Bit Flips

In Belgium, something had obviously gone wrong with an electronic voting machine: it was showing a mathematically impossible distribution of votes. The analysis of what had happened makes for an interesting podcast, as narrated by Simon Adler and Annie McEwen.

 

The experts were called in. They got all the ballots and reinserted and recounted them. The difference between the first and second count was 4096 votes. If you’re from a maths/computer science background, that number would be familiar. Yes, it 2 x 2 x 2… 13 times. I won’t get into how computer memory works, but suffice to say that the number mismatch (4096) is a hint that something had flipped (only) the 13th bit of the vote count on that one machine.

 

The team tested the software. No bugs there. Then they checked the hardware on the machine. No issue there either. Ok, but if it’s not hardware or software, what are we left with to look at?!

 

Well, in theory a cosmic ray could flip a bit if it hits the right transistor at the right instant. So they tested the idea by placing a computer in a cyclotron and bombarded it with those tiny particles. And a few bits did flip. Keep in mind most of these particles can pass through walls and building, so this was now a very real possibility of what may have happened to the voting machine. And there are a huge number of them hitting the earth every second. All of this led the podcasters to remark tongue in cheek that “democracy and stars don't get along”.

 

Much of the rest of the podcast is highly speculative as it gets into how many other such instances may have happened. For example, the number of such high cosmic rays is far higher in the upper atmosphere than near the surface of the earth. Which means more of them hit… aeroplanes. Most of which run on auto-pilot… you see where this is going? A bit flip in the auto-pilot could have disastrous consequences. Is that what happened to the Qantas flight that dropped 1,000 feet without reason one time, the podcast wonders.

 

So what’s the solution? Redundancy (Have 3 copies of everything. If they disagree on any part of the data, the majority wins). Of course, this increases the cost of things, so it is not practical in all cases.

 

If bit flips sound like interesting trivia but too improbable to care/worry about, you’re probably right. Then again, as we keep miniaturizing more and more, the energy needed to flip a bit would decrease (the smaller the transistor, the less energy it needs to flip a bit), thereby increasing the probability of such incidents. Combine this with our tendency to add electronics and software into everything (smart this, smart that), and bit flips may start to matter more and more in the not too distant future. The cosmic ray that spells doom may have already begun its journey “long, long ago in a galaxy far, far away”, Star Wars style.

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