Heaven is the invisible and exact blueprint of what Earth shall one day look like. It is the very culture that we incrementally pray into this visible, earthly realm when we cry, "Thy Kingdom come, Thy Will be done, on Earth as it is in Heaven"! Heaven & Earth are where God and mankind shall continue to dwell together forever. The air that we breathe is invisible, yet it is not far away. The same applies in an even deeper way to our relationship in and with The Father, The Son, and The Holy Spirit! An innumerable company of angels and a great cloud of witnesses (those who have "died" and long to be clothed again with their glorified, physical bodies) also surround us continually in this unseen, yet ever-so-near realm called heaven!
God didn't create Heaven because He was homeless. He created it as an invisible realm which would perfectly complement Earth forever and provide a perfect atmosphere where He could dwell with mankind in His visible creation. The Incarnation of Jesus and His resurrected and glorified, EARTHLY body are everlasting proof of Heaven's inseparability from Earth! Heaven isn't "somewhere out there". Heaven is closer than the air we breathe!