Thursday, March 31, 2005

W on Terri Schiavo

Terri Schiavo's body finally died this morning; her mind having died many years ago. The President, demonstrating his usual stunning ignorance of scientific evidence, had this to say
"The essence of civilization is that the strong have a duty to protect the weak. In cases where there are serious doubts and questions, the presumption should be in the favor of life."
I find this remarkable for two reasons. First, it is just plainly untrue that there were serious doubts and questions, where by "serious" I mean ones that were not clearly addressed by the respected medical experts who explained patiently that her cerebral cortex had been almost entirely replaced by spinal fluid. Second, where was this opinion when there were serious doubts and questions raised about the evidence used to send us to war in Iraq? How many lives (and their accompanying minds) could have been saved? I guess it only comes out when it serves to stimulate the religious right.

Wednesday, March 30, 2005

Topological Defects

Today's cosmology/relativity/particle physics seminar at Syracuse was given by Brandon Carter from the Observatoire de Paris-Meudon. Brandon spoke about the stability properties of the "solid dark matter" model of the accelerating universe, proposed by Bucher and Spergel. The main idea of Bucher and Spergel is that, under certain circumstances, topological defects may lead to an accelerated expansion. I'd like to post about this, and may do so tomorrow. However, as a prelude, I thought I'd better provide a version of what topological defects are.

Topological defects are extended solutions to field theories that can arise when the vacuum structure of the field theory is topologically nontrivial. As a somewhat simple example (and, I admit, a clumsy one, but its the best I can do right now), let us model a field theory by standing many pencils on their ends on a table top, and connecting the pencils to their nearest neighbor pencils by springs. What is the vacuum configuration of these pencils? Obviously, because of gravity, each individual pencil would like to lie down on the table, but doesn't care which direction it is pointing as long as it is lying down. So the vacuum configuration of the theory is all the pencils lying down, facing in the same direction, because if any pencil faces in a direction different from that of its neighbor, then there will be energy bound up in the spring which is stretched between them, which can be reduced by the two pencils aligning. Obviously, there are an infinite number of equivalent vacua, corresponding to all the pencils aligning in any of the possible directions in the plane of the table.

Now suppose that the table is very big (maybe even infinite), and pencils that are very far apart from each other fall down into different vacuum states, because causality doesn't permit information to travel between them so that they can align. You could imagine, in fact, that pencils that trace out a very large circle all fall down pointing outwards in different directions along that circle. All other pencils inside that circle will try to align with the pencil closest to them, in order to reduce the energy in the springs. However, if you think through this for a moment, you'll see that there will always be one pencil, the one at the center, which is equally pulled in all directions and so will remain standing up - now stably. In fact, a few pencils on each side of this one will be partially standing up, because of the spring tension.

These few pencils, and particularly the one at the center, represent what is meant by a topological defect. It is a small region of space, in which the field configuration is out of the vacuum manifold, but which remains metastably in that configuration because the topological properties of the vacua chosen by the field at infinity are nontrivial. I won't harp on about how these topological properties are defined, because it's more technical than the sketch above and won't buy us much clarity here.

In the model system above, the topological defect is point-like - it is just a single point in space. In three spatial dimensions one can have either point-like defects (monopoles), line-like defects (strings) or membrane-like defects (domain walls). Which, if any, of these exist depends on the particular particle physics model one considers. However, there are some generic situations that are important. The most well-known occurs if one has a grand unified theory, which unifies the strong, weak and electromagnetic forces so that they are described by one simple gauge group. In this case, when the group breaks to the standard model of particle physics, as it must, monopoles are inevitably formed. These can be problematic in the context of cosmology, and were one of the original motivations behind the development of the inflationary universe.

Monday, March 28, 2005

Doing Fourier Transforms at Caltech

I'm in the middle of my trip to Caltech, which I am enjoying very much. Given that I'm discussing physics with people most of the day and then flying out, there isn't much time to post. I just had a nice chat with Mark Wise about the much-discussed Kolb, Matarrese, Notari and Riotto paper. I know Rocky and Toni quite well and am, in general, a big fan of their work. I haven't been able to understand this paper sufficiently well to have an opinion yet (see Sean Carroll's take on this over at Preposterous Universe), although I confess that the result goes against my intuition (wouldn't be the first time a correct result had managed this though).

For some reason, Mark and I tied ourselves in knots trying to compute the particular variance calculated in their paper, but, I am happy to report, we did succeed in doing the Fourier transform correctly at the end. Given the amount of interest in this paper (perhaps because of the press release), I'm going to have to work through it in much more detail and will report here after doing so (hopefully).

