The Eerie Silence
If aliens exist, where are they?
To a physicist like me, life looks to be a little short of magic: all those dumb molecules conspiring to achieve such clever things! How do they do it? There is no orchestrator, no choreographer directing the performance, no esprit de corps, no collective will, no life force – just mindless atoms pushing and pulling on each other, kicked about by random thermal fluctuations. Yet the end product is an exquisite and highly distinctive form of order. Even chemists, who are familiar with the amazing transformative powers of molecules, find it breathtaking. George Whitesides, Professor of Chemistry at Harvard University, writes, “How remarkable is life? The answer is: very. Those of us who deal in networks of chemical reactions know of nothing like it.”
“So the arrangement is at once both random and highly specific – a peculiar, indeed unique, combination of qualities hard to explain by deterministic physical forces,” he writes.
Biology’s law of evolution may have played a role in life’s origin, since all that’s theoretically needed to get the system going is the replication of information. For life today, that replication occurs with DNA, but for the first life, patterns in a physical structure or even particular arrays of atoms may have been enough. While life’s origin from non-living materials is still a mystery, Davies says that life may be one possible outcome of complex self-organizing systems. Just like ant colonies, the stock market and the internet, life may result from a law of increasing complexity that occurs under certain circumstances.
To find out whether life was a bizarre accident unique to Earth, we need to search for life elsewhere. Davies points out that there has only been one successful mission by any space agency to search for life on another planet: NASA’s Viking mission.
“The media tend to present all Mars exploration as part of the search for life, but this is a sly piece of disinformation,” he writes. “It is true that some Mars exploration – looking for water, for example – bears indirectly on the question of life, but explicitly biological experiments have for thirty years been systematically eliminated by NASA missions.”
Most scientists think the Viking life experiments found no proof of life, although some, including Gilbert Levin, who designed Viking’s Labeled Release experiment, contest this conclusion. Even if we were to unquestionably find life on Mars, Davies notes, this wouldn’t tell us if there was life farther afield, since Earth and Mars swapped material back and forth over the history of the solar system. Meteorites striking Earth sent some of our rocks hurtling into space and on to Mars, and vice versa – and some of those rocks could have contained microbial life.
To really answer the question, we need to find evidence for life on a far-distant planet. However, Davies says another way to prove that life is more than a freak accident is to find a completely different kind of life on Earth.
“If life started more than once on Earth, we could be virtually certain that the universe is teeming with it,” Davies writes. “Unless there is something very peculiar about our planet, it is inconceivable that life would have begun twice on one Earth-like planet but hardly ever on the rest.”
All life on Earth can be placed on a diagram called the Tree of Life, which indicates how the various organisms can be traced back to a common ancestor. But a shadow biosphere would be composed of life that would not have a place on the Tree. Davies writes:
If you examine the innards of a microbe, chances are you will find the same stuff – DNA, proteins, ribosomes – as is found in you and me. At least, that has been the experience so far. But microbiologists have only just scratched the surface of the microbial realm. Our world is literally seething with these tiny organisms. Just one cubic centimeter (0.061 cubic inches) of soil might contain millions of different species adding up to billions of microbes in all, and the vast majority haven’t even been classified, let alone analyzed. Nobody knows for sure what they are; for all we know, some of them could be life as we do not know it.
Because scientists must culture microbes in a lab in order to study them, an entirely different form of life would go unnoticed because the tests are custom-made to handle known life forms. Davies says new tests need to be developed to see what might be hidden right in front of our eyes.
“At this time” is an important element of his estimate, since a barrier to interstellar communications is not only distance but time. Consider aliens living one thousand light years away. Davies points out that if they were able to see Earth in their telescopes, they would not see us as we are today, but as we were in the year 1010 A.D. – long before we invented radio dishes. And because human radio technology is only about 100 years old, it will take another 900 years for our first signals to reach them.
Communication signals on Earth are now mostly sent by optical fibers rather than by radio wavelengths, so Davies says there’s no reason to think advanced aliens would bother with that technology. Instead, he suggests they may use neutrino beams, various wavelength beacons, or a galaxy-wide internet system to communicate. We might even find clues to alien technology closer to home in the form of reproducing nanomachines, or microprobes that latch onto DNA. Davies thinks the SETI search should be expanded to include these, and it also should look for alien ‘footprints’ in space that indicate advanced mining or engineering projects, or waste dump sites.
Davies is equally dismissive of the plaques on the Pioneer 10 and 11 spacecraft, which depicted male and female human figures (with the male’s hand raised in greeting), and our solar system and its location in the galaxy:
This image may be worthless as far as signaling aliens is concerned, but it speaks volumes about humans. A brief message to an unknown alien community should presumably reflect the things that we consider most significant about ourselves. The picture is dominated by human shapes, yet our physical form is probably the least significant thing we can say. It is almost completely irrelevant both scientifically and culturally. To put it bluntly, who gives a damn what we look like? The raised hand part is the height of absurdity; such a culturally specific mannerism would be utterly incomprehensible to another species, especially one that might not have limbs.
Davies says if we ever do make contact, human society would be changed forever. He thinks religion would be especially hard-hit. But he also acknowledges that SETI itself has been described as a religion, since it is driven by faith rather than proof. Even if the hunt for aliens comes up empty after a million years of searching, he says that would not be absolute proof that they don’t exist.
As a scientist, Davies says he wouldn't be surprised if life on Earth turns out to be entirely unique. This lonely outlook makes him uneasy, but he also notes this would be a golden silence, because life on Earth would be even more precious if we really are alone.
Still, the fact that we don’t know and may never have the answer about alien life is reason enough to keep searching, says Davies. By stretching our minds to try to envision all the possibilities in our search for aliens, not only may we one day find what we seek, but in the process we also will learn about many other deep and enduring mysteries of the cosmos.