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.

5 Most Important Breakthroughs That My Field of Research Needs -- Nathan Seiberg

Nathan Seiberg [photo courtesy: Institute for Advanced Study, Princeton]

[Our guest today in the feature ‘5-Breakthroughs’ is Nathan Seiberg, Professor at the Institute for Advanced Study in Princeton, NJ. Prof. Seiberg’s work has spanned a wide spectrum of research revolving around particle physics phenomenology, field theory, gauge theory, Matrix theory, string theory, and supersymmetry.

In early 1990s, he formulated the application of holomorphy to calculations in gauge theories with supersymmetry. In his famous 1994 article “Electric-Magnetic Duality in Supersymmetric Non-Abelian Gauge Theories” (Abstract link) he conjectured a new kind of Strong-Weak duality or S-duality relating two different supersymmetric QCDs which are not identical, but agree at low energies. This is now well-known as Seiberg duality.

Working with Edward Witten, he also devised a series of partial differential equations that simplified the classification of 4-dimensional manifolds. The invariants of such compact smooth 4-manifolds are now known as Seiberg–Witten invariants. Later, they analyzed the appearance of non-commutative geometry in theories containing open strings, and identified a low energy limit of open string dynamics as a noncommutative quantum field theory.

Prof. Seiberg also made pioneering contribution in Matrix Theory, M Theory and various subfields of particle physics. Here is link to his list of publications: Google Scholar.

He received his Ph.D from the Weizmann Institute of Science in Israel in 1982. Before joining the Institute for Advanced Study, he had been a Professor of Physics at the Weizmann Institute for Science and at Rutgers University.

Prof. Seiberg is a member of National Academy of Sciences and Fellow of American Academy of Arts and Sciences. He received The John D. and Catherine T. MacArthur Fellowship (Genius Grant) in 1996. In 1998, American Physical Society awarded Dannie Heineman Prize for Mathematical Physics to Nathan Seiberg and Ed Witten "for their decisive advances in elucidating the dynamics of strongly coupled supersymmetric field and string theories. The deep physical and mathematical consequences of the electric-magnetic duality they exploited have broadened the scope of Mathematical Physics (quote from the citation)."

It’s an honor and privilege on our part to present 5 most important breakthroughs that Prof. Seiberg would like to see in his fields of research.
— 2Physics.com ]

1. Origin of electroweak symmetry breaking. This will shed light on the origin of mass of elementary particles. An effective description of this phenomenon in terms of the Higgs mechanism is known. The Large Hadron Collider (LHC) will explore it in detail and perhaps will point to a deeper structure. One possibility is that the LHC will discover supersymmetry – a new kind of symmetry which extends our understanding of space and time. Alternatively, it will find new particles which might have a description in terms of new space dimensions. If only the Higgs particle is discovered, its mass might be set anthropically. Is this true?

2. Origin of the elementary particles. What determines the properties of the quarks and the leptons (their quantum numbers)? Why do they appear in 3 generations? Most of the parameters of the Standard Model of particle physics are associated with the quark and lepton masses. It is possible that the underlying structure which controls them exists at very high energies which will not be explored soon. One possible explanation of the properties of the quarks, the leptons, and their interactions is the idea of grand unification. Is this idea correct?

3. Dark matter and dark energy of the Universe. Is the dark matter weakly interacting massive particles? This question could be settled soon either by detecting these particles, or the product of their interactions, or by creating them at the LHC. Is the dark energy a cosmological constant? What sets the value of the cosmological constant today? Is it anthropic?

4. Inflation. It seems that in the past the Universe had a period of rapid expansion known as inflation, during which the cosmological constant was large. What is the detailed description of this phenomenon? The study of inflation naturally leads to the idea of a multiverse – the Universe is a lot larger than what we observe and different parts of the Universe have different physics. How should we think about physics in such a setup? What are the correct observables? What is the precise role of anthropic ideas in this context?

5. Theory of quantum gravity. The correct theory of quantum gravity appears to be string theory. At the moment we do not have a clear conceptual formulation of the theory, nor do we have clear experimentally verifiable predictions of string theory. Can we solve these problems? Presumably, a deeper understanding of string theory will show that space and time are emergent concepts which are not present in the fundamental formulation of the theory. This could have important implications for the mysteries of the Big Bang.

Cosmology: 5 Needed Breakthroughs -- Robert Brandenberger

[Today's guest in our ongoing feature '5 Breakthroughs' is Robert Brandenberger, Canada Research Chair and Professor of Physics of McGill University, where he taught and conducted research since 2004. Before that he was a professor at Brown University for about 18 years.

In his long career spanning about a quarter of a century (He received his PhD from Harvard University in 1983; Thesis "Topics in Quantum Field Theory and Cosmology'), Prof. Brandenberger made crucial contributions in various important subfields of cosmology (link to a list of publications).

His current research interests cover a wide spectrum of topics in cosmology and related fields and include
(A) Conceptual problems in inflationary universe cosmology, in particular, trans-Planckian problem for cosmology,
(B) Theory of cosmological perturbations, in particular, back reaction problems, evolution of perturbations in nonsingular cosmologies, and parametric amplification of fluctuations during reheating,
(C) Superstring cosmology, in particular, string gas cosmology and structure formation, mechanisms for obtaining inflation from string theory, resolution of cosmological singularities in string theory, dualities and brane gases in the early universe,
(D) Topological defects in cosmology, in particular, topological defects and Baryogenesis, topological defects and direct signatures, stabilization of embedded defects by plasma effects,
(E) Nonequilibrium processes, in particular, parametric resonance during reheating in inflationary cosmology, nonequilibrium production of topological defects,
(F) Particle-Astrophysics, in particular, constraining physics beyond the Standard Model using cosmology, new mechanisms for CP violation and Baryogenesis,
(G) Large-scale structure, in particular, use of topological statistics to analyze large-scale redshift surveys, studies of weak gravitational lensing maps using new statistics.
(H) Formation of structure in the early universe, in particular, coupling of adiabatic and entropy fluctuations in multi-field, and cosmological models.

