**Antoine Tilloy**

Could we hear the pop of a wave-function collapse, and if so, what would it sound like? There exist reconstructions or modifications of quantum mechanics (collapse models) where this archetypal signature of randomness exists and can in principle be witnessed. But, perhaps surprisingly, the resulting sound is disappointingly banal, indistinguishable from any other click. The problem of finding the right description of the world between two completely different classes of models — where wave functions jump and where they do not — is empirically undecidable. Behind this seemingly trivial observation lie deep lessons about the rigidity of quantum mechanics, the difficulty to blame unpredictability on intrinsic randomness, and more generally the physical limitations to our knowledge of reality.

Read more at https://arxiv.org/abs/2007.15420

# Author Archives: physicsgg

# James Chadwick: ahead of his time

**Gerhard Ecker**

James Chadwick is known for his discovery of the neutron. Many of his earlier findings and ideas in the context of weak and strong nuclear forces are much less known. This biographical sketch attempts to highlight the achievements of a scientist who paved the way for contemporary subatomic physics.

Read more at https://arxiv.org/abs/2007.06926

# Method to measure Earth missed by ancient Greeks?

Fabio Falchi

I describe a simple method to calculate Earth dimensions using only local measurements and observations. I used modern technology (a digital photo camera and Google Earth) but the exact same method can be used without any aid, with naked eye observations and distances measured by walking, and so it was perfectly accessible to Ancient Greek science.

Read more at https://arxiv.org/abs/2007.02111

# Feynman Lectures on the Strong Interactions

**Richard P. Feynman, James M. Cline**

These twenty-two lectures, with exercises, comprise the extent of what was meant to be a full-year graduate-level course on the strong interactions and QCD, given at Caltech in 1987-88. The course was cut short by the illness that led to Feynman’s death. Several of the lectures were finalized in collaboration with Feynman for an anticipated monograph based on the course. The others, while retaining Feynman’s idiosyncrasies, are revised similarly to those he was able to check. His distinctive approach and manner of presentation are manifest throughout. Near the end he suggests a novel, nonperturbative formulation of quantum field theory in D dimensions. Supplementary material is provided in appendices and ancillary files, including verbatim transcriptions of three lectures and the corresponding audiotaped recordings.

Read more at https://arxiv.org/abs/2006.08594

# Packing Moons Inside the Earth

**Sunil K. Chebolu**

Using ideas of sphere packing problem we estimate the number of solid moons that can be packed inside the Earth, assuming that both the Moon and the Earth are perfect sphere.

Read more at https://arxiv.org/abs/2006.00603

# Physics and the Pythagorean Theorem

**James Overduin, Richard Conn Henry**

Pythagoras’ theorem lies at the heart of physics as well as mathematics, yet its historical origins are obscure. We highlight a purely pictorial, gestalt-like proof that may have originated during the Zhou Dynasty. Generalizations of the Pythagorean theorem to three, four and more dimensions undergird fundamental laws including the energy-momentum relation of particle physics and the field equations of general relativity, and may hint at future unified theories. The intuitive, “pre-mathematical” nature of this theorem thus lends support to the Eddingtonian view that “the stuff of the world is mind-stuff.”

Read more https://arxiv.org/abs/2005.10671

# Pi from the sky

**A null test of general relativity from a population of gravitational wave observations**

**Carl-Johan Haster**

Our understanding of observed Gravitational Waves (GWs) comes from matching data to known signal models describing General Relativity (GR). These models, expressed in the post-Newtonian formalism, contain the mathematical constant π. Allowing π to vary thus enables a strong, universal and generalisable null test of GR. From a population of 22 GW observations, we make an astrophysical measurement of π=3.115^{+0.048}_{−0.088}, and prefer GR as the correct theory of gravity with a Bayes factor of 321. We find the variable π test robust against simulated beyond-GR effects.

Read more at https://arxiv.org/abs/2005.05472