Expansion shock waves in the implosion process from a time-reversible molecular-dynamics simulation of a dual explosion process

Abstract

Why does not an expansion shock wave exist in a gaseous medium in nature? The reason has been widely believed to be the irreversibility in nature, while an obvious demonstration for this belief has not been accomplished yet. In order to resolve the question from a microscopic viewpoint, an implosion process dual to an explosion process was investigated by means of the molecular-dynamics method ͑MD͒. To this aim, we employed a "bit-reversible algorithm ͑Bit MD͒" that was completely time-reversible in a microscopic viewpoint and was free from any round-off error. Here we show that, through a dual implosion simulation ͑i.e., a time-reversible simulation of the explosion͒, a kind of expansion shock wave is successfully formed in the Bit MD simulation. Furthermore, we show that when the controlled noise is intentionally added to the Bit MD, the expansion shock wave disappears dramatically and turns into an isentropic expansion wave, even if the noise is extremely small. Since the controlled noise gives rise to the irreversibility in the Bit MD simulation, it can be concluded that the irreversibility in the system prohibits the expansion shock wave from appearing in the system.

Sculpted ultracold neutral plasmas

“…In contrast with the inner region of the plasma, the outer region is characterized by an outward blast wave moving through a hotter, locally kinetic outer layer. Such wave properties have been observed and studied previously [60][61][62][63][64][65][66].…”

Numerical irreversibility in self-gravitating small N-body systems, II: Influence of instability affected by softening parameters

“…However, irreversibility appearing in self-gravitating N-body systems has not yet been clarified from the viewpoint of time-reversible dynamics. In fact, even in short-range interacting systems [30][31][32], the influence of round-off errors or numerical irreversibility has not been investigated quantitatively, except for a few simple models [33][34][35] or for the works by the present authors [36][37][38].…”