3pm, NAC 8/130: New York Topology Seminar tea.
4pm, NAC 4/113, New York Topology Seminar talk: Rafael Sorkin,
Physics, Syracuse U., "Is spacetime a past-finite poset?"
11am, NAC 4/113: Ralph Kopperman, CCNY Mathematics, "Approximation of
topological spaces by finite partially ordered sets".
12:15pm, NAC 4/113: Yasuhiro Abe, CCNY Physics, "Gravity on the fuzzy
sphere".
1:30pm, Lunch, Marshak 418S.
2:30pm, CCNY Theoretical Physics Seminar Tea, Marshak 418S.
3pm, Marshak 418, CCNY Theoretical Physics Seminar talk: Rafael
Sorkin, Syracuse U., "Cosmological Constant from Poisson Fluctuations"
There is no registration fee, but please tell Ralph Kopperman, at
rdkcc@cunyvm.cuny.edu
if you plan to attend. This will help us have sufficient food at the lunch and teas,
and sufficient space at the talks.
Ralph Kopperman, CCNY Mathematics,
rdkcc@cunyvm.cuny.edu
Irina Gladkova, CCNY Computer Science,
csivg@cs.ccny.cuny.edu
Alexios Polychronakis, CCNY Physics,
alexios@sci.ccny.cuny.edu
May 6: Rafael Sorkin, "Is spacetime a past-finite poset?"
Abstract: The causal set -- mathematically a locally finite ordered set
or "poset" -- is a candidate discrete substratum for spacetime. I will
introduce this idea and describe some aspects of causal set kinematics,
dynamics, and phenomenology, including, as time permits, a notion of
fractal dimension, a stochastic growth dynamics, and an idea for
explaining some of the puzzling large numbers of cosmology. I will also
mention some questions of mathematical interest that have arisen in this
connection.
May 7: Ralph Kopperman, "Approximation of topological spaces by finite
partially ordered sets".
Abstract: People think of the world as a manifold, but how could one tell
that it is infinite at all? In this talk we discuss the approximation of
manifolds and other topological spaces by finite T0-spaces, which are
essentially finite posets. Early results on this subject are now over 70
years old, but there are many new results on how various properties of the
given infinite space are reflected in the approximation.
May 7: Yasuhiro Abe, "Gravity on the fuzzy sphere".
Abstract: Noncommutative (NC) analogues of compact spaces can be described
by finite dimensional matrices. Gravity on such spaces can then give a
finite mode truncation of ordinary commutative gravity. Focusing on the
case of NC two-sphere (fuzzy sphere), I will present an action for gravity
in terms of matrices. I will also discuss a general structure of some
NC-gravity actions, utilizing the fact that ordinary 4-dim gravity can be
expressed as some topological field theories. The commutative limit will
be mentioned as well.
May 7: Rafael Sorkin, "Cosmological Constant from Poisson Fluctuations"
Abstract: A variety of observations indicate that the cosmological
expansion rate is consistent with the Einstein equations only if one
includes in the latter terms analogous to the once discredited
"cosmological constant", Lambda. Moreover this cosmological term is
comparable in magnitude to the stress energy tensor of ordinary (baryonic
plus "dark") matter. We explore the possibility that Lambda is a residual
quantum effect of an underlying spatio-temporal discreteness of the type
hypothesized by causal set theory. By extending the latter's heuristic
prediction of a fluctuating Lambda to a more concrete ansatz, we obtain a
cosmological ``constant'' which fluctuates about zero, remaining always
comparable to the ambient energy density.