The tired light theory proposes that the redshift observed in distant galaxies is due to the gradual dissipation of light energy as it travels through space. However, it faces several problems, including the perceived brightness of galaxies and the pattern of light emission from supernovae. The big bang theory is favored by most astronomers and cosmologists due to its ability to explain a range of observations, including the Cosmic Microwave Background radiation. The tired light theory is considered fringe physics.
The tired light theory tries to provide an alternative explanation for the redshift observed in distant galaxies, which is conventionally explained by the expansion of the universe. According to this theory, the energy carried by photons of light is somewhat gradually dissipated as they travel through space, resulting in an increase in wavelength, so that light is shifted towards the longer wavelength, less energy, the red end of the spectrum. The big bang theory of the universe explains that this redshift is due to the Doppler effect. The tired-light hypothesis, in contrast, is compatible with steady-state models of the universe. It can be argued that this redshift explanation has not been completely debunked, but the vast majority of astronomers and cosmologists are in favor of the big bang theory, as it clearly explains a number of observations that cause serious problems for the tired-light model .
The theory was first proposed by Fritz Zwicky in 1929, following the discovery that the redshift of galaxies increased with distance. The process by which light energy is dissipated over large distances is, however, problematic. The most obvious process – the interaction of light with particles in space – was quickly dismissed by Zwicky himself, as this would lead to the scattering of light, which in turn would make images of distant galaxies blurry or out of focus. Observations of distant galaxies do not show this blurring. Zwicky preferred an alternative explanation that implies that light is affected by gravity, but this idea remains essentially speculative.
There are a number of other problems with tired light theory, one of which involves the perceived brightness of galaxies. For two similar galaxies at very different distances in a static universe, the calculated surface brightness, based on the amount of light the galaxies actually emit divided by the areas of sky they occupy when viewed from Earth, should be about the same. This is because the amount of light reaching us and the area of the galaxy, as seen from Earth, decreases with distance at the same rate. The observed surface brightness of the galaxies would be reduced by the redshift; however, observations show a much greater reduction in brightness than can be explained by redshift alone. This can also be explained by an expanding universe, where the more distant galaxy is receding at a faster rate.
Apparently it’s not an established thing, and it’s not a crux of discussion.
Another problem with the theory is that it doesn’t explain the pattern of light emission over time shown by supernova events. The time it takes for the light from a supernova to fade, as seen from Earth, increases with the distance to the supernova. This is consistent with an expanding universe, where time dilation effects due to special relativity become more significant with increasing distance and faster recession.
One of the strongest pieces of evidence for the big bang theory is Cosmic Microwave Background (CMB) radiation, discovered in 1956. Tired light theory can explain this background radiation as starlight that has lost energy over time to the point where it has been redshifted to the microwave wavelength, but the theory does not explain the spectrum of the radiation. In both theories, the number of photons remains the same, but in the tired light theory they are distributed over the same volume of space, whereas in an expanding universe the photons have been diluted in expanding space. These contrasting scenarios lead to different spectra for the CMB. The observed CMB spectrum is consistent with the big bang theory.
Apart from the major objections described above, there are a number of other problems for the non-expanding universe implied by the tired-light theory. These include Olbers’ paradox, the proportions of chemical elements observed in the universe today, and abundant evidence that the universe has changed over time. Proponents have attempted to provide answers — consistent with a somewhat tired model of light — to all of these objections, but most scientists in the fields of astrophysics and cosmology regard the theory as belonging to fringe physics.
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