- Critical to the plot, Earth needs to be taken out of the Sun's orbit around 2050 (i.e., not destroyed; nor merely darkened via "indirect" solutions such as alien Dyson swarms surrounding the Sun, blacking out the sky as in The Matrix, etc).
- Therefore, either the Sun has to be destroyed (including its mass), or the Earth needs to be accelerated by a further 12 km/s to achieve escape velocity from the solar system.
- This needs to happen with a warning period (e.g. 2 - 10 years) so that civilization has a change to get at least minimally ready, such as beginning underground bunker construction; the Earth's surface needs to remain at least somewhat habitable during this period.
- The Earth itself has to be preserved in a more or less intact way (though Hollywood style disasters like earthquakes, tsunamis, etc. are perfectly fine and even welcome).
- Source of disruption has to be within ~75 light-year "cone" of Earth, i.e. half of the time period from when we first started radio emissions (though can be handwaved if necessary).
Destroying the Sun's mass
- Massive increase in coronal mass ejections (Problem: Masses involved are far too big to be realistic, and if this happens, Earth will be fried).
- Sun going supernova prematurely. (Problem: Earth will get fried).
- One of Peter Hamilton's ideas: Nanomachines that exponentially multiply and transmute Sun's mass into elements that don't support fusion. (Problem: Sun's mass remains, so Earth doesn't deorbit).
- Micro-black hole tossed into center of Sun. (Problem: Will dissipate quickly due to Hawking radiation; the radiation pressure around its accretion disk will be too hot for any of the Sun's mass to actually fall into it; finally, the mass itself will remain, so Earth will remain in orbit anyway).
Therefore, I see no physically plausible way of doing it this way while fulfilling most of the conditions.
Knocking the Earth itself out of orbit ( Passing Rogue Planet or Rogue Star)
This seems a slightly easier challenge, since the Earth is so much smaller than the Sun.
- We know this happens frequently in the early stages of solar system formation; it's been estimated that half the planets in our galaxy are rogue/"Steppenwolf" planets.
- Passing rogue planet knocking Earth off orbit is what happens in the short story "A Pail of Air" by Fritz Leiber.
- Is physically plausible to laymen, so the fine details can be handwaved, if necesssary.
- The Rogue Object ("RO"), if it is traveling fast (which it probably has to be if it was launched within the past 150 years), will also have to be very heavy to exert sufficient gravitational force on Earth to fling it out of orbit as it passes by. I assume that all such objects, even rogue neutron stars and rogue black holes, would have already been detected within at least a 50 light year vicinity of Earth?
- If the RO is a rogue planet, then it will have to pass by the Earth more slowly, and closer to it, which risks running into the Earth's Roche limit and breaking it apart entirely.
- What would be the best way to triangulate between these considerations, i.e. less mass and higher speed for the RO; and non-violation of Earth's Roche limit?
- What would be the mathematical formula relating the mass and velocity of the rogue object, the mass of the Earth, the closest distance between them, and the resulting acceleration of the Earth?
Knocking the Earth itself out of orbit (exotic possibilites)
Focused gravitational beam, perhaps channeled through a wormhole "tethered" to Earth and a massive body somewhere else in the galaxy. The Earth's orbit slowly, but at an accelerating pace, becomes elliptic, and eventually flies off into space.
Problem: Requires some major handwaving. Gravity is far weaker than the other forces, and most likely can't really be focused as we don't know of any materials that can reflect them
Perhaps alien civilizations have mastered energy-to-mass conversion to such an extent that they can fire off a beam of focused energy (at light speed), then have it convert to mass object at a time of their choosing, such as a chunk of neutronium.
There must be many other possibilities I haven't considered, though I suspect many of them will be more and more purely fantastical. But I'll be happy to hear more suggestions.
Thanks in advance for your input!