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Physics
Special and General Relativity
Did the Big Bang separate space and time
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[QUOTE="PeterDonis, post: 5510287, member: 197831"] First, you should understand that these are two different questions about two different models that physicists use. The first one is a question about a model that is used in cosmology to describe the universe as a whole; this model is called "Friedmann-Lemaitre-Robertson-Walker spacetime" (or sometimes "FLRW" or "FRW" spacetime for short). The second one, given your illustration using a black hole, is a question about a model that is used to describe isolated objects; this model is called "Schwarzschild spacetime". The reason this is important is that the right answers to the questions you are asking are only going to apply to those specific models; they will not tell you general truths about gravity that work everywhere, in all situations. If you want to understand gravity in full generality, you need to understand the theory that underlies both of the above models (and all the other spacetime models that physicists use). This theory is General Relativity, and the general equation that underlies all of the models is the Einstein Field Equation. Both of the models I described above are particular solutions to this equation (and they are different solutions, so they have different properties). With those cautions out of the way, here are quick answers to your two questions: (1) The "Big Bang" is a term that describes the hot, dense, rapidly expanding state that the universe was in at the end of the inflationary epoch. The entire universe was in this state, which is why we say that the Big Bang happened everywhere. But this state did not stay the same; the universe rapidly expanded and cooled and got less dense, and has been doing so ever since. So the Big Bang is not "always" because it was not a static state; it rapidly changed into something else. (Note that your underlying intuition here seems to be that "relativity says space and time are the same, so everything that applies to space should also apply to time". This intuition is wrong, and the answer I just gave illustrates that. But to really understand why it's wrong, you need to learn the general theory, not just particular solutions.) (2) Nugatory's answer, "both", is correct, not only as a general statement about possible solutions to the Einstein Field Equation, but as a statement about the specific solution you asked about, the spacetime of a black hole (Schwarzschild spacetime). [/QUOTE]
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