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Twin Moons over Alien Desert City with Pyramids
Twin Moons over Alien Desert City with Pyramids

Is the Brief Window for Finding ET Closing?

According to some scenarios, we could be past our best-before date for contacting aliens

Readers will recall that we have been looking at science writer Matt Williams‘ analysis of the various reasons that we do not see extraterrestrials except at the movies. We’ve listed (below) the many interesting ideas he has covered but now here’s a new one!: What if there is only a brief window during which a space-faring civilization can even develop?

For the sake of the Brief Window Hypothesis, the key parameter is L. In this case, it can be defined as the amount of time a civilization can be expected to exist before succumbing to an extinction-level event. This could take the form of a natural disaster (an asteroid impact) or come in the form of self-destruction (nuclear or biological war). Using humanity as an example, these existential threats all appear as likely possibilities.

Whereas in the classical Drake Equation, L is defined as the length of time a civilization has to develop the necessary technology (ex. radio communications) and transmit a signal, the Brief Window hypothesis also considers the time it would take to get a reply. How long can a modern civilization expect to exist before a cataclysmic fate will claim it? Could this be the reason for the “Great Silence”?

Matt Williams, “Beyond “Fermi’s Paradox” IX: What Is the Brief Window hypothesis?” at Universe Today

In this version, we won’t be around long enough to attract attention or get a reply.

Some have attempted to put numbers to the conjecture, including Sebastian von Hoerner (1919– 2003), a colleague of Frank Drake, who published “The Search for Signals from Other Civilizations in 1961. As he put it at the time, “The waiting time for answers may be greater than the longevity of the technical state of mind.” (open access)

He thought civilizations would have an average 6500-year run before the technology that would enable us to even notice extraterrestrials would fade. They could have gone on ahead of us and we would not even know.

Others have offered different riffs on the basic idea but remember, it works both ways. The aliens could be dead long before we are:

in a 2018 study titled “Area Coverage of Expanding E.T. Signals in the Galaxy: SETI and Drake’s N.” In it, the team made two key assumptions about the Drake Equation: one, that ETIs emerge in our galaxy (N) at a constant rate; two, that they’ll only be able to send transmissions for a certain amount of time stop before they go extinct (L).

Long after these civilizations have died, these broadcasts will keep traveling outward at the speed of light (c). The transmissions would form an annulus (a donut-shaped wavefront) within which the radio signals would be detectable. The thickness of each annulus’ walls (measured in light-years) will correspond to how many years the civilization was able to broadcast radio signals to space before going silent.

Matt Williams, “Beyond “Fermi’s Paradox” IX: What Is the Brief Window hypothesis?” at Universe Today

Williams points out some obvious problems with the Brief Window hypothesis, including the fact that we really have no idea how long an “advanced civilization” might be expected to survive. Are we assuming that there is a law of nature concerning how long such civilizations last? Can someone state that law?

Many philosophers have noted that human consciousness broke out of the cage a long time ago and we are definitely a giant blip. As G.K. Chesterton noted last century, humans are actually the only wild animal:

We talk of wild animals but man is the only wild animal. It is man that has broken out. All other animals are tame animals; following the rugged respectability of the tribe or type.

– The Bodley Head G.K. Chesterton (ed. Vintage, 1985)

Chesterton goes on to say, “it is exactly where biology leaves off that all religion begins.”

Of course. Cats don’t need religion to make sense of their lives but humans need either religion or philosophy to make sense of ours.

Facts like that make it difficult to be sure who else in the universe might have broken out—and when they did and how long it will last. But the sci-fi film-making potential for various scenarios is potentially enormous. We must hope that indie filmmakers are listening.

You may also enjoy these accounts of why we do not see the aliens:

1.Are the Aliens We Never Find Obeying Star Trek’s Prime Directive? The Directive is, don’t interfere in the evolution of alien societies, even if you have good intentions. Assuming the aliens exist, perhaps it’s just as well, on the whole, if they do want to leave us alone. They could want to “fix” us instead…

2.How can we be sure we are not just an ET’s simulation? A number of books and films are based on the idea. Should we believe it? We make a faith-based decision that logic and evidence together are reasonable guides to what is true. Logical possibility alone does not make an idea true.

3.Did the smart machines destroy the aliens who invented them? That’s the Berserker hypothesis. A smart deadly weapon could well decide to do without its inventor and, lacking moral guidance, destroy everything in sight. Extinction of a highly advanced civilization by its own lethal technology may be more likely than extinction by natural disaster. They could control nature.

4.Researchers: The aliens exist but they are sleeping… And we wake them at our peril. The Aestivation hypothesis is that immensely powerful aliens are waiting in a digitized form for the universe to cool down from the heat their computers emit.

5.Maybe there are just very few aliens out there… The Rare Earth hypothesis offers science-based reasons that life in the universe is rare. Even if life is rare in the universe, Earth may be uniquely suited to space exploration, as the Privileged Planet hypothesis suggests.

6.Does science fiction hint that we are actually doomed? That’s the implication of an influential theory as to why we never see extraterrestrials. Depending how we read the Kardashev scale, civilizations disappear somewhere between where we are now and the advanced state needed for intergalactic travel.

7.Space aliens could in fact be watching us. Using the methods we use to spot exoplanets. But if they are technologically advanced, wouldn’t they be here by now? The Hart-Tipler conjecture (they don’t exist) is, of course, very unpopular in sci-fi. But let’s confront it, if only to move on to more promising speculations.


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Is the Brief Window for Finding ET Closing?