Since I returned to the working world I am reminded daily that quantum mechanics is everywhere and how great life is when you don't have to worry about it. Just about everyone who doesn't work at a particle accelerator lab doesn't worry about quantum mechanics and for all intent and purpose, that's everybody. And most times I wish I was an everybody.
If you're a farmer, you should thank your gods the only parasitic impact you need be concerned with are varieties of mites and birds. If you're a banker, you don't spend much time thinking about Schroedinger's wave functions and existence probabilities, money just is. If you're in the process of getting hit by a bus, the infinitesimal yet finite probability you may tunnel through the bus instead of being smooshed under its tires never occurs to you, nor should it.
To quote Steinbeck, for most people the world "runs in greased grooves". There are eminently predictable results for our actions. Even if we're watching The Matrix we don't worry about the uncertainty principle or wavefront refraction when we watch Neo blasting programmatic knots of consciousness played by Australian actors with stilted American accents.
That's because most of our world is macroscopic. Things we care about are our size, or comprehensible in terms of our size. Even Mount Everest can be seen in one single eye-filling vista. M31 in Andromeda is light-months across, and light-years away, and we can still imagine it. We can imagine how long it takes to climb Everest even if we've never done it. And even though nobody has ever left the solar system, we know in our hearts the trip to M31 would be even longer and more boring than riding in a decrepit Soviet-era passenger bus across the Gobi desert.
For the most part, things we care about every day are measurable in terms of fractions or multiples of our body parts. An elephant is one and a half to two humans tall. A housecat's back hits us at mid-shin. Most people could jog a mile in 15 minutes, or walk it in 30 without even consciously computing the distance was only a couple hundred strides.
And we all know you should never try to eat something bigger than your head.
Quantum mechanics evades our intuition. Even though we know it happens, we have no way to intuit what it means for matter to "tunnel" through other matter. We imagine a baseball flung at a brick wall that upon impact does not bounce off, but rather, appears on the other side without a scratch and keeps going. But that mental image is so illogical and such a poor physical model for actual tunneling that if we accept it in order to develop an intuition about the process, we begin to make serious errors in technical judgement.
Because the truth is that nobody knows what inertia is, just that it works and explains a lot of things in our lives. Similarly, nobody knows what tunneling is, but that it's happening all around us and we never see it or experience it until we try to do something absolutely insane, like connect our satellite receiver box to our television to make Tivo work. And then, if our lack of intuition about quantum tunneling stops our set-top box from recording all "The Simpsons" episodes, we get pissed.
So somebody has to worry about these things for you, and that person (among many) is me. I am an electrical engineer, so I worry about quantum mechanical effects in electronics.
It wasn't always this way. In the halcyon days of my youth, the physics of electronics was simple. We connected odd shaped slabs of metal and plastic with wires, and voila--there's a radio. A television. A microwave oven.
But in the new millennium, the physics of our hubris has finally caught up to us. We've been trying to cram more stuff into smaller spaces for years. We call this integration. Integration means your hand held calculator is now a computer is now a Palm Pilot which now acts as a cell phone, which now acts as a video camera, which now acts as a video game. Forget about the fact that 30 years ago the Christian church deemed the first handheld calculator the work of Satan (because the numbers were red)--now we embed calculators in sunglasses and banana peels so that our children can tell us they don't need to know how to add because there have always been electronic calculators, and always will.
Scrunching more functionality into smaller places requires smaller electronics. And in the quest to make things smaller we've run straight into quantum mechanics.
Here's why: the thickness of a typical human hair is about 200 microns. A micron is the millionth part of a meter--so if you can imagine 200 of them stacked end-to-end you have something the thickness of one of the hair strands in your comb. This is pretty intuitive. We can see hair, especially when it gets in our soup.
Now, the thickness of the average wire in a very modern integrated circuit--the kind that are in your super-gigahertz Pentiums or your satellite TV decoder box, are 130 nanometers wide. Speaking in terms of averages, then, the typical wire inside that black rectangle that sits on the motherboard of your computer is about 1500 times less thick than your hair.
