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On episode 10 of the original Cosmos TV series, Carl Sagan mentions that some scientist don't agree that the redshift observed in distant galaxies is evidence of the big bang, stating that probably the doppler effect is not responsible for this effect. What other explanations are there?

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The alternative was around the shift being an actual wavelength shift due to the age of those galaxies. Not sure that argument stacks up any more though (and it was always a bit difficult to argue) – Rory Alsop Mar 15 '14 at 16:50

Tired light has been used as an explanation before, whereby light loses energy whilst travelling through space---a sort of drag effect.

I don't think anyone actually supports it nowadays, though.

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Especially given the new gravity wave observational support for inflationary theory. – called2voyage Mar 20 '14 at 20:50

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