Tired light
The concept was first proposed in 1929 by Fritz Zwicky, who suggested that if photons lost energy over time through collisions with other particles in a regular way, the more distant objects would appear redder than more nearby ones.
[4] Tired light was an idea that came about due to the observation made by Edwin Hubble that distant galaxies have redshifts proportional to their distance.
Redshift is a shift in the spectrum of the emitted electromagnetic radiation from an object toward lower energies and frequencies, associated with the phenomenon of the Doppler effect.
More than a dozen physicists, astronomers and amateur scientists proposed in the 1930s tired-light ideas having in common the assumption of nebular photons interacting with intergalactic matter to which they transferred part of their energy."
[7] Tired light mechanisms were among the proposed alternatives to the Big Bang and the Steady State cosmologies, both of which relied on the general relativistic expansion of the universe of the FRW metric.
[9] By the 1990s and on into the twenty-first century, a number of falsifying observations have shown that "tired light" hypotheses are not viable explanations for cosmological redshifts.
This is known as the Tolman surface brightness test that in those studies favors the expanding universe hypothesis and rules out static tired light models.
For example, Zwicky considered whether an integrated Compton effect could account for the scale normalization of the above model: ... light coming from distant nebulae would undergo a shift to the red by Compton effect on those free electrons [in interstellar spaces] [...] But then the light scattered in all directions would make the interstellar space intolerably opaque which disposes of the above explanation.
[5]This expected "blurring" of cosmologically distant objects is not seen in the observational evidence, though it would take much larger telescopes than those available at that time to show this with certainty.
[5]Zwicky's proposals were carefully presented as falsifiable according to later observations: ... [a] gravitational analogue of the Compton effect [...] It is easy to see that the above redshift should broaden these absorption lines asymmetrically toward the red.
He writes, referring to sources of light within our galaxy: "It is especially desirable to determine the redshift independent of the proper velocities of the objects observed".
[15] Following after Zwicky in 1935, Edwin Hubble and Richard Tolman compared recessional redshift with a non-recessional one, writing that they both incline to the opinion, however, that if the red-shift is not due to recessional motion, its explanation will probably involve some quite new physical principles [... and] use of a static Einstein model of the universe, combined with the assumption that the photons emitted by a nebula lose energy on their journey to the observer by some unknown effect, which is linear with distance, and which leads to a decrease in frequency, without appreciable transverse deflection.
[16] These conditions became almost impossible to meet and the overall success of general relativistic explanations for the redshift-distance relation is one of the core reasons that the Big Bang model of the universe remains the cosmology preferred by researchers.
In the early 1950s, Erwin Finlay-Freundlich proposed a redshift as "the result of loss of energy by observed photons traversing a radiation field".
[17] which was cited and argued for as an explanation for the redshift-distance relation in a 1962 astrophysics theory Nature paper by University of Manchester physics professor P. F.
[18] The pre-eminent cosmologist Ralph Asher Alpher wrote a letter to Nature three months later in response to this suggestion heavily criticizing the approach, "No generally accepted physical mechanism has been proposed for this loss.
"[19] Still, until the so-called "Age of Precision Cosmology" was ushered in with results from the WMAP space probe and modern redshift surveys,[20] tired light models could occasionally get published in the mainstream journals, including one that was published in the February 1979 edition of Nature proposing "photon decay" in a curved spacetime[21] that was five months later criticized in the same journal as being wholly inconsistent with observations of the gravitational redshift observed in the solar limb.
[24] As cosmological measurements became more precise and the statistics in cosmological data sets improved, tired light proposals ended up being falsified,[1][2][3] to the extent that the theory was described in 2001 by science writer Charles Seife as being "firmly on the fringe of physics 30 years ago; still, scientists sought more direct proofs of the expansion of the cosmos".
