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A quantitative definition of life
A finite volume of spacetime can be described with a finite amount of information; see Wikipedia:Bekenstein Bound or arXiv:hep-th/0203101v2. Whether or not this is true—given a putative lifeform and the environment in which it is found—a good quantitative definition of life should:
- provide an unambiguous procedure for converting experimentally discoverable and relevant physical data into pure information (a large number of zeros and ones or bits);
- use standard techniques (eg. from information theory) to quantify the information from 1; and,
- degrade gracefully—given only partial information—so that the quality of the measure is proportional to the quality of the information available from 1.
Consider a ball of space around a putative lifeform. Within the ball record the position and momentum of every atom (and what type of atom it is.) Also record the position and momentum of every valent electron. Quantum mechanical limits prevent a perfect measurement of these quantities but this should not be a big obstacle to us. Thermal noise is jostling the atoms and electrons in our lifeform so that getting the positions and momenta exactly right is unnecessary. The quantity of information obtained in this way will be large but it is already a large reduction from the maximum possible information content as predicted by Bekenstein or Bousso type arguments. The position and momentum of a water molecule in our lifeform, clearly, is not as relevant as the position and momentum of a more biologically important molecule. If we define our "experimental data to information" procedure in this naive way then it will not "degrade" gracefully as required. Partial information—say a random sample of the positions and momenta in a ball of space around our lifeform— will not distinguish a rock from a person. Before focusing on the relevant information, however, it might be necessary to step back and ask if even perfect information under this procedure would be enough to recapitulate any physically possible lifeform.
An intriguing consideration is the discovery of quantum information over the last century.
to be continued...
101 Week 2
See a quantitative definition of life. Continued wiki curation.
101 Week 3
See a quantitative definition of life. More wiki curation. Upgraded to Mediawiki 1.5