Testing alternate cosmology using a cloud of atoms

While direct experimentation with the Universe remains beyond our reach, scientists have devised a method to replicate its early conditions. At the Kirchhoff-Institut für Physik in Germany, researchers have constructed a tabletop quantum field simulation mimicking the post-Big Bang Universe. This simulation involves manipulating a sample of potassium-39 atoms near absolute zero using magnets and lasers. By employing equations, they extrapolate findings at this miniature scale to explore potential characteristics of the early Universe.

Preliminary results indicate the feasibility of simulating a Universe with varied curvatures. In a positively curved Universe, traversing any direction in a straight line leads back to the starting point, while a negatively curved Universe exhibits a saddle-shaped space. Marius Sparn, a PhD student at Kirchhoff-Institut für Physik, notes that the current Universe is essentially flat or nearly flat. However, during its initial stages, it could have possessed a more positively or negatively curved configuration.

Navigating the Curvature

Sabine Hossenfelder, a member of the Munich Center for Mathematical Philosophy, ponders the philosophical implications of observing a fraction of a vast sphere like Earth. The curvature of this unseen part becomes a philosophical inquiry, given that our knowledge is limited to the observable Universe. The prevailing assumption is that, within our observed portion, the curvature aligns with zero.

In November 2022, Marius Sparn, a collaborator on the research paper "Quantum Field Simulator for Dynamics in Curved Spacetime," explored three early Universe expansion scenarios—constant, accelerated, and decelerated. The interdisciplinary team, spanning Belgium, Spain, and Germany, conducted a tabletop experiment manipulating potassium-39 in a two-dimensional layer using magnetic coils and lasers.

Cooled to 40 to 60 nanokelvins, the potassium-39 enters a quantum state known as a Bose-Einstein condensate, behaving as a single mega particle. Small density fluctuations, akin to ripples, are then probed for insights into quantum mechanics. Each experiment concludes with capturing absorption images, revealing density distributions and enabling statistical analysis.

The Alternate Universes

By integrating equations for the Universe and the Bose-Einstein condensate, the team simulated positive curvature by adjusting potassium-39 density outward and negative curvature by reducing it. Sparn affirms the feasibility of simulating spatially curved and expanding spacetime in a Bose-Einstein condensate, a valuable approach for understanding a homogeneous and isotropic universe on large scales. This interdisciplinary exploration bridges atomic physics and astrophysics, illustrating the evolving connection between quantum atomic systems and complex cosmic structures.

Published in Nature DOI: 10.1038/s41586-022-05313-9

Kat Friedrich is a former mechanical engineer who started out as an applied mathematics, engineering, and physics major at the University of Wisconsin-Madison. She has completed a graduate degree focusing on science and environmental journalism and has edited seven news publications, two of which she co-founded. She is the editor in chief of the energy magazine Solar Today.