Wednesday, February 23, 2011

The Dual Slit Experiment & Hawking's Implications

Below the picture is a conversation between three characters.  Kolin is a British guy, mid-twenties. Jordan is a freshman hockey player for The Big Red (age 18). He has an obsession with science and math.  Brianna is Jordan's friend. The setting is outside Uris library at Cornell University in Ithaca, NY where they go to school (Jordan's the only boy on his team with a major in physics).  The dual-slit enigma is something I love to ponder and I thought this conversation did the job in explaining what it is to those of you who may not be familiar with this "root" of quantum mechanics.

Kolin rubbed his shoulder where Jordan had slugged him.  He looked into Jordan’s eyes and he could see that his friend was deeply concerned that he’d hurt his feelings.  “—Well no need to get gutted about it.  Please, explain this double slit thing then,” he said, “as a starter.”
            “Okay—it’s a famous experiment that demonstrates beautifully the central mystery of quantum theory and before you ask what that is—just hold up.  I want to explain that first so that I don’t lose you here.  There's this standard explanation of what takes place at a quantum level known as the Copenhagen Interpretation.  It attempts to describe the behavior of very small objects because they are a zoo unto themselves.  Are you following what I’m saying thus far?”
Kolin nodded and opened the door to the library for Brianna and Jordan.   “You’re saying that we can’t study atoms the same as we’d observe the regular world,” he clarified.
“More or less,” Jordan said, agreeing with him.  He followed Bree into the library who led the way to the café by turning left.  Because it was lunchtime, there was a line of about seven people for food and a separate, even longer line for coffee.  “Okay, if light travels as particles let’s think of them as bullets for the purpose of envisioning what I’m talking about.”
“Got it—light photons are bullets.”
“Okay, you fire your bullets from a rifle at a brick wall with two holes in it, each hole being the same size and large enough to allow for the bullets to pass through.  Behind this wall is a second wall where the bullets will strike.  After firing off a few rounds you’d expect to see on the second wall two clusters of hits in line with the two holes. This is of course precisely what you get with bullets, so if we get the same result with photons we can conclude irrevocably that they’re particles.”
“That’s not what you get though, is it?” Kolin asked.  “I mean with respect to the light and not the bullets.”
“Not at all,” Jordan stated.  “We get an interference pattern, proving that light acts as a wave.  However, it gets weirder than that.  If the experiment is set up to fire individual photons, so that only one photon at a time goes through, it's logical to predict that we wouldn't expect to see the same interference pattern.  To clarify, what I’m saying is that we’d anticipate a single photon to act like a bullet and that a photon would only go through one hole or another, but not through both at the same time because it’s by itself and there are two holes.”
“I follow you old boy,” he said, winking at Brianna who was obviously enjoying Kolin’s English accent.
Jordan continued.  “If we wait until enough individual photons have passed through to build up a pattern—and this takes millions of photons— we don’t get two clusters opposite the two holes, we get the same interference pattern as before.  It’s as if each individual photon 'knows' that both holes are open and gives that result. Now, if we repeat the experiment, this time with only one hole open, the individual photons behave themselves and all cluster round a point on the detector screen behind the open hole, just as you’d expect. However, as soon as the second hole is opened they again immediately start to form an interference pattern. An individual photon passing through one of the holes is not only aware of the other hole, but also aware of whether or not it is open.”
“That's…fucking strange,” he said, moving up in the line.
“It gets weirder,” Bree said.  “Tell him what happens when we try to catch the photons misbehaving.”
Jordan smiled.  “Alright, if we set up detectors at the holes, looking for electrons passing through them, the light acts as a particle.  It doesn’t misbehave and doesn’t produce a pattern on the screen.  It acts exactly like a particle.  As soon as we aren’t looking, it goes back to acting like a wave again.  The light seems to know when it's being observed.”
“I don’t think I understand what all of that means,” Kolin said.  “Is there a point?”
Jordan nodded, “Yes.  Nothing is real until it's observed.  Or to restate that, until a thing has been observed, it simply doesn’t exist.”
“Hawking thinks that there's something outside of the universe that observes it and forces the universe to collapse into an existence that can be seen by all those inside the universe.  Others believe that the universe exists only so long as we're here on Earth to observe it.  Without us looking at the universe, it wouldn’t exist,” Brianna said.
Kolin didn’t say anything and turned around at the counter. He ordered a breakfast bagel and a mocha for himself; a spinach/red pepper panini sandwich and a large coffee for Jordan.

Now don't you think quantum mechanics is just about as cool as sliced bread?


  1. Wow. I had a conversation with my wife about this just the other day prompted by someone else's blog talking about the same experiment.

