A First-Principles Explanation of the Flyby Anomaly via a Biphasic Background Medium Model

This paper proposes a novel physical model that treats spacetime as a **Biphasic Background Medium (BGD medium)**, composed of repulsive ($F^+$) and attractive ($F^-$) fluid-like components. Based on this model, it is demonstrated that the long-standing **Flyby Anomaly** can be uniformly explained as a linear combination of two fundamental hydrodynamic responses:1. A **"polarization effect"** ($K_1$ term), related to the compression of the medium.2. A **"vortex generation effect"** ($K_2$ term), related to the medium's interaction with a rotating body. A core tenet of this theory is that the two universal coefficients governing the model are not fitting parameters but are **derived from first principles**. They incorporate:- The gravitational potential from General Relativity.- The geometric constant $\pi$.- The celestial body’s rotational velocity and internal structure. The theory successfully reproduces the observed data from **ten major spacecraft flybys**—including the deceleration of Galileo II and multiple null results from Rosetta—with a high degree of precision, achieving a Root Mean Square Error (RMSE) of **0.3190 mm/s**. This result strongly suggests that the Flyby Anomaly is a direct manifestation of the **dynamic nature of spacetime**. The full paper and the Python simulation code used to produce these results are included in the files below.