Back to Syracuse tonight so that I can teach tomorrow and host our seminar speaker, and my former collaborator, Brandon Carter - the man who coined the phrase "the anthropic principle". Now there's a topic begging to be blogged about.

Sunday, March 27, 2005

Travelin' Man

In a couple of hours I'm headed back to California for a quick visit to Caltech, where I'll be giving the High Energy Physics seminar tomorrow afternoon and then heading back on the red-eye in time to teach on Tuesday. This is a fun talk to deliver since, unlike the usual seminars I am invited to give, the audience here will be a mixed group of experimentalists and theorists. My seminar is titled "Connecting Cosmology and Fundamental Physics" and I'll be talking about a selection of topics. Some, like baryogenesis, I've already made an attempt to explain here at Orange Quark. Others, like dark energy and inflation , I've yet to discuss, but intend to get into before too long. The focus of the talk is the challenges to particle physics posed by cosmological issues and the fascinating possible solutions that theorists are contemplating

The other nice part of my trip is that, before my flight tomorrow evening, I'm having dinner with Marc Kamionkowski and his group. Marc's a smart and talented cosmologist and it'll be both fun and educational to discuss cosmology with him and his students and postdocs.

Barring delays and cancellations I should be spending this afternoon in glorious sunshine (last time I said that it rained for four straight days in San Francisco, but I'm an optimistic guy) sipping a glass of wine and working on my talk. Otherwise, surely there must be a few square meters of O'Hare that I haven't explored twenty times already.

Saturday, March 26, 2005

Electroweak Baryogenesis

In a recent post, I discussed the puzzle posed for cosmologists and particle physicists by the observation of the baryon asymmetry of the universe (BAU) - the fact that the universe is composed almost entirely of matter, with a negligible amount of antimatter. There was quite a bit of interest in this topic expressed in the comments for that post, and I thought it would be fun to go into a little more detail about one popular idea about how the BAU might be generated. Obviously, all my posts won't be as technical as this one, but it seemed like there would be some audience for such a description. If people are interested in even more (some might say excessive) detail, they could read this review article, or this one.

The precise question that concern us is; as the universe cooled from early times, at which one would expect equal amounts of matter and antimatter, to today, what processes, both particle physics and cosmological, were responsible for the generation of the BAU? In 1967, Andrei Sakharov established that any scenario for achieving this must satisfy the following three criteria;
  • Violation of the baryon number (B) symmetry
  • Violation of the discrete symmetries C (charge conjugation) and CP (the composition of parity and C)
  • A departure from thermal equilibrium.
In recent years, perhaps the most widely studied scenario for generating the BAU has been electroweak baryogenesis. In the standard electroweak theory baryon number is an exact global symmetry. However, baryon number is violated at the quantum level through nonperturbative processes - it is an anomalous symmetry. This feature is closely related to the nontrivial vacuum structure of the electroweak theory.

At zero temperature, baryon number violating events are exponentially suppressed (this is most certainly a good thing, since we would like the protons making up our bodies to remain stable). However, at temperatures above or comparable to the critical temperature of the electroweak phase transition, B-violating vacuum transitions may occur frequently due to thermal activation.

Fermions in the electroweak theory are chirally coupled to the gauge fields. In terms of the discrete symmetries of the theory, these chiral couplings result in the electroweak theory being maximally C-violating.
However, the issue of CP-violation is more complex. CP is known not to be an exact symmetry of the weak interactions (this is observed experimentally in the neutral Kaon system). However, the relevant effects are parametrized by a dimensionless constant which is no larger than 10-20. This appears to be much too small to account for the observed BAU and so it is usual to turn to extensions of the minimal theory. In particular the minimal supersymmetric standard model (MSSM).

The question of the order of the electroweak phase transition is central to electroweak baryogenesis. Since the equilibrium description of particle phenomena is extremely accurate at electroweak temperatures, baryogenesis cannot typically occur at such low scales without the aid of phase transitions. For a continuous transition, the associated departure from equilibrium is insufficient to lead to relevant baryon number production. For a first order transition, quantum tunneling occurs around a critical temperature, and nucleation of bubbles of the true vacuum in the sea of false begins. At a particular temperature below this, bubbles just large enough to grow nucleate. These are termed critical bubbles, and they expand, eventually filling all of space and completing the transition. As the bubble walls pass each point in space there is a significant departure from thermal equilibrium so that, if the phase transition is strongly enough first order, it is possible to satisfy the third Sakharov criterion.

