The Athens of the South

My friend Jonathan and I walked from the Scarrit-Bennet Center to the park on the other side of the Vanderbilt campus. In that park is a recreation (full-scale) of the Athenian Parthenon. I “snapped a whole bunch of photos”: of the place, which was really phenomenal. It included a 2-3 story statue of Athena, with depictions of Greek mythology throughout.

Last day of meetings at Vanderbilt

This is the last day of physics content meetings at the Frontiers in Contemporary Physics III meeting at Vanderbilt University in Tennessee. Today we closed with an overview of the theory of the strong interaction, referred to as “Quantum Chromodynamics”, or QCD. What amazed me was that this theory, whose development earned a nobel prize last year for David J. Gross, H. David Politzer, and Frank Wilczek, is now capable of computing critical interaction cross-sections at high-order in the perturbation expansion. Such calculations are needed at the LHC and Tevatron for a clearer understanding of multi-jet production from proton-(anti)proton collisions.

The talks on QCD were intermixed with an overview of the latest results from RHIC on its studies of the quark-gluon plasma, a liquid-like state that QCD says should have existed at very early times in the universe. The current evidence, gathered by colliding heavy atomic nuclei (i.e. Gold), suggests that this plasma acts like the most perfect fluid ever realized by nature. I was very exciting to the the evidence appear in the data, and when compared to control samples it was clear the effect was real.

After the RHIC talks, a question from the audience was posed to the speaker that asked him to comment on the politics in U.S. federal funding of nuclear physics. This is a program within the Department of Energy that does basic research using Brookhaven National Lab (i.e. RHIC), Jefferson National Lab (Virginia), and other facilities. The budget is way down this year, for a variety of reasons. The speaker commented that if you project to 2010, the cuts would total 25%. This would require the closing of a lab or the vast cutting back of university programs. He also commented that a review process is beginning now within the DOE to determine what programs are a priority for the U.S. There’s that “P” word again.

Don’t get me wrong – I believe that if a program has run out of steam, you have to cut back and put money into the more important programs. But for a facility like RHIC, whose investigation of the quark-gluon plasma has opened a new universe of fundamental physics and posed us many great questions, it seems like suicide for U.S. physics to pursue cutting it away. We’ll have to wait and see, I guess, how this process proceeds.

Unrelated to the conference, I saw a commercial for E-trade today that hyped its product by using images and words like, “When you set out to be a musician, you don’t set out to be an average musician” (picture of Bob Dylan). Near the end, they showed Stephen Hawking (and spoke similar words), and in the foreground of the picture were the words “…particle accelerator…” written on glass with a wax pencil. It was a little refreshing to see physics right up there with music, sports, etc. in that ad.

Tomorrow we close out the conference with a morning-only set of overview talks, and then I’m going to take the afternoon to wander around Nashville.

Frontiers in Contemporary Physics

It’s the end of day two of the “Frontiers in Contemporary Physics” conference here at Vanderbilt University in Nashville, TN. The days are divided into two large subsections: plenary talks, from 8:30 in the morning until 3:30-4:30 in the afternoon, followed by 1-1.5 hours of parallel sessions on a variety of topics (QCD, Electroweak physics, neutrinos, cosmology, etc.). So far, we’ve had major overviews of the big questions facing astrophysics and cosmology (dark matter, dark energy, big bang nucleosynthesis) and neutrino physics (mixing angles, absolute neutrino masses, the fundamental nature of the neutrino field).

Let me browse through my notes and give the highlights!

* What is the nature of “dark energy”? Given that this force, which acts opposite gravity, accounts for 70% of the makeup of the universe, what is its nature? One question that can be answered by experiment in the coming decade is “At what magnitude does the energy density of the dark energy enter into the acceleration of the universe?”. Will dark energy one day overpower gravity at the level of stars and planets, thus tearing apart the large-scale structure of the universe in a “big rip”?

* What is the nature of “dark matter”? We know that it definitely interacts gravitationally, since we observe it using this force (galactic rotation curves, gravitational lensing of distant galaxies by galaxies between them and us, the anisotropy of the microwave background radation). To “get rid” of enough dark matter in the early universe and obtain the matter we see today (baryons and leptons), dark matter needs to interact with baryonic matter at levels greater than those provided by gravity. The scale of this interaction coincides with the Weak interaction, suggesting that the weak force connects dark matter to baryonic matter. Can we detect dark matter using this observation?

