You've got the motive, but what about the means?
Well, forget about generation ships, suspended animation or ringworlds – the best way for you to explore, colonize and ultimately rule the Milky Way will be through the use of self-replicating robotic spacecraft – what are sometimes referred to as von Neumann probes.
Von Neumann's idea
Back in late 1940’s the brilliant mathematician John Von Neumann wondered if it might be possible to design a non-biological system that could replicate itself. Von Neumann wasn’t thinking about space exploration at the time, but other thinkers like Freeman Dyson, Eric Drexler, Ralph Merkle and Robert Freitas later took his idea and applied it to exactly that.
The strength of Von Neumann's idea lies in the brute efficiency of exponential growth. Given enough time and patience, a single self-replicating probe could produce millions upon millions of offspring; it would be like a massive bubble expanding outward into the Galaxy. It’s possible that these probes could come to occupy all four corners of the Milky Way in as little as half a million years – even if each probe travels at an average cruising speed of one tenth the speed of light.
In order to work, however, a von Neumann spacecraft would have to be put together using advanced nanotechnology and artificial intelligence -- technologies that we have yet to develop. In fact, the device itself would be a molecular assembler, capable of reconstituting matter into copies of itself.
A number of scientists and sci-fi writers have speculated over the years about the different kinds of probes we might want to construct once we're ready to explore space in this fashion. Other thinkers, namely astrosociobiologists, have wondered if extraterrestrials have constructed probes of their own.
I recently took a look at these visions and came up with a Von Neumann probe taxonomy. I came up with 7 basic spacecraft functions:
1. ExplorationThese tasks don’t have to be exclusive to a single probe. It’s possible that probes will be fairly versatile, able to change their functions as circumstances dictate. That said, you're likely going to need all these probes in your effort to take over and control the Milky Way.
Here’s how the different probes will work:
1. Exploration probes
These probes would be designed strictly for space exploration and surveillance; they would not contact or interact with other intelligent civilizations. We have already created such probes, namely Voyager 1 and 2 – although strictly speaking they are not von Neumann replicators.
Exploration probes could remain local and explore our Solar System (what has been dubbed Astrochicken probes), or they could be sent on interstellar missions to explore and transmit their findings back to Earth.
Admittedly, the timescales in question are significant – at least to modern human lifespans and our reasonable expectations for return on investment. But the information these probes could provide would be invaluable. They could study foreign solar systems in exquisite detail – and even alert us to the presence of extraterrestrial life.
These probes could also act as stationary reconnaissance stations. They could take residence in a data rich area and continuously beam that information back to Earth--all without ever being detected.
2. Communication probes (a.k.a. Bracewell probes)
The current SETI strategy of targeting stars and listening for radio signals has an extremely slim chance of success. It’s a needle-in-the-haystack approach. That said, given the assumption that civilizations want to communicate with us, a more efficient way for them to make contact would be to disseminate self-replicating communication probes across the Galaxy.
Dubbed Bracewell probes (named after Ronald N. Bracewell who thought of the idea back in 1960), these devices would work as an alternative to interstellar radio communication between widely separated civilizations. This strategy only makes sense given the inefficiency and weakness of radio signals emitted from the source planet.
Christopher Rose, an electrical engineer at Rutger’s University, has suggested that we should actually look for these probes in our own Solar System. He argues we should be checking the mail instead of waiting for a phone call.
Multiple Bracewell probes could also be set up as a distributed array of communication relay stations. Such a set-up was portrayed in Carl Sagan’s Contact. In this story, a dormant Bracewell probe was lying in wait in the Vega system. It began to transmit a strong signal after it received a radio signal from Earth. The device itself was part of a larger network of probes, as witnessed later by Ellie’s journey from probe to probe.
3. Worker probes
If we are going to embark on megascale engineering projects, we’re going to need robots. Lots of 'em. Projects like Dyson Spheres, Ringworlds and Alderson Disks would require fleets of specialized and artificially intelligent probes working in concert to construct these truly massive structures.
Given the sheer scale of these projects and the amount of matter that would have to be subverted, it’s not unreasonable to assume that millions of individual probes would be required. The most sensible way to construct and disseminate these probes would be through self-replication schemes.
These probes could also be put to work as mining machines that dig-out and transport matter across vast distances. Ideally, these probes would be programmed to work together and take advantage of swarming intelligence and emergent properties.
4. Colonization probes
The advent of molecular assembling nanotechnology will make it possible for probes to go about interstellar colonization. It’s conceivable that a von Neumann probe could find a suitable planet and use the matter around it to not just reproduce itself, but to establish a colony and seed actual settlers.
Such settlers would likely be uploaded consciousness patterns. This would obviously require an advanced mind emulation scheme, powerful artificial intelligence, and advanced supercomputing. Ideally, these consciousness patterns would be able to migrate to a robotic body for corporeal investigation of the environment. The number of settlers in any given location could be significant, limited only by computational resources.
Colonization probes could also construct data receivers and transmission stations so that uploaded persons could travel as digital data streams from one point to another. Consequently, the dream of traveling at the speed of light will some day be possible.
Colonization probes, sometimes referred to as seeder probes, could also perform double-duty as terraformers. Project Genesis, as portrayed in the Star Trek film series, utilized such a probe, which was able to transform a dead planet into one that suited the needs of its future inhabitants.
