Editing Tired light (section)

==Specific falsified models==
[[Image:Hubble ultra deep field high rez edit1.jpg|thumb|right|upright=1.5| The [[Hubble Ultra Deep Field]] is an image of galaxies that are in excess of 10 billion light years away. If tired light was a correct explanation, these galaxies would appear blurred in comparison to closer galaxies. That they do not rules out the suggestion that scattering processes are causing the redshift-distance relation.]]
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 blurring
*follow the detailed Hubble relation observed with [[supernova]] data (see [[accelerating universe]])
*explain associated [[time dilation]] of cosmologically distant events.

A number of tired light mechanisms have been suggested over the years. [[Fritz Zwicky]], in his paper proposing these models investigated a number of redshift explanations, ruling out some himself. The simplest form of a tired light theory assumes an exponential decrease in photon energy with distance traveled:<math display="block">E(x)=E_0 \exp\left(-\frac{x}{R_0}\right)</math>where <math>E(x)</math> is the energy of the photon at distance <math>x</math> from the source of light, <math>E_0</math> is the energy of the photon at the source of light, and <math>R_0</math> is a large constant characterizing the "resistance of the space". To correspond to [[Hubble's law]], the constant <math>R_0</math> must be several giga[[parsec]]s. <!--It must be large enough to take into account any deviation from Hubble's law--> For example, Zwicky considered whether an integrated [[Compton effect]] could account for the scale normalization of the above model:

{{blockquote|... 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. [...] it is evident that any explanation based on a scattering process like the Compton effect or the [[Raman effect]], etc., will be in a hopeless position regarding the good definition of the images.<ref name="Zwicky" />}}

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. Alternatively, Zwicky proposed a kind of [[Sachs–Wolfe effect]] explanation for the redshift distance relation:

{{blockquote|One might expect a shift of spectral lines due to the difference of the static gravitational potential at different distances from the center of a galaxy. This effect, of course, has no relation to the distance of the observed galaxy from our own system and, therefore, cannot provide any explanation of the phenomenon discussed in this paper.<ref name="Zwicky" />}}

Zwicky's proposals were carefully presented as falsifiable according to later observations:

{{blockquote|... [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. If these lines can be photographed with a high enough dispersion, the displacement of the center of gravity of the line will give the redshift independent of the velocity of the system from which the light is emitted.<ref name="Zwicky" />}}

Such broadening of absorption lines is not seen in high-redshift objects, thus falsifying this particular hypothesis.<ref>{{Cite web |last=Newton |first=Elisabeth |date=27 April 2011 |title=Prospecting for C IV at high redshifts |url=https://astrobites.org/2011/04/27/prospecting-for-c-iv-at-high-redshifts/ |access-date=4 November 2023 |website=[[astrobites.org]]}}</ref>

Zwicky also notes, in the same paper, that according to a tired light model a distance-redshift relationship would necessarily be present in the light from sources within our own galaxy (even if the redshift would be so small that it would be hard to measure), that do not appear under a recessional-velocity based theory. 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".<ref name="Zwicky" /> Subsequent to this, astronomers have patiently mapped out the three-dimensional velocity-position [[phase space]] for the galaxy and found the redshifts and blueshifts of galactic objects to accord well with the statistical distribution of a spiral galaxy, eliminating the [[intrinsic redshift]] component as an effect.<ref>Binney & Merrifield: ''Galactic Astronomy''. Princeton University Press, {{ISBN|978-0-691-02565-0}}.</ref>

Following after Zwicky in 1935, [[Edwin Hubble]] and [[Richard Tolman]] compared recessional redshift with a non-recessional one, writing that they

