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StarTalk Radio

Things You Thought You Knew - Quantum Cat

Published October 7, 2025
View Show Notes

About This Episode

Neil deGrasse Tyson and co-host Chuck Nice explore three classic concepts from astrophysics and quantum physics: death by black hole, Schrödinger's cat and the observer effect, and quantum tunneling. They explain tidal forces and spaghettification near black holes, clarify what the quantum observer effect really means, unpack the idea of superposition in Schrödinger's cat and qubits in quantum computing, and show how quantum tunneling enables nuclear fusion inside stars at temperatures lower than classical physics would predict.

Topics Covered

Black holes Quantum mechanics Schrodinger's cat Quantum tunneling Observer effect Quantum computing Entanglement Fusion energy Mathematics and physics

Disclaimer: We provide independent summaries of podcasts and are not affiliated with or endorsed in any way by any podcast or creator. All podcast names and content are the property of their respective owners. The views and opinions expressed within the podcasts belong solely to the original hosts and guests and do not reflect the views or positions of Summapod.

Quick Takeaways

  • Tidal forces-differences in gravitational pull across an object's length-are responsible for the extreme stretching and eventual disintegration ("spaghettification") of anything falling into a black hole.
  • The so‑called "observer effect" in quantum mechanics is really a measurement effect: the act of measuring tiny particles with light or other probes changes their state because the measuring tool itself transfers energy.
  • Schrödinger's cat is a thought experiment about quantum superposition: before measurement, a quantum system can exist in a combined state of multiple possibilities, such as "dead" and "alive."
  • Quantum bits (qubits) in quantum computing can exist in probabilistic superpositions of 0 and 1, greatly increasing computational versatility compared with classical bits.
  • A particle's wave function can extend beyond physical barriers, creating a nonzero probability that it appears on the far side without ever going "over" the barrier-this is quantum tunneling.
  • Quantum tunneling allows nuclear fusion to occur in stellar cores at about 10-15 million degrees, far below the billion-degree temperatures classical physics suggests are needed for protons to overcome their mutual repulsion.
  • The development of quantum mechanics and discoveries about the expanding universe in the 1920s solved previously intractable astrophysical puzzles and exemplify how new physics reshapes our understanding.
  • Distance is irrelevant to quantum tunneling: the particle doesn't travel through the barrier in time-it was already present probabilistically on both sides via its wave function and simply "shows up" when the wave function collapses.

Podcast Notes

Episode setup and overview of topics

Introduction to 'Things You Thought You Knew' segment

Host previews fan-favorite topics[1:16]
• They will cover Death by Black Hole, Schrödinger's Cat, and Quantum Tunneling in this episode.

StarTalk show identity

Framing of the show[1:32]
• StarTalk is described as "your place in the universe where science and pop culture collide."

Death by Black Hole and tidal forces

Introducing the idea of dying in a black hole

Neil sets up a descriptive explanation[1:50]
• Neil says he wants to describe what it is like to die while falling into a black hole, clarifying humorously that he has not personally experienced it.

Seinfeld anecdote about the Big Bang explanation

Compliment from Jerry Seinfeld[2:11]
• Neil recalls giving Seinfeld a tour of the newly renovated Hayden Planetarium and describing the Big Bang in exquisite detail.
• Seinfeld responded, "It sounds like you were there," which Neil considers one of the highest compliments he's received.

Defining tidal force using Earth's gravity

Gravitational difference between head and feet[3:34]
• Neil notes that when you are standing (or sitting) on Earth, your feet are closer to Earth's center than your head, so the gravitational force on your feet is slightly stronger.
• Because human height (~5-6 feet) is tiny compared to Earth's radius (~4,000 miles), the force difference is small and normally ignored.
Definition of tidal force[5:06]
• The difference in gravitational force between two separated points (e.g., head vs. feet) has a specific name: the tidal force.

