# Sidney Bludman

- Prof. Emeritus Staff Physicist, Lawrence Berkeley Laboratory and Lecturer, University of California (1952-61)
- Professor of Physics & Astronomy, University of Pennsylvania (1961-99)
- Visiting Fellow, Institute for Advanced Study (1956-57)
- Institute for Theoretical Physics, University of California, Santa Barbara (1985, 1997); Center for Particle Astrophysics, Berkeley (1990-93)
- Institute for Particle and Nuclear Astrophysics, Lawrence Berkeley Laboratory (1994-95)
- Institute for Nuclear Theory, University of Washington (1996)
- Deutsches Elektronen-Synchrotron, Hamburg (1998- )
- Visiting Professor Imperial College (1967-68)
- Tel-Aviv University (1971-72)
- Hebrew University (1976-77)
- Guggenheim Fellow (1983-84)
- Scientific Director, Les Houches Summer Institute on Supernovae (1990).
- Member of the Arts and Sciences Medal Awards Committee, Franklin Institute Visiting Professor, DESY Theory Group, Hamburg (1999- )
- Visiting Professor, DESY Theory Group, Hamburg (1999-2006)
- Visiting Professor, Universidad de Chile, Santiago (2006- )
- Visiting Professor, University of Maryland (2012- )

M.S., Ph.D. Yale University (1948, 1951)

A.B. Cornell University (1945)

**Neutrinos at the Particle Physics-Astrophysics Interface**

High energy astrophysics/cosmology deals with the testing and application of nuclear and elementary particle physics under extreme conditions that obtain only in compact objects or in the very early Universe. Bludman has studied the birth, evolution, and death of stars and of the Universe. He has studied astrophysical and cosmological constraints on neutrino masses and lifetimes and the role of neutrinos in the atmosphere, the Sun, supernovae, and the early Universe.

**Solar Neutrinos and Stellar Structure**

The core structure of cool stars, like the Sun, follows directly from pressure equilibrium and is insensitive to radiative opacities. This enabled Bludman and Kennedy to obtain a simple analytic fit to the mechanical and thermal structure of the present Sun, to adequately describe and interpret the energy and neutrino production in standard and non-standard solar models. In addition, they found a variational formulation for the four equations of mechanical and thermal equilibrium, that permits a new, global approach to stellar structure. Recently, they extended Noether's theorem, identifying variational symmetries and conservation laws, to scaling symmetries of the equations of motion. In mechanics, the resulting nonconservation law is the Law of Clausius, leading to the Virial Theorem. In the hydrostatics of self-gravitating spheres, the nonconservation law leads directly to well-known properties of polytropes and of chemically homogeneous stellar cores.

**Stellar Collapse and Supernova Explosions**

At the end of nuclear burning, massive stars suddenly implode, emitting 10-15% of their rest mass in neutrinos, ejected matter, and light. The general features of the type II supernova were dramatically confirmed in the supernova which exploded in a neighboring galaxy in 1987, but the explosion mechanism - involving nuclear physics, neutrino physics, radiative hydrodynamics, and general relativity- remains obscure. Bludman has focused on the role of neutrino transport in making a supernova explosion. Together with Cernohorsky and Smit, he found a simple analytic algorithm for the transport of neutrino flux and energy in a core collapse explosion.

**Accelerating Universe**

The homogeneous cosmological expansion, which measure only kinematic variables, cannot determine the dynamics driving the recent accelerated expansion. The minimal fit to the data, the flat Î›CDM model, consisting of cold dark matter and a small cosmological constant, interprets Î› geometrically as a classical spacetime curvature constant of nature, avoiding any reference to quantum vacuum energy. (The observed Uehling and Casimir effects measure any forces due to QED vacuum polarization, not any quantum material vacuum energies.) An Extended Anthropic Principle, that Dark Energy and Dark Gravity be indistinguishable, selects out flat Î›CDM. Prospective cosmic shear and galaxy clustering observations of the growth of fluctuations are intended to test whether the recent cosmological acceleration is static or moderately dynamic. Even if dynamic, observational differences between an additional negative-pressure material component within general relativity (Dark Energy) and low-curvature modifications of general relativity (Dark Gravity) will be extremely small.

- Is Cosmological Acceleration Driven by Classical Space-Time Geometry?, Intl. J. Mod. Physics D 17, 1-28, (2008). [Get article]
- Gravitational Vacuum Energy in our Recently Accelerating Universe, J. Physics Conf. Ser. 161, 012026(2009). [Get article]
- Invariant Relationships Deriving From Classical Scaling Transformations, with Dallas Kennedy (2010). [Get article]
- Scale Invariant Stellar Structure, with Dallas Kennedy (2010). [Get article]
- Kepler's 1604 Supernova and Star of Bethlehem [Get article]
- Measuring Dark Energy Parameters to Select Theoretical Models [Get article]