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StarTalk Radio

The Limits of Knowing with Elise Crull

with Elise Crull

Published November 4, 2025
View Show Notes

About This Episode

Neil deGrasse Tyson and co-host Chuck Nice talk with philosopher of physics Elise Crull about the historical and contemporary relationship between physics and philosophy. They trace how natural philosophy split into specialized disciplines, how foundational concepts like space, time, and objectivity shaped classical and modern physics, and why questions raised by quantum mechanics-such as entanglement and non-locality-force a reevaluation of those concepts. The conversation also explores academic specialization, the role of philosophy in guiding cutting-edge physics, and Neil's nuanced critique of modern academic philosophy.

Topics Covered

Mathematics and physics General relativity Quantum gravity String theory Education system Academic gatekeeping Quantum mechanics Entanglement Non-locality Philosophy of science

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Quick Takeaways

  • Historically, physics and philosophy were a single enterprise called natural philosophy, and many foundational works in physics were explicitly framed as philosophical projects.
  • Key figures like Descartes, Newton, Leibniz, and Emilie du Châtelet grounded their physics in explicit metaphysical and epistemological assumptions about space, time, and knowledge.
  • The Cold War era, especially post-Manhattan Project, pushed physics toward a "shut up and calculate" mentality and away from explicit philosophical reflection.
  • Quantum mechanics challenges classical ideas of objectivity and separability, particularly through entanglement and non-local correlations that defy straightforward classical explanation.
  • Debates about how to unify quantum theory and general relativity (e.g., string theory versus canonical approaches) are guided as much by philosophical commitments as by empirical data.
  • Concepts like causality, space, time, and objectivity are not fixed; they must be continually reexamined as physics probes regimes that are currently beyond empirical test.
  • Younger physicists around the world increasingly want training in history and philosophy of science to better navigate foundational questions in their research.
  • Neil clarifies that his criticism is not of philosophical thinking in physics, but of the reduced material impact of modern, purely philosophy-department-trained scholars on contemporary physical theory compared to a century ago.

Podcast Notes

Opening and setup: Philosophy meets physics again

Framing philosophy and physics as intertwined

Neil teases that this episode revisits the philosophy of physics due to strong audience interest in the previous discussion[2:54]
Chuck jokes that physics and philosophy are the "Reese's Pieces of science" that belong together and might be "entangled"[1:45]
Neil positions himself as an educator who wants listeners to leave more thoroughly informed and enlightened[5:03]

Guest reintroduction and background

Neil welcomes back Elise Crull as an "authentic philosopher" to talk philosophy of physics[3:41]
Elise confirms she is an associate professor of philosophy at CUNY City College in New York[5:29]
Neil notes his father was once an administrator at City College, connecting personally to her institution[5:16]
Elise's background combines physics, philosophy, and some history; she mentions being one class short of a math minor before choosing tap dance instead[5:59]
Her specialty is the history and philosophy of quantum physics, a domain with a lot of room for philosophical analysis[5:59]

What is philosophy and how has it changed over time?

Defining philosophy in changing contexts

Neil asks what philosophy is today compared with hundreds of years ago back to Aristotle and Greek philosophers[5:29]
Elise cites philosopher of science "Basven Frazen" who says philosophy may ask similar questions over time but always in a new scientific, cultural, and political context, with a changed person doing the asking[9:17]
• Because contexts change, each time a philosophical question is asked it is, in an important sense, asked anew
Elise challenges the expectation of perfectly coherent thought across a person's lifetime, arguing that people who think hard should often change their minds[11:06]

Aristotle and early notions of physics and metaphysics

Elise notes that Aristotle defined metaphysics in close relationship to physics, asking what kinds of things we encounter, their behaviors, and patterns[11:02]
She says this is still a decent way to describe science today: explaining natural phenomena and understanding their relationships and patterns[12:06]
• In Aristotle's time, what we now call physics and metaphysics were not sharply distinguished but part of the same inquiry

Historical entanglement of physics and philosophy

Philosopher-physicists up through the early 1900s

Elise lists early 20th-century figures like Ernst Mach, Einstein, Pierre Duhem, Poincaré, and Lorentz as philosopher-physicists[12:16]
Neil points out that earlier figures like Newton and Hooke didn't call themselves physicists but natural philosophers[13:29]

