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At least 217 records · Page 12Linked to original sources
arXiv2014

A Critical Look at the Standard Cosmological Picture

The discovery that the Universe is accelerating in its expansion has brought the basic concept of cosmic expansion into question. An analysis of the evolution of this concept suggests that the paradigm that was finally settled into prior to that discovery was not the best option, as the observed acceleration lends empirical support to an alternative which could incidentally explain expansion in general. I suggest, then, that incomplete reasoning regarding the nature of cosmic time in the derivation of the standard model is the reason why the theory cannot coincide with this alternative concept. Therefore, through an investigation of the theoretical and empirical facts surrounding the nature of cosmic time, I argue that an enduring three-dimensional cosmic present must necessarily be assumed in relativistic cosmology---and in a stricter sense than it has been. Finally, I point to a related result which could offer a better explanation of the empirically constrained expansion rate.

physics.hist-ph↗
arXiv2013

Universality of the Weak Interactions, Cabibbo theory and where they led us

Universality of the weak interactions is reviewed, with special emphasis on the origin of the Cabibbo theory of strange particles beta-decays and its role in the discovery of the unified Electroweak Theory. Achievements and present challenges of the Standard Theory of particles interactions are briefly illustrated. As an homage to Nicola Cabibbo, his leading role in the Roma school of theoretical physics and in the italian science in general is reviewed.

hep-ph↗
arXiv2018

The strange (hi)story of particles and waves

This is a non-technical presentation (in historical context) of the quantum theory that is strictly based on global unitarity. While the first part was written for a general readership, Sect. 5 may appear a bit provocative. I argue that the single-particle wave functions of quantum mechanics have to be correctly interpreted as field modes that are "occupied once" (that is, first excited states of the corresponding quantum oscillators in the case of a boson field). Multiple excitations lead non-relativistically to apparent many-particle wave functions, while the quantum states proper are defined by wave function(al)s on the configuration space of fundamental fields, or on another, as yet elusive, fundamental basis.

physics.hist-ph↗
arXiv2013

Hesiod's calendar and the star Spica

In Hesiod's calendar, circa 8th century BCE, the harvest times of cereals were indicated by the heliacal rising of Pleiades (harvest) and by that of Orion (thresh). We tried to verify which risings and settings of the brightest stars could have been used as indicators in the previous millennia, taking into account the precession and the dependence of the heliacal dates on the latitude. In the second half of the 9th millennium BCE there was essentially one bright star that could have been used both for the harvest (heliacal setting of the star) and for the thresh (heliacal rising of the star): Spica, i.e. ear (in Latin) of cereals. According to archaeologists, the domestication of barley and wheat occurred in Near East at the end of the 9th millennium BCE. Given the importance of the bright stars and asterisms for ancient farming activities, we have therefore proposed that the identification of the star alpha Virginis with an ear should date back to the beginning of Neolithic, possibly well before the identification of the constellation (Virgo) with a maiden.

physics.pop-ph↗
arXiv2015

The Discovery of Quasars and its Aftermath

Although the extragalactic nature of quasars was discussed as early as 1960, it was rejected largely because of preconceived ideas about what appeared to be an unrealistically high radio and optical luminosity. Following the 1962 occultations of the strong radio source 3C 273 at Parkes, and the subsequent identification with an apparent stellar object, Maarten Schmidt recognized that the relatively simple hydrogen line Balmer series spectrum implied a redshift of 0.16 Successive radio and optical measurements quickly led to the identification of other quasars with increasingly large redshifts and the general, although for some decades not universal, acceptance of quasars as being by far the most distant and the most luminous objects in the Universe. Curiously, 3C 273, which is one of the strongest extragalactic sources in the sky, was first cataloged in 1959 and the magnitude 13 optical counterpart was observed at least as early as 1887. Since 1960, much fainter optical counterparts were being routinely identified using accurate radio interferometer positions, measured primarily at the Caltech Owens Valley Radio Observatory. However, 3C 273 eluded identification until the series of lunar occultation observations led by Cyril Hazard, although inexplicably there was an earlier mis-identification with a faint galaxy located about an arc minute away from the true position. Ironically, due to calculation error, the occultation position used by Schmidt to determine the redshift of 3C 273 was in error by 14 arcseconds, and a good occultation position was not derived until after Schmidt had obtained his 200 inch spectrum.

physics.hist-ph↗
arXiv2013

International scientific cooperation during the 1930s. Bruno Rossi and the development of the status of cosmic rays into a branch of physics

