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At least 307 records · Page 17Linked to original sources
arXiv2013

Einstein and the conservation of energy-momentum in general relativity

The main purpose of the present paper is to show that a correction of one mistake was crucial for Einstein's pathway to the first version of the 1915 general theory of relativity, but also might have played a role in obtaining the final version of Einstein's 1915 field equations. In 1914 Einstein wrote the equations for conservation of energy-momentum for matter, and established a connection between these equations and the components of the gravitational field. He showed that a material point in gravitational fields moves on a geodesic line in space-time, the equation of which is written in terms of the Christoffel symbols. By November 4, 1915, Einstein found it advantageous to use for the components of the gravitational field, not the previous equation, but the Christoffel symbols. He corrected the 1914 equations of conservation of energy-momentum for matter. Einstein had already basically possessed the field equations in 1912 together with his mathematician friend Marcel Grossman, but because he had not recognized the formal importance of the Christoffel symbols as the components of the gravitational field, he could "not obtain a clear overview". Finally, considering the energy-momentum conservation equations for matter, an important similarity between equations suggests that, this equation could have assisted Einstein in obtaining the final form of the field equations (the November 25, 1915 ones) that were generally covariant.

physics.hist-ph↗
arXiv2017

Causality and the Modeling of the Measurement Process in Quantum Theory

In this paper we provide a general account of the causal models which attempt to provide a solution to the famous measurement problem of Quantum Mechanics (QM). We will argue that --leaving aside instrumentalism which restricts the physical meaning of QM to the algorithmic prediction of measurement outcomes-- the many interpretations which can be found in the literature can be distinguished through the way they model the measurement process, either in terms of the efficient cause or in terms of the final cause. We will discuss and analyze why both, 'final cause' and 'efficient cause' models, face severe difficulties to solve the measurement problem. In contradistinction to these schemes we will present a new model based on the immanent cause which, we will argue, provides an intuitive understanding of the measurement process in QM.

quant-ph↗
arXiv2013

The GRW flash theory: a relativistic quantum ontology of matter in space-time?

John Bell proposed an ontology for the GRW modification of quantum mechanics in terms of flashes occurring at space-time points. The paper spells out the motivation for this ontology, enquires into the status of the wave-function in it, critically examines the claim of its being Lorentz-invariant and considers whether it is a parsimonious, but nevertheless physically adequate ontology.

quant-ph↗
arXiv2013

A possible Harappan Astronomical Observatory at Dholavira

Astronomy arises very early in a civilization and evolves as the civilization advances. It is therefore reasonable to assume that a vibrant knowledge of astronomy would have been a feature of a civilization the size of the Harappan Civilization. We suggest that structures dedicated to astronomy existed in every major Harappan city. One such city was Dholavira, an important trading port that was located on an island in what is now the Rann of Kutch during the peak of the Harappan Civilization. We have analyzed an unusual structure at Dholavira that includes two circular rooms. Upon assuming strategically-placed holes in their ceilings we examine the internal movement of sunlight within these rooms and suggest that the larger structure of which they formed a part could have functioned as an astronomical observatory.

physics.hist-ph↗
arXiv2013

Einstein's 1916 derivation of the Field Equations

In his first November 4, 1915 paper Einstein wrote the Lagrangian form of his field equations. In the fourth November 25, 1915 paper, Einstein added a trace term of the energy-momentum tensor on the right-hand side of the generally covariant field equations. The main purpose of the present work is to show that in November 4, 1915, Einstein had already explored much of the main ingredients that were required for the formulation of the final form of the field equations of November 25, 1915. The present work suggests that the idea of adding the second-term on the right-hand side of the field equation might have originated in reconsideration of the November 4, 1915 field equations. In this regard, the final form of Einstein's field equations with the trace term may be linked with his work of November 4, 1915. The interesting history of the derivation of the final form of the field equations is inspired by the exchange of letters between Einstein and Paul Ehrenfest in winter 1916 and by Einstein's 1916 derivation of the November 25, 1915 field equations.

