Into the Unknown, page 8
To be clear, in this context I am not necessarily talking about a conventional “god” as I think might be commonly envisioned. Really any sort of higher power that resides outside our sphere of reality might do. This could be some sort of superintelligent being—at least superintelligent by our standards, though they could be profoundly idiotic among their own kind, but I hope for our sake this is not the case. All of the cosmos could even be an experiment, or part of a higher-power school science project. When I was in elementary school, I did an experiment with a set of plants that I suspect is fairly common—some plants got water, some didn’t. Some got sunlight, some didn’t. Some had bleach poured on them, some didn’t. Who knows, maybe our cosmos is someone’s homework.
And yet again, a “higher power” is not nothing.
Magical Thinking
As far as mysteries of the universe go, thinking about the origin of the universe sends me into more of an existential crisis than any other topic. Not only are the physics of this uncharted (and potentially unchartable?), but I end up tangled in philosophical knots. It is clear to me that my own intellect is not up to the task—there is an inherent problem embedded in the infinite regression that has no apparent solution that I can convince myself of. For this reason, I am often tempted to punt this issue as beyond human comprehension, and therefore into the realm of the supernatural.
Then another little voice in my mind speaks up to remind me that just because I don’t understand something, doesn’t mean it isn’t understandable. I am reasonably sure that no matter how hard I might try, there is just no way I could teach my dogs to understand general relativity. Heck, even thermodynamics would be a stretch—once I brought helium-filled balloons home for a party, and one of my cats at the time absolutely lost his mind in terror. It seemed obvious to my husband and me that Jinko’s feline brain was thinking along the lines of “Those things that float around the house violate the laws of nature.”
Here we are with our limited human brains—do we really have so much arrogance as to think just because we don’t understand something it must be supernatural? This is a good time to remind ourselves of the “God of the gaps” fallacy from the last chapter on epistemology. Of course, the inverse is also true—just because we think we understand something, doesn’t require that it not be supernatural. Also recall the third of Clarke’s three “laws”: “Any sufficiently advanced technology is indistinguishable from magic.”
Interstition
One question that often follows closely after “Why is there something instead of nothing?” is why this something happens to include life. This question predates modern science but may now be within our reach.
A confirmation of extraterrestrial (ET) life would arguably be the most profound discovery of human history—bigger even than fire, the wheel, or even sliced bread. Such a discovery would not necessarily impact our fundamental understandings in modern science, but it would undoubtedly affect how we see ourselves and our place in the universe.
The religion I grew up in forbade the existence of extraterrestrial life, which even at the time I thought was an odd thing to oppose. I was pointed to the Bible and given the argument that the universe was made for humans. I suppose if one doesn’t understand how expansive the universe is and thinks they are the center of it, the notion that humans are the point of it all doesn’t seem as ludicrous as it is.
4
Does Extraterrestrial Life Exist?
Extraterrestrial life. What image pops into your mind when you read that phrase?
If you’re like most people I’ve asked this question of, you probably envision something along the lines of a character from a movie or TV show that is, for all practical purposes, essentially humanoid. Perhaps your version of ET life has green skin or eight arms or a tail, but these characteristics are not terribly different from the basic physiology of people. Thanks mostly to Hollywood, people often have a shockingly uncreative image of what actual ET life might look like. If you did not envision a Hollywood-ish type character, give yourself a pat on the back with one of your likely two (and not eight) arms.
Whatever you might have thought of in the previous paragraph, why do you think that particular example is what you thought of and not something else? Even in our own biosphere on Earth, there are life-forms that are far more “alien” looking than many people think of at the mention of “ET life.” The ocean, for example, has forms of life that are much stranger than in most movies or TV shows.
A plush dumbo octopus would be cute, and if we ran into one in space, we might want to hug it (for the record, I have no idea how bad of an idea that would be). But coming across a human-sized amphipod in a dark space alley would be the thing of nightmares.
One of my favorite life-forms from Earth was once thought to be our great-great-great-great-(repeat for a long time) cousin, the Saccorhytus coronarius. This critter doesn’t exist now but appears to be a 540-million-year-ago example of life in the Cambrian era and looked more “alien” than almost anything in Hollywood. You might note that, among other interesting characteristics, Saccorhytus coronarius is not believed to have had an anus. There are so many jokes waiting to be made, and I am glad for its sake that middle school kids weren’t around at the same time.
Images of (left) Saccorhytus coronarius (based on visualization of Nobu Tamura, CC BY-SA 4.0); (middle) a dumbo octopus; and (right) an amphipod.
The point is that even on Earth we have a variety of life that calls into question whether ET life—in totally different environments—would be remotely humanoid. In fact, most of the life-forms that might come to mind are fairly macroscopic—but these “big” forms of life are by far in the minority. And speaking of microscopic forms of life—it’s worth considering to what extent your body is really your body. Fun fact: there are more bacterial cells in your body than human cells (roughly 38 trillion compared to 30 trillion). So, who are you really?