5. Uplift probes
Probes could also work to transform and 'uplift' other civilizations and their citizens. This scenario was explored in 2001: A Space Odyssey in which an advanced extraterrestrial civilization used probes (called monoliths) to steer the direction of evolution on Earth. In the story, these probes endowed primates with the capacity to use tools, and later, the human David Bowman was transformed into the next stage of evolution, the so-called Star Child.
This scenario was also explored in David Brin’s Uplift series in which advanced civilizations brought sapience to primitive life forms--what’s more accurately termed biological uplift. Also conceivable is technological or civilizational uplift in which an extraterrestrial intelligence brings an entire civilization up to its own advanced level.
Motivations for doing so could involve meta-ethical imperatives meant to reduce suffering, to prevent civilizations from destroying themselves, or to ensure the safe onset of non-threatening post-Singularity intelligences. Or, it could be part of your plan to take over the Galaxy.
Uplift probes could quickly bring a civilization to a post-Singularity, postbiological condition. Such a force might appear as a colonization wave that sweeps across the Galaxy, transforming all that it touches into computronium. Such a scenario has been projected by such thinkers as Hans Moravec and Ray Kurzweil.
6. Berserker probes
Unfortunately, you're going to have to look out for malevolent probes, what Fred Saberhagen dubbed Berserkers. Just as an intelligent civilization could use self-replicating probes to spread life across the Galaxy, another misguided or evil civilization could do quite the opposite and destroy everything.
Berserkers could be disseminated with the sole purpose of sterilizing every planetary system it encounters, forever eliminating the possibility for life to emerge and evolve. Should it encounter an inhabited planet, it could use any number of schemes, including nanotech instigated ecophagy, to quickly destroy all life in a matter of hours. By using a scorched galaxy policy, a civilization could sterilize the Milky Way in about 500,000 years.
Alternately, berserker probes could be disbursed across the entire Galaxy and lie dormant, patiently waiting for signs of intelligence.
Berserkers could also work to stamp out intelligent life that it deems dangerous. Anders Sandberg, Eliezer Yudkowsky and myself conceived of a strategy in which an advanced civilization (or Galactic club) could monitor for potentially dangerous post-Singularity mind-types and quickly stamp them out of existence.
7. Police probes
It’s not unreasonable to suggest that probe-making civilizations would also be thinking about defensive measures. Sandberg recently came up with an idea for anti-berserker policing probes (what I've started to call Sandberg probes). These devices would be on the lookout for bad news of any kind and take action.
Civilizations might want to establish quarantined areas; policing probes would ensure that nothing gets through the defenses and ensure the integrity of a specified region. Xenophobic civilizations might want to set up quarantined areas to prevent memetic infection, to protect themselves against invasion of any kind, or simply due to a fear of the unknown.
The best way of stopping a replicator, argues Sandberg, is to nip it in the bud. To do so, an advanced civilization would require widespread surveillance and enough power to deal with possible threats. And because replicators could emerge outside a given region of control, a civilization would want to have widely stockpiled defenses. The easiest way of doing this? Yup, you guessed it: make a replicator that spreads and builds these stockpiles and quietly waits for signs of something threatening.
So, where are all the probes?
Given all this technological potential, one must wonder why we haven’t encountered any extraterrestrial probes. Why haven't extraterrestrials communicated with us? Why haven't we be uplifted....or destroyed?
This conundrum was first articulated by Frank Tipler and has become a critical driver of the Fermi Paradox. It's been a cause of much the contact pessimism that has taken root since the 1970s (my own inclinations included). If it's so easy for probes to colonize the Galaxy, then where the heck are they? Tipler concluded that extraterrestrials simply don't exist.
Carl Sagan and William Newman came up with a different answer. They were convinced that Tipler had it all wrong and that all this talk of probes was sheer poppycock. Sagan and Newman, in their 1983 paper titled "The Solipsist Approach to Extraterrestrial Intelligence," calculated that von Neumann probes, should they exist, would eventually start to consume most of the mass in the Galaxy. Consequently, they concluded that intelligent civilizations would never dare construct such probes and would try to destroy any such device as soon as it was detected.
I'm not so convinced. Probes with even a modicum of AI and smart programming could be programmed to stop after a certain reproductive threshold has been achieved (time-to-produce schemes, maximum number of iterations, etc.). These probes wouldn't be simple mindless automatons. Moreover, the Sagan and Newman theory violates non-exclusivity; it might explain why most civilizations wouldn't dare embark on such colonization schemes, but not all. All it would take is just one.
And interestingly, Sagan and Newman seemed to be arguing for counter-measures against probes -- a strategy that Sandberg has argued would require self-replicating police probes. Moreover, as Sandberg writes,
One of the interesting things with police probes is that it makes strategic sense to announce that they are around to civilizations that might "break the law" - yet not reveal exactly how strong they are or what their modus operandi is. So the Fermi paradox appears to say that there are no police around here right now.Further, says Sandberg, one species' police is another species' invader - we would probably not like having some alien probe impose their view of what is an unacceptable activity on us, and vice versa. And the process of making police probes will likely be indistinguishable from making other replicators. Consequently, there might be a race to set up the first interstellar police force.
At any rate, the reason for the absence of probes is still a mystery. And as the future ruler of Galaxy, you're going to have to assume this is the case. So you better get going and create a fleet of self-replicating probe before somebody else does it first.