Why is it so hard to find ET? After 50 years of searching, the SETI project has so far found nothing. In the latest development, on April 14, 2015 Penn State researchers announced that after searching through satellite data on 100,000 galaxies, they saw no evidence, such as infrared signatures, indicative of advanced technological civilizations. Such civilizations might exist, but there was certainly no clear-cut evidence in their data.
In our Part I article, we mentioned how numerous scientists over the past 65 years, since Fermi first raised the question "Where is everybody?", have examined Fermi's paradox and have proposed solutions. We listed a number of these proposed solutions, such as the following, with common rejoinders that have been raised against them:
- They are under strict orders not to disclose their existence.
- They exist, but are too far away.
- They exist, but have lost interest in interstellar communication and/or exploration.
- They are calling, but we do not yet recognize the signal.
- Civilizations like us invariably self-destruct.
- Earth is a unique planet with characteristics fostering a long-lived biological regime leading to intelligent life.
- WE ARE ALONE, at least within our home in the Milky Way galaxy.
The problem with explanations such number one is that it just takes one small group in one distant civilization to break the pact of silence. Given our experience with human society, it is hardly credible that a "law"-forbidding contact with civilizations such as ours could be enforced over a vast and diverse interstellar society without any exceptions over millions of years. Similarly, with regards to number four, it is not credible that a global society could permanently enforce a global ban on communications, specifically targeted to nascent technological societies such as ours in a form that we could easily recognize.
With regards to number three, it also seems exceedingly unlikely that each and every individual of each and every ET society forever lacks interest in communication and/or exploration. This is doubly dubious given the fact that evolution, which is widely believed to be the driver behind intelligent life everywhere, strongly favors organisms that explore and expand their dominion. Similar difficulties torpedo other explanations that rely on a "sociological" scenario. See our Part I article for additional discussion.
Another class of explanation is "technological" -- extra-terrestrial civilizations may exist, but interstellar exploration and communication is simply too difficult (see number two above).
But such explanations typically ignore the potential of rapidly advancing technology, together with the fact that any ET society is almost certainly thousands or millions of years more advanced than us. For example, a society could deploy "von Neumann probes" that travel to a nearby star system, send data back to the home planet, construct replicas of themselves, and launch these craft to even more distant systems. In one recent analysis, researchers found that 99 percent of all star systems in the Milky Way could be explored in only about five million years, which is an eye-blink in the multi-billion-year age of the Milky Way.
Communication can be facilitated by similar high-tech means. For instance, von Neumann probes could easily be outfitted with facilities to view, communicate with and relay messages to the home planet. Already, "cube sats," namely small satellites just a few inches in size, are being deployed to monitor Earth. And NASA is developing telescopes that can detect signatures of biological activity on extrasolar planets.
More futuristically, SETI pioneer Frank Drake observes that we could employ a "gravitational lens," taking advantage of the curvature of light around the sun, to obtain high-resolution images of distant planets, and even listen in to their microwave or optical communications and respond in kind. Such a scheme should be feasible in just a few decades. So why isn't ET calling us using a gravitational lens on their end?
The great filter
As we mentioned in our Part I article, some have suggested that there is a great filter that explains the eerie silence -- some major barrier to a society becoming sufficiently advanced to explore the Milky Way.
Possibilities here range from the hypothesis that it might be extraordinarily unlikely for life to begin at all, or that the jump from prokaryote to eukaryote cells is similarly unlikely, or that our combination of planetary dynamics and plate tectonics is exceedingly unlikely, or, as suggested above, that civilizations like ours invariably self-destruct, or that some future calamity, such as a huge gamma-ray burst from a nearby star, invariably ends societies like ours before they can explore the cosmos.
Nick Bostrom, among others, hopes that the search for extraterrestrial life comes up empty-handed, because if life were found this would reduce the number of possible candidates for the great filter being behind us, and it would increase the likelihood that the great filter (possibly a great calamity) still lies ahead of us.
But even here, there are straightforward rejoinders. We have already survived more than 100 years of technological adolescence without destroying ourselves in a nuclear or a biological catastrophe. Climate change presents a challenge, but with numerous green energy technologies, even Al Gore is cautiously optimistic. Freak viruses and biological weapons are a concern, but we have developed much more effective defenses. And as for a gamma-ray burst, our planet has survived many millions of years, so the probability that we will be destroyed in the next few decades, before we venture to other planets and stars, is rather remote. So it does not seem credible that such calamities have destroyed each and every ET society.
Many have wondered whether, in our quest for ET, we are still being too parochially human. Maybe ET is completely different from anything we have imagined, or different from anything that we can imagine. Perhaps all our assumptions about the nature of intelligent life are simply too parochial. Our notions about what other terrestrial animals (from rooks to octopuses) can do have changed dramatically in the past twenty years.
Digital technology may hold a clue here as well. Even in our own time we have seen digital technology take over many of our lives, with hundreds of millions of people hopelessly attached to their smartphones. Such technology may even be rewiring our brains. Devices such as Apple Watch and Google Glass may further enhance our cognitive powers. Apple and IBM have struck a deal to further develop IBM's Watson machine learning technology, which defeated humans on Jeopardy!, for medical applications. Some amputees can now control prosthetic legs using thought alone.
Thus, we have to consider the possibility that extraterrestrial societies exist, but, as astronomer Paul Davies suggests, they have advanced to a "post-biological" or even "post-material" state, and now exist only as extremely advanced computer programs somewhere.
Similarly, SETI astronomer Seth Shostak argues, "Once any society invents the technology that could put them in touch with the cosmos, they are at most only a few hundred years away from changing their own paradigm of sentience to artificial intelligence." Thus, perhaps the solution to Fermi's paradox is simply that we have nothing useful to say to these advanced "spiritual" entities.
But, one can ask, in this supposedly vast civilization of post-biological intelligences, are there not at least a handful of entities that still wonder what biological organisms are like, and are curious to explore and communicate with them? After all, even in our society, while the vast majority of citizens are not the slightest bit interested in bees or similar insects, nonetheless a few are (melittologists), and they do scientific research on these creatures.
And we can now "communicate" with bees -- for example, researchers have identified that the dance patterns of honey bees communicate to other bees both distance and direction to food. So can we be so certain that absolutely no one in this post-biological or post-material society is capable of or interested in studying and communicating with humans?
While many have wondered, "Where is everybody?" there is still no easy answer.
Astronomer Paul Davies concludes his latest book (2011) on the topic by stating his own assessment: "my answer is that we are probably the only intelligent beings in the observable universe and I would not be very surprised if the solar system contains the only life in the observable universe." Nonetheless, Davies reflects, "I can think of no more thrilling a discovery than coming across clear evidence for extraterrestrial intelligence."