There is a further criterion to be satisfied. As the wall passes a point in space, the Higgs fields evolve rapidly and both CP violation and the departure from equilibrium occur. Afterwards, the point is in the true vacuum, baryogenesis has ended, and baryon number violation is suppressed. Since baryogenesis is now over, it is imperative that baryon number violation be small enough at this temperature in the broken phase, otherwise any baryonic excess generated will be equilibrated to zero. Such an effect is known as washout of the asymmetry and the criterion for this not to happen translates into, among other things, a bound on the mass of the lightest Higgs particle in the theory. In the minimal standard model, current experimental bounds on the Higgs mass imply that this criterion is not satisfied. This is therefore a second reason to turn to extensions of the minimal model.

One important example of a theory beyond the standard model, in which these requirements can be met, is the MSSM. In addition, there are also light stops (the superpartners of the top quark) in the theory, which can help to achieve a strongly first order phase transition. For those of you who care about the numbers, according to recent calculations, baryogenesis is possible if the lightest Higgs particle has a mass less than 120 GeV, and the lightest stop has a mass less than the top quark mass.

What would it take to have confidence that electroweak baryogenesis within a particular SUSY model actually occurred? First, there are some general predictions: if the Higgs is found, the next test will come from the search for the lightest stop, and important supporting evidence will come from CP-violating effects which may be observable in experiments involving B-mesons.

However, to establish a complete model, what are really necessary are precision measurements of the spectrum, masses, couplings and branching ratios to compare with theoretical requirements for a sufficient BAU. Such a convincing case would require both the Large Hadron Collider (LHC) and, ultimately, the International Linear Collider (ILC), in order to establish that this is truly how nature works.

Friday, March 25, 2005

Dark and Twisted Political Cartoons

The BBC is carrying the story of a Syrian cartoonist, whose work, while not explicitly mentioning any individuals or countries, wickedly lampoons authoritarian regimes. My favorite example is the one I've posted on the right. The artist, Ali Farzat, used to publish a satirical magazine, but that was ultimately banned, and it's an uphill struggle for him to get his cartoons published anywhere.

The BBC story is really about restrictions on the media in Syria and contains some interesting points about the roles that the internet and international satellite TV are playing in getting information through to the populace, despite the restrictions.

However, I mostly just enjoyed the cartoons, which are a lot of (dark) fun. There are a couple of other examples in the story, and you can find a few more in this slide show from the Guardian.

Thursday, March 24, 2005

Science Under Attack

Americans have played a crucial and profound role in much of the scientific and medical progress of the last century. During that time, Americans have won 242 Nobel prizes, more than the combined number won by the next four countries on the list (the United Kingdom, Germany, France and Sweden), according to Obviously, the sheer size of the country is a factor here, but the number is, nevertheless, remarkable. One of the factors behind these impressive achievements is the importance placed on the public funding of science. This dedication to American excellence does not only yield fancy Swedish prizes though. It lies behind the technology and information fields on which an increasing portion of our economy relies; it lies behind the increasing longevity of Americans; it lies behind our quality of life, particularly for the elderly, the infirm and the disabled; it lies behind our partial ability to predict and protect ourselves from natural disasters; it lies behind our national security, and, like it or not, it lies behind the dominance of our military. A comprehensive list would be much longer than this.

Equally important, particularly to those of us who devote our working lives to science, is that progress in science adds to our knowledge of our world, of our universe and of what it means to be humans exploring them. To paraphrase Robert Wilson, first director of what would become the Fermi National Accelerator Laboratory, when asked by Congress whether the laboratory would contribute to the national defense; the primary contribution of science is not to the defense of the nation but rather to what makes the nation worth defending.

These days, the tremendous American legacy in science and medicine is under attack and faces a crisis that, if not overcome, will result in us ceding leadership in these fields to other nations for generations to come. Decreased funding for basic science, the misguided direction of NASA, the suppression of scientific information involving contraception, abortion and sexual practices, and the denial of evolution and cosmology are but a fraction of the obstacles to progress that have sprung up in recent years.

This attack on the leading role the United States plays in science and medicine is happening because our value systems are being hijacked by a small number of well-organized and well-funded extremists on the far religious right. If you have a child and you want that child to grow up and succeed in the modern world, you need to take action now to prevent the education she so badly needs from being corrupted.

