US Physics Graduate Degrees - Through 2008

The latest statistics from AIP is out on the graduate physics degree in the US. This latest data covers up to 2008.

The overall number of PhD being granted has increased since the local minimum in 2004, with the largest movement made by a significant increase in US citizens being awarded PhDs.

Several interesting facts can be seen from the data:

1. It still takes slightly more than 6 years to get a PhD (starting from a B.Sc degree) in the US (Fig. 6). The average is 6.2 years.

2. The largest number of PhDs still comes out of Condensed Matter Physics (Fig. 7). In fact, if one were to count "Material Science" and "Surface Physics" as part of this subject, the number is even larger.

3. The one that caught my eye was Table 6. It asks for a response to the question "“If You Had To Do It Over Again, Would You Still Get a PhD in Physics?” Most US citizens overwhelmingly said yes, either to doing it at the same institution, or at a different institution. However, non-US citizens seem to have a consistently larger percentage of either not wanting to do it all over again at the same institution, not doing a PhD in physics, or even not getting a PhD at all! It would be fascinating to dig a little bit deeper here to see what's going on.

These statistics are always intriguing to read. To me, it is still the most definitive survey of students and professionals in this field in the US.

Zz.

Pendulum Waves

During the week when people are huffing and puffing about possible hints of the Higgs, what am I more fascinated with? These pendulum waves!

These are so cool!

What it shows: Fifteen uncoupled simple pendulums of monotonically increasing lengths dance together to produce visual traveling waves, standing waves, beating, and random motion. One might call this kinetic art and the choreography of the dance of the pendulums is stunning! Aliasing and quantum revival can also be shown.

How it works: The period of one complete cycle of the dance is 60 seconds. The length of the longest pendulum has been adjusted so that it executes 51 oscillations in this 60 second period. The length of each successive shorter pendulum is carefully adjusted so that it executes one additional oscillation in this period. Thus, the 15th pendulum (shortest) undergoes 65 oscillations. When all 15 pendulums are started together, they quickly fall out of sync—their relative phases continuously change because of their different periods of oscillation. However, after 60 seconds they will all have executed an integral number of oscillations and be back in sync again at that instant, ready to repeat the dance.

I will put the video here, but you should read the webpage given in the link above for the explanation, and useful references.



So you can have the Higgs, the supersymmetry, the dark matter, etc. I'll take any of these "mundane" stuff any day!

Zz.

Faster-Than-Light Expansion? Not So Fast, Buddy!

This is a very common question that I come across. Is the universe expanding faster than the speed of light? If so, then isn't this proof that SR basic postulate is incorrect?

Most people who asked that question usually don't have an understanding of General Relativity. But even for those who do, especially students studying that subject, a serious confusion can occur when it is applied to outlying, sufficiently-far away celestial bodies, where speed greater than c can be achieved.

This is a nice paper, to be published in AJP, that addressed this issue, and the restriction on the application of the Hubble Law.

Abstract: Naively applying Hubble's law to a sufficiently distant object gives a receding velocity larger than the speed of light. By discussing a very similar situation in special relativity, we argue that Hubble's law is meaningful only for nearby objects with non-relativistic receding speeds. To support this claim, we note that in a curved spacetime manifold it is not possible to directly compare tangent vectors at different points, and thus there is no natural definition of relative velocity between two spatially separated objects in cosmology. We clarify the geometrical meaning of the Hubble's receding speed v by showing that in a Friedmann-Robertson-Walker spacetime if the four-velocity vector of a comoving object is parallel-transported along the straight line in flat comoving coordinates to the position of a second comoving object, then v/c actually becomes the rapidity of the local Lorentz transformation, which maps the fixed four-velocity vector to the transported one. 

It also contains several references that tackle this apparent faster-than-light issue in terms of universe expansion. Hopefully, this will answer that vexing and common question.

Zz. 

No Asymmetry in Antiproton-Electron Ratio

A new measurement on the mass ratio of antiproton-electron shows no difference with the proton-electron mass ratio. So no asymmetry found so far with this one.

Zz.

Sports Versus Physics

Here's a video on a lot of issues related to sports, and the physics involved. The description says that this is from a 2004 lecture. Still, it actually is quite fascinating, if you have roughly 45 minutes to spare.



Zz.

Bookmaker Putting Odds Of Higgs Discovery At 1/3

I guess you can place bets on anything. This is true for the odds at a Higgs discovery this year. An Irish bookmaker has reduced the odds of a Higgs discovery this year from 12/1 to 1/3 after the recent report at this year's European Physical Review conference.

Paddy Power is now offering odds that favour finding the Higgs sometime this year. At 1/3, a £3 bet will pay out a measly £4 if the Higgs is discovered before January. By contrast, the same bet last week would pay a whopping £39.