During the 1920s and 1930s, Italian physicists established strong relationships with scientists from other European countries and the United States. The career of Bruno Rossi, a leading personality in the study of cosmic rays and an Italian pioneer of this field of research, provides a prominent example of this kind of international cooperation. Physics underwent major changes during these turbulent years, and the traditional internationalism of physics assumed a more institutionalised character. Against this backdrop, Rossi's early work was crucial in transforming the study of cosmic rays into a branch of modern physics. His friendly relationships with eminent scientists -notably Enrico Fermi, Walther Bothe, Werner Heisenberg, Hans Bethe, and Homi Bhabha- were instrumental both for the exchange of knowledge about experimental practises and theoretical discussions, and for attracting the attention of physicists such as Arthur Compton, Louis Leprince-Ringuet, Pierre Auger and Patrick Blackett to the problem of cosmic rays. Relying on material from different archives in Europe and United States, this case study aims to provide a glimpse of the intersection between national and international dimensions during the 1930s, at a time when the study of cosmic rays was still very much in its infancy, strongly interlaced with nuclear physics, and full of uncertain, contradictory, and puzzling results. Nevertheless, as a source of high-energy particles it became a proving ground for testing the validity of the laws of quantum electrodynamics, and made a fundamental contribution to the origins of particle physics.

physics.hist-ph↗
arXiv2013

On the Importance of Conceptual Thinking Outside the Simulation Box

Any ambitious construction project requires architects for its design and engineers who apply the design to the real world. As scientific research shifts towards large groups which focus on the engineering aspects of linking data to existing models, architectural skills are becoming rare among young theorists. Senior researchers should mentor qualified students and postdocs to think creatively about the big picture without unwarranted loyalty to ancient blueprints from past generations of architects.

physics.hist-ph↗
arXiv2013

The Ghost in the Quantum Turing Machine

In honor of Alan Turing's hundredth birthday, I unwisely set out some thoughts about one of Turing's obsessions throughout his life, the question of physics and free will. I focus relatively narrowly on a notion that I call "Knightian freedom": a certain kind of in-principle physical unpredictability that goes beyond probabilistic unpredictability. Other, more metaphysical aspects of free will I regard as possibly outside the scope of science. I examine a viewpoint, suggested independently by Carl Hoefer, Cristi Stoica, and even Turing himself, that tries to find scope for "freedom" in the universe's boundary conditions rather than in the dynamical laws. Taking this viewpoint seriously leads to many interesting conceptual problems. I investigate how far one can go toward solving those problems, and along the way, encounter (among other things) the No-Cloning Theorem, the measurement problem, decoherence, chaos, the arrow of time, the holographic principle, Newcomb's paradox, Boltzmann brains, algorithmic information theory, and the Common Prior Assumption. I also compare the viewpoint explored here to the more radical speculations of Roger Penrose. The result of all this is an unusual perspective on time, quantum mechanics, and causation, of which I myself remain skeptical, but which has several appealing features. Among other things, it suggests interesting empirical questions in neuroscience, physics, and cosmology; and takes a millennia-old philosophical debate into some underexplored territory.

quant-ph↗
arXiv2013

Aboriginal Oral Traditions of Australian Impact Craters

We explore Aboriginal oral traditions that relate to Australian meteorite craters. Using the literature, first-hand ethnographic records, and fieldtrip data, we identify oral traditions and artworks associated with four impact sites: Gosses Bluff, Henbury, Liverpool, and Wolfe Creek. Oral traditions describe impact origins for Gosses Bluff, Henbury, and Wolfe Creek craters and non-impact origins of Liverpool crater, with Wolfe Creek and Henbury having both impact and non-impact origins in oral tradition. Three impact sites that are believed to have formed during human habitation of Australia - Dalgaranga, Veevers, and Boxhole - do not have associated oral traditions that are reported in the literature.

physics.hist-ph↗
arXiv2013

Instants in physics - point mechanics and general relativity

Theories in physics usually do not address ``the present''or ``the now''. However, they usually have a precise notion of an ``instant'' (or state). I review how this notion appears in relational point mechanics and how it suffices to determine durations - a fact that is often ignored in modern presentations of analytical dynamics. An analogous discussion is attempted for General Relativity. Finally I critically remark on the difference between relationalism in point mechanics and field theory and the problematic foundational dependencies between fields and spacetime.

physics.hist-ph↗
arXiv2013

Where the "it from bit" come from?

In his 1989 essay, John Archibald Wheeler has tried to answer the eternal question of existence. He did it by searching for links between information, physics, and quanta. The main concept emerging from his essay is that "every physical quantity, every it, derives its ultimate significance from bits, binary yes-or-no indications". This concept has been summarized in the catchphrase "it from bit". In the Wheeler's essay, it is possible to read several times the echoes of the philosophy of Niels Bohr. The Danish physicist has pointed out how the quantum and relativistic physics - forcing us to abandon the anchor of the visual reference of common sense - have imposed a greater attention to the language. Bohr did not deny the physical reality, but recognizes that there is always need of a language no matter what a person wants to do. To put it as Carlo Sini, language is the first toolbox that man has at hands to analyze the experience. It is not a thought translated into words, because to think is to operate with signs as reminded us by various philosophers from Leonardo da Vinci to Ludwig Wittgenstein. [...]

