12. They're Here on Earth Undetected
This is the favorite solution of every UFO conspiracy theory: Aliens are among us, but they’ve either gone undetected or been covered up by government officials. Aside from the inability of governments to effectively harbor even menial secrets, no compelling evidence exists that this is in fact the case. A slightly more likely hypothesis would be that an extraterrestrial intelligence visited Earth at some time in past, although again, there’s no evidence to suggest that this has occurred.
11. They Fear our Technological Immaturity
Perhaps young civilizations such as ours are deemed too dangerous for contact. We’re a top predator species, and we’ve utilized those skills to exploit our planet and its resources. Perhaps this makes any mature species reluctant to initiate us into the galactic community until we’ve proven that we can reach a level of sustainable growth. Of course, this assumes that they also know of our emergence.
10. Their Communications are too Alien to Understand
We have intelligent species such as dolphins and whales right here on Earth, and the fact that we have yet to open up much of a meaningful dialog with them could signal that communication with a truly alien life form is hopeless. We will, however, have the language of science in common. The laws of physics hold true throughout the observable universe and may provide us with a common language.
9. Intelligent Life is Rare in the Cosmos
In 2000, Peter Ward and Donald Brownlee published a book entitled The Rare Earth Hypothesis, which posited that while the emergence of simple life may be common, the development of intelligence was perhaps a singular event. On Earth, life was the result of a fortunate chain of events — the existence of our Moon, plate tectonics, and even the planet Jupiter are evoked for reasons that we’re here in this stable niche of a dangerous universe. Humanity itself nearly became extinct at the end of the last Ice Age, and tantalizing clues suggest that those few Homo sapiens that did survive that genetic bottleneck possessed the lucky adaptations necessary to make the civilization of the last few thousand years possible. But just how often this sort of drama plays out in the cosmos, it’s hard to say with a sample size of one.
8. We’re the First lntelligent Species to Emerge
Someone has to be first, at least in this corner of the cosmos. We know that the universe began 13.7 billion years ago, and that the Earth formed 4.5 billion years ago and that it took life about a billion years to get started. Our Sun is a 3rd generation star, which means that the proto-solar nebula that our solar system condensed out of was seeded with enough heavy elements to give life a start. That path from hydrogen atoms to radio telescopes was a long one, and perhaps we’re just the first to emerge, though such a special fate for us would seem unlikely.
7. They Aren’t Interested in Earth
In the late 19th century, a proposal was made to signal a civilization believed to exist on Mars by setting large forest fires. This now-laughable proposal demonstrates that perhaps even our current technology may be obsolete when it comes to communicating with a civilization perhaps a million years ahead of our own. In addition, extraterrestrials may not be interested in us until we reach a certain level of development. Perhaps they communicate using high-frequency lasers or some method we haven’t discovered yet. Perhaps there’s an equivalent of a “two-drink minimum” for entering the galactic community, such as the ability to send gravity waves via resonating pulsars or some other exotic method.
6. They Don't Want to Interfere
This solution is familiar to many people thanks to Star Trek and the Prime Directive, where a sort of cosmic ethos exists barring space-faring civilizations from tampering with primitive ones. But like many of these solutions, this raises a question: how is it enforced?
5. Intelligent Species don’t Survive Technological Adolescence
This solution seemed all too applicable during the Cold War, when some feared the human race itself would die out soon after acquiring technology (nuclear bombs) capable of making us extinct. And we’re not out of the woods yet, as climate change, disease, and perhaps some unknown threat we’ve yet to address could still do us in. Perhaps intelligent civilizations spring up all the time, only to extinguish themselves after a century or so of unrestrained consumption.
4. We Haven’t Been Looking that Long
The original Project Ozma looked at two nearby star systems at a single frequency. Modern searches underway from the Allen Telescope Array can scan large swaths of the sky over millions of channels. But we have yet to scour every star in our galaxy over every conceivable frequency over the past 50 years, and we’ve only been transmitting high-power radar signals since the start of World War II. A civilization over 70 light years distant would scarcely know of our existence.
3. They're Not Interested in Interstellar Travel or Communication
As noted, whales are intelligent, but they don’t build radio telescopes. Perhaps it’s our mix of dexterity, curiosity, and problem solving that sparks our interest in space exploration. This combination of traits may not arise often with intelligence. Or perhaps, once a civilization can build a virtual reality more pleasing than the real one, they lose interest in space exploration.
2. The Galaxy has Certain “Goldilocks Zones" of Habitability
As we explore our place in the solar system, we’ve come to realize that the Earth occupies a zone where the temperature is just right, and water can exist in a liquid state. But we’re also starting to realize that the galaxy may also have a similar “Goldilocks Zone,” one where the radiation is not too intense and the right mix of elements necessary for life exists. This privileged belt encompassing our galaxy may cut down the number of civilizations that are out there waiting to be found.
1. The Nearest Civilization in Space and Time is too Distant
The last factor of the Drake equation may be the real kicker, and many solutions play off of this basic dilemma of just how long intelligent civilizations last. If the answer is millions of years, we may have neighbors next door, but if it’s a century or two, there may currently be no one to talk to within 1,000 light years. Certainly, we’ve been able to confirm factors of the Drake equation such as the prevalence of exoplanets via recent discoveries, and finding even simple life forms elsewhere in our own solar system would have stunning implications. Either solution is profound. Perhaps in our lifetime we’ll be able to point to a star in the sky and say that life has arisen there as well.
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