•Hart
75: calc, <1MY, if s=.1c, 20Y wait
•Jones
76: sims, wave v > 10s, .1c
=> <5MY
•Newman
& Sagan 81: diff. eqn., given
ZPG, 10-8/Y
emigration rate, takes 800MY.
•Fogg
87: sims, .7– 80MY if v = .1-.0001c
•Bainbridge
84: sim of 1000 stars, let prob colonize drift,
found selection effect.