Let There Be Light, Part I
I'm going to break from tradition today and do something a little different.
Instead of the usual kind of puzzle, I'm going to pose a particularly
intriguing kind of puzzle: an unsolved mystery. I'd like to give the Grey
Labyrinth a little change of pace, and maybe expose a few people to things
they don't normally think about.
Now, when many people think of unsolved mysteries, they think of crop
circles, the Bermuda Triangle, and the Loch Ness monster. But most of
these things are really not that mysterious when examined very carefully
and scientifically. They tend to be really normal things exaggerated by
human's powerful imaginations.
But today we're going to look at a REAL unsolved mystery... (enter Robert
And here it is:
OK, the first mystery is, "What is it?"
No, it's not the opening credits from The Matrix, but good guess.
It's actually an image generated by firing a laser through a pair of
thin slits onto a light sensitive detector.
And this may not impress you, but trust me, this grainy image is the
window onto what could be called the one of the most baffling questions
known to man.
You may know that light, and that's all lasers are, is composed of tiny
particles of energy called photons. Whenever you flip on a light, countless
photons radiate out into the room from the lightbulb, bounce off objects,
and some of these eventually collide with cells in your eyes. This is
how we see stuff.
Individual photons don't have quite enough energy to be visible to humans
unaided. If you were in a completely dark room, it would take a couple
dozen of them hitting the same part of your eye before you would notice
(some animals, incidentally, can see individual photons).
In the image above, photons were fired from a laser through two narrow
slits onto a flat surface producing the image. The tiny dots represent
individual photon strikes. Incidentally, the same pattern emerges no matter
how fast the photons are fired. If you fired one photon from the laser
every day, after a few years the same pattern would appear.
The image to the right shows how the experiment is performed (the size
of the slits A & B have been exaggerated). This isn't a complicated
experiment- the only sophisticated part is the laser. You could use a
laser pointer and see the same effect. The banded image would still be
visible, although your eye couldn't detect the individual photon strikes.
The $64,000 question is, what causes the photons to cluster in those
You may already have heard the answer to this. Sometimes light behaves
like a wave. Waves- like sound waves or even the waves on an ocean- can
create interference patterns: points where troughs and crests cancel each
other out. If we assume that light is a wave, then the banded pattern
is exactly what we would expect to see. Furthermore, this is supported
by other experiments we could perform by changing the number of slits.
This is extremely odd, because to produce the banded interference pattern
shown, a single photon would have to pass through both slits at the
same time, like a wave would. Even more bizarre, additional experiments
can be conducted that would show that the photon is spread out in a wave
all the time- except when we are looking at it. Any time we try to detect
photons, they reliably seem to be in one place.
If in the above experiment we placed detectors at slits A and B, no photon
would ever be observed going through both A and B. In fact, it seems to
be the case that light is always a wave, spread out through space, until
it is observed, when it suddenly is a particle.
So how does a photon know when somebody is looking at it?
Continue on to Part II...