Lorentz symmetry is the symmetry behind Einstein's theory of special relativity. It states that the laws of physics are the same for all nonaccelerating observers. In general relativity, Lorentz symmetry becomes a local symmetry, which holds in local Lorentz frames. CPT is a combined discrete symmetry which basically says that particles and antiparticles obey the same laws of physics. These symmetries are linked by a famous theorem -- the CPT theorem -- which states that Lorentz-invariant theories describing local particle interactions are also CPT invariant.

It has recently been realized that in possible quantum theories of gravity (including string theory and loop quantum gravity) Lorentz and CPT symmetry might be broken on ultra-short length scales called the Planck scale. The conventional wisdom is that to probe physics at the Planck scale one must perform experiments at extremely high energy -- out of reach of any accelerator -- making these experiments completely unfeasible. However, Robert and his collaborators have shown that another way to search for new physics at the Planck scale is by examining extremely low-energy Lorentz and CPT tests but with very high precision.

Robert's work has turned up a number of new candidate signals in experiments with electrons, muons, hydrogen and antihydrogen, experiments with a spin-polarized torsion pendulum, and clock-comparison experiments in space. A number of recent and upcoming experiments are now making measurements looking for these signals. In addition, Robert and collaborators are also investigating the effects of Lorentz violation in the context of gravity. These investigations will also likely lead to new ways of testing Einstein's relativity theories.

Additional Information on Lorentz and CPT Symmetry:

• Frequently asked questions about Lorentz and CPT symmetry
  
  
• Animations illustrating Lorentz and CPT symmetry
  
  
• J.P.L. Press Release (2002)
  
  
• Colby Magazine article (2005)
  
  

• Theoretical Physics - particle physics, atomic physics, quantum physics,
  string theory, gravity, and cosmology.
  
  

• Publication List:
  
  

• Sunrise Professor of Physics, Colby College, 2003 - present

• Associate Professor of Physics, Colby College, 1996 - 2003

• Chair, Department of Physics and Astronomy, Colby College, 1994-99, 2000-01

• Assistant Professor of Physics, Colby College, 1990 - 1996

• Postdoctoral Fellow, Indiana University, 1988 - 1990

• Ph.D., Theoretical Physics, Rockefeller University, 1988

• M.A., English Literature, Columbia University, 1984

• M.A., Physics, Princeton University, 1980

• B.A., Physics, New York University, 1978

Courses Taught at Colby:

• PH 111 Galileo to Einstein

• PH 143 Honors Physics

• PH 145 Foundations of Electromagnetism and Optics

• PH 241 Modern Physics I

• PH 242 Modern Physics II

• PH 332 Thermodynamics & Statistical Mechanics

• PH 335 General Relativity & Cosmology

• PH 338 Nuclear & Particle Physics

• PH 431 Quantum Physics

• PH 432 Advanced Quantum Physics