Do Cosmic Rays Get Bogged Down in the Cosmos?

A new report out of the Auger Observatory collaboration seems to indicate the presence of the GZK cutoff (link requires free registration to Physics World website) that was earlier claimed by the the HiRes observatory.

Physicists are closer to understanding how ultrahigh-energy cosmic rays make their way to Earth thanks to new measurements made at the Pierre Auger Observatory in Argentina. The study shows that the number of such cosmic rays reaching Earth drops off rapidly for rays with energies of more than about 4 x 10^19 eV.

The observations are consistent with a 40-year-old theory that ultrahigh-energy cosmic rays cannot travel very far through the universe without losing energy as they scatter off the cosmic microwave background.

4 x 10^19 eV... hum.. quick! How many orders of magnitude is that higher than the highest energy the LHC can ever reach?! And people are rabidly worried about the LHC creating blackholes?

Zz.

A Quiet Revolution in SEM

This is a good review of the current advancement in Scanning Electron Microscopy (SEM) technology.

However, there has been a quiet revolution in the world of the SEM, and slowly but surely, its capabilities are expanding. The instrument can now be used to study the surface of just about any bulk material at nanometre resolution and regardless of whether it is clean or dirty, wet or dry, hot or cold, conducting or insulating. Under the most favourable conditions, sub-nanometre resolution has been achieved — especially for thin specimens imaged in transmission mode.

If you're like me and have made frequent use of a SEM facility, you'll appreciate what this workhorse can do in a pinch.

Zz.

More Verification of Einstein's General Relativity

The more they test it, the more it is verified.

For the past 4 years, an international team has been carefully tracking the signals of one of the pulsars and monitoring the signals' direction during eclipses--a observational technique "that has never been employed before," says astrophysicist and co-author Rene Breton of McGill University in Montreal, Canada. The researchers determined that the precession of the pulsar's orbital axis advances by 4.77 degrees per year, plus or minus 0.66 degrees. Calculations based on Einstein's theory predicted it should advance by 5.07 degrees per year, well within the margin of error.

Zz.

High-Tc Superconductors Are Very Kinky - Update 2

A new update to my first essay on the kink feature in the ARPES spectra of high-Tc superconductors. This time, it could throw a major wrench into the analysis done previously on this high-energy kink feature that has been seen around 500 meV. The new paper[1] disputes the idea that this high energy kink is intrinsic to the band dispersion of the material. Rather, they argued that it is an artifact of the momentum distribution curve (MDC) method. Their analysis of the energy distribution cureve (EDC) does not show the same effect for that energy range.

It would be interesting to see if the previous authors who have done the analysis on this high energy kink would respond to this paper.

Zz.

[1] W. Zhang et al., Phys. Rev. lett. v.101, p.017002 (2008).

Earth Will Survive After All

This came out last Friday, but I've only finished reading the whole thing just now. As reported in The NY Times today, all the concerned regarding the safety of our Earth due to the LHC has no significant probability of happening. This is based on the report that was released a few days ago.

And note the argument that I've used all along from the Auger Observatory results.

Do I think this will silenced all those doomsday-sayers? Nope, because most of them have already made up their minds with their so-called "facts". They'll still be singing the same tune even 10 years after LHC has gone into operation, because people never learn. A few of the people that I know will probably be at there when the LHC begins not only the first particle beam this July, but also the first collision, which from what I've been told, probably will begin in Sept. I told everyone to take some pictures, especially if a black hole starts appearing. I want to be the first to post a picture of a black hole swallowing up a part of Earth!

:)

Zz.