As Frank Rich, writing in the New York Times, describes, as part of a much longer article that I encourage you to read:

"...polls consistently show that at most a fifth of the country subscribes to the religious views of those in the Republican base whom even George Will, speaking last Sunday on ABC's "This Week," acknowledged may be considered "extremists." In that famous Election Day exit poll, "moral values" voters amounted to only 22 percent. Similarly, an ABC News survey last weekend found that only 27 percent of Americans thought it was "appropriate" for Congress to "get involved" in the Schiavo case and only 16 percent said it would want to be kept alive in her condition. But a majority of American colonists didn't believe in witches during the Salem trials either - any more than the Taliban reflected the views of a majority of Afghans. At a certain point - and we seem to be at that point - fear takes over, allowing a mob to bully the majority over the short term. (Of course, if you believe the end is near, there is no long term.)

That bullying, stoked by politicians in power, has become omnipresent, leading television stations to practice self-censorship and high school teachers to avoid mentioning "the E word," evolution, in their classrooms, lest they arouse fundamentalist rancor. The president is on record as saying that the jury is still out on evolution, so perhaps it's no surprise that The Los Angeles Times has uncovered a three-year-old "religious rights" unit in the Justice Department that investigated a biology professor at Texas Tech because he refused to write letters of recommendation for students who do not accept evolution as "the central, unifying principle of biology." Cornelia Dean of The New York Times broke the story last weekend that some Imax theaters, even those in science centers, are now refusing to show documentaries like "Galápagos" or "Volcanoes of the Deep Sea" because their references to Darwin and the Big Bang theory might antagonize some audiences. Soon such films will disappear along with biology textbooks that don't give equal time to creationism."

This is a crisis for all of us, and every day we ignore it and hope it will go away, more ground is lost in the battle for facts against fiction. This is not about science versus religion – that is a different story. Indeed, when our elected officials replace scientific facts and analysis by theology, they not only devalue science, but also devalue religion, by using it to cast doubt on the beauty and wonder of the natural world. Rather, this is about the right of Americans to have free access to the wealth of well-established facts about this world that their hard-earned dollars have helped to discover. The scientific legacy of great American scientists belongs to all Americans and we should be outraged about any attempts to suppress it, to corrupt it or to undermine its future.

Wednesday, March 23, 2005

Relativity, Cosmology and Undergraduate Imaginations

I’ve spent a reasonable fraction of today meeting with students from my undergraduate relativity and cosmology class. The class is aimed at students with very little physics background, but with some mathematics, including two semesters of calculus. I inherited the class from my former colleague Don Marolf, who is now a Professor at U.C. Santa Barbara. Don had done a wonderful job with this course, developing a substantial reader with huge amounts of information about special and general relativity, and a small amount of cosmology.

This is my first year teaching the course. I’ve changed it around somewhat, removing some of the relativity in order to get to the black hole solution and its features by this week, so that I can then spend half the semester on cosmology. This doesn’t mean I didn’t love it the way Don had it, just that my personal interests lie in slightly different areas.

An integral part of the course are the student projects. Naturally, these must concern a topic related to the course material. However, beyond that there aren't many guidelines about what the project actually is allowed to be. The students in this class are a lot of fun to teach - smart and full of great questions that fill up the class time before I know it. Today's meetings were to discuss project ideas, and I must say it was a blast. Here are some examples of what they want to do:
  • A popular-style article about time travel
  • A computer code to calculate and describe how particles move around a black hole
  • A magazine article on relativity in more than four space-time dimensions
  • A review article on experimental tests of the inverse square law of gravity
  • A web site to teach high-school students about gravitational waves
  • A computer game in which rocket ships race and one can observe the race from different reference frames
  • An article about the evidence for an accelerating universe
  • A magazine-style article about experimental tests of general relativity
  • ...
The list goes on and on. The computer game is particularly inventive. The students not only have to complete these projects and turn them in; they also have to present them to the whole class. Its a lot of work, but they're clearly up to it.

I'm having a wonderful time watching them come to grips with material that is so fascinating to me personally. I truly think that most people are fascinated by science, but don't have enough easy opportunities to learn more about it. At Syracuse our Saturday Morning Physics Lecture Series is one attempt to give people such an opportunity. I'm planning to discuss this and a number of other outreach activities in a post in a few weeks time, after several upcoming and related events are completed.

