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The explanation of the observed redshift evolved since Hubble. At first the shift of visible spectral lines to longer wavelengths was ascribed, on the suggestion of Abbot Lemaître, to the Doppler’s effect owing to distant galaxies flying away. But now it is rather a matter of raisins in a rising loaf of bread. As clearly said : “ The cosmological redshift is more correctly thought of as a result of the ongoing expansion of the universe, which stretches the wavelength of light passing between galaxies. Emissions from more distant objects, having travelled for a greater time, become more redshifted than radiation from nearer sources.”

That seems simple, but rises immediately one question :

(A)- There is no reason a priori to limit this expanding phenomenon. We can’t say that stretching applies to space and radiation alone and not particles which fill space and which are after all made up with radiation. We are therefore compelled to admit that such particles were also smaller in the past. Since radiation is being produced by their interactions - by electron quantum jumps from one orbit to another within atoms - we can think in first instance that if these orbits prove smaller, radiation was emitted with shorter wavelengths. This explains that light has shifted towards blue at the very beginning of emission phase, all the more so since such emissions are more ancient. This original blueshift is exactly balanced by the expanding redshift, and we should not be able to observe any shift. In order to save the explanation of such redshift -due to space expansion- anyone must prove that only space and radiation stretched while particles didn’t. In other words we must know where the bread finishes and where the raisins begin.

In a recent article (2) the authors tempt to precise that limit explaining that coherent objets such as galaxies are not sensible to expansion of space due to gravitational force that holds components in position. Very well, but that rises new questions :

(B)- If space expands, we can't say nor if, neither how, gravitational force varies ; it is altogether a property of space. That gives uncertainty on evolution of galaxies.

(C)- And what about matter or living beings which are not keep in shape by gravitational force but by electromagnetic one ? This last force is supposed to come from the same origin as radiation, and if electromagnetic radiation feels expansion of space, electromagnetic force could feel some effect too.

(D)- And going further, things are far from being simple indeed. Emission of radiation is not necessarily related in a linear way to dimensions of the transmitter. Balmer’s formula, to quote but one, sets the emission spectrum of the hydrogen atom :

ν = R(1/p2-1/n2),

where R = 2π2me43.

In addition to quantum numbers, three constants are being involved : electromagnetic force e, Planck constant h, and electron mass m. Without entering into details we can underline :

- Electromagnetic force, e. Its ratio with gravitational force shows a large number of about 1039. This may lead some people to think that it is linked to universe dimensions, and that it has not always been of the same value in an expanding universe. (CF Dirac’s Large Number Theory).

- Electron mass, m. The well-known formula, hν = m0c2, associates it to a frequency, that is the inverse of a wavelength, which should have varied with universe expansion in the same way as other radiation did.

- Light speed c. It is thought to be a constant wherever and whenever we measure it in the Universe. But light is right a radiation strechted by expansion while wavelengths grow longer. So in order to keep speed steadfast, frequency must lessen with the same ratio. Are we sure of that ? Absolutly not. On the contrary physics teaches us that in a medium, the speed of waves propagation, including light ones, much depends on physical conditions of this medium, as temperature, density etc.. When we stretch à guitar string for instance, the faster propagation of vibration increases the frequency and then raises the sound. To point out that is from common sens of physicist, but the constancy of the speed of light is a postulate of Relativity theory. And to call it in question is to call Relativity in question.

- Structure fine constant. Furthemore, h, e and c are the components of Structure Fine Constant which, according to certain scientists, is varying with time. So must do one or more of these constants.

All that makes that theory of space expanding is difficult to hold. Its supporters can't assert, nor radiation was always emitted at the wavelength we now observe, neither, if it varied, it did it in direct ratio to changes of other sizes of Univers : due to the fact that several constants are involved, it could follow the expansion non linearly. In order to say more, one must precisely analyse how those values, and perhaps others, could evolve, or prove they stood.

The explanation of the redshift by Doppler's effect does not rise so much questions.

Personally, I would rather be in favour of a phenomenon of ageing of radiation. I will soon write a page on that, meanwhile I send back to the process of formation of light radiation.

(1)- (Craig J. Hogan and all- Revolution in Cosmology, in Scientific American magazine, January 1999).

(2)- (Charles Lineweaver and Tamara Davis in Pour La Science Avril 2005).

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