Get Your Weekly Digest

Receive the best podcast summaries and insights delivered to your inbox every week.

We respect your privacy. Unsubscribe anytime.

Radiolab

The Spark of Life

with Narosha Murugan

Published September 19, 2025
View Show Notes

About This Episode

Host Molly Webster speaks with applied biophysicist Narosha Murugan about the discovery that living cells emit extremely faint light tied to their metabolism, and explores how this challenges the traditional lock-and-key view of cellular signaling. They discuss possible mechanisms for how this light is generated in mitochondria and potentially guided through cellular structures, its hypothesized roles in brain function and consciousness, and how its distinct signatures can already be used experimentally to detect cancer and distinguish living from dead tissue. The conversation ends with reflections on "life flashes" at fertilization and death, and on thinking of living beings as organized patterns of energy and light.

Topics Covered

Mitochondrial function Neuroscience Cancer Consciousness Brain health Metabolic rate Hospice care Origins of life Science communication Cell signaling

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

  • Traditional lock-and-key models of molecular interaction struggle to explain how cellular signals propagate as fast as they do, prompting researchers like Murugan to look for additional mechanisms.
  • Experiments dating back to the 1920s and more recent work show that all metabolically active cells emit extremely weak, wavelength-specific light associated with their mitochondrial activity.
  • Different metabolic states and cell types, including cancer cells, have distinct light signatures that can be used as photonic biomarkers and have already enabled very early cancer detection in animal models.
  • There is growing but still preliminary evidence that intracellular structures like microtubules may guide photons in a fiber-optic-like way, suggesting light could play a purposeful role in neural signaling.
  • The same kinds of photons produced inside cells are also absorbed from the sun by various molecules in the body, linking internal and external light interactions in processes like vitamin D synthesis and circadian regulation.
  • Researchers can distinguish living from dead tissue by their photon emissions, and anecdotal reports of "death flashes" and observed flashes at fertilization frame life as a pattern of organized energy and light.
  • The biological meaning, if any, of intracellular light in processes like thought or consciousness remains unknown and is considered a risky but potentially transformative area of research.
  • Even if biophotons turn out not to be biologically purposeful signals, their consistent association with metabolism makes them promising tools for noninvasive diagnostics.

Podcast Notes

Introduction and separation between biology and physics

Radiolab opening and host introduction

Show branding and host identity[0:10]
• The episode opens with the Radiolab audio logo and the phrase "you're listening to Radiolab from WNYC" establishing the show and network context.
Host background in biology[1:04]
• Host Molly Webster shares that she was a biology major who only took one physics class and then never thought about physics again, reflecting a common divide in science education.

Perceived divide between biology and physics

Two "worlds" view of science[1:00]
• Molly describes biology as the world of environment, animals, bodies, and "organic, messy" physical stuff and physics as the abstract world of waves, energy, and invisible particles that feel like two different worlds.
Biophysics as a bridge[1:27]
• Molly notes that for guest Narosha Murugan, biology and physics go hand in hand rather than being separate disciplines.

Guest introduction and the lock-and-key problem

Introducing Narosha Murugan

Who Narosha is and her approach[1:45]
• She introduces herself as "an applied biophysicist from Waterloo, Canada" and says that while most biophysicists focus mostly on biology, she prefers a 50-50 balance of biology and physics.

Setup of the episode's core idea

A leap into the unknown about how living things work[1:54]
• Molly explains that the conversation will start from a simple idea about how living things-from bacteria to humans-do what they do, and that this idea made her rethink the mark we leave on the world.

Grad-school moment with burnt hand

Mashed potatoes accident as catalyst[2:17]
• As a grad student living in dorms, Narosha burned herself while making mashed potatoes and was struck by how quickly the signal to move her hand traveled through her body.
Wondering about signal speed in the body[2:38]
• She reflects on how the burn signal had to go up her arm, trigger changes, and come back down to move her hand, all in a split second, and finds that astonishing.

Classical view of protein interactions

Lock-and-key model of proteins and receptors[3:12]
• Narosha explains that proteins have specific shapes determining function, and receptors on cell surfaces also have shapes; traditional biology teaches that a protein (key) must physically fit into a receptor (lock) to induce signaling.
Host restates lock-and-key shorthand[3:37]
• Molly describes the shorthand as simply a lock and key coming together to make things happen in the cell, reflecting how it is commonly presented in education.

