Analogue Comeback
Anna Demming
1 Amid an epic haul of jewels and statues rescued from an ancient Greek shipwreck, it was a lump of corroded wood and bronze that would capture the worlds imagination. Pulled from the Meditrranean Sea in 1901, the Antikythera mechanism was an astonishingly sophisticated 2,000-year-old computer. The size of a shoebox, sporting chunky bronze gears rimmed with hundreds of triangular teeth, it was built to chart the paths of celestial bodies and was capable of addition, multiplication, subtraction and division--all by cranking a handle.
2 Nearly half a century would pass before its significance became apparent. By that time, the world had developed a new breed of calculators: the digital computers we still use today. Powered by electricity rather than a hand crank, they were a huge step forward and have proved fast and powerful enough to keep the modern world afloat.
3 But digtal computers aren't always the best tool for the job. Much of the mathematics used at the frontiers of moder science, for example, translates awkwardly into digital technology, where certain equations are cumbersome to solve. New approaches are increasingly sought after in the design of artificial intelligence, too, where digital computers struggle to mimic the complex processes of the human brain. As such, the latest hardware is often too expensive and inefficient to use in this area.
4 Mechanical devices are unlikely to be the answer. Even so, to better meet today's challenges, researchers at the cutting edge of computer development are looking to analogue techniques that have more in common with the Antikythera mechanism than today's conventional computers. To save computing's future, we need a blast from the past.
5 As the name suggests, analogue computers can provide a physical analogue of the system they are describing. In a device like the Antikythera mechanism that is made up of a set of rotating cogs, for example, the positions of certain cogs represent the locations of the sun and moon. You can always tell where those objects are just by looking at the cogs.
6 By contrast, a digital machine has no such exact mappings. Instead, it converts all information to numbers, such as the coordinates of the sun and moon, and performs calculations on those numbers to chart their change. By operating on the numbers independently of how the physical equipment itself works, digital computing can be hugely versatile. Swapping between different problems just means setting up a different set of mathematical commands, rather than re-engineering cogs or their equivalent for each type of calculation.
A Little Bit Better
7 A key characteristic of digital computers is the use of binary digits- -also known as bits-that represent all the processed or stored data as a string of 0s and 1s. In the first digital computers, information was stored and fed in via punch cards with holes representing 0s and solid card representing 1s. For the calculation itself, the computers read the information and translate it onto circuits equipped with transistors capable of switching between two states- -that is, routing a current one way or another. Processing the data then involves following a program thar flips the right set of switches at each stage of the calculation.
8 One drawback of storing data in the form of binary digits is that the values for variables are no longer continuous. Whereas a pointer on a cog can rotate seamlessly through everything between the numbers 4 and 5, for instance, a basic digital computer might jump from 4.1 to 4.2 without being able to represent the values in between. Adding more bits can make the gaps between numbers ever smaller, but graving to make jumps of some size is inevitable.
9 This doesn't necessarily mean a drop in accuracy. Think of a digital stopwatch versus an analogue one: Although a precise measurement of the angle of the second hand could, in theory, allow you to read off infinitely small units of time, in reality the eye won't read a simple dial with the same accuracy that digital figures can drill down to.
10 The first programmable, general-purpose digital computer was the Electronic Numerical Integrator and Computer (ENIAC), introduced in 1946. It was the size of a room and took days to program, but it was significantly more powerful than any computer that had come before. Analogue approaches kept up for a while, but they were little more than a quaint memory by the 1980s.
11 Yet even today the world isn't as digital as it seems. “The physical world is analogue," says Yannis Tsividis at Columbia University in New York. Analogue technology is still all around us. The electromagnetic radio signals that our smartphones use too communicate with each other, for instance, are analogue, requiring analogue-to digital converters to allow the phone's digital electronics to process them.
12 Analogue isn't just useful for shifting data from one place to another. There a situations where these technologies are proving superior to digital ones for processing data, too. One key area concerns the kinds of equations used for everything from modelling the effects of hormone levels in the body to understanding particle behavior, These differential and integral equations are mathematical expressions in which quantities are related in terms of their rate of change rather than just their values. The digital approach to tackling them involves calculating and storing the value of each point along a function relating two variables, and then performing calculations on those stored values. An analogue computer, by contrast, would be able to work on the whole function at once.
