- Oct 16, 2017
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With that in mind, let's presume here that the "Universe is Not Expanding After All" (or may not be) and that no practical system can be truly "isolated" or "closed" in reality. Does entropy really force time to go one-way? What if the Universe began shrinking?The arrow of time is the "one-way direction" or "asymmetry" of time. The thermodynamic arrow of time is provided by the second law of thermodynamics, which says that in an isolated system, entropy tends to increase with time. Entropy can be thought of as a measure of microscopic disorder; thus the second law implies that time is asymmetrical with respect to the amount of order in an isolated system: as a system advances through time, it becomes more statistically disordered. This asymmetry can be used empirically to distinguish between future and past, though measuring entropy does not accurately measure time. Also, in an open system, entropy can decrease with time.