Time appears to have a direction—the past lies behind, fixed and immutable, while the future lies ahead and is not necessarily fixed. Yet for the most part the laws of physics do not specify an arrow of time, and allow any process to proceed both forward and in reverse. This is generally a consequence of time being modeled by a parameter in the system being analyzed, where there is no "proper time": the direction of the arrow of time is sometimes arbitrary. Examples of this include the Second law of thermodynamics, which states that entropy must increase over time (see Entropy); the cosmological arrow of time, which points away from the Big Bang, CPT symmetry, and the radiative arrow of time, caused by light only traveling forwards in time (see light cone). In particle physics, the violation of CP symmetry implies that there should be a small counterbalancing time asymmetry to preserve CPT symmetry as stated above. The standard description of measurement in quantum mechanics is also time asymmetric (see Measurement in quantum mechanics). COUNT 5
QSN1 What laws do not specify an arrow of time? ANS1 the laws of physics QSN2 The standard description of measurement in quantum mechanics is what? ANS2 time asymmetric QSN3 The direction of the arrow of time is sometimes what? ANS3 arbitrary QSN4 Which law states that entropy must increase over time? ANS4 the Second law of thermodynamics, QSN5 The violation of what implies that there should be a small counterbalancing time asymmetry? ANS5 CP symmetry