In March, 2008 issue of 'Physics Today', Prof. Brandenberger presented an excellent account of current status of inflationary cosmology in his article 'Alternatives to cosmological inflation' (article link here).

Prof. Brandenberger is a Fellow of the American Physical Society. He was an Alfred P. Sloan Research Fellow in years 1988-1992 and received the Outstanding Junior Investigator award of Department of Energy in years 1988-1991.

It gives us great pleasure to present this list of 5 most important breakthroughs that Prof. Brandenberger would like to see in Cosmology.
-- 2Physics.com ]

Breakthrough 1:
Solution of the (old) cosmological constant problem: why is the cosmological constant not given by the cut off scale of relativistic quantum field theory?

Breakthrough 2:
Solution of the new cosmological constant problem: why is there an apparent cosmological constant which is beginning to dominate the evolution of the universe at the current cosmological epoch?

Breakthrough 3:
Resolution of the cosmological singularity: without resolving the cosmological singularity a cosmological model will always be incomplete. Standard Big Bang cosmology had to be replaced by a new early universe cosmology because of this problem. The current paradigm, scalar field-driven inflationary cosmology still suffers from this problem and is therefore incomplete.

Breakthrough 4:
Non-perturbative understanding of superstring theory: will lead to a new cosmological model of the very early universe which will either yield a convincing realization of inflationary cosmology or else to an alternative model.

Breakthrough 5:
An observational discovery of a cosmic superstring: this will cement the link between string theory and cosmology and will also lead to a new theory of the very early universe.

High Energy Physics: 5 Needed Breakthroughs -- Michael Dine

[Professor Michael Dine of the University of California at Santa Cruz is today's guest in our ongoing feature '5 Breakthroughs'. He is also a faculty member at the university's Santa Cruz Institute for Particle Physics (SCIPP).

In his long career spanning about 3 decades (He got his PhD from Yale University in 1978), Prof. Dine made major contributions in the areas of supersymmetry, string theory, and other efforts to develop a "new physics" beyond the standard model of particle physics.

He has been one of the principal contributors (with various collaborators) to the set of ideas associated with supersymmetry, and was among the first to propose that supersymmetry might well be broken at these energy scales. Prof. Dine developed some of the first potentially realistic models of supersymmetry phenomenology, and was among the first to explore the dynamics of supersymmetric theories, uncovering an array of surprising phenomena, some of potential relevance to experiments, and others of interest to mathematicians and more theoretically minded physicists. In recent years, he developed a proposal for the phenomenology of supersymmetry which has become a standard for both theoretical and experimental analyses. Currently, he is engaged in a number of projects exploring the experimental possibilities for the Large Hadron Collider (LHC).

Prof. Dine also made significant contributions in superstring theory. Most of his work has been motivated by the hope of making specific predictions from the theory for accelerators, but in the course of these efforts, he made several important contributions to the overall theoretical structure. Much of his current effort is involved with trying to understand whether one can make predictions from this theory relevant to the Large Hadron Collider (LHC). At the moment, he believes there is a promising (but not certain), approach, based on a popular set of ideas commonly referred to as the `landscape'.

In December, 2007 issue of 'Physics Today', Prof. Dine provided an excellent account of the relationship between string theory and particle experiments in an article entitled "String Theory in the era of the Large Hadron Collider" (p.33, Article Link).

He also authored a widely acclaimed book on this topic: "Supersymmetry and String Theory: Beyond the Standard Model" (Cambridge University, 2007).

In the field of cosmology, he made significant contributions to the theory of inflation, and to ideas about the dark energy and dark matter. Simultaneously with others, he proposed the axion as a dark matter candidate, which has remained, over the years, one of the two most plausible possibilities (the other arising in supersymmetric theories). He also proposed one of the most widely studied ideas for understanding the origin of the matter-antimatter asymmetry (known as the Affleck-Dine mechanism) explaining why there was not, initially, an equal amount of matter and antimatter, which could have simply annihilated each other.

It's our pleasure to present this list of 5 most important breakthroughs that Prof. Dine would like to see in the physics of elementary particles.
-- 2Physics.com ]

Five needed breakthroughs in elementary particle physics

1) Determination of the origin of electroweak symmetry breaking – the masses of the W and Z bosons, quarks and leptons. Is it a single Higgs field (particle), as in the simplest version of the standard model? Or is it associated with supersymmetry, large or warped extra dimensions, or something else? This question should be settled over the next three to five years by the Large Hadron Collider at CERN, due to be commissioned late this year.

2) Identifying the dark matter. There are several plausible, well-motivated candidates coming from particle physics: the lightest supersymmetric particle (LSP), the axion (a hypothetical particle seemingly required to understand features of the strong nuclear force), and others. There are ongoing, dedicated searches for both the LSP and the axion. If the LHC discovers supersymmetry, there is a good chance we will discover the dark matter particle in underground experiments, and we will be able to study in some detail how this particle was produced at the earliest stages of the big bang. The axion searches also have a real chance of finding something, if the axion is the dark matter, though detectors with a broader reach may be necessary.

3) Theoretically, one urgent question is: does string theory predict that supersymmetry, warping, or something else is responsible for electroweak symmetry breaking? Can we settle this question theoretically before the LHC? Can we make more detailed predictions? Recent developments associated with the string landscape suggest this might be possible, but the problem is challenging.

4) There are many problems of quark and lepton flavor (the occurrence of several types of quarks and leptons, and the puzzling features of their masses and couplings) which we would like to understand. What is the scale of baryon number violation? What can we understand, theoretically and experimentally, about the origin of neutrino mass? Can we develop a compelling theory, which explains the very different features of the charged fermion masses and those of the neutrinos? Can we establish experimentally the nature of the neutrino masses? Can we decide that leptogenesis, and not, say, coherent effects associated with supersymmetry, are responsible for the asymmetry between matter and antimatter in the universe?