    I was explaining to her how my magic system worked without being magic, but based on quantum physics and the idea that matter at its smallest seems to know and react to things that it should not. My novel takes place in an alternate universe where this quantum effect is even more sensitive to influence through language and willpower. At some point our brains cross over into this quantum realm. Nanotubes have been discovered there that some think may be involved in how our subconscious works. Our sense of smell may be tied to quantum tunneling.

    Sorry...I just get excited by quantum physics and I was surprised to see you suddenly bring them up. Great conversation to explain how crazy our universe really is. I like it and it flows well without being in the least confusing. The playfulness of the character also brings it down to earth.

  2. Your magic system for your book sounds amazing Charlie and definitely something that I'd want to read/purchase when it gets published. It's been a real struggle for me to find well-developed magic systems or hard science fiction in books. I dislike (am immediately turned off by) packaged books that gloss over science, math, or other details that to me, are the resounding heart of a story. However, there are few people like me as there is just no demand out there to warrant books of this kind. The science fiction book that I completed and someday want to publish has calculus in it--probably the kiss of death because no one wants to stare at integral or differential calculus, even if it is carefully explained and used in humor or as an essential part to explaining why something is working.

  3. Thanks. I hope I can explain it well and readers buy it. It is scifi but has magic, elves, dwarves, and dragons in it, but I plan to have that all explained somewhat in scientific terms by the end.

    I admit that, despite loving physics big and small, the beauty of chemistry as molecules interact, and the intricacies of biology, math makes my soul numb and part of me die inside. I blame my first grade teacher for making me do a problem in front of the class before I was ready. I have the mind of a biochemist who hates math. This is why I got a degree in English Lit. Ü

    Having said this, I would still read a scifi book with calculus. I would probably skim through the formulas and focus on the ideas behind them and love the book for the story and the characters. I look forward to reading your published book someday soon as well.

  4. Yes, I do think quantum mechanics is about as cool as sliced bread.

  5. Charlie...go check out some quantum entanglement via

    It's a fascinating read.

  6. I was cruising right along with the conversation until the seventh major paragraph ("Jordan continued.") I thought my brain was going to implode. The large block of information, not to mention the heavy topic, made it hard to get through and understand what was being said. Breaking it up might make it easier to consume. By the time I made it to the end I understood, though. You've got me thinking. My question is, what was observing matter and light before animals, people and dinosaurs existed?

  7. It's a difficult topic. The Dual Slit phenomenon fascinates me but without some kind of background on it, the terminology used by scientists can be challenging to relay. Hawking stated that buckyballs are a nickname for the Carbon-60 molecules that were said to produce the same effect and in his book "The Grand Design" there were many illustrations showing just this. His humor was really good too. To date, I think Carbon-60 is the largest form of matter to display this quantum peculiarity. At one time, there were scientists that wanted to see if something as large as a virus would behave this way.

  8. Also Laura, your question "what was observing matter and light before animals, people, and dinosaurs existed?" is the point of the post. Professor Hawking is a proponent of String Theory or more appropriately, M-Theory, which is the existence of multiple universes on these things called "branes". He believes that there just might be something outside the universes that acts as an "observer" and always has been forcing sub-atomic particles to behave appropriately. This opens up a whole new can of worms with the question "what determines shape?" and is related to the mission of C.E.R.N. (the huge particle collider in Europe) which is hunting for the elusive Higgs Boson particle (referred to as the God particle by some).

  9. Michael-

    I adore quantum physics, and your explanation went down like cold-brewed coffee ;).

    I much prefer books where the basis for behavior is based in scientific fact. Mind you, this can be physics or it can be behavioral science. I don't quite comprehend how calculus can tie into a story, but my non-linear mind has little basis for understanding.

    I'm sure you make it clear.

    Thank you for sharing this- sliced bread indeed!

  10. This is fascinating, Michael. Does you write about quantuum mechanics in your stories? You should.

  11. Aweeeeeee You did a fantasic job of this. Chaos theory is what got me started in this adoration of physics. S Hawking Rules! I love his string theory but it still has flaws. Once they get to the point they can represent an infinite wave - things will change. My characters, the Djinn, explain the things they can do with physics. "Microwaves existed before you could make popcorn with them. I exist within laws you can't observe yet."
    LOL I love that you watch supernatural AND know physics!

  12. Hi Michael. Thanks for stopping by the blog and commenting. I totally loved this post because I too think quantum mechanics rocks and often use it as a basis in my stories. One of my backburner stories is built on quantum entanglement. So way to go! I write about science at my blog on thursdays and posted something recently on time 'teleportation.' So cool.