Descartes, Newton, and principles of philosophy

Elise describes Newton building on Descartes, who in turn built on Galileo, Kepler, and Copernicus while trying not to anger the Catholic Church[13:20]
Descartes's major work "The Principles of Philosophy" has four books; the first sets up epistemology (theory of knowledge) and metaphysics as a prelude to physics in book two[15:18]
• For Descartes, talking about how we know anything and what exists with certainty was a necessary step before doing physics
Newton's "Philosophiæ Naturalis Principia Mathematica" (Mathematical Principles of Natural Philosophy) responds to and seeks to replace Descartes's "Principles of Philosophy"[15:18]
• Neil asks if Newton's title is poking at or building on Descartes; Elise says Newton is trying to replace Descartes
Elise explains that Newton's Principia begins with definitions, then a general scholium (explanatory section) where he argues philosophically for absolute space and absolute time before deriving the three laws of motion[16:16]
• Gravity is introduced later in the work, after Newton has laid his conceptual foundations about space and time
Early natural philosophers felt they had to first address questions like how we know what we know and whether we know that we know, before building physical theories[16:44]

From Newton to the 18th century: issues with gravity and action at a distance

Elise notes that 17th- and 18th-century thinkers recognized that Newton's law of gravity, as instantaneous action at a distance, left conceptual issues unresolved[21:09]
She describes the concern: if two masses suddenly appear in an otherwise empty universe, Newtonian gravity says they immediately feel a mutual force with no time delay[21:16]

Emilie du Châtelet and filling gaps in Newton

Elise highlights "Emily de Chateaubriand" (du Châtelet) as a key figure who wrote "The Foundations of Physics" and translated Newton's Principia into French[20:55]
• Du Châtelet hosted intellectual salons, taught her son physics, was dissatisfied with existing textbooks, and wrote her own starting from philosophical principles like sufficient reason and non-contradiction
Her translation did more than convert Latin to French; she added a thick commentary and filled in gaps, influencing the way French physicists learned Newtonian physics[24:02]
• Elise says modern French physicists still read her translation, illustrating her lasting impact

Women in early philosophy and physics

Elise remarks that while there may have been few women doing experiments, there were many women doing philosophy and corresponding with major figures like Leibniz and Hume[26:10]
• She notes that some women's letters influenced Leibniz's thought, even if they were not remembered as physicists
Neil recalls having a book of Leibniz's letters with many different correspondents and considers reexamining them for female contributors[25:51]

Leibniz, calculus, and relational space

Neil explains for Chuck that Leibniz invented calculus around the same time as Newton, leading to two independent formulations that both work[27:23]
Elise states that in physics we retain a lot of Newton's notation, while pure mathematics mostly uses Leibniz's notation like the integral sign[26:42]
She characterizes Leibniz's view of space as relational: space is not a substance but the set of relations between material objects[27:23]
• This contrasted with Newton's ontology, where absolute space and time exist independently of matter and are part of "what there is"

19th-20th century: specialization, institutions, and the split between physics and philosophy

Industrial Revolution and growth of scientific fields

Elise notes that better technology in the 19th century allowed physics to become more quantitative about energy conservation and biological phenomena like muscles (e.g., frog leg experiments)[35:23]
Disciplines such as psychology and sociology began to emerge and distinguish themselves during this period[35:29]
Universities, faculties, and professional societies like the Royal Society and Parisian scientific societies expanded, enabling international sharing of results in the West[35:46]
• She frames this as a story of increasing quantization and specialization: the more that is learned, the more there is to specialize in

Library of Alexandria thought experiment and limits of knowledge

Elise muses that in the era of the Library of Alexandria, or even up to around the 1500s, a highly educated person might realistically claim to have read "all the books"[36:32]
She contrasts that with the modern impossibility of mastering all written knowledge, emphasizing how much information and specialization have exploded[37:11]

Cold War, Manhattan Project, and the "shut up and calculate" era

Elise points to the Manhattan Project and post-World War II period as when physics became an established career with strong ties to national security[40:16]
In that era, physics in the U.S. shifted toward a pragmatic, calculation-focused mentality summarized as "shut up and calculate," leaving little room for philosophy[40:16]
She mentions Daniel Kevles's book "The Physicists" as a history of U.S. physics and its specialization (while acknowledging it may now be somewhat outdated)[40:16]

