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5 min readGravity's Missing Particle
Between the Earth and the Moon, every second, something like a trillion trillion trillion trillion trillion gravitons are being exchanged. That's a one followed by sixty zeros. And those particles are responsible for the gravitational pull that keeps the Moon in orbit. Yet if you wanted to detect a single graviton, you would need a detector with the mass of Jupiter—and even then, you might catch only one in the entire age of the universe.
Marcus Chown, former radio astronomer at Caltech and now a science writer, joined Dr. Karl to explain why the graviton—the hypothetical force-carrying particle of gravity—is both fundamental to our understanding of physics and almost certainly impossible to detect.
The Four Forces and Their Particles
Physicists have identified four fundamental forces that govern everything in the universe. Three of them—the electromagnetic force, the strong nuclear force, and the weak nuclear force—have been successfully described using quantum theory. This means they arise from the exchange of force-carrying particles, a concept Chown illustrated with a tennis analogy: two players whacking a ball back and forth, each recoiling from the impact. The ball is the force carrier.
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What you'll learn
- 1 (00:00) **Episode Introduction** - Dr. Karl introduces the topic: detecting the graviton, a particle so elusive it would require a detector bigger than Jupiter.
- 2 (00:32) **Marcus Chown’s Background** - Former radio astronomer at Caltech discusses his path from astrophysics to science writing.
- 3 (01:11) **The Graviton Problem** - A fundamental, poorly understood particle that may be impossible to detect, raising a philosophical question about its existence.
- 4 (01:39) **Gravitational Waves as Precedent** - Einstein proposed them in 1915; detection took a century and measured a change of 1/10,000th of a proton width, winning Nobel Prizes.
- 5 (03:10) **The Four Fundamental Forces** - Gravity, electromagnetism, strong nuclear, and weak nuclear forces are described, with gravity being the only one not yet quantized.
- 6 (04:02) **Force Carriers Explained** - Forces arise from exchanging particles (like tennis balls); the photon carries electromagnetism, gluons carry the strong force.
- 7 (07:38) **The Weak Nuclear Force** - It changes particle types, not glues things together; it makes sunlight possible by allowing protons to fuse over billions of years, and enables supernovae.
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Show Notes
Science writer and former astrophysicist Marcus Chown joins us to discuss the elusive graviton - the theoretical particle behind gravity.
In this chat we dig into the four fundamental forces of nature, why gravity is so uniquely hard to pin down, and why detecting a graviton would require a detector larger than Jupiter. Marcus also unpacks string theory, the only framework that manages to fold gravity in with the other forces, and why it's fallen out of favour with much of the physics community.
www.marcuschown.com/
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