Were my atoms once your atoms?

Episode Summary

Executive Summary: This episode of Crowd Science explores the likelihood that atoms in our bodies have been used in other people's bodies. Through expert interviews and calculations, it concludes that due to the vast number of atoms on Earth and their constant recycling, each person likely shares about a billion atoms with every human who has ever lived. The discussion also touches on philosophical questions of identity, emphasizing that while atoms are shared, the unique organization of molecules, cells, and consciousness defines individuality.

Main Topics: Atomic Recycling and Human Connection (Priority: 5/5): Explores how atoms are constantly recycled through the environment, including the atmosphere, food, and water, leading to shared atomic composition among all humans. Quantifying Atoms on Earth and in Humans (Priority: 4/5): Calculates the number of atoms available for recycling (1.3 × 10^48) and the number in a human body (10^27), using approximations and expert input. Historical Human Population and Lifespan (Priority: 4/5): Estimates that 108 billion humans have ever lived, with an average lifespan of 25 years, providing context for the scale of atomic recycling. Cell Turnover and Atom Exchange (Priority: 3/5): Discusses how cells in the body turn over at different rates, with 98% of atoms replaced annually, contributing to the mixing of atoms between individuals. Philosophical Implications of Shared Atoms (Priority: 3/5): Examines whether shared atoms affect personal identity, concluding that identity arises from higher-level organization, not just atomic composition. Breath as a Medium of Atomic Exchange (Priority: 4/5): Highlights that each breath contains atoms from other people, with about one atom per breath from any historical figure, illustrating immediate atomic connection.

Key Arguments: Atoms on Earth are constantly recycled through geological and biological processes, making them available for reuse in living organisms. The number of atoms available for recycling (1.3 × 10^48) vastly exceeds the number used by all humans (108 billion × 10^27 atoms each), but the turnover rate ensures mixing. Geometric series calculations show that it is 100% likely that any given atom in a human body has been in another human. Personal identity is not determined by atoms alone but by the unique organization of molecules, cells, and consciousness. The atmosphere mixes atoms globally, so each breath contains atoms from every person who has ever lived.

Data Points: Total atoms on Earth: 1.3 × 10^50 - Estimated by Jefferson Lab, used as starting point for calculations. Atoms available for recycling: 1.3 × 10^48 - Approximately 1% of Earth's atoms, based on top 5 km of crust and atmosphere. Atoms in a human body: 10^27 - Approximation for a 100 kg human, simplified as mostly water. Annual atom turnover rate: 98% - Based on a 1953 study using radioactive tracers. Total humans ever lived: 108 billion - Estimate from Population Reference Bureau, from 50,000 years ago to present. Average human lifespan historically: 25 years - Based on hunter-gatherer data, skewed by high infant mortality. Atoms per breath: 10^19 - Number of atoms inhaled or exhaled in a typical breath. Shared atoms with every person: 1 billion - Estimated number of atoms in a person that have been in any other human.

Pivotal Quotes: "You share probably about a billion atoms with every person that's ever lived on Earth, about a billion atoms that have been in someone else are now in you." — Ethan Siegel: Explaining the result of atomic mixing through breathing and environmental cycles. "What makes me are different level of organizations of reality. That goes well beyond what philosophers would call the myological sums of atoms, just a bunch of atoms." — Michaela Massami: Arguing that identity is not reducible to atoms but to higher-level structures. "I quite like how nice it is that you can hug the entire world, not anatomically, but atomically, by just taking a deep breath." — Marnie Chesterton: Reflecting on the comforting idea of atomic connection despite physical distance.

Implications: Listeners gain a profound sense of interconnectedness with all humanity and the environment. The findings challenge notions of individuality at the atomic level, while reinforcing that identity emerges from complex organization. This may foster greater empathy and environmental awareness.