Bridge Challenge

[Chesterton]

They just come out of the dark, man.

This is a bridge, right? Do grues fly?

 

[AirPo]

This is a bridge, right? Do grues fly?

Grues do what grues do.

 

[Sabertooth]

Do grues fly?

I seen a horsefly. I seen a housefly. But I ain't never seen a grue fly...!

 

[durangodawood]

But do they have the ability to magically appear behind you on a bridge you've just crossed?

Youre free to set up your own hypothetical where you dont find grue behavior so utterly improbable.

 

[Chesterton]

Youre free to set up your own hypothetical where you dont find grue behavior so utterly improbable.

How do walk across a bridge and not see grues, and there still be a risk of grues being on the bridge?

If there had been grues on the bridge, they'd have retreated backwards across the bridge, or I don't know, jumped to their death? A and B would not need a torch.

 

[Chesterton]

Youre free to set up your own hypothetical where you dont find grue behavior so utterly improbable.

Anyway, since nobody knows what a grue is, the OP probably should have used something we understand better, like maybe radical Islamic militants who are scared of torches.

 

[Sabertooth]

...like maybe radical Islamic militants who are scared of torches.

Or cannibalistic photophobes...

Morlocks...?

 

[Chesterton]

Or cannibalistic photophobes...

Morlocks...?

Frankenstein?

 

[durangodawood]

Anyway, since nobody knows what a grue is, the OP probably should have used something we understand better, like maybe radical Islamic militants who are scared of torches.

At some point you just have to admit you werent up to solving the puzzle (like me).

 

[Chesterton]

At some point you just have to admit you werent up to solving the puzzle (like me).

Explain to me where I'm wrong.

 

[essentialsaltes]

Some backstory, and I'll try to make good on my feeble promise to make this more relevant to the folder.

Apparently, the puzzle has been around for a few decades, but I don't think I'd ever run across it before. I found it in Dan Dennett's new book, and it kept my brain working so that I couldn't get to sleep until I'd cracked it.
In the book, and in the treatment on Wikipedia, the time-limit of 15 minutes is given, which sets something of a goal. I thought it more interesting here to have people generate their best answers and see how it played out.

Anyway, my exceedingly tenuous analogy was to scientific progress and replication.

I think a lot of brains, including my own, take an intelligent and interested experimental look at the problem and come up with the clear and obvious solution of 17 minutes. It's clear and obvious, but it turns out to be wrong. A comfortable consensus of sorts results. 17 minutes is the answer.

And then an alternative view appears, upsetting the consensus. We better check our work! Can we replicate this new result? 19? No, I understand my own solution is valid, so 17 is right. 10? No, I understand the question correctly, and can see that 10 is impossible.

But 15? Not obviously wrong. But can I replicate that result?

I think the drive that some of us felt to see if we could do better than our first attempt at the puzzle (when challenged by a new result from another person) is akin to the scientific curiosity that obtains in the world of science. When faced with a surprising result that upsets orthodoxy, the response of scientists is not "Burn/ignore the heretic" but "Let's just check and see if we can get the same result."

When the 17-ers read trunks2k's explanation of 15, we, perhaps with chagrin, realize the clear and correct answer, and spot the flaw in our own 'experimentation'. And 'science' progresses. Of course, we don't have much ego invested in 17 minutes, unlike scientists, who may stay attached to old theories longer than they should. Science may have to wait for the old guard to pass away before it can advance.

(Helpfully, Chesterton has portrayed the analogous role of the young earth creationist, who has received Revealed Information on the nature of grues, and is impervious to facts and the impossibility of his answer.)

I was also thinking of one of the discussions in the other thread, where the antiscientist was more or less saying "You don't have a full solution to abiogenesis, so you might as well just stop."

This kind of science-stopper is in many ways the exact opposite of the scientific curiosity. A problem is unsolved, or too hard... might as well not try. But if a big problem like abiogenesis is like a bridge puzzle with 358 people and 6 torches, we might have a solution of 47861 minutes that seems clear and obvious. And then someone has one with 46928 minutes, and we all set out to replicate it. And by ratcheting forward we get closer to the optimal solution, or the full explanation of abiogenesis. But we never get there if we throw up our hands and stop trying.

This idea again was motivated somewhat by Dennett's book, where he quotes a few sources:

For 40 years, efforts to understand the prebiotic synthesis of the ribonucleotide building blocks of RNA have been based on the assumption that they must have assembled from their three molecular components. … Of the many difficulties encountered by those in the field, the most frustrating has been the failure to find any way of properly joining the pyrimidine nucleabases to ribose … but Powner et al. … [provide] a remarkably efficient solution to the problem …

…

John Sutherland, one of Powner's coauthors, and in whose lab the work was done, worked on the problem for twelve years before he found the solution. What if he had given up after ten? Could we have concluded that no synthesis was possible? No. This work demonstrates the futility of all the various sorts of arguments---the argument from design, the God of the gaps, the argument from personal incredulity--that rely on ignorance as their chief premise.

 

[Chesterton]

(Helpfully, Chesterton has portrayed the analogous role of the young earth creationist, who has received Revealed Information on the nature of grues, and is impervious to facts and the impossibility of his answer.)

