So I was driving my mom's car tonight, and I looked at the speedometer. I'm not used to it...it's one of those analog needle/dial speedometers, and I've gotten accustomed to my Prius's digital speedometer. It made me think of why we even represent data digitally...it reduces noise. Electrical, optical, acoustic, radio...any kind of signal picks up noise while it's being transmitted. But by representing data digitally, by having discreet thresholds from one value to the next, it makes it much easier to recreate the information in a signal without having to perfectly reproduce that exact signal (as long as the noise is below a certain level).
For (a very roundabout) example: You go to Wal-Mart to buy an HDMI cable for your sexy, new, flatscreen TV. You get there, and you discover that the cheapest one they sell is like $40. And some cables go for over $100!! You're like, "Why the hell is that so expensive??" You decide not to buy the cable then and decide to look online for alternatives. Online, you see cables that sell for less than $20. How do you know that the manufacturers of the cables at Wal-Mart are ripping you off?
Easy.
Because your new TV is digital.
Sure, an HDMI cable running to from your set-top box or Blu-Ray player might pick up all sorts of electrical interference along the way - from your wireless router, from other nearby cables, from fluorescent lights, from your sound system, etc. But by representing each bit of information being transmitted to your TV digitally, and by making sure the threshold between a logical 1 and 0 is greater than any noise the signal might pick up along the way, all the audio/video information sent from your set-top box can be perfectly recreated on your TV! You're not going to get "better picture quality" with fancier gold- or silver-plated connectors. Each bit of information is either going to be represented accurately or not.
So as I was driving, I was thinking, "If digital information is so good for handling noise, then why is the natural world so analog-y? Why aren't we all digitally-controlled creatures?"
And then it hit me...We are!
I remembered (from AP Biology in high school!) that neurons only fire action potentials when voltage across their cell membrane exceeds a certain threshold. That means there's a discreet potential that represents the boundary between a logical 1 (fire!) and 0 (don't fire!) in each of our neurons! Furthermore, fired action potentials are pretty much the same in magnitude from a particular neuron. Neurons that receive stimuli of greater magnitudes don't fire off action potentials in greater magnitudes, but they do fire off action potentials in greater frequencies! So basically, each of our neurons acts as both an analog-to-digital converter as well as a digital-to-analog converter (it's not exactly pulse-width-modulation (PWM), but it is SOME kind of modulation (see: http://en.wikipedia.org/wiki/Modulation#Pulse_modulation_methods))!.
So really, our bodies receive all this messy input stimuli from our environment (sight, hearing, taste, touch, smell), convert and process that data digitally, and then form outputs that are ultimately expressed in analog (example: movement of muscles).
I think that's pretty neat!
Sure, none of this is new. All of this is well-understood by those people who make artificial body parts that interface seamlessly with the human nervous system (pacemakers, robotic prostheses, artificial retinas, cochlear implants, etc.). Still, it was a delightful epiphany to make driving home earlier today.
At work, I'm programming a microcontroller on an Arduino board to control some other devices that will create a temperature gradient over a laser-microscope sample. For the record, this is my first Arduino project, and I'm a complete n00b at it. But basically, I'm just trying to get this device to be "smart" enough to make changes in output given certain inputs (from user-interface as well as environmental changes). It's all just receiving analog signals, converting them to digital, processing them, converting output signals from digital to analog and transmitting them, which is basically what my neurons do all day!
I'm always amazed with nature's designs. Evolution just provides you with a gazillion working solutions for so many practical problems, which is why it can be such a great source of inspiration for me, an engineer-in-training. As another (the final) example of this, I remember, again in AP Biology class, how amazed I was when I discovered that the simple concept of harnessing energy from a fluid flowing from high pressure to low pressure was implemented in each of our cells in the ATP synthase enzyme (see: http://www.youtube.com/watch?v=uOoHKCMAUMc). The concept of a dam/turbine seems so mechanical and human, but really, nature thought of it way before we did.
Goddammit, evolution. Why are you so cool?
Okay I'm done geeking out now. Good night!
PS: Sorry for oversimplifying the science in this post. I haven't really backed up any of my claims with...anything else. Most of this is all just from my very faulty memory, which works even less reliably when it's ~5 in the morning and I'm super sleepy. Corrections are welcome.
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