wikipedia Wrote:For example, a drop of dye can dissolve in water, but the reverse transformation, the dye spontaneously clumping back together, is never observed in practice. While the microscopic laws of motion are time-reversible (meaning such a reversal is not strictly forbidden for individual trajectories, only astronomically unlikely), constructor theory reframes the question: rather than asking what will happen given initial conditions, it asks whether a constructor — a device that could reliably cause the reverse transformation and retain the ability to do so again — is possible. In constructor-theoretic terms, dissolving dye is a possible task, but its transpose is impossible: no constructor for reliably reversing the process can exist under the laws of physics, even though the underlying dynamics are time-symmetric.