Colloquium: Understanding Gravitational Redshifts in Clusters of Galaxies and in Cosmology
In 2011 astronomers reported in Nature a measurement of the gravitational redshift in massive clusters of galaxies. The results appeared to agree with Einstein's General Theory of Relativity, and to exclude some alternatives.
It turns out that this effect is rather more complicated than was initially thought and raises a number of interesting fundamental questions about the nature of redshifts in astronomy. For one thing, the result challenges the common notion of redshifts being ‵caused by the expansion of space’. Second, there are several special relativistic effects that need to be considered. One of these is the well known transverse Doppler redshift, but two others were unexpected.
I shall describe the observation; show how it provides a playground for exploring some aspects of special relativity and cosmology; and discuss what it tells us about alternative theories of gravity.
地點：香港大學 莊月明物理樓 LG1/F P4演講廳
講者：Prof. Nick KAISER (Institute for Astronomy, University of Hawaii)