Q: Why does light choose the “path of least time”?  Physicist:
Light travels at different speeds in different materials.  When
you shine a beam of light from one material into another (like
from air to water) it bends in such a way that the path it takes
from one point to another requires the least possible time.
Taking a straight line means traveling through a lot of the
"slow material". Traveling through lots of "fast material" to
make the path through the slow material as short as possible
means taking a longer path overall (and taking more time). The
path of "least time" is in between.  This should come across as
deeply spooky.  A particle that somehow “scouts the future” and
then picks the fastest path to get where it’s going seems
impossible.  And to be fair: it is.  The crux of the problem is
(as with damn near everything) wave/particle-ness.  Particles
can’t magically know what the shortest path will be, but waves
find it “accidentally” every time.  First, check out the path
that the “principle of le