COLLAPSING
A WAVE FUNCTION IN
THE
MOST PRIMITIVE PHYSICS EXPERIMENT EVER
After my last post
about the magic of quantum mechanics and its secrets, I wanted to replicate as
much of the double-slit experiment as I could[1]. And
I did – the simplest of experiments and with the most unsophisticated of
methods. Still, I was able to confirm some preliminary results.
Without
sophisticated lab equipment, I replicated what I could with, first, a laser
pointer that one uses during a lecture or to torture cats until they fall down
and then a laser level (which made more sense since it has a more intense light
beam and is more stable with its 16” length).
Here’s a picture of the setup. (Did I mention that it was primitive?) The laser level is sitting on a 15” ruler with a thumb drive at the rear to level the…uh, level. About 33cm (13”) in front is a business card with the end bent up at roughly 90 degrees to the light beam. I cut two very small slits in the now vertical edge of the card. I made the slits close enough that the light beam would span across both slits. I placed a large white card on a wall 7.32 meters (24 feet) in front of the beam as a background. (The distance from the beam origin to the slits or from the slits to the background are not critical to the results.)
The setup I described above is a system, granted a
very unsophisticated system, but still… Further, while conducting the various
experiments, the possible results of each – in this case, only two – will be a
function of all possible outcomes.[2]
Because we are investigating the possible outcomes of a system involving light
waves, all possible outcomes are termed a wave function. As we learned
from this video,
if we observe which of the two slits a photon passes through, we have collapsed
the wave function. That is, we have removed all possibilities of outcomes
by observing one outcome. Obviously, we cannot observe all
possible outcomes at the same time.
When
the beam was allowed to pass through one slit only, the pattern shown here was
displayed on the background. This is no surprise since it reflects the shape of
the slit in general with the photons displaying their particle-like properties.
Remember, if the observer knows which slit the
photon(s) is passing through, the wave function collapses and the result is a
“clump.”
When
the beam was allowed to pass through both slits, the following pattern appeared
on the background 7.32 meters away.
This is the expected result. The laser light beam is
passing through both slits and therefore setting up a wave interference which
results in the pattern shown here, much like the pattern that water through the
two slits would. It is important to understand a couple things about this
simple experiment. First, there is no way I could determine which slit each photon
went through, although it can be determined – even controlled – in a
sophisticated, well-funded laboratory setting. Second, if I could do so, the
pattern would be two “clumps,” as physicists so eloquently term them, one
behind each slit, similar to the simulated image below.
So, the question in many minds is, “Okay, what does
this have to do with me?”
If you are reading this on a computer, it has
everything to do with you. If this is printed on paper from a laser printer, it
has everything to do with you. If you use a cell phone, have undergone one of
many surgeries including ocular, use Blu-ray DVDs, use a flat-screen TV, or
many other routine activities in everyday life using transistors and IC chips,
you are immersed in the world of quantum mechanics.
Quantum mechanics is confusing – even to the most
knowledgeable physicists. As physicist James Kakalios states, “. . . One of the most amazing things about quantum
mechanics is that you can use it correctly and productively even if you're
confused by it.”[3]
As you might intuit, there is much more to the story
and I’ll address some of that in the next post. There are some very strange
possibilities out there, folks. For example, just to tickle your brain, the
chance that a photon will land on the background at a specific spot depends on
a probability wave. This means that there is a probability – a very low,
but non-zero probability – that one or more photons emanating from the laser
when I ran my primitive experiment landed on the surface of a planet or moon in
a faraway galaxy!
[1]
You
might ask why I’d replicate something that’s been done countless times before. Not
only do scientists replicate previous results to further confirm them, but
running the same experiments provides a different perspective than those who
came before. This may result in other hypotheses since no person thinks the
same as any other. Also, and most significantly, starting with the basic
experiments gives the experimenter a more solid foundation into the phenomena
being addressed. As a lab technician in a former life, I know how it works.
[2]
Don’t be
intimidated by the word, function. It simply means a relationship
between a set of initial conditions and all possible results where one input or
specific condition results in only one result. It’s a mathematical equation or
expression that puts all those words in mathematical shorthand. Otherwise, expressed
as a bunch of words, mathematics, physics and all other technical fields would
be very awkward and, more importantly, open to inaccurate interpretations.
[3]
Matson, John. “What is Quantum Mechanics Good For?” (interview with physicist
James Kakalios) https://www.scientificamerican.com,
Scientific American, Nov. 2, 2010, https://www.scientificamerican.com/article/everyday-quantum-physics/.
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