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No theory predicts which happens.","posed_since":"","precise":"Heavy point particles (diameter $d << \\eta$, $\\eta$ the Kolmogorov length) with Stokes number St and mass loading $\\Phi_m$ (particle-to-fluid mass ratio) of order 0.1 to 1 in homogeneous turbulence with two-way coupling. Determine the sign and magnitude of the change in carrier turbulent kinetic energy and dissipation rate as functions of $\\mathrm{St}, \\Phi_m, \\mathrm{Sv}\\text{ and }\\mathrm{Re}_\\lambda$, including the scale-by-scale energy exchange between phases. Answer: a predictive relation validated for St from about 0.1 to 10.","problem_ref":"b0b1c56a5ee79f6ab6d3eb3ece5e07553e266ce71146b3f3b1b75b108f2a03b5","references":"","settled_by":"Two-way coupled point-particle DNS with converged coupling schemes, checked against experiments with sub-Kolmogorov particles at matched St and $\\Phi_m$.","status_note":"","title":"Sign of turbulence modulation by heavy particles smaller than 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