Pale Blue Dot is a truly inspirational book. It has given me a new outlook on the fragility of life on Earth, and cultured new thoughts on what interplanetary travel might mean for the future of the human species.
Sagan lays out two over-arching requirements that must be met for the survival of the human species, which he reinforces in various ways throughout the book:
We must venture outside Earth, and ultimately outside the dependency of the Sun, if humans are to survive the end of the Earth.
The Sun and Earth have limited lifespans, albeit billions of years. The Sun will eventually turn into a red giant star (the current estimate being in about 5 billion years.) Increasing in size and amount of light energy emitted during this process, it will alter the atmospheric composition of Earth by increasing its surface temperature.
These atmospheric changes will cause a chain reaction in all living organisms on Earth as the atmosphere and oceans begin to boil away. The balance of life that has evolved while the Earth is in its current stage will cease to exist, perhaps giving way to a new quality of life and organisms better suited to tolerate the new conditions, before all atmosphere, water and upper layers of earth are burned away.
Finally, after all molten matter is stripped from the surface, Earth's iron core will be engulfed by the expanding horizon of the red giant star previously known as our Sun. All human creations, trees, grass, dirt, fossil fuels, buildings, gravestones, and all remains of every organism to ever grace the Earth... all planetary matter will have been broken down into other energy, and ultimately re-distributed into surrounding space, to one day be recombined into (anti?) matter or energy somewhere else in the Universe.
Our history as a species and everything every single human has ever worked for will be gone. The only remaining remnants of our existence will be the light and radio waves that were reflected and emitted during our existence on Earth. Anyone observing Earth from billions of light-years away would actually be observing Earth as we currently inhabit it. Wave to them.
That is unless we do destroy ourselves first.
We mustn't destroy ourselves.
Whether through rash decision by an ideologic or radical peoples, or by means of ignorance or plain selfishness, the human species has the ability to destroy itself. Whether through technological means such as nuclear war, or selfishness and shortsightedness in damaging the delicate life balance under which current organisms have evolved.
The human species, in its development of technology and its ever-increasing rate of advancement, has harnessed power capable of mass destruction. While this power might seem small in scope of the energy harnessed by the perpetual motion of the Universe, it is enough to destroy our entire world. Whether used recklessly by way of a political statement, or pure accident, the technology enabling this power is now a lit fuse that could easily disrupt our existence.
By establishing a human presence on surrounding worlds and stars, we can lower our vulnerability to catastrophe like this and the fragility of the Earth that ultimately cultivated us.
Sagan argues through much of the book that the first step in exploring the stars is sending humans to Mars. But his pessimistic outlook on the state of the human race suggests he believes humans will destroy themselves and their planet before spacefaring nations can foster the finances to accomplish such a feat.
Given the current financial state of the United States in 2011, it would seem increasingly unlikely for such an undertaking to see approval by its governing bodies anytime soon.
I do not imagine that it is precisely we, with our present customs and social conventions, who will be out there. If we continue to accumulate only power and not wisdom, we will surely destroy ourselves. Our very existence in that distant time requires that we will have changed our institutions and ourselves. How can I dare to guess about humans in the far future? It is, I think, only a matter of natural selection. If we become even slightly more violent, shortsighted, ignorant, and selfish than we are now, almost certainly we will have no future.
If you're young, it's just possible that we will be taking our first steps on near-Earth asteroids and Mars during your lifetime. To spread out to the moons of the Jovian planets and the Kuiper Comet Belt will take many generations more. The Oort Cloud will require much longer still. By the time we're ready to settle even the nearest other planetary systems, we will have changed. The simple passage of so many generations will have changed us. The different circumstances we will be living under will have changed us. Prostheses and genetic engineering will have changed us. Necessity will have changed us. We're an adaptable species.
It will not be we who reach Alpha Centauri and the other nearby stars. It will be a species very like us, but with more of our strengths and fewer of our weaknesses, a species returned to circumstances more like those for which it was originally evolved, more confident, farseeing, capable, and prudent—the sorts of beings we would want to represent us in a Universe that, for all we know, is filled with species much older, much more powerful, and very different.