 |
 |
Double Slit versus Overlapping Diffraction
Name: Julie
Status: other
Grade:
Location: Outside U.S.
Country: United Kingdom
Date: April 4, 2011
Question:
Why can't the double-slit experiment be explained by
overlapping diffraction effects? A few weeks ago I watched a
documentary called 'What Is Reality?' with my 15 year old daughter.
After the show we discussed the double-slit experiment because the
conclusions of this experiment, particles mysteriously splitting up
and then interfering with themselves, sounded way too far-fetched
for our liking. As I understand it, diffraction occurs at a single
edge, and if you put two edges close to enough to each other (to
form a slit) then the diffraction effects from the two edges will
make the slit appear like a new light source. If two slits were
close enough together, then there would be areas where the
diffraction effects would overlap. It seems much more plausible to
us that the interference is something related to the overlapping
diffraction zones rather than some mystical wave-like nature of
particles that nobody really understands. Thinking that many people
would have come to this obvious conclusion, we searched the Internet
(including your site) to find out why overlapping diffraction
effects could not explain these results - but to no avail. There is
an article on the Facebook Quantum Physics discussion page called
that mentions a diffraction explanation, but the author
then dismisses it without any good reason. Apparently, if a laser is
aimed close to, but not above, a knife edge, some photons will bend
over the top of the knife edge due to diffraction (demonstrating
that diffraction starts at the front edge). Therefore if the gap
between the two slits were small enough (close to the 'wavelength'
of the oscillating particles in question), then presumably
diffraction would pull some particles through one slit and some
through the other, possibly leading to an interference pattern as
opposed to a diffraction pattern? Furthermore, I have heard that
experiments have been done as long ago as 1987 that prove you can
detect which slit a particle has passed through without completely
destroying the interference pattern - debunking the theory that
particles mysteriously change their behaviour when we 'look at
them'. To the layman, like me and my daughter, a diffraction-based
explanation would make a lot more sense than the mystical
(practically magical) explanation put forward by quantum physicists.
It would explain why firing one particle at a time produces the same
interference pattern, and why the pattern is different to the sum of
two single-slit patterns. I realise that you may need to describe
some advanced concepts in your answer, but I would be very grateful
if you could try, as far as possible, to answer in layman's terms,
that both me and my daughter might understand,
Replies:
You are addressing a problem that has been studied by the best minds
in physics for a century (or so).
By no means are they "Idiots propose an alternative explanation of the
double-slit experiment". That assertion simply does not understand the
problem.
Among other issues are: 1. The interference not only occurs in the
case of "light", but also in the case of what we would call "light" in
laymen's terms, the interference pattern is observed between two slits
separated by a distance that exceeds the speed of light between the two
slits.
(2). The interference has also been observed between what we would call
"particles". So how does the information contained in one slit "communicate
that information" to the other slit if the distance is too great for that
information about its interference is too "slow" to occur before the two
beams reach the slits, before they can "communicate" with one another? And
how does interference occur between "particles" that are larger than the
"double slit". The "double slit" problem has received the attention of the
best minds in physics for about 100 years (or so). People who trivialize the
problem with simple minded "explanations" that the best minds in physics
have grappled with, simply do not understand the problem.
The "double slit" phenomenon has been studied from the
sub-microscopic level to the astronomical level. As scientists (regardless
of our level of study) we must accept the data. Our collective "job" is to
understand the experimental results. You are on sound ground that has
studied this weird behavior of our Universe, but rest (un) assured that the
best minds in physics have not been "duped".
Vince Calder
Click here to return to the Physics Archives
| |
Update: June 2012
|
|