James Conant and defending philosophy and history for physicists

Elise recalls that Harvard president and scientist James Conant fought for physics students to be taught history and philosophy of science[40:30]
Conant integrated history and philosophy courses into Harvard's physics program so that training went beyond lab notes and calculations[40:16]

Specialization, impermeable walls, and liberal arts

Elise argues that as universities evolved, they actively discouraged students from staying general, especially in graduate school[41:31]
She laments that liberal arts training has been marginalized despite its importance for appreciating multiple dimensions of life and society[41:56]
Elise believes impermeable walls between disciplines are detrimental to any field, not just science[41:17]
Neil observes that physics today still seems to suffer from "border problems" that make interdisciplinary exchange difficult[42:35]

Philosophical principles guiding scientific practice

Mach, Einstein, and asking about the goal of science

Elise recounts that Einstein, in an obituary for Mach, praised him for continually asking what the proper goal of science is[43:09]
• She characterizes this as a philosophical principle that guided Mach's scientific work and influenced Einstein
Elise notes that principles like simplicity, parsimony, and beauty often guide physics, but there is no reason to think nature must follow our aesthetic preferences[43:53]
She emphasizes that scientists must assume certain untestable principles, such as the uniformity of nature, for science to seem worthwhile at all[45:44]

Space, time, and revising basic concepts

Elise explains that by the late 19th century, physicists recognized tensions among pillars like thermodynamics, electrodynamics, and Newtonian mechanics[45:34]
Mach, Einstein, and others realized electrodynamics would not work in Newton's framework of absolute space and time, signaling a need to reevaluate basic concepts[45:13]
Einstein claimed that special relativity arose not from manipulating equations alone but from asking what is meant by terms like "simultaneous" and by reconsidering space and time across reference frames[47:26]
Elise frames the current search for quantum gravity and a quantum notion of causality as similarly requiring conceptual reevaluation[49:12]

Quantum mechanics, objectivity, and non-locality

Objectivity and the measurement problem

Elise says objectivity and capital-T "Truth" are often treated as special features of science, but such claims are themselves philosophical positions[57:16]
She characterizes one notion of objectivity as the ability to isolate a system from the measuring apparatus so it can be poked, prodded, and studied without fundamentally altering it[58:15]
She notes that even in classical contexts (e.g., dissecting a bird versus observing it in flight), the act of study changes the object, but classical physics can often "quotient out" these effects[58:00]
Quantum mechanics introduces regimes where interaction with the system cannot be factored out, bringing objectivity into question[59:56]

Entanglement as a new kind of interaction

Elise explains that Schrödinger described entanglement as the feature that marks the departure from classical to quantum theories[1:05:14]
Once two quantum subsystems have interacted, they become non-separable: a complete state description of one cannot be given without reference to the other, even after separation[1:03:28]
Einstein wanted a complete theory to allow a state for one subsystem that does not reference the other, reflecting a desire for separability[1:02:09]
• Elise uses the term "non-separability" to define entanglement and notes that it is a "new kind of thing" not present in classical interactions

Non-locality and Bell experiments

Elise attended a Helgoland conference marking 100 years of quantum mechanics, where Nobel laureates who designed Bell-type experiments debated the meaning of non-locality[1:16:59]
She says they agreed on experimental results but could not agree on what non-locality says about the world[1:17:10]
Elise distinguishes classical correlation (e.g., Chuck's mismatched socks) from quantum entanglement, where correlations cannot be explained by shared prior properties alone[1:18:47]
• In the sock analogy, seeing one brown sock lets you infer the other is non-brown without any non-local influence-that is purely classical
In quantum entanglement, measurements on one particle yield outcomes correlated with measurements on its partner in ways that exceed classical statistics, even when no communication can occur[1:20:29]
• Elise notes that if one assumes no faster-than-light signaling, the observed correlations still cannot be explained by local hidden variables
She describes non-locality as the measurable signature of entanglement, while emphasizing it is a label for a phenomenon we do not yet fully understand conceptually[1:19:23]

