The extreme deficit of physics undergraduates (APS April 2008)

April 13, 2008 | 4:00 pm

I’ve just been to a session about undergraduate education in physics. Ted Hodapp from the APS talked about an APS/AAPT statement that calls for a doubling of the number of physics undergrad students. (I can’t find the formal statement online–I only read it on a screen in the presentation.)

Hodapp presented a string of evidence that shows just how serious the dearth of physics undergraduates is. Because there was so much information, I’ll just post a couple of dot points about it.

• The nuclear power industry will soon be suffering a shortage of qualified physicists to work for them. About 33 new power plants have been approved in the United States and will be starting up from 2010. That industry needs people with good science/math/problem solving abilities and physics graduates are an obvious choice.
• The medical physics industry employs about 3200 physicists, and have about 300 new jobs each year more than the current capacity for people with undergrad physics degrees. 78% of those people work in radiation oncology, and 16% in medical imaging.
• The growth of occupations requiring science and engineering undergraduate degrees has much higher growth than the civilian labor force but S&E enrollments are not growing anywhere near that fast.
• School principals rated physics and maths teachers about the hardest to recruit along with special needs teachers, primarily due to a shortage of qualified people.
• Math and computer science have about 70,000 undergraduate degrees granted each year, life science about 260,000. Physics has a mere 5000.
• Unemployment for physics graduates is very low, and for physics PhDs is an all-time low of 2.5%
• There is a need for US citizens with advanced physics degrees to work in classified areas. Hodapp says that Cherry Murray called the lack of US citizens with advanced degrees as “a national crisis.”
• The Rising Above the Gathering Storm report, the America COMPETES act, and the Tapping America’s Potential (PDF) report all call for large increases in science, technology, engineering, and mathematics graduates.

All in all, it paints a picture of a serious undersupply of physics graduates for teaching, technical, and other skilled roles in US society, and the promise of a good job market in future years.

See all posts from the American Physical Society April 2008 conference here.

David Harris

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The charming case of X(3872) (APS April 2008)

April 13, 2008 | 1:28 pm

Most of the media attention in particle physics goes to the high-energy frontier. The big news stories tend to be discovery of new particles like the top quark and the likely discovery of the Higgs at the Large Hadron Collider.

However, there is a lot of lower-energy particle physics research going on and the whole field is getting very interesting. At the APS meeting this morning, Eric Swanson of the University of Pittsburgh gave a nice summary of what he calls “the new charmonia.” These are particles observed in collider experiments that have an energy suggesting they are contain charm and anti-charm quarks.

Swanson showed a table of particles that have been observed where he rated a dozen particles in terms of robustness of results and of interest to him. Sitting in the corner of extremely robust and very high interest is the particle called the X(3872). The 3872 refers to the energy of the particle which is measured as 3871.2 MeV and the X refers to some other technical properties of the particle but also indicates that it isn’t yet well understood.

The X(3872) is established as a real signal without any reasonable doubt. But what is it? The energy of the particle and the ways in which it decays suggest a few possibilities. It could be a tetraquark: a particle consisting of four quarks. It could also be a signal that doesn’t indicate an actual stable particle as such but the energy at which certain particle processes take place. Perhaps the most interesting case, and the one that Swanson favors is that this is a “molecule” of D⁰ and anti-D⁰ mesons. (A D⁰ is a combination of a charm and an anti-up quark.) These two particles would be bound together just like two hydrogen atoms can bind together to make a gaseous hydrogen molecule.

If that is true it would be first known case of this kind of matter. It opens up a whole host of interesting ideas about the chemistry of subatomic particles instead of a chemistry of atoms. It also really pushes physicists into a deeper understanding of their theories of quarks and the strong force that operates between them. The idea of particles being “merely” constituted of quarks is known to be an approximation that works at low energies, so there is bound to be a lot new to learn about how this matter behaves.

