I somehow expected this number − 10^63 to be put into relation to comparable search spaces—and not just to “really big”. The complete search space of chess positions is much bigger than this—but doesn’t rule out useful game play for example.
A related questions is: Why is there not a corresponding multitasking of silicon based molecules? Silicon also has four possible bonds but the only place where this seems to play a role is in semiconductors. Is that because there are no biological ways to make such molecules?
The lack of context for comparable search spaces is a fair criticism. The implicit assumption (which I now realize was inappropriate not to spell out for this audience) was that your search would, at some point, involve actually making the molecules in question in order to subject them to some form of experimental characterization. The comparison of the number of possible small molecules to the amount of available terrestrial carbon was intended to make the point that achieving sizable coverage of the search space experimentally is close to a non-starter. In practice, of course, there are all kinds of ways to bias your search in productive directions.
Some search-space context:
Number of possible chess games: Shannon conservatively estimated 10^120 possible games, 10^43 possible board positions.
Number of possible Go games: Wikipedia gives 10^172
Number of ways to order a standard 52-card deck: 8 x 10^67
As for why we don’t see complex silicon-containing compounds in biology, here’s an attempt at an answer: We do see silicates in structural roles, for example in phytoliths. However, low Si-Si bond strength relative to C-C, combined with very strong Si-O bonds mean that you tend to get Si-O-Si linkages (like in silicone polymers) rather than Si-Si bonds, and in the absence of Si-C bonds to prevent further oxidation, you form silicates pretty quickly.
Thanks for the explanation about silicon compounds. As oxygen is always more abundant than silicon, this makes it indeed unlikely to become the basis of silicon-based life.
Phosphorous and nitrogen are also interesting elements capable of forming lots of cool structures… the problem is they’d often rather be doing other things, and can insist quite energetically.
I somehow expected this number − 10^63 to be put into relation to comparable search spaces—and not just to “really big”. The complete search space of chess positions is much bigger than this—but doesn’t rule out useful game play for example.
A related questions is: Why is there not a corresponding multitasking of silicon based molecules? Silicon also has four possible bonds but the only place where this seems to play a role is in semiconductors. Is that because there are no biological ways to make such molecules?
The lack of context for comparable search spaces is a fair criticism. The implicit assumption (which I now realize was inappropriate not to spell out for this audience) was that your search would, at some point, involve actually making the molecules in question in order to subject them to some form of experimental characterization. The comparison of the number of possible small molecules to the amount of available terrestrial carbon was intended to make the point that achieving sizable coverage of the search space experimentally is close to a non-starter. In practice, of course, there are all kinds of ways to bias your search in productive directions.
Some search-space context:
Number of possible chess games: Shannon conservatively estimated 10^120 possible games, 10^43 possible board positions.
Number of possible Go games: Wikipedia gives 10^172
Number of ways to order a standard 52-card deck: 8 x 10^67
As for why we don’t see complex silicon-containing compounds in biology, here’s an attempt at an answer: We do see silicates in structural roles, for example in phytoliths. However, low Si-Si bond strength relative to C-C, combined with very strong Si-O bonds mean that you tend to get Si-O-Si linkages (like in silicone polymers) rather than Si-Si bonds, and in the absence of Si-C bonds to prevent further oxidation, you form silicates pretty quickly.
Thanks for the explanation about silicon compounds. As oxygen is always more abundant than silicon, this makes it indeed unlikely to become the basis of silicon-based life.
Phosphorous and nitrogen are also interesting elements capable of forming lots of cool structures… the problem is they’d often rather be doing other things, and can insist quite energetically.