# Was a universe as small as a atom at one point of time

since the universe is expanding shoudnt the universe have been as small as an atom at one point of time. Also what is the outer limit of the universe and what is present outside a frew centimeters away from this limit.

Time and all matter were created simultanously at the big bang. There is, therefore, no meaning to time before the big bang. Generally accepted theory says the universe had zero size and was infinetely hot at the big bang, and so was considerably smaller than an atom.
The size of the universe increases with time, so again it makes no sense to ask what is a few cm beyond the limit. The limit now will be smaller than the limit in the next microsecond

Time and all matter were created simultanously at the big bang. There is, therefore, no meaning to time before the big bang. Generally accepted theory says the universe had zero size and was infinitely hot at the big bang, and so was considerably smaller than an atom.
The size of the universe increases with time, so again it makes no sense to ask what is a few cm beyond the limit. The limit now will be smaller than the limit in the next microsecond

The Universe is quite possibly infinite, and it definitely has no boundaries, so it’s meaninless to ask “what’s beyound the boundary?”: It’s equivalent to asking “what happens when you walk off the edge of the Earth?”. If it’s infinite now, then it was always infinite, except possibly at t=0 exactly, when we can’t say much of anything meaningful.

What we can talk about, however, is finite regions of the Universe. For any given finite region of the Universe (say, for instance, the portion which is currently visible to us), there was a time when that portion was arbitrarily small. What’s beyond the edges of that portion of the Universe? Other portions, that look pretty much the same.

Unless you subscribe to string theory. In which case the universe was never smaller than about the planck length. However the planck length is about 10[sup]-33[/sup] cm which is a lot less than the size of an atom.

Quoting Graham Green:

Also String Theory requires a lot more than 3 spatial dimensions.