13 One way of doing this to harness the mathematics that governs electrical circuits themselves. Quantities like electric current, charge and capacitance are related by rates of change in their values. This means they ft differential equations, allowing electrical circuits to serve as analogues for all other systems governed by such mathematical expressions. That is why Tsividis and his colleagues have used these kinds of circuit elements to develop al-electrical analogue chips
14 Unlike the analogue computers of the 1940s and 1950s, with their punch cards and primitive wiring, these chips benefit from all the same advances in semiconductor research that have made digital computers smaller and faster. These new analogue chips can connect to each other as well as to conventional digital computers, and- -most importantly- -can solve certain problems faster and more efficiently than their digital counterparts. For example, multiplying two eight-digit binary values digitally would take about 3.000 transistors, but an analogue computer would need a maximum of eight ."People did not seem to have considered analogue computing in the context of modern technology", says Tsividis."We did, and things looked very promising."
15 It isn't only electronics that could be useful for analogue computing. Researchers are now turning to beams of light, not least because of the possibility of superfast data transfer. Optical technology offers other benefits as well. When you put objects in the way of light, for example, you get effects that provide a physical analogue for a wide range of phenomena, These range from simple dispersion- -which can also be used to describe the behavior of electrons- -to solitons, lone travelling waves that share mathematical descriptions with earthquakes and stock market behavior.
16 Nader Engheta at the University of Pennsylvania and his college have shown that fast optical analogue computing is possible using interactions between light and matter. They have used a complex structure known as a metamaterial to affect the path of light in such a way that it can solve integral equations. Their prototype, which looks like a Swiss cheese about half a meter or so across, is designed to work on the long wavelengths of microwave radiation. Future iterations could do so on optical or shorter wavelength radiation, allowing the structure to be a thousand times smaller and faster.
Brain Training
17 One particularly influential backer of analogue computing has been the US. Defense Advanced Research Projects Agency (DARPA), which invests in innovative technology.In2016,DARPA sought designs for analogue or hybrid analogue/digital devices that could provide the capabilities of a supercomputer in a desktop device. Some of the most promising ideas to come out of that scheme revolved around electronic devices called memristors.
18 Any time an electric current flows through a circuit, it encounters resistance. In a memristor, that resistance changes in response to previous use, and the altered resistance state is retained when the circuit is off, meaning it has memory, This is useful for computing as power-free data storage, but also interests scientists working on neuromorphic computing, in which electronic circuits are used to mimic the workings of a brain.
19 The strength of the connections, or synapses, between the brain's neurons grows stronger as more signals pass through them and weakens if signals become rare, giving them learning functions akin to muscle memory: This continuously varying connectivity is awkward to replicate with digital technology, which needs currents to be in one state or another- -on or of. Memristors are therefore seen as an attractive basis for neuromorphic computing.
20 Not everyone is convinced .“I see some marginal benefits of analogue circuits for neuromorphic implementations, but these benefits come with very high costs that are generally not worth paying," says Mike Davies, director of Intel's Neuromorphic Computing Lab. “Digital design methods optimistic the key figures of merit that matter--accuracy, power, speed and chip cost- -in ways that analogue approaches can't match." 
21 Few would argue that digital generally wins hands down in terms of precision .What seems to still be open to debate is how much that matters .“These [analogue] devices and system emulate real neural-processing system" ,says Giacomo Indiveri at the Swiss Federal Institute of Technology in Zurich ."As such，they are noisy ,imprecise and unreliable."Indiveri is an advocate for combining analogue with digital technologies to get the best from both .His view is that what biological neural-processing systems lack in precision ,they make up for with sophisticated feedback mechanisms for adaptation learning and plasticity . Designed correctly, neuromorphic devices and algorithms could also benefit from this trade-off.
22 That could have huge implications for the power and speed of computing. The tech giant IBM's Blue Gene was one of the most powerful supercomputers in the world in 2011, yet it sill struggled to simulate the billions of neurons and synapses in the brain of a cat, all while guzzling through enough energy to run a thousand domestic homes.
23 Memristor devices could not only be more compact, but stand a chance of matching the brain's energy efficiency, delivering the same results on a thousandth of the power. As ever more objects, from smart fridges to children's toys, become equipped with computational power as part of the much-touted Internet of things, Indiveri sees analogue-embracing hybrid technologies as a way to power these device mor efficiency.
24 He isn't alone. IBM has teams dedicated to analogue innovation for AI .One of the firm's researchers ,Hsinyu Tsai ,point out that such analogue devices are already finding use in everyday technology, such as the specialized chips that let you rouse your phone with a spoken command. "Analogue approaches ft especially well with today's AI applications, where models consist of a large number of computations, yet require only limited numerical precision," says Tsai.
25 It was two thousand years ago that the Antikythera mechanism sank to the sea floor. After all this time, perhaps we are only just coming to understand the true power of its analogue legacy.

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