Absolute Position: Finding a Meeting Point in Space over Billions of Years

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    Absolute Position
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Discussion Overview

The discussion revolves around the hypothetical scenario of two advanced civilizations attempting to coordinate a meeting point in space over billions of years, considering the challenges posed by changing celestial positions and the dynamics of the universe.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant suggests that a perfect star map could allow civilizations to agree on a rendezvous point, but acknowledges the uncertainty if celestial bodies change position during the long journey.
  • Another participant humorously notes the unpredictability of long-term planning, reflecting on the inherent uncertainties of such a scenario.
  • A different perspective emphasizes the importance of tracking and predicting celestial changes to maintain a fixed location for the rendezvous, drawing parallels to current spacecraft navigation.
  • One participant questions the feasibility of tracking celestial bodies over extended periods, suggesting that there may not be an absolute reference point in the universe.
  • Another argues that while space is largely empty, the probability of significant changes in a solar system over millions of years is low, allowing for a reasonable approximation of stability.
  • A participant raises a concern about the implications of the expanding universe, questioning whether it would eventually prevent two entities from meeting at all.
  • One participant admits a lack of knowledge in general relativity, indicating uncertainty about the implications of cosmic expansion on the scenario.

Areas of Agreement / Disagreement

Participants express various viewpoints on the feasibility and methods of determining a rendezvous point in space, with no consensus reached on the best approach or the implications of cosmic expansion.

Contextual Notes

Participants acknowledge limitations in their understanding of long-term celestial dynamics and the effects of cosmic expansion, which remain unresolved in the discussion.

DavidSnider
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"Absolute Position"

This is a bit of a contrived scenario, but I wonder how it might be solved..

Say you have two highly advanced civilizations that want to meet each other, but in order to do so the trip will take billions of years.

Now, in this time, solar systems collapse, orbits change, etc, etc..

Since you have no idea whether a relative point in space will still be valid in the future, how would you communicate the rendezvous point?

(Nevermind how they communicated with each other in the first place)
 
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Well assuming you have a perfect star map you could simply say "let's meet on planet X" and just compute where planet X is going to be in a million years and take off. Of course planet X might not be there in a million years but if nothing had changed for it by the time your message was received and your alien buddies took off it wouldn't matter because you'd still meet at the same spot (where planet X was supposed to be). If "where planet X is supposed to be" changed during transmission (say it got hit by a swarm of meteor's that you didn't consider and it changed its trajectory) then you're screwed.
 


That's why I never make plans for a million years in the future. I never know what my schedule is going to be like.
 


DavidSnider said:
This is a bit of a contrived scenario, but I wonder how it might be solved...
Well you provided an inarguable answer to the question:
Since you have no idea whether a relative point in space will still be valid in the future, how would you communicate the rendezvous point?
Well if you have no idea, then you have no idea.

That said, it is probably wrong to say you have no idea. The easy answer is that you simply track and predict the changes in order to keep your eye fixed on the location of the rendezvous. That's how it is done now with spacecraft sent to the outer solar system!
 


Tracking things in the outer solar system in a period of years is relatively deterministic I would think. I don't think you could track it on a larger scale...

So there is nothing absolute in the universe from which to make a reference point?
 


No, however space if very, very, very, empty so on the horizon of a couple million years the probability of a given solar system (where planet x is) passing close enough to another celestial entity (star, solar system, black hole, quasar, etc.) in that amount of time is slim. Therefore, even though it's millions of years, by the odds, it'll be a good approximation to treat the solar system where planet X is as a closed system. Of course you could also predict if this solar system has another object of interest in its path. All in all you could pick a rendezvous destination with an extremely high probability of being unchanged over the passage of a couple million years (given good star maps).
 


Since space is expanding, and from what I hear the expansion is accelerating.. doesn't this mean that at a certain distance it would be impossible for two entities to meet?
 


That sounds like a very good question to me but I haven't a clue. I don't do/know GR at all really.
 

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