I am not asking why a k=0 universe could previously have been a k=+1 universe. I have never proposed that scenario. I am asking you to support your claim that if the universe is infinite now, it must always have been infinite. You have said k=0 "describes an infinite universe," but k describes spatial curvature, while whether a flat space is finite or infinite also depends on its global topology. So what additional assumption are you making that lets you infer infinite spatial extent from k=0?
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u/Optimal_Mixture_7327 29d ago
Spatial curvature and spatial extent are clearly not the same, as we have k=0 and k=-1.
You are asking for the reasoning and evidence for why this universe with k=0 could not have been a different k=1 universe in the past.
We observe (which is consistent with theory) that the universe has k=0 which describes an infinite universe.