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I've read that astronomers have received a light (a photon) 13 billion years old. Here's my question:

If we start to turn the clock backwards all matter, energy, etc should start heading to the original "point" of the Big Bang. Then how come that the photon we have received and the stuff that makes planet Earth end up at the same location (the Big Bang), for the same amount of time (13 billion (+ a few millions but who cares)) by traveling with different speeds? (light travels with maximum speed, matter travels with less speed, etc)

EDIT: I know that the stuff that makes planet Earth was not even here, say 10 billion years ago: small particles form bigger ones, bigger ones gets shattered to smaller ones, etc. But imagine a hydrogen atom that some how managed to survive all the way up to here intact straight from the Big Bang (of a few million years after it). How come the atom gets here before the photon?

PAUSED: It looks like there are a lot of things I need to learn (or relearn) before asking the same question again.

yordan
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When I was in high school I wondered the same thing. According to the Inflation models space time expanded exponentially between $10^{-36}$ and $10^{-32}$ seconds after the Big Bang. According to the theory a piece of space the size of a nucleus expanded to the size of a galaxy (rough order of magnitude, possibly even larger) in that very short time. Mathematically this can be modelled by a parameter in the space-time metric that increases, the metric usually assumed is that of deSitter space, a homogenous positively curved space. In this geometric picture the initially large curvature rapidly flattens out. This is well motivated as this kind of homogenous and isotropic structure with very little variation is seen at large distances by astronomers. In other words the current observed large scale structure is believed to be best explained by assuming that it is a gigantic magnification of an initially tiny region.

The crucial point is that that as space itself is expanding during inflation, even points that initially were close together become causally separated. In particular light reaching us from galaxies far away is from the time just after inflation. The Planck satellite and a number of experiments at the poles are looking for evidence of gravitational waves from the inflationary time, which would substantiate the inflation theory further.

orbifold
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