This is totally bogus and unfair. In the real world of reality, the answer is 10. Things do not appear out of nowhere like Jesus did in the upper room. You cannot place into a riddle a supernatural variable which can just do anything. I am not impervious to facts, I am dealing with facts, and you are attempting deus ex machina. This will not stand!

And if you got this from Dennett, psh, no wonder you're wrong.

 

[durangodawood]

This is totally bogus and unfair. In the real world of reality, the answer is 10. Things do not appear out of nowhere like Jesus did in the upper room. You cannot place into a riddle a supernatural variable which can just do anything. I am not impervious to facts, I am dealing with facts, and you are attempting deus ex machina. This will not stand!

And if you got this from Dennett, psh, no wonder you're wrong.

"You need a torch to cross the bridge".

Next time I recommend you consult your lawyer before participating.

 

[durangodawood]

Some backstory, and I'll try to make good on my feeble promise to make this more relevant to the folder.

Apparently, the puzzle has been around for a few decades, but I don't think I'd ever run across it before. I found it in Dan Dennett's new book, and it kept my brain working so that I couldn't get to sleep until I'd cracked it.
In the book, and in the treatment on Wikipedia, the time-limit of 15 minutes is given, which sets something of a goal. I thought it more interesting here to have people generate their best answers and see how it played out.

Anyway, my exceedingly tenuous analogy was to scientific progress and replication.

I think a lot of brains, including my own, take an intelligent and interested experimental look at the problem and come up with the clear and obvious solution of 17 minutes. It's clear and obvious, but it turns out to be wrong. A comfortable consensus of sorts results. 17 minutes is the answer.

And then an alternative view appears, upsetting the consensus. We better check our work! Can we replicate this new result? 19? No, I understand my own solution is valid, so 17 is right. 10? No, I understand the question correctly, and can see that 10 is impossible.

But 15? Not obviously wrong. But can I replicate that result?

I think the drive that some of us felt to see if we could do better than our first attempt at the puzzle (when challenged by a new result from another person) is akin to the scientific curiosity that obtains in the world of science. When faced with a surprising result that upsets orthodoxy, the response of scientists is not "Burn/ignore the heretic" but "Let's just check and see if we can get the same result."

When the 17-ers read trunks2k's explanation of 15, we, perhaps with chagrin, realize the clear and correct answer, and spot the flaw in our own 'experimentation'. And 'science' progresses. Of course, we don't have much ego invested in 17 minutes, unlike scientists, who may stay attached to old theories longer than they should. Science may have to wait for the old guard to pass away before it can advance.

(Helpfully, Chesterton has portrayed the analogous role of the young earth creationist, who has received Revealed Information on the nature of grues, and is impervious to facts and the impossibility of his answer.)

I was also thinking of one of the discussions in the other thread, where the antiscientist was more or less saying "You don't have a full solution to abiogenesis, so you might as well just stop."

This kind of science-stopper is in many ways the exact opposite of the scientific curiosity. A problem is unsolved, or too hard... might as well not try. But if a big problem like abiogenesis is like a bridge puzzle with 358 people and 6 torches, we might have a solution of 47861 minutes that seems clear and obvious. And then someone has one with 46928 minutes, and we all set out to replicate it. And by ratcheting forward we get closer to the optimal solution, or the full explanation of abiogenesis. But we never get there if we throw up our hands and stop trying.

This idea again was motivated somewhat by Dennett's book, where he quotes a few sources:

For 40 years, efforts to understand the prebiotic synthesis of the ribonucleotide building blocks of RNA have been based on the assumption that they must have assembled from their three molecular components. … Of the many difficulties encountered by those in the field, the most frustrating has been the failure to find any way of properly joining the pyrimidine nucleabases to ribose … but Powner et al. … [provide] a remarkably efficient solution to the problem …

…

John Sutherland, one of Powner's coauthors, and in whose lab the work was done, worked on the problem for twelve years before he found the solution. What if he had given up after ten? Could we have concluded that no synthesis was possible? No. This work demonstrates the futility of all the various sorts of arguments---the argument from design, the God of the gaps, the argument from personal incredulity--that rely on ignorance as their chief premise.

Interesting analysis... and fun* puzzle. I really did go back and work harder to (unsuccessfully) bring it down from 17 to 15 when I detected a certain confidence level in 15.

*except for the abject misery of getting it wrong wrong wrong.... and publicly, no less.

 

[Justatruthseeker]

17 minutes.

Edit: ahh I see someone cheated, so it looks like the correct answer is 15....

 

[Chesterton]

"You need a torch to cross the bridge".

Correct, and a torch was used.

 

[Chesterton]

We've heard from AV, but I'm curious to hear @tulc and @Gene2memE explain why they answered 10.

 

[pitabread]

Looking up the 'solution', I now see how the answer is 15 minutes. Makes sense.

 

[durangodawood]

Correct, and a torch was used.

Correction: ES should have got a lawyer to write the problem.

 

[Chesterton]

Correction: ES should have got a lawyer to write the problem.

Thank you. I think the introduction of grues was a fun idea, but had unforeseen consequences.