Let's try to intuit this. If an integrated circuit wire was laying on its side on 34th street in Manhattan and it was 6 feet tall, a human hair laying next to it would be eight times higher than the Empire State Building.
Said another way, the difference between the thickness of your hair and the size of a wire, or a transistor, inside an integrated circuit is bigger than the difference between Bill Cosby's height and the depth of the Grand Canyon.
Clearly, Bill Cosby's world is different from the Grand Canyon's. In electronics, that difference shows up in very weird ways.
As I said before, in the old days, we connected devices with wires. We used to think of wires as "pipes" for electricity. Now, we all knew the analogy broke down in places. For instance, if you have a pipe coming from a reservoir bringing water to a city, and you break the pipe, the water comes out and spills all over the place.
That's not true for electricity. If you break a wire, the electricity doesn't spill on the floor. In fact, if you break the electrical pipe, the electricity simply ceases to exist. It becomes a "potential" to exist, instead of actually
"being". We call this potential to be--voltage. The more electricity wants to become real, the higher the voltage.
Current is the flow of electrons, which normal people call electricity. Unlike water in a pipe, electricity only exists when the pipe exists.
Now all this worked just fine when things were big--when we were putting calculators in hand-sized boxes and microwave ovens didn't worry if you were warming chateaubriand or thawing yesterday's meatloaf. Now we have to deal with really small wires that work so much differently from water pipes, we can't even imagine an analogy to the macroscopic world that helps us develop an intuition.
For instance, wires that are only 130 nanometers thick get distorted by the electrons that flow through them. The moving current inside the wire "drags" the wire material and causes it to break, as if you were trying to put water through a pipe made of jello, and the jello dissolves while the water flows.
Of course, it isn't EXACTLY that way. But it's something like that. And we call that effect electromigration.
Electromigration is insidious. It happens over time. The wires in your Pentium processor are indeed slowly eroding from the inside out. Lucky for you, the engineers at Intel know this happens and have designed the critical wires to be thick enough so the erosion doesn't cause a failure in your lifetime--you hope.
And there is coupling. No matter what we do or how we design a circuit the electricity in one wire on an integrated circuit jumps out and into any wires nearby.
And there are reflections--electricity traveling down a wire gets to the end and decides not to go out the open end, but rather, turns around and heads right back in the opposite direction in the same pipe at the same time other electricity is trying to flow out.
And there is tunneling. Electricity leaks out the pipes for no good reason other than the magic of the Heisenberg uncertainty principle. It's not that the wires are porous. There are no "holes" in the wire for the electricity to leak, if electricity could leak. It wouldn't matter what the wire was made out of. That just happens with really small wires.
Finally, there's an interesting problem we have in building wires that small. Typically, the process of building integrated circuits uses a "photolithographic" process. That means that some form of light is used to make a sort of picture that becomes the wires on the IC. (see:integrated circuits: a technology fable, or integrated circuits)
The wires we're trying to build when we make a DVD player chip are about the same size as the wavelength of the light we're using to make the wires.
What does that mean? It means we have zero resolution. It means we can't "see" the wires with the light we're using for manufacture. Literally. These wires have no definition or color under certain types of light, and that's very hard to imagine. But when we design and build these circuits we have to take into account that for all intent and purpose they're invisible.
So to get around that problem, we actually have to design a circuit that is not exactly the one we want--but one that when we expose it with the right kind of light, looks like the one we want. And this is not easy to do, as you can imagine.
None of these things happen in water pipes. In fact, most of these things don't happen in ways we can see. Yet, if you're building the latest computer processor, or a cool automotive MP3 player, you have to worry about these weird things happening every single day.
The driving factor for this technology is you. You who buy new computers, MP3 players, flat-panel TVs, Playstations, digital watches, or cell phones--we devise clever solutions to these problems so we can get products to you by Christmas.
In the 60's, the space program was a huge technical driver for engineering. But now, in the absence of interplanetary travel, the advances in electronics are driven by parents who want to make sure little Suzy or Bobby has a talking Elmo doll under the Christmas tree.
And that's how people like me feed our children.