Pet peeve: This shouldn't be called computers. Doing so blurs the difference between what they and <the natural conceptspace cluster normally called "computers"> do.<p>This is a <i>calculator</i>: a machine cable of doing a one-off operation (implementing something interpretable as a calculation) before requiring further intervention. "Computer" should be at least reserved for those that can do a lot of instructions, preferably indefinitely, without human involvement.<p>And I don't think this is a terminological nitpick, it bleeds into a fundamental disconnect that leaks out in their puffery:<p>>The aim is to demonstrate how very simple reactions, simple enough that they occur in real physics, can be combined to perform mathematical calculations — which hopefully helps explain how large numbers of transistors can combine to play Doom.<p>No, it doesn't. No matter how many of these domino calculators you string together, <i>you're not getting Doom</i> (even with the appropriate hardware to use the calculation's results). To model the core dynamic needed to run Doom, you at least need the ability to indefinitely run such calculations, in a way that subsequent ones depend on the results of earlier ones. By construction, these systems can't do that, and provide no insight into how you would.<p>It does provide a demonstration that a (non-electronic) physical system can implement the dynamic behind addition. Cool. But I'm not sure what layperson actually has trouble on that point. There are lots of physical systems that do that -- the confusion, I think, would lie in <i>how</i> you can bridge the gap to Doom. (At least, it was for me when computers seemed mysterious.)<p>Cool, they found one more physical way to implement a specific calculation. Call it a domino calculator. Don't call it a computer, don't imply it solves the core difficulties needed to run Doom.<p>Okay, rant over, now you can accuse me of making a mountain out of a molehill.