Saturday, June 7, 2008

Without Delay

In reel-to-reel tape decks, there is a record head and a play head and they are separated by a small gap. The play head comes after the record head, and the record and playback circuitry are separate, so it's possible to monitor a tape recording more or less as its being recorded, albeit with a small delay.

The small delay was often used to produce an "echo effect" on recordings and in the studio. For the echo effect, the tape output was mixed with the line in and patched back into the tape input. Depending on the tape speed, the echo delay could be controlled, and the gain between output and input controlled the echo strength. A gain of greater than 1 produced the "infinite echo" that rapidly became a sound pulsation with its frequency centered at the maximum frequency response of the system.

One practical joke that was often played at radio stations was to hook up a tape deck to generate a delay, then feed the announcer's voice back to him with a fraction of a second delay. I was once trying to get an echo effect on my voice and I found that I'd practical joked myself; I had to remove my headphones in order to continue. The delay makes it almost impossible to speak. It's hard to explain why, but the experience is compelling.

In a course, Voice and Image Processing, that I took at RPI there was a similar demonstration with video. A ball was placed behind a small barrier, and a video camera showed the ball on a TV screen. Normally, you could just watch the monitor and reach behind the wall to pick up the ball. But with a half-second time delay, such a seemingly ordinary task became almost impossible. You soon found yourself reaching for the ball, overshooting, then overcorrecting, then overshooting, etc.

Such a thing is called a 'limit cycle' in systems control theory, but it's pretty eerie to be a part of a limit cycle and unable to break out of it. Eventually, you just stop moving entirely, then veeeeerrrrrrrryyyyyy slowly move your hand to get the ball. It could literally take 30 seconds or more to do that simple task.

There's a bunch of mathematics in systems theory that deals with time delay and "controllability." The upshot is that if you add enough time delay into a control system, it becomes uncontrollable. Your ability to affect events is slower than those events. Imagine trying to pick up the ball behind the wall if it is moving erratically.

One of my favorite jokes is about the economics professor walking through the Quad with his students. One of his students says, 'Look, there's a ten dollar bill on the ground.' The professor replies, 'Can't be. If it were, someone would have picked it up already.'

For a long time, economics was dominated by what are called "equilibrium calculations," models of an economy under steady state conditions, no shortages, prices in equilibrium, all the usual assumptions. Those are the simplest conditions to model and to easy calculate, so they were the first results. Evolutionary biology tended toward the same simplifications, for the same reasons. The advent of the computer, and the growing access to massive amounts of computing power changed the landscape, but it took a while for theoretical models to catch up to the improved tools. In fact, the catch-up is still going on.

I had lunch with a colleague a while ago, and he asked my opinion about global warming/climate change/greenhouse gases. I told him that it was pretty obvious that the signal was out of the noise, the whole process was clearly underway, and was he surprised at this answer? He noted my well-known contrarian streak. I observed that James Hansen hadn't made a wrong prediction since 1988, and I wasn't going to challenge that sort of success.

In truth, I was a little late to the global warming party, partly because of that contrarian streak, but also because I was focusing on the science and not the policy. I was also perhaps yielding too much to my own libertarian leanings. So let's review why I should have been convinced sooner than I was, at least on the policy issues.

From the standpoint of political philosophy, one fact should be paramount: if we do not have a right to the air we breathe, then human rights, including property rights, are meaningless. And that should include the right to have that air remain unaltered. You shouldn't have to prove that harm is being done to you, any more than you should have to prove that people are harming you in order to not want a stream of trespassers walking across your lawn.

Now any given individual has no real impact on the contents of the entire atmosphere, although it's certainly possible for an individual to affect your current breathable air, and you generally have recourse. If someone smokes in your house and you don't like it, you can throw them out. If the neighbor's barbecue is noxious, you can usually complain to some agency, and I, for one, do not consider that to be an infringement on your neighbor's rights, though your neighbor may disagree.

But group behavior can, and does, affect urban, regional, and global resources. The industrial world's propensity for fossil fuels has had an undeniable effect on the concentration of some important trace gases in the atmosphere. Regulating group behavior is not the same as regulating individual behavior. Regulating corporations or national economies is not the same as regulating individuals, and giving free license to groups and organizations reduces individual freedom.

In the case of global climate change, regulating group behavior is essential. Actually, of course, group behavior is regulated. It just happens that it is regulated by those who rule, manage, control, and lead those organizations, the corporate boards, the CEOs, the congresses, presidents, agency heads, judges, and lawyers whose fingers are entwined with the strings of authority.

But authority and control are meaningless if the system is uncontrollable. The global climate system takes decades, if not centuries to equilibrate to any given greenhouse gas level. Glaciers take even longer to melt or rebuild. And the human political process likewise has major delays built into it.

There is a thin straw to clutch at, called feedforward in control theory. Using feedforward, you attempt to compensate for feedback delays by anticipating the system response. But feedforward control is seriously limited by your understanding of the underlying system. Without that understanding, feedforward is useless.

In regulatory policy, science is the feedforward control signal. Science, however, is currently under political attack from numerous quarters. And big money is being spent to target climate research in one part of that attack.

We're going to lose south Florida, and, my colleague suggests, most of Louisiana and Mississippi. California will acquire a new inland sea. Much of Bangladesh will vanish, as will plenty of islands in the Pacific and Indian Oceans. The fact that these things are going to happen long after you and I are dead does not make the future more palatable. It makes it more inevitable.

3 comments:

JP Stormcrow said...

Thanks for giving coherent voice to a concept that I have struggled to express very well in a number of discussions on global warming (and other longer term trends). About the only image I have had success with is steering a ship, which of course overstates the degree of control.

black dog barking said...

IIRC a tenet of the Kesey Merry Pranksters was an assault on the temporal gap between event and sensory recognition of same, the idea being the gap represents a loss of awareness, a leakage of consciousness. They engaged in some experimental musical improvs where the players donned headphones that delayed audio inputs so they were jamming to the near past. Can't imagine what that sounded like in relative real time.

(Don't know how this fits into the impending climate changes other than it only took the teensiest eensiest dab of LSD to effect some pretty big short term change. Maybe Novartis neé Sandoz is cooking up the answer as we speak.) (Instant gills?)

James Killus said...

We won't need gills. There will still be a lot of land around, just not as much as we have now.

"Son, stocks may rise and fall, utilities and transportation systems may collapse. People are no damn good, but they will always need land and they'll pay through the nose to get it! Remember," -- Lex Luthor quoting his father, in Superman, the Motion Picture