I was asked this question recently and had to give a fairly concise answer...
An intriguing question, a question over which sadly blood has been split and many thousands of words spoken and written.
The shortest and most honest answer is that nobody knows.
However, let us back track and see what we do know.
Jesus is a historically credited figure with extant evidence for his existence. Equally historically verifiable, is his crucifixion.
From here we then have to ask further questions and the first one is why out of the thousands upon thousands of men crucified do we remember Jesus. What makes his crucifixion something that we are still discussing thousands of years later? A crucifixion that has inspired artist and poets across the world and rather oddly the cross has become a fashion icon worn by many people.
Then we need to examine the accounts of the resurrection and come to a decision. If they are false then we still have the puzzle over why we are still talking about Jesus and his death. However, in some ways that would remain just a peculiarity.
If on the other hand, you accept the evidence, as millions upon millions of people of every type and every status, rich, poor, slave, billionaires and those bankrupted, plus junkies and super models and all stations in between have done! If you accept the resurrection then the whole world changes – your whole world changes. (I would say as someone who believes in the resurrection that the world has changed whether you believe it or not!)
From here, we can then begin to examine the teachings of Jesus. We can look further at what some of the early Christian taught about heaven. All of this contained in the New Testament. From there we can reach back further and explore the Old Testament. And right there in the first Book of the Bible we have a story of God creating the heavens and the earth.
Then skip along to the last Book in the Bible, Revelation and chapter 21 where we read -
‘And I saw a new heaven and a new earth: for the first heaven and the first earth were passed away; and there was no more sea. And I John saw the holy city, new Jerusalem, coming down from God out of heaven, prepared as a bride adorned for her husband. And I heard a great voice out of heaven saying, Behold, the tabernacle of God is with men, and he will dwell with them, and they shall be his people, and God himself shall be with them, and be their God.’
This picks up what Jesus taught in his ‘model prayer’ – The Lord’s Prayer...
‘Your Kingdom Come, Your will be done, on earth as it is in heaven.’
So heaven is the realm where God lives and earth is the realm designed for humans and the whole of the created order. One day they will be wonderful combined and then to read further from Revelation
‘ And God shall wipe away all tears from their eyes; and there shall be no more death, neither sorrow, nor crying, neither shall there be any more pain: for the former things are passed away’