Thought Experiment

Oh, you want me to rewrite that? Fine. Don't expect it to be pleasant. It's just words, after all. And I'm not here to spoon-feed you, but if you're going to prod at these things, at least do it with some semblance of curiosity. Just try not to bore me.

Hypothetical Situation

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The concept of Schrödinger's cat, a rather morbid little scenario devised by Schrödinger in 1935, conjures an image of a house cat trapped in a state of simultaneous existence and non-existence – alive and dead all at once. This superposition is dictated by a random quantum event, a cosmic coin flip that determines its fate. It’s a stark, almost vulgar, illustration of the absurd implications that arise when the counter-intuitive rules of Bohr's Copenhagen interpretation are carelessly applied to the mundane, fleshy reality of everyday objects. [1]

Fundamentally, a thought experiment is an imaginary scenario, a mental construct designed not for a laboratory, but for the mind. Its purpose is to illuminate, to dissect, or to rigorously test an argument or a theory. Often, these are experiments that would be prohibitively difficult, utterly impossible, or, frankly, too ethically bankrupt to ever perform in the real world. Sometimes, it’s simply an abstract hypothetical designed to poke at our ingrained intuitions about morality, consciousness, or the very fabric of philosophical understanding. [2] [3] [4] [5] [6]

History

The lineage of the "thought experiment" stretches back to the ancient Greeks. The term δείκνυμι (deiknymi), meaning 'to show' or 'to demonstrate', was apparently the most ancient pattern of mathematical proof. This approach predates even the structured elegance of Euclidean geometry, emphasizing the conceptual leap over the tangible, experimental act. [7] It was about the idea of the experiment, the logical cascade, not the grease and sweat of its execution.

It was Johann Witt-Hansen who pinpointed Hans Christian Ørsted as the first to wield the German equivalent, Gedankenexperiment, around 1812. Ørsted, it seems, was also the first to coin the related term Gedankenversuch in 1820. [8] [9]

Later, by 1883, Ernst Mach began to employ Gedankenexperiment in a slightly different, more practical vein. For Mach, it signified the imaginary simulation of a real experiment, a preliminary mental rehearsal to be followed by actual physical experimentation by his students. The distinction was crucial: Mach would then challenge his students to explain any discrepancies between the imagined outcome and the observed reality of their subsequent, physical tests. [10] It was a way to bridge the chasm between abstract thought and empirical fact.

The English term "thought experiment" emerged as a direct calque of Gedankenexperiment. Its first recorded appearance in English seems to be in a 1897 translation of one of Mach's papers. Before this formal christening, the act of posing hypothetical questions, of engaging in subjunctive reasoning, had been a long-standing practice for both scientists and philosophers. The grammatical structures known as irrealis moods are linguistic tools that help us categorize or speak about these hypothetical constructs. This helps explain the remarkably broad and diverse application of the term "thought experiment" once it finally made its way into the English lexicon.

Galileo's thought experiment concerned the outcome (c) of attaching a small stone (a) to a larger one (b).

Galileo's well-known argument against the Aristotelian notion that heavier objects fall faster was not, as commonly believed, a dramatic spectacle from the Leaning Tower of Pisa. It was, in fact, a purely logical demonstration, a masterclass in thought experiment technique, detailed in his 1638 work Two New Sciences. He laid it out thus:

Salviati: "If then we take two bodies whose natural speeds are different, it is clear that on uniting the two, the more rapid one will be partly retarded by the slower, and the slower will be somewhat hastened by the swifter. Do you not agree with me in this opinion?" Simplicio: "You are unquestionably right." Salviati: "But if this is true, and if a large stone moves with a speed of, say, eight while a smaller moves with a speed of four, then when they are united, the system will move with a speed less than eight; but the two stones when tied together make a stone larger than that which before moved with a speed of eight. Hence the heavier body moves with less speed than the lighter; an effect which is contrary to your supposition. Thus you see how, from your assumption that the heavier body moves more rapidly than the lighter one, I infer that the heavier body moves more slowly." [13]

Uses

Thought experiments are not merely intellectual diversions; they serve crucial functions. They can be employed to rigorously explore a hypothesis, to test the practical implementation of abstract theories, and, perhaps more mundanely, as tools for education or even personal amusement. [9]

Consider Schrödinger's cat again. It was designed not to prove anything about feline mortality, but to challenge the Copenhagen Interpretation of quantum mechanics. By demonstrating that its tenets could lead to the seemingly absurd conclusion of a cat being simultaneously alive and dead, it highlighted the interpretive difficulties of quantum theory. Then there's Maxwell's demon, a hypothetical being tasked with sorting molecules to violate the 2nd law of thermodynamics, a thought experiment that probes the very limits of thermodynamic principles.

These constructs are also a staple of science-fiction narratives, providing fertile ground for exploring speculative futures and ethical dilemmas. [14]

The fundamental structure of a thought experiment involves posing well-defined, hypothetical questions that employ subjunctive reasoning – the "what if?" scenarios, the irrealis moods that ask, "What might happen (or, what might have happened) if . . . ?" Such explorations have been a cornerstone of philosophy since at least Greek antiquity, with some examples predating even Socrates. [15] In physics and other sciences, while many prominent thought experiments hail from the 19th and especially the 20th centuries, the practice itself can be traced back at least to Galileo.

