to do this in both ways! They also learn that in science, it is always more convincing when you can show a consistent result from two different techniques (although, to be technically accurate, these are not really two different techniques, but this is a good enough demonstration at this level). Now the fun starts if they come up with very different answers. This is where they need to figure out (with the help of an instructor) on what went wrong. To me, figuring out what went wrong is as important and what went right.

After the students have done both, you then can pose an additional question such as this:

What you have now is a graph that you always need to use whenever you want to determine a mass. Is there a way to know the mass of something without having to resort to using such a graph? Can we figure out a way in which, if we know how much the spring extends, we can simply punch that number in and out comes the mass?

I think you know where I'm going with this, don't you? Considering that the students should have a background in sufficient mathematics, they would have seen a straight line equation. If not, a bit of help and hand-holding is called for, which, at this point, should be alright.

So in essence, we have done the mass-spring experiment, but done in a different manner. Rather than giving out the necessary steps that the students have to do, we instead "coerced" them into doing them by a series of questions and tasks that we want them to accomplish by themselves. Inadvertently, they "discover" Hooke's Law by themselves.

Zz.

"This Coincidence Cannot Be Accidental"

That's the most dramatic statement coming out of a newly-published paper in Science, and that was the title that Doug Scalapino used in his Perspective article on this paper in the same issue.

Just when we think that we know everything there is to know about conventional, metallic superconductors, Mother Nature throws a wrench at that fallacy. Reported today by Ayanajian et al.[1], metallic superconductors such as Pb and Nb still holds a mystery. This time, it appears that the exact phonon energies of the Kohn anomalies happen to coincide with the superconducting binding energies of the cooper pairs of that particular metal. This is something that was not expected, and current formalism of conventional superconductivity says nothing about such a thing. As Scalapino pointed out his is Perspective article[2],

... although the polarization created by the conduction electrons and the response to the ionic lattice contribute to determining both the Kohn anomaly and the pair binding energy, there must be something else at work that locks (the superconducting gap) to (Kohn anomaly energy). As noted, this could mean that there is some new physics that is not captured by the Eliashberg formulation.

I love it! I love unexpected surprises like this!

Zz.

[1] P. Ayanajian et al., Science v.319, p.1509 (2008).
[2] D.J. Scalapino, Science v.319, p.1492 (2008).

Dark Matter Music From CDMS

This is a bit out of the ordinary.

This is taken from Fermilab Today newsletter for March 13, 2008:

Karl Ramberg sometimes incorporates music into his artwork. But a trip with his brother, Fermilab physicist Erik Ramberg, added science to his palette. Karl, with the help of scientists, produced a full-scale, plastic model of a dark matter detector that translates its data into light and sound.

"The end result is that you get an experience, aurally and visually, of subatomic affects," Karl said. "You get a better understanding of what the data is saying."

The musical detector, a YouTube sensation, is modeled after the real Cryogenic Dark Matter Search, an underground experiment searching for dark matter particles. The actual CDMS experiment detects and records the energies of particles that strike its five towers. The model takes that one step further, expressing the data in color and tone according to particles and their properties. The idea for the model was inspired by a trip to the Soudan, Minn. mine that houses the CDMS experiment, where Erik, a CDMS collaborator, took shifts.

So this is essentially data translated into music.



It could pass for a New Age music, I would think. :)

Zz.

Revamping Intro Physics Laboratory - Part 3 (Follow-Up)

OK, I got some very interesting responses to my suggestion of an experiment that can be done for an intro physics lab. I think I didn't explain myself too clearly on the premise and how I'm going to present it on here, so I should do that now.

While I tried to be explicit in describing the experiment and what would be a good way to do it, I don't actually want to reveal the whole hand. That's why I went along with the idea that there could be a dependence of the period with varying weights, because that is a very likely path that the students might attempt. If someone is thinking of actually trying to introduce this experiment in an intro lab, I don't want the possibility that some student might google it and find my blog where the whole thing has been revealed. :) That would defeat the purpose of them doing this without any kind of "previous knowledge".

So while I'm trying to be as clear and complete as possible in the experimental description, and the "philosophy" behind it, I don't really want to reveal everything either. In fact, I'm hoping that there WILL be students who decided to figure out if they can do it by changing just the weights. I consider discovering something that cannot work to be very educational. In fact, in science, knowing what doesn't work can be quite important (re: Michaelson-Morley experiment). They at least now know that changing the weights would not work. If they are curious enough, they'll try to find out WHY it doesn't work, and this is where the physics can be introduced.

