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TEXTBOOK INTERPRETATION. “Sakurai prefers to regard Feynman's graphical method as a convenient pictorial device, rather than accept the motion of antiparticles backward in time as a suitable foundation for quantum electrodynamics.” https://lnkd.in/gDaxUYAS View in LinkedIn

“Tensegrity is a design principle that applies when a discontinuous set of compression elements is opposed and balanced by a continuous tensile force, thereby creating an internal prestress that stabilizes the entire structure.” https://lnkd.in/dnijBjC5 View in LinkedIn

PENROSE’S CONSEQUENCES. “During the U-process, symmetric in time, a superposition of states exists in which all the possible fates of the two particles exist.” https://lnkd.in/gDaxUYAS View in LinkedIn

A MATTER OF QUANTITY. “All substances are poisons; there is none which is not a poison. Solely the dose determines that a thing is not a poison,.” (Paracelsus, 1493–1541) https://lnkd.in/d8cAT8Cf View in LinkedIn

BACKWARDS IN TIME. “Feynman describes three otherwise identical electrons, one moving backwards in time. R. Penrose has popularized the concepts of unitary, deterministic evolution in time according to the Schrodinger equation, the "U-process", versus quantum state vector reduction, the "R-process", or collapse of the wave function.” https://lnkd.in/gDaxUYAS View in LinkedIn

SO ENDS this first of two weekends on the theme of mutations. Darwin’s theory of evolution depended on “descent with modification”, but at the time, nothing was known about genes or mutations. Today, mutations are exquisitely understood, but surprisingly rarer than expected, and even a single mutation can have an enormous phenotypic effect, causing diseases including Sickle-cell anemia, cancer, color blindness, Tay-Sachs disease, and neurofibromatosis. https://lnkd.in/dbDruwJm View in LinkedIn

EXAMPLE. “Imagine a physicist at time T1 creating an electron and a positron from a photon, storing them until time Tn when the antiparticle is annihilated by another electron. He describes the situation as negatively charged, positive energy electrons and a positively charged, negative energy positron, all moving forward in time.” https://lnkd.in/gDaxUYAS View in LinkedIn

BAD ACTORS? “How do hypermutators invade populations? The immediate effect of an increased mutation rate on fitness is invariably negative, on average, because more mutations are deleterious than beneficial (Box 1).” https://www.nature.com/articles/nrg3564 View in LinkedIn

POOR RECEPTION. “From our viewpoint of events proceeding from the past to the future, the general distaste for the Feynman-Stueckelberg interpretation is understandable, but is it justified?” https://lnkd.in/gDaxUYAS View in LinkedIn

HYPERMUTATORS. “It is fairly common for some populations in adaptive evolution experiments to become dominated by hypermutators that have increased mutation rates.” https://www.nature.com/articles/nrg3564 View in LinkedIn