If interstellar travel is as time- or energy- demanding as the above figures indicate, it is far from obvious what the motive for colonization might be. ↗
It would be a pity if, frustrated by the price of travel, we elected to become a society that never made contact, that never gave SETI a fair chance. ↗
The factor most ignored in discussing interstellar flight is the kinetic energy that must be invested in the ship to make its tons of matter move at a substantial fraction of the speed of light. ↗