Tuesday, March 22, 2005

Preserving Life at (almost) Any Cost

Yesterday the US Congress acted quickly and decisively to pass legislation to force reinsertion of the feeding tube into Terri Schiavo, the tragic Florida woman who is in a persistent vegetative state. The President, who returned early (yes, that's right, you didn't misread it) from Texas to sign the bill, said that " is wisest to always err on the side of life,". That Congress and the President were willing to override the established wishes of Ms. Schiavo and of her husband, and were willing to ignore separation of powers to take this extraordinary step, speaks volumes about their commitment to saving human life whenever possible.

Also in the news today, a Minnesota teen killed his grandparents, 6 students and a teacher before killing himself. His rampage used multiple weapons, including a shotgun and two pistols. I wonder what kind of rapid, special, sanctity-of-life preserving legislation could make it more difficult for this to happen again (and again and again)? It would, of course, have to be passed over the established wishes of those closest to the weapons.

In case you didn't catch the sarcasm in the opening paragraph (I was laying it on pretty thick though), I am dismayed to see the US Congress getting involved in this kind of matter. In my country of birth, England, government debates only weighty issues of national importance. For example, this morning I saw an interview with a Labour MP (one of those that used to devote their time to making life better for the working class) who was discussing his outrage that Camilla Parker Bowles might become Queen after she marries Prince Charles and after he becomes King. Note to the British government on behalf of my family who still live there: please put the antics of the anachronistic products of centuries of inbreeding further down your list than decent healthcare, education and law and order.

Matters of Antimatter

As promised in my last post, I thought I’d spend a bit of time discussing the source of the fuss that cosmologists make over matter and antimatter.

Antimatter is just like ordinary matter in every way, except that every quantity you can think of (apart from mass and spin), is reversed. As an example, the electron is a particle with a specific mass and carrying a specific amount of negative electric charge. The antiparticle of the electron is a positron, which has the identical mass to an electron, but precisely the opposite charge. The thing about particles and their antiparticles is that, if one puts them together, the net value of any quantity (called a quantum number by physicists) carried by the pair of them is zero. Therefore, a particle and an antiparticle together are merely mass which, thanks to Einstein’s E=mc2, can be converted entirely into energy. As a result of this, when matter and antimatter come together, they annihilate, producing energy in the form of light (photons).

We know so much about antimatter for two reasons. The first is that it is a natural part of quantum field theories, which we use to describe matter, and which are among the best-tested theories in all of science. The second is that we can make and investigate antimatter in large amounts. For example, the purpose of the Fermi National Accelerator Laboratory near Chicago is to make vast numbers of antiprotons to study how they annihilate with protons.

Antimatter is important in cosmology because of the extreme temperatures and densities of the early universe, as described in a previous post. One consequence of such an extreme environment is that there is so much energy around that any kind of matter (including antimatter) can be created. Therefore, in the early universe, one expects there to have been equal amounts of both matter and antimatter and then, as the universe cooled, for these particles to find each other, annihilate, and leave our present universe with very little matter around (and an equally small amount of antimatter).
This is clearly at odds with what we observe in the universe, where we have relatively large amounts of matter and essentially no evidence of primordial antimatter. In fact, this asymmetry between matter and antimatter can be made quantitative (for baryons such as protons and neutrons) through observations of the abundances of light elements in the universe (Big Bang Nucleosynthesis) and also from the pattern of anisotropies in the cosmic microwave background radiation (CMB). At some point in the future I will post about both these topics, which are fascinating in their own rights. However, for now, suffice it to say that there is clear evidence that the universe is composed of matter, with negligible antimatter.

This all constitutes a puzzle for cosmologists. How did the universe evolve from early times, in which there were equal numbers of baryons and antibaryons, to the present universe, in which there is a precisely measured baryon asymmetry of the universe (BAU)?

Potential solutions to this puzzle provide a wonderful example of the interplay between particle physics and cosmology. A beautiful feature of many theories beyond the standard model of particle physics is that, when considered in the context of the expanding universe, they automatically contain such a dynamical mechanism that can, in principle, explain the origin of the BAU. The generation of the BAU through one of these mechanisms is what is known as baryogenesis. This isn’t enough of course; we don’t yet know which, if any, of these theories might be the right one. However, upcoming experiments, such as those at the Large Hadron Collider (LHC), provide the exciting possibility of either ruling out some of them or providing significant evidence for one of them. Since I’ve worked a lot on such ideas during my career, this is a topic close to my heart.

