Cosmological Scalar Fields Link Astronomy and Fundamental Physics at Upcoming Conference
At the 'Phi in the Sky' conference in Porto, Portugal, physicists and astronomers from around the world will gather to discuss the role scalar fields play in cosmology. From the 8th to the 10th of July, 10 review talks and 20 communications will be presented on a wide range of topics, from the influence of scalar fields on the Big Bang and subsequent inflation, to how they shape the cosmos we see today, to how they might take part in the universe's end. The conference is sponsored by CFP (University of Porto) and the Portuguese research council (FCT) and is designed to bring together scientists from both sides of the theory/observation divide, as well as to bridge an even wider ideological gap -- that between the communities of particle physics and astronomy.
Scalar fields have long been part of the standard model of particle physics. The most famous example is the Higgs particle, known colloquially as the God particle, which is thought to be responsible for endowing the building blocks of matter with mass. Recently, observational and theoretical developments have begun to suggest that scalar fields are just as important in cosmology as they are in particle physics. Scalar fields are favored candidates to solve two of the most fundamental mysteries in cosmology today -- the exponential expansion of the early universe in cosmological inflation, and the dark energy that is responsible for another period of accelerated expansion today. If scalar fields do indeed play a role in one or both of these processes, they might also hold secrets to the formation of structure in the universe, how the universe might end, and the possible variation of what have been considered fundamental constants of nature.
The conference brings together experts on a wide range of cosmological problems, making clear the way in which scalar fields can link together seemingly disparate topics. One such unlikely pairing occurs in models of scalar field dark energy. In these models, the scalar field may lead to variations of the fundamental constants, whereas experiments searching for a new force of nature (fifth force experiments) are needed to set observational constraints. String theory offers us a geometrical framework for scalar fields involved in the inflation of the early universe. This scenario envisions our universe as a fourth-dimensional slice (or brane) in a higher- dimensional space. For such a universe, the potential driving inflation is the force of attraction of two branes, and the value of the scalar field (the inflaton) is the distance between them. The existence of scalar fields may also have consequences for extreme objects in the universe, such as black holes and topological defects. In any of these applications, the confirmation of scalar fields would be an unmistakable signal of new physics, making this one of the most exciting areas of research in cosmology today.
Invited Speakers and Topics:
*Eric Adelberger (Univ. of Washington): Tests of Newton's Inverse-Square Law: Probing the Geometry of the Universe
*Raul Jimenez (U. Penn.): Observational Constraints on Scalar Fields
*Jean-Philippe Uzan (Paris): Variation of the Constants in the Early and Late Universe
*Pedro Ferreira (Oxford): The Concordance Model and Dark Energy
*Roy Maartens (Portsmouth): Brane World Cosmology
*Gilles Esposito-Farese (Paris): Tests of Scalar-Tensor Gravity
*Anthony Lasenby (Cambridge): Closed Universe Boundary Conditions for Inflation and Predictions for the CMB
*David Wands (Portsmouth): Inflation and the Origin of Large-Scale Structure
*Paul Shellard (Cambridge): Cosmic String Evolution and Cosmological Consequences
*Fernando Quevedo (Cambridge): Inflation from String Theory
In addition to the invited speakers there will be a number of young scientists giving short talks on recent results.
For more information, please contact:
Carlos Martins (Organizing Committee)
phone: +44 1223 766 833
e-mail: C.J.A.P.Martins@damtp.cam.ac.uk
Katherine Mack (Scientific Secretary)
phone: +44 1223 337 532
e-mail: kmack@ugcs.caltech.edu
Alexandra Ferreira (Administrative Secretary)
phone: +351 226 082 623
e-mail: phisky@fc.up.pt
fax: +351 22 6082 622
Further information:
Historically, particle physicists and astrophysicists have seldom worked together. In fact, it has been rumored that they don't even always get along. However, in recent years, scalar fields are becoming so fundamental to both theoretical particle physics and astrophysics that they are exhibiting a unique ability to bring these disciplines together.
