Barbara Ryden

Barbara Ryden, Ohio State University

Interpreting Hubble’s Law

Observational cosmology provides an excellent platform for teaching important concepts in physics. In part, this is because modern observations create a "gee-whiz" reaction that captures students' imaginations. In part, however, it's because even familiar warhorses of cosmology, such as Olbers' Paradox and Hubble's Law, demonstrate how our underlying assumptions affect our interpretations of data.

Focusing on Hubble's Law as my example, I'll dissect how (and why) Edwin Hubble leapt from measured redshifts and fluxes to interpreted velocities and distances. Then I'll examine how, at levels from Astro 101 to graduate courses, Hubble's Law can lead to discussion of the nature of space and of motion. In particular, since a Hubble-like relation can occur both in Newton's universe and Einstein's universe, Hubble's Law provides an opening for discussing the conceptual and observational differences between the Newtonian concepts of gravity, space, and time, and the general relativistic concept of spacetime.