If you have been to fanfiction.net there are quite a number
of theories of neither can live while the other survives. I came
across one from the author "max-wiseacre" whom I borrowed
this expert of his story from. I think one might find it rather
contridicting to the theories above of neither can live while the
other survives ;
"You're getting stronger Harry."
"Well, yeah." Harry said as
if it was obvious. "I'm older, and I've gotten a lot of practice
defending myself recently."
"No, Harry." Dumbledore sighed.
"Your age and experience have increased your skill level, not
your strength. You are getting stronger because Voldemort is getting
Harry didn't know what to make of that
at all. He looked to Lupin to see if he was confused as well, but
his serious expression showed that he knew exactly what Dumbledore
was talking about.
"When he gave you the scar,"
Dumbledore continued, "Voldemort created the means by which
you share your mental connection. When he used your blood to create
his new body, he bound his life force to yours. He is tied to you,
and you to him. As Voldemort's strength increases, so does yours.
It has been steadily happening for some time now. Your recently
acquired ability to see into Voldemort's mind is another example.
Also, just months ago you battled a number of Death Eaters."
"I didn't do it by myself."
Harry protested. "I had help from my friends."
"Friends that you trained."
Lupin added. "None of them would have been able to cope with
that situation had it not been for you."
"But, Peter Pettigrew added his hand
to the potion. Isn't he affected by this too?"
Dumbledore shook his head. "Pettigrew's
sacrifice was of a different nature since he was a willing participant.
His connection to Voldemort was also very different than yours.
I don't believe that Tom fully understood the consequences of the
magic he used. That is, of course, very fortunate for us."
Harry was confronted with a mixture of
emotions. He was somewhat frightened of this new connection with
his enemy, but he was also pleased that he was gaining strength.
Something didn't quite add up though. "Wait a minute, if we
share life force, there's got to be some kind of limit, right?"
"Yes Harry." Dumbledore answered.
"As you grow older, you claim more of that shared power for
yourself. At some point there will not be enough life force for
both of you. One of you will have to go."
"Neither can live while the other
survives." Lupin said ominously.
"I never really understood that part
of the prophecy." Harry said. "I mean, I've been alive
for sixteen years now. Voldemort's still around. If both of us can't
live, why isn't one of us dead already?"
Dumbledore seemed to be prepared for this
question. "Living is more than just existence, Harry. Living
means fulfilling your dreams, enjoying the pleasures of life, being
with the people that you love. We are all alive Harry, but not everyone
truly lives. As long as Voldemort is alive, you will be hunted.
You will never be at peace. Already, Voldemort's presence has cost
you so much. In many ways he has taken what should have been the
best part of your life, your childhood. Conversely, as long as you
draw breath, Voldemort will never be able to attain the level of
power he seeks. He always be threatened by your very existence.
Neither of you can reach your full potential while the other walks
this earth." (Abma)