Physicist, MIT; Researcher, Precision Cosmology; Scientific Director, Foundational Questions Institute; President, Future of Life Institute; Author, Our Mathematical Universe

What do waves, computations and conscious experiences have in common, that provides crucial clues about the future of intelligence? They all share an intriguing ability to take on a life of their own that’s rather independent of their physical substrate. 

Waves have properties such as speed, wavelength and frequency, and we physicists can study the equations they obey without even needing to know what substance they are waves in. When you hear something, you're detecting sound waves caused by molecules bouncing around in the mixture of gases we call air, and we can calculate all sorts of interesting things about these waves—how their intensity fades as the square of the distance, how they bend when they pass through open doors, how they reflect off of walls and cause echoes, etc.—without knowing what air is made of.

We can ignore all details about oxygen, nitrogen, carbon dioxide, etc., because the only property of the wave's substrate that matters and enters into the famous wave equation is a single number that we can measure: the wave speed, which in this case is about 300 meters per second. Indeed, this wave equation that MIT students are now studying was first discovered and put to great use long before physicists had even established that atoms and molecules existed! 

Alan Turing famously proved that computations are substrate-independent as well: There’s a vast variety of different computer architectures that are “universal” in the sense that they can all perform the exact same computations. So if you're a conscious superintelligent character in a future computer game, you'd have no way of knowing whether you ran on a desktop, a tablet or a phone, because you would be substrate-independent.

Nor could you tell whether the logic gates of the computer were made of transistors, optical circuits or other hardware, or even what the fundamental laws of physics were. Because of this substrate-independence, shrewd engineers have been able to repeatedly replace the technologies inside our computers with dramatically better ones without changing the software, making computation twice as cheap roughly every couple of years for over a century, cutting the computer cost a whopping million million million times since my grandmothers were born. It’s precisely this substrate-independence of computation that implies that artificial intelligence is possible: Intelligence doesn't require flesh, blood or carbon atoms. 

This example illustrates three important points.

First, substrate-independence doesn't mean that a substrate is unnecessary, but that most details of it don't matter. You obviously can't have sound waves in a gas if there's no gas, but any gas whatsoever will suffice. Similarly, you obviously can't have computation without matter, but any matter will do as long as it can be arranged into logic gates, connected neurons or some other building block enabling universal computation.

Second, the substrate-independent phenomenon takes on a life of its own, independent of its substrate. A wave can travel across a lake, even though none of its water molecules do—they mostly bob up and down.

Third, it's often only the substrate-independent aspect that we're interested in: A surfer usually cares more about the position and height of a wave than about its detailed molecular composition, and if two programmers are jointly hunting a bug in their code, they're probably not discussing transistors.

Since childhood, I’ve wondered how tangible physical stuff such as flesh and blood can give rise to something that feels as intangible, abstract and ethereal as intelligence and consciousness. We’ve now arrived at the answer: these phenomena feel so non-physical because they're substrate-independent, taking on a life of their own that doesn't depend on or reflect the physical details. We still don’t understand intelligence to the point of building machines that can match all human abilities, but AI researchers are striking ever more abilities from their can’t-do list, from image classification to Go-playing, speech recognition, translation and driving.

But what about consciousness, by which I mean simply "subjective experience"? When you’re driving a car, you’re having a conscious experience of colors, sounds, emotions, etc. But why are you experiencing anything at all? Does it feel like anything to be a self-driving car? This is what David Chalmers calls the "hard problem," and it’s distinct from merely asking how intelligence works. 

I've been arguing for decades that consciousness is the way information feels when being processed in certain complex ways. This leads to a radical idea that I really like: If consciousness is the way that information feels when it’s processed in certain ways, then it must be substrate-independent; it's only the structure of the information processing that matters, not the structure of the matter doing the information processing. In other words, consciousness is substrate-independent twice over!

We know that when particles move around in spacetime in patterns obeying certain principles, they give rise to substrate-independent phenomena—e.g. waves and computations. We've now taken this idea to another level: If the information processing itself obeys certain principles, it can give rise to the higher level substrate-independent phenomenon that we call consciousness. This places your conscious experience not one but two levels up from the matter. No wonder your mind feels non-physical! We don’t yet know what principles information processing needs to obey to be conscious, but concrete proposals have been made that neuroscientists are trying to test experimentally.

However, one lesson from substrate-independence is already clear: we should reject carbon-chauvinism and the common view that our intelligent machines will always be our unconscious slaves. Computation, intelligence and consciousness are patterns in the spacetime arrangement of particles that take on a life of their own, and it's not the particles but the patterns that really matter! Matter doesn't matter.