What are the chances of Desmond being Charles "Charlie" Widmore's father?

Seems to me that would violate some space-time rule in that the same person can not exist as two physical (and spiritual) beings at the same point in time.

I'm My Own Grandpa
( Lonzo & Oscar )

It sounds funny, I know,
But it really is so,
Oh, I'm my own grandpa.

I'm my own grandpa.
I'm my own grandpa.
It sounds funny, I know,
But it really is so,
Oh, I'm my own grandpa.

Now many, many years ago, when I was twenty-three,
I was married to a widow who was pretty as could be.
This widow had a grown-up daughter who had hair of red.
My father fell in love with her, and soon they, too, were wed.

This made my dad my son-in-law and changed my very life,
My daughter was my mother, cause she was my father's wife.
To complicate the matter, even though it brought me joy,
I soon became the father of a bouncing baby boy.

My little baby then became a brother-in-law to Dad,
And so became my uncle, though it made me very sad.
For if he was my uncle, then that also made him brother
Of the widow's grown-up daughter, who, of course, was my stepmother.

Father's wife then had a son who kept him on the run,
And he became my grandchild, for he was my daughter's son.
My wife is now my mother's mother, and it makes me blue,
Because, although she is my wife, she's my grandmother, too.

Now if my wife is my grandmother, then I'm her grandchild,
And everytime I think of it, it nearly drives me wild,
For now I have become the strangest case you ever saw
As husband of my grandmother, I am my own grandpa!

I'm my own grandpa.
I'm my own grandpa.
It sounds funny, I know, but it really is so,
Oh, I'm my own grandpa.