EDIT: The preprint by Giddings and Mangano has now appeared on ArXiv.

http://arxiv.org/abs/0806.3381

The abstract is VERY clear:

Abstract: We analyze macroscopic effects of TeV-scale black holes, such as could possibly be produced at the LHC, in what is regarded as an extremely hypothetical scenario in which they are stable and, if trapped inside Earth, begin to accrete matter. We examine a wide variety of TeV-scale gravity scenarios, basing the resulting accretion models on first-principles, basic, and well-tested physical laws. These scenarios fall into two classes, depending on whether accretion could have any macroscopic effect on the Earth at times shorter than the Sun's natural lifetime. We argue that cases with such effect at shorter times than the solar lifetime are ruled out, since in these scenarios black holes produced by cosmic rays impinging on much denser white dwarfs and neutron stars would then catalyze their decay on timescales incompatible with their known lifetimes. We also comment on relevant lifetimes for astronomical objects that capture primordial black holes. In short, this study finds no basis for concerns that TeV-scale black holes from the LHC could pose a risk to Earth on time scales shorter than the Earth's natural lifetime. Indeed, conservative arguments based on detailed calculations and the best-available scientific knowledge, including solid astronomical data, conclude, from multiple perspectives, that there is no risk of any significance whatsoever from such black holes.

Any challenges MUST be done with physics, using at least the same level of meticulous study, and not by a series of quotations attributed via 2nd hand information from other people.

A Constant Constant

One of the issues that physics is trying to investigate is whether our physical constants are the same everywhere else in the universe. This just doesn't mean that it could be different in a different location of the universe due to the exotic conditions, but also at different times throughout the evolution of the universe. We have heard about the controversial idea that the fine structure constants could have varied at different times during the life of our universe.

Now comes the latest verification that comes from 6 billion light years away regarding the ratio of the mass of the proton to the mass of the electron. Murphy et al.[1] have reported that, within the limits of their experiment (which is the most accurate so far), they see no variation in this ratio. This means that this constant is the same even back that far in time.

You may read a review of this work here as well.

Zz.

[1] M.T. Murphy et al., Science v.320, p.1611 (2008).

Physics Experiment With Your Microwave

This article describes a rather simple physics experiment that one can try with a microwave oven.

2 microwave-safe glasses

1 incandescent light bulb (60 watts works well)

1 microwave oven

Directions: Fill one glass with water. Put the light bulb in the other glass so it doesn't roll around. Put both glasses in the microwave. Turn the microwave on for three seconds (use the low-power setting if it has one).

Watch: If your microwave has a turntable, you will see the light bulb glow and dim as it travels. If your microwave doesn't have a turntable, repeat the experiment several times, moving the light bulb to different spots. Be careful, the light bulb gets hot! And don't run the microwave longer than five seconds at a time.

The science: Light bulbs glow when electrons speed across a thin metal wire called a filament, heating it to several thousand degrees. In this experiment, you harnessed the energy of the microwave radiation generated by your microwave oven.

It sounds interesting enough. But I can't help thinking "Holy Cow! Someone's not going to follow the instruction and will blow up his/her microwave oven!" Then again, a spark in a microwave oven is, in itself, a fun physics experiment. :)

Zz.

High-Tc Superconductors Are Very Kinky - Update 1

Since I last completed the essay on the "kink" that is observed in ARPES spectrum of high-Tc superconductors, I've made 2 updates on the list of references. There have been 2 preprints appearing on arXiv that argued for the phonon origin of this kink. It there does not seem to be any end to this issue in sight, at least for now.

I wonder how the ARPES spectrum for the FeAs-based superconductors are going to look at. I bet many people are scurrying to be the first to report on that, assuming of course that one has a sizable single-crystal sample that can be easily cleaved in vacuum.

Zz.

A BCS-Like Gap for the New Iron-Arsenic Superconductor

This ought to throw a large wrench into any similarities between the copper-oxide superconductors and the newly-found iron-arsenic superconductors. A new measurement of the superconducting gap of the latter found that they behave very much like that predicted by the conventional, good-old BCS theory[1]. This means that, even though the crystal structure has similarities with the copper-oxide superconductor (and the notion that maybe the same theory might be applicable as well), the behavior so far rules out many of the exotic theories that have been set up for the copper-oxide superconductors. The authors argue that in light of this, new theories may be needed to describe the iron-arsenic superconductors.

Fasten your seatbelts, folks. It's going to be a long and bumpy ride here as more experimental data pour in.

Zz.

[1] T.Y. Chen et al., Nature v.453, p.761 (2008).

