"We can say little, if anything, about what these patterns [above] signify, why they were cut into rocks, or who created them. For all intents and purposes, they might have been made by aliens." When a new NASA book on alien communications has a paragraph like that, you had better pay attention.
Of course, the scientists and scholars who contributed to Archaeology, Anthropology and Interstellar Communications — a new 300-page volume [PDF] edited by Douglas A. Vakoch — are not saying these carvings were definitely made by aliens. They're saying that, since we don't really know the origin and meaning of these markings — which were made thousands of years ago all across Europe, America and India — we can assume that they are made by aliens as a test to what we may encounter when we actually make contact with a civilisation from another planet.
It's a serious book — deep and complex, but quite accessible. I have been going through it and it is truly fascinating stuff. And I'm not only talking about the gem at the top of this article:
Consider again, therefore, the desirability of establishing symbolic/linguistic communication with ETI [Extra-Terrestrial Intelligence]. It is helpful to review some parallels from human existence that pose problems for us today. One of these is "rock art," which consists of patterns or shapes cut into rock many thousands of years ago. Such ancient stone carvings can be found in many countries [...]
We can say little, if anything, about what these patterns [above] signify, why they were cut into rocks, or who created them. For all intents and purposes, they might have been made by aliens.
A replica of an unusual cup-and-ring-marked stone from Dalgarven, North Ayrshire, Scotland.
The larger picture
That's only a tiny part of a much larger logical chain that takes into consideration our knowledge on historical and prehistorical Earth, as well as our understanding of biology, evolution, and physics. For example, after going through a number of assumptions about the potential physical and biophysical differences in Chapter 15 — titled Constraints on Message Construction for Communication with Extraterrestrial Intelligence — Vakoch writes about the implications (emphasis mine):
Implications — I
If the reader accepts these assumptions, then our first constraint on possible messages is simple: don't think of "sound worlds" or music or speech as the domains, vehicles, or contents of ETI messages. Regardless of semiotic concerns (see below), the accessibility of acoustic messaging must remain doubtful. Furthermore, there will be intended and unintended aspects of performance, which elaborate the difficulties of using sound. In my view avoidance of the sound world need not be controversial.
On the other hand, vision and the use of images would appear to be at least plausible. Although spectral details cannot be considered universal, the physical arrangement of objects on a habitable planet's surface will be shaped in part by gravity (the notion of a horizon might well be universal) and thus multispectral images might plausibly be considered worthwhile for messages. More generally, the implications for considering SETI/CETI as some sort of anthropological challenge need teasing out.
Makes total sense to me.
I won't quote more of the book here because that would be a worthless exercise, but so far — I'm still eagerly reading it — it's a really great read.
It's comforting that NASA is thinking about human-alien communication under a new focus, one that is not purely based on the physical sciences of planetary research or exobiology, but that ties it with our current experience in trying to decipher our own archeological and anthropological past. That, according to Vakoch, is the objective of this volume (emphasis mine):
The chapters in this volume combine incisive critique with hope that there is a response to the scepticism behind these critiques. Addressing a field that has been dominated by astronomers, physicists, engineers, and computer scientists, the contributors to this collection raise questions that may have been overlooked by physical scientists about the ease of establishing meaningful communication with an extraterrestrial intelligence.
These scholars are grappling with some of the enormous challenges that will face humanity if an information-rich signal emanating from another world is detected. By drawing on issues at the core of contemporary archaeology and anthropology, we can be much better prepared for contact with an extraterrestrial civilisation, should that day ever come.