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When Scientific Worlds Collide: The Berkeley Statistical Mechanics Meeting

Each January for the previous 20 years, scientists from around
the world have come to Berkeley for a singular conference. Chemists, biologists, and
physicists collect to speak about subjects as numerous as liquid water, organic
membranes, nanoparticle meeting, and quantum spins. What do these all have in
widespread? What brings such a various set of scientists, all working in seemingly disparate
fields, collectively?

It turns out that each one of those subjects come underneath the purview of statistical mechanics, a area that offers with the conduct of methods with many interacting, changing elements. The late David Chandler, former professor of chemistry at UC Berkeley, put it extra poetically: “Statistical mechanics is the theory with which we analyze the behavior of natural or spontaneous fluctuations. It is the ubiquitous presence of fluctuations that makes observations interesting and worthwhile. Indeed, without such random processes, liquids would not boil, the sky would not scatter light, indeed every dynamic process in life would cease.” Take a pond, for example. Its floor may look placid, but microscopically, it is the fixed motion of the molecules that comprise it—their fluctuations—which give rise to liquid water’s acquainted properties. There isn’t any single configuration of molecules that characterizes a liquid, but slightly an infinitely giant setof configurations characterized by a chance distribution. Obtaining and learning the properties of these distributions, and connecting them to the noticed properties of matter, is the business of statistical mechanics.

Although statistical mechanics was developed as a department of
physics and chemistry and used to elucidate the properties of gases and other
states of matter, its generality has made it a useful gizmo in lots of different
fields, including biology, materials science, and even finance. Every time one is
learning numerous issues, and a few property of these things is
fluctuating, statistical mechanics could be useful.  This might be colloids diffusing randomly in a
liquid, stock costs altering, or even headbangers forming mosh pits at a heavy
metallic live performance.

Chandler’s broad pursuits have been the impetus for the statistical mechanics conference. Originally a spin-off of one other chemistry convention at Berkeley, the “mini” Berkeley Statistical Mechanics Meeting grew through the years into a fully-fledged and much-anticipated assembly. Chandler introduced collectively scientists from many walks of life, reflecting the number of fields dealing with phenomena pervaded by fluctuations. Along with his own main subject—the research of liquids—Chandler invited scientists engaged on organic methods, supplies science, and quantum physics. Chandler was also notorious for his robust (and sometimes even confrontational) questions and his excessive requirements of scientific rigor. This made for vigorous, albeit intimidating, discussions. Chandler passed away in April 2017 after an extended battle with most cancers. Though he’s gone, the spirit of curiosity and openness to subjects from numerous fields that he fostered was alive and nicely at this yr’s conference.

The conference kicked off on Friday evening with a quick introduction by conference organizer Phillip Geissler, a UC Berkeley professor of chemistry and a former graduate scholar of Chandler. Two-minute talks by graduate students and junior scientists adopted this introduction. These talks served as ads for the next poster session and have gotten fairly elaborate at current conferences. Presenters projected eye-catching pictures of their research and even confirmed movies. One scholar who opted to not use flashy visuals wryly famous that she was too old style for such things, garnering some sheepish laughs from the audience. The posters themselves encompassed a broad assortment of subjects, ranging from biological regulatory networks to statistical methods for determining the structure of molecules. In the course of the poster session, there was a substantial amount of interaction between younger and older scientists, and among individuals in very totally different fields. My own poster was visited by scientists of all totally different stripes, from undergraduates to professors emeriti, and from biologists to engineers. The physical proximity of individuals at the session, in addition to the interdisciplinary spirit of the conference, encouraged discussion between researchers engaged on very totally different subjects who otherwise may by no means have crossed paths. After the poster session, conversations (scientific and in any other case) continued at local restaurants and bars.