Why the lock-and-key story felt incomplete

Time and probability problem[4:30]
• Narosha says that imagining one specific molecule finding the perfect receptor so quickly felt "too easy" given the short time scales like one thousandth of a second.
Janitor with a big ring of keys analogy[4:25]
• She compares the situation to a janitor with a large key ring trying to find the right key for a lock in a very short time, having to iterate through many keys by random chance.
Crowded cell interior complicates encounters[4:42]
• Molly notes that the inside of a cell is full of thousands of proteins, trash, the nucleus, endoplasmic reticulum, and other structures between the lock and key, making random encounters even less likely.
Throwing keys at a lock metaphor[5:11]
• They liken the needed speed to a janitor throwing the entire key ring at the lock and somehow the right key finds its way into the lock across a cluttered space.
Conclusion that something is missing[5:40]
• Breaking interactions down this way led Narosha to feel that things were not adding up, suggesting to her that some additional mechanism must be inducing cellular signaling.

Challenging the professor and deciding to investigate

Questioning advanced immunology teacher[5:45]
• After class, she asked her advanced immunology professor how the lock-and-key model could work, pointing out time and probability issues, and he repeatedly answered that he didn't know but that this is how it works.
Motivation from "I don't know" answer[6:10]
• The professor's admission that he did not know how it worked was enough to push her to try to find out for herself, becoming the seed of her research direction.

Discovery that living cells emit light

Turning to physics and the idea of non-physical interactions

Looking for faster modes than physical contact[6:46]
• To fill the gap between chemistry and the observed speed of interactions, she wondered if non-physical interactions, rather than only physical collisions, could mediate signaling.
Tap-card vs mechanical key analogy[6:55]
• She compares the traditional model to an old-school lock and key and introduces an analogy of a tap-card access door, where a wireless signal opens the door much faster than inserting a key.
Identifying light as the fastest signal[7:27]
• She reasons that since light is the fastest known modality in the universe, it is a candidate for how cells might communicate quickly.

Finding historical evidence that biology emits light

Literature search and Gurvich's work[7:35]
• Researching whether anyone had asked similar questions led her to original papers showing that biological systems emit light.
Alexander Gurvich and onion root experiments[8:11]
• She describes how Russian biologist Alexander Gurvich, in the 1920s, while studying how onion roots grow, unexpectedly discovered that onion cells appeared to be making and releasing their own light.
First articulation of "biology emits light"[8:52]
• Narosha calls this the first instance where someone thought "biology emits light," marking the origin of this experimental idea.

All living cells glow faintly

Every cell in the body emits light[8:57]
• She states that every cell in the body-heart, liver, brain, cheek, skin, tongue, and more-gives off light, as do plants, shrimp, and "literally everything that is alive" so long as it can metabolize.
Why we can't see our own glow[9:27]
• Although Molly jokingly asks if she is glowing, Narosha explains that we cannot see this light because its intensity is extremely weak and must pass through tissue before reaching the outside.
Need for ultra-sensitive detection[10:29]
• To detect this emission from cells in a dish, researchers need an ultra-dark room and highly sensitive detectors capable of detecting single photons.

Metabolism, mitochondria, and light generation

Wavelength-specific emission tied to metabolism[10:01]
• She notes that different metabolic rates produce different wavelengths (colors) of light, so cells not only emit light but can emit different colors depending on metabolic state.
Hypothesis that mitochondria are main source[11:03]
• When asked about mechanism, Narosha says the common question is where the light comes from, and her hypothesis is that most of it comes from mitochondria.
Basic description of mitochondria[11:12]
• She describes mitochondria as kidney bean-shaped structures with folds, known as the powerhouse of the cell because they generate the energy underlying neurons firing, muscles contracting, and bodily functions.
Electron transport and light release[12:12]
• In mitochondria, molecules pass electrons along the inner folds; as electrons go from a high-energy to a low-energy state, they release energy in the form of light.
• Molly summarizes the idea as us giving off light because we are "doing fun things" with electrons, and Narosha reframes it simply as emitting light because we are alive.
Other possible light-generating mechanisms[12:12]
• She mentions additional hypotheses including buildup and release of charged particles and processes involving fatty acids, or combinations thereof, as possible contributors to cellular light.
Experimental link between electron chain and light[12:45]
• Her group is finding that interrupting the electron transport chain changes the emitted light; logically, if the electron does not complete its path, there should be no light, and their data are beginning to support this.

