Falling from Rest: Particle Creation in a Dropped Cavity

• Main Author: Francesco Sorge
• Format: Article
• Language: English
• Published: MDPI AG 2021-06-01
• Series: Symmetry
• Subjects: acceleration; particle creation; quantum fields; general relativity
• Online Access: https://www.mdpi.com/2073-8994/13/7/1139

We discuss the process of particle creation in the case of a scalar quantum field confined to a small cavity, initially at rest, which is suddenly dropped in a static gravitational field. We show that, due to the transition from a Schwarzschild to a Minkowski background, as perceived by a comoving observer, field particles are excited out of the quantum vacuum. The density of the created quanta depends on the proper gravitational acceleration as well as on a parameter <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>α</mi><mo>≃</mo><mn>1</mn><mo>/</mo><mo>Δ</mo><mi>t</mi></mrow></semantics></math></inline-formula>, with <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>Δ</mo><mi>t</mi></mrow></semantics></math></inline-formula> representing the typical time duration of the transition. For the specific acceleration profile considered, the energy spectrum of the created quanta roughly resembles a two-dimensional Planckian distribution, whose equivalent temperature mimics the Hawking-Unruh temperature, with the detector acceleration (or the black hole surface gravity) replaced by the parameter <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>c</mi><mi>α</mi></mrow></semantics></math></inline-formula>. We briefly comment on possible issues related to local Lorentz symmetry.