Quantum decoherence and the classical world

Elise rejects the idea that Bohr believed in a hard classical-quantum split; instead, he saw a continuous situation but stressed the pragmatic need to talk about measurement devices classically[1:08:46]
She clarifies that what makes macroscopic objects appear classical is not simple averaging but quantum decoherence, due to unavoidable interactions with the environment[1:07:59]
She states that we can now give good physics explanations for why macroscopic objects like humans do not exhibit obvious entanglement, despite being composed of quantum parts[1:06:09]

Competing approaches to quantum gravity and philosophical commitments

String theory vs canonical approaches

Elise sketches two major families of approaches to uniting general relativity and quantum theory: string theory and canonical approaches like loop quantum gravity[53:33]
She describes string theory as trying to build a theory of everything from the ground up, while canonical approaches treat quantum theory as fundamental and try to bring GR into its framework[53:33]
Neil says he intuitively leans toward quantum theory as the more fundamental framework because quantum predictions have not yet failed, whereas general relativity has known limits[54:27]
• He notes GR fails at the center of black holes and at the moment of the Big Bang, while quantum theory has no identified breakdown so far
Elise adds that sociological factors like hiring, funding, and availability of good graduate students influence which approaches are pursued, making it hard for "fringe" alternatives to flourish[56:12]

Guiding principles and the risk of dogma

Elise emphasizes that guiding principles (e.g., beauty, simplicity) are important and unavoidable, but elevating them to dogma can misdirect research[50:12]
She notes such principles affect decisions about which frameworks seem compelling, who gets funded, and where to send the best graduate students[50:26]

Limits of intuition and the role of philosophy going forward

Can quantum physics ever be intuitive?

Elise doubts quantum mechanics will ever be intuitive in the way classical mechanics is, because humans evolved to think in terms of macroscopic positions and trajectories[1:28:21]
She argues that knowing quantum theory might even be evolutionarily "maladaptive" in a narrow sense, since it leads people to sit doing problem sets while predators approach[1:29:01]
Because of our classical evolutionary background, she believes we must work deliberately-using philosophical reflection-to "unmoor" ourselves from classical intuitions[1:31:43]

Philosophy as a tool to avoid ossification

Chuck likens disciplinary rigidity to ossification caused by habitual practice, and suggests philosophy can restore elasticity in thinking[1:32:06]
Elise agrees and says that ideally training in physics would involve stepping back to look at the field's history and to ask philosophical questions about its concepts and methods[1:32:39]

Younger generation and global interest in philosophy of physics

At the Helgoland event, Elise met many early-career physicists across Europe, China, South America, and some in the U.S. who are eager to study these foundational questions[1:35:28]
She observes that many European labs hope to attract top U.S. scientists who are leaving, and says this exodus is a real phenomenon[1:35:51]
She believes younger physicists recognize how closely philosophical issues are tied to cutting-edge physics and want more education in history and philosophy of science[1:36:43]

Neil's critique of modern philosophy and closing reflections

Neil clarifies his stance on philosophy's contribution to physics

Elise asks Neil directly about past comments he has made on philosophy, noting that he seems genuinely curious despite those remarks[1:37:26]
Neil says his comments on philosophy have been caricatured and narrows his claim: he has not seen someone with a 20th-century PhD solely from a philosophy department materially advance the physical sciences[1:38:31]
He distinguishes this from his view of philosophical thinking in physics, stating that no good physicist avoids thinking philosophically at some level[1:40:15]
Neil contrasts the apparent frequency of philosophers' contributions to physics a century ago with what he perceives now, framing his point as an empirical observation about institutional separation[1:40:41]

Abner Shimony example and cross-trained scholars

Elise invokes Abner "Shimoni" as someone formally trained in both physics and philosophy whose work uses philosophical reasoning to address physical questions[1:39:02]
Neil notes that Shimony had training in both fields, illustrating that effective work often comes from people conversant in both science and philosophy[1:40:03]

Value of philosophy beyond service to science

Elise argues it is dangerous to say something is only important insofar as it contributes to science, and maintains philosophy of science is worth doing in its own right[1:41:55]
She notes that there is no rigid line between disciplines: for thousands of years they were one pursuit, and in some areas they are beginning to merge again[1:42:16]
Elise emphasizes that valuable philosophy of physics requires genuine engagement with current science and scientists, which happens through conversations like the one in the episode[1:43:30]

