Talk:Simurgh year
From ErrantryWiki
I'm curious as to where the given length of the Simurgh year comes from:
First, there are some obvious difficulties with interpreting it, for, even with the obvious assumption that this return to the same configuration is approximate, and taking the fiducial tolerance to be that of each planet's size, I'm not sure that we know the planets' positions and velocities (not to mention those of large asteroids and comets) accurately enough at the present to predict to that tolerance over the given timescale (though we might, as it's not that long, and we know a lot about the solar system very precisely from spacecraft and radar ranging). And this quibble even neglects tidal effects, and similar consequences of the fact that the solar system is not actually an assemblage of point particles, which might also prove important over this timescale. For that matter, we have to worry about collisions of planets with asteroids, though these would most likely be small enough that they would not affect the impacted body's orbit considerably.
Thus, I wonder whether the given value refers to some simpler mechanistic model of the solar system—perhaps even one that ignores the (gravitational) interactions between the planets, for this would display exactly periodic behaviour as a whole. (Given that the Titius-Bode law appears in DD's AWOM research file1, it might be relevant. For that matter, Kepler's model involving the Platonic solids might also be a possibility—this apparently even has some physical basis, in that the orbital radii thus obtained have significant stability.) However, I can't reproduce the given result (or even get anything close to it) with any of the possible naïve calculations I've tried, based upon various mechanistic models, though the chaotic nature (i.e., extreme sensitivity to truncation) of even these naïve calculations means that I would probably have to know the exact accuracy of the individual periods used in order to get even reasonable agreement.
Another possibility is that the given length of the Simurgh year was actually determined more accurately by a computer simulation. (The timescale is short enough that an ordinary planetarium program's approximations might be accurate enough, though probably to some lesser tolerance than the fiducial one given above, but I don't know nearly enough about this to say one way or another—the solar system's chaotic nature is not an issue here, as the given length is considerably smaller than the solar system's Lyapunov time of 5-10 million years2.) In this more realistic case, I would expect the length of the Simurgh year to change over time, though the change might be exceedingly small over a reasonable timescale (say, a few Simurgh years), as the solar system does exhibit approximate periodicity.
Finally, I have to wonder about the definition of the Simurgh year as only involving the inner five planets, particularly as this doesn't match up with any reasonable division of the solar system (unless this counts Ceres as the fifth planet—cf. the IAU proposal3, and/or the Titius-Bode law). However, it just misses being either the four terrestrial planets (though these could be extended to include Ceres) or the six classical planets (i.e., those easily visible to the unaided eye). Was this just done to make the length of the Simurgh year approximately that of the Simurgh's mythical lifespan, or is there a deeper reason, perhaps one that will be revealed in AWOM?
1 This appears to be unavailable at the moment, as is all of owlsprings.com—I get a 403 Forbidden error attempting to access any of it. However, it is still available using the Wayback Machine here: http://web.archive.org/web/20060219210106/http://www.owlsprings.com/marspublic2/. (I couldn't get this to work properly as a named link—the renderer wigged out due to the second 'http...'. Is there any way to get around this?)
2 See, e.g., this article; Ivars Peterson's popularization Newton's Clock: Chaos in the Solar System is an excellent general reference.
3 Note that I'm not sure how much of the IAU proposal was public—or at least speculation—at the time DD posted this, much less when she actually came up with the idea, as that most likely predates its posting significantly. —Nathan 22:46, 21 Nov 2006 (EST)
