May 31, 2017

Laplace's demon takes a walk in Borges' garden

"Uncertainty is an uncomfortable position. But certainty is an absurd one."


In his Philosophical Essay on Probabilities Pierre-Simon Laplace writes:

We ought then to regard the present state of the universe as the effect of its anterior state and as the cause of the one which is to follow. Given for one instant an intelligence which could comprehend all the forces by which nature is animated and the respective situation of the beings who compose it an intelligence sufficiently vast to submit these data to analysis it would embrace in the same formula the movements of the greatest bodies of the universe and those of the lightest atom; for it, nothing would be uncertain and the future, as the past, would be present to its eyes.

Later on this became to be labeled Laplace's demon. Such a deterministic approach to understand how the world works is not possible because we lack the capacity and the instruments for such an endeavor. In the preface of his book Understanding Uncertainty Dennis Lindley writes:

There are some things that you, the reader of this preface, know to be true, and others that you know to be false; yet, despite this extensive knowledge that you have, there remain many things whose truth or falsity is not known to you. We say that you are uncertain about them. You are uncertain, to varying degrees, about everything in the future; much of the past is hidden from you; and there is a lot of the present about which you do not have full information. Uncertainty is everywhere and you cannot escape from it.

Dennis V. Lindley, Understanding Uncertainty, 2006
This following quote is from a 2016 NEJM article:

In medicine today, uncertainty is generally suppressed and ignored, consciously and subconsciously. Its suppression makes intuitive sense: being uncertain instills a sense of vulnerability in us — a sense of fear about what lies ahead. It is unsettling and makes us crave black-and-white zones, to escape this gray-scale space. Our protocols and checklists emphasize the black-and-white aspects of medicine. Doctors often fear that by expressing uncertainty, they will project ignorance to patients and colleagues, so they internalize and mask it. We are still strongly influenced by a rationalist tradition that seeks to provide a world of apparent security.


Our curricula should recognize diagnosis as dynamic and evolving — an iterative process that accounts for multiple, changing perspectives. We can speak about “hypotheses” rather than “diagnoses,” thereby changing the expectations of both patients and physicians and facilitating a shift in culture. This shift may entail discussing uncertainty directly with patients, intentionally reflecting on its origins — subjectivity in the illness narrative, diagnostic sensitivity and specificity, unpredictability of treatment outcomes, and our own hidden assumptions and unconscious biases, to name a few. We can then teach physicians specifically how to communicate scientific uncertainty, which is essential if patients are to truly share in decision making, and we can reduce everyone’s discomfort by reframing uncertainty as a surmountable challenge rather than as a threat.

We don't have the capacity of knowing the past or predicting the world in a deterministic sense, but we can use devices to learn of different possibilities under uncertainty. In his fictional short story The Garden of Forking Paths Jorge Luis Borges writes:

I lingered, naturally, on the sentence: I leave to the various futures (not to all) my garden of forking paths. Almost instantly, I understood: ‘the garden of forking paths’ was the chaotic novel; the phrase ‘the various futures (not to all)’ suggested to me the forking in time, not in space. A broad rereading of the work confirmed the theory. In all fictional works, each time a man is confronted with several alternatives, he chooses one and eliminates the others in the fiction of Ts’ui Pên, he chooses—simultaneously—all of them. He creates, in this way, diverse futures, diverse times which themselves also proliferate and fork.


The Garden of Forking Paths is an incomplete, but not false, image of the universe as Ts’ui Pên conceived it. In contrast to Newton and Schopenhauer, your ancestor did not believe in a uniform, absolute time. He believed in an infinite series of times, in a growing, dizzying net of divergent, convergent and parallel times. This network of times which approached one another, forked, broke off, or were unaware of one another for centuries, embraces all possibilities of time. We do not exist in the majority of these times; in some you exist, and not I; in others I, and not you; in others, both of us. In the present one, which a favorable fate has granted me, you have arrived at my house; in another, while crossing the garden, you found me dead; in still another, I utter these same words, but I am a mistake, a ghost.”

“In every one,” I pronounced, not without a tremble to my voice, “I am grateful to you and revere you for your re-creation of the garden of Ts’ui Pên.”

“Not in all,” he murmured with a smile. “Time forks perpetually toward innumerable futures. In one of them I am your enemy.”

Bottom line is that we don't have the capabilities to be Laplace's demons, so it's important to take uncertainty into account and acknowledge it for what it is. It represents part of our cognitive limitations and that's why multiple paths should be considered and studied in depth. It is very discomforting when I see deterministic conclusions based on one or only a few scientific studies, sometimes not even on any studies at all. Also troubling is not taking into account the study's methodology, the statistical procedures, or disregarding how the community behaves in its research practices. There's more to uncertainty than just feeling uncertain.

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1. You should attempt to re-express your target’s position so clearly, vividly, and fairly that your target says, “Thanks, I wish I’d thought of putting it that way.
2. You should list any points of agreement (especially if they are not matters of general or widespread agreement).
3. You should mention anything you have learned from your target.
4. Only then are you permitted to say so much as a word of rebuttal or criticism.
Daniel Dennett, Intuition pumps and other tools for thinking.

Valid criticism is doing you a favor. - Carl Sagan