A sheet of paper stretches rapidly in all directions. On it are drawn tiny arrow-particles, and the stretching makes them move and interact differently than they would on a stationary table. That's roughly how space behaves in an expanding universe, where curvature isn't just an abstraction but a real factor influencing the very foundations of matter.
In this new study, physicists examined what happens to a charged Standard Model fermion (a particle like an electron) in such a stretching space when a uniform magnetic field passes through it. Normally, in a strong magnetic field, even massless fermions can acquire mass — an effect known as magnetic catalysis. It's similar to how passengers in a crowded bus, pressed together, start moving in a coordinated way, forming a stable group. Here, particles and antiparticles, squeezed by the magnetic field, form pairs that behave like massive particles.
However, in an expanding universe, where space has curvature, the picture changes. Curvature acts like a stretching force that prevents particles from staying together. If the magnetic field tries to 'glue' particles into a massive state, the expansion of space pulls them apart. The authors found that for sufficiently large curvature, magnetic catalysis completely disappears — dark energy wins, and the symmetry (the property of particles being massless) is restored. This is like trying to assemble a puzzle on a rubber mat: the more you stretch the mat, the harder it is to keep the pieces together.
This dance between the magnetic field and the curvature of space determines the phase structure of the vacuum: at low curvature, a massive phase prevails, and at high curvature, a massless one. This isn't just theory: understanding these processes sheds light on how, in the first moments after the big bang, particles acquired their properties. That same sheet of paper from the beginning, as it stretches, prevents the arrows from sticking together, and it's this very struggle that paints the picture of mass being born in our world.
In strong magnetic fields, like those near neutron stars, the electron's mass can effectively increase by hundreds of times, but only in terms of its behavior in matter, not in the sense of its true rest mass.
In Peter Watts's novel Blindsight, alien creatures use magnetic fields to manipulate matter at the quantum level — much like in this work, where field and space battle over particle mass.