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One reason to believe that the background is expanding rather than objects are moving in an static background is that this would require objects to move through space at superluminal speeds. A second reason would be that what ever force (which is proportional to the distance in space) is driving this accelerated expansion would be likely to dilute if objects were moving through space and the expansion should slow ; however if the expansion is through the creation of more space then the expansion can remain proportional to the distance which agrees with observations.
Imatfaal explanations are very good. The best way to see it is in 2D with a stretching rubber sheet or an inflatable ball. Before, observations was best modeled by a uniform stretching. Now, with dark energy, the stretching rate is linear. But we look to the past and we don't have a unified theory yet, so i doubt the official timeline of the universe is near perfection...
Would it be fair to say that the observed cosmological red-shift is wholly attributed to the Hubble law which means that the Universe is expanding and that expansion is accelerating?
Quote from: MikeS on 05/09/2011 09:48:01Would it be fair to say that the observed cosmological red-shift is wholly attributed to the Hubble law which means that the Universe is expanding and that expansion is accelerating?No. There is other evidence - if the universe was static we would expect to see a certain time line as we looked further away, but we see a more accelerated change; events that we expect are further away and dimmer than would be predicted in a static sold state or simply expanding universe.Remember that dark energy is a catch-all term for all the explanations that could drive universal accelerated expansion and that the cosmological constant is by no means agreed upon