Absence Of Evidence

In 1952 the composer John Cage produced his most minimalist of all scores, entitled 4'33", which directs a pianist to play nothing for four minutes and thirty-three seconds. Some regard this as a pretentious intellectual game. Others see a statement about stillness, and the sounds we hear inside our own heads when given space to listen.

What is the significance of the more than forty years of silence heard by SETI? Researchers rightfully point out that the search is just beginning, that we have listened to only a tiny fraction of the stars in our galaxy. Success would mean everything. Failure means little. Or does it?

One of SETI's sayings is "Absence of evidence is not evidence of absence."* In fact, there is no possible evidence of absence. How could we ever prove that the aliens aren't out there? Yet, cumulatively, the silence is a kind of evidence. If the galaxy was thick with signals,

*Also recently invoked by Donald Rumsfeld to justify attacking a country for harboring weapons that we cannot be sure are not there.

swarming with radio-noisy species, we would know it by now. We can rule out the most optimistic end of the range of possibilities permitted by the Drake Equation.

Let's face it: the Drake Equation is so loosely constrained that you can conclude whatever you want and prop it up with a mathematical crutch. Sometimes, I think of it as a way for nerds to justify our religion with an equation.

Rationally, I know that it's a big universe, and we've only sniffed around in our front yard. Still, I find myself noticing the four decades of silence and wondering. oh, I don't doubt that they're out there, but perhaps they are not on the airwaves. The question of the existence of intellectually advanced aliens has, in my mind, become more detached from the question of our achieving radio contact. I am hopeful by constitution. But, my "adolescent optimism" has morphed into a more detached cosmic optimism. I still see the universe evolving toward a state of more fully developed intelligence and self-understanding, but I'm no longer sure the human experiment is a part of that process.

We should keep listening for the next thousand years, message or no message. If we succeed in doing that, whether or not we find anyone else, then we'll be well on the way to bringing to fruition the cosmic intelligence that we seek. If we get our act together to the point where we can commit to anything on such long timescales, then eventually there will be messages blasting loudly through our galaxy. Let's make sure and include some Bob Marley.

So, yes, let's get billionaires to spend millions, or taxpayers to spend pennies, to build huge radio arrays. Let's scan all the stars we can in any way we can think of, for as long as we can. Because you never know. Still, after more than forty years, you do start to wonder:

Where are they?

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