5) Theoretically and experimentally, what more can we learn about inflation, the period of rapid expansion in the very early universe for which there is growing observational evidence, as well as strong theoretical arguments? At a microscopic level, we are far from understanding how inflation comes about. All existing models have troubling features. Can we get beyond this situation? Can supersymmetry or string theory help? If we have improved theories, they will be subject to some experimental tests; how far can we go?

High Energy Physics : 5 Needed Breakthroughs -- Mark Wise

[In the ongoing feature '5 Breakthroughs', our guest today is Mark Wise, the John A. McCone Professor of High Energy Physics at California Institute of Technology.

Prof. Wise is a fellow of the American Physical Society, and member of the American Academy of Arts and Sciences and the National Academy of Sciences. He was a fellow of the Alfred P. Sloan Foundation from 1984 to 1987.

Although Prof. Wise has done some research in cosmology and nuclear physics, his interests are primarily in theoretical elementary particle physics. Much of his research has focused on the nature and implications of the symmetries of the strong and weak interactions. He is best known for his role in the development of heavy quark effective theory (HQET), a mathematical formalism that has allowed physicists to make predictions about otherwise intractable problems in the theory of the strong nuclear interactions.

To provide a background of his current research activities, Prof. Wise said,"Currently we have a theory for the strong, weak and electromagnetic interactions of elementary particles that has been extensively tested in experiments. It is usually called the standard model. Even with this theory many features of the data are not explained. For example, the quark and lepton masses are free parameters in the standard model and are not predicted. Furthermore the theory has some unattractive aspects -- the most noteworthy of them being the extreme fine tuning needed to keep the Higgs mass small compared to the ultraviolet cutoff for the theory. This is sometimes called the hierarchy problem."

He explained,"My own research breaks into two parts. One part is using the standard model to predict experimental observables. Just because you have a theory doesn’t mean it’s straightforward to use it to compare with experiment. Usually such comparisons involve expansions in some small quantity. One area I have done considerable research on is the development of methods to make predictions for the properties of hadrons that contain a single heavy quark".

He elaborated,"The other part is research on physics that is beyond what is in the standard model. In particular I have worked on the development of several extensions of the standard model that solve the hierarchy problem: low energy supersymmetry, the Randall-Sundrum model and most recently the Lee-Wick standard model. This work is very speculative. It is possible that none of the extensions of the standard model discussed in the scientific literature are realized in nature."

Prof. Wise shared the 2001 Sakurai Prize for Theoretical Particle Physics with Nathan Isgur and Mikhail Voloshin. The citation mentioned his work on "the construction of the heavy quark mass expansion and the discovery of the heavy quark symmetry in quantum chromodynamics, which led to a quantitative theory of the decays of c and b flavored hadrons."

He obtained his PhD from Stanford University in 1980. While doing his thesis work, he also co-authored the book 'From Physical Concept to Mathematical Structure: an Introduction to Theoretical Physics' (U. Toronto Press, 1980) with Prof Lynn Trainor of the University of Toronto (where he did his B.S. in 1976 and M.S. in 1977). He also coauthored, with Aneesh Manohar, a monograph on 'Heavy Quark Physics' (Cambridge Univ Press, 2000).

We are pleased to present the list of 5 needed breakthroughs that Prof. Mark Wise would be happy to see in the field of high energy physics.
-- 2Physics.com]

"Here go five breakthroughs that would be great to see:

1) An understanding of the mechanism that breaks the weak interaction symmetry giving the W's and Z's mass. This we should know the answer to in my lifetime since it will be studied at the LHC (Large Hadron Collider) and I am trying to stay healthy.

2) Reconciling gravity with quantum mechanics. Currently the favored candidate for a quantum theory of gravity is String Theory. However, there is no evidence from experiment that this is the correct theory. Perhaps quantum mechanics itself gives way to a more fundamental theory at extremely short distances.

3) An answer to the question, why is the value of the cosmological constant so small? I am assuming here that dark energy is a cosmological constant. (Hey if it looks like a duck and quacks like a duck it's probably a duck.) A cosmological constant is a very simple term in the effective low energy Lagrangian for General Relativity. The weird thing about dark energy is not what it is but rather why it's so small.

4) An understanding of why the scale at which the weak symmetry is broken is so small compared to the scale at which quantum effects in gravity become strong. This is usually called the hierarchy problem. Breakthrough (1) might provide the solution to the hierarchy problem or it might not.

5) Discovery of the particle that makes up the dark matter of the universe and the measurement of its properties (e.g., spin, mass, ...).

There are other things I would love to know. For example, is there a way to explain the values of the quark and lepton masses? But you asked for five."

Particle Astrophysics: 5 Needed Breakthroughs -- James Hough

James Hough [Photo Courtesy: Institute for Gravitational Research, University of Glasgow]

[Today's guest in our ongoing feature '5-Breakthroughs' is James Hough, Director of the Institute for Gravitational Research, and Professor of Experimental Physics in the Department of Physics and Astronomy, University of Glasgow.

Prof. Hough is also the Chairperson of Gravitational Wave International Committee (GWIC) which was formed in 1997 by the directors and representatives of projects and research groups around the world whose research is aimed at the detection of gravitational radiation. The purpose of GWIC is to encourage coordination of research and development across the groups and collaboration in the scheduling of detector operation and data analysis. GWIC also advises on the location, timing and programme of the Edoardo Amaldi Conferences on Gravitational Waves which are held every 2 years, and presents a prize for the best Ph.D. thesis submitted each year (for details, visit 'GWIC Thesis Prize')

His current research interests are in the investigation of materials for test masses and mirror coatings, and in the development of suspension systems of ultra-low mechanical loss towards
a) second generation gravitational wave detectors, in particular Advanced LIGO – upgrade to the US LIGO gravitational wave detector systems (Advanced LIGO is now approved by the National Science Board in the USA and supported by a significant capital contribution from PPARC in the UK and MPG in Germany).
b) third generation long baseline gravitational wave detectors, in particular the proposed Einstein Telescope in Europe, and towards LISA the ESA/NASA space borne gravitational wave detector.