Considering the situation, it was inevitable that the two would have to put aside their long-standing differences and start talking, if only out of scientific necessity. Although widely accepted theories on both sides rely on the existence of scalar fields, neither has been able to produce definitive observational or experimental evidence. If that's not enough to bring the groups together, one need only consider the overlapping theoretical consequences of scalar fields in either discipline. Both physicists and astronomers are finding themselves more and more frequently stepping over the divide simply to understand the implications of their own results. A particle physicist doing string theory, a fundamental theory of the nature of matter and energy, might suddenly be studying the cosmic microwave background to search for evidence of a higher-dimensional space. An observational astrophysicist looking at distant supernovae finds evidence for an accelerating universe, only to discover that the leading explanation requires some brushing up on basic particle theory. These links are becoming more and more common as scalar fields offer possible explanations to an array of fundamental and cosmological problems. The result is an unprecedented level of cooperation between the two fields, leading to the kinds of innovations that can only be made by venturing into the interface. In the quest for cosmological scalar fields, physicists and astronomers are working together to use the universe itself as a laboratory for fundamental physics.
The "Phi in the Sky" conference relies on these new links to produce an opportunity for scientists on all parts of the physics-astronomy spectrum to bring their ideas to the table. The invited speakers include top-level experts in astrophysics, cosmology, and theoretical physics, all sharing an interest in boundary-blurring science.
The conference kicks off with a talk by Professor Eric Adelberger, a physics professor at the University of Washington. His research group is developing new ways to test Newton's theory of gravity in the laboratory. Although the work is certainly rooted in experimental physics, the motivation lies in cosmology. Some current theories of the geometry of the universe suggest that we may be living on a four-dimensional slice (3 space + 1 time) of a higher-dimensional universe, and while most of the forces are confined to our slice, gravity may leak off. If this is true, it will alter the inverse-square law put forward by Newton centuries ago.
Cosmological models such as these are known as brane world models (a brane is a lower-dimensional slice -- from "membrane"). The original motivation for altering gravity with extra dimensions is to unify it with the other forces. It turns out that at a certain very high energy level, electromagnetism and the nuclear forces have about the same strength. At everyday energy levels, nuclear forces are much stronger, which is why it's easier to pass a current through a wire than to rip an atom apart. The only force that cannot be unified with the others is gravity, despite the fact most physicists assume that deep down, all the forces should in essence be different manifestations of the same basic thing. This is how extra dimensions come into play. If extra dimensions exist, they give physicists hope that gravity does in fact link up with the other forces, and the only reason we haven't been able to see it is that we're only thinking fourth-dimensionally. Brane world theories will be explored in more detail later on in the conference when Professor Roy Maartens of Portsmouth University gives his review talk on the subject.
Extra dimensional theories are not the only possibilities for the altered gravity Professor Adelberger and his colleagues are looking for. String theory predictions of new scalar particles also hint at changes in the strength of gravity on certain scales. Professor Adelberger will review his own and other gravity experiments, as well as discuss how the results of these tests may have the added bonus of reconciling quantum mechanical predictions with the expansion of the universe.
Professor Gilles Esposito-Farese of the Institut d'Astrophysique in Paris approaches the problem of alterations in gravity from a different, more theoretical angle. His research focuses on scalar-tensor theories of gravity, which are alternatives to Einstein's general relativity. In Einstein's theory, gravitational fields occur through the exchange of particles called gravitons. Scalar-tensor theories hypothesize that gravity is mediated not only by the graviton, but also by a scalar field. These types of theories are appealing because they are mathematically consistent and they respect most of the symmetries that appear in Einstein's original treatment. As well as giving an overview of the theoretical framework, Professor Esposito-Farese will discuss the constraints on scalar-tensor gravity placed by an array of observational tests, ranging from studies of the motion of bodies in our own solar system to cosmological observations. These tests are a complement to the experiments being carried out by Eric Adelberger and other experimental physicists as they work toward a better understanding of gravity's role in the universe.
Einstein's relativity is not the only time-honored wisdom coming under scrutiny. New theories involving scalar fields argue for the variation of not only the behavior of gravity in the universe but also of fundamental constants related to other physical processes. Recent results hinting at a variation in the fine-structure constant, which is a key value in electromagnetism, have motivated scientists to look more carefully at the link between the constants in a theory and the theory itself. Professor Jean-Philippe Uzan, who speaks to the "Phi in the Sky" conference on this topic, points out that the scientific method is highly dependent on our understanding of the constants.
"Comparing and reproducing experiments is [...] a root of the scientific approach which makes sense only if the laws of nature [do] not depend on time and space." Describing fundamental constants as parameters that "can not be calculated with our present knowledge of physics," Professor Uzan states that "Each free parameter of a theory is in fact a challenge for future theories to explain its value."
