When isolated systems change state, they are more likely to change to state with higher-probability energy distribution. Statistically, motions become more random, and objects become more evenly dispersed {time, entropy} {entropy, time}. In isolated systems, entropy can decrease only temporarily and locally.
questions
Why was entropy low in the past? If time reversed, how can entropy decrease toward the past? Why is there entropy gradient, entropy flow, with time?
symmetry and heat
Higher heat means more symmetry. Heat release makes less symmetry.
curvature
Smooth curvature has less entropy than jagged curvature.
gravity
If no gravity, entropy is proportional to volume. If gravity, entropy is proportional to surface area. Perhaps, surface has no gravity, and gravity adds extra dimension.
addition
Entropy is an extensive quantity, because it is arrangement-number logarithm. If two systems merge, arrangement number is arrangement-number product, and total entropy is entropy sum.
low entropy in past
System is more likely to have higher entropy in the future. System is more likely to have had lower entropy in the past. If system had higher entropy in the past and low entropy now, intermediate steps were jumps down to lower entropy, which are unlikely. Universe entropy was lowest at first.
entropy change with time
Perhaps, at universe origin, everything was evenly distributed, with only one particle type, with lowest entropy. During inflation, there was negative gravity, making more even dispersal, with higher entropy, and less clumpiness, with low entropy. When inflation ended, many particles appeared, making more entropy. Particles spread through space, making lower entropy. Primordial gas had low entropy, and then gravity decreased entropy as it clumped matter, but overall entropy increased because potential energy changed into heat kinetic energy. Sun original gas cloud had medium-low entropy and temperature, and then Sun had higher entropy and temperature. Sunlight has medium entropy, and then heat has higher entropy. Food has medium-high entropy, and then waste has higher entropy.
black hole
Black holes have maximum entropy density: Boltzmann constant times surface area in Planck units divided by 4. Surface unit {Planck square} has one unit of entropy flux.
Physical Sciences>Physics>Time>Asymmetry
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Date Modified: 2022.0224