Many people think of the brain as a big complex powerful computer but it is more than that. Classical computers are Turing machines. The human brain is more than a Turing machine - it can solve problems no Turing machine can solve.

This means the subtlety and power of human thought surpasses what any Turing machine can do. Not just any that we can build today, but any that could ever be built, even theoretically, with no limit to technology, size or complexity.

For just one example, Goedel's Incompleteness Theorem tells us there are truths that no Turing machine could ever prove, yet human brains can indeed know their truth with mathematical certainty. To use a metaphor, our brains can think outside the box - Turing machines cannot.

It may be possible some day to build computers that rival the human brain. We don't know what such machines would be, but we know they must be more than Turing machines, yet the idea of a computer that is somehow more than a Turing machine is virtually incomprehensible.

When I say the sublety and power of human thought surpasses any Turing machine, I don't mean in speed. It is trivial to build a computer that does arithmetic or other operations faster than a human brain. That's not the point. It's about the kind of logical paths and insights that can be realized and followed. The human brain can follow logical paths and insights that go where no Turing machine can reach and arrive at conclusions that are still mathematically precise and provable.

For one example, consider Goedel's Incompleteness Theorem. There are other examples, but a single one is sufficient to establish that the human brain is more than a Turing machine.

A universal truth machine cannot exist. But that doesn't imply that truth is not universal. It only means a machine (Turing machine) can never know or prove all knowable things. It would be ridiculous to claim that humans can know or prove all knowable things. But we know with certainty at least some things that no Turing machine ever could.