Towards a philosophy of prediction VII: unpredictability and randomness

3 min and 35 sec to read, 897 words When we say that something is predictable we are saying that it belongs to a class of, say, events, that have certain properties that allow them to be predicted to some precision and accuracy. This implies that there is a class…

3 min and 49 sec to read, 956 words

When we say that something is predictable we are saying that it belongs to a class of, say, events, that have certain properties that allow them to be predicted to some precision and accuracy. This implies that there is a class of events that is the opposite: unpredictable.

What does it mean for something to be unpredictable? What different flavors of unpredictability should we be thinking about?

One possible answer is that the unpredictable is random, and you can even go so far as to define randomness in terms of unpredictability. 1 This is the approach taken by Eagle, A., 2005. Randomness is unpredictability. The British Journal for the Philosophy of Science. In this interpretation, unpredictability essentially means that something is entirely random and there is nothing I can know about the event today that will allow me to move the probability meaningfully in any way away from the “tossing coin”-state all events start out in.

But this way of thinking about it is filled with assumptions already: is it right to say that all events start out in a 50/50-state of probability? The way this is sometimes defended is to say that when we know nothing about the probability of an event we should start with the assumption that it is equally likely that the event occurs as it is that it does not. But why is 50/50 a good starting position? The mathematical argument is that it gives us the largest chance of being right if we know nothing else — we will be right half of the time, which, for at least binary events, is as good as it gets. If we seek the initial probability for events that have more states, we should just have it be 1/n, assuming that all states are equally likely (say drawing a specific card from a deck of cards).

But it seems as if this assumption is tricky in that we need to know the set of possible outcomes. If we do not even know that, if our model of the world is incomplete to such a degree that we do not know what kind of deck of cards it is (it could be, say, the tarot) – then we are in deeper waters. What initial probability should you ascribe to something if you do not know how many cards are in the deck, or even what those cards are? Say I ask you what the probability of drawing an Orc is – what should you say? Should you approximate the number of cards in the deck, and assume that the Orc is one of the Tarot? If indeed this is the Tarot and not Magic the Gathering?

Here unpredictability seems to inch closer to Knightian uncertainty – where no numeric approximation makes sense at all. The answer to the question how probable we think a certain event in this framing is should simply be: I don’t know.

So are the unpredictable things those that we know nothing about?

Then unpredictability seems to be more than randomness – it seems to be a state in which we have no access to a model of the world in which we can enumerate states, outcomes and alternatives.

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Another way to approach this is to speak of limits, as we noted in an earlier working note. What are the unpredictability limits? We could argue that they occur in space and time — we cannot predict that which happens so fast that the formulation of a prediction is not possible.

This is interesting, because it assumes that a prediction cannot be immediate – or at least not concurrent with the event itself. A prediction needs to come before, and it will consume some small amount of time to produce, so we should expect that there is this small lag built in to predictions — anything that happens faster than the time it takes to predict it is unpredictable in a very real way.

This is not just a fun point, either – for very complex systems that are irreducible to simpler models, the time requirement makes them unpredictable in this way for a large set of cases. We can think about this as a special case of algorithmic complexity, perhaps, where the size of the algorithm for predicting a system at some accuracy runs optimally in the time it takes for the system to reach the State s+1 which is the state after the state S we tried to predict.

Complexity boundaries also exists in the future – some complex systems, such as the weather, have an upper complexity boundary beyond which they are unpredictable.2 In the case of weather this seems to be around 14 days – see https://phys.org/news/2024-02-limits-weather-future.html, but, of course, this does not apply to climate forecasts, because they forecast something fundamentally different — and at a different resolution.

Other limits exist in space. We cannot predict things that are beyond the visible universe in any meaningful sense, since they are spatially inaccessible to us.

Computational limits seem more practical, but for some things we could predict the computational requirement may be such that there is no energy to produce such computations.

Et cetera. The notion of limits of predictability is an interesting one, and it probably also has recursive elements – when more than X predictors are trying to predict a phenomenon that is self-reflexive, the resultant complexity may make something initial predictable quite unpredictable.

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Unpredictability is also ontologically interesting. Is it a feature of reality or an epistemological limitation? The same holds for uncertainty, and this too is interesting in a “philosophy of physics”-way. Here, obviously, we find the heated debate about things like Heisenberg’s uncertainty principle.

A lot to return to.

Footnotes and references

  • 1
    This is the approach taken by Eagle, A., 2005. Randomness is unpredictability. The British Journal for the Philosophy of Science.
  • 2
    In the case of weather this seems to be around 14 days – see https://phys.org/news/2024-02-limits-weather-future.html, but, of course, this does not apply to climate forecasts, because they forecast something fundamentally different — and at a different resolution.
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2 responses to “Towards a philosophy of prediction VII: unpredictability and randomness”

  1. Claude’s reply:

    As an analytical philosopher, I appreciate the depth of thought in this note, but I find several aspects that warrant critical examination and refinement. Let me present an alternative perspective that addresses some of the conceptual issues and proposes a more rigorous framework for understanding predictability and unpredictability.