Swanson provocatively asked, “The constituent quark model must fail somewhere. Have we seen it?”

See all posts from the American Physical Society April 2008 conference here.

David Harris

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Pioneer spacecraft a step closer to being boring (APS April 2008)

April 13, 2008 | 9:51 am

For many years, scientists have known that the Pioneer spacecraft have not been exactly where they thought they should be. Each year the spacecraft falls behind where it should be by about 5000 km. The spacecraft seem to have been undergoing a very small acceleration toward the Sun and, so far, scientists haven’t been to explain it.

Explanations for this have ranged from the prosaic (heat is being radiated into space and providing an acceleration) to the speculative (gravity might not act the way we expect). One thing is certain. The debate about the cause of the Pioneer anomaly, as it is known, has been raging for years.

Newly released telemetry data, incorporating over 100 measured properties including the temperatures of many points on the spacecraft, have been released. At the APS April meeting in St. Louis, Slava Turyshev from the Jet Propulsion Laboratory described his group’s efforts to build a very detailed computer model of the spacecraft geometry and heat flow, and showed the comparison of the model to the new data.

Their model manages to match the measured temperatures of Pioneer to within 3 degrees Celsius at every measured point, which Turyshev seemed extremely pleased with. Having a good thermal model meant that the scientists could start to really ask whether thermal effects could account for the anomaly.

Indeed, when Turyshev’s team calculated the emissions from the Pioneer spacecraft, it found that heat is given off in some directions preferentially, enough to account for 28-36% of the anomalous acceleration.

So what does this result now mean? It weakens some previous claims that the thermal emissions weren’t significant, an argument that not many physicists really believed anyway. However, there is still two thirds of the anomaly to account for? Could there be mysterious physics hiding in the gaps? Turyshev thinks that there is a lot more to take into account such as whether the optical properties of the spacecraft have changed over time-perhaps there is a layer of dust on some surfaces now, for example.

In May, new data about the speed of the spacecraft will be released and that could further clarify the situation, or just add to the debate!

I find the fact that this argument has received so much attention quite amusing. After all, nobody is going to really believe that the laws of physics are different, based on interpretation of Pioneer’s flight. And the immense amounts of work that have to go into trying to model the system properly is quite incredible. Scientists need to dig out information from decades ago to try to get everything they need and there are a lot of uncertainties. Turyshev quipped, “It’s like being on CSI.”

The exercise is certainly improving scientists modeling skills, which could then be used for much more practical purposes like building structures or vehicles on earth. It could even be quite useful in future space missions, although the problem will always be much easier in the future as the engineers will have better data about any spacecraft they send up.

Perhaps the story just reflects human’s unending fascination with the exploration of space and a desire to be part of that exploration, in whatever form it can take.

See all posts from the American Physical Society April 2008 conference here.

Note: This post has been edited since it was first posted to correct the distance Pioneer is falling behind each year.

David Harris

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Can the Tevatron find the Higgs? (APS April 2008)

April 12, 2008 | 8:27 pm

In the past year, there has been a lot of discussion about whether the Tevatron collider at Fermilab can find the Higgs boson before the Large Hadron Collider can. There have been all kinds of claims, and even stories of hints of sightings. In a session today, Brian Winer from Ohio State University gave a very clear presentation about just how close the Tevatron is to potentially finding the Higgs.

Cutting to the chase: Can the Tevatron find the Higgs? Yes, if Nature is kind.

But first let me set the scene.

What do we know about the Higgs now?

The Standard Model of particle physics predicts that a Higgs boson is most likely to have a mass of 87 GeV. (Physicists like to express masses in terms of energies. If you want to convert to an actual mass number, divide the energy by the speed of light squared.) The nature of this prediction is that the Higgs won’t necessarily have that mass but it is likely to have it somewhere in a range centered on that number. There is roughly a 2/3 chance that the Higgs will have mass between 60 GeV and 123 GeV.