Ha! Can't even make money out of gambling on the Higgs!BTW, those who work at CMS and ATLAS could be considered as having "insider" information. I'd buddy up with those people if I were you before making your bets! :)

Zz.

Physics Central At Comic-Con

The folks at Physics Central were at Comic-Con last week and passing out physic comic books to the attendees.

Looks like they had fun, and a long and tiring outing. I'm guessing that what they handed out was their publication on Spectra comic books, which you can download from their site.

Zz.

Aharonov-Bohm Effect

Physical Review Focus this week highlights the landmark paper by Yakir Aharonov and David Bohm of the effect of the electromagnetic potential that the phase of the wavefunction of a quantum particle.

In quantum mechanics, the electromagnetic potential alters the descriptions of charged particles only by shifting their phase--that is, by advancing or retarding the crests and troughs in their quantum wavefunctions. In general, however, such a phase change does not lead to any difference in the measurable properties of a particle.


But in 1959 Yakir Aharonov and David Bohm of the University of Bristol, England, devised a "thought experiment" that linked the potential to a measurable result. In their scenario, a beam of electrons is split, with the two halves made to travel around opposite sides of a cylindrical electromagnet, or solenoid. The magnetic field is concentrated inside the solenoid and can be made arbitrarily weak outside by making the cylinder extremely narrow. So Aharonov and Bohm argued that the two electron paths can travel through an essentially field-free region that surrounds the concentrated field within the electromagnet.

In this field-free region, however, the electromagnetic potential is not zero. Aharonov and Bohm showed theoretically that electrons on the two paths would experience different phase changes, and that recombining the electron beams would produce detectable interference effects. That is, the intensity of the recombined beam would vary according to whether the phase-shifted wavefunctions reinforced or canceled each other--a measurable physical effect directly related to the potential, contrary to standard wisdom. However, the phase shift can also be calculated from the strength of the magnetic field, so that interference can be interpreted as an effect of a magnetic field that the electrons never actually pass through. Aharonov and Bohm argued that physicists must accept that in quantum mechanics the electromagnetic potential has genuine physical significance. They expanded on this point in a second paper in 1961.

This effect now bears their names. It's a triumph of theoretical physics and of quantum mechanics. This discovery is a Nobel Prize caliber.

P.S. I think the link gives you a free download of the actual paper.

Zz.

Amazing Water Fountain Illustrates Basic Kinematics

Rhett Allain at Dot.Physics found this video of an amazing water fountain show at a Japanese mall. While the whole thing is jaw-dropping, there's a small puzzle that anyone seeing it might start to wonder. Why do all the patterns made by the water show get bigger vertically as they fall down?

This, of course, can be explained by simple kinematics that any First Year intro physics student can understand. Allain explained it clearly in his blog entry that you can read for yourself. But again, this is another one of those "mundane" observations that I really love and it is fun to figure out why such things occur.

For your convenience, here's the video in question.



Zz.

Weak Hints Of The Higgs

Finally, after years of results where large energy range are excluded for the Higgs, we are starting to get hints of the Higgs signature, and it came out of ATLAS and CMS at the LHC. Both were reported at this week's EPS meeting.

Both experiments found excesses in the 130-150 GeV mass region. But the excesses did not have enough statistical significance to count as evidence of the Higgs.

Scientists measure statistical significance in units called sigma, written as the Greek letter σ. These high-energy experiments usually require 3σ  level of confidence, about 99.7 percent certainty, to claim they’ve seen evidence of something. They need 5σ to claim a discovery. The ATLAS experiment reported excesses at confidence levels between 2 and 2.8σ, and the CMS experiment found similar excesses at close to 3σ.

Still, there's a very long way to go (and more data collection and analysis) before one can actually claim discovery. Unlike pseudosciences where even a weak correlation seems to be sufficient to claim that a phenomenon exists, in high energy physics, not only do you need a high confidence level that your result isn't simply due to chance, but you also need another independent detector, measuring things differently, to agree with your result! The fact that both ATLAS and CMS are getting almost the identical result is a very good start. And it is only a start.

Interestingly enough, the energy range where this is detected is also accessible at the Tevatron. I wonder if CDF and DZero might zero in (no pun intended) in this range and see what their data looks like with various background subtraction schemes.

Zz.

Pioneer Anomaly Has A "Dull" Explantion

Whether we like it or not, the Pioneer anomaly may finally have an explanation that should put to rest all the other exotic, wild theories.

The quartet’s painstaking analysis of telemetry data suggests that the anomalous acceleration of both spacecraft is decreasing with time. While the exact nature of this decrease is not certain, there is a good chance that it is exponential. This would be consistent with the decay of radioactive material with a half-life of about 27 years. Both spacecraft have radioactive power sources that are still running – so mystery solved.

