Unruh Effect: The Thermal Glow of Acceleration
Guido Da Re, TAPIR, SXS / Caltech
In the conventional framework of relativistic quantum field theory, the vacuum state is considered to be the same for all inertial observers. That is, if one inertial observer measures zero temperature using a thermometer, all other inertial observers will find the same result. But what happens when we extend this analysis to observers in arbitrary states of motion? In this seminar, we will explore the simplest case of non-inertial motion—uniform proper acceleration in special relativity—and uncover a surprising effect: for accelerated observers, the vacuum is no longer perceived as empty. Instead, they experience a thermal bath, feeling a temperature! This phenomenon, known as the Unruh effect, is a fundamental relativistic quantum effect with far-reaching implications. We will derive the Unruh temperature starting from a scalar field theory, revealing how this seemingly simple model intertwines with the equivalence principle. This connection offers valuable insights into Hawking radiation near the horizon of a black hole. Moreover, the analysis highlights the complexities that arise when attempting to construct a quantum field theory that fully respects diffeomorphism invariance, posing intriguing challenges for our understanding of fundamental physics.
Host: Knapp