[ExI] Milky Way is on the outskirts of 'immeasurable heaven' supercluster

[Anders Sandberg]

BillK <pharos at gmail.com> , 5/9/2014 11:17 AM:
The stellar thrust would have to be small otherwise you risk leaving 
the planetary system behind. But over millions of years the speed does 
build up. 
Yes, but this is not much of a problem. Current ideas for Shkladov thrusters have accelerations on the order of tens of meters/s over a million years. Planets are hardly disturbed. Besides, when building them you are already in Dyson shell territory: picking apart planets is by definition going to be within reach.
The real trick is to get a decent acceleration: 0.03 ly in one million years is not much of a displacement. But if you make a close pass near another star, you can now get a gravity assist on the order of km/s. So you use the thrusters for steering and to get close to a passing star, which likely takes a few million years. But once that is done you can speed up the process significantly. 

I see another problem also. Building a thruster around every star in 
the galaxy means you run into relativity problems. The Milky way is 
about 100,000 light years across. First, you have to get a 
construction system to every star in the galaxy. Then wait until every 
star has built a thruster system and reported back to central control. 
Now how do you synchronize all the thrusters when you have huge light 
speed communication delays? With such huge time delays how can you 
tell what is happening at every star system? Have they built a better 
thruster? Have they gone extinct? Do they still want to obey Galactic 
Central Control orders? 
Depends on what kind of civilization you are running. Using a system such as the one in http://www.fhi.ox.ac.uk/intergalactic-spreading.pdf would essentially emplace a robotic infrastructure. Now, doing a few cycles of observation, data fusion and action over 10 million years doesn't seem too out of place - I think one could design distributed swarm robotics for it, or use some central computer. The thing is, stars move slowly compared to communication.
I think that after even a million years the civilization will be pretty technologically mature (and can transmit blueprints to the systems). 
What you need is a map of all stars (relatively easy, you potentially have at least 10^11 telescopes AUs across) and their velocities, as well as resources to model their dynamics well enough - and you can adjust that dynamics once you are up and running. The fact that normal galactic dynamics is chaotic is no matter if you have M-brain resources, a 1-to-1 map, and can nudge things towards your desired solutions. In fact, it is that very sensitivity to initial conditions you are going to use to steer the galaxy. 

I think trying to move a galaxy might be a bridge too far. Getting our 
own star system to tour the galaxy and perhaps cross interstellar 
space to another galaxy might be sufficiently amusing. 
 
Depends on what you want to do. Taking the old solar system for a spin, sure! But I am one of those boring workaholics who also want to get entire universes of computational power for the really long-term future. 
(Although this afternoon I found a *really* annoying problem with cooling supercold computing infrastructure in the post-trillion year universe that is playing havoc with part of my plans. The time it takes to cool down my hypercluster computer after erasing one bit of information is loooong... almost a trillion years. But on the other hand, I think I can get error correction so good that bit erasure happens very rarely even for "hot" 10^-6 K computing...) 

Anders Sandberg, Future of Humanity Institute Philosophy Faculty of Oxford University

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