Consider again the ET life-form you thought of at the beginning of this section: What aspects of its environment would have caused it to evolve that way? If you end up basically recreating the surface of Earth, I challenge you to push your thinking further; think of a planet very different from Earth. What characteristics might life need to evolve and survive in this radically different environment? Or what about life not on a planet at all? There are good reasons to start by using what we know about life on Earth to envision life elsewhere. But there are also good reasons to step back and consider that life might develop in the universe under radically different conditions. If we’re asking whether there is any ET life, we need to know what we mean by “life,” and we must be open to the idea that “life” somewhere else in the universe might be extremely different than life on Earth.
Being “alive” is one of those things that it is tempting to say, “I know it when I see it.” But are you sure? Trying to actually define life is a bit tricky. The renown physicist Erwin Schrödinger attempted to define “life” in terms of physics in his 1944 book What Is Life? The Physical Aspect of the Living Cell. Schrödinger argued that life is defined by its ability to resist decay to equilibrium (or in more physics-like terms, to resist “entropy”). We are going to talk a whole lot more about entropy later. Try not to let this physics-y term freak you out, it really isn’t that bad, and it has huge implications for the universe. For now, I will just leave the term here and not derail your reading about ET life with a tangent about physics.
This is an interesting working definition, but there are subtleties—for example, over what time period should we say something has to resist decay? If we want to consider ourselves to be alive, and most people I know are fond of this idea, we must acknowledge that as we age, we decay, and once we are dead, we decay a whole lot more until—eventually—we reach equilibrium with our environment again. The point is that we don’t 100 percent resist decay. In fact, you are decaying at this very moment.
Even biologists debate the definition of life, so if you are having trouble coming up with a robust definition, you shouldn’t feel too bad. A general working set of requirements for something to be considered “alive” might include some subset of the list below. But it only takes a few questions to throw a wrench in the mix.
Is composed of cells. What exactly do we mean by “cell”? Does it have to be the straight-up biologically understood definition? Why? That seems awfully narrow-minded of us.
Has a metabolism (uses energy). One might argue that rocks don’t use energy, but what about refrigerators? Or computers? Does it have to use energy for a purpose (if so, who gets to decide what counts as a “purpose”)?
Can grow. I don’t a priori see why growing is required for being alive. And what about a person who is no longer capable of growing? We’re in big trouble if people are only considered “alive” through their adolescent growth period (which I say with some degree of bias as a middle-aged woman).
Can adapt. What range of conditions does something need to adapt to? Humans can adapt to a small range of conditions, but we have our limits. Some people I know are really pretty terrible at adapting to pretty much anything.
Can respond to stimuli. Responding to stimuli is interesting because of physics. There is this whole Newton’s third law thing—actions and reactions, which means, at some level, that everything in the universe meets this criterion. For the sake of argument, let’s assume “responding” is more nuanced in some way. (What way?) Does an active choice have to be involved? In which case, what about nonconscious forms of life, like plants? And what if we don’t have free will to begin with?
Can reproduce and display heredity. Lots of things that normal people would generally consider to be alive are not able to reproduce. Take mules, for example, which are the result of a donkey and a horse being special friends. Donkeys have sixty-two chromosomes, horses have sixty-four, and mules end up with sixty-three—resulting in mules being infertile (OK, to be fair, there have been a few confirmed cases of a mule giving birth—but it is exceedingly rare). Just because someone can’t have offspring, would that mean they are not alive? Or do we only need the criterion to be statistically met by the particular class of things, while individuals can fail?
Maintains homeostasis (stable internal conditions). Homeostasis is a big one. If you can’t maintain homeostasis, you die. Well, at least according to our working definition of life (which is admittedly pretty crummy). Humans can maintain homeostasis through a limited range of environmental conditions (pressure, temperature, chemical composition, etc.), but we are not actually all that robust as far as life-forms go. Drop someone in an Arctic winter without shelter, and they are not likely to be able to maintain a “stable internal condition” for very long. What about computers? They have fans that turn on if they start to overheat. Does that count? What about the Earth itself, which has numerous processes that try to keep the planet in homeostasis, like the geological carbon cycle, which takes millions of years (and which we humans have screwed up in just a couple centuries).
Can evolve. What exactly do we mean by “evolve”? Is it just that each generation is different than the last? (Which requires reproduction, by the way.) Or does each generation need to be “better” in some way? (Who gets to decide what is “better”?) What if a life-form reached a hypothetical apex of evolution and there were no more “evolved” it could get? The very presence of this criterion also means that we can’t define something as “alive” unless we can see what its kin have done over multiple generations.
Can die. The ability to die puts us straight into a semantic loop, because to most people dead = not alive (Schrödinger’s cat aside). To say whether something is “dead,” we need to be able to define what it means to be “alive.” What if (hypothetically) in the science of the future we found a path to immortality. Would that mean that our future immortal offspring would not be alive?
