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In the early 1980s, IBM engineers had a problem.
In most of the US, when a computer’s memory module failed, a few tests would make it clear
what was wrong.
But in Denver, Colorado, 80% of failures were inexplicable.
Every test would show the modules working perfectly.
When IBM finally cracked the puzzle, the cause turned out to be otherworldly.
And I am not saying it’s aliens because it wasn’t aliens, it was cosmic rays.
These intergalactic visitors can wreak havoc on electronics, and they’re playing an ever-greater
role in how computers are designed.
A cosmic ray is actually a tiny particle, usually a hydrogen or helium nucleus.
And they get flung toward us at up to 99% of the speed of light by a far-away supernova
or some other astronomical mayhem.
Scientists had known since the 1950s that radiation made electronics go haywire, whether
the high-energy particles came from the Sun or atomic bombs.
And spacecraft had been dealing with cosmic radiation for decades.
But down on Earth, everyone had thought we were protected by the atmosphere.
And it’s true that the atmosphere protects us from direct hits.
But cosmic rays are packed with energy.
***So when one smacks into an air molecule, it doesn’t just disappear.
Instead, the collision spews out a zoo of other particles called secondary rays, each
carrying just a bit of the energy—but still enough to come out moving fast.
Most of these secondary rays get absorbed or deflected by other air molecules.
But every so often, one makes it all the way down to the ground.
And you know what else hangs out on the ground?
Computers.
Inside of your computer, electrons are flowing around—there’re the physical embodiment
of your emails, software, and Netflix streams.
Many of the electrons park in your computer’s memory—the RAM chip.
They’re moving in and out of microscopic electrical reservoirs to store 1’s and 0’s,
or bits,
Now, a stray neutron from that secondary ray shower might crash into the nucleus of a silicon
atom in the RAM, passing on a jolt of energy that tears apart that nucleus.
It’s a tiny nuclear fission reaction, the same thing that’s happening in a nuclear
reactor!
And as positively-charged fragments of the nucleus zoom through the chip, they yank around
negatively-charged electrons.
And sometimes, a few thousand electrons get dragged into or out of a reservoir in the
RAM.
When that happens, a 1 becomes a 0 , or vice versa.
And the cosmic ray has corrupted the contents of the computer’s memory.
Scientists call this a single-event upset, or SEU.
“Single event” just means there’s no lasting damage to the chip.
So if you test the memory afterwards, everything’s A-OK.
It’s what people call a “soft error.”
Even though secondary rays are everywhere, the higher up you are, the more neutrons reach
you, since they’ve had fewer chances to collide with air molecules.
And that’s why computers in Denver, the mile-high city, were having extra temporary
memory failures.
Mystery solved.
Aside from the occasional blue screen of death, most SEUs don’t cause noticeable problems.
After all, who cares if one pixel in Game of Thrones is off?
But every so often, things have gotten more dramatic.
In 2003, a voting machine in Schaerbeek, Belgium added 4,096 votes to one candidate’s total
because of a single flipped bit.
And in 2008, a Qantas passenger jet suddenly nose-dived hundreds of feet in 20 seconds,
sending passengers crashing into the ceiling.
It’s hard to say for sure, but the most likely explanation in both cases is cosmic rays.
Because of the need to guard against high-altitude incidents like the Qantas flight, the aerospace
industry has done a lot of the research on protecting electronics against radiation.
And devices with lots of memory or that work continuously for days need some extra protection
too, like supercomputers, server farms, even networking equipment.
But as technology advances, SEUs are a growing problem even for things like cell phones,
computerized car engines, and smart doorbells.
And circuits keep getting smaller, making it easier to flip a bit.
At the same time, we keep packing in more transistors, the key silicon component in
RAM and other electronics, giving more targets for particles to disrupt.
So engineers have come up with three main lines of defense.
First, by changing the spacing of the transistor components to limit how much charge can move
around, they can minimize the chance of errors.
The second strategy is to detect and reverse errors right in the RAM.
Error checking and correcting RAM, or ECC RAM keeps tabs on how many 1s there should
be in each block of memory, which allows the chip to locate the error and flip it back.
ECC RAM is widely used in data centers, and you can get it for home computers, too.
And finally, you can just accept that errors are going to happen and try to work around
them.
The extreme version of this, used in spacecraft and planes, is to run multiple identical circuits
at the same time and restart any calculation when their results don’t match.
But you can also just have software stay on the lookout for fishy-looking data or tolerate
some imprecision.
Each solution has its cost, whether in power, size, speed, or money.
But sometimes it’s worth it, especially if the electronics are keeping people alive.
And as we keep using more, smaller electronics, we have to pay more attention to fending off
these cosmic rays that are slamming into our planet from across the universe.
As we’re well aware at SciShow, humans are skilled at building things to survive pretty
much any environment.
Whether it’s protecting our electronics against cosmic radiation or protecting 100-story
skyscrapers from earthquakes, there’s a lot of math and physics involved in maintaining
our way of life.
SciShow’s sponsor Brilliant.org teaches you to think like a scientist with dozens
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And since high-altitude is the theme of the day, I thought we could try this Skyscrapers
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[Go to b-roll of this quiz: https://brilliant.org/practice/skyscrapers/?chapter=infrastructure.]
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Which I think that’s pretty cool.
So if you wanna check it out yourself and help support SciShow, the first 77 viewers
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