Osama bin Laden's whereabouts are a puzzle. We can't find him because we don't have enough information. The key to the puzzle will probably come from someone close to bi Laden, and until we can find that source bin Laden will remain at large.
The problem of what would happen in Iraq after the toppling of Saddam Hussein was, by contrast, a mystery. It wasn't a question that had a simple, factual answer. Mysteries require judgments and the assessment of uncertainty, and the hard part is not that we have too little information but that we have too much. The C.I.A. had a position on what a post-invasion Iraq would look like, and so did the Pentagon and the State Department and Colin Powell and Dick Cheney and any number of political scientists and journalists and think-tank fellows. For that matter, so did every cabdriver in Baghdad.
As far as I can tell, the best way to distinguish between puzzles and mysteries is figuring out whether or not more information is helpful. (This assumes, of course, that you don't have all the information. Omniscience is impossible.)
If things go wrong with a puzzle, identifying the culprit is easy: it's the person who withheld information. Mysteries, though, are a lot murkier: sometimes the information we've been given is inadequate, and sometimes we aren't very smart about making sense of what we've been given, and sometimes the question itself cannot be answered. Puzzles come to satisfying conclusions. Mysteries often don't.
But here's my question: can the history of science be parsed in terms of puzzles and mysteries? The standard view of scientific progress is that intractable mysteries - like the movement of planets, or the history of life - eventually become nothing but puzzles. Phenomena that used to seem like miracles - life emerging from stardust, or a brain containing a mind - now seem like natural properties of a mechanical universe.
And yet, it's also important to acknowledge that many scientific puzzles have also become mysteries. The history of physics - the scientific description of reality at its most fundamental - perfectly demonstrates this point. Once upon a time physicists thought they had the universe solved. Some obscure details remained, but the basic structure of the cosmos was understood. Out of this naivete, relativity theory emerged, shattering classical notions about the relationship of time and space. Then came Heisenberg's Uncertainty Principle, which showed that we can't know everything about a single particle, let alone everything about all the particles in the universe. Then came Quantum physics. Soon light was both a particle and a wave. String theorists, in their attempts to reconcile these gaping schisms of theory, spread rumors of 11 dimensions, maybe more. Even the Big Bang is now being criticized. I think it's fair to say that the universe seems more mysterious now than it seemed a century ago. Although our knowledge has vastly increased, that knowledge is often contradictory in nature. We are farther away from a unified theory, from turning the night sky into nothing but a neat puzzle.
Or what about the brain? When you read old science books on consciousness, they all use the same obsolete phrase: bridging properties. Scientists used to assume that we would one day discover some new neural phenomenon - the "bridge" - that allowed subjective experience to arise from shuttling ions and squirts of neurotransmitter. In other words, scientists were waiting for a little more information to help them solve the cortical puzzle. Now, of course, we know better. Even though we know much, much more about the brain than we did twenty years ago, scientists seem more mystified than ever about how some fatty membrane and minor electrical voltages create the illusion of the self. We have stopped looking for some simple bridging properties. The puzzle of consciousness has not been solved. It has become a mystery.
Of course, if the history of science is any indication, these mysteries will once again become puzzles. All we need is another Einstein.
All of which leads to two versions of what it is possible to know:
First, from now till whenever the last light blinks out, what's going to happen is people will turn mysteries into puzzles, solve the puzzles, only to find that each solution points to a new mystery, which turns to a new puzzle...and so on and so on, with no end, no final encyclopedia of everything. No matter how smart we are, no matter how much smarter we get, there will always be more mysteries.
Or: One day we will know everything.
My hunch? There never will be a Know-It-All day.
People may imagine one. Maybe even celebrate one. But then some one off in a corner somwhere will raise his/her hand and say, "But what about....?"
Lovely. Although isn't every puzzle a mystery until we find the needed bit of information? Or is it that mysteries don't require more information per se, but an entirely new way of thiking about the problem?
I'm not sure if I agree with Gladwell's distinction. Usually when people talk about puzzles (at least recreational puzzles), all the information needed to solve it is already present, although it often seems otherwise. If you fail to solve it, it isn't because anyone withheld information, it is because you overlooked some possibility, or dismissed it too quickly.
I agree with his other distinction: Puzzles come to satisfying conclusions. Mysteries often don't.