The Milky Way Gets a Facelift

Or rather, our understanding of the Milky Way gets a facelift!

This was reported in today's Science's daily news update.

Forget what you thought the Milky Way looked like. The galaxy is far from the simple and elegant spiral-armed structure so often portrayed. New observations, presented today at the 212th meeting of the American Astronomical Society in St. Louis, Missouri, reveal, among other things, that the Milky Way is missing two of the four spiral arms it was thought to have. The findings should force a significant rethinking about how the Milky Way evolved and how its stars formed.

Horrors! We live in a "deformed" galaxy? :)

Zz.

Behind a Scientific Success, a Failed Texas Experiment

As the dawn of the LHC is upon us and the excitement growing by the day, a relic of what could have been the most powerful particle collider ever built sat decaying and gathering dusts in Texas. This article looks back at the debacle that was the Superconducting Supercollider what was supposed to be built just outside of Dallas.

The Tevatron ring measures about 4 miles in circumference. The SSC ring was to have been 54 miles in circumference, producing collisions 20 times more intense than the Tevatron.

The new European accelerator, called the Large Hadron Collider, will not be as powerful as the mighty SSC would have been. The Large Hadron Collider's ring, about 17 miles in circumference, should be capable of producing collisions about one-third as powerful.

The collapse of the SSC is also an example on how politics got into the way of a science project, especially in how Fermilab lost the opportunity to build it there. It also shows very clearly for the first time that physicists are not united behind such huge and horribly expensive machine. Phil Anderson, for example, testified on why he was opposed to such a facility.

The SSC would have made the LHC moot. However, the SSC collapse has also foreign partnerships with the US more weary about the US commitment to such endeavor. The recent budget cutbacks on the ILC and ITER only reinforced such point of view.

Zz.

Arsenic Poison Didn't Kill Napoleon

Another myth bites the dust.

A new study by physicists at INFN in Milano-Bicocca and Pavia, Italy, has shown that there's no difference in the arsenic level in Napoleon's hair during his last days when compared to when he was a child. This means that he wasn't deliberately poisoned by arsenic during his last days. Instead, it was more likely that it was due to a lifetime's worth of exposure to arsenic.

Zz.

Accelerator Disaster Scenarios, the Unabomber, and Scientific Risks

I just want to say that I had a lot of fun reading this preprint by Joseph Kapusta. It is entertaining, insightful, and has a ton of information for both scientists and non-scientists alike. It reinforces the point that I've been trying to make, which is the constant miscommunication between scientists and non-scientists. The blame goes on both sides - scientists for not considering how what they say is being interpreted by the public, and the public for not self-educating themselves into trying to understand not just the science, but the vocabulary that science uses. Not being aware that there are discontinuity in the communications and understanding of the two parties is the first significant problem. This is also a very good opportunity to again highlights the wonderful essay written by Helen Quinn that I've mentioned a while back. Everyone should read it!

If you have some time, I'd recommend reading this article by Kapusta, even for just for its "storytelling" aspect.

Zz.

A Memristor?

Quick, before you read this, what do you think is a "memristor"?

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Give up? It's a resistor with a "memory"!! I didn't know that either!

The existence of the memristor, short for 'memory resistor', was first suggested in 1971, but only now have researchers succeeded in creating a real, working example. They hope that the new components could revolutionize computing, promising an end to frustrating waits for your computer to boot up.

"A memristor is essentially a resistor with memory," explains Stan Williams of HP Labs in Palo Alto, California, who reports the memristor's creation in this week's Nature. "The actual resistance of the memristor changes depending on the amount of voltage and the time for which that voltage has been applied to the device."

The reference to the paper is:

D.B. Strukov et al., Nature 453, 80–83 (2008).

Fascinating!

Zz.

Revamping Intro Physics Laboratory - Part 5

{{Note: If you wish to follow what has transpired so far in this series, here are Part 1, Part 2, Part 3, Part 3-Follow-up, Part 4, and Part 5}

This may be a bit misleading because it is not strictly a "laboratory exercise". In fact, I think it might be more suitable to be presented during class. Still, it involves the students doing something, so that fits in with the spirit of a laboratory.

