[sangnoir]

We'll need even bigger[1] breakthroughs in propulsion if it's going to be self-propelling itself back to Sol at relativistic speeds.

1. A "simpler" sci-fi solution foe a 1-way trip that's still out of our reach is a large light sail and huge Earth-based laser, but his required "smaller" breakthroughs in material science

[DCH3416]

Well if you can propel something forward you can propel it backwards as well.

I'm assuming some sort of fixed laser type propulsion mechanism would leverage a type of solar sail technology. Maybe you could send a phased laser signal that "vibrates" a solar sail towards the source of energy instead of away.

[sangnoir]

> Well if you can propel something forward you can propel it backwards as well

Not necessarily - at least with currently known science. Light sails work ok transferring momentum from photons, allowing positive acceleration from a giant laser Earth. Return trip requires a giant laser on the other side.

[SoftTalker]

As well as a way around Newton's Third Law.

[sangnoir]

I meant to say the "simpler" (but still very complicated) solar sail approach was for a one-way trip. On paper, our civilization can muster the energy required to accelerate tiny masses to relativistic speeds. A return trip at those speeds would require a nee type of science to concentrate that amount of energy in a small mass and use it for controlled propulsion.