physics.hist-ph↗
arXiv2013

Meteors in the Maori Astronomical Traditions of New Zealand

We review the literature for perceptions of meteors in the Maori cultures of New Zealand. We examine representations of meteors in religion, story, and ceremony. We find that meteors are sometimes personified as gods or children, or are seen as omens of death and destruction. The stories we found highlight the broad perception of meteors found throughout the Maori culture and demonstrate that some early scholars conflated the terms comet and meteor.

physics.hist-ph↗
arXiv2013

The Discovery and History of the Dalgaranga Meteorite Crater, Western Australia

The Dalgaranga meteorite crater, 100 km northeast of Yalgoo, Western Australia, was one of the first impact structures identified in Australia, the smallest isolated crater found in Australia, and the only confirmed crater in the world associated with a mesosiderite projectile. 17 years passed before the Dalgaranga meteorites were described in the scientific literature and nearly 40 years passed before a survey of the structure was published. The reasons for the time-gap were never explained and a number of factual errors about the discovery and early history remain uncorrected in the scientific literature. Using historical and archival documents, and discussions with people involved in Dalgaranga research, the reasons for this time gap are explained by a series of minor misidentifications and coincidences. The age of the crater has yet to be determined, but using published data, we estimate the projectile mass to be 500-1000 kg.

physics.geo-ph↗
arXiv2014

Einstein's physical geometry at play: inertial motion, the boostability assumption, the Lorentz transformations, and the so-called conventionality of the one-way speed of light

In this work, Einstein's view of geometry as physical geometry is taken into account in the analysis of diverse issues related to the notions of inertial motion and inertial reference frame. Einstein's physical geometry enables a non-conventional view on Euclidean geometry (as the geometry associated to inertial motion and inertial reference frames) and on the uniform time. Also, by taking into account the implications of the view of geometry as a physical geometry, it is presented a critical reassessment of the so-called boostability assumption (implicit according to Einstein in the formulation of the theory) and also of 'alternative' derivations of the Lorentz transformations that do not take into account the so-called 'light postulate'. Finally it is addressed the issue of the eventual conventionality of the one-way speed of light or, what is the same, the conventionality of simultaneity (within the same inertial reference frame). It turns out that it is possible to see the (possible) conventionality of distant simultaneity as a case of conventionality of geometry (in Einstein's reinterpretation of Poincaré's views). By taking into account synchronization procedures that do not make reference to light propagation (which is necessary in the derivation of the Lorentz transformations without the 'light postulate'), it can be shown that the synchronization of distant clocks does not need any conventional element. This implies that the whole of chronogeometry (and because of this the physical part of the theory) does not have any conventional element in it, and it is a physical chronogeometry.

physics.hist-ph↗
arXiv2013

New Views of Crystal Symmetry

Already Hermann Grassmann's father Justus (1829, 1830) published two works on the geometrical description of crystals, influenced by the earlier works of C.S. Weiss (1780-1856) on three main crystal forces governing crystal formation. In his 1840 essay on the derivation of crystal shapes from the general law of crystal formation Hermann established the notion of a three-dimensional vectorial system of forces with rational coefficients, that represent the interior crystal structure, regulate its formation, its shape and physical behavior. In the Ausdehnungslehre 1844 (Paragraph 171) he finally writes: I shall conclude this presentation by one of the most beautiful applications which can be made of the science treated, i.e. the application to crystal figures (Scholz, 1996). The geometry of crystals thus certainly influenced the Ausdehnungslehre. In this paper we see how Grassmann's work influenced Clifford's creation of geometric algebras, which in turn leads to a new geometric description of crystal symmetry suitable for modern computer algebra graphics.

cond-mat.mtrl-sci↗
arXiv2013

Does the first part of the second law also imply its second part?

Sommerfeld called the first part of the second law to be the entropy axiom, which is about the existence of the state function entropy. It was usually thought that the second part of the second law, which is about the non-decreasing nature of entropy of thermally isolated systems, did not follow from the first part. In this note, we point out the surprise that the first part in fact implies the second part.

physics.hist-ph↗
arXiv2013

Aspects of Gond Astronomy

The Gond community is considered to be one of the most ancient tribes of India with a continuing history of several thousand years. They are also known for their largely isolated history which they have retained through the millennia. Several of their intellectual traditions therefore are a record of parallel aspects of human intellectual growth, and still preserve their original flavour and have not been homogenised by the later traditions of India. In view of this, the Gonds provide a special window to the different currents that constitute contemporary India. In the present study, we summarise their mythology, genetics and script. We then investigate their astronomical traditions and try to understand this community through a survey of 15 Gond villages spread over Maharashtra, Andhra Pradesh and Madhya Pradesh. We show that they have a distinctly different view of the sky from the conventional astronomical ideas encountered elsewhere in India, which is both interesting and informative. We briefly comment on other aspects of their life as culled from our encounters with different members of the Gond community.

physics.hist-ph↗