Well, not quite. Both spacecraft are powered by plutonium-238, which has a half-life of about 88 years. However, the team believes that the more rapid drop in acceleration could be the result of degradation and changes to the thermal properties of the spacecraft over time. When these factors are considered, claim the researchers, a half-life of 27 years seems reasonable.

 This sounds like a tedious, painstaking task. So bravo to them for the monumental effort.

Zz.

We Are Not Special

Sorry kids. Contrary to what your parents told you when you were young, you and I and everyone else are not special. Well, we are not special in terms of our place in the universe.

Y'see, once upon a time, we thought that we are at the center of the universe, and everything revolves around us. We believed that we are in a privileged location in the universe. Well, someone by the name of Copernicus, and later on, Galileo, practically destroyed that delusion.

Yet, there are still ideas (some call them theories) even today that still want to place us at this special location in the universe, and if they do that, they said that they can explain the universe accelerating expansion without any need to invoke dark energy. As always, Mother Universe can throw a wrench into the best-laid theory. This latest wrench comes in the form of the latest observational data that basically conclude that the universe is homogeneous at a length scale up to a gigaparsec.

In a paper appearing in Physical Review Letters, Pengjie Zhang at the Shanghai Astronomical Observatory and Albert Stebbins at Fermilab show that a popular void model, and many others aiming to replace dark energy, don’t stand up against telescope observation.

Galaxy surveys show the universe is homogeneous, at least on length scales up to a gigaparsec. Zhang and Stebbins argue that if larger scale inhomogeneities exist, they should be detectable as a temperature shift in the cosmic microwave background—relic photons from about 400,000 years after the big bang—that occurs because of electron-photon (inverse Compton) scattering. Focusing on the “Hubble bubble” void model, they show that in such a scenario, some regions of the universe would expand faster than others, causing this temperature shift to be greater than what is expected. But telescopes that study the microwave background, such as the Atacama telescope in Chile or the South Pole telescope, don’t see such a large shift.

 So for now, we are nothing special in our place in the Universe. But that's OK. I still like myself, and I still like you!

Edit: read another review of this work here.

Zz.

"Speed Of Gravity Is 9.8 m/s^2"

OK, if you think I was nitpicking when I criticized the use of the phrase "rate of speed", you'll have an aneurysm with this one! So look away now! :)

I was driving into work this morning, and I happen to be listening to a local station here - 93.9 Lite FM (I know, it makes me sound kinda lame!). Still, the show Valentine in the Morning can be quite funny at times when they discuss certain topics. But this morning, following up on their geography quiz, they had a science quiz with a set of questions related to science. One of the questions that was asked was "What is the speed of gravity?"

Immediately, the host of the show (Valentine) answered "9.8 m/s^2!" And he was deemed by the person asking the question to be CORRECT!

Now, I think I don't need to explain why this is NOT correct, do I? I do? Oh brother!

1. Just looking at the units alone, one can tell something isn't kosher. Speed (and velocity) has units of length/time. The units given "m/s^2" is length/time^2, which is acceleration.

2. 9.8 m/s^2 is the acceleration due to gravity at Earth's sea level. It's a value at a specific location. It means that it isn't a constant, and certainly changes when one is elsewhere. g is different at higher elevation, and even more different on the surface of the moon.

3. As far as we know (and this has yet to be explicitly verified experimentally), the "speed of gravity" is equal to the speed of light. If sun suddenly disappears, we'll now about it not instantaneously, but at the same time that our sky goes dark a few minutes later.

The issue here isn't that the answer is wrong. More importantly, is that while people remember certain information, the CONTEXT of what they remember can be faulty. Facts are useless if they dangle in mid-air and without understanding what they mean and how they are used. Seeing something like this kinda let me to believe that there's a lot more people who think that speed of gravity is 9/8 m/s^2. Could this be that this is another example where what you say (or teach) is not what they understand?

Zz.

Stability of Bicycles on Rollers

A lot has been made of the stability of riding a bicycle. In most elementary, intro physics text, this is used as an example of conservation of angular momentum. But of course, most of us know that the stability in riding a bicycle involves a bit more than that (such as steering into the direction of tilt, etc.).

This is a rather interesting paper[1] that investigate the stability of riding a bicycle on rollers. The bicycle isn't moving, but the wheels are still turning. So if one thinks that the stability in riding a bicycle is due mainly to conservation of angular momentum of the wheels, this is a very good test because here since the motion isn't there, but the wheels can still turn, thus preserving the angular momentum.

So what do they observe?

Riding a bicycle on rollers is unique because of the absence of the forward inertia which aids in bicycle handling for stability, instead of isolating and restricting the degrees of freedom in handling. Adopting one’s riding style to ride on rollers is quite difficult, with many avid cyclists falling off their bicycles on the first few attempts. Given that all riders struggle somewhat with the apparatus, but some more than others, the degree of struggle to ride on rollers may also indicate how different riders rely on specific factors for bicycle stability, which has not been addressed in many studies up to now. We use the example of riding bicycles on rollers as a test case on the individual factors that lead to bicycle stability.

