At Nautilus, astrophysicist (and astrobiologist) Caleb A. Scharf offers some sobering reflections on the diligent search for extraterrestrial intelligences (ET) in recent decades:

Despite this effort, there has been no evidence to date of extraterrestrial life. But that lack of evidence is not because the scientific enterprise is uniformly conservative, rigid, and close-minded, as implied by [astronomer Avi] Loeb and uncritically echoed by some columnists. It’s because no discovery or event has risen to the level where it is inexplicable in any other way. Could greater funding and support change that story? Perhaps, but the same could be said for almost any other ambitious scientific enterprise, and the answer cannot be known beforehand.

Caleb Scharf, “The Alien-Haunted World” at Nautilus (February 15, 2021)

Scarf writes in the wake of controversies surrounding Harvard astronomer Avi Loeb’s new book Extraterrestrial:The First Sign of Intelligent Life Beyond Earth. Loeb has famously argued that the space object Oumuamua might be an extraterrestrial light sail.

Scarf says it is a very unusual space object but natural explanations are available:

‘Oumuamua certainly had puzzling characteristics. It was small for an interstellar comet, it was elongated and, despite being barely caught by our best telescopes and nimblest astronomers as it wended its tumbling way back out of the solar system, it exhibited an ethereal acceleration away from the Sun. But even these puzzles are explicable by known processes and are not wildly inconsistent with the properties of other cometary-like objects. Indeed, a number of comparatively straightforward, testable, explanations seem compatible, including the possibility that the object was a frozen nitrogen “iceberg,” a chip off the block of some distant Pluto-like world.

Caleb Scharf, “The Alien-Haunted World” at Nautilus (February 15, 2021)

He warns against equating scientific skepticism with mere conservatism:

Scientific conservatism is present. But so too is a clear memory of the many times where enthusiasm for a provocative idea about alien life has given way to disappointment—from fossils in Martian meteorites to arsenic-laced microbes. Fingers have been burnt before in the quest to find clues to life in the universe.

Caleb Scharf, “The Alien-Haunted World” at Nautilus (February 15, 2021)

Here’s another way of looking at it, from information theory: The artifact or signal of an intelligent being should show “specified complexity. That is,

Specified complexity: A long sequence of random letters is complex without being specified [it is hard to duplicate but it also doesn’t mean anything]. A short sequence of letters like “so,” is specified without being complex. [It means something but what it means is not very significant by itself]. A Shakespearean sonnet is both complex and specified. [It is both complex and hard to duplicate and it means a lot in a few words]

That’s what we should be looking for in signals from intelligent beings — orderly patterns that hold meanings not found in inanimate nature.

If a roommate comes home and finds Scrabble letters on the board spelling out: IT’S YOUR TURN TO DO THE DISHES TONIGHT, he will hardly suppose that the arrangement resulted from someone dumping the bag of letters on the board.

If we can find signals like that, they will be hard to argue with. Meanwhile, informed skepticism is best.

Note: Here’s a quick introduction to some basic concepts in information theory — how we can know if an unusual object or event is a signal or message. Also: Part II, Part III, and Part IV.

You may also wish to read: Astrophysicist warns: The aliens may be boring or unreachable. Researchers are taking the emissions from the vicinity of exoplanet Proxima B seriously. But if it is truly a technological signal, what would follow? Science fiction would be prophetic in the sense that Proxima B might show that They’re Out There. But maybe too optimistic about our chances of making contact.