Monday, March 21, 2005

Wine Snobs Rock

I just returned from the LCWS2005 conference banquet, which was combined with the conference outing, and took place aboard a cruise ship around the Bay. We've had quite poor weather while I've been out here on this trip. It even poured down with rain while we were on the bus to San Francisco, and Wim de Boer and I made good use of the time discussing some details of electroweak baryogenesis. This is a particularly interesting approach to understanding why the observable universe is composed almost entirely of matter, with negligible amounts of antimatter. I've worked on this a lot in my career and will devote a whole post to this fascinating topic some time soon.

Luckily, the weather cleared up beautifully for the cruise and the views were spectacular. We took a slow pass past Alcatraz island before heading under both the Golden Gate and Bay bridges. As night fell the sky cleared nicely and revealed a beautiful view of the city as we came back to the pier.

All this was wonderful, but, if forced to, I'd trade good views at a banquet for fine food and wine any time. Fortunately, I didn't have to make that choice. The food was perfectly fine banquet food. However, the wine was something else. I was lucky enough to sit with my friends JoAnne Hewett and Tom Rizzo at dinner. These people are serious wine connoisseurs (did I accidentally write "snobs" in the title of this?) and were kind enough to bring a few selected bottles to share with their table-mates. Believe me, these were well worth the $15 a bottle corking fee the wait staff charged us when they saw what was going on. Many thanks to JoAnne and Tom for this crucial component of a lovely evening.

Tomorrow I head back to Syracuse so that I'm back in time to teach on Tuesday. The conference is over a day later. Wish me the luck that one needs to fly from A to B without significant delays these days.

Sunday, March 20, 2005

A Signal of Dark Matter Annihilation?

This afternoon (Saturday for me here in California, even though the blog will register this as a Sunday post) I chaired the first session of talks on the connections between cosmology and the International Linear Collider. The talks were all excellent, but I particularly enjoyed the one delivered by Wim de Boer, from the University of Karlsruhe in Germany.

Wim was concerned with data from the Energetic Gamma Ray Experiment Telescope (EGRET) on the Compton Gamma Ray Observatory. This experiment discovered an excess of diffuse gamma rays in all directions on the sky, which has puzzled physicists for a while now. Wim's claim is that this observation is well explained by the hypothesis that the gamma rays arise from the annihilations of dark matter particles with each other. Working with this hypothesis, Wim and collaborators were able to reconstruct the distribution of dark matter in the galaxy required to yield the observed gamma ray excess. This is a very tempting idea and, if verified, it would be a wonderful piece of evidence for dark matter.

There is more to this story though. The predicted distribution contains a ring of excess dark matter in the galaxy. What is fascinating is that two years ago the Sloan Digital Sky Survey (SDSS) announced the discovery of a corresponding ring of stars in the galaxy, thought to be left over from the collision of a smaller, dwarf galaxy with our galaxy billions of years ago. It is natural that there would be an associated ring of dark matter in the same location. Together these two pieces of data may therefore be our first tantalizing hint of dark matter annihilation.

(Wim went further, considering a particular dark matter candidate - the neutralino in minimal supergravity (mSUGRA) models. This part was more technical and model-specific, and while it was also fascinating, I won't go into the details here.)

The last talk of the day was a colloquium on collider-cosmology connections. A year ago, at the LCWS2004 meeting in Paris, I gave this talk. This year Jonathan Feng delivered it and did a truly masterful job, providing material at a variety of levels to match the varied levels of expertise in the audience. These connections are important to particle physics and to cosmology and Jonathan described them perfectly.

All in all a great day of physics.

Saturday, March 19, 2005

The Future of NASA

We physicists are a pretty inclusive bunch. We love to point out that a physics training makes one ideal for many other careers in which one can make a real contribution to society, and we love to claim people who've demonstrated this successfully as our own. We do this partly because its actually true, partly because we want more physics majors, and partly because we think a scientifically literate society will benefit everyone. To give just one example, physicists will often point out that Congressman Rush Holt (D - NJ) is a physicist. His economic development plan for central New Jersey is even called Einstein's Alley. (The other physicist-Congressman is Vern Ehlers (R - MI)). Sometimes, however, it's best for us to hold off until we see how things work out.

