The UniverseEvolution of the Universe |
What is the universe expanding into? |
The whole universe is expanding. That means that all of space is expanding, and every location in space is moving away from every other location in space, unless there is mass nearby creating gravity. So our three-dimensional space cannot be expanding into another three-dimensional space.
One way to think of this is to imagine a balloon being inflated. The balloon is a curved, two-dimensional piece of elastic rubber that is expanding as it is inflated. It is not expanding into another two-dimensional surface, however. Rather, the balloon is expanding into a three-dimensional space. By adding one dimension to this example, our universe is a three-dimensional space that can be thought of as expanding into an extra dimension. In the case of the universe, this is the four-dimensional spacetime that composes the cosmos.