Writers have modeled the arrival of an extraterrestrial probe in our Solar System in a number of interesting science fiction texts, from Clarke’s Rendezvous with Rama (1973) to the enigmatic visitors of Ted Chiang’s “Story of Your Life,” which Hollywood translated into the film Arrival (2016). In between I might add the classic ‘saucer landing on the White House lawn’ trope of The Day the Earth Stood Still (1951), based on a Harry Bates short story. All these and many other stories raise the question: What if before we make a radio or optical SETI detection, an extraterrestrial scout actually shows up?

Graeme Smith (UC: Santa Cruz) goes to work on the idea in a recent paper in the International Journal of Astrobiology, where he focuses on the mechanism of interstellar dispersion. The model has obvious ramifications for ourselves. We are beings who have begun probing nearby space with vehicles like Pioneer and Voyager, and in our early stages of exploration we could conceivably be reached by an extraterrestrial civilization (ETC) before we can make such journeys ourselves. Smith is asking what form such contact would take. His paper cautiously tries to quantify how interstellar exploration likely proceeds based on velocity and distance in a steadily advancing technological culture.

This takes us back to the so-called ‘Wait Equation’ explored by Andrew Kennedy in 2006, where he dug into what he called ‘the incentive trap of progress.’ Kennedy made the natural assumption that as an interstellar program of exploration proceeded, it would continue to produce faster travel speeds, so that one probe might be overtaken by another (thus A. E. van Vogt’s ‘Far Centaurus’ scenario, where a starship crew comes out of hibernation at Alpha Centauri to find a thriving civilization of humans, all of whom came by much speedier means while the original exploration team slumbered enroute).

The question, then, becomes whether we should postpone an interstellar launch until a certain amount of further progress can be made. And exactly how long should we wait? But Smith looks at this from a different angle: What kind of probes would be first to arrive in a planetary system where a civilization like ours can receive them? Would they be the ‘lurkers’ Jim Benford has written about, left by beings who expected them to report home on what evolved in our Solar System? Or might they be more overt, making themselves known in some way, and advanced well beyond our understanding?

Image: Is this really what we might expect if an ETC arrived on Earth? From the 1951 version of The Day the Earth Stood Still. Frank Lloyd Wright is said to have been involved in the design of the craft for this movie, though some believe this to be no more than a Hollywood legend. It’s an interesting one if so. And about that spacecraft: Is it too low-tech to be realistic? Read on.

In Smith’s parlance, a civilization like ours is ‘passive,’ a specific usage meaning that it is able to probe its own system with spacecraft but does not yet have interstellar capabilities. He imagines two ETCs, one in this passive state and one capable of interstellar flight. Smith’s calculations then consider probes launched by an extraterrestrial civilization that are followed by increasingly advanced probes over time. You can see from this that the farther away the sending civilization is, the more likely that what will arrive at the passive ETC will be one of its more advanced probes, the earlier ones being still in transit.

If an active ETC is evolving rapidly in technology, or is exceedingly distant, then a vehicle of relatively advanced state may be more likely to first reach a passive collecting civilization. In this case, there could be a considerable mismatch in the technology level of the first-arrival probe and that of the passive ETC that it encounters. This would presumably have ramifications for what might eventuate if an artefact from an ETC were to arrive within the Solar System and enable first-contact with terrestrials. Hypothetical reverse engineering, for example, might be difficult given the technology gap.

Assuming the probe speed scales linearly with launch date, Smith uses as an example the Voyager probes and spins out increasingly fast generations of probes, noting how many such generations will be required to reach first the closest stars and then stars farther out, and calculating the time that separates the first encounter spacecraft with the initial, zero-generation probes. The situation accelerates if we assume probe speeds that scale exponentially with launch date. I send you to the paper for his equations, but the upshot is that this scenario heightens the likelihood that a first encounter probe will display a major disparity in technology from what it finds at the receiving end.

And depending on the distance of the sending civilization, the disparity between the ETC technology and our own could be such that we would have difficulty understanding, even comprehending, what we were looking at. Smith again (italics mine):

The key implication of this paper can be summarized as followed: if an actively space-faring ETC embarks on a program to send probes to interstellar destinations, and if the technology of this ETC advances with time, then the first probe to arrive at the destination of a less-advanced ETC is less likely to be one of the earliest probes launched, but one of more advanced capability. There may thus be a substantial disparity between the level of technology comprising the first-arrival probe and that developed by the receiving ETC, if it has no interstellar capability itself. The greater the initial separation of the two ETCs, or the greater the rate of probe development by the active ETC, the greater is the potential for a technological mismatch at first encounter.

Image: A language that can alter our perception of time, under study in the film Arrival, where the probes in question represent a technology that is baffling to Earth scientists.

The situation would change, of course, if the receiving civilization is also one possessing interstellar capabilities, in which case contact might not even occur on the home world or system of the receiving culture. As we are a passive civilization in Smith’s terms, we are likely to encounter a markedly advanced civilization if an artifact ever does show up in our system. David Kipping calls this result ‘contact inequality,’ and remember, “…increasing the distance Dmax of the first-contact horizon increases the likely generation number of a probe of first encounter, thereby enhancing a contact inequality with a passive ETC.”

Something entering our Solar System from another civilization should be highly sophisticated, well beyond our technological levels, and perhaps utterly opaque to our scrutiny. The scenario of, for example, the Strugatsky brothers’ Roadside Picnic seems more likely than that of The Day the Earth Stood Still. The 1972 novel depicts the ‘stalker’ Red Schuhart as he enters a ‘zone of visitation’ where an alien civilization has come to Earth and left behind bizarre and inexplicable traces. Now they’ve moved on. What is human culture to make of their detritus? From the novel:

He had never experienced anything like this before outside the Zone. And it had happened in the Zone only two or three times. It was as though he were in a different world. A million odors cascaded in on him at once—sharp, sweet, metallic, gentle, dangerous ones, as crude as cobblestones, as delicate and complex as watch mechanisms, as huge as a house and as tiny as a dust particle. The air became hard, it developed edges, surfaces, and corners, like space was filled with huge, stiff balloons, slippery pyramids, gigantic prickly crystals, and he had to push his way through it all, making his way in a dream through a junk store stuffed with ancient ugly furniture … It lasted a second. He opened his eyes, and everything was gone. It hadn’t been a different world—it was this world turning a new, unknown side to him. This side was revealed to him for a second and then disappeared, before he had time to figure it out.

Image: From the 1979 film Stalker, based loosely on the Strugatsky novel. No spacecraft, no aliens here, just the mystery of what they left and what it means.

It should hardly surprise us that an arriving interstellar probe would be well beyond our technology; otherwise, it couldn’t have gotten here. But if we factor in what Smith is saying, it appears that depending on how far away the sending ETC is, the technology gap between us and them becomes greater and greater. We’re talking about baffling and perplexing morphing into the all but unknowable. Indistinguishable from magic?

No grand arrivals, no opportunities for trade, no galactic encyclopedias. This is first contact as enigma, and if I had to put money on it, I suspect this is closer to what would happen if contact is achieved by a visitation to our planet. I return to Rendezvous with Rama, where odd geometric structures and a ‘cylindrical sea’ are found within the probe slingshotting around the Sun, and the vehicle departs as mysteriously as it came, leaving behind only one overwhelming fact: We are not alone.

The paper is Smith, “On the first probe to transit between two interstellar civilizations,”
International Journal of Astrobiology 22 (2023), 185-196 (abstract).