There is a part of the bible where Jesus says something like the kingdom of heaven is smaller than a mustard seed. Does this mean that heaven exists in the sub-atomic world?

I think you should first examine the context but here is the expression....

Lk 13:18,19 He said, "What is the Kingdom of God like? To what shall I compare it? It is like a grain of mustard seed, which a man took, and put in his own garden. It grew, and became a large tree, and the birds of the sky lodged in its branches."

As you can see he said 'It grew' and therefore is no longer a mustard seed....maybe now it's a pumpkin lol? No you can see the point I'm making though....he describes an 'expansion' does he not?

Ben

Heaven does exist in other dimention that more delicate than material that we can see but it's right where you are.

that explains so well but what exactly does it mean? as my thought it toward that message it means heaven is result of something good and then it glows up to be a nice place to live. and I believe in that sentence tries to tell us that we should have that seed which is believing in Christ and we shall have heaven. but for me, even we don't believe in Christ we can do some good things to let it glow up and be nice to others, a beautiful place to live.