One of John von Neumann’s biggest contributions to science was the first rigorous study of self-replicating machines. The Von Neumann probe, named after the physicist, is a hypothetical self-reproducing intelligent device with interstellar capabilities, that one day can be manipulated to explore entire the Milky Way in a relatively small period of time.

The probes would be growing exponentially, expanding outwards at an appreciable fraction of the speed of light. It has been estimated to take around half a million years to dispatch millions of probes across our galaxy, presupposing each one travels at approximately a tenth of the speed of light, or 30,000 km per second. Whilst this may seem an overwhelming time period to us at the moment, in the grand scheme of time, it is miniscule.

The concept of how we would use the probes is surprisingly simple: the general process would be to construct a device on Earth from materials that are readily available and easily accessible out in space, then once it finds a suitable destination, it lands and mines the material it needs, to build even more devices, which, in turn, land on other planets and moons and self-replicate.

There are several proposed engineering approaches for constructing Von Neumann probes. One possible design for Von Neumann probes involves using nanotechnology to create a swarm of microscopic robots which construct copies of themselves. Being microscopic, they would not require the substantial resources of rocky planets to reproduce, but could instead power up using hydrogen atoms available interstellar dust. They would also be more efficient- it is estimated that by the time descendants of an initial population of 100 had travelled one parsec (around four light years), there would be roughly 1 x 1033 probes. Another approach to building Von Neumann probes involves using 3D printing technology to create modular spacecraft components that can be assembled in space. These components could include propulsion systems, energy sources, and communication systems. The probes would also need to be equipped with advanced artificial intelligence to allow them to make decisions autonomously and adapt to changing environments.

Regardless of the specific engineering approach used, Von Neumann probes would need to be designed to operate in harsh and often unknown environments for extended periods of time. They would also need to be able to self-replicate and repair themselves, as well as communicate with one another and with Earth. Achieving all of these requirements would require significant advances in multiple fields, including materials science, robotics, and artificial intelligence. Based off of trends from existing technologies, the Von Neumann probe development and operation will most likely be constrained and driven by three aspects: its power generation ability, the power requirement for the payload, and heat rejection capabilities. The probes must be able to replicate themselves accurately and efficiently, and their propulsion and power systems must be designed to operate for long periods of time without requiring maintenance or resupply. Communication and control systems must also be robust enough to operate over the vast distances involved in interstellar travel. A likely mission for such a probe is to get into an orbit close to the star in order to generate maximum power for computational activities, and then to prepare for further exploration activities. This is similar to the concept of a Dyson Sphere- perhaps Von Neumann probes could be used in a Dyson Swarm to harness the solar output of the sun.

Von Neumann probes provide copious arguments to the Fermi paradox. Aside from humans, the probes would very likely be used by a space-faring civilization themselves as a way to occupy much or all of the Milky Way galaxy. In 1981, Frank Tipler put forth an argument that extra-terrestrial intelligences do not exist, based on the fact that von Neumann probes have not been observed. Given even a moderate rate of replication and considering the immense history of the galaxy as we know it, such probes should already be common throughout space and thus, we should have already encountered them. Because we have not, Tipler explained that this shows that extra-terrestrial intelligences do not exist. This is one resolution to the Fermi paradox.

However, the lack of recognition of Von Neumann probes does not necessarily suggest that they do not exist, in fact, it could possibly mean the opposite. The berserker hypothesis, also known as the deadly probes scenario, is the idea that the reason humans have not yet detected intelligent alien life is due to all external life having been systematically destroyed by a series of lethal Von Neumann probes, probes that could be present even in our atmosphere, in micro-machines that are just a nanometre long.

Another response came from Carl Sagan and William Newman. Sagan’s Response, as it is now known, argued that Tipler had actually underestimated the pace of replication and that von Neumann probes should have already begun consuming the majority of the galaxy’s mass by now. They reasoned that any intelligent race would therefore not create von Neumann probes first, but rather would attempt to destroy such probes as soon as they were discovered. This contrasts with the theory of the Great Filter, which explains that civilizations that could have potentially created such devices may have inherently short lifetimes, and self-destruct before so advanced a stage is reached, through such events as nano-terrorism, biological or nuclear warfare , resource exhaustion or other catastrophes.

Von Neumann probes represent an intriguing and thought-provoking concept that raises important questions about the future of space exploration and the potential for intelligent life beyond Earth. The production of these probes could be revolutionary, not only in exploring space, but to fund the resources and energy required to build a Dyson Sphere- or could be used in the Dyson sphere itself.

Ultimately, the decision to build and launch Von Neumann probes will depend on a complex interaction of technological, ethical, and societal factors, and will certainly play a crucial part in unlocking the mysteries of our universe.