Cosmology: 5 Needed Breakthroughs -- Alexander Vilenkin

Alexander Vilenkin [photo courtesy: Institute of Cosmology, Tufts University]

[In our ongoing feature '5-Breakthroughs' we invited today Prof. Alexander Vilenkin, Director of Institute of Cosmology and L. and J. Bernstein Professor of Evolutionary Science at Tufts University.

Prof. Vilenkin's current research interests cover a wide range of subtopics in cosmology, quantum field theory and gravitation: cosmic inflation, dark energy, cosmic strings and monopoles, quantum cosmology, high energy cosmic rays, the multiverse, anthropic selection etc.

He received his undergraduate degree in physics in 1971 at Kharkov State University in the former Soviet Union. In 1976 he emigrated to USA and received his PhD at SUNY Buffalo in 1977. In 1978 he joined the faculty at Tufts.

During what has been a very productive and creative span of last thirty-five years, Prof. Vilenkin wrote over 200 research papers and contributed some crucial components of modern cosmology. His work on cosmic strings has been pivotal and his ideas on 'eternal inflation' and 'quantum creation of the universe from nothing' paved the path for new fields of investigation. Occasionally, he also took time to work on condensed matter physics and even topics like statistical analysis of DNA sequences. His work has been featured in numerous newspaper and magazine articles all over the world, as well as in many popular books. Here is a link to a list of his published work: Google Scholar.

Prof. Vilenkin is a Fellow of the American Physical Society. During 1984-89, he received Presidential Young Investigator award from National Science Foundation.

In 1994 he (with P. Shellard) wrote a monograph on "Cosmic Strings and Other Topological Defects" (Cambridge University Press, 1994). In 2006 he authored the well-acclaimed book "Many Worlds in One: The Search for Other Universes" (Hill & Wang, 2006) which has been translated into many languages.

It gives us lot of pleasure for having the opportunity of presenting to you this list of 5 breakthroughs that Prof. Vilenkin would like to see in the field of Cosmology.
-- 2Physics.com]

1. Cosmic superstrings. Some superstring inspired cosmological models predict the existence of fundamental strings of astronomical dimensions. Discovery of cosmic superstrings may be the only way to test superstring theory by direct observation. In fact, discovery of cosmic strings of any kind ("super" or not) would be a great breakthrough, since it will open new windows into particle physics of ultra-high energies and into the early universe cosmology.

2. Further evidence for inflation. We have substantial evidence for cosmic inflation, but the details are very uncertain and a large number of models are consistent with the data. Discovery of gravitational waves from inflation or of non-Gaussian features in the cosmic microwave background would be important breakthroughs in this area.

3. Evidence for the multiverse. Inflationary cosmology leads to the multiverse picture, with multiple "bubble universes" expanding and occasionally colliding with one another. Collisions of our bubble with others may have observational signatures in cosmic microwave background and in gravitational waves. A discovery of such a collision would provide a direct evidence for the existence of the multiverse.

4. Solution to the measure problem. This is a perplexing problem in inflationary cosmology. Inflation is generically eternal, and bubble universes like ours are constantly being produced. Anything that can happen will happen in the eternally inflating universe, and it will happen an infinite number of times. We have to learn how to compare these infinities, since otherwise we cannot distinguish probable events from highly improbable, which makes it hard to make any predictions at all.

5. Discovery of supersymmetry. Non-discovery at Large Hadron Collider (LHC) would also have important implications.

You may be wondering why "dark energy" is not on my list. This is because I believe it is cosmological constant. But if I am wrong, and the dark energy density is changing with time, the discovery of this fact would be a great breakthrough.

