Quest for the Perfect Liquid: Connecting Heavy Ions, String Theory, and Cold Atoms
Date: Sunday, February 15, 2009, 10:30 a.m. – Noon
Physicists built the Relativistic Heavy Ion Collider (RHIC), a particle accelerator at the U.S. Department of Energy’s Brookhaven National Laboratory, to recreate a form of matter that last existed mere microseconds after the Big Bang. Their aim was to create and probe this predicted gaseous plasma of free quarks and gluons — the most basic constituents of matter — to better understand the forces that hold the universe and everything in it together.
What they found instead was surprising, and much more interesting — attracting the attention of scientists and others outside their field. Instead of behaving like a gas of free quarks and gluons, the matter created at RHIC appears to be more like a liquid. In fact, it’s the most "perfect" liquid ever observed, with virtually no viscosity, or resistance to flow.
As it turns out, calculations of the perfect liquid’s viscosity can be derived using methods of string theory, linking RHIC with that theory’s search for extra dimensions of space and time and theoretical black holes. RHIC experiments may even provide ways to test predictions of string theory, which to date has not been possible.
In addition, RHIC’s findings of what happens with hot, dense matter help in understanding ultra-cold matter and possibly even high-temperature superconductors and neutron stars.
This symposium brings together experts from RHIC, string theory/cosmology, and atomic physics, as well as a science journalist to explore these connections and lead a discussion of the relevance of this research.
Moderator: Peter Steinberg, Physics Department, Brookhaven National Laboratory, collaborator on research at the Relativistic Heavy Ion Collider. Introductory slides (PDF)
Surprises at RHIC: The 'Perfect' Liquid and Beyond
Barbara Jacak, Department of Physics and Astronomy, Stony Brook University and spokesperson for the PHENIX collaboration at the Relativistic Heavy Ion Collider
Experiments at RHIC produce a remarkable new form of matter. With a temperature greater than 300 million electron volts (MeV) (3.5 x 10^12 Kelvin) this is the hottest matter ever produced in a laboratory. Astonishingly, it flows like a perfect liquid rather than like a gas, and the viscosity is miniscule. It is extremely opaque, even stopping heavy quarks that traverse it. Experiments show tantalizing hints that energy deposited by the stopped particles may shock the matter. It shines brightly, emitting photons both real and virtual. Experimenters and theorists are working together to establish the properties of this novel plasma of quarks and gluons. The challenge of understanding the dynamics of this system is catalyzing conceptual advances outside the traditional theories of quarks and gluons, notably the connections with string theory, and other strongly-coupled systems.
Presentation slides (PDF)
‘Perfect’ Fluidity in Cold Atomic Gases
John E. Thomas, Physics Department, Duke University
RHIC physicists have created a trillion-degree quark-gluon plasma, which expands as a nearly “perfect” fluid. Remarkably, an ultracold gas of Fermi atoms at one tenth of a microkelvin behaves similarly, and is the most strongly interacting nonrelativistic system known, testing theories of hightemperature superconductors and nuclear matter. The extremely low viscosity of the gas is of great interest to RHIC physicists and string theorists, who have conjectured that the ratio of the shear viscosity to the entropy density has a universal lower bound, defining a perfect fluid. I will describe how we produce a strongly interacting lithium-6 gas using a bias magnetic field and an optical trap. We observe a high temperature superfluid transition in measurements of the entropy, while our studies of the hydrodynamic expansion of rotating clouds determine the shear viscosity. Together, these results suggest that a strongly interacting Fermi gas may be the most perfect quantum fluid ever studied.
Presentation slides (PDF)
New Dimensions of Quarks and Gluons: Strings Return to Their Roots
Clifford Johnson, Department of Physics and Astronomy, University of Southern California
There are strong signs that for many key physics questions, the most natural tools for describing the new form of matter discovered at RHIC are to be found in string theory, including concepts such as extra spatial dimensions, extended objects called branes, and quantum black holes – ideas that were not thought to be relevant! This connection between theory and experiment seems to confirm suggestions that even though the string models are somewhat simplified they may be useful. Much more research is needed to see how far this can be taken, but it is already exciting: On the one hand, a new form of matter has been created in the laboratory and the techniques of string theory may be useful for understanding it; On the other, exotic physics such as quantum black holes and higher dimensions, even if only as mathematical tools, may have found an application. This endeavor may also give us important insights into applications of string theory to the rest of the universe.
Presentation slides (PDF)
Discussants: Glennda Chui, Deputy Editor, Symmetry Magazine and William A. Zajc, Physics Department, Columbia University