MadSci Network: Physics

Re: Did time pass slower at the Big Bang than it does now?

Date: Wed Oct 12 14:35:06 2005
Posted By: Ken Rines, Grad student, Astronomy, Harvard-Smithsonian Center for Astrophysics
Area of science: Physics
ID: 1127878349.Ph

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. Here's 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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