Young's Slit Experiment
In Thomas Young's double slit experiment:
How is it possible that an electron takes multiple paths through the
Dosen't this violate the laws governing constant mass?
The electron does not take multiple paths through the slits.
Interference fringes result from the mere fact that the different paths
the electron *could* take (from the source, through the slits, to a
particular spot) have different lengths. Very strange -- spooky, even
-- but very well established by experiment, and mimicking precisely
the pattern one would expect if a wave spreading out from the source
encountered those slits.
Well, it's somewhat misleading to say that the electron "takes multiple
paths through the slits." It would be more accurate to say that it acts as
if it goes through both slits at once. What actually happens is that an
electron fired at the barrier either makes it through the slits and to the
screen on the other side, or it doesn't. If it makes it through, it strikes
the screen somewhere. You can't predict exactly where it will strike the
screen. When it strikes the screen somewhere, you can't know for sure which
slit it passed through to get there.
When enough electrons land on the screen, their impacts form a
diffraction pattern as if they are waves, not particles. Waves, as you
know, can pass through two slits at once, forming two wavefronts that can
interfere with each other. How can individual, non-interacting electrons
form a diffraction pattern unless each one somehow passes through both
slits? Oddly, even though electrons are detected at only one spot, they act
in a way as if they are waves. Otherwise, how would they form a diffraction
Sounds weird, but it's true. Quantum mechanics is like that.
Richard E. Barrans Jr., Ph.D.
PG Research Foundation, Darien, Illinois
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Update: June 2012