Tidal forces from the Moon on Earth and ocean tides

Moon's differential pull on Earth[5:17]
• The side of Earth facing the Moon feels a stronger gravitational force from the Moon than the far side does.
• This difference stretches the entire Earth along the Moon-Earth line, with the solid Earth stretching slightly and the oceans stretching more noticeably.
Tidal bulge description[5:54]
• The oceans form a "tidal bulge" elongated in the direction of the Moon; in a simplified picture, it is aligned with the Moon.

Shrinking Earth into a black hole and increasing tidal forces

Effect of shrinking Earth while keeping mass constant[6:18]
• Neil imagines shrinking Earth without changing its mass: as the radius shrinks, the surface gets closer to the center, increasing surface gravity.
• Two variables determine your weight: distance from the mass's center and the amount of mass pulling on you.
Human height becomes significant compared to shrunken Earth[6:20]
• As Earth shrinks below its normal 4,000‑mile radius, a fixed human height (e.g., 5'10") becomes a larger fraction of Earth's radius.
• Mathematically, the difference between gravitational forces at head and feet grows larger as the body size becomes less negligible relative to the planet/black hole size.

Falling into a black hole and experiencing tidal stretching

Initial pleasant stretch turning into torture[8:22]
• Neil imagines a person falling feet-first into a black hole; at first the tidal stretch might feel good, like a satisfying body stretch.
• As the person gets closer, the stretch becomes relentless and increasingly painful, evoking "medieval" torture imagery.
Comparison to historical torture methods[8:59]
• They discuss gruesome medieval methods such as disembowelment over fire and being drawn and quartered by horses, emphasizing how deliberately cruel such devices were.
• Neil points out that in drawn-and-quartered executions, limbs would not detach simultaneously; tissue strength differences mean one limb goes first, then others, making it even more horrific.

Spaghettification: tidal forces exceed molecular bonds

Breaking the body apart via tidal forces[11:59]
• As one falls closer to a black hole, tidal forces eventually exceed the molecular forces holding the body together.
• Neil says the body will "snap" into parts, and based on his calculations, the first break would likely occur in the lower spine.
Progressive fragmentation into smaller pieces[12:46]
• The original body splits into two pieces, then each half continues to experience tidal forces and splits again, likely at the base of the neck for the upper body.
• This fragmentation continues: 2, 4, 8, 16, 32, 64 pieces, and so on, until the person becomes a stream of individual atoms.
Brain awareness during dismemberment comparison[12:55]
• Neil references historical reports from the French Revolution that after guillotine decapitation, people tested whether severed heads could still perceive by asking for blinks in response to finger counts.
• He notes that in such experiments, the eyes send signals directly to the brain, so some momentary perception may persist before oxygen deprivation takes effect.

Extrusion through spacetime and naming of spaghettification

Spacetime funnel and atomic stream[13:59]
• Neil explains that the fabric of space and time around a black hole funnels down towards a singularity, narrowing as it goes.
• The horizontally extended body (now a string of atoms) is extruded through this narrowing spacetime geometry "like toothpaste through a tube."
Term spaghettification[14:46]
• The process of extreme stretching and thinning of objects falling into a black hole is called "spaghettification."
• Chuck comments on the contrast between the horrific process and its almost whimsical food-related name.

Neil's book 'Death by Black Hole' and short rhyme

Publishing story and bestseller moment[15:33]
• Neil wrote a book titled "Death by Black Hole"; his publisher doubted it would sell well and printed too few copies at first.
• The book sold out in a day and hit #15 on the bestseller list for one week, which Neil calls a "minimum bestseller," and he jokes about lording this over his publisher.
Recitation of a rhyme about death by black hole[15:59]
• Neil shares a self-described rhyme (rather than a formal poem) that playfully yet ominously describes a feet‑first dive into a black hole, tidal forces, and being eaten by the singularity.
• Chuck compares it humorously to the scariest Dr. Seuss book he has ever heard, imagining it as a bedtime story to scare a child into behaving.