{{blockquote|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.<ref>{{cite journal |last1=Hubble |first1=Edwin |last2=Tolman |first2=Richard C. |authorlink1=Edwin Hubble |authorlink2=Richard C. Tolman |title=Two Methods of Investigating the Nature of the Nebular Redshift |date=November 1935 |journal=Astrophysical Journal |volume=82 |page=302 |doi=10.1086/143682 |bibcode=1935ApJ....82..302H}}</ref>}} 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".<ref name="finlay">{{cite journal | last1 = Finlay-Freundlich | first1 = E. | date = 1954 | title = Red-Shifts in the Spectra of Celestial Bodies | journal = Proceedings of the Physical Society A | volume = 67 | issue = 2| pages = 192–193 | doi = 10.1088/0370-1298/67/2/114 |bibcode = 1954PPSA...67..192F }}</ref> which was cited and argued for as an explanation for the redshift-distance relation in a 1962 astrophysics theory ''[[Nature (journal)|Nature]]'' paper by [[University of Manchester]] physics professor P. F. Browne.<ref>{{cite journal | last1 = Brown | first1 = P. F. | date = 1962 | title = The Case for an Exponential Red Shift Law | journal = Nature | volume = 193 | issue = 4820| pages = 1019–1021 | doi=10.1038/1931019a0|bibcode = 1962Natur.193.1019B | s2cid = 4154001 }}</ref> 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."<ref>{{cite journal | last1 = Alpher | first1 = R. A. | date = 1962 | title = Laboratory Test of the Finlay-Freundlich Red Shift Hypothesis | journal = Nature | volume = 196 | issue = 4852| pages = 367–368 | doi=10.1038/196367b0|bibcode = 1962Natur.196..367A | s2cid = 4197527 }}</ref> Still, until the so-called "Age of Precision Cosmology" was ushered in with results from the [[WMAP]] space probe and modern [[redshift survey]]s,<ref>[[George Smoot|Smoot, George S.]] "Our Age of Precision Cosmology". Proceedings of the 2002 International Symposium on Cosmology and Particle Astrophysics (CosPA 02), Taipei, Taiwan, 31 May – 2 June 2002, pp. 314–325.</ref> 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<ref>{{cite journal |first=D. F. |last=Crawford |title=Photon Decay in Curved Space-time |journal=[[Nature (journal)|Nature]] |volume=277 |issue=5698 |pages=633–635 |year=1979|doi=10.1038/277633a0 |bibcode=1979Natur.277..633C |s2cid=4317887 }}</ref> that was five months later criticized in the same journal as being wholly inconsistent with observations of the [[gravitational redshift]] observed in the [[limb darkening|solar limb]].<ref>{{cite journal |last1= Beckers |first1=J. M. |last2 = Cram |first2=L. E. |title = Use of the solar limb effect to test photon decay and cosmological redshift theories |journal = [[Nature (journal)|Nature]] |date=July 1979 |volume = 280 |issue = 5719 |pages = 255–256 |doi = 10.1038/280255a0 |bibcode = 1979Natur.280..255B|s2cid=43273035 }}</ref> In 1986, a paper claiming tired light theories explained redshift better than cosmic expansion was published in the ''Astrophysical Journal'',<ref>{{cite journal|last=LaViolette |first=P. A. |title=Is the universe really expanding? |journal=Astrophysical Journal |date=April 1986 |volume=301 |pages=544–553|bibcode = 1986ApJ...301..544L |doi = 10.1086/163922 }}</ref> but ten months later, in the same journal, such tired light models were shown to be inconsistent with extant observations.<ref>{{cite journal|last=Wright |first=E. L.|author-link=Ned Wright|title=Source counts in the chronometric cosmology|journal=Astrophysical Journal|date=February 1987|volume=313|pages=551–555|bibcode = 1987ApJ...313..551W|doi =10.1086/164996 }}</ref> As cosmological measurements became more precise and the statistics in cosmological data sets improved, tired light proposals ended up being falsified,<ref name=nedwright /><ref name=treu /><ref name=Peebles /> to the extent that the theory was described in 2001 by science writer [[Charles Seife]] as being "firmly on the [[fringe physics|fringe of physics]] 30 years ago; still, scientists sought more direct proofs of the expansion of the cosmos".<ref name="Seife">{{cite news |author=Seife |first=Charles |author-link=Charles Seife |date=28 June 2001 |title='Tired-Light' Hypothesis Gets Re-Tired |url=https://www.science.org/content/article/tired-light-hypothesis-gets-re-tired |accessdate=2016-06-03 |work=[[Science (journal)|Science]] |quote=Measurements of the cosmic microwave background put the theory firmly on the fringe of physics 30 years ago; still, scientists sought more direct proofs of the expansion of the cosmos.}}</ref>