Note that the experiment that I had suggested does NOT require that they have learned anything in intro physics. It is quite independent of the lesson they might have received in class. So in principle, this experiment could be done even during the first week of class. It doesn't require that they had learned about simple pendulum.

Zz.

New WMAP Data Once Again Agrees With Cosmological Model

The more they test it, the more convincing it becomes.

The new report out of the new analysis of WMAP data on the neutrino background has again produced a result consistent with the Big Bang Nucleosynthesis.

As such, the cosmic microwave background provides an independent estimate of the number of neutrino “families” in nature: 4.4 ± 1.5. Despite having been inferred from a totally different cosmological epoch, this value agrees with constraints from Big-Bang nucleosynthesis, the first few minutes of the universe during which light nuclei were manufactured, and with precision measurements at particle accelerators which fix the number of families at three. The WMAP5 data also constrain the combined mass of all types of neutrino to be less than 0.61 eV.

“The discovery of the neutrino background tells us that our models are pretty much right,” says cosmologist Pedro Ferreira of the University of Oxford. “Stuff from particle physics that you’re not putting in by hand just drops out of them — that’s pretty cool if you ask me.”

Yes, very cool! :)

Zz.

Revamping Intro Physics Laboratory - Part 3

OK, I haven't forgotten this yet.

To me, the biggest problem with the current structure of intro physics lab is that we give students a list of things they have to do and measure, and hand-hold them into getting the result. In other words, they don't have to think too much to complete the exercise. They may have to do a bit of thinking and understanding of physics to complete the write-up, but the actual part of performing the experiment requires simply the ability to follow instructions.

I believe that we should have a more open-ended experiment to be given to the students. So I'll give an example. Note that while thing is something that I've thought about for a while, I'm still writing this off the top of my head. So there may be other problems with it that I haven't carefully considered.

Give them a problem to solve such as something like this:

Construct a pendulum clock. To make this clock useful, it would be helpful if the pendulum can swing back and forth once as close to 1 second as possible. Then each complete oscillation will take just one second. That way, this clock and measure time in increments of one second. You may use a stop watch to calibrate your pendulum to verify that it makes a one-second swing. Try to build this as accurately as possible. You must describe in detail in your lab report how you accomplish this task and why you chose to do it this way.

Now, as apparatus, give them a length of string, a set of weights, and a stop watch, plus other necessary items for them to be able to mount the pendulum on something.

Here's what I expect to occur. You'll have some students doing this by trial-and-error. They'll mount a length of string, and then start changing the weights to change the period of oscillation. Of course, there's no guarantee here that there is JUST the right weight for that length of pendulum to produce a 1-second period of oscillation. So students doing it this way may face a problem, but that's OK, because at the end when we discuss on to do such a thing, they'll discover why their technique isn't the best way.

You'll also get a bunch of student who would use a fixed weight, but tries to vary the pendulum's length. Again, they may try this simply by trial-and-error, adjusting it a little bit at a time until the period is close to 1-second interval. This technique is of course, more "refined" than the earlier one, since there's a high possibility of getting the right period.

Of course, what should be done, rather than simply doing a trial and error method, is simply to use a fixed weight, then measure a set of period corresponding to a set of pendulum lengths. Using the table, one can plot period versus lengths, and from there, interpolate (or extrapolate, depending on the range of lengths that were used) the exact length to produce a period of 1 second can be read off. So after the experiment is done and the students write their report, the lab instructor can start a discussion on the best possible technique to get the most accurate result. One can even make it a bit more complicated and ask the students how accurate is their clock as they let it swing for a length of time. This is where if they constructed a clock that swings over a large angle of oscillation, they may discover that it doesn't keep time very well.

What this type of lab forces them to do is think on the relationship between two measured variables. The first group had to figure out how the period changes as they change the weights. The second group is finding out the relationship between the period and the length of the pendulum. There may be a 3rd group that may be changing both the length and the weights simultaneous. If they do, and they're doing this by trial-and-error, god help them! :) But no matter what, the students are forced to think of what to do, and why they're doing it, to accomplish the task. They are not told how to do it. The experiment and the equipment give are familiar enough to them that this isn't something out of the ordinary. In fact, when they were kids, they probably played with something like this. The curiosity with finding how to do things is the purpose of the lab exercise. It is really playing, it is just that now, they have to think on what they are doing, why they are doing it, and how to present it in writing.

Next time, I'll try to present another possible laboratory exercise along this line.

Zz.

