The Two Generals’ Problem

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 https://www.dashlane.com/tomscott

Two messengers meet in the valley, signs a note saying order was received, then comes back with a note with both messengers signature. PROBLEM SOLVED.

Just use smoke signals

a possible "solution" to the two generals problem. send 3 messages with an identical identifier (so that it's clear that it is the same message), respond to each individual message with it's own acknowledge, respond to those individual responses with an acknowledge and as long as those are all done at slightly different intervals (say a few milliseconds for the app, or 15 minutes for the problem itself), the chances of all 3 failing are greatly reduced, though not zero

Not bad videos, but having been a computer engineer for many many years now I can say there are many many times huge issues caused by a single person.

I think the solution to it would be that both of the generals know that the only logical thing to do would be to attack immediately right when they pop into existence, since without doing that it would be unsolvable.

Why would anyone order food to their home when they can cook a good meal in half the time for 1/10th the cost?

"a single human error is never the root cause"

Didn't Cloudflare's servers break all because of one single regular expression?

My solution which is dumb but would probably work. When each general thinks they’ve received a lot of acknowledgments, say 7 or 8, they just go.

Why did I read the title as genitals lmao...

I’d just send a messenger to the other general, and tell him to send a messenger at a specific time to confirm the time to attack, then both parties would send a messenger.

The real problem is that you need at least 5 more armies or you'll never conquer Byzantium!

What if they need the messenger to come back so they know that the message has received

Says certain delivery app in beginning just a couple seconds later shows news articles accusing deliveroo of unethical practices.

Could army A send two messengers over then at the halfway point, one of them turn back to give army A the all-clear, while the other messenger delivers the message?

A. Send a message announcing a time of attack and ask for them to send a messenger back as proof
B. Sends a message back saying that they've read the message
A. Send a message announcing that the decision is final and to send a messenger back as proof, but this time without expecting a response.
If you get a message back, then you just attack at the determined time
A and B are the 2 generals

Just send three, if one makes it, the B sends another back, if that one makes it the other sends one back. Then they know they both recieved it and the time is right.

Well I mean if you have three acknowledgements I think it's fair to assume the other got the message.




If A send B a message then A wont know B got the message but if they did and sent an acknowledgment back then A got the message but B doesn't know that. So now both A and B know to go at 8 since As the one that made the message and also received an acknowledgment and B got the message and sent it back but even if they didn't know A got it, A still was the one that made the time so they'd go anyway. Just to be safe, A can send another acknowledgment and if B gets it, they'll know both sides are going to go at 8.

Mans looks like the hobbit

what about quantum entaglement? uwu

Smoke. Done.

Here's a computer science suggestion: Use transactional promise driven model and thus make your confirmations explicit. In the same way actual payments work.(i.e. reserve and confirm) While the theoretical problem has no guaranteed solution the practical problem does have reasonably guaranteed solutions and that app was poorly designed.

That example doesn't seem to work because they would just need A to tell B 8pm, B acknowledges, then A acknowledges. Both armys know the other knows to attack at 8pm.

I actually came up with a better solution : Dont attack and dont make war at all :D.

Imagine paying again after it's said you've already paid.

dont show up with two armies, there done.

just send 1 person from each general at the same time

what if they walk to the castle?
the other side will see them and walk aswell

Possible solution to the Two General Problem.

One general sends two messengers to the other general. One messenger stays back before it passes the castle, and the other messenger passes the castle. The messenger that stayed back will watch the other messenger pass the castle, and will be able to tell if the messenger passing the castle has been killed or has safely passed the castle.
The messenger that passed the castle would have a time for the generals to attack. The messenger that watched would report back to the general who had sent the two.

Have both go at the same time, and meet in the center, thus letting them both confirm a time, and success

Can we get an f for our fallen messengers

I was working at a burger restaurant at the time that this issue was happening. 7 drivers arrived with the request for the same meal. You were smart for recognizing this issue initially and ordering one order

Best solution: Ignore the generals and go to the local pub for some food. :P

Morse code via smoke

I what if u send someone with one person behind and another behind them etc. so that when one gets confirmation they can give the army info right before the others get to The Valley ? I can’t quite explain

Solution for the problem is : arrange a certain time /sun stand ( other certain events that are global and recognizable to both armies ) and trust ;).

Realistically, couldn’t the other general just fire off a cannon or two in acknowledgement to the letter? I understand I am ignoring the computer science portion of this, but I came here for generals and armies and I will leave on those terms.

Possible solution: One general could send a letter saying what time to attack. It would also say to shoot a flaming arrow in the air if they got the message and if they agree. If one general sees the arrow then the other would also shoot an arrow signaling that they both agree to attack at a specific time.

Surely after 300 messengers confirming it, I don't REALLY need to confirm the 301st.

The two generals problem might be solved by sending a letter every day for a thousand days that says "Once every day for the next one thousand days (more or less depending on how arbitrarily difficult the valley is to pass) send a letter in confirmation of this letter. Mark down instances of letters getting through in your correspondence. On a specific date (at least 1,000 days in the future) we will attack, pending your confirmation."
If it is reasonably possible for a letter to get through the dangerous valley this will work. If it is not then no coordinated attack is possible and no attack will take place.

I was like signal fires

Using flags in the general problem is badically using quantum entanglement

...There is castle in the middle of the valley... *Sun Tzu left the group*

Could the general write we will attack at 12pm light a fire If you received it or we will not attack

Clicked this video genuinely thinking this was a hypothetical war paradoxical scenario, like if The Metatron and Vsauce2 collaborated or something. It's apparently not.


I can't say I disliked it.

Didn't they create war horn for that exact purpose?

What if I actually wanted to order the same thing twice in a short ammount of time?

my phone's messenger app is bugged where it will receive the same text message from someone over and over again. i didnt know about the two generals problem till now. though i figured out that is what was happening my phone. it was getting the message but the "i got it" signal wasnt going through so the other person's phone kept sending the message it didnt show for them but i would get the same text more then 20 times within a few seconds