Upcoming Physics Conferences

[To add an upcoming physics conference to this list, please send an email to 2Physics@gmail.com ]

Apr 12-19: International Conference: String Field Theory and Related Aspects (Moscow, Russia)
Apr 20-23: The Sun, The Stars, The Universe and General Relativity -- Intl conference in honor of Ya. B. Zeldovich 95th Anniversary (Minsk, Belarus)
Apr 27-May 01: Relativity in Astrometry (Virginia Beach, VA, USA)
May 03-17: PhD School on Quantum Information and Many-Body Systems (Cortona, Italy)
May 11-13: Workshop on Theory of Quantum Computation, Communication, and Cryptography (Waterloo, Canada)
May 11-13: Phenomenology 2009 Symposium: LHC Turn On (Madison, WI, USA)
May 11-15: Gravity: Where do we stand? (Como, Italy)
May 19-21: Relativistic Astrophysics (Atlanta, USA)
May 25-29: From the Planck Scale to the Electroweak Scale (Padova, Italy)
May 31-Jun 05: Cosmological Magnetic Fields (Ascona, Switzerland)
Jun 04-05: Standard Model of Universe (Paris, France)
Jun 17-19: Itzykson Meeting on String Theory: Recent Advances in String Theory (Saclay, France)
Jun 18-19 Mathematical Relativity (Lisbon, Portugal)
Jun 21-26: 8th Edoardo Amaldi Conference on Gravitational Waves (NY, USA)
Jun 29-Jul 01: Unity of the Universe (Portsmouth, UK)
Jun 29-Jul 03: Invisible Universe (Paris, France)
Jul 12-18: Marcel Grossmann MG12 (Paris, France)
Jul 14-18: Ultrafast and Nonlinear Optics (Burgas, Bulgaria)
Jul 20-21: International Workshop on Nonlinear Dynamics and Synchronization (Klagenfurt, Austria)
Jul 20-25: 6th International Symposium on Quantum Theory and Symmetries(QTS6) (Lexington, KY, USA)
Jul 26-31: CosmoSTATS 09 (Ascona, Switzerland)
Jul 26-31: Geometry, Field Theory and Solitons (Leeds, UK)
Jul 27-31: New Trends in Quantum Integrable Systems (Kyoto, Japan)
Aug 17-23: Astrophysics and Cosmology after Gamow: Recent progress and new horizons: 4-th Gamow International Conference and 9-th Gamow Summer School "Astronomy and beyond: Astrophysics, Cosmology, Radioastronomy, High Energy Physics and Astrobiology" (Odessa, Ukraine)
Aug 18-28: International Summer School on Astroparticle Physics (Nijmegen, Netherlands)
Aug 21-27: Bogolyubov Conference "Problems of Theoretical and Mathematical Physics" (Moscow-Dubna, Russia)
Aug 30-Sep 03: Joint International Hadron Structure Conference (Tatranska Strba, Slovak Republic)
Sep 02-05: Challenges in Cosmology (Talloires, France)
Sep 07-11: Cosmo-09 (CERN, Geneva)
Sep 14-19: International Workshop on Weak Interactions and Neutrinos (L'Aquila, Italy)
Sep 15-18: Bogolyubov Kyiv Conference "Modern Problems of Theoretical and Mathematical Physics" (Kyiv, Ukraine)
Sep 24-28: International Conference on Electron Dynamics in Semiconductors, Optoelectronics and Nanostructures (Montpellier, France)
Sep 28-Oct 02: Physical Properties of Nanosystems (Yalta, Ukraine)
Oct 08-09: Space, Time and Beyond (Golm, Germany)
Oct 11-14: 50 years of the Aharonov-Bohm Effect: Concepts and Applications (Tel Aviv, Israel)
Oct 26-30: Galileo - Xu Guangqi Meeting on the Sun, the Stars, the Universe and General Relativity (Shanghai, China)
Nov 29-Dec 04: Intl Conference on Hadron Spectroscopy (Tallahassee, FL, USA)
Nov 30-Dec 03: International Symposium on Computational Mechanics (Hong Kong and Macau, China)

Bose Gas in 2D Flatland and Mysteries of Superfluidity

Kristian Helmerson [photo courtesy: Joint Quantum Institute, University of Maryland]

In a paper accepted for publication in Physical Review Letters, a team of physicists led by Kristian Helmerson of Joint Quantum Institute [JQI, a partnership of National Institute of Standards and Technology (NIST) and the University of Maryland] presents some exciting aspects of physics happening in a 2D Flatland.

