. This approach serves as a robust approximation for environments where gravity is strong but quantum gravitational effects—such as fluctuations of the metric itself—are not yet dominant. 1. The Fundamental Shift: From Particles to Fields
To relate the perspectives of different observers or the state of fields at different times in an expanding universe, physicists use : Field Decomposition : A scalar field is expanded into a set of basis modes with creation and annihilation operators
: Strong gravitational fields near a black hole's event horizon polarize the vacuum, causing the black hole to emit thermal radiation and gradually lose mass. Quantum Field Theory in Curved Spacetime: Quant...
: In the early, rapidly expanding universe, time-varying gravitational fields can "excite" the vacuum, creating elementary particles that seed the large-scale structure of the universe. Robert Wald - Quantum Field Theory in Curved Spacetime
: The concept of a "particle" becomes local and observer-dependent. Different observers (e.g., one inertial and one accelerating) may disagree on whether a state contains particles or is a vacuum. The Fundamental Shift: From Particles to Fields To
Quantum Field Theory in Curved Spacetime: Quantized Fields and Semiclassical Gravity
: Because global constructs like Fourier transforms are unavailable, QFTCS must be formulated locally using quantum field operators rather than particle counts. 2. Mathematical Framework: Bogoliubov Transformations Different observers (e
: An observer accelerating through a Minkowski vacuum will perceive it as a thermal bath of particles at a temperature proportional to their acceleration.