Observer effect, Schrödinger's cat, and quantum superposition

Cultural presence of Schrödinger's cat

Reference in jokes and culture[20:35]
• Chuck notes that Schrödinger's cat is referenced frequently in jokes and popular culture, even by comedians who may not fully understand it.
• Neil observes that the concept has entered culture and even politics.

Clarifying the observer effect as a measurement effect

Misinterpretations involving consciousness[22:07]
• Neil says it is unfortunate the term "observer effect" was used because some scientifically illiterate people turned it into claims about consciousness affecting reality and a "consciousness field."
Physical explanation using light and photons[22:53]
• He explains that seeing an object involves light (photons) hitting it, bouncing off, and reaching our eyes; each photon carries energy.
• On large scales, like a human face, the energy of each photon is negligible relative to the object's mass and doesn't noticeably move it.
Shrinking to microscopic size and being moved by measurement[25:17]
• If you were shrunk down to a microscopic particle, there is a size threshold below which incoming light used to observe you would impart enough energy to change your state or position.
• He notes that at such scales, trying to see where the particle is by shining light on it causes it to "pop" into another location.
• Therefore, for sufficiently small particles, observation via light fundamentally alters what you are trying to measure, making it impossible to know the pre-measurement state.
Measurement vs. human consciousness[25:17]
• Neil emphasizes that it is not human consciousness that changes the system, but the physical act of measurement with energy-carrying probes (like photons).

Albedo, skin color, and climate reflection joke

Skin color and absorption of light[23:49]
• Darker skin absorbs more photons than lighter skin; this is described using the concept of albedo (the fraction of incident energy absorbed vs. reflected).
Earth's albedo and climate[24:00]
• Neil notes Earth's albedo is critical for climate, as absorbed sunlight drives climate while reflected light escapes back to space.
• He lists glaciers, cloud tops, and oceans as reflective components affecting Earth's energy balance.

Schrödinger's cat thought experiment

Setup of the quantum cat in a box[26:40]
• Neil describes a cat in a box that can exist in two possible states: dead or alive; while the box is closed, the observer has no idea which state it's in.
• He stresses that in the original concept, the cat is a hypothetical quantum cat, not an ordinary macroscopic cat like an internet-famous pet.
Superposition of states[28:28]
• In quantum physics language, the cat's existence is described as a superposition of being dead and being alive until observed.
• The detailed original proposal involved a radioactive source that might decay and trigger a mechanism affecting the cat, but Neil simplifies away those details to focus on the superposition idea.
Analogy to the movie "Seven"[29:54]
• Chuck compares Schrödinger's cat to the box scene in the film "Seven," where Brad Pitt's character desperately wants to know what is inside a box that likely contains his wife's head, while Morgan Freeman's character tells him not to look.
• Neil calls this the most morbid analogy to the Schrödinger's cat example he has ever heard and notes that in the thought experiment, the "cat" should be a quantum entity, not an ordinary head.

Quantum computing and qubits

Classical bits vs quantum bits[31:16]
• Neil contrasts regular computing bits, which can only be 0 or 1, with quantum bits (qubits), which can be 0, 1, or any probabilistic combination of both.
• A qubit can represent states like 80% 1 and 20% 0, 50-50, or 80% 0 and 20% 1, and so on, providing greater computational versatility.
Connection back to superposition[31:56]
• He explains that, like Schrödinger's cat's superposed alive/dead states, qubits exist in superpositions that algorithms can exploit during computation.

Wave functions, tunneling preview, and entanglement

Wave function extending beyond boundaries[34:53]
• Neil notes that a particle's wave function extends outside the box boundaries, with a rapidly dropping but nonzero probability of being found outside.
• Because of this, something inside the box can sometimes spontaneously disappear from inside and appear outside, an effect called tunneling.
Instantaneous tunneling and quantum entanglement hint[34:40]
• He says tunneling appears to happen instantaneously, seemingly faster than light, which ties into broader quantum phenomena like entanglement.
• Neil mentions that two entangled particles can have wave functions that interact such that manipulations of one are known to the other instantly via their shared wave function.

