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The Dead Man's Switch

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Last night's LOST season finale made mention of a "Dead Man's Trigger," which is another term for a Dead Man's Switch. Although these devices are well known to some geeks, I thought I'd write a little explainer to introduce the notion more broadly. (Warning: very minor LOST spoilers follow.) While the LOST switch was in fact a "fail-deadly" (the opposite of a fail-safe), the concept is similar. In fact, this isn't the first time we've seen a Dead Man's Switch on LOST: Season 2 was all about Desmond's switch.

The Dead Man's Switch is generally a fail-safe device intended to take action if a human fails to routinely activate it -- in other words, if the human dies, the switch goes off, and something happens.

Historically, a Dead Man's Switch was installed in potentially dangerous machinery like locomotives, streetcars, and subways. The switch itself could take many forms, though typically it was a handle of some sort that needed to be operated by the user. By forcing the human operator of these machines to occasionally (or even continuously) activate the switch, you could (theoretically) ensure that the machine would shut down if the operator was dead, incapacitated, or missing. Common mechanical Dead Man's Switches exist in New York subways and even lawnmowers and tractors. Here's a snippet from Wikipedia:

In many modern New York Subway trains, for example, the dead man's switch is incorporated into the train's speed control. On the R142A the train operator must continually hold the lever in place. This was depicted in the movie and book The Taking of Pelham 123, in which a group of men hijack a New York City subway train for ransom, but because of the Dead-man's feature, cannot escape while the train is moving.

Every lawn mower sold in the US since 1982 has an "operator-presence" device, which by law must stop the blades within 3 seconds after the user lets go of the controls.

Many modern systems could benefit from a Dead Man's Switch. For example, typical automative Cruise Control systems don't have such a switch, which could allow a vehicle to effectively drive itself after the user falls asleep. Of course, this doesn't last long, as the vehicle hits something sooner or later -- but wouldn't a better failure mode be to slow down rather than keep going?

In high tech, ubergeeks have been using Dead Man's Switches to protect their data or implement disaster-containment protocols in case something goes terribly wrong. If you're a political dissident or involved in something else potentially dicey, a Dead Man's Switch can be implemented as software, a sort of "nuclear option" that will zap your data -- or contact trusted compatriots -- if you fail to activate it. Slashdot held a discussion entitled What Does Your Dead Man's Switch Do? in 2007, leading to several interesting stories (and tons of off-topic discussion). Here's a good example:

I often take part in political protests, and have on occasion been arrested and held for days.

So, I put together a quick routine using perl and chron that dispatches email to my workplace, the local legal rep contact, and some friends. The later includes directions to a hidden key and asks them to feed my cat until they hear from me. I only enable the system when I'm expecting a significant risk of arrest. Once it's started, if I don't either log into the machine or send myself an email containing a specific string once every 24 hours, the alarm goes off.

The Dead Man's Switch has also appeared in literature; one popular example I can recall is the nuclear trigger on Raven's motorcycle in Neal Stephenson's Snow Crash. But I'm sure there are more examples out there. Have you come across a Dead Man's Switch, in life or in fiction? Share in the comments!

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science
Why a Howling Wind Sounds So Spooky, According to Science
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Halloween is swiftly approaching, meaning you'll likely soon hear creepy soundtracks—replete with screams, clanking chains, and howling winds—blaring from haunted houses and home displays. While the sound of human suffering is frightful for obvious reasons, what is it, exactly, about a brisk fall gust that sends shivers up our spines? In horror movie scenes and ghost stories, these spooky gales are always presented as blowing through dead trees. Do bare branches actually make the natural wailing noises louder, or is this detail added simply for atmospheric purposes?

As the SciShow's Hank Green explains in the video below, wind howls because it curves around obstacles like trees or buildings. When fast-moving air goes around, say, a tree, it splits up as it whips past, before coming back together on the other side. Due to factors such as natural randomness, air speed, and the tree's surface, one side's wind is going to be slightly stronger when the two currents rejoin, pushing the other side's gust out of the way. The two continue to interact back-and-forth in what could be likened to an invisible wrestling match, as high-pressure airwaves and whirlpools mix together and vibrate the air. If the wind is fast enough, this phenomenon will produce the eerie noise we've all come to recognize in horror films.

Leafy trees "will absorb some of the vibrations in the air and dull the sound, but without leaves—like if it's the middle of the winter or the entire forest is dead—the howling will travel a lot farther," Green explains. That's why a dead forest on a windy night sounds so much like the undead.

Learn more by watching SciShow's video below.

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Space
SpaceX's Landing Blooper Reel Shows That Even Rocket Scientists Make Mistakes
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SpaceX's Falcon 9 rocket launches.
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On March 30, 2017, SpaceX did something no space program had done before: They relaunched an orbital class rocket from Earth that had successfully achieved lift-off just a year earlier. It wasn't the first time Elon Musk's company broke new ground: In December 2015, it nailed the landing on a reusable rocket—the first time that had been done—and five months later landed a rocket on a droneship in the middle of the ocean, which was also unprecedented. These feats marked significant moments in the history of space travel, but they were just a few of the steps in the long, messy journey to achieve them. In SpaceX's new blooper reel, spotted by Ars Technica, you can see just some of the many failures the company has had along the way.

The video demonstrates that failure is an important part of the scientific process. Of course when the science you're working in deals with launching and landing rockets, failure can be a lot more dramatic than it is in a lab. SpaceX has filmed their rockets blowing up in the air, disintegrating in the ocean, and smashing against landing pads, often because of something small like a radar glitch or lack of propellant.

While explosions—or "rapid unscheduled disassemblies," as the video calls them—are never ideal, some are preferable to others. The Falcon 9 explosion that shook buildings for miles last year, for instance, ended up destroying the $200 million Facebook satellite onboard. But even costly hiccups such as that one are important to future successes. As Musk once said, "If things are not failing, you are not innovating enough."

You can watch the fiery compilation below.

[h/t Ars Technica]

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