---
title: "Exchange Particles and Reading a Feynman Diagram"
description: "Every interaction between particles is carried by an exchanged boson, and which boson it is decides the range and the timescale. A Feynman diagram is the bookkeeping for that exchange, with the vertic"
canonical: https://lightmysky.com/learn/science/exchange-particles-and-reading-a-feynman-diagram-mt_7Ka5cVpTVL
source: https://lightmysky.com/learn/science/exchange-particles-and-reading-a-feynman-diagram-mt_7Ka5cVpTVL.md
retrieved: 2026-09-12
---

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# Exchange Particles and Reading a Feynman Diagram

Every interaction between particles is carried by an exchanged boson, and which boson it is decides the range and the timescale. A Feynman diagram is the bookkeeping for that exchange, with the vertices doing the conserving and the internal line naming the force.

Subject: Science · Area: Matter & Materials · Ages 17 to 18
Page: https://lightmysky.com/learn/science/exchange-particles-and-reading-a-feynman-diagram-mt_7Ka5cVpTVL

## Ready when they can

- Names the exchange particle for each of the four interactions and links its mass to the range of the force
- Draws the diagram for beta-minus decay, beta-plus decay and electron capture, with the W labelled and the arrows right
- Checks charge, baryon number and lepton number at each vertex of a diagram they did not draw

## Lesson: The messengers between particles

Every interaction is carried by an exchanged boson, and which boson it is decides the range. The photon carries electromagnetism, the gluon carries the strong force, the W and Z carry the weak force, and the graviton for gravity stays hypothetical. Heavy carriers can borrow their energy for only a tiny moment, so they travel almost no distance, while the massless photon has unlimited range.

Beta-minus decay shows the bookkeeping in action. Time runs upward and a W boson leaves the vertex, turning a down quark into an up quark, while the W becomes an electron plus an antineutrino. Arrows carry meaning too: an arrow pointing backward in time is an antiparticle moving forward, with its charges flipped.

At every vertex you audit three small account books: charge, baryon number, and lepton number. Each total going in must equal the total coming out, and that rule alone kills most impossible diagrams. Electron capture uses the same exchange: an atomic electron joins a proton to make a neutron plus a neutrino, with a W doing the carrying.

**Tip.** To tell electron capture from beta-plus decay, look at the start: capture pulls an atomic electron into a proton, while beta-plus emits from the nucleus. Both balance the same three books through a W.

**Recap.** Bosons carry each force, vertices balance three books, and the W runs beta decay.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Particles, Antiparticles and Annihilation](https://lightmysky.com/learn/science/particles-antiparticles-and-annihilation-mt_-Ud20HRNJz)
- [Quarks, Leptons and the Conservation Laws](https://lightmysky.com/learn/science/quarks-leptons-and-the-conservation-laws-mt_kCGc5Neub_)

## Opens up

- [The Standard Model and the Four Interactions](https://lightmysky.com/learn/science/the-standard-model-and-the-four-interactions-mt_GYB4UMS0D9)