If the universe is expanding, what is it expanding into? Here’s an explanation from theoretical physicist Michio Kaku, who teaches at the City College and the Graduate Center of the City University of New York. Kaku is the author of several books about science and hosts a weekly show on WBAI-FM in New York.
What is the universe expanding into? Where did the Big Bang take place?
To answer these questions, think of an ant walking on the surface of an expanding bubble. Since the ant can only see in two dimensions, asking where the original bubble came from, and where it is expanding, makes no sense to it.
But to us, the answer to both these questions is obvious: the third dimension.
Now imagine we are the ants, on the surface of our expanding universe or bubble.
Then it is clear now that the universe is expanding in hyperspace, and that the original Big Bang took place in hyperspace. If we cannot visualize hyperspace, it is only because we spend our time in the third dimension.