
God's Number is 20 - mjackson
http://www.cube20.org/
======
patmcguire
Sort of like the Four Color Theorem, in that it's something that was proven
with computers and brute force. I remembering hearing mathemeticians were
upset about it because it just felt wrong to prove it that way (this was the
70s, it may have been the first proof that was done by machine)
[http://en.wikipedia.org/wiki/Four_color_theorem](http://en.wikipedia.org/wiki/Four_color_theorem)

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Pitarou
That's right, The Four Color Theorem was the first such proof.

Mathematicians weren't so much "upset" as "not sure what to make of it".
Technically, the "proof" wasn't really a proof at all, because it relied on
the operation of a computer program, and the compiler / OS / hardware stack
upon which the program operated had not been rigorously verified.

Even if it HAD been verified, there's still the question of whether
transistors always work in the way we believe....

Of course, over the years, the Four Color Theorem has been checked 100s of
times, with many different software / hardware stacks. But to a purist, this
still only counts as "strong evidence" rather than "proof".

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lincolnq
It's weird to say that and still count written proofs. There's still the
question of whether _neurons_ always work in the way we believe...

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Pitarou
Shh! Don't tell them that. You'll hurt their feelings.

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eli_gottlieb
I genuinely find it hard to believe mathematicians could function
professionally as mind-body dualists, especially given how many major
mathematicians are non-neurotypical.

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namenotrequired
_We broke the problem down into 2,217,093,120 smaller problems_

Off topic, but this is a brilliant sentence to use especially outside of the
original context. Like if you broke someone else's ugly vase.

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justinpombrio
If it's in _that_ many pieces, I think the word is vaporized.

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saalweachter
Aerosolized. Starting from a couple dozen moles, you'd end up with
quintillions of atoms in each piece, which would be solid, invisible to the
naked eye, but visible under a microscope (about an order of magnitude larger
than the average eukaryote).

Vaporization would imply a complete dissociation of all the atoms.

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ColinWright
There was significant discussion of this in an earlier submission:
[https://news.ycombinator.com/item?id=1587340](https://news.ycombinator.com/item?id=1587340)

Discussion there is closed as it's so old, so if you want to say anything new,
this is the place to do it.

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kyberias
These results are really cool because first when you look at such a problem
space, the size may look insurmountable but with clever algorithms one can
always hope to solve it in reasonable time. Whether 35 CPU years is
reasonable, I don't know. :)

~~~
nathancahill
It's not. But if you've been donated the spare cycles, it's easier to use them
than to spend time optimizing a difficult algorithm.

I wonder why Google donated spare cycles to solve the Rubik's cube when there
are problems like Fold.it that could use it for science.

~~~
existencebox
Probably? (jadedly) It's a cheap one off that earns them a lot of free
publicity.

Folding and SETI have been at it for decades, and will be for decades more.
That'd be a lot of power/hardware costs for little net gain modulo time spent.

(Note: 30 cpu years really isn't a lot of time when you start getting truly
massive parallelism, and google is certainly at that scale. I'm honestly
surprised to see this is pthreads based, I would have expected it to lean
heavily on CUDA (or maybe I'm just showing my naivete to the field of parallel
programming))

~~~
birken
Just to put some numbers behind this:

35 CPU years = 35 * 365 = 12,775 CPU days

Let's assume that your standard Google machine has 2 8-core processors, that
is 16 cores per machine

12,775 / 16 = 798 machines

800 machines is a lot for your average person, but for a company like Google
it is a very small drop in the bucket. And that is assuming you need to do all
of the calculations in one day. If you are willing to do the calculations over
a month, you only need 26 machines.

Even if "CPU year" applies to one 8-core processor, that still means it is
just 26 * 8 = 416 machines, which is a very small number for Google.

And remember, the machines are still doing other things, this is just using
idle CPU (generally a plentiful resource for your standard internet giant
workload).

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dionyziz
I'm surprised we couldn't have proven this analytically.

~~~
elwell
I'm more surprised that they were able to prove it computationally.

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aaron695
It's a shame about the religious babble brought into this by the people who
ran it.

"One may suppose God would use a much more efficient algorithm"

It still could have been fun and been along the lines of "One may suppose a
god would use a much more efficient algorithm"

But there's only one true god evidently. Lets ignore those stupid religions
that have many gods.

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freyrs3
It's a metaphor that's probably understood by everyone who reads it, which is
the point. Besides, the English lexicon is full of vestigial words and phrases
relating to Greek polytheism, they're just as detached as this metaphor is.

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rational_indian
>they're just as detached as this metaphor is.

Except it isn't. You are delusional if you think it is.

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freyrs3
That's a great argument, I'm convinced.

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kimonos
Interesting!

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Gepser
There are asians who solve the cube in less than 30 moves every time. ¿Are
asians closest to be God?

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vonnik
i thought god's number was seven:
[https://www.youtube.com/watch?v=HsHITZRCgqs&feature=kp](https://www.youtube.com/watch?v=HsHITZRCgqs&feature=kp)

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Gepser
Not really
[http://en.wikipedia.org/wiki/God's_algorithm](http://en.wikipedia.org/wiki/God's_algorithm)

