This is part of IEEE Spectrum's SPECIAL REPORT: THE SINGULARITY

PHOTO: Caltech

The role of the conscious observer has been hotly debated since the inception of quantum mechanics in the 1920s. More recently, the Oxford University cosmologist Roger Penrose has surmised that a yet-to-be-discovered quantum theory of gravity lies at the core of consciousness. There are no principled reasons why macroscopic quantum effects, such as entanglement, could not have been selected for by natural selection to subserve brain functions. If that is true, you would not be able to upload your consciousness into a classical machine. It would have to be a machine that exploited quantum entanglement at the level of its elementary gates. You'd need, in other words, a quantum computer, with the processing and memory capacity of a human brain. Indeed, the University of Arizona anesthesiologist Stuart Hameroff has popularized the notion that microtubules—proteins that form the cytoskeleton of all cells, including neurons—implement quantum gates that underlie consciousness.

However, there is no compelling evidence that brains exploit any of the special features of quantum mechanics. The components of the nervous system—a warm, wet tissue strongly coupled to its environment—would make it very difficult to retain entangled states, or qubits, over the necessary spatial-temporal dimensions. It is likely that to simulate or emulate brain-based functions, including consciousness, computers built out of classical, nonquantum gates will suffice.

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