Explainer's colleague The Earthling has theorized that humankind functions like a global brain. To hell with theory, Explainer proves it! After Explainer posed questions about this week's events, Slate readers went to work, as did Slate and other news sources. We haven't gotten all the answers, but it's a start.

1. Why can you turn off a transponder?

Some readers thought Explainer wanted to know why terrorists would want to turn off a transponder, but most realized that the question referred to why the devices are configured to allow non-homicidal pilots to do such a thing. Reader James Iry might have put it best:

"Two reasons. The first is that on the ground it's useless and just generates more noise for the air traffic control system to sort out. The second is that it can malfunction.  A misbehaving transponder might broadcast continually, send an incorrect altitude, or send the wrong code. In any of these cases it's probably better to send no signal at all than send a bad signal. Giving the pilot the ability to turn off a transponder is really just nod in the direction of Murphy."

2. Can you turn off a plane's cockpit voice recorder or flight data recorder?

Yes. The Christian Science Monitor interviewed the air traffic controllers who dealt with Flight 11. One of them "speculates that anyone knowledgeable enough to cut off the transponder might also have pulled the circuit breaker for the cockpit voice recorder in the so-called black box, deactivating it, to minimize information available to authorities." And Slate reader Ken Shirriff referred Explainer to thisAviation Week article about the 1997 SilkAir crash of a 737. In that crash, U.S. officials suspect that the pilot activated the circuit breaker to cut power to both recorders.

3. What rules govern when a president can prohibit congressional intelligence briefings?

Explainer is still working on this one, but the Chicago Tribune reports that Sen. John McCain, R-Ariz., says the Bush administration's briefings have become gradually less informative over the past few days. McCain (who's not complaining) says he receives "much less information than I do from turning on the television set." Sen. Dick Durbin, D-Ill., goes further, calling the briefings "a colossal waste of time." Explainer recommends they address their thank-you notes to Sen. Orrin Hatch, R-Utah.

3. Cell phones work on airplanes? Why does the FAA discourage their use? What's the maximum altitude at which a cell phone will work?

From this morning's New York Times: "According to industry experts, it is possible to use cell phones with varying success during the ascent and descent of commercial airline flights, although the difficulty of maintaining a signal appears to increase as planes gain altitude. Some older phones, which have stronger transmitters and operate on analog networks, can be used at a maximum altitude of 10 miles, while phones on newer digital systems can work at altitudes of 5 to 6 miles. A typical airline cruising altitude would be 35,000 feet, or about 6.6 miles."