Experiments at the Large Electron Position collider at CERN showed that the Higgs does not exist at any mass lower than 114 GeV however, and the theory predicts that the mass will be less than 160 GeV with a 95% probability. So physicists are really trying to look in this region of 114 to 160 GeV.

How sensitive do experiments need to be to find the Higgs?

Experiments have different sensitivities to the Higgs depending on its mass. Physicists can estimate how close they are to observing the Higgs by comparing their measurements to theoretical predictions.

At the moment, the performance of experiments is expressed as a factor of how much better the measurements need to be to start to have a chance of being sure that any Higgs-like signal is really a Higgs boson. It is a game of statistics and it gets pretty complicated so I’ll just take the simplest possible path through this, warning that the full story is much more detailed.

The biggest problem to start with is that what a collider detector measures is a set of particles, none of which is specifically the particle you are looking for. The Higgs decays into certain sets of particles but other decays look very similar. So when your detector sees a set of particles, you need to make extra sure that you are looking at what you think you are looking at! You can predict how many of certain types of known particles you should see and then look for any excess if you are hunting a Higgs or some other unknown particle.

This “background” of decays from known particles must all be excluded from analysis before you can see the Higgs. The big problem is that the backgrounds are a factor of 100 billion times larger than the signal from the Higgs! Higgs would make up only tens of events out of the trillions measured.

Fortunately, detectors are very good at finding the presence of b and anti-b quarks (they create characteristic jets of particle from the collision). Higgs will tend to decay into b and anti-b quarks along with other particles so the bs can be used to identify most of the collisions you are interested in. In fact, this “b-tagging” can reduce the background by a factor of one billion.

But as Winer put it today, “the first factor of a billion is easy, the last factor of 100 is hard.”

How low can you go?

In trying to get this factor of 100 down to a factor of 1, a lot depends on the energy the Higgs has. If the Higgs has an energy at the bottom end of the range, about 115 GeV, and then you combine all the data from both the CDF and DZero experiments, you end up about a factor of 5 short of where you need to be to have a chance at the Higgs. But given that the Tevatron is hoping to collect 4-8 times more data than was used in this analysis, it potentially comes in range though it would still be a real stretch.

If the Higgs has a mass of 160 GeV, then the combined data already brings us to a factor of a mere 1.1 times where we need to be. In other words, a 10% improvement and “Game on!”

Of course, it is not as simple as collecting 10% more data. That would be too easy. That level is really the starting point for when your detectors and dataset have the statistical power to resolve Higgs hiding in the flood of collisions.

But if the Higgs really sits around that mass, then the Tevatron has a genuine chance of finding it soon. Winer said today, “As early as summer, we can start excluding masses around 160 GeV.” In other words, the data will be sensitive enough to say either that there is definitely no Higgs at that mass, or it will see signals that look like the Higgs and it will just be a matter of some more data to determine if they really are Higgs bosons.

Is this the Higgs?

And just to tease you a little more, this event could even be a Higgs.

It is event 6577 from run 196170 and has all the characteristics of a Higgs. It was found on April 5, 2005, at 8:09 a.m. Unfortunately, there is just no way to tell if it is truly a Higgs because the statistics don’t allow anybody to prove what this is. But there is some change that you are looking at the first identified Higgs boson!

The possibility of finding the Higgs at the Tevatron is real and the race is really on.

See all posts from the American Physical Society April 2008 conference here.

David Harris

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Dark matter discovered? (APS April 2008)

April 12, 2008 | 5:01 pm

Has dark matter been discovered? Rumors floating about suggest that the DAMA-LIBRA collaboration will announce that they have detected dark matter after repetition of their controversial experiment which released results in 2000.

