Seth Lloyd

In: Quantum Aspects of Life – Eds. Paul Davies & Arun Pati Imperial College Press ISBN: 13: 978-1-84816-267-9

Quantum mechanics is regarded as having two features important for the emergence of a complex system such as life. First it is digital or discrete, in the sense of being composed of a finite number of distinguishable states. The second is randomness. Taking these two features together is interpreted to mean that the universe as described in quantum mechanics is an information processor or a computer that is programmed by quantum fluctuations.

Each discrete unit described by quantum mechanics is envisaged as a computing bit that represents the distinction between 0 and 1 or between yes and no. The spin of an electron or the polarisation of a photon can be regarded as a bit. At the sub-atomic level, bits are referred to as quantum bits or qubits. The interaction between these qubits can be regarded as a computation. Quantum mechanical interactions form the basis of chemistry, which is seen as representing a further layer of computing related to life forms.

The randomness of quantum mechanics is apparent when a measurement is made, or when interaction with one of many features in the environment causes a particle to decohere. As an example a photon passing through a filter, such as the lens of a pair of sunglasses will decohere from a superposition of polarisations to a particular polarisation. Bits are also seen as a measure of entropy, with entropy proportional to the number of bits in a system as registered by quantum particles.

The author remarks that at the Big bang, the universe was in a simple state, and that the laws of physics that have governed its development since then are also simple. He argues from the fact that in a computer when 0s and 1s are generated randomly, if any programme is generated, it is more likely to be a short programme than a long programme, but it is argued that short programmes might be more suitable to eventually produce the complexity of life.

Lloyd rounds off by arguing that complexity cannot derive from computation by itself, but also requires the variation which is introduced by the randomness of quantum mechanics. The superpositions of quantum mechanics reflect or explore all possibilities at once. The article thus seems to imply, although it does not specifically argue for, the idea of a quantum search engine that would eventually hit on the right sequence of molecules to produce a replicator.

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