Alien Universe (23 page)
Authors: Don Lincoln
In summary, the study of biology on Earth certainly teaches us something of what is possible when discussing what an Alien might be like. Surely this brief survey has not explored all the possibilities. It is also clearly very Earth-centric. However, it does show some of the range of what we might encounter. While we realize that our conversation here does not span all possibilities, we might close with the following thought: Knowing something is better than knowing nothing, as long as you know it’s not everything.
SIX
ELEMENTS
The third planet is incapable of supporting life … Our scientists have said there’s far too much oxygen in their atmosphere.
Ray Bradbury,
The Martian Chronicles
In the previous chapter, we looked at what sorts of lessons familiar Earth life might tell us about what an Alien might be like. These observations were not meant to be exhaustive, as they were based on a very limited range of biochemistry. Animals breathing oxygen and converting glucose into energy and plants converting sunlight doesn’t even span the range of observed biochemistry here on Earth, let alone the range of the possible. There are creatures on Earth that use methane to exist and others who extract energy purely from chemicals, rather than exploiting (directly or indirectly) light from the sun. Then there is sulfur respiration and fermentation, just to name a few alternatives.
At the end of this chapter, we will talk about more “exotic” forms of Earth life. Our real interest is about Aliens who could potentially visit our planet, but their story is inextricably tied up in the question of non-Alien alien life.
One must have the second to have the first. Accordingly, we will spend some time exploring what we know about alien life and the limitations placed on such life by simple considerations of chemistry and physical law.
The reader should be aware that any writing on this subject is bound to be incomplete. As noted popular science essayist and pioneer geneticist J. B. S. Haldane wrote in his 1927 book
Possible Worlds and Other Papers
, “The Universe is not only queerer than we suppose, but queerer than we can suppose.” It is quite reasonable to suppose that the universe will have a trick or two up its sleeves and we will be surprised more than once. Still, we can talk about what we know about the relevant chemistry. If nothing else, we will learn what the important considerations are for modern astrobiology.
What Is Life?
This question is seemingly so simple, and yet it has vexed some of the most knowledgeable scientists and philosophers for decades. While hardly the first writing on the subject, physicist Erwin Schrödinger’s (of Schrödinger’s cat fame) 1944 book
What Is Life?
is one such example. It is an interesting early attempt to use the ideas of modern physics to address the question. Both James Watson and Francis Crick, codiscoverers of DNA, credited this book as being an inspiration for their subsequent research.
The definition of life is not settled even today. Modern scientists have managed to list a series of critical features that seems to identify life. A living being should have most, if not all, of the following features:
It must be able to regulate the internal environment of the organism.
These features distinguish it from inanimate matter.
While these properties can help one identify life when one encounters it, they don’t really give us a sense of the limitations imposed by the universe on what life might be like. The purpose of this section is to get a sense of whether a would-be science fiction writer is being ludicrous when he or she bases a story around an Alien with bones made of gold and liquid sodium for blood. So what does our current best understanding tell us that life requires? A combination
of theory and experimentation suggests that there are four crucial requirements for life. They are (in decreasing order of certainty):
