How come Astronomers Do not spend time seeking a vast area of absolutely nothing to prove their theory of the big bang?

Lets assume the big bang theory is fact.  It happened .  The entire universe as we think we know it emerged from a tiny dot  that exploded.   Now we also have the thesis of an accelerating expanding universe.  Deductions then tell us that if this big bang really happened there ought to be an area  in the cosmos that  is now completely devoid of any mater what so ever.  It seems to me that the proof of the big bang is find that incredibly empty space at the center of everything.