This from the always-insightful Bob Park's What's New column
Described in media stories as a Johns Hopkins physicist, Michael D. Griffin is at the Applied Physics Lab, a government contract lab far from the campus, and although he has a B.A. in physics, his Ph.D. is in Aerospace Engineering from the Univ. of Maryland. During the Reagan years he was Deputy for Technology of SDI (Star Wars), which managed to squander $30B on mythical weapons. Eighteen months ago, Griffin testified before the House Science Committee on "The Future of Human Space Flight". ...
NASA has the experience and potential to do wonderful things for science; given the right direction and a leader who can make it happen. In my opinion one component needs to be a commitment to robotic missions for scientific exploration, which have been a remarkable success so far, and lack the cost, danger and technological constraints of manned missions. The second requirement is a drive to investigate the universe with great observatories, with new probes of inflation, of black holes and of the nature of the dark energy, and to have the vision to go further. Like many other physicists, I'll be watching carefully, with fingers crossed.

Friday, March 18, 2005

Putting the International in "International Linear Collider"

I'm sitting in the conference hall for the first day of sessions at the International Linear Collider Workshop (LCWS2005) at Stanford University. A large part of the first day's presentations are concerned with collaborative, political and management issues associated with this effort. For the large collaborations that are common in experimental particle physics, such issues are central to the project's success, although they remain largely invisible to anyone outside the collaboration. For the ILC this is even more true and, although I'm itching to get on to the physics part of the conference, I do find it somewhat fascinating to see how the cogs and wheels of a project like this are arranged to get the job done.

Perhaps the most important part of the ILC effort is its international nature. An incredibly rewarding part of being a physicist is that one is constantly engaged in intellectual endeavours with colleagues from across the planet. For a practicing physicist this is as natural as breathing and essential to making progress in our increasingly complex field. As an example, off the top of my head, during my career I've written papers with physicists from Albania, Algeria, America, Brazil, Canada, Croatia, England, Finland, Germany, Greece, Hong Kong, India, Italy, Romania, Russia, Spain and Switzerland (and I guarantee you I'm forgetting some).

Translating this natural international collaboration on intellectual topics into the political, financial and technological areas required to get the ILC to work is another challenge. To be successful one requires an ironclad physics case for the project, and coherent scientific and organizational messages from the physics community as a whole (not just high-energy physicists) for governments and the general public alike. Without these, the obstacles to a successful ILC may be insurmountable. People here seem very optimistic, but then again you'd expect them to be. I'll try to provide updates to this story at various points in the future, as things progress.

Thursday, March 17, 2005

Of Colliders and Cosmology

I'm now into my second day of blogging and must say that I am surprised and delighted by the supportive and encouraging comments I've been receiving. Thanks to all who dropped by.

This afternoon I'm headed to California to take part in the International Linear Collider Workshop (LCWS2005) at Stanford University. The ILC is a proposal for the next large particle-smashing machine after the imminent (2007) turn-on of the Large Hadron Collider (LHC) in Geneva. I and my counterparts from Europe (Wim de Boer) and Asia (Nobuchika Okada) are co-conveners of the Cosmological Connections group, which is organizing three sessions of talks about the connections between extending our understanding of the universe and improving our knowledge about particle physics. The connections are many and I may devote a later post to a detailed description. Since I have to pack, feed the cats, call a cab and perform a host of other chores before then, I'll just give a quick summary here.

The main connection is to the search for dark matter. There is overwhelming evidence that the universe contains matter of a type other than that which we see forming galaxies, stars, planets and us (called baryons). In fact, the evidence shows that there is five times more of this so-called dark matter in the universe than there are baryons. It is observed indirectly through many different cosmological methods and, indeed, is the reason that galaxies are able to form the way they do. However, so far we have not been able to determine what the particles that make up the dark matter are. There is a good reason for this. The reason the dark matter is not seen glowing along with much of the rest of the material in galaxies is that it does not experience electromagnetism, the force of nature that leads to light. We think that dark matter particles must be only weakly interacting (electromagnetism is quite a strong force) and a consequence of this is that it is hard to get them to do anything measureable to material on Earth in order to betray their presence.

There are two ways to get around this. one is to build very sensitive detectors to measure even the smallest effects of dark matter on normal matter. After all, if there is five times more dark matter than baryons around, there should be lots passing through the Earth all the time as our solar system orbits the galaxy. There are many people devoted to these efforts and there are reasons to think that success is lurking in the not too distant future. The second way is, rather than waiting for cosmological dark matter to hit something in your detector, to smash particles together hard enough to create some of it all for yourself. If one can do this, then one would be able to measure its properties (its mass and the strengths of its interactions) and study how it fits into the overall structure of particle physics. This is where our colliders are indispensible.

