Evolution and irreversibility: Two distinct phenomena and their distinct laws of nature.

To clarify the place of time direction of change in nature (time arrow), the present article shows why Evolution and Irreversibility are two distinct phenomena. Their distinct laws of nature are the Constructal Law and the Second Law, respectively. The demonstration is based on the simplest setting imaginable: a solid body moving in a pool of water. The view is holistic: the system selected for analysis is the body and the pool, not the body alone, and the phenomenon is the evolution of the image (configuration) of the whole. New is also the answer to the question of what flows in this evolving flow configuration. Along the way, important terms are defined: phenomenon, law, irreversibility, nature, design, freedom, theory versus empiricism, information, knowledge, selection, purpose, engine, refrigeration, and wheel. More complex natural settings for the demonstration are in the second part of the article: engines, refrigeration, heating and cooling, the wheel, and a pushed boat sliding on water.

Locomotion rhythm makes power and speed.

This article addresses two questions, why certain animals (frogs, breaststroke swimmers, hovering fliers, jellyfish) push rapidly against the surrounding fluid and then reach forward slowly, and whether this rhythm of propulsion is a manifestation of the universal phenomenon of design evolution in nature. Emphasis is on the distribution of time periods of locomotion in which, during the driving phase of cyclic movement (the motive stroke, phases 1 and 2, in alternating sequence with the dissipative stroke, phase 3), the work is generated (phase 1) and dissipated (phase 2). The relative lengths of the characteristic times t1 and t2 of the phases 1 and 2, are predicted. The relative duration of the proposed three phases of a cycle is the 'rhythm'. The analysis is based on a model of how the effective cross-sections of the stroking body parts impact the surrounding medium, water, or air, and the total power required to account for the kinetic energy losses during phases 2 and 3, which are due to drag forces posed by the surrounding medium. The body configuration (limbs' cross-sections) determines the limbs' velocities that maximize mean power, and the times t1 and t2 within the motive stroke. Emphasis is placed on the freedom to change the evolving design. Freedom is represented in two ways: the number of degrees of freedom in changing the dimensions of the model and its deformation in time, and the effect that evolutionary changes have on the access that the body has to its available space. Freedom to change the locomotion design leads to greater power and speed.

The fastest animals and vehicles are neither the biggest nor the fastest over lifetime.

Here we show how the size of a body affects its maximum average speed of movement through its environment. The theoretical challenge was to predict that 'outliers' must exist, such as the cheetah for terrestrial animals and the jet fighter for airplanes. We show that during a travel that starts from rest and continues at cruising speed, the body size for minimum travel time, or maximum average speed, is not the biggest. The results are compared with extensive data for military aircraft for chase, attack and reconnaissance, in addition to data for commercial aircraft. The paper also explains why in earlier studies of flying (animals, airplanes) the airplane data deviated upward (toward greater speeds) relative to the theoretical trend followed by flying animals, and why the fastest animal flyers are one thousand times smaller than the fastest swimmers. Unlike the biggest animals and airplanes (elephant, whale, commercial jet), which move constantly, the fastest animals and airplanes spend most of their lives at rest. When judged for speed averaged over lifetime, the fastest 'sprinters' are in fact the slowest movers (as in Aesop's fable 'The Tortoise and the Hare').