The Two Generals’ Problem Great Oceans Liners: Speed 1 day ago   08:26

Tom Scott
Time to tell a story about idempotency, computer science, and the Night of the Multiple Orders. • Sponsored by Dashlane —try 30 days for free at:


Written by Sean M Elliott and Tom Scott
Directed by Tomek
Graphics by Mooviemakers
Audio mix by Haerther Productions

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Comments 2062 Comments

Tom Scott
Yes, I had help with the graphics for this series. There's no way I'd have animated that myself! On that note, thanks to Dashlane for sponsoring and helping me hire an animator: their free trial link is
Nubby Tope
The main problem is that they built a castle in a valley.
Zen Lucas-Divers
wouldn't the best option to just meet somewhere else, send a message to one side and keep doing so until a messenger gets through and tell them to meet a one point so that you can attack together.
And then that "idempotency key" resets when you hit "try again" :D
Maybe a joke comment cause excuse my incompetence but why isn’t the problem set in 3D? Cause then they could just go around?
Zachary Wilson
Are you in the Centre for Computing History in Cambridge?
Caleb_ Artzs
Why not A send a messager at same time as B? So both can meet at the middle and both can go back and inform there general's
Deep hug
to prevent jamming of wireless signals.
soap's alt
The messengers could meet in the valley and then return with an agreement.
this is a really cool problem. and a really great explanation. Not being a software engineer myself, a lot of why I'm here is through sheer curiosity, but your explanations are always entertaining and easy to understand, so I keep them on a backlog for the day they become relevant to me. Thanks for keeping this channel awesome.
couldnt you just send one messenger with a message to have the a messenger from each side to meet at some kind of halfway point and then return to their general
George Hugh
Castles aren't built in valleys, generally, generally.
You could just get past the castle with your whole force, telling the other force to attack with you - so you become one big army. Problem solved?
CS:GO сФинщини
Bitcoin solved the Byzantine generals' problem
Emily An
I earn like 20 quid an hour for deliveroo it’s not bad 😂
I've never heard it referred to as an idempotency key. I've always heard it called a "nonce"
Giovanni Joe
Super informative! Thanks very much for the great content!
flutty bitch
You are my new favorite channel. Subscribed.

BTW, I had the same problem when purchasing Dragon Age: Inquisition. Took a month for EA to return my money.
Michael Thomas
"A single human error is never the root cause"

Tell that to my development manager who came in to the position with nothing more than a background in marketing & graphic design and understands absolutely nothing about coding anything more complicated than changing a few things on an HTML template.

edit: I don't even work in tech currently, so I'm just meme-ing not speaking from experience.
Dan Scherck
Interesting factoid: The Spanning Tree Protocol, used in Networking to prevent network loops, was invented by Radia Perlman, whose doctoral thesis at MIT was on something very close to this idea. Her paper was entitled "Network layer protocols with Byzantine robustness"
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Great Oceans Liners: Speed The Two Generals’ Problem 1 day ago   48:08

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The 1930s was a highpoint for ocean-going liners. Crossing the Atlantic by boat was the only way to reach the US, and competition between the French and British shipyards was never less than fierce, a focus for patriotic pride. The British Queen Mary and French Normandie epitomised the golden age of the ocean liners. They were among the floating Art Deco palaces that competed intensely to win the Blue Riband - a prize for the fastest Atlantic crossing. A Holy Grail for the two countries, this prize was also a great bit of marketing.

Originally broadcast in 2003. Content licensed by DRG Distributions. Any queries, contact us at [email protected]

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