The kinematic origin of the cosmological redshift
Abstract
A common belief about big-bang cosmology is that the cosmological redshift cannot be properly viewed as a Doppler shift (that is, as evidence for a recession velocity) but must be viewed in terms of the stretching of space. We argue that, contrary to this view, the most natural interpretation of the redshift is as a Doppler shift, or rather as the accumulation of many infinitesimal Doppler shifts. The stretching-of-space interpretation obscures a central idea of relativity, namely that it is always valid to choose a coordinate system that is locally Minkowskian. We show that an observed frequency shift in any spacetime can be interpreted either as a kinematic (Doppler) shift or a gravitational shift by imagining a suitable family of observers along the photon's path. In the context of the expanding universe, the kinematic interpretation corresponds to a family of comoving observers and hence is more natural.
- Publication:
-
American Journal of Physics
- Pub Date:
- August 2009
- DOI:
- 10.1119/1.3129103
- arXiv:
- arXiv:0808.1081
- Bibcode:
- 2009AmJPh..77..688B
- Keywords:
-
- 04.00.00;
- General relativity and gravitation;
- Physics - Popular Physics;
- Astrophysics;
- General Relativity and Quantum Cosmology;
- Physics - Physics Education
- E-Print:
- Accepted for publication in Am. J. Phys. Many small changes from previous version, but basic argument remains unchanged