* What is the nature of inflation? Can inflation be explained by the action of a scalar field that, early on, influenced the expansion of the universe and thus allowed causally disconnected regions of the universe to be homogeneous? What is the energy scale associated with inflation (weak, Planck, GUT, string)? This will tell us when inflation ended. We should be able to observe the imprint of inflation on the cosmic microwave background, in the form of polarization oscillations imprinted by quadrupole gravitational interactions. This is a tough, precision measurement.

John Feng put a lot of this stuff in perspective when he likened our current knowledge of the universe to the knowledge Eratosthenes had of the Earth in 200BC. He conducted a very clever experiment, using the length of shadows in different locations on Earth at the same time of day to estimate the size of the Earth, assuming it was round. He was right to about 10% of the true value, though at the time he knew the most about the nature of the Earth when compared to his contemporaries. But knowing that the Earth is round is only a step to understanding the Earth, and it was a long time before we learned its features and dynamics. One can see this period as one similar to that of Eratosthenes.

More details:

* Big bang nucleosynthesis (BBN) uses information about baryon abundances after the big bang, and the cooling and expansion rate of the universe, to predict relative abundances of light atoms in the early universe. BBN occurred within the first 20 minutes of the beginning of the universe, and left its indelible imprint on today’s universe (hydrogen, deuterium, helium, lithium, and other atomic abundances in the universe). What is astounding is that abunances determined using observations of ancient cosmic objects (i.e. quasi-stellar objects, or QSOs) and information about such abundances as determined from the cosmic microwave background (CMB) agree astoundingly well. Considering that the physics of BBN occurs within 20 minutes of the big bang, while the CMB was created 400,000 years after the big bang, the agreement in evidence from both is remarkable. Despite this, the fact remains that lithium and deuterium abundances calculated using standard BBN mathematics are overpredicted compared to the numbers from data observations. What is the cause of this discrepancy?

* There are many big questions in neutrino physics. Here are a few, as highlighted by Boris Kayser. How many neutrinos are there? What are the masses of the individual mass eigenstates of the neutrino? Are neutrinos their own antiparticles (Majorana), or are the anti-neutrinos a separate class of particles with their own properties (Dirac)? Do neutrino interactions violate CP symmetry, as the corresponding quark sector does? Is the mixing between the second and third neutrino mass eigenstate truly maximal?

It’s been very exciting, and I’ll give more reports as the days go by. What I find remarkable is the level of agreement that so many observations yield. For instance, supernova redshifts and CMB structure both require that the universe be accelerating in its growth, yet these are totally unrelated phenomena. The gravitational lensing of distant galaxies, the rotation speeds of stars on the outer extents of galaxies, and CMB structure all demand a large dark matter component to the universe, yet these are all remarkably different phenomena. The universe is putting up more signs, and we need to find the pattern. The theories we have now are remarkably incomplete in the wake of this, and it’s clear that our explorations of the universe will only begin to shed light on the principles of nature yet hidden from our sight.

Summer at the Frist

I am in Nashville, TN for the third in the conference series “Frontiers in Contemporary Physics”: This conference is held at Vanderbilt University, a lovely Methodist university nestled just beside the heart of Nashville. I arrived late last night and spent today finishing my talks, then taking a walk around the Vanderbilt campus.

If you check out the maps below, you can see the walk I took. I started by finding the Scarritt-Bennett Center, the conference venue. This cluster of stone buildings, including a lovely chapel, reminded me of Yale University. One step off the street, and your inside a quaint green lawn surrounded by the center’s buildings. Archways connect different courtyards, with benches scattered all along the pathways.

The yellow line indicates my path before lunch, while the green indicates my path after lunch. One of the things that I noticed was the Frist Center (I can only assume it’s named after a member of the family Frist, to which Senator Bill Frist belongs). There were posters all over the place advertising art exhibits at the Frist Center, all with the header “Summer at the Frist”. I got a kick out of it all.

Tomorrow the conference begins, with my first of two talks in the late afternoon at 4:20 pm. Whew! It’s good to be here!