The DArk MAtter (DAMA) experiment, situated in an underground laboratory in Gran Sasso, Italy, will announce the results of a new experiment using the same technology that led to the 2000 result. The collaboration has been very quiet for the past few years but will break silence on Wednesday, April 16, at the NO-VE neutrino oscillation workshop in Venice, Italy. Sources here at the APS meeting tell me that DAMA plans to claim they have again seen a signal for dark matter detection. People here don’t have more details at this time.

The DAMA result was controversial because it relies on looking for a small variation in a signal in a sodium iodide detector which has a lot of background noise. Other attempts since to see dark matter have not found anything with the properties DAMA claimed. Might the signal have been due to a systematic error? To see the signal, the detector needs to run for at least a year and look for variation over the year due to the motion of the Earth through the cosmic dark matter background. The quantity of data measured in this new experiment is as much as what led to the original claim of dark matter observation in 2000.

Whatever the DAMA-LIBRA collaboration says, physicists will not be entirely convinced of any claim for detection of dark matter until it is repeated in other types of experiments. However, prepare for another media storm if the announcement is indeed what the rumors are saying. I am certain the collaboration will be much more prepared to answer their challengers and will have a much tighter argument ready if they do indeed try to claim a result.

One of the reasons I’m telling this story is that it highlights another aspect of the value of conferences for physicists. They hear about all kinds of things that are going through the strength of personal connections instead of just having to wait for official publications. A lot of work gets done over a beer in the evenings, and a lot of news spreads through casual conversations.

See all posts from the American Physical Society April 2008 conference here.

David Harris

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The cosmic quantum bounce (APS April 2008)

April 12, 2008 | 2:57 pm

Was the big bang the beginning? There have been plenty of theories put forth that suggest there was something before the big bang, like the cyclic universe and ekpyrotic universe models. They all tend to involve some exotic physics like the collision of branes (multidimensional sheets of spacetime intersecting, nothing to do with zombies) or other ideas that would take a book rather than a short piece here to explain.

This morning I heard more about an interesting addition to the list of pre-big bang models that involves what the speaker Abhay Ashtekar, of Penn State University, called a “quantum bounce.” Ashtekar described some work in loop quantum gravity, one of the more promising alternatives to string theory as a possible theory of quantum gravity. The idea has been floating around for a while but he has made considerable progress in developing the model.

When physicists studying the big bang talk, they tend to run the universe in reverse and they talk about the evolution of the universe going backward so you hear descriptions about the universe getting closer to the big bang, but it is coming from this end of time, not the beginning. It takes a minute to adjust your head to, but it starts to make sense eventually.

Ashtekar talked about how within loop quantum gravity, the universe can look like a normal universe governed by Einstein’s general theory of relativity until very close to the big bang, at which point the quantum aspects of loop quantum gravity take over. In general relativity everything would become what is called a singularity at the point of the big bang. A singularity is a place where the mathematics turns, to use a technical term, “stupid.” There are infinities to deal with and the laws of physics break down.

But within loop quantum gravity, no singularity appears. Without having to invent any new rules, the theory transitions from being like the classical laws into the quantum laws and there is essentially a patch of spacetime, ruled by the laws of quantum geometry, that joins it all together and prevents a singularity appearing.

However, if you push this to its conclusion, you find that you come out the other side of the quantum geometry region with a bounce–the quantum bounce Ashtekar talked about. Then the universe turns back into something like a classical universe. This process can repeat many times over with the universe repeatedly undergoing these cosmic quantum bounces. During the transition, the laws of loop quantum gravity are well-behaved and deterministic (not random).

Furthermore, within the classes of models Ashtekar and his coworkers have investigated, the quantum bounce seems to happen in every case. The research comes with a lot of other technical results that were very interesting but that I don’t understand well enough to talk about here! This is all early work and you can’t take it as a given that this is the way the universe works.

It is, however, intriguing to consider a universe where, as Ashtekar said, “Physics does not end at the big bang.” Nor does it begin there.

See all posts from the American Physical Society April 2008 conference here.

