Stanley Deser’s Influence on the 2017 Nobel Prize for Physics

Written by Albion Lawrence

Deser, Arnowitt, & Miser

Bornholm 1959
From the left, Richard Arnowitt, Charles Misner and Stanley Deser

Today’s Physics Nobel Prize to Rai Weiss, Kip Thorne, and Barry Barish for the detection by the LIGO experiment of gravitational waves is a well-deserved recognition of a remarkable achievement through perseverance. However, it is the nature of prizes such as the Nobel that they obscure the important efforts and insights of many scientists across space and time that lead to the result in question.

Stanley DeserThe extraction of a gravitational wave signal from the output of the LIGO detector requires understanding in advance what signals can be produced; these are based on numerical simulations of astrophysical events which provide templates that a signal must match.

This is possible due to the seminal work of Brandeis emeritus faculty Stanley Deser, with his colleagues Richard Arnowitt and Charles Misner, who developed the mathematical framework known as the ADM formalism, to treat general relativity as a Hamiltonian system; with this, the evolution in time of the gravitational field can be computed from initial conditions.

In addition, Stanley was instrumental in the LIGO experiment being funded in the first place. The story is best told by him in his inimitable style (here quoted from an email, and lightly expurgated):

“Marcel Bardon, then [director] of NSF physics, made me an offer I’d better not refuse. I was nominated to some advisory committee in order to plead for LIGO in front of my betters, who would then go to Congress, if convinced. Those were dark days for waves, experimentally; we (ADM) of course knew the Lord was not evil, but 3 suns’ worth we did not expect!….It worked quite well, and was duly made a line item.”

Additional information:

Gregory Widberg named State Command Sergeant Major for the Massachusetts National Guard

Greg Widberg, Senior Mechanical Engineer in Physics, has been selected to be the 8th State Command Sergeant Major for the Massachusetts National Guard. Greg, who also performs repair work in the Division of Science, will be the senior enlisted advisor to Gary W. Keefe, Major General and The Adjutant General for the Massachusetts National Guard.

Roland Maher, Operations Manager for the Physics Department, said, As Gregory Widberg’s supervisor, I want to congratulate Greg on this opportunity with the Massachusetts National Guard.  All of us who know and respect Greg are proud of his accomplishments and wish him the all best with this wonderful opportunity. I am very sorry that we will be without Greg’s services and look forward to his return upon completion of his service to the Massachusetts National Guard.

Congratulations to Greg on his achievement!

Bjoern Penning is New Assistant Professor of Physics

Bjoern PenningBjoern Penning has joined the Physics department as a new Assistant Professor. He researches dark matter (DM) and has performed direct DM searches at the LUX-Zeplin (LZ) experiment and collider DM searches with CMS and ATLAS.

At Brandeis, he is a member of the High-Energy Physics Group. He will focus on direct dark matter searches with LZ and phenomenological dark matter research.

Penning received his Ph.D. from the University of Freiburg. Previous to his arrival at Brandeis, Penning was a Lecturer in Experimental Particle Physics at the University of Bristol.

Penning will teach Particle Physics (PHYS 107b) during the Fall 2017 semester.

Marcelle Soares-Santos Joins the Physics Department

Marcelle Soares-Santos

Marcelle Soares-Santos is joining Brandeis as an Assistant Professor in the Physics department starting in September 2017. Soares-Santos will continue her research into the nature of the accelerated expansion of the Universe.  She is also a member of the Dark Energy Survey (DES) Collaboration and the Large Synoptic Survey Telescope Dark Energy Science Collaboration (LSST/DESC).

Nature recently profiled Marcelle in “Turning point: Galactic groundbreaker. In the article, she discusses her research, career trajectory and future plans.

SciFest VII Wraps Up Summer 2017 Undergraduate Research Session

The Brandeis University Division of Science held its annual undergraduate research poster session SciFest VII on August 3, 2017, as more than one hundred student researchers presented summer’s (or last year’s) worth of independent research. We had a great audience of grad students and postdocs (many of whom were mentors), faculty, proud parents, friends, and senior administrators.

More pictures and abstract books are available at the SciFest site.

SciFest VII by numbers

Chakraborty lab provides new understanding on the physics of granular materials

By Kabir Ramola, Ph.D

In the late 1980’s Sir Sam Edwards proposed a framework for describing the large scale properties of granular materials, such as sand or salt. In this description, similar to the well-established framework of statistical mechanics, the global properties of a complex system are determined by an average over all possible microscopic configurations consistent with a given global property. This is usually attributable to the very fast dynamics of the constituent particles making up the system. The extension of such treatments to granular systems where particles are static or ‘jammed’ represents a fundamental challenge in this field. Even so, Edwards’ conjecture postulated that for given external parameters such as volume, all possible packings of a granular material are equally likely. Such a conjecture, like Boltzmann’s hypothesis in statistical mechanics, can then be used as a starting point to develop new physical theories for such materials based on statistical principles. Indeed, several frameworks have been developed assuming this conjecture to be true.

Figure 1 : Snapshot of the system studied and illustration of the associated energy landscape at different volume fractions.

A simple illustration of this conjecture would be, if one were to pour sand into a bowl, and not bias the preparation in any way, then all the trillion trillions of configurations allowed for the grains would be equally likely. Clearly such a conjecture is utterly infeasible to test experimentally.  In a recent paper that appeared in Nature Physics, we instead performed detailed numerical computations on a theoretical system of soft disks (in two dimensions) with hard internal cores. We focused on a system of 64 disks which already pushed the limits of current computational power. We found that if one fixes the density of a given system of disks, the probability of a packing occurring depends on the pressure, violating Edwards’ proposition. However, at a critical density, where particles just begin to touch or ‘jam’, this probability remarkably becomes independent of the pressure, and all configurations are indeed equally likely to occur. This jamming point is in fact very interesting in its own right since most granular materials are found at the threshold of being jammed and ‘unjammed’. To be fair to Edwards, the hypothesis was made for ‘hard’ grains in which particles are precisely at this threshold, and therefore our numerics seem to confirm the original statement. This is the first time that this statement has been out to a direct test and will no doubt lead to many interesting directions in the future.

Links to news sources describing this article:

doi: 10.1038/nphys4168
Numerical test of the Edwards conjecture shows that all packings are equally probable at jamming.
Stefano Martiniani, K. Julian Schrenk, Kabir Ramola, Bulbul Chakraborty & Daan Frenkel.
Nature Physics
2017

 

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