Re: Universal Schelling points (was SPORT: Ready? . . . Break!)

Hal Finney (
Tue, 11 Feb 1997 09:09:59 -0800

From: Anders Sandberg <>
> On Mon, 10 Feb 1997, The Low Willow wrote:
> > [2] I think gravity-tethered solar sails should work. Huge sails at the
> > height where they're supported by radiation, and inflecting most of the
> > light back around (not at) the star. Photons go one way, something has
> > to go the other, and if the sails can be kept stable over the star, both
> > star and sail should slowly glide off.
> For the sun, you have around 10^26 W to play with, I think it would
> definitely be intergalactically visible if you used a directed beam.

According to my reference, the force per watt of radiation is about
3e-9 newtons. This implies a total force if we could capture all
the light from the sun of about 3e17 newtons. Divided by the mass of
the sun, 2e30 kg, gives an acceleration of 1.5e-13 meters per second.
If we wanted to move the sun one light year, accelerating for half that
time and decelerating for half, we'd have to accelerate it about 4.7e15
meters, twice. d = 1/2 a t^2 so this gives us a t of 5e14 seconds for
the whole trip, or about 10,000,000 years.

So we will have to be patient to use this method.