I remember being 13 and sitting in a boring math class where the teacher was drilling meaningless equations into the numbed skulls of my peers. This was a common situation and during these times. I often found myself mentally floating off into a very strange state of mind where I entertained whatever thought floated feather-like into my periphery, no matter how crazy.
One day in particular, amidst the mosquito-like hum of an overhead projector and the less than enthusiastic Ben-Steinian tone of voice my teacher taught with, I caught the word "probability" embedded in the lecture and it sent me off on another tangent. I started thinking about probability and its nature. I tried to imagine exactly what probability was. It seemed to me that trying to solve probability was admission of something that fundamentally conflicted with what everyone took to be true. I felt that the very fact that more than one outcome was possible from a given situation obviously meant that there was more than one reality. The example I immediately pointed to was a deck of cards.
Take a shuffled deck of cards, placed face down. The fact was that there were 52 different realities each of which had one of 52 different cards on the top of the deck. And the only way to know which reality you were existing in was to look at the top card. If the universe only hosted one reality, a single experience simultaneously shared by every living thing in existence then there would only be one possibility for which card was on top of the deck. And mathematically solving the probability of which card it was would yield a result of 100 for the correct card and 0 for the 51 other cards. But math didn't work like that. Math gave each card an equal shot at being on top.
I talked about this to my math teacher. But, seeing as how I wasn't exactly the best student and was currently pulling a 19% in the class, he turned my idea into joke and said that I would have ample time to ponder the nature of the universe while I was flipping beef patties at Burger King. Then he sent me home with a note to my mom about how I don't pay enough attention in class. I wish I could remember this insignificant man's name, I would buy him a whopper and fries.
Ever since that day I have been fascinated by probability. I have always felt like the concept of probability was a false wall. Something that kept the minds of mankind and the implications of mathematics corralled into a nice, orderly line where we all lived in one nicely packaged universe and shared one existence. So imagine my elation when I picked up the spring, 2001 issue of 2600 and read the article Computing With The Fabric Of Reality by Chris Silva aka Sarah Jane Smith.
This article was all about the possibility and applications of quantum computers. While I found quantum computers to be intriguing, the real value I found in this article was the explanation of a concept called "quantum superposition". This concept seemed to be exactly what I was trying to explain to my math teacher when I was 13. Reading the article I found myself excited and unable to sit still. I couldn't read fast enough. I read every paragraph dozens of times, trying to understand everything I could. I still, weeks later pick up the article and read it every day. I will try to explain quantum superposition the best I can.
The theory of quantum superposition states that any given particle which is unobserved and has more than one possible state is simultaneously in all possible states until it is observed. Consider the deck of cards once again. We can not see the face of the top card. Thus we do not know which card it is. There are 52 possible cards that it could be. The top card is therefore in a state of quantum superposition until it is observed. This means that the top card is all 52 cards at once, until we observe it, at which point the laws of probability and possibility decide which card it actually is. I say possibility because sometimes a particular state is not possible. For instance, if we remove the 2 of clubs from the deck it is no longer possible for the top card to be the 2 of clubs.
It turns out that I was not exactly right with my ideas, but I was definitely on the right track. The deck of cards is great for explaining the concept, but it is not considered to be a true application of quantum superposition. True superposition happens only on an atomic level. Objects as large as a playing card are not believed to inhabit more than one universe. It is the individual particles that compose the card, which are believed to have the inherent ability to shift from one universe to another based on probability. The top card of the deck is determined by the shuffling process and is only ever in one state.
Even though I was ultimately incorrect with my original idea, that a playing card simultaneously inhabits 52 different realities until somebody flips it over and looks at it. I still gain a great deal of satisfaction from the fact that the fundamental concept of this idea has been tested and turns out to be true. Above all, I can't wait to see how we can harness this knowledge and use it to super-power our computational abilities.
For a better understanding of this, and a much more thorough explanation, check out the spring 2001 issue of 2600. There is also an amazing paper entitled Quantum Superposition, Necessity and the Identity of Indecernables written by Allan F. Randall. This paper is available at the url http://home.ican.net/~arandall/Indiscernibles/.
December 3, 2002: Oneiromancer
says in The Deck of Cards Quandary: Quantum Superposition you assert that objects as large as a deck of cards do not display quantum superposition. They do. Everything does. However, the only way for us to measure superposition, interference, becomes so messy for large objects that it is impossible. However, that does not in principle mean that it is not superimposed. So you're right to the core. Just -- your being right beyond the subatomic level doesn't yet have practical consequences for us.