Complexity: Open Questions

What are the right theoretical tools to address complexity?
How does one connect models to reality?
What are artifacts of the model?
What if the model is harder to understand than the physical system it is describing?
How to make quantifiable, falsifiable predictions (following Popper)?
How do the macroscopic systems properties depend on the microscopic interactions of the agents?
What are the unifying concepts?

For a general outline on complexity theory go to the j-node section.