If we are to use the methods of physics, we can prove that the space aliens cannot come from anywhere but here
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Not so. By many reports from a number of qualified folks.
There are other dimensions to consider.
There are propulsion; space bending etc. sorts of phenomena which we evidently are only in kindergarten about, if that.
I don't think we know much about physics at all.
We see lots of things through the Biblical "glass darkly."
It matter not at all if distance or time is a constraint. It matters not at all if the space aliens can traverse the entire visible universe or beyond in an instant. Best assume they can. It matter not at all how many dimensions there are, let an infinite number be as is done in thermodynamics.