The Mystery of the Pre-Big Bang Universe

[thomshere]

If all the matter in the universe was compressed into single tiny space before the big bang, where was it? I mean "Out past Orion" would do.

 

[bapowell]

It wasn't. The big bang did not happen in a specific location in a pre-existing space. Big bang cosmology does not address the "bang" itself -- it describes the uniform, isotropic expansion of the universe from an early hot, dense phase. By isotropic I mean that there is no preferred direction to the expansion -- no matter what direction we look, all the galaxies are receding from us more or less uniformly. This is true from the vantage points of people in those other galaxies too! Everyone sees everyone else rushing away from them. The best way to model this is with a balloon -- imagine living on the surface of the balloon (the 2D surface of the balloon is analogous to the 3D space of the universe -- there is no inside of the balloon in the analogy with the universe). The balloon is expanding, and all objects affixed to its surface move apart from each other on account of this expansion. There's no center to the expansion. The big bang was some event that might have started this expansion going, but cosmology doesn't deal with that -- it picks up about a Planck time afterwards, at which time the universe can be thought of expanding and evolving in this way.

 

[Mordred]

Everywhere, the entire observable universe would contract to a single point. Key note I stated Observable. No matter which direction you look, the further you look the farther back in time your looking. So essentially it doesn't matter which direction you choose to look

edit just saw Bapowells reply with the balloon analogy