The paper gives quite a few references to various treatment on the issue of stability on bicycles.

Zz.

[1] P.A. Cleary and P. Mohazzabi, Eur. J. Phys. v.32, p.1293 (2011).

High-Tc Superconductivity At 25

This is a wonderful historical account (and the internal fighting) of high-Tc superconductivity as it turns 25 this year. The link is open for free only for a short period of time, so read it while you can.

Zz.

New Evidence For Spin-Charge Separation in 1D System

A new report out of an experiment on the 1D system of blue-bronze shows a severe violation of the Wiedemann-Franz Law, which is a very good indication of a spin-charge separation.

The experimental group, led by Professor Nigel Hussey of the Correlated Electron Systems Group at the University of Bristol, tested this prediction on a purple bronze material comprising atomic chains along which the electrons prefer to travel.

Remarkably, the researchers found that the material conducted heat 100,000 times better than would have been expected if it had obeyed the Wiedemann-Franz law like other metals.  Not only does this remarkable capability of this compound to conduct heat have potential from a technological perspective, such unprecedented violation of the Wiedemann-Franz law provides striking evidence for this unusual separation of the spin and charge of an electron in the one-dimensional world.

Strangely enough, the press release here made it seemed as if this is the first such instance of the violation of the Wiedemann-Franz Law. This is certainly not true since I've cited at least one other before. A quick search on Google Scholar will also reveal other previous observations.

Zz.

Your Workout May Cause The Building To Shake!

Who needs a volcanic eruption or an earthquake? Just a group of people doing a vigorous Tae Bo workout is enough to send a tremor to a 39-story building in Seoul, Korea.

Prime Group, owner of the 39-story TechnoMart commercial-residential high-rise in Seoul, said 17 middle-aged people were working out to the pop song "The Power" by Snap on July 5 when their movements set the upper floors of the tower shaking for 10 minutes, according to a report from the Korea JoongAng Daily.

Scientists recreated the event in the 12th floor gym, according to a report in the Korea Times.

Hysterical!

Of course, being there is a reason for that to happen:

“It just happens to be that the vibration cycle caused by Tae Bo collided with the vertical vibration cycle unique to the building,” Chung told the Korea Times. The action amplified the building's vibration and caused the shaking, he said.

In other words, it's a variation to the infamous Tacoma Narrows bridge incident, without the completely collapse of the structure!

Still, I wonder if there will be a different effect if the gym moves to a different floor....

Zz.

How To Reproduce "Washboard" Road

This is an informative review of a work on figuring out the physics of washboard roads. It's based on work done quite a while back (2007) and published in PRL[1].

This is another one of those "mundane" stuff that perks up my interest and what got me into physics in the first place. Of course, these things APPEAR to be mundane, but the physics of these things have wide-ranging impact and application. It is just that the phenomena that manifest the principles looks so benign. Still these are the stuff that I find most fascinating. You can go solve the mysteries of dark matter and CP-violation. Just give me rippled roads and grapes that bounce up and down in sodas!

Zz.

[1] N. Taberlet et al.,Phys. Rev. Lett. v.99, p068003 (2007)
 

T2K Results On Neutrino Oscillation

I mentioned earlier of the results out of T2K of the muon neutrino oscillation into electron neutrino. The paper has now been published in PRL, and it is also reviewed in APS Physics this week. That means you get a free copy of the paper as well!

As I've mentioned, this seems to be consistent (roughly) with the recent MINOS results.

Zz.

"Do You Watch "The Big Bang Theory"?"

I get that question a lot from people who I've just met. When they find out that I'm a physicist, other than asking what's going on at the LHC, they tend to ask if I watch the popular TV series "The Big Bang Theory". Unfortunately, my answer to that question is "No, I don't".

I know that it is a wonderful comedy depicting scientists/physicists (nerds?), and that other famous physicists have made cameo appearances on the show, but I've never had the inclination to watch it. It's not that I have anything against it. However, my TV channels (and I have 4 TVs in the house) are stuck on HGTV, Food Network, Bravo, TLC, Travel Channel, PBS, BBC America, Animal Planet, Tennis Channel, and Discovery. I normally don't watch any network TV shows (ABC, CBS, NBC, FOX), so that means I don't watch the Big Bang Theory.

Now and then, some of my friends would ask me certain episodes of the show, because they said that these episodes would probably had been a lot funnier if they understood some physics and the inside joke that went along with them. That's probably true from what I've read on the research done for that TV series. I gathered that there's a big college following for that show, which isn't surprising.

Still, I have never watched, and don't plan on watching, "The Big Bang Theory".

Zz.