Unifying Classical mechanics and QM?

[misogynisticfeminist]

Is there a particular theory and a set of equations which unify classical mechanics and QM? I know Feynman did a little bit of this in QED, but that mainly talked about classical optics and photons AFAIK. And if there isn't, what impact will this have on physics as a whole if there was one?

 

[ramollari]

Classical mechanics is an approximation of quantum mechanics under certain conditions, isn't it?

 

[marlon]

Is there a particular theory and a set of equations which unify classical mechanics and QM?

this is not necessary because indeed QM is an extension of classical mechanics. You are forgetting about the socalled regimes in physics. When the object's dimension gets smaller and smaller, classical physics does not do a good job in explaining such small-scaled phenomena. This is the point where QM takes over. Now, when working with QM, we absolutely need to recover the results of classical mechanics when the distance-scale gets higher and higher so that in this limit, Newtonian results are recovered. This is the correspondence principle.

I know Feynman did a little bit of this in QED, but that mainly talked about classical optics and photons AFAIK. And if there isn't, what impact will this have on physics as a whole if there was one?

This is not true. QED is a FIELDtheory that explains the nature of EM-interactions. It is born as an unification of special relativity and QM. And yes the results of classical EM (like the Maxwell-equations) are certainly incorporated in this model. "What QED is for photons, QCD is for quarks"

So basically you always need to take into account both regime and correspondence principle...Unifying is not just about throwing some theories together...


regards
marlon