quantum mechanics - On the nature of the collapse of the wave function

The collapse of the wave function by measurements is one of the most mysterious properties of quantum mechanics.

1. 
   

   At what scale does the wave function collapse? What are the conditions for a collapse?

   
   


2. 
   

   Can it be made precise?

   
   


3. 
   
   

   Does the collapse happen instantaneously, or is it spread out in time?

   
   


4. 
   

   What is the precise equation for the collapse?

   
   


5. 
   

   Why is the collapse time-asymmetric, and can this explain the arrow of time?