1. How can you place the space that we know as a 3 dimensional space in the space that is the universe and which in turn can best be represented (as I understand it) as the surface of a balloon being inflated (being the expansion of the universe)? The surface of that balloon only has 2 dimensions, right?
2. Would it also be possible to take a shortcut around the inside of that balloon as being a hole in time?
Answer
You should not imagine the space at all, that is not a moral imperative. You can try.
Our space has (at least) three dimensions. If we also consider time as a dimension (and there are good reasons to do so), then we are at a minimum of four. And our imagination is limited to the three spatial dimensions with which we are familiar. That model with the balloon tries to help us to understand with our three-dimensional imagination how we should see a four-dimensional time-space. Indeed, in that MODEL, space only fills two dimensions, because the third is time. The ‘real’ space-time is then a four-dimensional sphere instead of a three-dimensional one, but we cannot make a picture of that.
Any ‘shortcut’ as you suggest can only be physical if time advances along that path.
Your question illustrates the strengths and weaknesses of models. They can help us understand something, but should not lead a life of their own regardless of the question that was initially asked.
Answered by
Prof. dr. Christopher Waelkens
Astronomy
Old Market 13 3000 Leuven
https://www.kuleuven.be/
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