David Harris

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Atoms that barely exist (APS April 2008)

April 12, 2008 | 10:14 am

There are a lot of atoms out there that live on the verge of existence. These are called rare isotopes and tend to only be created in experiments designed to specifically create them. Most of them almost immediately decay back out of existence in tiny fractions of a second. But these short-lived creatures can tell us a lot about other areas of science, and also have many applications. The rare isotopes are unusual and unstable because they have a either a strange number of neutrons or protons in the nucleus.

Witold Nazarewicz of the University of Tennessee, Knoxville, and Oak Ridge National Laboratory said in the opening plenary talk here, “The study of rare isotopes makes the connection between the Standard Model, complex systems, and the cosmos.”

In a whirlwind 36 minutes, Nazarewicz crammed in an overview of many hours worth of material that left me reeling with fascinating ideas and information.

Here are a few highlights for me.

The alpha-knife for cancer treatment

Radioactive nuclei can be used for a bunch of different purposes, including a host of medical applications. One example that is now being explored is the “alpha-knife”. (The name plays off the gamma knife.)

Terbium-149 emits alpha particles (the nucleus of helium, with two protons and two neutrons) which can be used to target tumors. Test on mice at the ISOLDE facility at CERN have shown that applications of the alpha-knife have extended the lives of mice with cancer remarkably well. It’s early days but this could be a new application of radioactive particles for cancer treatment

How to skin an atom: Pygmy dipoles and neutron stars

Some neutron-rich nuclei develop an outer skin of neutrons, with the protons more confined in the center. For example, consider the isotopes that have a total of 100 neutrons and protons. Sn-100 (tin with 50 protons and 50 neutrons) has the protons and neutrons distributed in the same way through the nucleus. However Zn-100 (zinc with 30 protons and 70 neutrons) has a very identifiable skin of neutrons. This can even be measured.

Many nuclei wobble about in various ways and a nucleus like Sn-100 has the bulk of protons and neutrons slightly separated on average (called a dipole) and it oscillates back and forth. A nucleus like Zn-100 has an additional kind of dipole caused by the neutron skin. This has been called a “pygmy dipole”.

The useful part of the pygmy dipole is that it reveals a lot of information about what a dense collection of neutrons is like, and so can tell us about what neutron stars must be like, without having to try to measure a neutron star itself. Neutron stars are fascinating objects and I mentioned them in a previous post about black holes. This is just one of the cosmic implications of nuclear physics!

When the laws of physics go pear-shaped

Radium-225 (88 protons, 137 neutrons) has a configuration of protons and neutrons that makes the whole nucleus have the shape of a pear. Experiments on this nucleus allow physicists to test fundamental properties of the laws of nature including CP violation. (See our 60 seconds on the topic). This is an area that is usually studied through the decay of particles in collider experiments but this different approach give other complementary information.

Has magic gone awry?

A long-standing understanding of nuclear structure suggests that certain nuclei are more stable than others. These happen when the number of protons or neutrons is one of the so-called “magic numbers“–2, 8, 20, 28 for example. A bunch of new experiments have shown that perhaps these numbers aren’t as magical as previously thought. Experimenters are finding nuclei that are more stable with 14, 16, or 32 protons or neutrons in the nucleus. It’s not quite time to rewrite the textbooks but it is enough to cause a rethink of just how magical the magic numbers really are. And it will lead to a better understanding of what makes a nucleus stable in the first place.

With all this physics in just one talk, I’m not sure my brain will be able to keep it all in, but it’s been a great start to the conference!

See all posts from the American Physical Society April 2008 conference here.

David Harris

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But how fast can I download my rumors?

April 11, 2008 | 7:39 pm

Grid computing is revolutionizing the way scientists share and analyze data. Grid projects worldwide are helping researchers search for new wheat genes, predict storms, or simulate the sun’s interior. The 7000-odd physicists working on experiments at the Large Hadron Collider will rely entirely on grid computing to connect them with LHC data.