In his talk, Professor Uzan will discuss current observational constraints on the variation of constants, linking the results to clues about the recent acceleration of the universe's expansion. Until only a couple of decades ago, it was believed that the expansion of the universe set off by the Big Bang must be slowing down, since the gravitational attraction of massive objects will work as a contracting force. In fact, this was so natural an idea that even before it could be definitively measured, astrophysicists employed the "deceleration parameter" as a measure of how quickly the expansion was slowing down. It was quite a shock to the astrophysics community when careful observations of distant supernovae found that the expansion was actually speeding up, despite the presence of all those gravitating bodies that should be pulling it back together. Evidently, some mysterious force that could not be directly observed (dubbed "dark energy") must be working as a kind of "anti-gravity," actively pushing the universe apart.
Interestingly, Albert Einstein originally included such a term in his equations of general relativity. Calling it the cosmological constant, he conceived it as a way to counteract gravity for the purpose of keeping the universe in a steady state. When the universe was discovered to be expanding, he retracted the term, famously calling it, "the biggest blunder of my life." It is true that the steady-state universe idea has long been abandoned for a universe that is dynamic and expanding. However, due to the similarity between the accelerated expansion and the concept of a cosmological constant, the discovery of dark energy has been considered to be a vindication of Einstein's original instinct.
These days, most experts attribute dark energy to a scalar field -- the same scalar field that allows a possible variation of constants. This correspondence gives researchers an essential link between the behavior of dark energy and that of the fundamental constants. If both are varying with time, it is possible to constrain the behavior of one by observing the behavior of the other, in the context of a specific model. This method can also be inverted -- given data on both, one can reconstruct the form of the theory that must be used to describe them.
Uncovering the nature of the scalar field that makes up dark energy may not be as daunting a task as most experts originally feared. Professor Raul Jimenez of the University of Pennsylvania will give a talk on the current observational constraints and how they can be improved in the near future -- within the next year or two. If Professor Jimenez is correct, we are tantalizingly close to understanding one of the greatest mysteries in cosmology today. About his presentation, Professor Jimenez says: "I will argue that we might be able to have a good constraint on [dark energy] much sooner than we thought."
Over the course of the conference, scientists from around the world will present theoretical and observational approaches to a wide range of cosmological problems involving scalar fields. One of the most accepted applications of scalar fields is in cosmological inflation -- the exponential expansion of the universe just after the Big Bang. Anthony Lasenby from Cambridge University will explore the role of inflation in so-called closed universe models. In a such a model, gravity eventually overcomes dark energy and reverses the expansion, causing the universe to finally collapse in a Big Crunch. Professor Lasenby will discuss his new approach to inflationary models in this scenario and relate it to cosmic microwave background observations. Scalar field models of cosmological inflation will also be the topic of David Wands' presentation. He will discuss inflation's impact on the layout of galaxies and clusters in the universe.
Scalar fields might also influence the structure of the cosmos through topological defects, one example of which is a cosmic string. Strings form when a scalar field assumes a particular stable configuration, resulting in an object of extremely high energy and infinitesimal thickness that might stretch across the observable universe. In his review talk, Paul Shellard will discuss the possible consequences of topological defects and how they can be constrained by cosmic microwave background observations.
The "Phi in the Sky" conference also includes many short talks by young scientists presenting their current research. Theoretical, observational, and phenomenological results will be given to enrich the big picture ideas from the review talks with a glimpse of the diversity of projects being undertaken in the field today. These presentations run the gamut from current observational constraints to theories that link scalar fields to the mass density of the universe. Among the less conventional talks are discussions of gravastars (an alternative to black holes) and cosmic phantom fields. The latter refers to an extension of dark energy in which the acceleration of the universe's expansion continues to increase without limit. If this scenario holds true, the expansion will eventually tear the universe apart in a catastrophic Big Rip.
Like most conferences, "Phi in the Sky" is not just an opportunity for researchers to present their work, but is also a chance for members of the international cosmology community to come together for collaboration and the free sharing of ideas. This is perhaps the greatest value of a scientific meeting, allowing dialog to spark innovation in the same way it has since the days of the ancient philosopher-scientists. To promote this kind of interaction, the "Phi in the Sky" conference includes a social program with a reception and banquet, as well as time set aside for informal discussion.
The proliferation of scalar field theories in astronomy and fundamental physics has already promoted an unprecedented level of interaction among scientists in seemingly disparate areas of study. Now scalar fields are changing our picture of the universe, from the first moment of creation to the way it will all come to an end. By continuing the age-old tradition of discussion, innovation, and original research, we inch ever closer to a deeper understanding of the nature of the cosmos.