Already is used to say that something had happened earlier than expected or earlier than it might have happened.
As:-
The gate had already closed.
The court had already assembled.
The meeting has already begun.
All ready:-
All ready is not the same as 'already' .
It's simply means fully ready or prepared.
Means all is ready.
All are ready.
Ex:- When is your friend coming? He has all ready come.
Are you all ready ? Yes, we're.