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
This framework predicts several landmark effects that bridge the gap between thermodynamics, gravity, and quantum mechanics:
: 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 Quantum Field Theory in Curved Spacetime: Quant...
: An observer accelerating through a Minkowski vacuum will perceive it as a thermal bath of particles at a temperature proportional to their acceleration.
: 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. To relate the perspectives of different observers or
. 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
Quantum Field Theory in Curved Spacetime: Quantized Fields and Semiclassical Gravity : The concept of a "particle" becomes local
: 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