Talk:Tired light/3O Sources
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[edit] Routledge Companion
Barrow, John D. The Routledge Companion to the New Cosmology. Peter Coles, editor. Routledge (2001). ISBN 0-415-24312-2. (pp 308-09) states:
"REDSHIFT (z) The change in position of emission lines or absorption lines in the spectrum of electromagnetic radiation produced by a galaxy, quasar or other extragalactic object. Because the observed wavelength is greater than the emitted one for objects moving with the expansion of the Universe, the redshift is positive. The simplest way to see how this effect arises it is to regard the wavelength as being stretched by the cosmological expansion as it travels from source to receiver."
"The redshift of a distant source therefore acts as a direct measure of the time when the light was emitted. It is possible to solve the Friedmann equation that determines the expansion rate of the standard Friedmann models to calculate the behaviour of a(t); this can then be used in the Robertson-Walker metric to calculate a relation between redshift z and cosmological proper time t at emission. Because redshifts are directly observable quantities, many cosmologists refer to the various stages of evolution of the thermal history of the Universe in terms of redshift rather than of time. For example, the cosmic microwave background radiation was produced at an epoch corresponding to a redshift of the order of 1000, the epoch of domination by radiation at z of the order of 100,000, and so on. The Big Bang itself happened at the origin of time where the scale factor was zero, the redshift of which was therefore infinite.
This interpretation of redshifts in terms of the expansion of the Universe is accepted by most cosmologists, but there was once considerable controversy over this issue. For example, quasars have been observed at such high redshifts, corresponding to lookback times greater than 90% of the age of the Universe, that their energy output must be phenomenal. (As of the end of 1997, the astrophysical object with the highest known redshift was a pair of gravitationally lensed galaxies with a redshift of 4.92.) This, together with apparent associations between quasars and galaxies with very different redshifts, has led some cosmologists—including Geoffrey Burbidge and Halton Arp (see quasar)—to question the cosmological interpretation.
Alternative interpretations are possible because there are other effects beside the Doppler effect (which is the origin of the cosmological redshift) that could in principle produce a redshift. For example, according to Einstein's theory of general relativity, strong gravitational fields give rise to a gravitational redshift: light loses energy has it climbs out of a gravitational potential well. Other ideas included the so-called tired-light cosmologies based on alternative theories of gravity which do not produce an expanding Universe at all. There have also been claims, hotly disputed by mainstream scientists, that quasar redshifts are quantised. If this is true, it would again be difficult to explain within the framework of standard cosmological models based on general relativity."
[edit] Anthropic
Barrow, John D. & Tipler, Frank J. The Anthropic Cosmological Principle. Oxford University Press (1988). states on page 236:
As early as, 1874, Thomson [Lord Kelvin] and Tait had claimed to observe a systematic decrease with time in the velocity of light, c, of 8 km s-1 century-1. By the early 1930's several other authors had claimed to measure a significant diminution in c over a span of fifty years. Variations of this type had been incorporated into unconventional cosmological models by Stewart, Buc and Wold to create the first 'tired light' explanations for the redshifting of spectral lines in distant nebulae relative to their values on earth. A decay of the photon energy, E = hc/λ, as c changes during the transit time between emission and detection for light of wavelength A was invoked to explain the dependence of redshift with distance from its source in preference to the standard explanation based upon Doppler recession. The same qualitative effect could be achieved superficially by supposing the magnitude of Planck's constant decreases in time, or a secular increase in the wavelength of radiation takes place. Various suggestions of that type were made in the period 1935-7 by Chalmers, Nernst, and Sambursky. In 1931, Sir James Jeans proposed an interesting scenario, wherein, in effect the atomic size decreases in time. This would, he claimed, give the appearance of an expanding Universe,
“ Another possibility . . . is that the Universe retains its size, while we and all material bodies shrink uniformly. The redshift we observe in the spectra of the nebulae is then due to the fact that the atoms which emitted the light millions of years ago were larger than the present-day atoms with which we measured the light--the shift is, of course, proportional to distance. ” According to this view, the galaxies are not receding because of a universal Hubble expansion but rather, everything inside the galaxies, including us, is shrinking! If the atomic mass increases but the charge of the electron remains constant then the electrons will orbit, closer to the nucleus (until they fall within the range of the nuclear force). This is similar to the electrons simply occupying a higher energy state and so radiation emitted by these 'smaller' atoms during an atomic transition would have higher frequency than that from a less tightly bound atom. The atoms we now see in remote galaxies would be larger than those here and so the light we receive from them would be redder than that seen in the corresponding local emission spectra.
Not surprisingly, dispute arose over the meaning of change in dimensional quantities like c or h. When examined critically it is clear that only a variation in dimensionless quantities possesses an invariant meaning. (We shall have more to say about this later). For this reason, supporters of the conventional expansion hypothesis were fairly critical of these heretical ideas. Lemaitres contested Jean's suggestion (which has also been resurrected recently by Hoyle incidentally). He remarks that
“ it is clear that any artificial expansion could be provided by arbitrarily varying the units of length, time and mass . . . the expansion of the Universe is in some sense relative to the whole set of essential properties of matter being assumed to be constant. ” Writing some years later, Eddington argued that all such alternative explanations for the redshift were without a logical foundation:
“ The ratio of the wavelength to the period H α light is the velocity of H α light. Thus it follows from the definition of the ultimate standards of length and time that the velocity of light is constant everywhere and everywhen. Alleged experimental evidence for a rather large change of the velocity of light in the last 70 years has been put forward. From the nature of the case there can be no such evidence; if anything is put in doubt by the experimental results, it is the agreement of the standards used by the various observers. More baleful, because it has received more credence, is the speculation of various writers that the velocity of light has changed slowly in the long periods of cosmological time, which has seriously distracted the sane development of cosmological theory. The speculation is nonsensical because a change in the velocity of light is selfcontradictory. ”
