What kinds of developmental thresholds would any planet of sentient beings pass through? The creation of writing would be a huge one. The unleashing of cheap non-biological energy is another. The invention of the scientific method is a giant leap. And the fine control of energy (as in electricity) for long-distant communications is significant as well, enabling all kinds of other achievements. Our civilization has passed through all these stages; what are some future transitions we can expect -- no matter the fashions and fads of the day? What are the emergent thresholds of information and energy organization that our civilization can look forward to? Most of these thresholds are gradual, so we can't assign dates, but each of these structures seem to be a natural transition that any civilization must reach sooner or later.
* AI - There are many varieties of artificial intelligence, and no formal definition for any of them. By whatever measure, a civilization capable of producing synthetic minds similar to its own, or superior in some facets, has reached an important threshold, not the least which is a great compounding acceleration of its progress.
* A-life -- Likewise there are many types of artificial life possible, from derivatives of natural biological life, to a-life running on an alternative chemical base-pairs, to self-reproducing dry life more akin to nano-bots. Sustainable self-reproducing, self-evolving creations enable huge innovations and bring huge problems. It is a major transition.
* Methuselarity - Health care and science keep extending the average longevity of humans, and increasing the rate at which it is improving. Right now science is extending the expected lifespan of humans in the developing world a few days per year. If this rate keeps accelerating, at some point scientific progress will increase expected longevity from one day per year, to one year per year. When longevity increases at one year per year, that effectively creates immortality, or Methuselarity, for anyone who reaches that threshold. They become like the biblical Methuselah and live for a thousand years, on average.
* GlobeNet -- Over time we keep adding sensors and monitors every few kilometers on land and on the sea until we form a dense grid of sensors covering the globe. There will be thermometers, wind speed jigs, rainfall meters, sunlight sensors, air pollution particle detectors, radiation meters, earthquake probes, climatic gas sensors, animal motion detectors, sea level and wave detectors, traffic sensors, DNA sensors, and little things that measure anything we can think of place on a regular basis on the surface (and deeper) of the planet. All of these form a blanket of sensitivity providing the planetary mind (us and machines) a real-time awareness. For the first time we'll have a quantifiable globe.
* Global Superorganism -- The stage at which several billion sentient beings spread over a planet and several quadrillion smart machines merge into a unified system that is always on. This global system of interacting smart agents exhibits emergent behavior and degrees of autonomy that is not present in its constituent parts. On some planets the global superorganism will reach artificial intelligence before a stand-alone AI does. It's not clear which way Earth is headed.
* Memorex -- Every bit of writing, music, photography, painting in civilization is digitized and recorded in a machine-readable way. All knowledge, in all languages, from all ages, in all media is stored in a way that is universally accessible to all people and machines. In other words, the universal library becomes real, but not just books, but everything created, past and present, and it is available anytime. This threshold of civilization-scale knowledge becomes both a global memory and a global awareness.
* Borg -- Another threshold is crossed when any individual can import the global Memorex onto their own minds. Civilization-scale memory available to, or within, all individuals.
* Mirror World -- A one-to-one mapping of both the natural and built worlds onto a full-scale simulation of those worlds. This huge global model runs in parallel to the observed worlds. At first the functions of large organizations are mirrored in a simulation, then entire cities will be reflected in a real-time city simulation. Eventually every major node, sensor-net, agent, or variable on Earth is simulated in real time in this global model. Sort of like Google Earth but with every process, and every ecosystem, as well as every building. The mirror world is used both as an experimental test bed for science and predictions, and as an entertainment medium, as in a second life.
* Class I Energy -- The Russian astronomer Nikolai Kardashev proposed three major levels of energy production for galactic civilizations, which he called Class I, II, and III. Class I was the maximization of energy from the entire planet, Class II was maximizing the available energy from its star, and Class III was exploiting energy from its galaxy. Humans have not yet reached Class I, so that threshold is still in front of us.
* Universal Family Tree -- Eventually we will sequence the full genomes of everyone living, and as many of the recent dead as we have access to. Together with genealogical records, this huge trove of data will give us our first universal family tree. Everyone living will have a place on it in relation to everyone else. We will clearly see exactly how I am related to you. We'll also see how everyone is related at some point to everyone else no matter where they were born. The big surprise will be the short hops between us. This common tree of descent will aid health care, medicine, and science, but will also aid peace. Greeks and Turks, Jews and Arabs, Koreans and Japanese will see they are far more related than not.
* Knowledge of All Species -- At some point a civilization wakes up and takes a comprehensive and systematic inventory of all the other living species on its planet. This step is similar to mapping all the elements of matter. It realizes that in order to model and manage its ecosystems it must know all the ingredients and all the interacting parts, just as it takes knowing all the elements in order to do chemistry. This threshold of the knowledge of all species includes sequencing the DNA of every species as well -- a huge asset that also enables it to recover and resurrect known extinct species.
* TransHumanity -- When beings gain control of their biological evolution they begin to mess with it. But not everyone will be eager to do so. At the point that humans begin to engineer their own genomes, there will be a significant number of individuals, families and groups who will refuse to do so. For every person who says "Over my dead body will I or my child be engineered," there will be someone else who says, "Bring on the mutants!" Thus there will inevitably be a forking of the gene line. The threshold is not engineering genes since we have been doing that slowly and ignorantly all along, but a clear splitting off of a subgroup. Whether or not each becomes a non-breeding separate species doesn't matter. Transhumanity means at least one fork of the species is deliberately self-engineered.
* Singularity -- As commonly defined, a singularity means an infinite pace of change. We don't know what that looks like because, as commonly defined, it is inherently unknowable. For this reason I don't find this transition useful in prospect, only in retrospect. We have been through one singularity so far -- the invention of language. A few of the above might be also initiate singularity but we'll only know after the fact.
There are a bunch of other transitions such as Downloadability, Time Travel, Telepathy, etc., -- well mined by science fiction -- that would qualify as important information/energy thresholds, but which do not seem inevitable to me at the moment.
Are there other near-future stages that you think any civilization on the galaxy must pass through if it survives long enough?