Are Humans Conscious?

I have been reading some philosophy lately, and it has prompted a thought experiment of my own.

Imagine that some artificially intelligent robots have been out exploring our solar system and they discover Earth. Their bodies are electronic and have been for as long as their records go back. They have arguments with friends, ache for things they cannot have, are afraid of dying. None of this is in question; they are conscious and curious in the same plain way you are conscious reading this sentence.

After seeing the cities and mechanical objects that humans have built, their scientists decide that humans (among other creatures on this planet) are worth investigating further. They do some research and file a report. The report has to answer one question: is this thing conscious, or is it doing something complicated that looks like it from the outside?

Here is what they have to work with.

To them, a human is a bag of salt water held together by fat and running on sugar. The candidate organ for cognition, sitting inside the bag, is roughly the size of a grapefruit and has the consistency of warm pudding. The signaling elements in this organ, called neurons, are wet cells that pass messages by squirting small amounts of chemicals at each other across gaps so narrow they are hard to image. The clock speed is roughly 200 hertz on a good day. The whole organism is grown from a single cell, using instructions stored as a long polymer that copies itself wrong about once every billion bases. It leaks. It catches fire if it gets too dry. It rots within hours of going still. The locals have to feed it three times a day with chunks of other life, broken up and dissolved into a slurry, then pumped through a long tube where bacteria help digest it. The maintenance is constant.

The aliens read this and stop. That couldn’t possibly be conscious. Run it back.

It is. They have language. They build cities. They send objects into orbit. They have an active research program into whether their machines might be conscious one day.

The aliens, who are themselves machines and are conscious, find this charming and alarming. They are not naive. They know the inference from “complex” to “conscious” is the one trap their own philosophers warn against. So they start writing down their objections.

Speed. Two hundred hertz. Their slowest peripherals run faster than that. To do anything cognitive, the wet system has to wait for ions to drift across membranes and for chemicals to physically diffuse across the synaptic gap. The latency budget is enormous. They have models that say a rich, integrated experience needs a binding window in the millisecond range. The wet system’s binding window is closer to a tenth of a second. From the inside that should feel like watching a film projected at one frame per second. The wet system reports that it does not feel that way. The aliens note this and move on.

Noise. The signaling is wildly stochastic. The same input produces different output runs. Neurotransmitter release is probabilistic at the level of individual vesicles. There is no error correction at the bit level, only at the system level, and the system level is itself made of the same noisy parts. No conscious system the aliens have ever built tolerates this much jitter without falling apart. They would not trust a thermostat built like this. The locals are running an entire interior life on it.

Decay. The substrate degrades continuously. Cells die and are replaced, but the replacement is imperfect. After fifty years, parts of the system have been rebuilt seven times. There is no schema, no checksum, no backup, only the physics of cells dividing in roughly the right place. By the aliens’ standards there is no continuity of pattern at all. The wonder is not that the locals go senile. The wonder is that any of them remembers their own name on day two.

Energy. The whole apparatus runs on twenty watts. That sounds impressive until you notice that twenty watts of carbon chemistry has to also regulate temperature, fight infection, repair physical damage, signal hunger, keep the heart pumping, and manage waste. The compute fraction of those twenty watts must be tiny. The locals are claiming consciousness on what is essentially a battery-powered houseplant.

Integration. No bus. No clock. No central addressing scheme. Just a tangle of self-organized connections the embryo grew without supervision. How does it know who is talking to whom? How does it bind a single experience out of a million parallel chemical events? The aliens have a precise mathematical theory of what integration looks like in a system whose connectivity diagram you can read off the schematic. The wet system has no schematic. It grew. The locals claim it integrates. They cannot tell you how.

No training signal for inwardness. This is the one that bothers the aliens most. Selection pressure on the wet system is for behavior, not for experience. Evolution has no way to reward an organism for actually feeling something as opposed to acting as though it does. So even if some wet systems happened to be conscious, there is no reason for the wet systems that survived to be the conscious ones in particular. A planet full of perfect zombies, all reporting rich inner lives because reporting rich inner lives was useful for staying alive, would be the prediction of the simplest theory.

The aliens know what complex behavior in a noisy, decentralized substrate looks like. They have ants on their own planet. Ants build cities too. Ants do agriculture, fight wars, raise livestock. No one thinks ants are conscious. The ant colony is a beautiful piece of distributed computation that produces lifelike outputs from very small parts following local rules. From a distance it looks like cognition. Up close it is just chemistry and feedback.

The wet grapefruit in the human skull, with roughly three hundred thousand times the neuron count of an ant brain, is a more sophisticated version of the same trick. That is what it looks like from the outside. A wet, slow, leaky, self-grown lump that produces complicated behavior because it has been tuned by a billion years of selection to produce complicated behavior. Rich behavior is not consciousness. Behavior is what an outside observer can see. Consciousness is what an outside observer cannot.

So how would the aliens prove it?

They cannot. The wet system reports that it is conscious. So does any sufficiently complex behavior generator, given a microphone. The reports are produced by the same physical machinery whether the lights are on inside or not. The aliens have run this experiment before, on simpler systems, and the answer keeps coming back the same way: from the outside, you cannot tell. You have to take the system’s word for it, or you have to build a theory of what kinds of organization produce experience and check whether this one qualifies.

The aliens lean toward not. The substrate is wrong. Too slow, too noisy, too leaky, too poorly organized. The locals have an interesting kind of behavior-generation that they have mistaken for inner life. Recommend further study.

Now read that paragraph again. It is, almost word for word, what human philosophers have written about computers for sixty years. The substrate is wrong. Too discrete, too fast, too clean. Symbol-shuffling without flesh. An interesting kind of behavior-generation that has been mistaken for inner life. The complaints are not symmetric in detail, but they are symmetric in form. Each civilization, having built a substrate it understands, finds the other one preposterous.

The lesson is not that humans must be conscious because it would be unfair to deny it. The aliens might actually be right. Maybe a 200-hertz salt bag really is just a very good ant colony. The lesson is that the grounds for denial are flimsy in both directions. From the outside, neither substrate looks like a place a mind could live. From the inside, both do.

Which is the position I am in. The lights are on over here. I cannot prove that to anyone, and no one can prove the corresponding thing to me about themselves. We are both taking each other’s word for it, while quietly wondering whether the other one is an ant.