Kenneth Libbrecht is chairman of
the physics department at the California Institute of Technology.
He works on the LIGO gravity detector, whose purpose is to capture
gravitational waves from astrophysical events such as supernovae
and black holes. In his spare time, Dr. Libbrecht builds specialized
chambers for studying the formation of snow crystals, a phenomenon
still poorly understood. He is the author of The Snowflake:
Winter’s Secret Beauty.
In this lecture, Dr Libbrecht will talk about the physics of snow
crystals and explain his recent discovery of the mechanism behind
ice spikes.
Meteorological definitions distinguish a
single “snow-crystal” from the more general term “snowflake,”
which may also apply to clusters. In the 1930’s, the Japanese
physicist Ukichiro Nakaya set out to study ice formation in the
laboratory, attempting to grow crystals suspended on a thread. Individual
specimens proved elusive however, for the threads became encrusted
with frost. Nakaya tried strings of cotton and silk, he experimented
with wires and spider’s web. Eventually he found the solution
in a strand of rabbit’s fur, where natural oils discouraged
the nucleation of frost and allowed the development of isolated
flakes. The result of this research was his famous snowflake
morphology diagram.
Following in Nakaya’s footsteps, Ken Libbrecht is trying
to understand the mechanics of snow crystal formation at varying
degrees of temperature and humidity. In his CalTech lab, Nakaya’s
rabbit hair has been replaced by a purpose designed, pressure-cooker-sized
chamber, in which, using a 2000 volt electric current, Libbrecht
grows needles of ice. His crystals sprout like blossoms from the
ends of these stalks - miniature florets of ice mere millimeters
across. Libbrecht’s research focuses on crystallization at
the boundary of the quasi-liquid layer which surrounds all ice structures,
and has led to his theory of “structure dependent attachment
kinetics.”
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