Historical context: 1920s as a watershed decade in physics

Discoveries in cosmology[35:59]
• Neil notes that in the 1920s, Edwin Hubble discovered that the Milky Way is not the only galaxy; Andromeda is another galaxy with around 400 billion stars.
• In 1929, Hubble discovered the expansion of the universe, and combined with Einstein's relativity, this supported the idea of the Big Bang decades before confirming data arrived.
Quantum mechanics development timeline[36:27]
• Most of what physicists now know and use about quantum physics was discovered in the 1920s, before even the neutron was discovered.
Pre-calculator era work[37:31]
• Neil points out that these foundational quantum calculations were done before electronic calculators like the Texas Instruments scientific calculator existed.

Quantum tunneling and its role in stellar nuclear fusion

Classical picture: climbing a hill vs. tunneling through it

Macroscopic tunneling analogy[41:10]
• Neil compares getting from one side of a hill to the other by climbing over versus boring a tunnel through the hill, defining a tunnel as the easier path through a barrier.
• Chuck relates this example to New Jersey-Manhattan tunnels, appreciating the concept in a real-world commuting context.

Potential barriers and particles as waves

Energy barrier and particle limitations[41:59]
• In quantum physics, Neil likens the hill to an energy barrier (a potential barrier); a particle on one side needs enough energy to climb over to the other side.
• If the particle lacks sufficient energy, classically it would simply remain on its original side of the barrier.
Wave function and probability distribution[42:36]
• Neil explains that particles also behave as waves, described by a wave function that encodes the probability of finding the particle at various locations.
• The highest probability corresponds to the wave's peaks, while tails of the wave function represent lower but nonzero probabilities of finding the particle far from the peak.

Quantum mechanical tunneling defined

Wave function presence beyond the barrier[43:04]
• The particle's wave function does not "care" about the mountain; it can extend through and beyond the barrier, implying some probability that the particle is found on the far side.
Tunneling as barrier-crossing without climbing[44:01]
• Quantum tunneling is defined as the particle being found on the other side of the barrier, even when it did not have enough classical energy to climb over.
• Neil characterizes this as the particle "showing up" where it was not classically invited, thanks to its wave nature.

Early mystery of the origin of chemical elements

Questioning where elements come from[45:04]
• Neil recalls asking his high school chemistry teacher where the elements come from; the teacher answered they were "in the Earth," which Neil later learned was incorrect or incomplete.
• He notes that many elements were in fact forged in stars, and jokes that his chemistry teacher should have looked up at the sky for the answer.

Proton-proton fusion and required temperatures

Electrostatic repulsion vs strong nuclear force[47:02]
• Hydrogen nuclei (single protons) must merge to form helium nuclei; however, both protons are positively charged and repel each other electromagnetically.
• To fuse, they must be brought close enough for the strong nuclear force-much stronger than electromagnetism at short range-to bind them together.
Classical temperature requirement[48:38]
• Calculations based on classical physics indicate that protons would need temperatures on the order of a billion degrees to overcome their electrostatic repulsion and get close enough to fuse.
• In contrast, the centers of stars like the Sun are only about 10-15 million degrees, far lower than the calculated billion-degree requirement.

Eddington's insight and the need for new physics

Eddington's statement about fusion in stars[49:36]
• Astrophysicist Arthur Eddington said he did not know exactly how elements are built, but if it happens anywhere, it must be in the centers of stars.
• He asserted this despite the temperature mismatch, because he saw no other plausible environment in the universe that could even approach the needed conditions.
Problem remained unsolved until quantum mechanics[51:24]
• For a time, the discrepancy between required and actual stellar core temperatures remained an unsolved problem in astrophysics.
• Quantum mechanics later provided the missing piece via tunneling, enabling fusion without the billion-degree temperatures.

