When Edwin Hubble discovered a linear relationship between the distance to a galaxy and its redshift expressed as a velocity, Zwicky immediately speculated that the effect was due not to motions of the galaxy, but to an unknown phenomenon that caused photons to lose energy as they traveled through space. He considered the most likely candidate process to be a drag effect in which photons transfer momentum to surrounding masses through gravitational interactions; and proposed that an attempt be made to put this effect on a sound theoretical footing with general relativity. He also considered and rejected explanations involving interactions with free electrons, or the expansion of space.
Zwicky was skeptical of the expansion of space in 1929, because the rates measured at that time seemed too large. It was not until 1956 that Walter Baade corrected the distance scale based on Cepheid variable stars, and ushered in the first accurate measures of the expansion rate. Cosmological redshift is now conventionally understood to be a consequence of the expansion of space; a feature of Big Bang cosmology.
Other articles related to "tired light, light, tired":
... The tired light effect was proposed by Fritz Zwicky in 1929 as a possible alternative explanation for the observed cosmological redshift ... The basic proposal amounted to light losing energy ("getting tired") due to the distance it traveled rather than any metric expansion or physical recession of sources from observers ... for explaining how photons could lose energy included the scattering of light by intervening material in a process similar to observed interstellar reddening ...
... In general, any "tired light" mechanism must solve some basic problems, in that the observed redshift must admit the same measurement in any wavelength-band not exhibit ... A number of tired light mechanisms have been suggested over the years ... The simplest form of a tired light theory assumes an exponential decrease in photon energy with distance traveled where is the energy of the photon at distance from the source of light, is the energy of ...
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