Modeling Simple N-body in Hypothetical Relativistic Dark Flow w/ Netlogo

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Discussion Overview

The discussion focuses on modeling simple N-body systems within the context of relativistic dark flow, specifically a scenario where a planet orbits a star while experiencing relativistic velocities of approximately 0.8 to 0.9 times the speed of light. The conversation includes considerations for simulation tools, particularly Netlogo and C++, and explores the implications of relativistic effects on gravitational interactions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant seeks guidance on building simulations of N-body systems in relativistic contexts, specifically using Netlogo initially and potentially switching to C++ for more computational power.
  • Another participant suggests that the solar system dynamics without dark flow could be treated as a near-Newtonian two-body problem, inquiring about the existence of an analytic metric modified by dark matter flow.
  • A different participant raises concerns that relativistic dark matter flow may invalidate typical approximations that assume non-relativistic velocities, expressing uncertainty about the implications for non-relativistic bodies.
  • One participant expresses interest in existing relativity models, particularly for Mercury, and desires an N-body model that incorporates an additional uniform velocity.
  • A participant references a paper by Folkner et al. as a potential starting point for N-body simulations, noting that it lacks the relativistic dark matter features desired. They provide excerpts discussing the translational equations of motion and gravitational acceleration derived from a post-Newtonian metric.
  • The same participant mentions the PPN approximation and its discussion in textbooks, while expressing uncertainty about how the dark matter background affects its application.
  • References to IAU recommendations and updates regarding the solar system metric are also suggested as potentially relevant to the discussion.

Areas of Agreement / Disagreement

Participants express a range of views regarding the modeling of N-body systems under relativistic conditions, with no consensus reached on the implications of relativistic dark flow or the applicability of existing models and metrics.

Contextual Notes

Participants highlight limitations regarding the assumptions underlying their discussions, particularly concerning the validity of approximations in relativistic contexts and the need for further exploration of relevant literature.

nearc
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Looking for existing examples of or guidance on building computer simulations of simple N-bodies in relativist situations. Of particular interest is the simulation of a planet orbiting a star whilst that trivial solar system is caught in a dark flow of relativist velocity; maybe .8 or .9 C.

Not that it should matter but I plan to start out with Netlogo since that is what most of my students use and if I need more computational power I will switch over to C++ with openMP.
 
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Sounds like the solar system part without the dark flow would be solvable as a two body near-Newtonian problem. Do you have an analytic metric as modified by such a dark mater flow? (no expert here, just someone who's numerically integrated a few ODEs in the day)
 
The relativisitc dark matter flow may break some of the usual approximations, which usually state non-relativistic velocities. While I'd guess that it _might_ not matter as long as the bodies are not relativistic, I can't even say that I'm sure it won't.
 
i assume there are already several basic relativity models, at least one for mercury? i would prefer an N-body model one that would allow me to add an additional uniform velocity in one direction, but any model would be a starting point.
 
Folkner, et a's paper, "The Planetary and Lunar Ephemerides DE430 and DE431" might be a starting place for an N-body simulator. But it doesn't have the relativistic dark mater backround features you want.

Some quotes from the paper that address some of your question:

Folkner et al said:
The translational equations of motion include contributions from: (a) the point mass inter-
actions among the Sun, Moon, planets, and asteroids; (b) the effects of the figure of the Sun
on the Moon and planets; (c) the effects of the figures of the Earth and Moon on each other
and on the Sun and planets from Mercury through Jupiter; (d) the effects upon the Moon’s
motion caused by tides raised upon the Earth by the Moon and Sun; and (e) the effects on
the Moon’s orbit of tides raised on the Moon by the Earth.

The gravitational acceleration of each body due to external point masses is derived from the
isotropic, parametrized post-Newtonian (PPN) n-body metric [24–26]. For each body
A, the acceleration due to interaction with other point masses is given by ...

Tracking down references 24-26 above might be the next step in your search.

The PPN approximation is discussed in a lot of textbooks (including MTW's text "Gravitation"), the questions I can't answer are how the dark matter background impacts the use of this approximation. The IAU 2000 recommendations and the various revisions thereof for the metric of the solar system (see for instance resolution B1.3 at https://syrte.obspm.fr/IAU_resolutions/Resol-UAI.htm AND the various updates since that date which I haven't linked to) are also potentially of some interest, basically the IAU extended the PPN metric mentioned by Folkner et al to make it easier to convert from barycentric to geocentric coordinates and back.
 
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