Prof. Hough is Fellow of the Royal Society of London (2003), the American Physical Society (2001), the Institute of Physics (1993) and the Royal Society of Edinburgh (1991). He received Duddell Prize and Medal of the Institute of Physics in 2004 and Max Planck Research Prize in 2001.

It's our pleasure to present the 5 most important breakthroughs that Prof. Hough would like to see in the field of Particle Astrophysics.
-- 2Physics.com Team]

1) The direct detection of gravitational radiation
It is very important to make a direct detection to verify one of the few unproven predictions of Einstein's General Relativity and even more importantly to lead to the birth of a new astronomy. Gravitational wave astronomy will let us look into the hearts of some of the most violent events in the Universe.

2) The quantisation of Gravity
The challenge of developing a quantum theory of gravity and unifying gravity with the other fundamental forces in nature will undoubtedly lead to new discoveries about our Universe

3) The understanding of Dark Energy
Dark Energy - the mysterious reason for our Universe expanding anomalously - is not understood. Solving this enigma may help with understanding quantum gravity and will certainly give us a new perspective on fundamental interactions.

4) The successful launching of LISA, the space-borne gravitational wave detector
LISA will allow the study of the birth and interaction of massive black holes in the Universe in a way that cannot be achieved by any other mission.

5) The identification of dark matter
Observations suggest that there is much more matter in the Universe than we observe by standard means. Finding out the nature of the unseen 'dark' matter is a challenging problem for experimental physicists.

High Energy Physics: 5 Needed Breakthroughs -- Pierre Ramond

Pierre Ramond [photo courtesy: University of Florida, Gainesville]

[ Prof. Pierre Ramond, Distinguished Professor of Physics at University of Florida in Gainesville, is today's guest in our ongoing feature '5-Breakthroughs'.

During his long career starting with the PhD work at Syracuse University in 1969, Prof. Ramond contributed in some significant developments in the study of elementary particles and fields. Notable among those is the crucial role he played in the early development of superstring theory.

Early string theory proposed by Yoichiro Nambu and others in 1970 was based on bosonic string. At that point, Pierre Ramond took the crucial step of generalizing the Virasoro algebra, the symmetry algebra of the bosonic string, to a superconformal algebra including anticommuting operators. The inclusion of a fermionic string to accompany the bosonic ones completed the theory of strings. In 1971, he generalized Dirac's equation for point-like particles to string-like ones, which laid a solid foundation for the superstring theory. A comprehensive list of the variety of work he did can be found in Google Scholar link.

Prof. Ramond is a Fellow of American Physical Society and American Academy of Arts & Sciences. In August 2004, he was awarded Oskar Klein Medal by Swedish Royal Academy of Sciences and Stockholm University.

Many of us grew up with his celebrated book "Field Theory: A Modern Primer" (Addison / Wesley, 1981) and also experienced the pleasure of "Journeys Beyond the Standard Model"(Perseus, 1999), his other book. It's thus our pleasure to present the 5 most important breakthroughs that Prof. Ramond would like to see in High Energy Physics.
-- 2Physics.com Team]

Here is my list of five:

Finding Supersymmetry with the Large Hadronic Collider, and if found, understanding Supersymmetry breaking.

Understanding why there are three chiral families of Elementary Particles (closely related to finding the organizing principle behind chiral symmetry breaking, e.g. Yukawa interactions).

Observation of Proton Decay in the Laboratory.

Determining the Character (Majorana or Dirac) of Neutrino masses.

Identifying Dark Matter.

Superstring Theory: 5 Needed Breakthroughs -- John H. Schwarz

John H. Schwarz (photo credit: Patricia Schwarz)

[In 2001, Prof. John Preskill of Caltech wrote a poem "To John Schwarz" (full text here) which started as ..

"Thirty years ago or more
John saw what physics had in store.
He had a vision of a string
And focused on that one big thing."

The name 'Schwarz' is intimately associated with the origin and evolution of Superstring theory. In 1971 John Schwarz and André Neveu developed an early version of superstring theory, which led among other things to the discovery of supersymmetry. In 1974 Joël Scherk and he proposed that string theory should be used to construct a unified quantum theory containing gravitation.

In 1984 Michael Green and he discovered an anomaly cancellation mechanism, which resulted in string theory becoming one of the hottest areas in theoretical physics. As Prof. Preskill's poem describes:

If you weren't there you couldn't know
The impact of that mightly blow:
"The Green-Schwarz theory could be true ---
It works for S-O-thirty-two!"

John Schwarz is the Harold Brown Professor of Theoretical Physics at California Institute of Technology (Caltech) where he taught and conducted research since 1972. He received the Dirac Medal of the International Centre for Theoretical Physics, Trieste in 1989, as well as the Dannie Heineman Prize for Mathematical Physics of the American Physical Society in 2002. He was a fellow of the MacArthur Foundation in 1987 and in 1997 he was elected to the National Academy of Sciences.

Prof. Schwarz coauthored a new string theory textbook entitled `String Theory and M-Theory: A Modern Introduction,' which was published earlier this year by Cambridge University Press.

We can't resist ending this note quoting again from John Preskill's poem:

Because he never would give in,
Pursued his dream with discipline,
John Schwarz has been a hero to me.
So please, don't spell it with a "t"!

Ladies and Gentlemen, it's our honor and privilege to share with you the excitement of superstring theory by presenting this list of 5 breakthroughs that John Schwarz would like to see.
-- 2Physics.com Team]

5 most important breakthroughs that I would like to see in
SUPERSTRING THEORY
by John H. Schwarz

(1) Discovery of supersymmetry at the Large Hadron Collider (LHC):

Supersymmetry is an intrinsic feature of superstring theory, and therefore I am convinced that it exists at a fundamental level. The big question is whether it is broken at a sufficiently low energy (the TeV scale) that supersymmetry partner particles can be discovered at the LHC. There are several well-known arguments for why this is likely. Discovery of supersymmetry would not prove that superstring theory is the correct fundamental theory and nondiscovery would not prove that it is wrong. Still, if it is discovered, string theory would deserve credit for spawning the study of supersymmetry in the first place.