This exercise has 2 parts to it. The first is in class where the students are asked to think about a situation, and write down what they think should occur. Then, they get to go out and test it themselves and observe the situation. They then come back and write down what they observe, and compare it to what they wrote earlier of what they THINK should occur. Finally, they get to explain their observations, especially if what they wrote earlier is different than what actually occurred.

So what is the exercise? Here goes...

You are in a stationary vehicle (a train, bus, or a large vehicle). You have a helium balloon attached at the end of a length of string, so the balloon floats freely (without being confined or rubbing against other objects), while you hold the other end of the string. The vehicle then accelerates forward. What happens to the balloon?

The whole point here is to see the effect of the acceleration in a vehicle (on earth) on an object that is less dense than air. You first give this in a class (or a lab) towards the end of the session, and then ask the students to write down what they think they will observe. They don't have to give you any reason, just what they expect to happen.

Then, give them some way to get a helium balloon. This shouldn't be too expensive, should it? Maybe they can get on a train to go downtown, let's say, with a group of their friends. That would be a great way to observe the balloon. Advice them that maybe it would be a good idea to write down there and then some notes on what they observe, and any relevant circumstances surrounding the observation (i.e. was the train packed? Did the balloon float freely? Were the windows open? Was the air conditioning blasting right at them? etc.) Then when they come back, they need to write down exactly what they observed, and compare that to what they wrote earlier before they did the "experiment".

I would then suggest that everyone discussion what they have done. Who predicted an observation that is consistent with what they actually observed? Who didn't see what they thought would happen? Why?

Now, it would be OK to tell the students before they did this that they need to make sure that there are no significant moving air, because that would ruin any effects of the acceleration. But I'm even tempted not to say that. This is because if there are students who did not consider this effect, then there could easily be a discussion on the nature of the 'experiment', and why the result that these students get doesn't quite tell you the effects of the acceleration. The "observation" isn't valid as far as finding the effect of the acceleration in a vehicle on the balloon, because other external factors have intruded into the observation. If these students acknowledged this extra factor, then they have been observant, and understands the non-validity of their observation. If the students did not realize this, then hopefully, other students will point it out during the discussion.

I'm hoping that during the discussion session is where the students start "argue" about the validity of each other's observation, such as the possibility that the wind or other factors might affect some other's observations. I'm also hoping that they might try to come up with some physics on what exactly is the most valid observation for a balloon in an accelerating vehicle that isn't affected by any other external factors. As the instructors, I would suggest you simply stay out of the way, and see how the students are thinking and reasoning their way through this. You can certainly offer some guidance, but the "thinking process" may take awhile, especially if there are many students who observe things differently from each other. They need to weed out which observation is "faulty" as far as answering the question at hand. Once they figured out the valid observation, then they need to figure out why it happened that way. It is the students that need to make their own self-discovery.

BTW, the valid observation in this case is that the balloon will tilt FORWARD, in the direction of the motion of the vehicle. This is, at first, counter-intuitive, because when a vehicle accelerates, objects tend to get pushed back in the opposite direction of motion. So the first inclination is to expect the balloon to tilt backwards. However, a floating balloon is less dense than the air surrounding it. So when the vehicle accelerates, the air surrounding the balloon gets pushed to the back of the vehicle more than the balloon, and thus displacing the balloon forward.

Strangely enough, it observation shouldn't be THAT unusual, because there's an identical situation to this that we are quite familiar with. If we apply Einstein's equivalence of gravity to acceleration, then technically, we are accelerating "upwards" at 9.8 m/s^2. Now try letting go of a helium balloon. It floats UP, in the direction of our "motion". It's the same effect we see in the accelerating vehicle. Yet, I'm sure, for many people, the observation of the balloon tilting forward is non-intuitive. If you are lucky enough to have students who actually argue using this point, then you have one heck of a student! I consider the ability to see the similarities of something "new" with something that they are familiar with as a major accomplishment. It is how we can describe many things that appear to be "different", yet share almost the same type of description or phenomena. I would suggest that if no students realize this, that you bring it up at the end of the discussion.

