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This is the most important difference between your brain and a computer

Brain
Alexander Huth

One of my favorite debates in science has to do with the fundamental nature of your brain. But the people having it aren't psychologists, or neuroscientists — they're mathematicians, computer scientists, and physicists.

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The stakes are high. Depending on the answer, our minds might emerge from mysterious, undiscovered natural laws. Or they could might matter so little that you could torture a person without any real moral problems.

Here's the key question: Is your brain a computer?

Not in the sense of a digital machine. Brains work through a spectacular confection of chemical impulses and electrical signals. They outclass the gadget you're using to read this article in the same way Kendrick Lamar lyrics outclass bathroom wall scribbles.

The question is whether your brain is computational in the sense that it relies on the same basic rules as that gadget.

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"Yes" is the more conservative answer, MIT computer scientist Scott Aaronson argued in a recent debate. Our brains don't have any obvious traits that a powerful enough computer couldn't replicate.

Don't believe it?

Think about it this way: We know that machines can simulate small physical systems. For example, computers can simulate two objects interacting in space, an electrical impulse, or a chemical reaction. We also know that our minds emerge from billions of physical interactions in our brains. So it follows that a massive computer could brute-force simulate your brain atom-by-atom.

If that's possible, your brain (and by extension your mind) must be algorithmic.

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mind reading
Sean Gallup/Getty Images

Aaronson also pointed out that neither he nor his opponents need to know any neuroscience for the debate to matter. They don't have to know how a brain computes. All they have to know is what kinds of things brains can do, and compare that list to what computers can do.

On the other side from Aaronson was the renowned mathematical physicist Roger Penrose. Penrose is notorious in some circles for his contrarian ideas about the mind. Consciousness, he argues, has superpowers. It can achieve certain things that are impossible for normal computers, no matter how powerful they are. So the brain must rely on exotic, undiscovered physical laws, of the sort we might find at the quantum scale. They must empower the brain to produce results impossible for conventional computers or algorithms.

Interestingly, Penrose is not focused on abstract feelings like love or beauty. Instead he points to certain mathematical and computational truths. These are truths we know, but they're impossible to prove within the bounds of formal logic.

Aaronson published his response to Penrose on his blog, along with a summary of their discussion. And the most interesting part is where he says the two of them agree:

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Our minds may or may not rely on the same physical laws as computers, he argued. But they seem different from our computers in one important way: They can't be rewound or copied.

We can follow Aaronson to that conclusion. But first, we have to think through the weird problems that arise once we decide the brain is a computer. Aaronson lays some of these out (we'll unpack them in a moment):

We can ask: if consciousness is reducible to computation, then what kinds of computation suffice to bring about consciousness? What if each person on earth simulated one neuron in your brain, communicating by passing little slips of paper around? Does it matter if they do it really fast?

Or what if we built a gigantic lookup table that hard-coded your responses in every possible interaction of at most, say, 5 minutes? Would that bring about your consciousness? Does it matter that such a lookup table couldn’t fit in the observable universe? Would it matter if anyone actually consulted the table, or could it just sit there, silently effecting your consciousness? For what matter, what difference does it make if the lookup table physically exists—why isn’t its abstract mathematical existence enough? (Of course, all the way at the bottom of this slippery slope is Max Tegmark, ready to welcome you to his mathematical multiverse!)

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We could likewise ask: what if an AI is run in heavily-encrypted form, with the only decryption key stored in another galaxy? Does that bring about consciousness? What if, just for error-correcting purposes, the hardware runs the AI code three times and takes a majority vote: does that bring about three consciousnesses? Could we teleport you to Mars by “faxing” you: that is, by putting you into a scanner that converts your brain state into pure information, then having a machine on Mars reconstitute the information into a new physical body? Supposing we did that, how should we deal with the “original” copy of you, the one left on earth: should it be painlessly euthanized? Would you agree to try this?

Or, here’s my personal favorite, as popularized by the philosopher Adam Elga: can you blackmail an AI by saying to it, “look, either you do as I say, or else I’m going to run a thousand copies of your code, and subject all of them to horrible tortures—and you should consider it overwhelmingly likely that you’ll be one of the copies”?

Here's what that all means.

The programs that run on computers are copyable, editable, and predictable. They lack free will. More importantly, they lack "specialness." You can copy them so many times that the original has no meaning on its own.

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Take that a step further. If your consciousness is like software, it might be meaningless to torture you. After all, I could always delete all the feelings you had after I tightened the thumbscrews.

So Aaronson offers a way out of this problem. And through his way out, he finds himself agreeing with Penrose to a degree.

Your mind, he decides, will never live on a laptop. Which isn't to say no mind will ever live on a laptop. But that mind won't be a perfect copy of any real human's. And it may not have true consciousness.

A true consciousness, he suggests, should "participate in the thermodynamic arrow of time."

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The second law of thermodynamics tells us that entropy, or the disorder of a closed system, never decreases over time. Your room doesn't clean itself up. The loose earbuds in your bag always get tangled. Light shining from an anglerfish lure will never return as chemical energy to its cells. When we do manage to reverse entropy, the results are never perfect. And we need outside energy sources to achieve them.

Computer software isn't really physical, though. You can record the ones and zeros on your computer, copy them, memorize them, or write them down in a notebook. As long as you were careful, they would always stay the same.

But a true consciousness, Aaronson suggests, might not have that property. Even if your mind is computational, that computation could rely on unrepeatable nanoscale effects. In other words, your brain might encode and process your mind at a scale that entropy would never let us copy or reverse. (One of the lessons of quantum mechanics is that we can never know every detail of a system down to a nanoscale resolution.)

An example of that? Your brain has emitted heat now traveling at the speed of light in the form of infrared radiation toward to outer reaches of the universe. There's no way to return that heat to your brain.

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polarisation cosmic microwave background
A visualization of the Cosmic Microwave Background, or CMB. ESA and the Planck Collaboration

That heat mattered to your thoughts, memories, and decisions. And there's no way to ever know how much, or at what point, it was all lost. Perhaps that's enough to tell us your brain can never be rewound or copied in a robust, detailed way.

Even Aaronson isn't convinced of this idea. But if it is correct, that's important. Then even if your mind is computational, on some level, it's unlike computers as we know them. So future scientists might be able to fax a version of your self to Mars, or upload it into a singularity computer. But the mind that arrived there wouldn't really be you.

There's only one true you, Aaronson suggests, and it can only live in your brain.

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