Quantifying photon emission from brain cells

Photon counts at rest vs activation[12:58]
• In experiments with a dish containing about one million rat brain cells, they measure around 100 photons per second when the cells are at rest and 1,000 to 2,000 photons per second when the neurons are activated.
Fireworks imagery for mitochondrial light[13:50]
• Molly imagines mitochondria as constantly releasing fireworks, likening it to a post-baseball game Fourth of July show, and Narosha agrees that this imagery is "probably accurate" for the light emission.

Scientific resistance and evolving acceptance

Backlash at early conference presentation[14:25]
• About ten years prior, as a graduate student, when she first presented this work at a conference, she was told by critics that the signals were noise, not science, and warned she would jeopardize her career if she pursued it.
Shift from denial to seeing light as noise[14:46]
• She notes that within the last decade, multiple groups worldwide have joined this research area, and the field has moved from denying biological light emission to accepting that it exists but often dismissing it as meaningless noise.
Current research question: Is the light meaningful?[15:27]
• Her current focus is testing whether the light generated by mitochondria carries information that cells can use to perform their functions, i.e., whether it is purposeful and utilized by the body.

Interactions with external light and internal photons

Considering sunlight and physiology

Bath of light from the sun[15:46]
• Before fully tackling internal light, she asks what the constant bath of light from the sun does to our physiology, given that internal and external photons are fundamentally the same.
Opsins and circadian rhythms[16:21]
• She points to opsin proteins in the eyes that absorb specific wavelengths of light and help regulate circadian rhythms as a clear example of light interacting with biology.
Vitamin D synthesis in the skin[16:47]
• She cites vitamin D synthesis as another well-known interaction: precursors in the skin absorb certain wavelengths from the sun, change shape, and become usable vitamin D, which Molly likens to a plant-like behavior.

Additional light-absorbing components in the body

Light receptors beyond the eyes[17:36]
• Narosha says there are light receptors in the brain despite its darkness, and also mentions melanocytes and hemoglobin as examples of pigment-containing molecules that absorb light.
Evolution with the sun and widespread absorption[17:32]
• Because organisms have evolved with sunlight for a long time, many cellular elements have inherent abilities to absorb light, and more such interactions are being discovered as people look for them.

Could internal light be re-absorbed and used?

Hypothesis that internal photons are absorbed[18:17]
• Molly asks whether light coming from inside cells could also be absorbed; Narosha responds "absolutely" and states her hypothesis that cell-generated light is purposeful, though she emphasizes they lack strong evidence so far.
Acknowledging theoretical nature and open questions[18:40]
• They emphasize that beyond the revelation that biological material emits light, the questions of how, why, when, and what it means remain to be determined and represent "next steps" in the research.

Guiding photons inside cells and in the brain

From fireworks to possibly guided light

Question of how light could travel purposefully[21:54]
• Molly asks if the cellular fireworks might actually behave more like a laser, and how light would get from point A to point B inside a cell if it carries information.
Photon scattering vs directed signaling[22:21]
• Narosha notes that photons naturally scatter rather than choosing a direction, so if the light is purposeful it needs guidance rather than exploding randomly.

Cytoskeleton and microtubules as potential waveguides

Introducing the cytoskeleton and microtubules[22:58]
• She defines the cytoskeleton as the cell's scaffold, made of various proteins, and focuses on microtubules, which are long rod-like structures that help form the cell's shape.
Mitochondria proximity to microtubules[23:44]
• In cellular images, mitochondria are seen very close to cytoskeletal rods; mitochondria attach to microtubules and are moved along them like on train tracks by proteins called kinesins and dyneins.
Hypothesis of microtubules as biological fiber optics[24:31]
• Because of this proximity, she hypothesizes that light emitted by mitochondria could be absorbed by microtubules and propagated along them, similar to how fiber-optic cables guide light.
Current experiments on photon guidance[24:46]
• Her team is conducting experiments to test whether microtubules indeed function as biological fiber-optic cables for photons inside cells.

