I know that a PC can have multiple network adapters each of which with different network identifiers (IP,MAC etc.). 

My question is, can a certain PC have more than one active default gateway? And if so, how does the PC (or better say the OS) knows to what adapter use for any given packet?


Question: Scalar product of coherent states 
Answer: Use the Baker-Campbell-Hausdorff identities. They are your best friends for this. Two links, for example, http://planetmath.org/encyclopedia/BCHFormula.html , and http://www.mathematics.thetangentbundle.net/wiki/Linear_algebra/Baker-Campbell-Hausdorff_formula . Wikipedia has a page, http://en.wikipedia.org/wiki/Baker%E2%80%93Campbell%E2%80%93Hausdorff_formula , that has an example under the heading "Application in Quantum Mechanics" that is pretty much what you need.
Best, Peter.