But a spate of recent reports on “the Grid” being developed for the Large Hadron Collider have promised way more than the technology can now–and in some cases will ever–deliver. (The first report in the The Sunday Times spurred many other articles that seemed to become shorter and less accurate as the days went by.) Here I try to separate fact from fiction.

Fiction: The Grid will replace the Internet.

Fact: The Grid, like the Web, is an application of the Internet. When the LHC turns on, data will be transferred from CERN to 11 large computing centers around the world at rates of up to 10 gigabits per second. Those large centers will then send and receive data from 200 smaller centers worldwide. All of this data transfer takes place over the Internet. Dedicated fiber optic links are used between CERN and the large centers; research networks and sometimes the plain old commercial Internet are used between the smaller centers.

Fiction: I will be able to download movies 10,000 times faster using the Grid.

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Katie Yurkewicz

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This Conference Life: APS April 2008-The arrival

April 11, 2008 | 4:52 pm

I’ve just arrived in St. Louis, Missouri, for the American Physical Society’s annual April meeting. For the next four days I’ll be reporting on what is happening here at the conference to give you a flavor of what happens at a large physics conference. There will be a lot of science presented but the value of conferences goes far beyond the merely sharing the latest research results.

Conference culture is unusual the first time you encounter it so for those of you who have never had the chance to go native with the physicists, I’ll chat about what it is like to be here.

When you arrive at one of these meetings, the first big challenge is actually checking in and getting to your room. Not because there are any problems with the hotels, but because there are so many people who you haven’t seen in person for a while that it’s next to impossible to walk more than a few steps before running into yet another acquaintance. If I wanted to be a true physicist, I’d make a crack about there being a very short mean free path, but I’ll leave the physicist readers to insert their own quip here.

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David Harris

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Embracing the politics of science

April 11, 2008 | 5:21 am

Global warming. Alternative energy. New pharmaceuticals. The next wave of technology. Many of today’s big policy debates center on science.

The key to getting the most from those debates is to arm policy makers with the scientific knowledge needed to distinguish valid arguments from poorly researched claims.

Yet very few members of today’s Congress have backgrounds in science or science-related fields. A more diversified Congress could offer a more diversified, and possibly more discerning, look at scientific issues.

At least that’s what the advocacy group Scientists and Engineers for America, or SEA, thinks. The group has launched a campaign to give you more chances to vote for representatives who have technical and scientific expertise to bring to these deliberations.

“Scientists and engineers can help the government understand the language of some of the most important issues of our time. They can be a bridge between science and politics. They have a valuable way of thinking–of making decisions based on facts,” says Lesley Stone, SEA executive director. Stone goes into more detail in the upcoming print issue of symmetry; you can read an advance copy of her commentary now.

To inject more evidence-based reasoning into policy debates, more scientists and engineers need to run for office, the SEA says. With the help of a group of scientific societies, it has launched a campaign to get scientists and engineers elected to everything from school, park and township boards to state offices and all the way up to the Congressional level.

Eight members of the current US House of Representatives have science PhDs, including three physicists. Anecdotally, Stone says, physicists seem to have made some of the largest inroads into politics at all levels.

“They are pretty into politics,” she says.

To ease the transition from laboratory to campaign trail, SEA is hosting its second conference on May 10 at Georgetown University to give advice on how to register as a candidate, raise funds, and formulate campaign messages. A video unveiled last week shows politically active scientists and engineers, including Illinois State Rep. Michael Fortner, of Fermilab, offering tips and encouragement.

“If you can learn nuclear physics, you can learn politics,” says Michigan Congressman Vern Ehlers, who holds a physics PhD.

SEA plans to periodically update its Web site with information on how to enter the political arena and eventually hopes scientists and engineers will write in with advice and serve as chat room mentors for novice politicians.

Lesley Stone on running for public office (PDF)

Tona Kunz

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