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Physics, Astronomy & Cosmology / Re: Why does red-shift mean the Universe is expanding?
« on: 21/07/2016 15:13:59 »
I've done some more thinking on this issue and came to a different understanding that I had before. Before I was wrong. I erroneously thought that by "expanding universe" that cosmologists were speaking of expanding space and that cosmological redshift was evidence of that. The correct understanding is that by an "expanding universe" galaxies are all moving away from each other. That is to say that if you were in an observer in one galaxy and observed another galaxy then you'd determine that light from that galaxy was redshifted and as such was moving away from you. You'd then determine through observations that the speed of the galaxy was a linear function of the distance to the galaxy.
It should be noted that the expansion of space is consistent with this determination but is not proved by it. Especially since nothing can actually be proved in science. So in the past when I claimed that cosmological redshift implied that space was expanding, I was wrong. It means that the universe is expanding. That space is expanding is another issue. It would take a force other than gravity to restrain a galaxy from moving away from ours even if it was moving at constant speed. Also, if space wasn't expanding then no galaxy would move away from us at speeds faster than the speed of light.
It should be noted that the expansion of space is consistent with this determination but is not proved by it. Especially since nothing can actually be proved in science. So in the past when I claimed that cosmological redshift implied that space was expanding, I was wrong. It means that the universe is expanding. That space is expanding is another issue. It would take a force other than gravity to restrain a galaxy from moving away from ours even if it was moving at constant speed. Also, if space wasn't expanding then no galaxy would move away from us at speeds faster than the speed of light.
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