Researchers have created a theoretical model that explains how a polymer like poly(methyl methacrylate), commonly known as PMMA or acrylic glass, behaves under different types of stress over an extremely wide range of time scales. This model, published in The Journal of Chemical Physics, connects the microscopic movement of atoms to the macroscopic properties observed in laboratory tests, such as how the material bends or stretches. The study used an atomistic model containing 9,920 atoms of PMMA and applied a method called non-affine lattice dynamics (NALD), developed by the researchers and their collaborator Dr. Tim Sirk from the U.S. Army Research Laboratory. This approach accounts for the irregular structure of amorphous materials, where atoms don’t all move in the same way during deformation. Instead, they rearrange locally, which can cause the material to soften overall. A key feature of the model is its ability to link the vibrations of atoms to the forces that arise when the material is deformed. This allows scientists to calculate a property known as the shear modulus, which measures a material’s resistance to shear stress. The model uses a power-law memory kernel, which considers how past deformations affect the material’s current behavior. This non-Markovian approach is essential for accurately capturing the wide range of relaxation processes that occur in glassy polymers over long timescales. The model successfully predicts the shear modulus of PMMA across an enormous range of frequencies—spanning more than 20 orders of magnitude—from above the terahertz range (used in high-speed measurements) down to the millihertz range (used in slow deformation tests). This wide range of predictions connects various experimental techniques, including molecular dynamics simulations, light scattering, and mechanical testing, into a unified framework. At very high frequencies, PMMA behaves like a rigid elastic material, with its response determined by the strength of its molecular bonds. In the terahertz range, specific molecular vibrations, such as those involving carbon–oxygen and carbon–hydrogen bonds, become detectable. As the deformation rate slows, the material’s response becomes more complex, with local atomic movements reducing its stiffness. At around 1 hertz, PMMA shows a secondary relaxation known as the β relaxation, which occurs over a time scale of about one second. This research demonstrates how atomic-scale information can be used to predict the mechanical behavior of polymers across a vast range of timescales, linking detailed simulations with practical engineering tests. Future studies aim to refine the model further, particularly near the glass transition temperature, and to apply it to more complex polymer structures.