How can the universe be infinite (in the case of a “flat universe” or an “open curvature”, I think that is the case), if it originated from the big bang? Unless the original universe was already infinite from the moment of its creation? After all, it is impossible to evolve from a finite universe to an infinite universe in a finite time span. But if the universe was infinite from the beginning, how should we interpret the big bang?
Answer
An infinite universe is one that you can find no end to, no matter how far you step. A finite universe is one where you return to the same place after a long walk. Like on the two-dimensional surface of the spherical Earth.
Perhaps your question has something to do with an image in which the expansion of the universe takes place ‘in’ an infinite space that was already there ‘before’. But universe and space-time go together, the expansion is an expansion of space rather than an expansion in space. In the sentence described above, space was infinite from the beginning, even if it began as a point. And ‘out of space’ is a contradiction in terms.
Answered by
Prof. dr. Christopher Waelkens
Astronomy
Old Market 13 3000 Leuven
https://www.kuleuven.be/
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