|MadSci Network: Physics|
Thanks for the question. The key here is that because space and time do
not exist before the Big Bang, the Big Bang happens everywhere in the
universe at the same time. Any clock that existed would be in a huge
gravitational field. Because there are no clocks in small gravitational
fields, there is no way to compare a 'Big Bang' clock to any outside
reference. Thus, 'observers' just after the Big Bang experience time in
the same way we do.
a similar take on this question.
An analogy is the thought experiment of an astronaut crossing the event horizon of a black hole. The astronaut sees her watch ticking 'normally' even though she's in a strong gravitational field, but her friend outside the event horizon sees her about to cross the event horizon with her clock ticking ever more slowly. Similarly, 'observers' at the Big Bang see their clocks tick at one second per second. One set of 'observers' that experiences these conditions are the nuclei of atoms: the density of baryons (protons and neutrons) shortly after the Big Bang determines how long protons and neutrons are close enough together to form nuclei. The relative abundances of these different nuclei tells us how long nucleosynthesis lasted and thus the density of baryons in the very early universe.
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