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عمومی::
کیهانشناس
In the words of the cosmologist Andrei Linde, "The nonstationary char- acter of the Big Bang theory [based on the] Friedmann cosmological models seemed very unpleasant to many scientists in the 1950s."8 As late as 1959, a sur- vey of leading American astronomers and physicists found that two-thirds of them believed that the universe had no beginning.9 This was forty-three years after Einstein's equations were discovered, and thirty years after Hubble and Humason's results.
There are two reasons why cosmologists often assume the universe to be homogeneous and isotropic.
It is true that on what cosmologists consider "small" scales, such as the scale of the solar system or even that of the Milky Way, the universe is not at all homo- geneous and isotropic.
When cosmologists say that the universe is expanding they in no way mean to imply that it is finite in volume.
Observations suggest that earlier in its history the expansion of the universe was slowing down, but that "recently," in cosmologist's terms, i.e.
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