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