New Video on "Dark Matter" With Teacher Notes to Benefit Students, From Perimeter Institute

Hum.... a video on "dark matter" for high school students? With teacher's notes?

I haven't seen this yet, but this was the press release from the Perimeter Institute on something they are producing. If you have time and want to view it, you can directly go to this link.

Tell me what you think after viewing it. Do you think this can be an effective tool to introduce dark matter to students at that level? Would the teachers be able to understand it, even with the teachers guide?

A More Accurate Clock, and Fine Structure Constant Isn't Changing

Talk about killing 2 birds with one stone.

A new paper out of physicists from NIST has managed to accomplish to very important task. The first is the use of an optical clock that is way more sensitive and accurate than the atomic clock. Secondly, due to the highly sensitive and accurate nature of the clock, they have shown essentially that the fine structure constant isn't changing over time.

I wonder if the J.K. Webb camp will be responding to this report....

Zz.

Review: The Mystery of the Missing Antimatter

This is a book review of Helen R. Quinn and Yossi Nir's "The Mystery of the Missing Antimatter". As the reviewer has noted, there are only 3 major mysteries in cosmology today: the nature of Dark Energy, the nature of Dark Matter, and why matter dominates antimatter in our universe today.

This might be something I might try to get in the next few months. Helen Quinn, if you've read this blog for any considerable period of time, wrote a while back an article that I had characterized as something all scientists and science students must read. So she certainly has a clarity of thought and a concise use of words.

Zz.

'Expatriates' From Physics Careers Find Funding, Fulfillment in Medicine

I think the field of Medical Physics has not been getting enough publicity among incoming students, which is too bad considering the graduates from this field continually fetch good starting salary and continue to be highly sought after.

This news article highlights the migration into Medical physics by students who suddenly face funding shortage and cutbacks. Considering the economic outlook especially in the rest of physics, these setbacks may be a blessing for these students going into this field of study.

Zz.

Bill Foster Wins Election

It's no secret that I've mentioned about physicist Bill Foster campaign to win the House of Representative seat vacated by Dennis Hastert. He has done the upset and won the special election yesterday against Republican Jim Oberweis. So we have another physicists in Congress.

Unfortunately, this is only to serve the remaining term that was vacated by Hastert. We will have deja vu all over again this coming November when the two of them fight it out for the full term.

Zz.

The Wave-Particle Duality of Light: A Demonstration Experiment

Other than the fact that I don't quite like the title, this is an excellent demonstration paper that was published recently in AJP. Very much like the J.J. Thorn et al. paper on the which-way experiment, these profound phenomena can actually be performed in an undergraduate physics lab.

First, the exact citation:

T.L. Dimitrova and A. Weis, Am. J. Phys. v.76, p.137 (2008).

They basically performed a Mach-Zehnder interferometer experiment using very low intensity light so much so that only one photon is in the apparatus at any given time. They also have a second stronger laser beam that traverse the same apparatus, but slightly displaced that exhibit the clear wave-like interference pattern.

So far, this is fine and dandy, and it would not have caught my eye because it would be a nice, undergraduate physics lab exercise. But at they end, they did something simple, yet, can be quite profound to a student. I'll quote what they said:

The demonstration, whose result is astonishing for students, is realized in the following way. First the fringe pattern is locked to a photodiode as explained in Sec. IV B, and the photomultiplier is moved to a fringe minimum, as characterized by a low photon count rate which can also be displayed acoustically. If now path A of beam 1 is blocked inside the interferometer, it is possible to hear (and see) a distinct increase of the click rate. This result demonstrates that if we give each photon the choice of taking either path A or path B, it has a low probability to appear at the detector. In contrast, if we force the photon to follow a specific path by blocking the other path, then the probability to arrive at the detector is much higher. The puzzling fact that a two-path alternative for each photon prevents it from reaching the detector, while blocking one of the paths leads to a revival of the clicks, is most intriguing for beginning students. This experiment is well suited for illustrating this remarkable quantum mechanical effect, which can be explained only if we assume that each photon simultaneously takes both paths A and B; that is, each photon, in the phrasing of Dirac, "interferes with itself."

Gorgeous!

It is something we know would happen, but the way this is demonstrated is so clear that I would say this is an experiment worth doing at every undergraduate level. Well done to the authors!!

Zz.

Campus Ceremony Will Celebrate New Stamp for Physicist John Bardeen

I mentioned about the new US Post Office stamps set celebrating American scientists which includes a stamp of John Bardeen. Well, if you happen to be at the University of Illinois campus today (March 6), there is a small ceremony to mark the unveiling of the stamp.

