Cosmos

by Carl Sagan

With four generations per century, twenty-three centuries occupies almost a hundred generations of human beings.

The farther back the critical events occur, the more powerfully can they influence the present.

until the invention of nuclear weapons, intelligence powerfully aided survival.

The author of Nature … has made it impossible for us to have any communication from this earth with the other great bodies of the universe, in our present state; and it is highly possible that he has likewise cut off all communication betwixt the other planets, and betwixt the different systems.… We observe, in all of them, enough to raise our curiosity, but not to satisfy it … It does not appear to be suitable to the wisdom that shines throughout all nature, to suppose that we should see so far, and have our curiosity so much raised … only to be disappointed at the end … This, therefore, naturally leads us to consider our present state as only the dawn or beginning of our existence, and as a state of preparation or probation for farther advancement.… —Colin Maclaurin, 1748

No civilization can possibly survive to an interstellar spacefaring phase unless it limits its numbers. Any society with a marked population explosion will be forced to devote all its energies and technological skills to feeding and caring for the population on its home planet.

Travel is broadening.

Henry Kissinger, a contemporary politician, wrote: “Deterrence depends, above all, on psychological criteria. For purposes of deterrence, a bluff taken seriously is more useful than a serious threat interpreted as a bluff.”

Military secrecy makes the military the most difficult sector of any society for the citizens to monitor. If we do not know what they do, it is very hard for us to stop them.

To take a modern example, consider the aphorism by the great twentieth-century physicist, Niels Bohr: “The opposite of every great idea is another great idea.”