Bose-Einstein Condensate Mimics Expanding Universe, Amplifying Phonon Waves

The behaviour of sound waves within exotic states of matter offers surprising insights into fundamental physics, and recent research explores this connection by recreating aspects of the universe within a Bose-Einstein condensate. J. Austin Chunn from Harding University, Ruotong Zhai and Daniel E. Sheehy from Louisiana State University, and their colleagues investigate how sound waves, known as phonons, propagate through a specially shaped condensate that mimics the curved spacetime of an expanding universe. This innovative approach allows researchers to observe the dynamics of these phonons as if they are travelling through a cosmos governed by the same principles as our own, revealing how sudden expansions create ripples and even generate new sound waves from seemingly empty space. The findings represent a significant step towards understanding the very early universe and the origins of cosmic structure, offering a novel laboratory for testing theories about the Big Bang.

The team creates a curved spacetime within the condensate, analogous to the Friedmann-Lemaître-Robertson-Walker (FLRW) metric, which describes the geometry of the expanding universe. Their investigations reveal that sudden changes in the expansion rate generate ripples in wave motion, representing distortions in spacetime itself. Furthermore, the research demonstrates that these changes also lead to the creation of new particles from the quantum vacuum, a phenomenon known as vacuum amplification. This process, where quantum fluctuations become real particles, is quantified and linked directly to the expansion of the simulated universe, building on the field of analog gravity which aims to recreate astrophysical processes in a controlled laboratory environment.

Simulated Universe Ripples Mirror Early Cosmos

Researchers have successfully created a system that simulates the expansion of the universe using a Bose-Einstein condensate, allowing them to study wave behaviour in an expanding spacetime without relying on astronomical observations. The team precisely controls the density of the condensate to create a curved spacetime analogous to the Friedmann-Lemaître-Robertson-Walker (FLRW) metric. A key finding is that sudden changes in the expansion rate induce ripples in wave motion, representing distortions in spacetime, offering a novel way to visualise and study the effects of cosmic expansion on waves. Furthermore, the researchers observed the creation of new particles due to the changing scale of the simulated universe, demonstrating a direct link between expansion and particle production. This level of control and observation surpasses previous analog simulations, offering a more detailed and accurate model of early universe phenomena.

Expanding Condensate Mimics Quantum Vacuum Amplification

This research investigates the behaviour of waves within a Bose-Einstein condensate engineered to mimic the expansion of the universe, specifically a spherical Friedmann-Lemaître-Robertson-Walker (FLRW) geometry. By manipulating the density profile of the condensate, the team created a system where the propagation of phonons, quanta of vibrational energy, resembles wave behaviour in an expanding spacetime. The results demonstrate that abrupt changes in the condensate’s expansion rate generate additional waves that propagate in the opposite direction to the primary wave motion. Furthermore, the study reveals that an initial vacuum state within the expanding condensate leads to the creation of quantum particles, effectively amplifying the quantum vacuum. Future work will explore the effects of different initial states and extend the calculations to more complex universes, connecting these findings to existing mathematical physics literature on wave propagation in curved spacetimes.