BẢN CHÉP ÂM THANH 🔗
I asked how noise canceling headphones work and the answer sent me looking through wildfires, bank runs and computer worms.
Tiny microphones on the headphones pick up the noise around you, like a plane engine. A small computer inside flips that sound wave upside down and plays it through the speakers.
Where the engine pushes the air up, the flipped wave pulls it down by the same amount. The 2 waves cancel out and the engine goes quiet.
That made me wonder where else something gets inverted to cancel something out.
In 1949 Wag Dodge led a crew of firefighters who parachuted into Mann Gulch in Montana. A wildfire raced up the slope at them.
Dodge lit a fire in front of himself and lay down in the burned ground. Since his fire burned the fuel first, the wildfire passed over him. He pressed his face to the dirt to breathe the air near the ground.
He lived.
If a wildfire came at you, you'd likely run.
His crew ran and wouldn't follow him in. 13 men died. Norman Maclean wrote Young Men and Fire about them.
Dodge fought a fire with a fire. In Uzbekistan, Soviet engineers fought one with a bomb.
A gas well there caught fire in 1963 and burned for nearly 3 years.
Gas kept pushing up out of the ground. The engineers set off a nuclear bomb underground beside the well and the blast pushed the rock in on it. The flame went out in about 23 seconds.
That fire ran on gas. The panic of 1825 ran on fear.
People rushed to pull their money out of British banks.
If you ran a bank that week, you'd want to hold on to each pound you had. The Bank lent instead. A director named Jeremiah Harman later testified that it lent "by every possible means."
One account says the Bank found a box of about 600,000 old one-pound banknotes and put those into circulation.
The panic faded once people believed they could get their money.
The Bank stopped a run on its money by handing out more money. In 2003 someone tried the same move with a computer worm.
A worm called Blaster was spreading across Windows computers. If your PC caught it, Windows might shut down and restart on its own.
Then someone released a second worm, Welchia, to fight it.
Welchia spread from machine to machine, removed Blaster and installed Microsoft's patch.
Nobody ever claimed it. Hidden in its code was a note from its writer about loving their wife and baby, plus a promise that the worm would remove itself in 2004. It reads like the work of a vigilante trying to rid computers of Blaster.
A sound wave against a sound wave. A fire against a fire. Money against a run on money. A worm against a worm.
The fix for a problem can be the same thing pointed the other way.
What problem in your work could you cancel by inverting it?