The experimental discovery of superpartner particles (and hence supersymmetry)would be very exciting for several reasons: It would set the agenda for experimental particle physics for decades to come ensuring the vitality of high-energy physics research. It would be enormously informative, leading eventually to the formulation of a "supersymmetric standard model'' extending the current standard model to much higher energies. Such a supersymmetric standard model would provide a much better target for string theorists to try to relate to Planck scale physics, where string theory is most directly applicable, by "top-down reasoning". String theorists would like to predict all of this in advance, of course,but that does not seem to be possible.

(2) Other experimental evidence for string theory:

Aside from supersymmetry, there are a number of other possible experimental signals for string theory that have been considered, and there may be others that nobody has thought of yet. In my opinion, all of the following are unlikely to be observed, because the Planck scale (the natural energy scale of quantum gravity) is so far beyond what is experimentally accessible. However, there are scenarios in which quantum gravity phenomena can extend to much lower energies, and thereby possibly become observable, which certainly are worth exploring. The methodologies for making such a discovery fall into two broad categories: astronomical/cosmological observations and accelerator experiments. The first category can look for cosmic strings, primordial gravity waves, and certain subtle features of the cosmic microwave background. Accelerators, such as the LHC, can look for signals indicating the presence of extra dimensions, black holes, gravitons, or fundamental strings.

(3) More fundamental formulation of string theory/M-theory; emergent spacetime :

The current understanding of string theory is based on perturbation theory expansions of various symmetrical limits supplemented by a beautiful web of conjectured duality relations. What is missing is a single complete formulation of the theory that accounts for these various symmetrical limits and dualities. Such a formulation is likely to implement some deep principle that has not yet been recognized. It is also likely to be completely unique without any adjustable parameters or other features that can be altered.

There are various reasons to believe that the existence of space and time is not something built into the theory itself, but rather emerges as a property of certain classes of solutions. If this is correct, the theory will be radically different from any previous physical theory all of which describe what happens in a given spacetime. Even Einstein's theory of gravity (the general theory of relativity), in which the geometry of spacetime is determined dynamically,assumes the prior existence of a spacetime manifold.

(4) Determine whether time is emergent and clarify the status of quantum mechanics:

The previous item suggested that space and time are emergent properties of solutions to string theory rather than intrinsic features of the underlying theory. There is considerable evidence for the emergence of spatial dimensions in various settings, but there is no compelling evidence for the emergence of time. Experience with relativity makes it hard to imagine that space and time could be radically different in this regard. On the other hand, the notion of time is central in quantum mechanics, which is formulated as unitary time evolution. If time is emergent, some extension of the rules of quantum mechanics would seem to be required. The consistency of string theory requires that quantum mechanics is exactly correct. I am not questioning that this will continue to be the case in the future, only that quantum mechanics may need to be generalized somewhat to extend its domain of applicability.

(5) Determine the correct solution of the theory:

A unique equation can have many different solutions. By the same token, string theory can describe a rich variety of physical realities. We are still in the early stages of mapping out the possibilities, but the indications are that the number of possibilities is enormous. The picture that has been proposed, whose validity is not completely evident, is that there is an energy function that is a complicated function of many variables (called moduli) and that each of the minima of this function corresponds to a different solution of the theory. Assuming its validity, this picture raises a lot of questions: How is the "correct'' solution (i.e., the one that describes the Universe that we observe) determined? Is it a cosmological accident or is there some other principle? How can we determine the correct solution? How much empirical information needs to be input in order to determine it uniquely and make everything else computable (in principle)? These types of questions are very important to explore. They are stimulating a lot of serious research, as well as some spirited debate that is even spilling over into the public domain.

High Energy Physics : 5 Needed Breakthroughs -- Guenakh Mitselmakher

[ Our guest today in the ongoing feature,
'5-Breakthroughs' is Guenakh Mitselmakher, Distinguished Professor of Physics and Director of the Institute for High Energy Physics and Astrophysics at University of Florida, Gainesville.

Currently, he is also the leader of the Muon system development for the CMS detector. CMS is one of two major universal detectors at the Large Hadron Collider at CERN, Geneva, Switzerland, which will begin operations in 2007-2008. He is also a member of the LIGO Science Collaboration, looking for the so called "burst" signals of Gravitational Wave (signals of limited duration), which may originate at a variety of astrophysical sources like supernova explosion.

In the long career starting from his PhD work in 1974 at the Joint Institute for Nuclear Research, Dubna, Russia, Prof. Mitselmakher made numerous important contributions in the field of Experimental high energy physics. Notable among those are studies of the lepton number conservation in rare decays of muons, investigations of the electromagnetic structure of pions, including the first measurements of the pion charge radius and polarizability, studies of the Standard Model and Beyond with the DELPHI detector at CERN and with the CDF detector at Fermilab. He also proposed a new type of Particle detectors (what is now called Quantum Calorimetry or bolometry), now broadly used in Paricle Physics and Astrophysics.

Here are 5 important breakthroughs that Prof. Mitselmakher would like to see in High Energy Physics.
-- 2Physics.com Team]

1. To understand the origin of "Dark Energy".

2. To understand the origin of "Dark Matter".

3. To find the Higgs or an alternative explanation for the spontaneous symmetry breaking in the Standard Model.

4. To explain (and calculate) the parameters of the Standard Model, such as masses and mixing angles of quarks and leptons.

5. To test if quarks (and other particles considered to be point-like) have a substructure.

Interferometric Detection of Gravitational Waves : 5 Needed Breakthroughs -- Rana Adhikari

[Rana Adhikari is a young, charismatic and dependable leader in the field of gravitational wave interferometry. His knowledge and experience with the operation of LIGO detectors with its variety of noise sources, feedback loops and subsystems are held in high respect by his fellow researchers. (Note: LIGO Laboratory operates 3 L-shaped long-baseline interferometers at two locations: Livingston, Louisiana has one of 4 Km arm length and Hanford, WA has one of 4Km and another of 2 Km armlength within the same vacuum enclosure) .

