In the third and final installment of John’s discussion with Lord Martin Rees, the Astronomer Royal, they discuss Martin’s views on the future of space travel and astronauts, and whether some robotic future progeny of humankind will eventually replace us in exploring the universe. Would this be any bad thing, or should we resist efforts to gradually supplement and even supplant our biology with novel biotech? And without any Christian belief, how can we justify our ethical reservations about transhumanism or explain the correspondence between our minds and the cosmos we are understanding better every year.