
Mechanical Turing Machine in Wood - ColinWright
https://www.youtube.com/watch?v=vo8izCKHiF0
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avian
This is fascinating. It reminds me of an art display I saw years ago that
looked similar. However I was disappointed to learn that in that case the
mechanical stuff was only for show and the algorithm was driven by an Arduino
hidden behind the scenes. I'm so happy someone actually made the real thing!

Don't miss the document linked in the video description. It gives some details
on how the machine works.

The alphabet on the tape has 3 symbols: "b", "0", "1" \- they are encoded as
different positions of pegs in the physical tape. Three non-functional tape
blocks mounted on the machine demonstrate the encoding of the alphabet.

There are 3 machine states "a", "b", "c". They are encoded as the major
position of the plate on the left of the machine that moves up and down. The
plate also has a minor position that depends on the current tape input.

The minimal universal Turing machine the author talks about is [1].

[1]
[https://en.wikipedia.org/wiki/Wolfram%27s_2-state_3-symbol_T...](https://en.wikipedia.org/wiki/Wolfram%27s_2-state_3-symbol_Turing_machine)

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tabtab
I once floated the idea of a "simplest Turing Machine" contest that limited
materials to wood, nails, screws, and string. The one with the least number of
parts wins. Each Nail and screw would be considered half a part, but total
score would be rounded up. This is because people tend to consider fasteners
as ancillary, but not counting them at all would create too many loopholes and
oddities.

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twic
A wonderful piece of work!

But this remark in the accompanying document did make me laugh:

> Another search on the internet yielded a small list of machines built by
> others. Several had electronic controllers controlling the mechanics. I can
> hear Mr. Turing say, “A computer running a computer. Whaaaat?”

I'm not sure Dr Turing would have expressed surprise in that manner, and even
less sure that he would have been surprised that one computing machine could
simulate the behaviour of another.

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SilasX
My first question is, could this have been made at the time Babbage was trying
to build the Analytical Engine, which (had he completed it) would have been
the first Turing-complete machine? Would it have accomplished the same
practical results (at least with some scale-up)?

[https://en.wikipedia.org/wiki/Analytical_Engine](https://en.wikipedia.org/wiki/Analytical_Engine)

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ColinWright
Personal speculation:

There's nothing about this that someone in Babbage's time could not have
build. Removing the negatives from that statement ... this could easily have
been built in Babbage's time.

However, it would not have been. A literal Turing machine needs a huge tape
and a very, very long time to be able to do useful calculations. Babbage's
Difference Engine could be seen to be immediately useful performing a task
that was essential at the time. Babbage's proposed Analytical Engine was less
obviously immediately useful, but it could do things that were obviously on
the way to be useful, so might have got some speculative funding.

But a naked, vanilla Turing Machine is so obviously _not_ (directly) useful,
and no one of the time would having funding building one that was big enough
to do anything of practical interest.

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hermitcrab
Indeed. The 'Turing machine' was proposed by Turing as a thought experiment.
It was the simplest implentation of a universal computing machine that he
could think of. Any physical implementation of it would be incredibly
inefficient.

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mLuby
Forget nanobots; I believe that a "clanking" self-replicating machine can be
made from sources of wood and metal feedstock (and mechanical power). This
could be the control unit.

Is anyone else interested in this kind of thing? Looking for community.

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daralthus
L.S. and S.V. Penrose did some experiments around this:
[https://www.youtube.com/watch?v=2_9ohFWR0Vs](https://www.youtube.com/watch?v=2_9ohFWR0Vs)

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mLuby
Thanks for the link, that's interesting.

All the "self-replicators" I've come across are either digital (e.g. Conway's
Game of Life) or like the ones in this video, that is they require specialized
parts as their "food." You could say they are all "carnivores" in the sense
that they consume other machines. My interest is in "herbivore" self-
replicators, those that reproduce by consuming raw materials and energy from
their environment.

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Gravityloss
The cell does some mind boggling stuff. What the macro organism achieves is
boring in comparison. Hence clanking replication could be very hard.

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mLuby
Agreed; I'm proud of our little constituent buddies!

I can't help thinking about how close a water-powered lumber mill feels to
full closure (i.e. it produces all the parts it uses). Humans perform the
chopping, move things from station to station, and assemble the finished parts
into new buildings and machines.

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Gravityloss
What about the saw blade? It's probably hard to cut wood with wood...

Usually you require a few different material "paths" for replication. You have
a hard material that can be softened with chemicals for example, so it can be
shaped with machinery that is softer than the end product.

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teekert
Somehow I expect there to exist a minimal mechanical Turing machine, I expect
it to be highly symmetrical and I expect it to be very beautiful and
fascinating to watch.

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d33
So could one enter the code of an universal turing machine here and write a
program directly on the tape?

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simonebrunozzi
Being able to take the configuration "table" and change the input quickly is a
neat feature!!

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djaque
Too bad they didn't give it an infinite wooden tape :)

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tabtab
I cheated by letting it sit around a long time, and termites ended up doing
all the work.

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thelazydogsback
Want! :)

