[MR] Antikythera Mechanism by Apple Software Engineer

Thu Dec 23 18:58:30 PST 2010

 This is, of course, an early (very early) analog computer. I've forwarded
some links previously. A lot of interesting links in the original. Sorry I
don't have at hand the URL for this.

 ------ Original Message ------
  Received: Thu, 23 Dec 2010 08:34:12 PM EST
  From: David Bolduc
  Subject: [johnmacsgroup] Antikythera Mechanism by Apple Software Engineer

   interesting video and photos in original.

     Watch an Apple Engineer Recreate a 2,000-Year-Old Computer Using Legos

       Here's a brand new stop-motion video showing the device's inner
workings -- and an interview with its creator, Andrew Carol.

       Remember that old commercial about "Zack, the Lego maniac"? Well, Zack
ain't got nothing on Andrew Carol. When Carol's not working on improving the
finer points of OS X as a software engineer at Apple, he's hard at work
building analog computers -- like the Babbage difference engine -- entirely
out of Legos.

       Recently, Carol has completed his biggest challenge yet: a working Lego
replica of the famous Antikythera Mechanism, created by ancient Greeks in 100
B.C. as a way of predicting astronomical events like eclipses. Though pictures
of Carol's device have surfaced before, few people have delved into how it
functions. Working with Digital Science, I directed a short film about the
device using stop-motion animation to explain how it works -- and talked to
Andy about his design process.

         Why did you choose the Antikythera Mechanism, and where did you
start?

         Andy Carol: It was an email out of the blue from Adam Rutherford at
Nature.com that got me thinking about this. Over Christmas of 2009, I was
already working on a Lego machine that plays tic-tac-toe mechanically. But
Adam had seen my difference engine and contacted me, wondering if it would be
plausible to build an Antikythera Mechanism out of Lego instead. That got me
thinking it over and researching it. I had a crude prototype a week later, and
a decent prototype two or three weeks after that. My proof of concept was just
these little boxes of Lego gears I built all in a row. One box did one bit of
math with an axle that ran to the next box. It just went from box to box in a
straight line and proved that it was plausible.

           The original Mechanism and your model use physical gears to perform
mathematical calculations. How does that work?

           It's pretty simple; it's all about ratios between the numbers of
teeth on two gears meshed together. If one gear has 50 teeth and another has
25, that's a 2-to-1 ratio -- which means that turning the axle one full
revolution on the first gear will multiply by two, because it turns the second
gear twice as fast.

           But the tradeoff is that when you make it go fast, you lose power.
It's fast, but it's not strong, and vice versa -- and those mechanical effects
pile up quickly when you've got over 100 gears working together in exotic
ratios. When I have to multiply by 127, it's got to turn very fast, but with
little power, which means that whatever amount of friction there is, I've
effectively multiplied it by 127. So I had to put a lot of thought into
designing the optimal layout of gears that would minimize the friction enough
to make that kind of calculation physically work.

             The original Mechanism was made out of metal, but you had to work
with plastic toys. How did that affect your design?

             Regular Lego bricks are problematic because they constantly want
to pop apart, so I had to use cross-bracing to keep everything rigid enough to
withstand all the mechanical force. And unlike my previous machines which were
made from classic bricks, the new machine is purely made from Lego Technic
pieces because the gearing is so complicated.

             I also designed it using a modular system with racks of gears
that I could remove or pop back in easily. For example, I made one module that
does nothing but divide by 19. It makes the design problem smaller: all I have
to do is focus on getting each module right, then figure out the next one. The
hardest part was physically linking the output of one module to the input of
the next; sometimes the output of one bit was physically far away from the
input of the next one. But modularity really was the secret to making it all
work.

               The original Mechanism was a lso quite a bit smaller than your
version, and used about half as many gears. Why did yours end up being bigger
and more complicated?

               The Greek guy who made the original could cut his own metal
gears to the exact ratios he needed, so he only needed 50 or 60 gears total
and could fit them together very compactly. But I have to use the gears and
ratios that Lego happens to make. That's why I might need eight gears to
accomplish a bit of math that the original machine accomplished with two.

               My machine uses about 110 gears, and 7 complete differentials,
to do most of what the original one did. But their calendar and ours are
completely incompatible, so I also had to add complexity to make the eclipse
predictions understandable. My machine has two extra indicators: one for the
decade and one for the year. That way, as you turn the crank on the machine,
you can read the dials and say "OK, a solar eclipse will happen in April of
2024."

                 Is it really accurate to call the Mechanism a "computer"?

                 Yes, but in a slightly different way than we're used to using
that word. It's an analog computer, which means it can't execute programs. But
the word "computer" used to be the name given to people who could do tedious
math. In the 19th century there were rooms of people called "computers" who
were skilled at arithmetic, supervised by a mathematician, who would create
tables at great expense that navigators and sailors would use. But when we
finally had mechanical devices that could do similar things, they got that
name: computer.

                 But analog computers were still very useful up through the
1940s. World War II battleships would have a mechanical computer in their
artillery, so that when you wanted to fire, you'd turn cranks to figure out
how many times is this gun to be fired, how far is the other ship, what's the
wind velocity, that sort of thing. And when you turned all the cranks, the
gear ratios would tell you how to adjust your aim. So the Antikythera
Mechanism, and my Lego version, are both just simple mechanical computers: you
turn the crank at one speed and all the wheels move at a another speed, which
you've calibrated to have a particular meaning -- in this case, predicting the
cycles of astronomical bodies.

                   So you're saying the ancient Greeks had technology
equivalent to what we were using in 20th-century battleships?

                   We don't give people credit for how smart they were 2000
years ago. There were other mechanical devices as well, that we know about
because they've been referenced in ancient books. They even had machines to
dispense holy water in temples: you'd put a coin in a box and it would move a
series of levers to dole out an amount of water to you, just like a vending
machine. Kings would commission mechanical novelties because it was considered
amazing and clever. But the Antikythera Mechanism is singular because no one
is aware of anything else that complicated. To have actually found it, versus
just reading about it -- you don't know if those ancient accounts are
exaggerated -- that's what's amazing. It took us 100 years just to analyze how
it worked, but over time we've found that it's more and more sophisticated.
And we don't know there were 20 of these things, or if this was the only one.

                   The Mechanism is interesting to me because people think of
these astronomical predictions only being possible with sophisticated NA SA
computers. But to realize that someone actually built a mechanical machine to
do that 2000 years ago is pretty impressive -- and figuring out to to do it
myself in Lego is fascinating too.