(News & views on the paper by Yi Xie, RAA, 2013, vol.13, 1-4)
Binary pulsars offer a view into modern physics
(Department of Astronomy, Nanjing University, Nanjing 210093, China)
General relativity, governing the macroscopic domain of gravitation, and quantum mechanics, ruling the microscopic realm of particles, seem not to affect each other. Bridging the gap between them is one of the greatest challenges in the field of modern physics. Some proposed approaches require breaking Lorentz symmetry (for reviews see Kostelecky 2005 and Mattingly 2005). Detecting and testing those violations would shed light on the "theory of everything."
However, these effects are very subtle. With gravitational and non-gravitational disturbances occurring in intrinsically weak gravitational fields, our solar system does not necessarily provide a suitable environment for tests that yield tightly constrained results, sometimes even with highly controlled experiments. A natural option is to step into the environment of binary pulsars. Since being discovered, these systems have been deeply involved in tests of fundamental physics as a clean test-bed with strong fields, e.g. the relativistic periastron in such a system is greater than Mercury's by five orders of magnitude and its orbit observably decays due to gravitational radiation (Kramer et al. 2006).
Xie (2013) tests Lorentz violation with five binary pulsars under the framework of the standard model extension (SME). SME is an effective theory, combining general relativity and the standard model of particle physics to allow possible breaking of Lorentz symmetry (Bailey & Kostelecky 2006). Observational timing data show, in these systems, Lorentz invariance holds at the 10-10 level, which is 10 times larger than previous estimations (Bailey & Kostelecky 2006).
Benefiting from the development of giant radio telescopes, such as SKA and FAST, more double pulsars, and even black hole-pulsar systems, will be available in the not-too-distant future. Together with LHC and other large experiments on the ground, the timing observations from these compact systems might open a new window to modern physics.