Naturens programmeringsspråk

Det finns tecken på att fysik och datavetenskap långsamt sammanstrålar, och bland de mest intressanta artiklar i det ämnet jag läst nyligen finns denna artikel om hur kvantsökning kan vara en naturlig egenskap hos elektroner. Författarna går emelletid längre och menar att detta också kan förklara grundläggande biologiska strukturer, och det är nu det blir verkligt WTF:

In other words, this is evidence that free electrons naturally implement the Grover search algorithm when moving across the surface of certain crystals.

That has immediate implications for quantum computing. “[This work] may be the path to a serious technological leap, whereby experimentalist would bypass the need for a full-fledged scalable and error-correcting Quantum Computer, and take the shortcut of looking for ‘natural occurrences’ of the Grover search instead,” say the team.

The work also has implications for our thinking about the genetic code and the origin of life. Every living creature on Earth uses the same code, in which DNA stores information using four nucleotide bases. The sequences of nucleotides encode information for constructing proteins from an alphabet of 20 amino acids.

But why these numbers—four and 20—and not some others? Back in 2000, just a few years after Grover published his work, Apoorva Patel at the Indian Institute of Science in Bangalore showed how Grover’s algorithm could explain these numbers.

Patel’s idea is related to the way DNA is assembled inside cells. In this situation, the molecular machinery inside a cell must search through the molecular soup of nucleotide bases to find the right one. If there are four choices, a classical search takes four steps on average. So the machinery would have to try four different bases during each assembly step.

But a quantum search using Grover’s algorithm is much quicker: Patel showed that when there are four choices, a quantum search can distinguish between four alternatives in a single step. Indeed, four is optimal number.

This thinking also explains why there are 20 amino acids. In DNA, each set of three nucleotides defines a single amino acid. So the sequence of triplets in DNA defines the sequence of amino acids in a protein.

But during protein assembly, each amino acid must be chosen from a soup of 20 different options. Grover’s algorithm explains these numbers: a three-step quantum search can find an object in a database containing up to 20 kinds of entry. Again, 20 is the optimal number.

In other words, if the search processes involved in assembling DNA and proteins is to be as efficient as possible, the number of bases should be four and the number of amino acids should to be 20—exactly as is found. The only caveat is that the searches must be quantum in nature.

Livets strukturer och matematiska val följer alltså av fysikaliska kvantegenskaper och organiserar sig efter hur dessa optimerar sökningar. Och nu skriver vi kod utifrån dessa grundläggande samband.

Okej, spekulativt som tusan – men jag ryste när jag läste detta. Att livets organisation och struktur – minns Schrödingers definition av livet som en aperiodisk kristall – matchar upp över biologi och kvantfysik är en svindlande möjlighet, samtidigt som det kanske inte borde överraska oss alls.

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