We should describe the notable models but I think the issue whether cosmic time zero is a real moment in time is a non issue any serious physicist knows that in all variants this pertains to a model of which we don t know how well it fits reality which really means how well it conforms to present and future observations and they also know that in models with a genuine mathematical singularity the accepted experimentally confirmed laws of physics break down anyway rendering claims of this being real experimentally unfalsifiable and hence meaningless Lambiam