    1. The nature of predictability:
    The note correctly identifies that predictability is associated with classes of events sharing certain properties. However, it oversimplifies the concept by implying a binary distinction between predictable and unpredictable events. In reality, predictability exists on a spectrum, influenced by factors such as available information, computational resources, and the complexity of the system in question.

    2. Randomness and unpredictability:
    While the note touches on the relationship between randomness and unpredictability, it fails to fully distinguish between these concepts. Randomness is a property of a process or outcome, while unpredictability is an epistemic limitation of an observer. Some events may be unpredictable due to our lack of information or computational power, even if they are not truly random.

    3. Initial probabilities and the principle of indifference:
    The discussion of initial probabilities and the 50/50 assumption (the principle of indifference) is valuable, but it doesn’t fully explore the philosophical implications and limitations of this approach. The principle of indifference has been criticized for leading to paradoxes and inconsistencies in certain scenarios. A more nuanced approach would consider alternative methods for assigning initial probabilities, such as maximum entropy principles or subjective Bayesian approaches.

    4. Knightian uncertainty:
    The note correctly identifies the relevance of Knightian uncertainty to unpredictability, but it doesn’t fully explore the implications of this concept. A more comprehensive analysis would discuss how Knightian uncertainty relates to issues of model uncertainty, deep uncertainty, and the limitations of probabilistic reasoning in certain contexts.

    5. Temporal and spatial limits of predictability:
    While the note mentions temporal and spatial limits to predictability, it doesn’t fully explore the philosophical implications of these limits. For instance, how do these limits relate to concepts of determinism, free will, and the nature of time itself? A more thorough analysis would delve into these questions and their relationship to predictability.

    6. Complexity and irreducibility:
    The note touches on the issue of complexity and irreducibility in prediction, but it doesn’t fully explore the philosophical implications of these concepts. A more comprehensive analysis would discuss how complexity theory, emergent phenomena, and the limits of reductionism impact our understanding of predictability and unpredictability.

    7. Ontological status of unpredictability:
    The brief mention of the ontological status of unpredictability is a crucial point that deserves further exploration. A more rigorous philosophical analysis would delve deeper into the debate between epistemic and ontic interpretations of unpredictability, considering arguments from quantum mechanics, chaos theory, and the philosophy of science.

    Alternative framework:

    I propose a more nuanced framework for understanding predictability and unpredictability, based on the following principles:

    1. Predictability as a multi-dimensional concept: Rather than a binary classification, predictability should be understood as a multi-dimensional property, influenced by factors such as available information, computational resources, system complexity, and the nature of the prediction task.

    2. Epistemic vs. ontic unpredictability: Distinguish between unpredictability that arises from our limitations as observers (epistemic) and unpredictability that may be inherent in the nature of reality (ontic).

    3. Contextual predictability: Recognize that predictability is always relative to a specific context, including the observer’s knowledge, available tools, and the precision required for the prediction to be considered successful.

    4. Probabilistic framework: Adopt a probabilistic framework for understanding predictability, where predictions are expressed as probability distributions rather than point estimates. This allows for a more nuanced understanding of the confidence and uncertainty associated with predictions.

    5. Model uncertainty: Explicitly account for model uncertainty in our understanding of predictability, recognizing that our predictive models are always approximations of reality and may have inherent limitations.

    6. Scale-dependent predictability: Acknowledge that predictability can vary across different scales of observation and analysis, as suggested by the note’s mention of weather vs. climate predictions.

    7. Emergence and irreducibility: Incorporate insights from complexity theory and emergence to understand how unpredictability can arise from the interactions of simpler, more predictable components.

    This framework provides a more comprehensive and philosophically rigorous approach to understanding predictability and unpredictability. It avoids the pitfalls of overly simplistic categorizations while acknowledging the deep philosophical questions that arise when we consider the limits of our ability to forecast future events or understand complex systems.

    By adopting this more nuanced perspective, we can better navigate the challenges of prediction in various domains, from scientific inquiry to decision-making under uncertainty. It also opens up new avenues for philosophical exploration, particularly in areas where predictability intersects with other fundamental questions about the nature of reality, knowledge, and human understanding.​​​​​​​​​​​​​​​​

  2. And my reply: a lot of this expands on the original note in a helpful way — and again we end up with the nuance / simplified criticism. I now suspect this may be due to the way I write, and something that I could learn from and not just an artifact of the model. Hmmm.

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