physics.hist-ph↗
arXiv2013

Relativistic Achilles

This manuscript presents a problem on special relativity theory (SRT) which embodies an apparent paradox relying on the concept of simultaneity. The problem is represented in the framework of Greek epic poetry and structured in a didactic way. Owing to the characteristic properties of Lorenz transformations, three events which are simultaneous in a given inertial reference system, occur at different times in the other two reference frames. In contrast to the famous twin paradox, in the present case there are three, not two, different inertial observers. This feature provides a better framework to expose some of the main characteristics of SRT, in particular, the concept of velocity and the relativistic rule of addition of velocities.

physics.hist-ph↗
arXiv2014

Isaac Newton's sinister heraldry

After Isaac Newton was knighted by Queen Anne in 1705 he adopted an unusual coat of arms: a pair of human tibiae crossed on a black background, like a pirate flag without the skull. After some general reflections on Newton's monumental scientific achievements and on his enigmatic life, we investigate the story of his coat of arms. We also discuss how its simple design illustrates the concept of chirality, which would later play an important role in the philosophical arguments about Newton's conception of space, as well as in the development of modern chemistry and particle physics.

physics.hist-ph↗
arXiv2014

Il fisico del neutrino

In memory of the famous physicist Bruno Pontecorvo, whereof is just occurred the centenary anniversary of the birth and the twentieth anniversary of the death, this paper traces the scientific and human adventure of the italian scientist, from the pioneering studies of nuclear physics together with his master Enrico Fermi, to the excellent results in particle physics, in particular his research and insights about the neutrino. As much attention is paid to the human experience, his relationship with politics and the choice to embrace the Soviet socialist model. A short portrait to commemorate a scientist symbol of the twentieth century.

physics.hist-ph↗
arXiv2013

Temporal naturalism

Two people may claim both to be naturalists, but have divergent conceptions of basic elements of the natural world which lead them to mean different things when they talk about laws of nature, or states, or the role of mathematics in physics. These disagreements do not much affect the ordinary practice of science which is about small subsystems of the universe, described or explained against a background, idealized to be fixed. But these issues become crucial when we consider including the whole universe within our system, for then there is no fixed background to reference observables to. I argue here that the key issue responsible for divergent versions of naturalism and divergent approaches to cosmology is the conception of time. One version, which I call temporal naturalism, holds that time, in the sense of the succession of present moments, is real, and that laws of nature evolve in that time. This is contrasted with timeless naturalism, which holds that laws are immutable and the present moment and its passage are illusions. I argue that temporal naturalism is empirically more adequate than the alternatives, because it offers testable explanations for puzzles its rivals cannot address, and is likely a better basis for solving major puzzles that presently face cosmology and physics. This essay also addresses the problem of qualia and experience within naturalism and argues that only temporal naturalism can make a place for qualia as intrinsic qualities of matter.

physics.hist-ph↗
arXiv2013

Relative information at the foundation of physics

Shannon's notion of relative information between two physical systems can function as foundation for statistical mechanics and quantum mechanics, without referring to subjectivism or idealism. It can also represent a key missing element in the foundation of the naturalistic picture of the world, providing the conceptual tool for dealing with its apparent limitations. I comment on the relation between these ideas and Democritus.

hep-th↗
arXiv2013

The Astronomy of the Kamilaroi People and their Neighbours

The Kamilaroi people and their neighbours, the Euahlayi, Ngemba, and Murrawarri, are an Aboriginal cultural grouping located in the northwest and north central of New South Wales. They have a rich history, but have been missed in much of the literature concerned with sky knowledge in culture. This study collected stories, some of which have not previously been reported in an academic format, from Aboriginal people practicing their culture, augmented with stories from the literature, and analysed the data to create a database of sky knowledge that will be added to the larger body of Aboriginal cultural knowledge in Australia. We found that there is a strong sky culture reflected in the stories, and we also explored the stories for evidence of an ethnoscientific approach to knowledge of the sky.