Rana started working on laser interferometers in LIGO around the turn of the century as a graduate student at MIT. He spent some time living with the Livingston interferometer and helped to reduce the noise in all 3 of the LIGO interferometers. In 2005, he received the first LIGO thesis prize. On that occasion, his thesis-supervisor Rai Weiss said,"He taught us how to make the interferometers sing and did this with wit and good humor coupled to precision and clear thinking".

Now, as an Assistant Professor of Physics at Caltech, he works on designing, prototyping and debugging the next generations of interferometric observatories. Here is a list of 5 breakthroughs Rana would like to see in gravitational wave interferometry.
-- 2Physics.com Team]

1) Development of the 'wonder' material (e.g. ultra hard Fullerite): capable of being grown to a 1 ton mass and a 1 meter diameter. Would be incredibly high purity (no mechanical loss), high thermal conductivity (no thermal lens) and very low thermal expansion. In one stroke this would make interferometric detectors immune to quantum radiation pressure noise, lower thermal noise (especially because of larger beam size), and reduce noise due to stray forces.

2) Neural networks for tuning the all digital control systems: in the future the machines will run simulations exploring the possible parameter space of mirror positions, laser power, feedback topologies, etc. They will also then tune themselves for maximum sensitivity and iteratively design their own signal analysis algorithms with only qualitative input from scientists.

3) More Laser Power: the upcoming generation of interferometers in 2011 will be able to sense a part in 10¹¹ of a wavelength. This sensitivity will scale with the square root of the laser power. Quiet lasers with ~10 kW power levels would enable interferometry good enough to hear coalescing binaries anywhere in the universe.

4) Long baseline interferometers: 50 km scale interferometers would reduce the contribution of the low frequency (displacement) noise by a factor of 10 in a very clean way. One can find such sites using Google Earth.

5) Squeezed light injection through the interferometer's dark port to reduce the 'shot noise', phase sensing limit. With 1 ton masses (reducing the effects of photon pressure fluctuations) and very long arms, the gravitational wave sensitivity would be 30 to 300x better than the current generation and only limited by light scattering off of the 10^-8 torr of residual molecular hydrogen in the interferometer's beam tubes. Doing better than the LIGO vacuum system would be a real challenge.

Quantum Theory : 5 Needed Breakthroughs -- Stephen Adler

Stephen Adler with grandchild in 2004 (photo courtesy: Institute for Advanced Study, Princeton)

[Prof. Stephen Adler of the School of Natural Sciences at the Institute of Advanced Study, Princeton is a widely respected authority in the field of Quantum Theory.

During the long career starting with Ph.D work in 1964 from Princeton University, Prof. Adler
continued to make important contribution in the field of Elementary Particles, Quantum Field Theory and Foundation of Quantum Physics.
His recent works can be best described by citing the following classic books that he wrote on his various research projects:

-- ``Adventures in Theoretical Physics: Selected Papers with Commentaries '' (World Scientific Publishing, January, 2006)
-- ``Quantum Theory as an Emergent Phenomenon'' (Cambridge University Press, 2004).
-- ``Quaternionic Quantum Mechanics and Quantum Fields'' (Oxford University Press, 1995).

During his long career, he held many important positions. He was Divisional Associate Editor for Particles and Fields of Physical Review Letters and also the Chairman of the Division of Particles and Fields of American Physical Society. He was a member of the Editorial Board of Physical Review D and Journal of Mathematical Physics. He is a member of the 'National Academy of Sciences' and Fellow of 'American Physical Society', 'American Academy of Arts and Sciences' and 'American Association for the Advancement of Science'.

Prof. Adler received J.J. Sakurai Prize from American Physical Society in 1988. In 1998 he was awarded the Dirac Medal of the Abdus Salam International Centre for Theoretical Physics, Trieste, Italy.

We thought it would be great to hear from Prof. Adler his choice of 5 most important breakthroughs that the Quantum Theory needs.
- 2Physics.com Team]

1. To understand why there are three families of quarks and leptons.

2. To understand the hierarchy problem - why the electroweak scale is so much smaller than the Planck scale.

3. To understand why the cosmological constant is so small.

4. To understand how to get a satisfactory quantum theory of measurement.

5. To reconcile relativistic quantum theory with general relativity.

Interferometric Detection of Gravitational Waves : 5 Needed Breakthroughs -- David Reitze

[In our ongoing feature '5-Breakthroughs' , today's guest is Prof. David Reitze of University of Florida, Gainesville.

Prof. Reitze is the newly elected Spokesperson of the LIGO Science Collaboration (LSC), a self-governing collaboration seeking to detect gravitational waves, use them to explore the fundamental physics of gravity, and develop gravitational wave observations as a tool of astronomical discovery. It includes scientists from the LIGO Laboratory as well as collaborating institutions from US, Australia, Germany, India, Japan, Russia, UK. The mission of LSC is to insure equal scientific opportunity for individual participants and institutions by organizing research, publications, and all other scientific activities. In fact, the March meeting of LSC on scientific collaborations between LIGO and the French-Italian group Virgo is starting tomorrow in Baton Rouge, Louisianna.

In the field of gravitational wave interferometry, Prof. Reitze's research activities spanned a wide range of topics crucial for successful operation and improvement of the sensitivity of interferometric detectors: Investigation of thermal lensing in passive and active optical elements; development of high power optical components; development of new interferometer topologies for next generation detectors; design, construction and operation of the LIGO interferometers.

Here we present the 5 important breakthroughs that the new Spokesperson of LIGO Science Collaboration (LSC) wishes to see in the worldwide effort for the detection of gravitational waves.-- 2Physics.com Team]

"In order from 'most possible in the near term' to 'most ambitious' are my five most important breakthroughs needed for gravitational wave astrophysics :

1) The direct detection of gravitational waves from astrophysical events such as the inspiral and merger phases of binary neutron star or black hole systems. Observations of these events will reveal significant astrophysical information about neutron stars and black holes, including their masses, spins, and the nature of strong-field gravity in regions of high space-time curvature. As a side wish, I would like to see the development of computational waveform templates for BH-BH collisions as well as supernovae waveforms.