On Saturday and Sunday, invited speakers gave talks. Whereas the particular subjects of those talks, just like the posters, have been far-flung, all of them had in widespread themes of chance and fluctuations. Talks with extra particular shared themes have been usually grouped into periods. One such theme was that of amorphous supplies. In contrast to crystalline solids, the place molecular constituents organize themselves in regular spatial patterns, amorphous solids lack simple, regular spatial order. As an alternative, their local molecular environments are heterogeneous, very similar to these of liquids. This forces scientists to cope with not one single geometry, but an entire distribution of buildings—making it a topic of perennial curiosity for statistical mechanicians. A large distribution was obvious in these speakers’ experience as nicely. These ranged from Baron Peters’s methods for interrogating catalysis in amorphous solids, to Marina Guenza’s fashions for learning the structure and dynamics of polymers, to Jean-Louis Barrat’s research of defects and their move in densely packed solids.

Whereas amorphous supplies
are fascinating in their own right, scientists are often concerned as an alternative with
find out how to go from a disordered set of elements into an orderly configuration—a
course of generally known as self-assembly. Self-assembly is typified by such natural
processes because the formation of membranes and vesicles from mixtures of oil, water,
and surfactants. It is intently associated to a standard matter of research in
statistical mechanics—part transitions. These phenomena, exemplified by the
crystallization of ice from liquid water, are hanging manifestations of
fluctuations in molecular preparations. Most of the concepts developed to
understand part transitions have been adopted to review self-assembly. On the
practical aspect, self-assembly is a subject of keen interest to supplies
scientists, who hope to harness it to manufacture units like photo voltaic cells.
Concept and apply have been both on show at the convention. Jasna Brujic showed
how her lab engineered tiny colloidal droplets to assemble into polymer-like
chains. She was adopted by Michael Grünwald, who used pc
simulations to review the assembly of nanoparticles coated with lengthy, natural
molecules. The fluctuating interactions of those molecules dictate the geometry
of the lattice into which the nanoparticles assemble. Grünwald’s
speak was a crowd favourite—his partaking type, along with molecular films and a
pinch of humor, stored the viewers entertained. Tom Lubensky informed stories about
the inverse course of—how ordered mechanical lattices turn out to be unstable and
collapse, which he illustrated with do-it-yourself movies of lattices made with
development toys.

It was an indication of how
interdisciplinary the convention was that a session on supplies self-assembly
was followed by one on organic techniques, and even more so that a biologist, a
physicist, and an engineer all spoke in that very same session. Their talks have been as
numerous as their backgrounds, from Ilya Levental’s studies of the fatty acid mixtures that comprise cell membranes,
to Ariel Amir’s speak on the connection between cell genetic variability and
population progress, to Elizabeth Learn’s statistical fashions of epigenetics (how
genes work together with and are affected by their setting). Particularly hanging
was the variety of scales that the talks coated – from the speedy microscopic jittering
of biomolecules, to gradual oscillations within the populations of species over
time. The wide selection of size and time scales that biology reveals are
related by the concepts of statistical mechanics.  Though biomolecules and populations are
bodily very totally different entities, their fluctuations are ruled by the identical
laws of chance. This widespread mathematical framework enabled scientists
working on vastly totally different features of biology to know and have interaction with
each other.

Concepts from statistical
mechanics even discover relevance in locations where quantum physics guidelines. Classical
methods obey Newton’s legal guidelines of movement. Their constituents trace out trajectories
with well-defined positions and velocities—consider billiard balls rolling on a
clean surface. At finite temperatures, fluctuations arise from collisions
between shifting particles; at zero temperature, motion ceases. Against this, quantum
techniques, like electrons in a metallic, admit fluctuations even at zero
temperature. This can be a consequence of the celebrated Heisenberg uncertainty
principle, which states that it’s unimaginable to simultaneously measure the
actual position and actual velocity of a quantum-mechanical particle. Relatively than
having precise values, these quantities are as an alternative described by chance
distributions. This makes the research
of quantum methods amenable to the methods of statistical mechanics.Romain Vassuer showed how statistical
mechanical ideas about diffusion—that are sometimes applied to classical
methods at excessive temperature, like proteins in a cell—can be utilized to explain the
dynamics of ultra-cold quantum spins. Monika Schleier-Smith then adopted up by
displaying how comparable methods may be realized and probed experimentally. Abraham
Nitzan took both thermal and quantum fluctuations under consideration together with his research
of molecular wires—tiny junctions by means of which electrons are pressured to movement
separately. It was superb to study that, even in complicated and
counterintuitive quantum techniques, one can study an awesome deal by using
comparatively simple concepts of chance.