Evidence that neural light is non-random

Link between neural activity and light[24:56]
• Although they are still working on direct proof of guided A-to-B photon travel, she says they have strong evidence that light generated by neural cells is not random but is tied to purposeful neuron activity.
White matter as potential photon carrier[26:16]
• She notes that the white matter (axons) connecting brain regions can carry photons and suggests bundles of nerves might act like fiber-optic cables, similar to telecommunications systems that carry information via light pulses.
Speculation about thoughts and consciousness[26:55]
• She speculates that thoughts might be transported as light and that photons could be involved in helping us understand consciousness, framing this as a far-ahead but intriguing possibility.

Biophotons as biomarkers and tools for cancer detection

Using photons to discriminate tissues

Photons as photonic biomarkers[26:52]
• Regardless of whether internal light is biologically purposeful, she and other researchers are exploring whether photon emissions can serve as biomarkers to distinguish hearts, tumors, kidneys, and other tissues.

Targeting cancer via mitochondrial light signatures

Cancer's dysfunctional mitochondria[28:07]
• She notes that cancer cells have dysfunctional or non-normal mitochondria, which should alter their light emission compared to healthy cells.
Goal of detecting cancer at inception via photons[28:26]
• Her vision is that if early metabolic changes can be picked up through photon signatures, cancer could be detected at its inception, rather than waiting for sufficient mutations and mass to be visible as a tumor.
Demonstrated differences in light signatures[28:54]
• In their published work, they have shown that cancer cells and non-cancer cells have distinct light signatures, enabling discrimination between them.

Animal experiments detecting early melanoma

Rat melanoma injection model[29:19]
• In experiments, they inject melanoma cells under the skin of rats and then use detectors to measure photon emissions from animals that were injected versus controls.
Day-one detection in double-blind setup[29:25]
• In a double-blind procedure where a grad student measured animals without knowing which had been injected, they could tell within one day of injection that an animal had cancer based solely on its photon emission.
Diagnostic utility even if biologically purposeless[29:49]
• Molly emphasizes that even if biophotons were not purposeful within the body, they could still be diagnostically useful, and Narosha agrees.

Life, death, and the temporal dynamics of light

Universal photon emission and alive-vs-dead signatures

Every examined cell emits photons[30:07]
• After listing brain, tumor, and normal cells, Molly recaps that all the cell types they've looked at emit photons, and Narosha confirms this.
Distinguishing alive vs dead animals by photons[30:12]
• She mentions a published paper showing that researchers can tell when an animal is alive or dead just by looking at its photon signatures, which dissipate after death.

Open questions: When does the light start and stop?

Dissipation of photon signatures at death[30:22]
• In the alive-vs-dead study she cites, the photon signal clearly dissipated after the animal died, but that work did not pinpoint exactly when during the dying process the glow ended.
Curiosity about timing of glow cessation[30:56]
• She agrees it would be very interesting to know at what timescale the signature ends-"when does the glow stop when you're dead"-but says that has not yet been determined.

Reports of a "death flash" and speculative explanation

Anecdotal reports from surgeons and hospice nurses[30:59]
• She recounts learning at a consciousness conference about a cardiothoracic surgeon and OR staff reporting a sudden flash of light at the moment of death or when stopping/starting a heart, and says hospice nurses have also anecdotally mentioned a similar "death flash."
Lack of experimental evidence for death flash[31:01]
• When Molly asks if there is experimental evidence, she responds that she does not know of any and acknowledges confounds like bright OR lights.
Hypothesis: Energy release when biological order collapses[32:01]
• Narosha speculates that when things die, electrons that are no longer being passed along proteins must go somewhere, and as high-energy electrons dissipate, they may release light as they return to purely physical, non-organized states.
• She describes this as the system "going back to physics" when biological organization is lost, and likens the resulting energy release to fireworks.

Reframing cells as energetic bodies

Organization of energy by biomolecules[32:24]
• She argues that cell membranes and internal biomolecules organize energy into meaningful processes, and that viewing cells as energetic bodies makes the physical dimension of biology more intuitive.

The "life flash" at fertilization

Video of calcium influx at sperm-egg fusion[33:07]
• Narosha mentions a video depicting a "life flash" when a sperm enters an egg, showing a huge calcium influx and a visible flash at fertilization.
Host's reaction to the fertilization flash video[33:28]
• Molly searches for and watches the video, describing an egg with a sperm at the edge followed by an explosion or flash propagating over the surface, which she finds striking.