If physicists lived in Flatland—the fictional two-dimensional world invented by Edwin Abbott in his 1884 novel —some of their quantum physics experiments would turn out differently (not just thinner) than those in our world. The distinction has taken another step from speculative fiction to real-world puzzle with this paper reporting on a Flatland arrangement of ultracold gas atoms [1]. The new results, which don’t quite jibe with earlier Flatland experiments in Paris [2,3], might help clarify a strange property: “superfluidity.”

In three dimensions, cooling a gas of certain atoms to sufficiently low temperatures turns them into a Bose-Einstein condensate (BEC). As predicted in the 1920s (and first demonstrated in 1995) the once individualistic gas atoms begin to move as a single, coordinated entity. But back in 1970, theorists predicted that something different would happen in two dimensions: an ultracold gas of interacting atoms would undergo the analogous “Berezinskii, Kosterlitz and Thouless” (BKT) transition, in which atoms don’t quite move in lockstep as they do in a BEC, but mysteriously share some of a BEC’s properties, such as superfluidity, or frictionless flow.

In these new experiments, the team at JQI has achieved the latest experimental observation of the BKT transition. The JQI researchers trap and cool a micron-thick layer of sodium atoms, confined to move in only two dimensions. At higher temperatures, the atoms have normal “thermal” behavior in which they act as individual entities, but then as the temperature lowers, the gas transforms into a “quasi-condensate,” consisting of little islands each behaving like a tiny BEC.

[Image credit: Kristian Helmerson, JQI] A gas of atoms arranged in a single, flat layer ordinarily has ‘thermal’ behavior (left) in which the atoms act as individual entities. At lowered temperatures, the gas transforms into a ‘quasi-condensate‘ (middle) consisting of little islands (schematically represented as colored blobs) that fluctuate in time; within each island atoms act as a single coordinated entity. At lower temperatures still, the gas enters the superfluid ‘BKT’ phase (right): the islands start to coalesce and atoms can flow frictionlessly within the merged area.

By further lowering the temperature, the gas makes the transition to a BKT superfluid where the islands begin to merge into a sort of “United States” of superfluidity. In this situation, an atom can flow unimpeded between neighboring “states” since the borders of the former islands are not well defined, but one can tell that the atom is “not in Kansas anymore,” in contrast to a BEC where one cannot pinpoint the location of a particular atom anywhere in the gas.

When a group from Ecole Normale Supérieure (Paris) lowered the temperature of their 2-D gas in earlier experiments [2,3], they only saw a sharp transition from thermal behavior to a BKT superfluid, rather than the additional step of the non-superfluid quasi-condensate. But the Paris group used rubidium atoms, which are heavier and more strongly interacting, possibly exhibiting a qualitatively different behavior. These new results may cast light on superfluidity, which decades after its discovery still seems to hold new mysteries.

References
[1] "Observation of a 2D Bose-gas: From thermal to quasi-condensate to superfluid",
P. Cladé, C. Ryu, A. Ramanathan, K. Helmerson and W.D. Phillips, Physical Review Letters, accepted for publication [link will be added after it's published]. arXiv:0805.3519.
[2] "Berezinskii–Kosterlitz–Thouless crossover in a trapped atomic gas", Zoran Hadzibabic, Peter Krüger, Marc Cheneau, Baptiste Battelier and Jean Dalibard, Nature 441, 1118 (2006). Abstract.
[3] "Critical Point of an Interacting Two-Dimensional Atomic Bose Gas",
Peter Krüger, Zoran Hadzibabic, and Jean Dalibard, Phys. Rev. Lett. 99, 040402 (2007). Abstract.

[We thank National Institute of Standards and Technology for materials used in this posting]