Origin of Space

Question:

How does something explode into a non existent space? It would seem to me that would be theoretically impossible!

Answer:

In the Standard Big Bang theory, matter does not "explode into a non-existent space". Indeed, matter doesn't explode "into" anything. What happens is that the space BETWEEN things stretches. Here is a standard analogy: Consider a sheet of very stretchable rubber with little bugs on it. If you stretch the sheet in every direction by 50%, then every bug gets 50% farther away from every other bug, even if the bugs are not walking. Bugs that were an inch apart are now and inch and a half apart, while bugs that were a foot apart are now 18 inches apart. The bugs seem to have scattered in every direction, as if they were running away from each other. But it is not because the bugs are moving across the rubber sheet --- they could even be glued onto it. Rather it is because the rubber is stretching.

The space of the universe is like that, except that space has three dimensions and the sheet of rubber has only two. But you could imagine, instead of a sheet of rubber, a volume of stretchable rubber with lots of bugs stuck in it, with the volume getting stretched in every direction. (For the actual universe, do not think of "bugs" but of galaxies located at various places in stretchable space.)

-Stephen Barr