Physics

Rim and back geometry determine much of the behavior of sound inside the pot, whose effect on total, produced sound is subtle but discernible. The theory of sound inside a cylinder is reviewed and demonstrated. And previous work on the Helmholtz resonance and the interplay between the Helmholtz resonance and the lowest head mode is revisited using some improved techniques.

A novel bridge and tailpiece design allows direct comparison of the sound of zero break angle with same banjo (and all its parts) configured to have an angle of 13 degrees. This lends additional support to the 2014 proposal that a key element in banjo sound is the frequency modulation produced by string stretching due to a floating bridge, break angle, and head with substantial motion. When playing a banjo tune in the 0 degree configuration, there are enough audio clues that it still sounds like a banjo. The comparison allows you to judge for yourself to what extent it's lost its ring or sparkle.

The evolution of the fireball resulting from the August 2020 Beirut explosion is traced using amateur footage taken during the first ∼ 230 ms after the detonation. 38 frames separated by ∼ 16.66 - 33.33 ms are extracted from 6 different videos located precisely on the map. Measurements of the time evolution of the radius R t of the shock wave are traced by the fireball at consecutive time sequence t . Pixel scales for the videos are calibrated by de-projecting the existing grains silos building for which accurate drawings are available and by defining the line of sight incident angles. The energy available to drive the shock wave at early times can be calculated through E= 10 2b K ρ o where b is a fitted parameter dependant on the relation between R t and t . K is a constant depending on the ratio of specific heats of the atmosphere and ρ 0 is the undisturbed gas density. A total energy yield of E≈1.3× 10 12 Joules with a lower bound of 9.8× 10 11 and an upper bound of ∼1.7× 10 12 or the equivalent of ∼ 310 405 235 tons of T.N.T. is found. Our energy yields are different from other published studies using the same method. This can present an argument that if the compound that exploded is fuel rich ammonium nitrate (ANFO), then the actual mass that detonated is less than officially claimed.

The 2016 Physics Nobel Prize honors a variety of discoveries related to topological phases and phase transitions. Here we sketch two exciting facets: the groundbreaking works by John Kosterlitz and David Thouless on phase transitions of infinite order, and by Duncan Haldane on the energy gaps in quantum spin chains. These insights came as surprises in the 1970s and 1980s, respectively, and they have both initiated new fields of research in theoretical and experimental physics.

Estimates of the number and potential energy of molecules, aerosols, cloud droplets, insects, birds, planes and satellites in the atmosphere yield a distribution which is for potential energies below 10^2 kBT described by the Boltzmann distribution, but for the range from 10^2 kBT to 10^33 kBT by a power law with an exponent of approximately -1. An explanation for this surprising behavior is not found.

Since its discovery in 1930, Pluto's mass has been a value that has repeatedly been calculated. Additionally, the search for Planet X prior to Pluto's discovery results in mass calculations that date back several decades earlier. Over its observed history, the mass of Pluto has consistently decreased. We reassess earlier predictions of Pluto's fate, and rule out the hypothesis that Pluto's mass has been constant over the last century. We are able to fit linear and quadratic equations to Pluto's mass as a function of both time and distance. The observations that will be made by New Horizons will help to determine if we can expect Pluto to continue to shrink until it has negative mass, or if it will begin to increase in mass again.

The number of people able to end Earth's technical civilization has heretofore been small. Emerging dual-use technologies, such as biotechnology, may give similar power to thousands or millions of individuals. To quantitatively investigate the ramifications of such a marked shift on the survival of both terrestrial and extraterrestrial technical civilizations, this paper presents a two-parameter model for civilizational lifespans, i.e. the quantity L in Drake's equation for the number of communicating extraterrestrial civilizations. One parameter characterizes the population lethality of a civilization's biotechnology and the other characterizes the civilization's psychosociology. L is demonstrated to be less than the inverse of the product of these two parameters. Using empiric data from Pubmed to inform the biotechnology parameter, the model predicts human civilization's median survival time as decades to centuries, even with optimistic psychosociological parameter values, thereby positioning biotechnology as a proximate threat to human civilization. For an ensemble of civilizations having some median calculated survival time, the model predicts that, after 80 times that duration, only one in 10 24 civilizations will survive -- a tempo and degree of winnowing compatible with Hanson's "Great Filter." Thus, assuming that civilizations universally develop advanced biotechnology, before they become vigorous interstellar colonizers, the model provides a resolution to the Fermi paradox.

I propose that if the universe was born as a baby universe on the other side of the event horizon of a black hole existing in a parent universe, then the corresponding white hole provides the absolute inertial frame of reference in the universe. The principle of relativity then allows to construct an infinity of other inertial frames. Consequently, this scenario could give the origin of inertia and complete Einstein's general theory of relativity by making it consistent with Mach's principle.

Arguably, black hole is perhaps the most popular scientific term among the lay person. Perhaps it is the phrasing of the term 'black hole' which appeals to the popular imagination, offering some exotic visual of a cosmic object to the mind's eye.

This essay gives a very general introduction to Schwarzschild black holes. First, it focuses on some of its classical features as solutions to Einstein's theory of gravity. In the second part it discusses briefly some specific quantum aspects and how a black hole processes quantum information. No previous knowledge about black holes, gravity or quantum mechanics is required.