The U. of I. physics department will host Urbana Postmaster Kathleen J. Burr, regional U.S. Postal Service officials, university administrators, and family and friends of Bardeen (1908-1991) at the ceremony. The event is free and open to the public. It will begin at 12:15 p.m., in room 144 of Loomis Laboratory, 1110 W. Green St., Urbana.

I can only hope that those who don't know much about him will now have the impetus to learn more about what Bardeen has done and how he has directly influenced how we live today.

Zz.

Follow-Up On Fredrick Seitz

I mentioned in a previous blog entry of the passing of Fredrick Seitz. Someone asked me why I didn't mention anything about his later-years opposition to Global Warming. After all, he was one of the more prominent skeptic of that effect.

I'm not sure why that would be relevant, frankly. The Fredrick Seitz that I know and admire came from his work on Solid State Physics. That was how he made his name, and that was how he became prominent. I'm sure he has his reasons for looking at the available data to be convinced that global warming isn't what it has been claimed. He's entitled to that. It's not as if he's supporting massive human extermination, which was the issue surrounding most German scientists during World War II.

So even though I don't agree with him regarding the issue of global warming, it remains a fact that he has a major influence in the field of solid state physics/condensed matter. Just for that, he deserves to be saluted.

Zz.

Frederick Seitz Dies at 96

The name "Frederick Seitz" should be very familiar to anyone who has studied Solid State Physics. Seitz is one of the instrumental figures in Solid State Physics and may even be one of its founding fathers.

This distinguished physicist passed away this past March 2nd, 2008. Our modern civilization, in no small part, has be shaped by his work.

Thank you, and rest in peace.

Zz.

The Best Years of Your Life?

It may not feel that way when you're embarking on pursuing your Ph.D, but it can be. This is an article from PhysicsWorld that reviews several students in the middle of their Ph.D program in physics. It has several good advices for anyone thinking of pursuing a physics Ph.D, especially if you are in Europe. This should plug some holes in my "So You Want To Be A Physicist" essay that essentially focused mainly on the US Ph.D program. Note the important difference between the US and UK/Europe program:

Having a research topic in mind is absolutely essential when applying for PhD positions in the UK and elsewhere in Europe, since you will usually begin working on your chosen research problem straight away. In the US, however, PhD students spend two years doing coursework and exams in all areas of physics and only then begin proper research.

“Most physics students in the US start their PhDs without a specific research field in mind,” says Jayatilaka. This adds at least an extra year to the process, but it makes the US a good option for those who want to learn a bit more physics before choosing an area to specialize in, or for students who want to undertake a PhD project in an area that they do not have much experience in.

Zz.

Journal Club For Condensed Matter Physics

This is such a terrific idea.

The Division of Condensed Matter Physics of the American Physical Society (APS) has sent out e-mail highlighting the existence of a "Journal Club for Condensed Matter Physics". This is where prominent physicists recommend papers and preprints that they find important, fascinating, or have a passion for. You get a more in-depth review of the paper/preprint, especially a discussion on the salient point being made.

I will include this link in the Blog's Physics Links collection.

Zz.

Physicists Successfully Store and Retrieve Nothing

This could easily fit in as an episode of the Jerry Seinfeld series.

It appears that there is such a thing as a "squeezed vacuum", and it takes some effort to store and retrieve this "nothingness".

To see what this is, begin with a normal light wave. Classically, this is a smooth wave of electromagnetic fields with equally spaced peaks and dips. But throw in quantum mechanics and things get more complicated. The precise height of the wave becomes uncertain, so the wave gets fuzzy (see figure). Physicists have learned how to manipulate that inevitable uncertainty--for example, making it smaller at the peaks and larger in between. That makes "phase-squeezed light." Now imagine turning down the intensity of the phase-squeezed light to zero. The wave itself goes away, but the waxing and waning uncertainty remains, creating a squeezed vacuum.

It's interesting that two separate groups produced work on this at almost the same time. This, of course, is not unusual, and PRL, Nature, and Science have been known to put such things in the same issue. It serves to reinforce the discovery.

Zz.

I'm Back!

I'm back from a short vacation. It was great to be away for a while, but now I feel so out of touch with what has been happening. So I'll need at least a couple of days to get back up to speed. Hope I didn't miss any earth-shattering "we found proof of aliens" or "convincing evidence for the mechanism of high-Tc superconductors" news.

Zz.