Bridge Challenge

[Tanj]

An explanation of grue behaviour...

 

[Chesterton]

An explanation of grue behaviour...

Oh wow, the racism in this thread! One short video of a small group of grues...and AHA, THAT IS GRUE BEHAVIOR! For shame.

 

[AV1611VET]

Oh wow, the racism in this thread! One short video of a small group of grues...and AHA, THAT IS GRUE BEHAVIOR! For shame.

Troglodyte!

 

[Bungle_Bear]

17 minutes.

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

Who cheated?

 

[tulc]

My thought was: the two slowest cross (8 minutes) when they step on the other side they toss the torch into the middle of the bridge because the two fast ones start across when the slow ones are about 30 seconds from the end the fastest guy runs to the middle grabs the torch runs back to the slower guy and they make it across in two minutes. 10 minutes. I'm pretty sure that's not right but it beats my original theory: none of them were afraid of the dark. which still makes it 10 minutes.
tulc(actually prefers the dark)

 

[Bungle_Bear]

If the fastest guy gives the others a piggy back then we're down to a little over 5 minutes.

 

[AV1611VET]

If the fastest guy gives the others a piggy back then we're down to a little over 5 minutes.

Keep in mind though:

It's still a bridge!

 

[Bungle_Bear]

Keep in mind though:

It's still a bridge!

And.....? Did I miss the sign saying "No Piggy Backing"? Can he use a fireman's lift instead?

 

[AV1611VET]

And.....? Did I miss the sign saying "No Piggy Backing"? Can he use a fireman's lift instead?

A crossed over on the Hindenburg.

B crossed over on the Titanic.

C crossed over on the Challenger.

D crossed over with the torch and made it ... to L'Aquila.

 

[Bungle_Bear]

A crossed over on the Hindenburg.

B crossed over on the Titanic.

C crossed over on the Challenger.

D crossed over with the torch and made it ... to L'Aquila.

 

[essentialsaltes]

And.....? Did I miss the sign saying "No Piggy Backing"? Can he use a fireman's lift instead?

"When two people travel together, they can only go as fast as the slower person."

 

[Bungle_Bear]

"When two people travel together, they can only go as fast as the slower person."

The inference is that they walk together. I see now that thinking outside the box is not allowed. You should have said

 

[Sabertooth]

No, that's not in line with the rules.

Spoiler: Real spoiler for 15

A and B go across the bridge (2 minutes)
A comes back with torch (1 minute)
C and D cross the bridge (8 minutes)
B comes back with torch (2 minutes)
A and B go back across the bridge (2 minutes)

2+1+8+2+2 = 15.

If either one of your first two went back, it would still be 15 mins.

 

[46AND2]

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.

It was quite clear to me that the grues and the torch were just an entertaining plot instrument. Well, maybe not at first. My first thought was maybe Grues only come out after a certain elapsed time of darkness or had some other helpful trait, so I looked up their characteristics. lol.

He could have just as easily written the basic rules:

1. How long it takes each person to cross
2. Each crossing must be complete
3. All 4 start on near side
4. No more than one person at a time dropped off on the far side, except for the last trip

17 seemed too easy to be a worthy riddle, so I figured there must be some way to get the soft and infirm to cross together. Took a bit, but I got it. But I did go back and try to figure out the 10 minute possibility after I read that claim, and nearly asked how far the light of the torch reached, until it was made clear that complete crossings were required. Don't know if that would have helped anyway.

 

[DogmaHunter]

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.

Ow, didn't see that coming.

Nice analogy. Indeed, eventhough I hit the bullseye correct answer on the first try (//flex ), I totally get it.

When I came to the answers of 10 and 12, eventhough I was as good as certain that those were impossible without doing any calculation, I still reflected back on my 15 to see if I missed something.

Some kind of uncertainty, no matter how small, that feeds our personal insecurity. That coupled with the "public shame" of getting it wrong of looking stupid. Peer pressure and reputation and all that. I think a psychologist could have a field day and write an entire book on this topic.

 

[DogmaHunter]

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.

I was just thinking about some other study that can be somewhat related to this....

In such public riddles, indeed, I do have a sense of "peer pressure" or some kind of "personal insecurity" and/or fear of "public shame" for getting it wrong.

The study I'm talking about, was about a psychological difference between atheists and theists. In the study, people had to just answer a series of questions. All kinds of questions. Riddles, general knowledge, etc. The study wasn't really about the actual answers given, but rather about how one goes about in answering the questions. Especially those questions that were more dificult. What methodology is used to come to an answer and if an answer is not forthcoming, how does one deal with that.


The conclusion was that in general atheists seemed a lot more worried to getting answers wrong. It gave them actual physical stress. Heart rate / blood pressure increased etc. This was a clear statistical signal when compared to the theists.

Atheists thus were a lot less likely to simply "settle" on some answer when they didn't know or were not certain enough for their taste.

It's a shame I don't remember much about where it was carried out etc. It might make it dificult to find and I really don't have time to spare now to look it up. Perhaps I'll do so this weekend.

 

[Sabertooth]

The conclusion was that in general atheists seemed a lot more worried to getting answers wrong.

This is common for gifteds & autistics, as well (whether they are theistic are not). I just didn't have a lot riding on this.

 

[DogmaHunter]

This is common for gifteds & autistics, as well (whether they are theistic are not). I just didn't have a lot riding on this.

Neither did anyone have anything riding on the relatively random questions in that experiment.
That's why I said "in general".

 

[zippy2006]

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."

Interesting thread. Some devil's advocate:

1. The model fits quantitative modern science much better than philosophy or theology.
2. Good Intelligent Design arguments are philosophical or logical rather than scientific. Ironically enough, "Burn the heretic" does seem to apply to ID theorists in the form of "Burn the science-stopper!"
3. Addressing an Intelligent Design argument may actually do more to further science than not due to the fact that a good ID argument is going to illustrate a fundamental incompatibility between some scientific premises and the inferred conclusion. The proper response is not to ignore, but to examine premises and in the best cases to effect a paradigm shift--something which advances science much more effectively than any particular formula or methodology.

Good Intelligent Design arguments may be few and far between, but in principle they aren't a threat to science so much as an opportunity, especially in an era when science and philosophy are estranged. The modern heretic is the science-stopper, and he is burned, but the ID theorist need not always fall into that category.

 

[essentialsaltes]

Ironically enough, "Burn the heretic" does seem to apply to ID theorists in the form of "Burn the science-stopper!"

Who, exactly has been burned, rather than ignored for not having presented a coherent argument?