Why a Weak Dark Energy Is Sufficient to Drive Cosmic Acceleration? A Dynamical Clarification of the Orbital Angular Momentum Between Galaxy Clusters

Since the discovery of cosmic acceleration in 1998, a widespread intuition has heldthat dark energy must provide a repulsive force strong enough to “counteract” gravity and prevent the universe from collapsing under its own weight. Yet this picturefaces a sharp contradiction with observational facts: the dark energy density ismerely ρΛ ≈ 10−29 g/cm3, and on the scale of galaxy clusters its equivalent repulsive acceleration is about six orders of magnitude weaker than the gravitationalacceleration. How can such a feeble dark energy “overcome” gravity? This paperidentifies the root of this paradox as a fundamental misunderstanding of the rolethat gravity actually plays in large-scale cosmic structure: galaxy clusters arenot in a static, radially aligned arrangement awaiting collapse; rather,they have acquired orbital angular momentum through primordial tidaltorques, and are engaged in complex orbital motions around one another. In this dynamical picture, the primary role of gravity is to provide thecentripetal force required to sustain orbital motion, not to cause linear collapse. Dark energy therefore does not need to “overwhelm” gravity—it need onlyprovide a weak, persistent radial stretching, sufficient to disrupt the delicately balanced orbital equilibrium between clusters and cause them to drift apart. This paperdemonstrates the self-consistency of this picture through explicit calculation, rules1out alternative mechanisms such as radiation pressure and mass loss by quantitative estimation, and presents three quantitative predictions testable by forthcomingsurveys. This conceptual clarification offers a natural direction for resolving the“coincidence problem” of dark energy, consistent with Newtonian mechanics andthe equivalence principle of general relativity.