Tired Light - Specific Falsified Models

Specific Falsified Models

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:

where is the energy of the photon at distance from the source of light, is the energy of the photon at the source of light, and is a large constant characterizing the "resistance of the space". To correspond to Hubble's law, the constant must be several gigaparsecs. 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 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.

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:

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.

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

... 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.

Such broadening of absorption lines is not seen in high-redshift objects, thus falsifying this particular hypothesis.

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". 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.

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 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.

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." 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. Browne. 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," Still, until the so-called "Age of Precision Cosmology" was ushered in with results from the WMAP space probe and modern redshift surveys, 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 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. In 1986 a paper claiming tired light theories explained redshift better than cosmic expansion was published in the Astrophysical Journal, but ten months later, in the same journal, such tired light models were shown to be inconsistent with extant observations. As cosmological measurements became more precise and the statistics in cosmological data sets improved, tired light proposals ended up being falsified, 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", however tired light theories still appear occasionally in speculative journals.