Expansion in the long... (very) long term

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Ciber
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Expansion in the long... (very) long term

Postby Ciber » Tue Feb 06, 2018 4:25 am UTC

Given that the expansion of the universe means that our local galexies will ultimately merge while further ones recede beyond our ability to reach them. Assume that in a cosmic eyeblink humanity is harvesting a sizeable portion of our galexies energy output. We then send out ultrarelevistic seed factories or perhaps even artificial aimed quasars modulated to carry information with the hope that a civilization exists at the destination to read it.
Essentially, assume that starting now humanities information begins propagating outward at lightspeed.
How far will we get before expansion stymes us?
How much of the current observable universe could we reach before it recedes?
Could we get far enough that some of us eventually get cut off by expansion from the rest?
If we engage in galactic scale engineering, could we cause redirect galexies to fall within our eventual local bubble that would not have origionally?
I know people have thought about what it would take to move a star, but what about a galexy, or a cluster?

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Eebster the Great
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Re: Expansion in the long... (very) long term

Postby Eebster the Great » Tue Feb 06, 2018 8:01 am UTC

Moving galaxies any meaningful distance seems fundamentally impossible based on the usable energy density of galaxies. Ultimately, no galaxy beyond Milkdromeda should be observable.

p1t1o
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Re: Expansion in the long... (very) long term

Postby p1t1o » Tue Feb 06, 2018 9:01 am UTC

If space keeps expanding then yes, our "local bubble" will get smaller and smaller until eventually it only contains the milky way, and then eventually only the solar system...but it doesnt stop.

If the hypothesis pans out and certain constants are certain values, then the expansion will keep accelerating and eventually cause a "big rip".

The "big rip" is the very last moments of the universe where the expansion accelerates dramatically and the "local bubble" reduces to the Planck scale and all fundamental particles are destroyed.

This is one possible future for the universe, Im not sure what the current state of the art is though so others might take precedent.


From https://en.wikipedia.org/wiki/Big_Rip

Spoiler:
In their paper, the authors consider a hypothetical example with w = −1.5, H0 = 70 km/s/Mpc, and Ωm = 0.3, in which case the Big Rip will happen approximately 22 billion years from the present.
For w = −1.5, the galaxies would first be separated from each other. About 60 million years before the Big Rip, gravity would be too weak to hold the Milky Way and other individual galaxies together. Approximately three months before the Big Rip, the Solar System (or systems similar to our own at this time, as the fate of the Solar System 22 billion years in the future is questionable) would be gravitationally unbound. In the last minutes, stars and planets would be torn apart, and an extremely short amount of time before the Big Rip, atoms would be destroyed. At the time the Big Rip occurs, even spacetime itself will be ripped apart and the scale factor will be infinity.

Tub
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Re: Expansion in the long... (very) long term

Postby Tub » Tue Feb 06, 2018 12:13 pm UTC

p1t1o wrote:If space keeps expanding then yes, our "local bubble" will get smaller and smaller until eventually it only contains the milky way, and then eventually only the solar system...but it doesnt stop.

If the future of our universe contains a big rip, then it'll be very far in the future, based on our observations of the relevant constants. The values from the wikipedia article you linked (w = -1.5) are most certainly not the true values, and it'll take longer than the 22 billion years it claims.
By the time the solar system gets isolated, it has long stopped being a solar system. At the very least, the sun would have ended its lifecycle, swallowed mercury, venus and earth, and collapsed into a black dwarf. I'm not sure about the fate of the other planets (except being severely burned), but if they haven't been swallowed or ejected from the solar system, then their orbits will eventually decay and merge with the sun's remnants as well. Also, entropic heat death may or may not appear faster than the big rip.

In any case, the big rip won't be what kills us.

p1t1o wrote:If the hypothesis pans out and certain constants are certain values, then the expansion will keep accelerating and eventually cause a "big rip".

Those certain values are one requirement, the other is that we can extrapolate our formulas to these extreme cases. General relativity is inaccurate at quantum scales, QM is inaccurate when gravity is involved, I'd expect both to be inaccurate at very high dark energy pressures and accelerations, so take any predictions wth a grain of salt.

p1t1o
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Re: Expansion in the long... (very) long term

Postby p1t1o » Tue Feb 06, 2018 1:52 pm UTC

Tub wrote:
p1t1o wrote:If space keeps expanding then yes, our "local bubble" will get smaller and smaller until eventually it only contains the milky way, and then eventually only the solar system...but it doesnt stop.

If the future of our universe contains a big rip, then it'll be very far in the future, based on our observations of the relevant constants. The values from the wikipedia article you linked (w = -1.5) are most certainly not the true values, and it'll take longer than the 22 billion years it claims.
By the time the solar system gets isolated, it has long stopped being a solar system. At the very least, the sun would have ended its lifecycle, swallowed mercury, venus and earth, and collapsed into a black dwarf. I'm not sure about the fate of the other planets (except being severely burned), but if they haven't been swallowed or ejected from the solar system, then their orbits will eventually decay and merge with the sun's remnants as well. Also, entropic heat death may or may not appear faster than the big rip.

In any case, the big rip won't be what kills us.

p1t1o wrote:If the hypothesis pans out and certain constants are certain values, then the expansion will keep accelerating and eventually cause a "big rip".

Those certain values are one requirement, the other is that we can extrapolate our formulas to these extreme cases. General relativity is inaccurate at quantum scales, QM is inaccurate when gravity is involved, I'd expect both to be inaccurate at very high dark energy pressures and accelerations, so take any predictions wth a grain of salt.


Of course the worked example is using a set of assumption, as we do not have the answers to those assumptions (yet). But it shows that there is no minimum size of a "local bubble", other than using some other arbitrarily chosen set of variables.

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Eebster the Great
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Re: Expansion in the long... (very) long term

Postby Eebster the Great » Wed Feb 07, 2018 3:00 am UTC

No, the Big Rip scenario is not expected even based on current models, though it is possible. Heat death is more probable.

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Himself
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Re: Expansion in the long... (very) long term

Postby Himself » Wed Feb 07, 2018 6:45 am UTC

Manipulating quasars and possibly moving galaxies would suggest the ability to control spacetime curvature. If we get up to that level then I figure we could build a working Alcubierre drive.
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Zamfir
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Re: Expansion in the long... (very) long term

Postby Zamfir » Thu Feb 08, 2018 2:42 pm UTC

Manipulating quasars and possibly moving galaxies would suggest the ability to control spacetime curvature.

Then again, moving a jug of milk also controls space time curvature.

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Soupspoon
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Re: Expansion in the long... (very) long term

Postby Soupspoon » Thu Feb 08, 2018 3:00 pm UTC

Zamfir wrote:
Manipulating quasars and possibly moving galaxies would suggest the ability to control spacetime curvature.

Then again, moving a jug of milk also controls space time curvature.

Even semi-skimmed?

/rethinks implications of current diet.

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Zamfir
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Re: Expansion in the long... (very) long term

Postby Zamfir » Thu Feb 08, 2018 6:20 pm UTC

Hmm, that's a good question. I think that depends whether the stress-energy tensor is semidefinite.


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