| Not so bad. Assuming a spherical Earth in a vacuum and a bunch of other slightly less reasonable assumptions we have: 1E+45 photons from sun per second 1.49598E+11 distance to sun in meters 6365000 earth radius in meters 2.81229E+23 surface area of solar flux at earth orbit 1.27276E+14 surface area of earth exposed to sun 4.5257E-10 ration earth area to solar flux 4.5257E+35 photons hitting earth per second 6.49E+15 one light year in meters 1.947E+25 meters in 3 billion light years 4.76367E+51 surface are of sphere 3 billion ly across 9.50046E-17 photons per m^2 at 3B ly 1.05258E+16 m^2 per photon 57883255.23 radius in meters for mirror to reflect 1 photon/second 57883.25523 radus in km (Only 10x larger than Earth!) Then given a reasonably competent engineer to make a descent mirror with no aberration and a good telescope on a clear night away from the city, and a good bit a patience, you could watch a replay of the last 3 billion years. |