Complex Numbers

DeTECHtion

From Cracked, a countdown of the unseen:

5 Ways to Detect the Invisible Stuff Hiding From Us  
Surround yourself with the right sensors, and they might just save us all

All around you are signals you have no way of perceiving on your own. For example, did you know that invisible waves travel through the air, transmitting words and images, decodable by the right device?

We only see a remarkably thin slice of the electromagnetic spectrum. There are good evolutionary reasons for this, but why interrupt a fact-comedy with pure fact?

Not everything imperceptible is on the EM spectrum, though.

5. Seismometers Spot Quakes and Save Trains

Not a single person has died in an accident aboard Japan’s bullet trains.

There was a movie a couple of years back called Bullet Train, set on a Japanese bullet train. Action/comedy, so the title is a pun. It's not much of a spoiler to say that bad things happen on the train and people die. But not in an accident caused by an earthquake. I had the opportunity to watch the movie again on a recent long flight, and it was even better than I thought it was the first time.

Even in 2011, when that 9.0 earthquake hit Japan, collapsing a bunch of bullet train stations and ripping up the track, seismometers on the ocean floor detected the first tremors and shut down the trains in time.

EM waves, including radio, travel faster than seismic waves, so these early detection systems aren't magic, but science.

4. The Mountain Pool of Ultrapure Water

Japan is also home to Super-Kamiokande, an observatory for detecting neutrinos. It’s a tank a hundred feet tall and hundred feet wide, located in a mine a thousand feet under a mountain.

Neutrinos are the second hardest things to detect, after dark matter. Well, maybe third, after dark matter and something so invisible we don't even know it exists, yet.

Also, I'm pretty sure the tank is measured in SI units, as is its depth.

Neutrinos travel at the speed of light and pass through the planet without affecting much of anything, but we still manage to detect them using Super-Kamiokande.

Far be it from me to quibble about something on a comedy site, but I'm going to do it anyway: Neutrinos have mass, and therefore don't quite travel at the speed of light. But, you know... close enough. (There was some sensationalist reporting a while back on neutrinos that appeared to exceed the speed of light, but that turned out to be a mistake.)

3. ShotSpotter, the Gunshot Detector

Sometimes, you hear a gunshot outside, and you shrug your shoulders, saying, “Eh, what can you do?”

Emigrate?

Starting in 1997, several cities in the U.S. set up a system of sensors that pick up the sounds of gunfire and relay the location of the source directly to police. In D.C., for example, the sensors picked up some 40,000 shots in a 20-square-mile area over the course of seven years.

That's the sound of freedom.

2. The Detectors that Detect Radar Detector Detectors

Naturally, such devices use waves of their own, which means they’re vulnerable to being spotted by radar detector detectors. Of course, that means you should equip your radar detector with a radar detector detector detector, which will shut your device down as soon as it realizes it’s being spotted.

And so the arms race continues.

Pretty sure my state is still the only one in the US where radar detectors are illegal, but I can't be arsed to find out for sure. Yes, I drive around a good bit. No, I don't have a radar detector.

1. The Parkinson’s Sniffer

This one may seem out of place, being a mutant superpower instead of a tech device. But if you read to the end, you see that they used the mutant's superpower to create the tech needed for a Parkinson's test.

No mention in the article of radiation and Geiger counters, but I suppose most people know about that one, anyway. In any case, all of these were known invisible things. It's the unknown invisible things you really have to worry about.