physics.hist-ph↗
arXiv2013

Some Notes on the Rapanui Archaeoastronomy

This paper is dedicated to the research of secrets of Easter Island (Rapa Nui), a remote plot of land in the Pacific; the work includes not only necessary ethnological data, but also some results on the archaeoastronomy. The analysis of several rock drawings lets us date them. The priests Hina Mango and Rahu (Rahi) were not only experts on the script, but also great astronomers. There is abundant evidence that the priests-astronomers used the astrolabe in their studies. The local astronomical terminology has been decoded. The observatory at the ceremonial platform Ahu Tongariki has been investigated carefully. The orientation of a female statue on the slope of the Rano Raraku volcano allows us to suggest that it was an image of the Moon (the moon goddess). A number of additional astronomical and calendar records in the rock art and in the writing have been deciphered.

physics.hist-ph↗
arXiv2013

Quantization of the Atom plus Attempting to Answer Heilbron & Kuhn

The idea of atoms is old but X-rays provided the first probe into the physical atom. Photographs of X-ray scattering from crystals -Laue spots- were the first visual proof for the physical existence of atoms arranged in a perfect geometric pattern. Thereby conclusively established the stability and physical reality of atoms. The Braggs developed Laue technique to study atoms. Moseley applied (Bragg) X-ray spectroscopy to determine the nuclear charge number of Rutherford atom. We argue that Bohr also at Manchester and contemporary of Moseley likely was inspired by Laue discovery to get busy with the mechanics of the nuclear atom. Roentgens discovery was awarded the first Nobel prize ever in 1901, Laue was honored in 1914, the Braggs in 1915, making Lawrence Bragg then at 25 the youngest ever. Eleven of the cited authors (Bohr himself included) in the trilogy (but not Nicholson the most cited), were later recognized by ten Noble prize awards, seven Laureates in physics and four in chemistry. The ensuing synergy between science and Nobel honors has been critical.

physics.hist-ph↗
arXiv2018

Is the world made of loops?

I see no good reason to prefer (any version I know of) the `holonomy interpretation' to the `potential interpretation' of the Aharonov-Bohm effect. Everyone agrees that the inverse image $[A]=[A+dλ]_λ=d^{-1}F$ of the electromagnetic field $F$ is a class, full of individuals; and that the circulation $\small{\textsf{C}}$ of the electromagnetic potential $A$ around a loop $σ_0$ encircling the solenoid is common to the whole class $[A]$, and to the homotopy class or \emph{hoop} $[σ_0]$. If picking individuals out of classes is the problem, picking an individual potential out of $[A]$ should be no worse than picking an individual loop out of $[σ_0]$. The individuals of $[A]$ can moreover be transcended---punctually, without integration around loops---by an appropriate version of the electromagnetic connection.

physics.hist-ph↗
arXiv2015

The Tao of It and Bit

The main mystery of quantum mechanics is contained in Wheeler's delayed choice experiment, which shows that the past is determined by our choice of what quantum property to observe. This gives the observer a participatory role in deciding the past history of the universe. Wheeler extended this participatory role to the emergence of the physical laws ("law without law"). Since what we know about the universe comes in yes/no answers to our interrogations, this led him to the idea of "it from bit" (which includes the participatory role of the observer as a key component). The yes/no answers to our observations ("bit") should always be compatible with the existence of at least a possible reality - a global solution ("it") of the Schrodinger equation. I argue that there is in fact an interplay between "it" and "bit". The requirement of global consistency leads to apparently acausal and nonlocal behavior, explaining the weirdness of quantum phenomena. As an interpretation of Wheeler's "it from bit" and "law without law", I discuss the possibility that the universe is mathematical, and that there is a "mother of all possible worlds" - named the "Axiom Zero".

quant-ph↗
arXiv2014

"It from bit" and the quantum probability rule

I argue that, on the subjective Bayesian interpretation of probability, "it from bit" requires a generalization of probability theory. This does not get us all the way to the quantum probability rule because an extra constraint, known as noncontextuality, is required. I outline the prospects for a derivation of noncontextuality within this approach and argue that it requires a realist approach to physics, or "bit from it". I then explain why this does not conflict with "it from bit". This version of the essay includes an addendum responding to the open discussion that occurred on the FQXi website. It is otherwise identical to the version submitted to the contest.

quant-ph↗