2) Large scale interferometer implementations of quantum optical methods which circumvent the 'standard quantum limit' imposed by the statistics of photons. Such methods include but are not limited to the use of non-classical states of light, ponderomotive squeezing, and line-broadened cavities. Any of these methods would enable GW astrophysicists to improve the sensitivity of interferometers, resulting in an improved rate of detection for gravitational wave events. In order to make these techniques work, however, we would need to develop mirrors which possess lower thermal noise, so I would like to see that too!

3) The development of large scale interferometers underground to push the sensitivity of ground-based instruments below a few Hz. Placing interferometers even 100 m underground dramatically reduces the disturbances due to seismic motion and improves the detection efficiency and event rates for low frequency emitters such as 20-50 solar mass black holes.

4) The development of the Laser Interferometer Space Antenna. LISA will allow astrophysicists to look at even lower frequencies and observe high mass black hole collisions.

5) The observation of the residual gravitational wave radiation from the Big Bang. Unlike the cosmic microwave background, the observation of relic gravitational waves provides a direct snapshot of the universe at the moment of its birth (or about 10^-43 sec after). "

Interferometric Detection of Gravitational Waves: 5 Needed Breakthroughs -- Seiji Kawamura

[ In our ongoing feature '5-Breakthroughs', so far most of our guests were from the exciting field of research on detection of gravitational waves. It started with David Shoemaker of LIGO and we also had Jean-Yves Vinet from French-Italian Virgo project and David Blair of the Australian effort, AIGO. Our today's guest is Prof. Seiji Kawamura of the Japanese endeavor, TAMA.

Seiji Kawamura is an associate professor at National Astronomical Observatory(NAO) at Mitaka, Tokyo, Japan. He was involved in joint Caltech-MIT LIGO project from its early days and worked on the 40m prototype interferometer (at Caltech), suspension system, and advanced R&D for the LIGO project between 1989 and 1997.

In 1997 he joined the TAMA project, the Japanese 300 meter interferometer for the detection of gravitational waves. As the leader of the detector group, he could lead TAMA to attain the world-best sensitivity at that time.

In addition he initiated and has been in charge of the resonant sideband extraction experiment, quantum non-demolition experiment, super-high frequency gravitational wave detection, and displacement-noise-free interferometer. He also leads the Japanese space gravitational wave antenna DECIGO.

Here is Seiji's list of 5 breakthroughs he would like to see in the ongoing worldwide effort to detect gravitational waves using interferometric antennas.
-- 2Physics.com Team]

"- homodyne detection with ponderomotive squeezing to suppress radiation pressure noise

- high-power laser to suppress shot noise

- cryogenic mirror/suspension to suppress thermal noise

- interferometer in space to remove seismic noise and to enhance gravitational wave signals

- displacement-noise-free interferometer to cancel all kinds of displacement noise"

High Energy Physics: 5 Needed Breakthroughs -- Barry Barish

[Our today's guest in the ongoing feature '5 Breakthroughs' is Prof. Barry Barish (photo courtesy: Caltech).

Barry Barish is a Linde Professor of Physics, Emeritus at the California Institute of Technology, where he taught and conducted research since 1963. He is also the Director of the Global Design Effort for the International Linear Collider.

One of Prof. Barish's noteworthy experiments was at Fermilab using high energy neutrinos to reveal the quark substructure of the nucleon. These experiments were among the first to observe the weak neutral current, a linchpin in the Eletro-Weak unification theory of Glasgow, Salam and Weinberg.

In 1980s Prof. Barish led an international effort to build a sophisticated underground detector (MACRO) in Italy to search for magnetic monopole and solve other related problems in the emerging field of particle astrophysics. The experiment provided the best limits for the Grand Unified magnetic monopoles and some of the key evidences that neutrinos have mass.

In 1994, Prof. Barish became Principal Investigator of the joint Caltech-MIT LIGO project for the detection of gravitational waves and later became Director of the Laboratory from 1997 to 2005.

In 2002 he was nominated to the National Science Board that helps oversee the National Science Foundation (NSF) and advises the President and Congress on policy issues related to science, engineering and education. In 2002 he received the Klopsteg award of the American Association of Physics Teachers (AAPT) and was elected to the National Academy of Sciences. In 2003, he served as a member of the special panel for NASA that considered the future of the Hubble Space Telescope and the transition to the James Webb Space Telescope. Prof. Barish also served as co-chair of the subpanel of the High Energy Physics Advisory Panel (HEPAP) that developed the long-range plan for high energy physics in USA.

Here is Prof. Barish's list of 5 breakthroughs that he would like to see in high energy physics.
-- 2Physics.com Team]

"5 most important breakthroughs that are needed for particle physics:

1) Understanding what is the dark energy in the universe? (We don't even have a good idea here)

2) What is the dark matter? (This is the other big unknown, but at least we have some handles. We know it is non-baryonic and evidence points to either supersymmetric particles, or maybe axions. Perhaps it is neither)

3) What causes mass? (We have a very successful theory of particle physics, but the particles are massless. We need to understand the source of mass. The leading idea is that it is the Higgs mechanism, and we need to see if there is a Higgs particle or variant to make the next step. The Large Hadron Collider at CERN should answer this question)

4) Is the neutrino its own antiparticle? (This is a puzzle going back to Fermi and perhaps the next generation of experiments will resolve it by looking for neutrino-less double beta decay)

5) Is there ultimate unification of the forces of nature? (This is a long term intriguing simplification on our understanding of particles and fields, but present data does not support it. However, if there is a new symmetry in nature (supersymmetry) it could bring this unification.

These are all questions and there is hope we will have much better understanding within a decade or two."