One in every of statistical
mechanics’ frontier areas is the research of nonequilibrium
techniques. At thermal equilibrium—where variables like temperature, strain,
and composition are held fixed—the mathematical tools of statistical
mechanics are properly established. These instruments may even be extended to techniques
that are out of, however not too removed from, equilibrium, like a dye molecule in a
liquid which has been struck by a laser pulse. Far out of equilibrium, although,
the assumptions which underpin typical statistical mechanics break down. Variables
like temperature and strain might differ or even be ill-defined. One of the
intriguing out-of-equilibrium situations is present in so-called lively matter, in
which particular person elements eat inner power and convert it into movement.
Examples embrace bacterial colonies and the cytoskeleton of eukaryotic cells. Because
the tools to explain such methods are usually not but absolutely established, collaboration
between principle and experiment and between disparate fields with totally different concepts
is important.

The talks on nonequilibrium
methods have been representative of the range of views vital to construct
such instruments. Suri Vaikuntanathan mentioned theoretical models displaying that
membranes can adopt fascinating morphologies when grown underneath extremely
non-equilibrium circumstances. Vincenzo Vitelli gave a colorful speak on the idea
of elastic conduct that arises when one attaches miniature motors to atoms on
a lattice. He was adopted by Dan Needleman, who showed experimentally how
mixtures of microtubules and motor proteins (reconstituted from cells) pushing
and pulling towards each other can create movement very similar to that of an actual cell.
David Sivak tied concept and follow collectively as he explained how one can use
statistical mechanical concept to provide you with protocols that experimentalists
might use to effectively operate molecular machines.

The last nonequilibrium speak
was given by utilized mathematician Hugo Touchette. He travelled all the best way
from South Africa to discuss giant deviation principle, a mathematical framework
which may provide the idea for a common principle of nonequilibrium statistical
mechanics.  While the framework itself is
now on agency footing, making use of it to practical molecular methods is challenging
and largely uncharted territory.  Within the
past a number of years, a couple of courageous research groups have embraced this challenge.
David Limmer’s group right here at Berkeley is certainly one of them. The group’s current
efforts have led to some potential breakthroughs within the research of liquids pushed
out of thermal equilibrium.  In truth, to paraphrase
Hugo Touchette, “The leading research institute for giant deviation principle is
the UC Berkeley Division of Chemistry.” Touchette and members of Limmer’s group
worked intently together over the next days, a testomony to the interdisciplinary
nature of statistical mechanics.

Geissler gave brief closing
remarks to an viewers worn out from the intensity of the convention and ready
for the annual Dim Sum social gathering. Here, one of the thrilling occasions of the
convention occurred: the announcement of poster prizes. As individuals ate,
they tried to guess who the judges have been (which is often not too troublesome)
and who would win (which is much less straightforward to guess). As lunch was winding down, Geissler
referred to as everyone to attention and announced the winners. Their work ranged from research
of the organic networks underlying circadian rhythms, to the thermodynamics
and kinetics of chemical reactions in nanocrystals, to using giant
deviation concept to review nanoscale warmth stream, to pc simulations of polymer
progress. The variety of the profitable shows mirrored the range of
subjects addressed all through the conference.

For Chandler, the statistical mechanics
convention was one of the highlights of the yr. Lots of his scientific
buddies and trainees returned to the convention every year. After Chandler passed
away, Geissler feared that there can be nothing to convey everybody together
anymore. His fears have been assuaged, nevertheless—the group of scientists that Chandler
educated is a strong and lively one, they usually have shaped a wide-ranging, however
shut, group that continues to reconvene at Berkeley. It’s this, Geissler says,
that helped make this yr’s conference, by many individuals’s accounts, one of the
strongest. The embracing of numerous fields of research, coupled with rigorous
discussion and bold exploration of statistical mechanics’ frontiers, provides one
confidence that this area of fluctuations which Chandler championed will proceed
to thrive.


David Chandler, Introduction to Trendy Statistical Mechanics (Oxford College Press, New York, 1987.)


Featured photograph by Leslie Dietterick.

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