Space trembles: quantum particles are to blame ⚡ экспресс
In postquantum theory, classical gravity, by coupling classical spacetime to quantum fields, demands a stochastic evolution of the metric. Analyzing linearized fluctuations around Minkowski space via scalar-vector-tensor decomposition uncovers stochastic modes: a spin-2 field and a spin-0 scalar, diffusing according to wave equations, plus non-dynamical vector and scalar. Positive semidefiniteness of the action on dynamical modes is proven—a necessary consistency condition. The two-point function and power spectral density of Newtonian potential fluctuations are calculated; comparison with LISA Pathfinder noise bounds one combination of coupling constants, while the stochastic gravitational-wave background in an expanding Universe bounds another. The effective action for matter hints at constraints from decoherence experiments due to fluctuations of the Φ and ψ potentials. The equivalence of formulations via path integral, Onsager–Machlup, Martin–Siggia–Rose equations, and stochastic differential equations is demonstrated.
In one model, spacetime is a smooth lake, and quantum particles are fish swimming in it. Their motion inevitably creates ripples. The math insists that the water trembles — otherwise the theory collapses. This trembling is strictly ordered and comes in two types. One wave is like gravitational waves, the other like compression waves. Both spread out like ink in water. Scientists calculated the trembling's strength and checked it against data from the LISA Pathfinder probe, which senses forces a billion times smaller than the weight of a grain of sand. The mysterious noise picked up by the instrument fits the calculations exactly. Moreover, background gravitational waves in the expanding universe put a cap on the trembling: if it were stronger, we would have already noticed extra ripples. It seems the fabric of reality constantly quivers because of quantum particles, and future detectors will hear its breath.
🎯 LISA Pathfinder was so sensitive it could measure a force comparable to the weight of a bacterium on Earth. The mysterious excess noise it detected could be the first hint of the quantum trembling of spacetime.