The Spacetime Metric

Profile

Stefano Liberati

professor of theoretical physics, SISSA Trieste

Liberati investigates how quantum physics and gravity fit together, including laboratory systems that mimic aspects of curved spacetime. With Carlos Barceló and Matt Visser, he surveys analogue-gravity models: other physical systems used to explore related gravitational questions. With Stefano Finazzi and Barceló, he calculates quantum-field effects in a model where a faster-than-light warp bubble develops from initially flat spacetime. Their 2009 analysis finds growing field energy near the front wall and an instability of that model when the field’s effect on the geometry is considered.

Affiliations

  • SISSA (International School for Advanced Studies), Trieste; INFN

Channels

Bibliography

A bibliography listing does not establish authorship. Credits appear under attribution.

Published bibliography entries: 2. Showing 1–2 of 2.

  1. Listed work

    Paper · 2011

    Analogue Gravity

    1. Carlos Barceló(Author)
    2. Stefano Liberati(Author)
    3. Matt Visser(Author)

    In this 2011 review, Barceló, Liberati and Visser explain how waves in materials can follow equations resembling those for fields in curved spacetime. A sufficiently fast fluid flow can prevent sound from travelling upstream, creating an acoustic counterpart of a black-hole horizon. The review compares water waves, ultracold atomic condensates and optical systems, examining where each analogy applies. It reports classical stimulated Hawking emission in water-wave experiments and a sonic horizon in a condensate kept stable for about eight milliseconds. At that time, reproducible detection of spontaneous quantum Hawking radiation remained an experimental target. The authors distinguish this effective geometry for waves from the equations governing gravity itself: reproducing curved-spacetime propagation does not automatically reproduce Einstein’s gravitational dynamics.

  2. Listed work

    Paper · 2009

    Semiclassical instability of dynamical warp drives

    1. Stefano Finazzi(Author)
    2. Stefano Liberati(Author)
    3. Carlos Barceló(Author)

    Finazzi, Liberati and Barceló extend quantum corrections for warp drives from eternal bubbles at fixed speed to the more realistic case of a superluminal bubble created from initially flat spacetime. They map the causal structure of eternal and dynamical warp spacetimes and compute the renormalised stress-energy tensor of a quantum field in them. An observer at the centre of a superluminal bubble generically sees a thermal flux of Hawking particles, which becomes extremely high if the exotic matter comes from a quantum field obeying quantum inequalities. The stress-energy grows exponentially at the bubble's front wall, so these geometries are unstable to semiclassical backreaction.