Where did the Big Bang happen?

[hoshang]

The answer is 'everywhere and nowhere'.

First of all, remember that our entire foundation is the cosmological principle, telling
us that no point in the Universe is special. If there were a particular point where the 'Bang'
happened, that would clearly be a special point and violate the cosmological principle.
Rather, space and time themselves were created at the instant of the Big Bang (unlike a
conventional explosion where the material flies through pre-existing space). If we take any
point in the present Universe and trace back its history, it would start out at the explosion
point, and in that sense the Big Bang happened everywhere in space.

In another sense, the location of the Big Bang is nowhere, because space itself is
evolving and expanding, and it has changed since the Big Bang took place. Imagine the
Universe as an expanding sphere; at any instant 'space' is the surface of the sphere, which
is becoming bigger with time (again I'm thinking of a two-dimensional analogy to our real
three-dimensional space). The place where the 'Bang' happened is at the centre of the
sphere, but that's no longer part of the space, the surface of the sphere, in which we live.
In particular, being constrained to the surface of the sphere means we are unable to 'point'
to the place where the explosion is supposed to have happened. However, all the points in
our current space were once at the centre of the sphere, when the Big Bang took place.
what do you say about this?

 

[HallsofIvy]

You are making the error of thinking that the 'big bang' did happen at a specific point in a space that existed before the big bang. That is an error because space itself was created in the big bang- previous to the big bang there was no "place' for it to occur. Every point in space was "where" the big bag occured.

 

[Mark M]

As HoI said, the big bang didn't just 'happen'. It's the state that the universe began in, in the standard picture.

However, this is a very good explanation for explaining why the big bang wasn't some bomb going off in space.

 

[bcrowell]

We have a FAQ about this: https://www.physicsforums.com/showthread.php?t=506991

 

[Naty1]

what do you say about this?

The first section lacks evidenciary proof; the rest is a reasonable reflection of our best
understanding...except this:

However, all the points in our current space were once at the centre of the sphere,

does anyone know of any model that suggests this??

 

[Mark M]

does anyone know of any model that suggests this??

I believe the OP is referring to the fact that a big bang singularity (as predicted by GR) would involve the universe having zero total size. However, we know that this can't be true, because quantum mechanics forbids a particle from being stuffed into a space smaller than it's wavelength (think uncertainty principle). So, we conclude that GR can't handle extremely small distances at extremely high energies.

 

[Chronos]

My guess is space, time and the known laws of the universe were all emergent, so I consider it risky to assume any of the usual rules applied to the birthing process.

 

[Mark M]

My guess is space, time and the known laws of the universe were all emergent, so I consider it risky to assume any of the usual rules applied to the birthing process.

Well, the situation doesn't just come up at the big bang. GR has similar issues with the center of a black hole, as you know. They're both the territory of quantum gravity, which we'll need to describe the big bang in any meaningful way. Loop quantum cosmology has made significant progress in this region in recent years.