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Universe may not be expanding at all - it's just that the mass of all the particles within it is steadily increasing, a cosmologist has suggested.
The conventional model of cosmology is that most galaxies recede from one another as space itself inflates like the surface of a balloon - which would explain why other galaxies appear red-shifted from our own galaxy's point of view.
However, Christof Wetterich, a theoretical physicist at the University of Heidelberg in Germany, has devised a different cosmology in which the universe is not expanding but the mass of everything has been increasing.
Such an interpretation could help physicists to understand problematic issues such as the so-called singularity present at the Big Bang, he said.
"I think it's fascinating to explore this alternative representation. His treatment seems rigorous enough to be entertained," Journal Nature quoted Hongsheng Zhao, a cosmologist at the University of St Andrews, UK, as saying.
In the 1920s, astronomers including Georges Lemaitre and Edwin Hubble found that most galaxies exhibit a redshift - and that the redshift was greater for more distant galaxies. From these observations, they deduced that the Universe must be expanding.
But, as Wetterich points out, the characteristic light emitted by atoms is also governed by the masses of the atoms' elementary particles, and in particular of their electrons.
If an atom were to grow in mass, the photons it emits would become more energetic. Because higher energies correspond to higher frequencies, the emission and absorption frequencies would move towards the blue part of the spectrum. Conversely, if the particles were to become lighter, the frequencies would become redshifted.
Because the speed of light is finite, when we look at distant galaxies we are looking backwards in time.
If all masses were once lower, and had been constantly increasing, the colours of old galaxies would look redshifted in comparison to current frequencies, and the amount of redshift would be proportionate to their distances from Earth. Thus, the redshift would make galaxies seem to be receding even if they were not, he noted.
Prior to inflation, according to Wetterich, the Big Bang no longer contains a 'singularity' where the density of the Universe would be infinite.
Instead, the Big Bang stretches out in the past over an essentially infinite period of time. And the current cosmos could be static, or even beginning to contract, he said.