Zz.

Towards A No-Loophole Bell-Type Experiment?

Looks like we are well on our way to achieving that and nailing the coffin shut on Local Realism..... or are we?

The paper published last week in PRL[1] seems to point to the possibility of a loophole-free Bell experiment. While entanglement experiments with photons have closed down the locality loophole, and experiments with "particles" such as protons, neutrons, etc... have closed down the detection loophole, no experiments have managed to close both of them simultaneously.

This experiment with Yb+ atoms is well on its way to getting there. While they have certainly closed the detection loophole, they have reduced the possibility of the locality loophole by separating the atoms by 1 m (previously, the spatial separation was of the order of microns). So this is a tremendous improvement.

Eventually, it will be convincing enough, if it isn't already.

Zz.

[1] D.N. Matsukevich et al., PRL v.100, p.150404 (2008).

Quasar Tests General Relativity to the Limit

Wow. This is a rather impressive piece of work in terms of prediction and subsequent measurement. A group of astronomers have made what appears to be the most compelling evidence of the validity of General Relativity (GR) in strong gravitational field, and in the process, produced a more direct evidence of the existence of black holes, and an indirect evidence for gravitational waves.

The quasar pulse occurred right on schedule, strongly suggesting that OJ287 is a binary black hole system (Nature 452 851). In addition to verifying the enormous mass of the primary black hole, the result shows that the orbit of the secondary black hole precesses at a rate of 39 degrees per period. For comparison, the distorting effect of the Sun on the local space–time causes Mercury's orbit to precess by little more than 0.1 degrees per century.

Furthermore, the work suggests that the binary system is losing energy by emitting gravitational waves — a key prediction of Einstein's theory that is yet to be verified directly. When this emission is not included in the model, the quasar outburst is predicted to occur 20 days later, providing indirect support for gravitational waves.

Excellent!

Zz.

April 14, 1932 : The Era of Accelerator-Based Particle Physics is Born

A good piece of history in this article on the historic occasion that happened today in 1932.

Zz.

No "Glue" For Cuprate Superconductors?

There are finally some startling evidence that points to the very unconventional nature of the cuprate superconductors. A paper just published in Science[1], heading by Ali Yazdani, has found that while there are coupling between the electrons and a bosonic mode, this coupling may not be responsible at all for superconductivity.

You can read a review of this at the Science Daily website. This discovery certainly is consistent with what Phil Anderson has been trying to push. It also could mean that the "kink" in the ARPES spectrum that I've mentioned may be another red herring that isn't directly connected to the superconducting mechanism.

But as always, this isn't the first time something of this nature has occurred in the study of high-Tc superconductors, to later turn out to be insufficient in formulating a theory of these material. So to say that this is still a controversial (in terms of interpreting what it means theoretically) result is to put it mildly.

Zz.

[1] A.N. Pasupathy et al., Science v.320, p.196 (2008).

Revamping Intro Physics Laboratory - Part 5

{Note: If you wish to follow what has transpired so far in this series, here are Part 1, Part 2, Part 3, Part 3-Follow-up, and Part 4}

I read this post in PhysicsForums and immediately realized that this is an excellent laboratory experiment and a perfect one to follow what I've described in Part 4. This was done as part of a test, but I can see this as being quite suitable for an intro undergraduate lab, especially after they had just done springs and Hooke's law.

Again, this gives them a task, rather than an explicit set of instructions on what to do. They will need to know about the elastic spring extension and also simple, basic mechanics. So this may not be that suitable to be done at the very beginning of the course, but maybe after a couple of weeks or so to make sure the students have been introduced to simple 1D kinematics. But the fact that this student could have done it, and done it well, indicates that this is certainly doable.

BTW, do most "elastic bands" obey Hooke's law rather well? I remember testing a typical rubber band one time, and it deviated from linearity rather easily. It would be a cruel thing to do to give the students such elastic bands! :)

Zz.