I hope you are feeling deeply unsatisfied with any working definition of life. If we break this list down, we find we need to keep making exceptions under different circumstances. Do all these criteria need to be met? If not, how many of them are necessary? Does it matter over what range of times or conditions the criteria are met? If there are enough “exceptions” to the rule, then eventually the “rule” has very little value. Settling for “we will know life when we see it” is not particularly satisfactory. My sense is that we may eventually need to establish a continuum of “aliveness,” from, say, zero to 10. I’m sure that we would consider ourselves to be the apex of living and rank ourselves a 10 on this scale, with typical human hubris.
Life-as-We-Know-It (e.g., Life on Earth)
We find ourselves in a quandary. We know that we don’t know everything there is to know about possible life in the universe, but we must start somewhere. Even just in our own biosphere, we have some spectacular life-forms that can survive in crazy conditions. We have found life living (and flourishing) in conditions that are hostile to human existence, which has implications for physical conditions in which life-as-we-know-it is possible.
Some of the critters that can withstand (and even flourish) in hostile-to-human conditions firmly land in the category of creepy-crawlies, like special kinds of worms. I grew up learning that without sunlight we wouldn’t have life. It turns out that is not quite true, and giant tube worms are a great example of why. In the case of these worms, they get their energy by living on and near undersea thermal vents. There are also methane ice worms. These inch-ish-long critters have an ideal vacation spot in the deep, cold, dark ocean, buried in toxic (to humans) material. Like the giant tube worms, these ice worms don’t use light from the sun as part of their ecosystem; instead, they prefer to feast on bacteria that, in turn, feast on mounds of methane ice.
On the other end of the spectrum of temperature from methane ice worms, we have Pyrococcus furiosus—even the name alone sounds like it should be part of a grimoire and translates roughly into “raging fireball.” That should give you a solid hint at their superpower. The ideal temperature for these little beasts is 100°C or 212°F. Think about that the next time you are hoping to sterilize water for drinking by boiling it.
Another physical condition that is bad for people is exposure to high-energy radiation, which is a big concern in human space flight. But once again, humans are relative wimps in this respect. Enter Deinococcus radiodurans, which literally means “dreadful berry that withstands radiation.”1 Fortunately, it has a nickname that you can use instead—Conan the Bacterium, because it is so freaking tough. Conan the B. is so badass that it actually holds a place in Guinness World Records as the toughest known bacterium. It can survive all kinds of nasty things like dehydration, extreme cold, acidic environments, and the vacuum of outer space (making it a polyextremophile). But where Conan the B. really leaves the competition in the dust is its radiation resistance. Conan the B. can withstand one thousand times more radiation than humans with essentially no damage.
Another trick that might be helpful for life in space is suspended animation (cryptobiosis), which is deployed by lots of critters, including bdelloid rotifers, which can go into a state of cryptobiosis for tens of thousands of years and come back to life like nothing happened and wonder what’s for lunch. They are only one example of something that has survived below the permafrost in Siberia and come back to life when thawed. What could possibly go wrong with global warming?
Finally, you just can’t talk about extremophiles and not talk about tardigrades, and I saved them for last because they’re my favorite (I even have a pair of plush tardigrade slippers gifted to me by friends). As far as polyextremophiles go, these are at the top of my list. They can survive temps close to absolute zero and more than 150°C or 300°F. You can hit them with up to almost a thousand times more radiation than humans, and they’ll walk away (literally, because they have cute little squishy legs). They can also withstand the vacuum of space and at least a decade without water. What’s not to love? I’ve even found some living on lichen near my house and kept them as “pets” for a time.
The point is that it’s clear that even life-as-we-know-it can survive—and even flourish—in a range of conditions. As far as life-as-we-know-it, there are some physical conditions that seem like requirements. We think. As far as we can tell, most (all?) life on Earth needs a few basic things. But then again, if these conditions didn’t exist, we can’t say with certainty that life wouldn’t have evolved and adapted with different requirements.
Perhaps the top requirement for life-as-we-know-it is some type of energy source. As we saw with the methane ice worms, there are sources of energy other than the Sun that can and do also support life, including thermal energy and chemical reactions. If we really want to think outside the box, we could even try to envision some form of life-not-as-we-know-it tapping into radically diverse sources of energy like magnetic fields or gravitational waves. There are a vast range of energy sources in the universe that could be harnessed in creative ways.
For life-as-we-know-it, complex molecules also seem essential, and these complex molecules require heavy elements. When the universe first kicked off, hydrogen and helium were the only elements around—until stars started dying and churning out heavier elements forged in their cores. Hydrogen and helium are great, and we owe them a debt of gratitude, but they suck at making complex molecules. Carbon is vital—the fact that carbon can make such complex molecules is what makes organic chemistry so infamous for its difficulty. Silicon, which sits right under carbon in the periodic table, can also make complex molecules, but the bonds aren’t as strong, and as a result, molecules based on silicon are more fragile. The need for complex molecules suggests that life-as-we-know-it could not have emerged in the universe until enough stars had enough time to live and die and distribute their heavy elements around. As a reminder, you are literally made of these elements that were churned out of stars over billions of years.