Personal reflection on hospice and energetic "salute"

Connecting the science to her father's impending death[34:08]
• Molly shares that after the interview she will travel to South Carolina where her father is in hospice near the end of his life, and that this makes her wonder what is unfolding at death.
Idea of a final energetic signal[34:42]
• She says she does not expect to literally see a flash but is moved by the notion of a final, perhaps invisible, light signal as a "signature" or "final salute" from a person as their patterned energy returns to be transformed into something else.

Closing, fact-check clarification, and dedication

Guest affiliation and availability

Where to find Narosha[35:44]
• Molly thanks "Narosha Marugan" and notes that listeners can find her at Wilfrid Laurier University in Canada.

Clarification about the fertilization flash video

Fluorescent dye vs biophotons[36:08]
• She explains that in the widely shared life-flash video, the big visible flash is from a fluorescent dye added by researchers to make the event visible, and that beneath that dye is a very quiet, gentle light.

Dedication to Molly's father

Emotional closing and personal note[36:00]
• Molly dedicates the episode to her dad, saying she did not see a flash of light when he died but certainly felt one, and thanks him for always listening.

Radiolab staff credits and support

Show creators and editors[37:12]
• A staff member on a fishing boat in Alaska reads credits, stating that Radiolab was created by Jad Abumrad and is edited by Soren Wheeler, with co-hosts Lulu Miller and Latif Nasser and director of sound design Dylan Keefe.
Production staff and fact-checkers[37:39]
• They list numerous staff producers, contributors, and fact-checkers, including that this particular episode was fact-checked by Natalie Middleton.
Foundational support acknowledgments[37:58]
• They mention leadership and foundational support for Radiolab's science programming from organizations including the Simons Foundation, the John Templeton Foundation, and the Alfred P. Sloan Foundation.

Lessons Learned

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

1

Questioning widely accepted models, especially when their timing or probabilities don't add up, can open up entirely new lines of inquiry and innovation.

Reflection Questions:

  • • Where in my work or life am I accepting an explanation that feels incomplete simply because it's the standard story everyone repeats?
  • • How could I more systematically examine the time scales, probabilities, or constraints of a process I take for granted to see if something is missing?
  • • What is one "this is just how it works" assumption I could investigate or test more deeply over the next month?
2

Bringing together insights from different disciplines, like biology and physics, can reveal mechanisms and opportunities that are invisible when you stay inside a single field.

Reflection Questions:

  • • What adjacent field or discipline could shed new light on a problem I'm currently stuck on?
  • • How might talking to someone with a very different training background change the way I frame or tackle my biggest challenge right now?
  • • When in the coming weeks can I carve out time to learn the basic concepts of a neighboring field that intersects with my interests?
3

Even if a phenomenon seems like "noise" or an irrelevant byproduct, it can still become a powerful signal or diagnostic tool once you learn how to measure and interpret it.

Reflection Questions:

  • • What data, feedback, or side effects in my environment am I currently treating as noise that might actually contain useful information?
  • • How could I design a simple way to track or quantify one of these "background" signals to see if it correlates with outcomes I care about?
  • • What is one area of my work where reframing side effects or byproducts as potential indicators could improve my decisions?
4

Viewing living systems as organized patterns of energy rather than just static structures can shift how you think about change, resilience, and beginnings and endings.

Reflection Questions:

  • • How would my attitude toward personal change shift if I saw myself more as a changing pattern of energy than as a fixed identity?
  • • In what situations do I cling to rigid structures instead of asking how the underlying energy or dynamics could be reorganized more effectively?
  • • What is one transition (a start or an ending) in my life right now that I could reinterpret through the lens of energy being redistributed rather than simply lost?
5

Working at the frontier of knowledge often means tolerating uncertainty and social resistance while still grounding your work in careful measurement and testable hypotheses.

Reflection Questions:

  • • Where am I avoiding a promising but uncertain path because I fear skepticism or backlash from others?
  • • How can I better balance bold hypotheses with rigorous testing so that I can explore new ideas without drifting into speculation?
  • • What is one small, concrete experiment I could run in the next few weeks to probe an unconventional idea I care about?

Episode Summary - Notes by Finley

The Spark of Life
0:00 0:00