Your room can be measured & observed in many ways. So can the elephant.
If you can determine a way to measure God, then you can determine if He's there or not.
Until that happens, none of you can honestly say that God is in our minds & only in our minds.
You can only believe that.
There is no indication it's anywhere else, so why would we think it was. Besides someone saying it is, which is the same as saying there is a IPU in your bedroom.