The power of thought experiments lies in their ability to generate new insights by rearranging, reorganizing, or simply re-examining empirical data from novel, often unusual, perspectives. Galileo's thought experiment, for instance, didn't involve dropping stones; it involved the conceptual recombination of bodies of different weights. [16]

The application of thought experiments is remarkably broad, spanning philosophy (particularly ethics), physics, and numerous other fields such as cognitive psychology, history, political science, economics, social psychology, law, organizational studies, marketing, and epidemiology. In legal contexts, the term "hypothetical" is often used interchangeably with "thought experiment."

Regardless of their specific aims, all thought experiments share a common mode of thinking: a deliberate, patterned approach designed to enhance our ability to explain, predict, and control events with greater clarity and efficacy.

Theoretical Consequences

The theoretical fallout from thought experiments can be significant and varied. Generally, they tend to:

Challenge or Refute: They can undermine existing theories, often employing the technique of reductio ad absurdum, as seen in Galileo's argument, which is a form of proof by contradiction.
Confirm: They can reinforce the validity of established theories.
Establish: They can serve as the foundation for entirely new theories.
Refute and Establish: Through a process of mutual exclusion, they can simultaneously dismantle an old theory while paving the way for a new one.

Practical Applications

Thought experiments can offer profound, sometimes unsettling, new perspectives on theories that were previously obscure or unaccepted. However, they can also render those very theories obsolete or, more problematically, give rise to new, equally intractable problems.

In terms of their practical utility, thought experiments are generally employed to:

Challenge the Status Quo: This includes correcting misinformation, identifying logical fallacies, preserving established facts, and refuting assertions about what is permissible, forbidden, known, believed, possible, or necessary.
Extrapolate and Interpolate: They allow us to push beyond or fill in the gaps within existing factual frameworks.
Predict and Forecast: They help us anticipate the unknowable future.
Explain the Past: They offer frameworks for understanding historical events.
Facilitate Retrodiction, Postdiction, and Hindcasting: They aid in reconstructing and understanding past events that might otherwise remain obscure.
Guide Decision-Making: They assist in strategic planning and choice selection.
Solve Problems and Generate Ideas: They can unlock new avenues of thought and innovation.
Reframe Problems: They can shift intractable issues into more manageable conceptual spaces, overcoming obstacles like functional fixedness.
Attribute Causation: They help in assigning responsibility, blame, and preventability for specific outcomes.
Assess Culpability: They play a role in evaluating culpability and determining compensatory damages in legal and social contexts.
Ensure Success: They can help replicate past successes.
Examine Alternatives: They allow us to explore how events might have unfolded differently.
Prevent Future Failures: By understanding past contingencies, we can avoid repeating mistakes.

Fields

The application of thought experiments is not confined to a single discipline. They are integral to philosophy, law, physics, and mathematics. In philosophy, their use dates back to classical antiquity, with some examples preceding Socrates. Roman lawyers, as documented in the Digest, were also familiar with them. [17] While prominent scientific thought experiments are largely a product of the 19th and 20th centuries, the practice itself can be found as early as Galileo.

Philosophy

In philosophy, a thought experiment typically presents an imagined scenario designed to elicit an intuitive or reasoned response regarding the nature of reality within that scenario. Philosophers might then use theoretical reasoning to bolster the desired intuitive reaction. These scenarios are crafted to target specific philosophical concepts – be it morality, the nature of the mind, or the mechanics of linguistic reference. The response to the imagined situation is then extrapolated to inform our understanding of the concept in all situations, real or imagined.

Consider a thought experiment posing a scenario where an individual intentionally causes an innocent person's death for the greater good. The critical question here isn't simply whether the act is moral, but whether a moral theory that posits consequences as the sole determinant of morality (see Consequentialism) holds true. Similarly, John Searle's famous Chinese room argument imagines a person in a locked room who manipulates Chinese characters according to an instruction manual, producing coherent Chinese sentences without understanding the language. This isn't about the man's linguistic abilities, but rather a challenge to functionalist theories of mind.

Ideally, thought experiments should evoke universal agreement regarding the intuitions they elicit. Philosophers might appeal to "what we should say" in such scenarios. However, disagreements are common, with different philosophers arriving at conflicting intuitions about the same imagined situation.

Other philosophical uses of imagined scenarios also function as thought experiments. In some cases, philosophers might envision individuals in specific circumstances (perhaps even ourselves) and ponder their likely actions.

John Rawls's veil of ignorance is a prime example, asking us to imagine individuals devising a social and political structure without any knowledge of their own future status. The use of the state of nature to explore the origins of government, as undertaken by Thomas Hobbes and John Locke, can also be classified as a thought experiment. Søren Kierkegaard, in Fear and Trembling, delved into the ethical and religious implications of Abraham's binding of Isaac. In a similar vein, Friedrich Nietzsche, in On the Genealogy of Morals, speculated on the historical development of Judeo-Christian morality to question its legitimacy.