Interferometric Detection of Gravitational Waves : 5 Needed Breakthroughs -- David Blair

[ After David Shoemaker of LIGO and Jean-Yves Vinet of Virgo, today we present Prof. David Blair's list of 5 breakthroughs that he expects to see in his field of research -- the interferometric detection of gravitational waves -- the topic that we are currently focusing on.

David Blair is Director of the Australian International Gravitational Research Centre (AIGRC) and a Professor of the University of Western Australia, Nedlands. Since late 1980's he is leading the Australian research effort for the detection of gravitational waves.

In the 1980's he built a very sensitive resonant mass detector called NIOBE, consisting of a huge bar of the metal niobium cooled to a few degrees above absolute zero. This detector operated as part of a world wide network which set upper limits on the number of bursts from our galaxy. These results implied that there was no unexpected population of sources such as coalescing black holes in our Milky Way.

In the 1990's Blair with colleagues across Australia proposed setting up an Australian large scale interferometer detector AIGO. Phase 1 of this project has been substantially completed. It is located at Gingin, Western Australia, on a large site set aside for a long baseline detector. The current facility is working to develop the technology for the next stage, an Advanced high optical power interferometer. It uses high power lasers developed by Prof Jesper Munch's group at the University of Adelaide, and control systems developed by LIGO and by Prof David McClelland's group of the Australian National University.

The Gingin facility is a joint facility of the Australian Consortium for Gravitational Astronomy and the LIGO Scientific Collaboration. The main focus of research is on developing control systems for very high power suspended optics in which thermal effects and radiation pressure effects must be carefully controlled. When the Australian detector is developed into a full scale observatory it will contribute a large improvement to the angular resolution of the world wide network, and enable signals to be identified with distant host galaxies - roughly a 16 fold increase in the number of potential host galaxies.

He also plays an important role in the activities of the Gravity Discovery Centre, the associated award winning public education centre on the AIGO site. It's an inspirational self supporting, non-profit public education and tourism centre that focusses on the big questions of Life and the Universe, and the extraordinary biodiversity of Wallingup Plain.
- 2Physics.com Team ]

"1.First detection of a single event to prove the viability of gravitational wave detection and the existence of detectable waves.

2. Demonstration of high optical power interferometry to pave the way for advanced detectors.

3. Operation of advanced detectors and the detection of frequent GW signals.

4.Operation of detectors with sensitivity better than the standard quantum limit.

5. Detection of cosmological gravitational waves from the big bang and tests of the theory of inflation. "

Relevant Links:     AIGRC     Gravity Discovery Centre     LIGO Science Colloaboration

Interferometric Detection of Gravitational Waves : 5 Needed Breakthroughs -- Jean-Yves Vinet

[We are continuing our feature on '5-Breakthroughs' -- this time with inputs from Prof. Jean-Yves Vinet ....

Jean-Yves Vinet was involved in the French-Italian Virgo project for the detection of gravitational waves since the very beginning (Year 1984!) as a collaborator of Alain Brillet, who, with A. Giazotto, promoted the idea of the Virgo project.

Regarding terrestrial instruments like Virgo or LIGO, his interest lies mainly in the theory of the instrument itself (optics, thermal noise, R&D for advanced instruments...). He is also involved in NASA's proposed space-based detector LISA where again he finds his interest in the instrument itself (transfer function, low frequency regime, time delay interferometry...) and also the data Analysis issues.
Jean-Yves is currently a "Directeur de Recherche" at C.N.R.S, France. He is a member of the LISA International Science Team and also of the Fundamental Physics committee of the Centre National d'Etudes Spatiales (the French space agency). He was a professor at Ecole Nationale de Techniques Avancées (Paris) (Laser Physics, 1991-99) and then a searcher at Département d'Astrophysique Relativiste (Observatoire de Paris-Meudon) (1999) and thereafter a searcher at Artemis (Observatoire de la Côte d'Azur, Nice, France) since 2000.

He teaches a master's course on Experimental Gravitation at Université de Nice-Sophia-Antipolis.
-- 2Physics.com Team]

"In my opinion, important breakthroughs would be for instance:

1) Find an optical design matched to light beams homogeneously distributed on the mirror surfaces in order to reduce the spurious thermal effects, the thermal noise and the thermodynamical noise.

2) Then find a laser able to produce such beams (fiber laser).

3) Adopt the continuous detection scheme (no modulation).

4) Organize a full cooperation among existing antennas (this seems to be on the way).

5) Get more funding for R&D (Europe!)"

Relevant links:     Virgo Project     LISA

"Interferometric Detection of Gravitational Waves : 4 Needed Breakthroughs" -- David Shoemaker

David Shoemaker standing next to the full-scale interferometer testbed in LIGO MIT Lab (photo courtsey: LIGO MIT Laboratory)

[We asked leading scientists of various fields to point out 5 needed breakthroughs that they would like to see in their own field of research. We are starting this feature today with the input from Dr. David Shoemaker.

David Shoemaker played an important role in both the R&D effort and commissioning of the joint Caltech-MIT LIGO laboratory for the detection of gravitational waves. Currently, he is Director of the LIGO MIT Laboratory at Kavli Institute for Astrophysics and Space Research, MIT. He also leads the LIGO research group on Advanced LIGO Development.
-- 2Physics.com team]

"Four, rather than five, breakthroughs would satisfy me:

- A means to significantly reduce (through changes in formulation or process) or circumvent (via an alternative optical topology) the thermal noise in the reflective dielectric coating on the test masses (and in the bulk of the test masses as the next step!)

- Successful application of prepared states of light to improve the sensitivity of full-scale gravitational-wave detectors while keeping circulating power at technically acceptable levels.

- A practical application of a method to regress out (via e.g., an array of seismometers) or reduce (via e.g., a mechanical design) the gravitational gradient noise, allowing lower frequency operation on the ground.

- ....and, slightly different in character: The first direct detection of a gravitational wave."

Relevant Links:
LIGO Laboratory     LIGO MIT Laboratory    LIGO Science Collaboration