Gravitational redshifts in cosmology
Gravitational redshifts in cosmology
- Event time: 1:00pm
- Event date: 8th August 2014
- Speaker: Nick Kaiser (IfA, University of Hawaii)
- Location: Higgs Centre Seminar Room, Room 4305, James Clerk Maxwell Building (JCMB) James Clerk Maxwell Building Peter Guthrie Tait Road Edinburgh EH9 3FD GB
Event details
Abstract
Wojtak, Hansen and Hjorth (Nature, 2011) have measured the long-predicted gravitational redshifts in galaxy clusters using Sloan Digital Sky Survey data. The effect is very small, corresponding to a velocity shift of only ~10 km/s in clusters with internal random motions ~600 km/s, but is in good agreement with general relativity predictions and possibly in conflict with some alternative gravity theories. Zhao, Peacock and Li (2012) showed that the measured shift includes a competing special relativistic effect - the transverse Doppler (TD) redshift - which is of similar magnitude.
In this talk I will describe how there are two more kinematic effects that need to be considered in interpreting these observations; a `light cone' effect that augments the TD shift and a competing effect caused by modulation of the surface brightness of galaxies by relativistic beaming.
I will discuss how these observations constrain gravitation theory, and along the way discuss some issues concerning the interpretation of astronomical redshifts in a broader context. I will also mention how the physics here echoes an interesting debate that took place in the 60's regarding the transformation of thermodynamic variables under Lorentz boosts.
About Higgs Centre colloquia
The Higgs Centre Colloquia are a fortnightly series of talks aimed at a wide-range of topical Theoretical Physics issues..