Question of the Week: From where did the universe begin? What is the universe expanding into or out of?
My Answer: The beginning of the universe was the beginning of space and time, as the space-time theorems prove and as the Bible declared thousands of years ago. The universe began as an infinitesimally tiny volume of space and time. All the matter and energy of the universe is constrained to the space-time surface of the universe. It is impossible for us humans to detect anything interior to or beyond the cosmic space-time surface. Hence, we cannot pinpoint the location of the cosmic creation event.
The universe is not expanding into empty space. There is no space (or time) beyond the expanding cosmic space-time surface. Neither is there any space or time interior to the cosmic space-time surface. An analogy that may help is our planet. It is a 3-dimensional body where we humans are constrained to the 2-dimensional surface of our 3-dimensional Earth. Likewise, all the matter and energy in the universe is constrained to the 3-dimensional surface of our 4-dimensional universe.