Lack of everyday interaction between departments

Neil reports that at several academic institutions he has seen, philosophy departments do not have regular interactions like lunch with chemists, physicists, and other scientists[1:44:11]
He suggests his criticism largely reflects this empirical reality of separation rather than a denial of philosophy's potential value[1:46:18]
Elise agrees more interaction is needed and says when scientists and philosophers do talk, the exchange can change how each side thinks about their work[1:45:38]

Einstein's view: physics as a kind of metaphysics

Elise reads from a letter Einstein wrote to Schrödinger in June (referenced from the book "The Einstein Paradox") in which Einstein says physics is a kind of metaphysics[1:48:09]
In the quoted passage, Einstein writes that physics describes reality, but we do not know what reality is; we only know it through our physical descriptions[1:48:46]
• Elise uses this to underscore that physics and philosophy are fundamentally intertwined in grappling with what "reality" means

Closing remarks

Neil thanks Elise for returning, says it is good to converse with her, and jokes that City College is just up the street from the Hayden Planetarium[1:50:13]
Chuck playfully reasserts his title as "Lord of Comedy" as the show signs off[1:50:24]
Neil closes by branding the episode as a "Physics of Philosophy Edition" of StarTalk and ends with his usual encouragement to "keep looking up"[1:50:24]

Lessons Learned

Actionable insights and wisdom you can apply to your business, career, and personal life.

1

Foundational concepts like space, time, causality, and objectivity are not fixed; periodically stepping back to question what you mean by your basic terms can unlock new ways of thinking and problem-solving.

Reflection Questions:

  • • What core concepts or assumptions in your field or life have you never really defined or questioned for yourself?
  • • How might clarifying what you mean by key terms (like 'success', 'risk', or 'fairness') change the options you see in front of you right now?
  • • When this week could you pause and explicitly write down the assumptions behind a decision you are making, then challenge each one?
2

Hyper-specialization brings power but also blind spots; deliberately cultivating generalist perspectives and cross-disciplinary conversations can prevent intellectual ossification.

Reflection Questions:

  • • Where in your work or interests have you become so specialized that you rarely talk to people outside your niche?
  • • How could bringing in perspectives from a very different discipline (or background) help you see a current problem in a new way?
  • • What is one concrete step you could take this month to broaden your inputs-such as a course, book, or person from outside your usual domain?
3

Guiding principles like simplicity, elegance, or beauty are useful heuristics, but turning them into dogma can misdirect effort and close off promising avenues.

Reflection Questions:

  • • Which aesthetic or stylistic preferences do you treat as if they were universal truths in your work or personal decisions?
  • • How might your current project look different if you temporarily set aside your usual preference (for speed, neatness, minimalism, etc.) and tried an opposite approach?
  • • What is one decision you can revisit this week and ask, 'Did I choose this because it genuinely works best, or because it fit my preferred style?'
4

Our intuitions are shaped by the contexts in which we evolved and learned; in unfamiliar domains, you often need deliberate, reflective thinking rather than relying on gut feeling.

Reflection Questions:

  • • In which situations do you most strongly rely on intuition, and how often are those situations truly similar to the ones that shaped your instincts?
  • • How could you build in a short 'reflection checkpoint' before big decisions where your gut feeling might be misleading?
  • • What new domain are you working in now where you should assume your intuitions are unreliable and instead seek models, mentors, or data?
5

Interdisciplinary dialogue-like that between scientists and philosophers-can surface hidden assumptions and reveal conceptual gaps that insiders may overlook.

Reflection Questions:

  • • What problem are you facing that might benefit from the perspective of someone who does very different work from you?
  • • How might you structure a conversation with a person from another discipline so that you both uncover assumptions rather than just defending positions?
  • • Who outside your usual circle could you schedule a 30-minute call with this month to discuss a challenge you are stuck on?
6

Recognizing the limits of current tools and theories, without dismissing their power, helps you bet wisely on future directions and stay open to transformative change.

Reflection Questions:

  • • Which of your current tools, methods, or beliefs work very well in some situations but clearly break down in others?
  • • How could mapping out where your favorite frameworks fail help you identify where innovation or new learning is most needed?
  • • What is one area where you could explicitly document the 'known limits' of your current approach and explore at least one alternative?

Episode Summary - Notes by Reagan

The Limits of Knowing with Elise Crull
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