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S4g. How real are Feynman's paths?
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In Feynman's version of quantum mechanics, amplitudes are calculated 
as sum over all possible classical paths a particle (or a system) 
can take in a classical phase space. 

The paths in the Feynman picture of QM should not be regarded as real.
All possible paths are about as real as all possible books that can
be written, or - closer to physics - all possible items in a 
statistical ensemble modeling a classical ideal gas. Of course only one 
state is realized, not all conceivable ones; all others are just there
to compare to and compute probabilities. 

In QM things are slightly more complicated, however, since the 'true' 
path is smeared by the uncertainty principle. (Even in the many-wolds 
interpretation, quantum objects have no sharp paths, while the paths 
integrated over in a path integral must be perfectly accurate.)

The paths are just calculational devices that stop to exist once a
different approach to computations are taken. This is why I don't 
ascribe any reality to them. The real objects remain present in
_any_ sensible description; the unreal one's don't.