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Expansion of the Universe inside mattar [duplicate]
When talking about the expansion of the universe we usually refer to the Friedman equations so we assume homogeneous and isotropic solution to Einstein field equation which is true on cosmological ...
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Why do matter and radiation densities scale differently in expanding universe, when all matter is energy and all energy is matter? [duplicate]
I sometimes see the first Friedmann equation expressed with different terms for the density of "matter" and the density of "radiation". It is said that with an increase in scale ...
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Would "gravity" and the "law of gravity" have a meaning in a universe without matter?
I was discussing the fact that if there was no matter in the universe, just vacuum and radiation, can we say that anything called gravity wouldn't exist?
In that universe, the Friedman equations ...
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