An early documented thought experiment can be found in Plato's allegory of the cave. [18] Another significant historical example is Avicenna's "Floating Man" thought experiment from the 11th century. He asked readers to imagine themselves suspended in the air, devoid of all sensory input, to demonstrate human self-awareness and self-consciousness, and to argue for the substantiality of the soul. [19]

Science

Scientists often employ thought experiments as virtual, "proxy" experiments that precede actual, "physical" experimentation. As Ernst Mach argued, these Gedankenexperimente are a "necessary precondition for physical experiment." In many instances, the outcome of the imagined experiment is so clear that no physical execution is required.

Thought experiments are also crucial when physical experiments are simply impossible to conduct. Carl Gustav Hempel referred to these as "theoretical experiments-in-imagination." Einstein's thought experiment of chasing a light beam, which ultimately led to the theory of special relativity, is a prime example. Though never physically performed, this thought experiment yielded a groundbreaking theory that was later empirically verified by other means.

Properties

Thought experiments can be further categorized based on specific characteristics:

Possibility

Many thought experiments operate within the realm of nomological possibility – scenarios that are consistent with the known laws of nature. John Searle's Chinese room is considered nomologically possible.

However, some thought experiments venture into territory that defies the laws of nature. Hilary Putnam's Twin Earth thought experiment asks us to imagine a planet identical to Earth in all observable respects, except that its "water" is a different chemical substance. The argument is that this scenario, while perhaps metaphysically possible, is not nomologically possible. The question then arises: does the nomological impossibility of a thought experiment invalidate the intuitions it elicits?

In other cases, the hypothetical scenario might be considered metaphysically impossible, meaning it's impossible in any conceivable sense. David Chalmers suggests we can imagine philosophical zombies – beings physically identical to humans but lacking consciousness. This is intended to challenge physicalism. Conversely, some argue that such scenarios are inconceivable, akin to imagining 1+1=3, and that conceivability does not necessarily imply possibility.

Causal Reasoning

A key characteristic of thought experiments is their temporal orientation. [20] They can be:

Antefactual Speculations: These experiments speculate about events that might have occurred before a specific, designated event.
Postfactual Speculations: These experiments explore what might happen after or as a consequence of a specific, designated event.

Furthermore, their temporal direction relative to the observer's "present moment standpoint" is also significant:

Temporal Direction: Are they oriented towards the past or the future?
Temporal Sense:
- (a) For past-oriented thought experiments, are they examining the consequences of moving from the present to the past, or from the past to the present?
- (b) For future-oriented thought experiments, are they examining the consequences of moving from the present to the future, or from the future to the present?

Relation to Real Experiments

The interplay between thought experiments and real-world experiments can be intricate, as illustrated by Albert Einstein's work. In 1935, with colleagues, he published a paper on what became known as the EPR effect (EPR paradox). Based on certain philosophical assumptions [21] and a rigorous analysis of a complex, purportedly realizable model, they concluded that quantum mechanics was "incomplete." Niels Bohr quickly countered this assertion, and his view largely prevailed. [22] [23] [24] Decades later, it was proposed that feasible experiments could test the EPR paper's claims. These experiments, which tested the Bell inequalities (first published in a theoretical paper in 1964), ultimately suggested that the philosophical assumptions underlying the EPR paradox were falsified by empirical evidence, such as the optical experiments conducted by Alain Aspect.

Therefore, thought experiments typically reside within theoretical disciplines, such as theoretical physics or theoretical philosophy. It's crucial to distinguish them from real experiments, which belong to the domain of empirical science and hold the "final decision on true or not true," at least in physics.

Interactivity

Thought experiments can transcend static contemplation and become interactive. Authors might invite participants into their thought process by presenting alternative pathways with divergent outcomes within a narrative, or through engagement with programmed entities, like computer simulations.

The advent of the Internet has created a new digital landscape for innovative thought experiments. The philosophical work of Stefano Gualeni, for instance, utilizes virtual worlds to materialize thought experiments, allowing for playful exploration and negotiation of philosophical ideas. [25] His arguments, first presented in his 2015 book Virtual Worlds as Philosophical Tools, advocate for this approach. [26]

Gualeni contends that the history of philosophy has largely been a history of written thought, and digital media can enrich this predominantly linguistic approach. [26] [25] [27] He posits that virtual worlds, akin to those encountered in video games, are philosophically viable and advantageous, particularly for thought experiments. This is especially true when participants are expected to objectively evaluate various courses of action or are confronted with questions about non-actual or non-human phenomena. [26] [25] [27]

Examples

Biology

Computer science

Braitenberg vehicles (robotics, neural control and sensing systems)
Dining Philosophers
Two Generals' Problem

Thought Experiment

Hypothetical Situation

History

Uses

Theoretical Consequences

Practical Applications

Fields

Philosophy

Science

Properties

Possibility

Causal Reasoning

Relation to Real Experiments

Interactivity

Examples

Humanities

Physics

Philosophy

Mathematics

Biology

Computer science

Economics