No one said anything about a vessel. Why should there be one? If I send up a bomb and explode it in space to make a bang, there is no need for a container.

You might argue that there is no bang either, not in space anyway, but you would be wrong. There would be a bang within the expanding gas at least, and at any collision between the expanding gas and anything it impinges on.

well, according to m-theory, there are multiverse ie., several universes. these universes are like the bubbles in water. they move, collide, form new universes & expand. expand? and this is what you want to get. actually, these universes expand as bubbles in the water expand. from my viewpoint, i think that they expand in space like bubbles. then, sometimes, they expand to such extend that they collide with other universes & this is the fate of universe. by these, a new kind of universe generate & this is the bigbang in that universe. again, expand & the whole process went on.