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Comment by memset | Hacker News Reader

In a similar vein, here is a video from the US Navy in the 1950s which describes how mechanical computers work (for calculating trajectories of missiles being shot from ships.)

Utterly fascinating to see how very simple mechanical devices, like differing gear ratios, can be used to calculate things like logarithms.

http://www.youtube.com/watch?v=mpkTHyfr0pM

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Fascinating, an analog computer. Reading about it on wikipedia, it seems analog computers have been almost completely forgotten in the digital age. It makes me wonder what kind of analog computer would be possible now with 21st century technology, especially because of discoveries in condensed matter.

For example, could an electrical analog system be a way of carrying out large-time molecular dynamics simulations? With proper tuning of the material, might you be able to create arbitrary potentials between the electrons within it so that they would interact roughly like atoms in an MD simulation? Or, perhaps you could create an analog chip where the electrons would 'naturally' solve various NP-hard problems, effectively by brute force?

Based on your comment, I did a little searching for the terms (single electron circuit) and found this interesting document. Maybe it's the kind of thing you're talking about:

http://www.worldscientific.com/doi/suppl/10.1142/p650/suppl_...

For a completely different portrayal of futuristic mechanical computers, check out Neal Stephenson's story The Diamond Age. It's set in an era of nanotech, and the computers are nanoscale clockwork computers.

Rod-logic! http://www.halcyon.com/nanojbl/NanoConProc/nanocon2.html

Reading about it on wikipedia, it seems analog computers have been almost completely forgotten in the digital age.

Musicians are still using them. Modular synthesizers are the bomb.

You might also enjoy reading about this experiment: http://en.wikipedia.org/wiki/MONIAC_Computer

The concept of a really advanced mechanical/analogue computer is covered really well in "The Diamond Age".

http://en.wikipedia.org/wiki/The_Diamond_Age

Actually, people are all the time now going the other direction (or proposing to): they use cold atoms to simulate setups from condensed matter. The general idea is that you can use lasers to site the atoms on a lattice, and then tune the interactions between the atoms to get all sorts of physics. A quick Google Scholar search turns up http://www.nature.com/nature/journal/v415/n6867/abs/415039a.... , wherein Greiner et al. simulate the Hubbard model (it would appear---I don't have access to the paper at the moment.

This is cool, because the Hubbard model is a simple and displays interesting phenomena, but understanding it is a hard problem. The Hamiltonian (that is to say, the energy) consists only of a kinetic energy plus an interaction between the spin up and spin down particles on the same site (e.g. if I have two spin up bosons and four spin down bosons, the interaction contribution to the energy is 8 U, where U is a constant parameter---the strength of the interaction.) Depending on this interaction strength U, the system might behave either like a conductor or an insulator.

The problem is hard to deal with analytically (for reasons I can't say I understand) and, as I understand it, the space of possible states is so huge that the numerics become computationally intractible at about a lattice 5 sites x 5 sites x 5 sites. So being able to see the phase transition happen is very neat, and exactly what you expect from an "analog quantum computer": simulating with cold atoms a system that we can't really simulate with ordinary computers.

> In a similar vein, here is a video from the US Navy in the 1950s which describes how mechanical computers work (for calculating trajectories of missiles being shot from ships.)

Guns, not missiles. At 0:50, the narrator refers to "initial shell velocity."

They were last used in combat in the 1990s, when the Iowa-class battleships fired their 16-inch guns at Iraqi positions in Kuwait. The Navy never bothered to replace them with digital computers, because they were already accurate enough for the guns they controlled.

That was a great video, thank you! Knowing basic gear mechanics helps a lot in understanding how cars function.

This 1937 video about differentials is also enlightening:

http://www.youtube.com/watch?v=yYAw79386WI

Why is it that old tutorial videos are so thorough and informative?

There was no Internet to fill in the details?

It was also a big deal to make a film like this. Today you can just prop up your phone on something and go to town, but these videos would have been a huge amount of work. Once you're putting in that much work, you had better make sure the result is good.

For Bay Area folk (or visitors), there's a restored mechanical targeting computer at the SF88 Nike Missile base in the Marin Headlands

http://www.nps.gov/goga/nike-missile-site.htm

Highly worth a visit if you're interested in this sort of mechanical computing stuff…

That was, as you said, utterly fascinating. It's amazing to see mathematical problems being solved with mechanical solutions. To think the leaps it took to translate these problems to digital solutions (e.g. what was [technically] an infinite set of inputs now recorded as a 32-bit floating point representation).

I don't know if any of these[1] ~50s videos are still shown in school but I found them amazingly efficient at conveying understanding.

[1] So far I saw : analog target computations, wheel differentials, wave diffusion

Would you mind sharing the link for the "analog target computations" video? I couldn't find it.

Thanks!

Sorry for the confusion, but by "analog target computations" I meant the videos about trajectories mentioned in the post above https://news.ycombinator.com/item?id=6231166

Another vintage series, about Fluid Mechanics by John Lumley (. Penn St Univ)

http://www.youtube.com/watch?v=mdN8OOkx2ko

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