Quarks Collisions and the Fate of the Universe: A Royal Institution Talk by Kate Shaw

In this Royal Institution talk, Kate Shaw outlines how collider physics reveals the fundamental particles that compose matter, the role of the Higgs field in giving them mass, and the profound question of the universe’s fate. She weaves history, experiment, and future plans into a narrative about quarks, Higgs bosons, and the fate of reality itself.

• Protons are collided at the Large Hadron Collider to explore the fundamental particles and forces.
• Quarks, gluons, and confinement explain why protons and neutrons are built from a sea of particles inside them.
• The Higgs boson and top quark connect the mass of particles to the structure of the vacuum and the stability of the universe.
• Future plans like the High-Luminosity LHC and the Future Circular Collider aim to refine measurements and probe new physics.

Introduction: What are quarks and colliders

Kate Shaw begins by describing the Large Hadron Collider (LHC) as a machine that accelerates protons to velocities approaching the speed of light and smashes them together deep underground. The goal is to recreate conditions similar to the Big Bang and to study the fundamental constituents of matter. The talk emphasizes the practicalities of the accelerator, including superconducting magnets kept at cryogenic temperatures around 1.9 Kelvin, and the scale of the collisions which produce showers of particles known as jets.

From atoms to quarks: a historical journey

The narrative then traces the development from the early atomic model to the discovery of subatomic particles. Rutherford’s gold foil experiments overturned the plum pudding model and revealed a concentrated nucleus. The talk then surveys the emergence of quarks as the basic building blocks of hadrons, simplifying the understanding of protons, neutrons, pions, and kaons. The Standard Model is introduced as a framework organizing these particles into families and generations.

Quarks, hadrons, and confinement

Quarks come in flavors such as up and down, and they must exist in groups of three (baryons) or a quark–antiquark pair (mesons). Gluons, the carriers of the strong force, bind quarks together. A vivid metaphor compares the strong force to a stretched spring that grows stronger as quarks separate, making isolation of a single quark impossible—a phenomenon known as confinement. The internal structure of protons includes a sea of quark–antiquark pairs and gluons constantly fluctuating inside the bound state.

Collision outcomes: jets, Higgs, and tops

When protons collide, a variety of particles can emerge, including Higgs bosons and heavy quarks. The speaker explains how jets—collimated sprays of particles—are used to study the underlying quarks and gluons. A representative Atlas event shows a Higgs decaying to bottom quarks while other products (like W bosons or neutrinos) appear as distinctive signatures in detectors. The top quark is introduced as the heaviest known fundamental particle, with a very short lifetime that prevents hadronization and enables direct study of the bare quark.

Higgs, top quark, and the fate of the vacuum

The talk then connects the Higgs boson to the mechanism that endows particles with mass. It explains how the Higgs field pervades all space and how interactions with this field yield particle masses. The mass of the top quark, together with the Higgs mass, constrains the Higgs potential and the stability of our universe. A visual plot shows regions of stability and metastability for the vacuum, suggesting that our universe may presently be in a metastable state but not in immediate danger of decay. The concepts of quantum tunneling and the role of the Higgs potential in setting the ground state of the universe are discussed with careful caveats about timescales and energy scales involved.

Future directions: HL-LHC and FCC

The final sections look ahead to the next generation of accelerators. Upgrades to the LHC will increase luminosity, enabling more precise measurements of the Higgs self-coupling and heavier states. Beyond that, the Future Circular Collider (FCC) envisions a 100-kilometer tunnel to explore even higher energies and to search for new particles that could alter the Higgs–top mass relationship and potentially stabilize the vacuum. The talk emphasizes the synergy between experimental advances, theoretical developments, and the broader quest to understand dark matter, dark energy, gravity in a quantum framework, and the nature of matter itself.

Conclusion: curiosity with credibility

Shaw reiterates that the pursuit of fundamental physics is a long-term, collaborative enterprise combining big machines, small particles, and careful reasoning. The FCC is framed as a bold step toward a deeper, more complete picture of the universe while acknowledging that current findings point to a metastable vacuum rather than an imminent catastrophe. The talk leaves the audience contemplating how future discoveries may reshape our understanding of reality.