The concept of exploring the galaxy with self-replicating probes, most typically termed Von Neumann
probes after the eminent mathematician that first proposed the concept, constitutes what
might be the most efficient way to at least explore a galaxy, if not maintain a permanent
presence throughout it.
At first glance, this concept seems reasonable.
Build a probe that can mine materials and replicate itself and send it out into the
galaxy to make copies of itself.
In time, hypothetically speaking, you could have a probe in every system in a galaxy.
The trouble is, the galaxy is well old enough for a civilization, or any number of civilizations,
to have done this many times over.
But we see no evidence that this has happened which led to an argument originally by Frank
Tipler that says that since we do not openly see von Neumann probes within our solar system,
then that would indicate the absence of other advanced civilizations existing within the
Milky Way.
Carl Sagan and William Newman took a somewhat different approach to the question and pointed
out that self-replicating von Neumann probes wouldn’t just be everywhere, they would
be inherently dangerous.
If left unchecked and replicating rapidly, they calculated that such probes, if they
existed, would have consumed much of the Milky Way by now.
Further, they hypothesized that no civilization in its right mind would ever design such a
thing.
It could be likened to the galactic equivalent of a doomsday device, and space-faring civilizations
might destroy such probes whenever they encounter them, or possibly even destroy any civilization
attempting to create them.
Robert Freitas countered these arguments by noting that those points were coming from
extremes, and that in reality von Neumann probes might not be easily visible and might
not go rogue, and only replicate according to need rather than replication for replication’s
sake.
In short, toned down functional machines rather than insane probes eating galaxies.
But, machines can malfunction and if control of a probe’s reproduction was lost, it could
still reproduce without limit and eventually destroy a galaxy.
So far, looking at the nearest galaxies that could have civilizations present within them,
we’ve seen no evidence that anyone has ever lost control of their self-replicating probes.
There are no examples, so far as we can tell, of the galactic equivalent of a technological
cancer.
Perhaps this is again controlled.
Maybe alien civilizations monitor each other’s probes to ensure that the moment one malfunctions
and goes rogue, it gets destroyed by the nearest probe that might be able to reproduce fast
enough to outnumber it.
But that creates more questions than it answers, and there could be technical issues with the
whole idea once put into practice.
For example, how do you power a self-replicating probe for long distance travel?
Is there a materials constraint, such as plutonium availability?
These questions aside, say a civilization could safely produce a network of such probes
and solves any potential replication issues with them.
Could they be detected if they were out there?
In our solar system, they might be literally a needle in a haystack.
We don’t know how big such a thing would be, but it need not necessarily be a battlestar
galactica sized ship.
It could actually be quite small, and if its radio emissions weren’t pointed at us, we
might not see them at all.
But aside from anything in our solar system, what of detecting probes in other nearby star
systems?
In a paper by Michael Gillon a method for detecting alien von Neumann probes in other
star systems is presented through searching for leakage from their communications signals
in a very specific way.
Straightforward Interstellar communication is difficult and energy intensive.
This would normally make it very difficult for a network of von Neumann probes to communicate
with each other.
But there’s a trick.
Stars are strong gravity sources, and gravity can bend and even focus light like a lens.
Gravitational lenses can be used to concentrate signals, so von Neumann probes positioned
to take advantage of this effect could communicate using far lower energies.
So by looking across as much of the spectrum as possible at the solar focus points of nearby
stars, you might pick up the communications leakage from a network of alien von Neumann
probes.
But this begs a question, if such a communications network is possible, and most suitable star
systems contain a probe at this point, or multiple probes from different civilizations
for that matter, would there be probes stationed at our own sun’s focus point.
We don’t know, but if there are, they would extremely difficult to detect.
Thanks for listening!
I am futurist and science fiction author John Michael Godier currently randomly releasing
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