Lightning Started: From Ben Franklin to Runaway Electrons and Cosmic Rays

In this Quanta Magazine podcast, Hannah Waters talks with Charlie Wood about the ongoing mystery of how lightning begins. The discussion traverses Ben Franklin’s early electricity experiments, the role of point-like sharp features in clouds, gamma ray emissions from storms, and cutting edge models that involve runaway electrons and cosmic ray showers. The hosts compare competing theories and highlight recent field evidence that supports complex, multi-scale physics behind lightning.

• Lightning initiation remains an active area of research with multiple competing mechanisms.
• Sharp points and ice crystals in clouds can dramatically enhance electric fields, potentially triggering avalanches.
• Energetic gamma rays and runaway electrons may arise from cloud processes, not just simple electrical breakdown.
• Observational campaigns and simulations are converging on a nuanced picture in which several mechanisms may cooperate.

Introduction: The Wonder and the Open Question

The podcast begins with a celebration of the spectacle of lightning and a clear statement of the central mystery: how does a spark start in a storm cloud? Hannah Waters interviews Charlie Wood, Quanta Magazine’s physics reporter, who describes lightning as much more than a big static discharge. The conversation frames the problem as a progression from historical intuition to modern, high-energy physics, and sets up the core idea: the initiation of lightning likely involves extreme, high-energy subatomic processes that are not part of everyday cloud dynamics.

Lightning Fundamentals: Plasma, Avalanches, and Field Thresholds

Charlie explains what a lightning bolt is at the microscopic level: a plasma channel formed by an electron avalanche that propagates through air, heating it to white-hot temperatures and driving the thunder that accompanies it. A key puzzle is the electric field needed to start avalanching. Traditional lab analogies use sharp conductors to initiate sparks, but measurements in clouds show fields far weaker than the commonly cited threshold of about 3 million volts per meter. This gap motivates further theory about how initiation could occur in real storms, including the role of pointed ice particles and microphysical cloud processes that intensify fields locally.

Power of Points: How Clouds Could Reach Breakthrough Conditions

The discussion turns to the “power of points” idea that Ben Franklin helped popularize. Pointed objects concentrate electric fields, and in clouds, sharp ice fragments could act like lightning rods. The ice particles, ranging from tiny spheres to centimeters-long shards, could locally amplify fields by roughly an order of magnitude, potentially bridging the gap to avalanche conditions. The host and guest discuss the dynamic and chaotic nature of clouds, where icy microstructures interact with the overall charged environment to create regions of enhanced field strength sufficient to spark breakdowns.

Beyond Initiation: Gamma Rays and Energetic Feedback in Clouds

Shifting from initiation to the high-energy aftermath, the podcast discusses satellites that detected gamma rays emanating from storms. Gamma rays are produced when electrons accelerate and emit high-energy photons, and under certain circumstances, those photons can produce additional electrons and positrons, which in turn drive further radiation and ionization in a feedback loop. This leads to the idea that subatomic processes inside clouds can generate bright gamma-ray flashes that satellites can observe, linking lightning physics to accelerator-like phenomena in the atmosphere.

Dwyer’s Runaway Electron Model and the Aloft Evidence

Joseph Dwyer’s model is highlighted: runaway electrons — electrons accelerated to near-light speeds — can seed a cascading avalanche that amplifies gamma-ray production. The model includes an amplification mechanism with gamma-ray photons undergoing pair production, creating a self-reinforcing loop of electrons, positrons, and further gamma rays. The podcast recounts the Aloft campaign, a NASA high-altitude research effort that observed gamma-ray activity in storms from near space. The Aloft data, particularly flickering gamma-ray emissions, align closely with Dwyer’s simulations, providing strong field observations to support the idea that gamma rays originate from atmospheric particle cascades rather than solely from large-scale electrical discharges.

Competing Theories: Ice Crystals, Cosmic Rays, and Hybrid Scenarios

The conversation outlines alternative theories, including the ice crystal theory where specific cloud microphysics could prime the field, and a cosmic ray shower theory in which external high-energy particles seed atmospheric breakdown. The ice-crystal theory faces challenges in producing sufficiently strong conditions universally, while the cosmic-ray theory offers an external driver for initiation. The guest emphasizes that current evidence does not deliver a final verdict; rather, the most probable picture may be a mosaic in which multiple pathways contribute to different lightning events depending on location and weather conditions.

Cosmic Ray Link and Deep Space Weather Connections

An especially striking idea is the cosmic ray shower theory, which connects deep space events to terrestrial lightning. A cosmic ray shower from a distant supernova could pepper the upper atmosphere with high-energy particles that seed breakdown when they interact with cloud particles. The panel notes some supportive radio and imaging evidence, including a study showing bolt initiation angles not perfectly aligned with the local electric field, which could hint at an external or angled trigger. While intriguing, this theory remains one of several plausible mechanisms under discussion.

Toward a Unified View: Mixtures, Geography, and Future Tests

The podcast concludes with a cautious synthesis: it is plausible that lightning initiation is not a single, universal mechanism but a mixture whose prevalence varies by region, storm type, and environmental conditions. The host and guest discuss the value of combining laboratory experiments, cloud-scale simulations, and field campaigns to identify how often each mechanism dominates in different contexts. They also reflect on the beauty of lightning as a cross-cutting problem in physics that engages relativity, quantum field theory, and classical electromagnetism within a single atmospheric phenomenon.

Closing: A Look Ahead

The episode closes with a light note offering a media recommendation and a Beethoven movement as a reflection on the thunderstorm theme. The conversation reinforces the sense that our understanding of lightning is evolving, revealing a richer, more interconnected physical picture than the venerable Ben Franklin ever imagined.