Applying quantum tunneling to stellar fusion

Protons as waves with overlapping wave functions[52:09]
• In quantum physics, approaching protons are treated as waves whose wave functions can extend into the domain where the strong nuclear force can act.
• Even if most protons lack the classical energy to overcome repulsion, there is a nonzero tunneling probability that allows some to fuse.
Matching tunneling probabilities to solar output[52:41]
• Physicists calculated, at a core temperature around 10 million degrees, what fraction of proton encounters would tunnel through the barrier and fuse.
• When this quantum tunneling rate is used, the resulting fusion energy matches the observed total energy output of the Sun.
• Neil notes that it is fortunate that not every encounter results in fusion; otherwise, the Sun would release energy too violently and could be catastrophically unstable.

Physicists' attitude toward new physics

Value of new theoretical frameworks[55:05]
• Neil emphasizes that astrophysicists are excited when new physics emerges because it can resolve longstanding problems like the stellar fusion puzzle.
• He pushes back on the notion that scientists resist new ideas to protect old work, clarifying that robust, testable new physics is welcomed for the deeper understanding it provides.

Distance independence and instantaneity of tunneling

Wave function collapse perspective[56:24]
• Neil states that no matter how large the potential barrier, the wave function includes some probability on the other side, and tunneling results from wave function collapse, not a literal traversal.
• When the wave function collapses and the particle is detected, it appears instantaneously on the other side; it did not travel through space in time but was always present probabilistically there.
Freakiness of quantum phenomena[57:35]
• Neil calls quantum tunneling only about the "12th freakiest" thing in quantum physics, implying there are even stranger phenomena.
• He teases future discussion of Bose-Einstein condensates as another "freaky, wacky" quantum phenomenon.

Closing remarks and future topics

Teasing Bose-Einstein condensate

Future explainer topic[58:30]
• Neil and Chuck mention Bose-Einstein condensate as a topic they will save for another explainer, joking that the name sounds like a fancy menu item.

Final sign-off

Encouragement to stay curious[52:41]
• Neil signs off with his usual line, "Keep looking up," signaling the end of the quantum tunneling explainer and the episode's main content.

Lessons Learned

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

1

Small differences can have profound effects when the scale or context changes, as seen with tidal forces that are negligible on Earth's surface but become lethal near a black hole.

Reflection Questions:

  • • Where in your life or work are you dismissing a small difference that might become critical as the situation scales up?
  • • How could changing the scale-timeframe, size, or intensity-reveal hidden stresses or risks in a project you're managing?
  • • What is one "tiny" variable you could start tracking this week to better understand its long-term impact on your goals?
2

The act of measurement can change the system being measured, so any attempt to observe or evaluate people or processes needs to account for the influence of the observation itself.

Reflection Questions:

  • • In what situations do people in your team or organization behave differently simply because they know they are being evaluated?
  • • How might you redesign a feedback or measurement process so that it captures more authentic behavior and fewer "performance for the camera" effects?
  • • What is one current metric or test you rely on that you should re-examine for unintended side effects on behavior?
3

New frameworks and theories often emerge to solve contradictions that old models cannot explain, so staying open to new ideas is essential when data and predictions stop aligning.

Reflection Questions:

  • • Where are you seeing consistent mismatches between your expectations and actual outcomes in your work or personal life?
  • • How could you temporarily set aside your current assumptions and imagine an alternative framework that better fits the evidence you see?
  • • What is one longstanding puzzle or recurring problem you could revisit this month with a willingness to consider a fundamentally different approach?
4

Low-probability events can cumulatively drive major outcomes, much like rare quantum tunneling events in stellar cores power the continuous energy output of the Sun.

Reflection Questions:

  • • Which low-probability but high-impact opportunities or risks are you currently overlooking because they seem too unlikely in isolation?
  • • How might repeated small chances-such as daily outreach, experiments, or skill practice-compound over time in your favor?
  • • What is one small, low-effort action you could start doing consistently that has a modest chance of creating outsized benefits over the next year?

Episode Summary - Notes by Cameron

Things You Thought You Knew - Quantum Cat
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