Speculative physics: without the strong force

Problem

Imagine that the strong nuclear force suddenly vanished throughout the Universe. What would happen to the nuclei of the ordinary matter around us? Consider in particular what would become of the protons and neutrons bound in nuclei, and what effects would be observed in terms of light and heat produced. Justify the answer with the balance of forces inside the nucleus.

Solution

What holds the nucleus together. Inside a nucleus, protons (positively charged) and neutrons coexist. The protons repel each other via the Coulomb force, but at distances of the order of a femtometre the strong nuclear force, attractive and intense, prevails over this repulsion and keeps the nucleus compact. It is a balance: attractive strong force against repulsive Coulomb force.

What happens if we remove the strong force. Without the strong force, nothing would any longer counter the electric repulsion between protons. Every nucleus with more than one proton would fragment instantaneously: the protons would fly apart violently, driven by Coulomb repulsion. The only exception would be hydrogen-1, whose nucleus is a single proton and therefore has nothing to hold together.

Effects on light and heat. The Coulomb potential energy stored in every nucleus would all be released at once as kinetic energy of the fragments. On a macroscopic scale, ordinary matter would turn into an incandescent plasma of protons and electrons, with a huge release of energy: an intense flash of $\gamma$ rays, light and heat. The free neutrons, no longer bound, would then decay via the weak interaction.

Chemical consequence. Stable nuclei with $Z > 1$ would no longer exist: chemistry as we know it would cease to exist, because atoms and molecules require cohesive nuclei.

$\ev{\text{immediate Coulomb fragmentation: incandescent plasma} + \gamma \text{ flash}}$

Connections

Topics: Nuclear physics Skills: Analysis of limiting cases and speculative physics Objects: Atomic nucleus