Month: September 2022

FEYNMAN-STUECKELBERG ANTIMATTER. “This interpretation states that all the properties of antimatter are consistent with the view that antimatter and matter are identical except that their particles move in opposite directions in time.” https://lnkd.in/dPumvhdU View in LinkedIn

LOST IN THE WEEDS. “This view has never been refuted, but it is seldom discussed. The textbooks devote a few paragraphs to the topic: for example "Quarks and leptons" by Halzen and Martin.” https://lnkd.in/gDaxUYAS View in LinkedIn

RECOGNITION. “Yet the concept was central to Feynman's work in quantum electrodynamics. J.J. Sakurai's textbook praises the simplicity and elegance of Feynman's approach, pointing out its mathematical equivalence to Tomonaga and Schwinger's more conventional and complex version.” https://lnkd.in/gDaxUYAS View in LinkedIn

“MIND, n, A mysterious form of matter secreted by the brain. Its chief activity consists in the endeavor to ascertain its own nature, the futility of the attempt being due to the fact that it has nothing but self to know itself with.” Ambrose Bierce, The Devil’s Dictionary (1909). https://lnkd.in/d6WmmHTS View in LinkedIn

Time for bed, daddy. View in LinkedIn

FRAGMENT FROM NATURE highlights a 2013 paper titled ‘Genome dynamics during experimental evolution’, by Jeffrey E. Barrick & Richard E. Lenski. The paper shows that “Genomic analyses show that adaptation rarely occurs by periodic sweeps of single beneficial mutations through asexual populations. Rather, divergent paths that involve multiple mutations are often explored before any one evolved type can displace its competitors.” https://lnkd.in/dfp9nRAQ View in LinkedIn

RARE MUTATIONS IN LOWER ANIMALS. “Mutation accumulation experiments with bacteria and single-celled eukaryotes typically find that the rate of single base mutations is of the order of 10(-10) - 10(-9) per base pair per replication. Given that the typical genome sizes in these organisms are of the order of 10(6) - 10(7) base pairs, these rates correspond to only one point mutation in every few hundred to several thousand cell divisions.” https://www.nature.com/articles/nrg3564 View in LinkedIn

LOW RATES IN HIGHER ANIMALS. “Rates of point mutations in multicellular eukaryotes are of the order of 0.05–1.0 per generation across the entire protein-coding portions of these genomes, which is still fairly low given the much longer generation times and the multiple cell divisions in the germ line between generations in these organisms.” https://www.nature.com/articles/nrg3564 View in LinkedIn

BACTERIAL EXAMPLE. “For example, whole-genome sequencing of experimentally evolved Myxococcus xanthus strains found that 14 mutations were substituted after 1,000 generations in a liquid medium, while social motility and the capability to form fruiting bodies were lost, but only one mutation was involved in the subsequent restoration of those functions.” https://www.nature.com/articles/nrg3564 View in LinkedIn

BACTERIAL SURPRISE. “That key mutation did not revert any of the previous mutations but occurred instead in a previously uncharacterized small RNA.” https://www.nature.com/articles/nrg3564 View in LinkedIn