Why not faster computation via evolution and diffracted light

20.47, Tuesday 20 Apr 2021

Something I wonder is: what if computation, with today’s technology but done differently, could be - say - a million times faster? Here’s my thinking.

If there’s a defining feature of what computers are, I would say it’s abstraction layers.

You can tap buttons and move windows without thinking about what’s going on behind the screen. The programmer of that app sets out the instructions to draw those windows, and how they should behave, all without having to think about how exactly the instructions will be carried out.

Those instructions are defined in simpler instructions, and so on, and so on. Eventually there are instructions that tell the chip what to do – but even that isn’t the end of it. Because, as I learnt recently, the chip itself turns its instructions into still more fundamental operations: microcode. Microcode choreographs the physical building blocks of the machine… registers, adders, flip-flops. And below those are gates. And below those are transistors.

It is absurd that a finely inscribed piece of silicon, with electricity running across it - the pattern on the stone - can be this thing, the computer. And yet!

Each abstraction layer hides the complexity beneath, and provides general purpose flexibility to the layer above.


Here’s my question. Abstraction means reliability and composability. But surely each layer comes at a cost? And there are so. many. layers.

Let’s say you just wanted to perform just one task. Say, recognise a face. Or know whether a number is prime or not. And you didn’t care about flexibility at all.

Could that task be performed by simply the right set of transistors, at the hardware level, no matter how insanely arranged?

What shortcuts could be taken?

Here’s my evidence that this is a valid question to ask: a paper from 1996 on the topic of evolvable hardware.

‘Intrinsic’ Hardware Evolution is the use of artificial evolution – such as a Genetic Algorithm – to design an electronic circuit automatically, where each fitness evaluation is the measurement of a circuit ‘s performance when physically instantiated in a real reconfigurable VLSI chip. This paper makes a detailed case-study of the first such application of evolution directly to the configuration of a Field Programmable Gate Array (FPGA). Evolution is allowed to explore beyond the scope of conventional design methods, resulting in a highly efficient circuit with a richer structure and dynamics and a greater respect for the natural properties of the implementation medium than is usual.

I want to unpack that abstract:

  • Thompson designed an electric circuit to perform a tone-discrimination task – it listens to a sound, and can tell you which of two expected tones it has heard.
  • Thompson then evolved the circuit by taking its computer representation, introducing randomness, and making multiple variations.
  • The critical part: the evolved circuit was selected not as a simulation, but by making a physical version and - experimentally - measuring how well it performed.

This line in the abstract is far too modest: a greater respect for the natural properties of the implementation medium than is usual – because what happens is - excuse my French - BATSHIT INSANE.

Jumping to Section 5. Analysis in the PDF:

The evolved circuit is a mess.

So, of that tangle: Parts of the circuit that could not possibly affect the output can be pruned away. (By tracing what is connected.)

BUT! It turns out: if these parts of the circuit are prunes, the circuit no longer performs as well.

It turns out that 20% of the components cannot be removed even though there is no connected path by which they could influence the output.

What has happened? Thompson has evolved a circuit from a ‘primordial soup’ of reconfigurable electronic components – and he speculates that some of the components are interacting via the power-supply wiring or electromagnetic coupling. Not by conventional means.

(The circuit also stops working outside the 10 degrees Celsius range in which it was trained.)

In 1996, the idea of “training” a computer to perform a task was slightly absurd – yes, there were expert systems and there was AI, but it was a toy. 25 years later, and computers are fast enough such that machine learning is standard practice at every tech firm… and we’re still figuring out how far it can go. If trainable software’s time has come, how about trainable hardware?

Given a single task, such as recognising a few simple words or a face, or performing protein folding, and so on, would it be possible to discard the complexity we currently devote to general purpose computing, and train a primordial soup of transistors to perform only that exact task – taking advantage of whatever nonlinear local effects and physics is available, abstraction layers be damned?

Here’s another type of computer that makes use of deep physics: Artificial Intelligence Device Identifies Objects at the Speed of Light. It’s called a diffractive deep neural network.

The existing way for a camera to recognise an object is for the camera to convert light to pixel data, then the computer has, in software, a trained neural network (that’s machine learning again) that runs matrix maths on the grid of pixels until an object category pops out at the other end. The matrix math is fearsomely complex, and is trained in a process called machine learning. The result: It’s a dog! It’s a face! It’s a tree! Etc.

This new way still uses machine learning, but the maths is replaced by a series of very thin, semi-transparent 8-centimeter-square polymer wafers. Each wafer diffracts the light that comes through it. And:

A series of pixelated layers functions as an “optical network” that shapes how incoming light from the object travels through them. The network identifies an object because the light coming from the object is mostly diffracted toward a single pixel that is assigned to that type of object.

So you don’t need a camera.

You don’t need software.

You take a stack of FINELY ETCHED TRAINED PLASTIC WAFERS, and you look through it at an object, like using a monocle. But instead of seeing the object more clearly in focus, you see a cryptic constellation of glittering pixels. You look up the constellation in your handbook, and… It’s a dog! It’s a face! It’s a tree! Etc. Only, at the speed of light. With no power required.

Physics performing computation at the granularity of the universe.

By using the interference of light with itself.

The analogy for me is that you have a swimming pool, the shape of which is ingeniously and carefully constructed, such that when you throw in an object, the ripples all bounce around and reflect off the edges and change in speed given the depth, and all collide in such a way that the shape of the splash spells a word in the air: the name of the object you threw in.

I can’t help but cross these ideas in my head.

What if we disregarded general purpose computing and abstraction layers in favour of speed?

What if we could evolve hardware to make use of hidden physics?

What if we used light?

What then?

Perhaps a computer, for a specific task, would be a million times faster. Or to put it another way, that’s 20 Moore’s Law cycles: 40 years of performance gain. That’s like saying we could leapfrog from 1981 computers to 2021 computers.

The speed of computers now is what has made machine learning possible. Advanced statistics, neural networks, etc, all of this was known pretty well decades before. But it was impossible to run.

So what today is impossible to run?

What if you could make a single-purpose, zero power lens that looks at a handwritten number and breaks cryptography?

Or sequences a gene?

Or runs a thousand faster than realtime simulations and drives your car for you? Or predicts behaviour of a person in a negotiation? What about computational photography that can look around corners by integrating the possibility of photons, or can brute force prove or disprove any mathematical theorem?

Or understands and can generate natural language just like GPT-3 but a million times better? Or, as in that speculation about an AI overhang: Intel’s expected 2020 revenue is $73bn. What if they could train a $1bn A.I. to design computer chips that are 100x faster per watt-dollar? (And then use those chips to train an even better A.I…)

What is the ultimate limit of computational operations per gram of the cosmos, and why don’t we have compilers that are targeting that as a substrate? I would like to know that multiple.

And, a question for computer scientists, what single question would you ask if you have a dedicated computer that was [that multiplier] faster? Because I would like to know.

I guess what I’m saying is that it might be possible, with today’s technology, to make a monocle, perhaps one that you fold down like a pirate’s patch, that when you look through it with your eye performs - with zero power - a single massively complex AI computation on whatever you’re looking at, as fast as computers will run decades in the future.

If I were the US government, I would be pouring billions into this.

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