With my friend Jonathan Feng from U.C. Irvine, I co-Chair the Working Group on Cosmology and the Linear Collider subgroup of the American Linear Collider Physics Group. With Marco Battaglia, Norman Graf and Michael Peskin we will, in the next month or so, complete a long document detailing this and other connections between colliders and cosmology. When this is completed I'll try to post a more comprehensive discussion of the topic.

I'm hoping to post a few times from the conference if I can demonstrate the self control required not to sprint out into the sunshine as soon as the sessions are over.

Wednesday, March 16, 2005

Beyond the Bang

My Dad works in a warehouse in Wigan in the North-West of England. I'll have some more about him in other posts. A few days ago he forwarded a cosmology question to me from Paul, a former co-worker of his. It's one of the classics that cosmologists get pretty often. The question is "What happened before the big bang?" My Dad's friend began wondering about this after reading an article in the Daily Express in which Michio Kaku said that this is the most embarrassing question to ask physicists. People are fascinated by this stuff and the question is a good one. However, I don't think of this as an embarrassing question; rather just one to which, at present, we don't know the answer.

Physicists arrive at the idea of the big bang by first making observations of the universe today and understanding how these are described by well-established theories of gravity and particle physics. We then extrapolate back in time to infer what the early universe must have been like, and then test the theory by working out what new predictions result and checking whether they agree with observations. This methodology works remarkably well and has provided us with an extremely well tested, self-consistent and coherent understanding of the universe.

The central result that arises from this work is that the universe is expanding - all distant galaxies are moving away from us and the further away they are, the faster they are moving. Of course, this means that in the past all galaxies were closer together. When you get far enough back in time, what inevitably results is that one has a very high density of matter in a very small region. This means that one is no longer able to use gravity (describing the physics of space and time and understood by Einstein's General Relativity) and quantum mechanics (describing the physics of the very small) separately, but is forced to take into account their mutual effects. However, at present we do not have a theoretical framework that allows us to answer questions about gravity and particle physics working together in this way. There are some promising attempts to develop such a theory, such as string theory, but so far this has not allowed us to provide a definitive answer to the question.

If one just blindly continues to use General Relativity past this point of its breakdown (not something that should really make sense), one reaches a mathematically unacceptable result known as a singularity. At this point, time, space and matter do not exist. The emergence of time, space and matter after this is what we loosely refer to as the big bang. Since we don't have a theory to understand these extremely early times (much less than a nanosecond after the big bang) the right answer to Paul's question is that we don't know.

This in no way diminishes the remarkable progress in cosmology during the last century. It is just a natural part of science - there are things we're still working on. To be precise, the big bang theory only refers to the fact that the observable universe originated as a very small, highly energetic region about 13.7 billion years ago. The evidence for this is overwhelming and it is a firmly established pillar of modern science. Of course, one can speculate about the earliest times - maybe time has no meaning before this and the question is really meaningless, or perhaps the universe has to be understood in the context of a multi-universe theory, or maybe the expanding universe we see today arose after an earlier collapsing phase. These speculations are crucial to eventually extending our firm understanding to earlier and earlier times. However, for now, all I can say is that we're working on it and it is great fun.

A First Adventure in BlogLand

Well, I’ve been toying with the idea of entering the blogsphere for a while now and have finally decided to take the plunge. I think it was the election that finally pushed me off the fence – I found a lot of deep and useful analysis in the blogs that I read during the lead up to the big day, and I developed some extra respect for the medium through this experience.

I know some other bloggers personally. Some of my inspiration for getting started is that my good friend Sean Carroll is behind the thoughtful, fun and intellectually refreshing Preposterous Universe blog. I originally thought this was something of a waste of his time, especially given the amount of time it takes to post daily. However, I have changed my mind somewhat, and can see that this may be a way to reach out to a wider community about the work we do and also, perhaps, to find a way to link up with others to “make a difference”. I am an academic and, while I love this life and wouldn’t trade it for anything, outside of one's actual work one does find oneself having the same conversations with the same people, complaining about the same problems day after day (no offence to my good friends; I love our conversations, but it is true we don’t achieve much through them). I don’t know if I’ll feel better discussing such things among this wider group, but we’ll see.

I'm tempted to run on a bit longer to introduce myself more properly, but think it might be best to keep this first post short and simple. At this early stage I don’t know how this will turn out. Maybe I won’t have anything interesting to say, and almost certainly I’ll be unable to post daily. This first post is also somewhat terrifying. Does this feeling pass? It is fun to get started though.