Below is a short summary and detailed review of this video written by FutureFactual:
Universe in a Box: Simulating Spacetime with Superfluid Helium and Interferometry
Physicists describe a laboratory analog that turns a rotating vortex of superfluid helium inside a cryostat into a proxy for space-time around a rotating black hole. Surface waves on the superfluid stand in for light trapped near horizons, while high-speed imaging tracks their dynamics. A second laser probe coupled with interference measurements creates a holographic map of these fluctuations, enabling exploration of quantum-field behavior in a curved space-time and probing whether gravity behaves as a quantum field or remains fundamentally classical. This setup also investigates the influence of observer motion on particle counts, touching the Unruh effect and deep questions about the objectivity of reality.
Experiment setup: from black holes to universes in boxes
The transcript frames the project as a progression toward simulators for phenomena inaccessible in the lab. It begins with a rotating vortex of superfluid helium inside a glass cryostat, which serves as a stand-in for space-time around a rotating black hole. Surface waves on the helium film mimic light waves trapped near an event horizon, and high-speed cameras capture the resulting dynamics of these waves to study behavior in an otherwise unreachable region. The researchers describe the transition to a “universe in a box” by creating a flat 2 + 1 dimensional space-time within a closed experimental cell that is cooled to a superfluid. The helium film forms a thin layer on the cell’s interior; even minor mechanical vibrations from pumps generate surface waves that act as excitations of a quantum field in this toy space-time and help researchers probe how observers would perceive such a space.
"We're creating simulators for phenomena in the universe that we have no direct access to in the lab. So what we have here is really a black hole in a box, and in the new experiment, we've moved to a universe in a box." - Dr Chris Goodwin
Observational methods: holography and particle counting
To study these analog excitations, the setup uses a pair of laser beams from a single source. The beams are split, with one beam traveling through the cryostat and interacting with the thin film of helium before recombining with the original beam. Interference patterns at various spatial points generate a hologram of the surface fluctuations, providing a map of the excitations. In parallel, a second laser probe is positioned to rotate, tracing a circular path around the film to examine how excitations look to observers in different motions. The researchers interpret the density and distribution of waves of various wavelengths as a proxy for counting particles across the toy universe, drawing a parallel to particle content in a quantum field.
"The equivalent here in the analog system is if we can measure, the kind of density of all of these different waves of different wavelengths in the system, that's akin to counting the particles of different energies in our toy universe." - Dr Chris Goodwin
Unruh effect and the role of observer motion
The core experimental aim is to compare stationary and accelerating observers. In 1976, Unruh predicted that an accelerating observer should detect particles that a stationary observer would not, providing a tangible target for encrypted quantum- gravity questions to be tested in a laboratory analog. By counting excitations and comparing observer frames, the experiment provides a way to search for Unruh particles in a controlled setting rather than in the faint signals of the cosmos. This section emphasizes that the work is not merely technical but also a route to testing deep quantum-gravity hypotheses using an accessible platform.
"Unruh predicted that the accelerating observer should see particles that a stationary observer wouldn't." - Dr Chris Goodwin
Philosophical implications: reality, objectivity, and observation
Beyond experimental mechanics, the project probes a foundational question: Are particle counts objective features of the universe, or are they shaped by the observer's frame? The transcript asks what it means for something to be real if different observers disagree about the contents of the universe, suggesting that this analog experiment could illuminate debates about the objectivity of physical reality and the role of observation in physics.
"What does real even mean when you start asking how many particles are in the universe." - Dr Chris Goodwin