Thursday, February 28, 2013

A Sample Size Of One and The Search For Life (part 1)

We can never know everything about anything. No matter how narrow our focus or determined our effort, there will always remain unknowns. Our information is never complete; the gaps in our knowledge stubbornly persist. It is this fact that drives us to conduct experiments; to ask questions of the Universe and compare the answers with our best predictions, to see how close we are for now.

But the Universe is vast, and our reach comparatively minute. How do we know if we have asked the right question? Or gathered enough data? How do we know when we have observed a sufficient number of meteors, for example, before we can say anything about them, with confidence? Perhaps all of our observations on meteors are peculiar to this remote location of our solar system, or local group, or galaxy. How do we quantify our confidence? How can we ever know for sure?

What if we only had one example of a thing? Found just one meteor, or experienced just one hurricane? What can we learn from a sample size of one?

Before we answer we need to consider exactly what it is we are trying to learn, and the nature of the thing to be sampled. For example, if we are trying to learn the best time to pick and eat a newly discovered fruit, a sample size of one is inadequate. Even if our fruit tasted good (or bad), we wouldn’t know if it’s flavor improves or worsens given more time. The inherent variation in fruit flavor, ripening time, etc., makes it impossible to determine the optimum time to pick from a sample of just one. Now consider trying to determine if our soup is properly salted. We only need a single taste to find out. Why? The principle of diffusion, and the properties of dissolved salt, guarantees that every sample will have nearly the same amount, so a sample size of one is all we need.

Considerations like these are not trivial, they are essential when we consider bigger questions such as “What will life on other worlds be like?” Science fiction has offered up numerous hypothetical life forms spanning a range from bipedal, bilaterally symmetrical, hominids (complete with two eyes, a single nose, a mouth and ear, and all in the right place) to life as a formless, boundless “pure energy” capable of traveling back and forth through time. Given this apparent “the-sky’s-the-limit” attitude, how can we know what we are looking for? Couldn’t life easily escape our notice? If not for their clever camouflage but for our own inadequate means of detection? Couldn’t a time-traveling organism of pure energy be sitting right behind me, looking over my shoulder as I type these words, and go unnoticed? Doesn’t our sample size of one (one planet, one life1) fundamentally handicap our attempts at finding life elsewhere in the Cosmos? How do we build a “life-detector” if we don’t know what we are looking for?

You may be surprised to learn that we do have an idea of what to look for, as well as when and where. Our “life-detector” is fined tuned to look for life within very narrowly defined limits. And it’s not likely to miss the invisible, time-travelling, pure energy aliens, because there aren’t any.

-End of part 1   (Part 2)

1One look at the diversity of life on this planet gives the false impression that we are surrounded with millions of samples of life. We are not. All living things, past and present, are modifications on a single theme of life. The essential living machinery –the hardware, appeared only one. But the software of the genetic code has been repeatedly modified. Just as there can be many different types of guitars, each playing many different tunes, there is only one type of instrument called “guitar”. If we wish to enumerate the instances of “life” on this planet, the total is just one.

Copyright 2013 by theBIOguy