Neil deGrasse Tyson said that what keeps him awake at night is the possibility of aliens so much smarter than humans that we could never grasp what they know, any more than chimpanzees --- with whom we share 98.8% of our DNA --- can understand physics. Why should we --- who have had radio for only about 128 years, and have understood that galaxies are enormous island universes for only about 100 years, and have confirmed the existence of extra-solar planets only 30 years ago --- assume that we can speculate accurately about the sum of all knowledge when it comes to travel between the stars? That's called hubris, and perhaps we should set it aside. There are undoubtedly things we don't know we don't know.