Cosmogenesis (6) : The Creation in the Renaissance

Sequel of the preceding post Cosmogenesis (5) : The Order of the Creation

The Creation in the Renaissance

Hartmann Schedel’s Nuremberg Chronicle, published in 1493, effectively marks the watershed between medieval scholarship and Renaissance speculation. It is the manifestation of a desire for completeness, amalgamating the principal accounts of the Creation (Genesis, Plato’s Timaeus, Hesiod’s Theogony, Ovid’s Metamorphoses) into a single, all-embracing narrative.

The Creation in a Renaissance Edition of Ovid's Metamorphoses. Ovide moralisé (Ovid Moralised) is a French text written in the late Middle Ages which regards Ovid's Metamorphoses as having anticipated the scriptures. The early humanists inherited this view and, throughout the 16th century, the Metamorphoses were treated as a manual of morality and wisdom and subjected to numerous glosses and commentaries. This edition, published in Lyons in 1519, includes commentaries by Raphael Regius, an Italian teacher of grammar and rhetoric, and Petrus Lavinius, a Dominican monk who was part of the humanist circle in Lyon. The engraving illustrating the Creation was inspired by the Italian woodcuts in the first edition of Regius' commentary, which was published in Venice in 1493. The fact that the artist drew the Creator as Christ rather than Jupiter shows how Ovid's poem had been adapted to match Christian legend. Ovid, P. Ovidii Nasonis Metamorphoseos Libri Moralizati, Cum Pulcherrimis Fabularum Principalium Figuris, Lyons, Jacques Mareschal, 1519.
The Creation in a Renaissance Edition of Ovid’s Metamorphoses.
Ovide moralisé (Ovid Moralised) is a French text written in the late Middle Ages which regards Ovid’s Metamorphoses as having anticipated the scriptures. The early humanists inherited this view and, throughout the 16th century, the Metamorphoses were treated as a manual of morality and wisdom and subjected to numerous glosses and commentaries. This edition, published in Lyons in 1519, includes commentaries by Raphael Regius, an Italian teacher of grammar and rhetoric, and Petrus Lavinius, a Dominican monk who was part of the humanist circle in Lyon. The engraving illustrating the Creation was inspired by the Italian woodcuts in the first edition of Regius’ commentary, which was published in Venice in 1493. The fact that the artist drew the Creator as Christ rather than Jupiter shows how Ovid’s poem had been adapted to match Christian legend. Ovid, P. Ovidii Nasonis Metamorphoseos Libri Moralizati, Cum Pulcherrimis Fabularum Principalium Figuris, Lyons, Jacques Mareschal, 1519.

Heptaplus (1490), by the Italian philosopher Pico Della Mirandola, is a scholarly exercise in seven volumes, each of seven chapters, which attempts to synthesise the various traditions deriving from the Creation myth: that of the Platonists and the Peripatetic School, that of the Evangelists, Church Fathers and Cabbalists, and that of the Islamic philosophers such as Avicenna (Ibn Sina) and Averroes (Ibn Rushd). In particular Mirandola tries to find a hidden meaning to the first two words of Genesis, “In principio”, using the Cabbalist method of making anagrams.

In 1578 Guillaume de Saluste, known as Du Bartas, published an epic poem based on Genesis and inspired by Ovid’s Metamorphoses entitled La Sepmaine (The Week). In “The First Day” Du Bartas attempts to describe chaos by using words in a confused way, using puns and antonyms:

This primordial world was form without form,
A confused heap, a shapeless melange,
A void of voids, an uncontrolled mass,
A Chaos of Chaos, a random mound
Where all the elements were heaped together,
Where liquid quarrelled with solid,
Blunt with sharp, cold with hot,
Hard with soft, low with high,
Bitter with sweet: in short a war
In which the earth was one with the sky. [i]
Continue reading

A brief history of space (3/4) : from Descartes to Schwarzschild

Sequel of the preceding post A Brief History of Space (2/4) : From Ptolemy to Galileo

At the beginning of XVIIth century, the way was open for new cosmologies, constructed on the basis of infinite space. Until then, the notion of space was conceived in the cosmological and physical order of nature, and not as the “background” of the figures and geometric constructions of Euclid. In other terms, physical space was not mathematicized. It became so thanks to René Descartes (1596 – 1650), who had the idea of specifying each point by three real numbers: its coordinates. The introduction of a universal system of coordinates which entirely criss-crossed space and allowed for the measurement of distances was a reflection of the fact that, for Descartes, the unification and uniformization of the universe in its physical content and its geometric laws was a given. Space is a substance in the same class as material bodies, an infinite ether agitated by vortices without number, at the centers of which were held the stars and their planetary systems.

A portrait of René Descartes

This new conception of the cosmos upset philosophical thought and led it far from the initial enthusiasm of the atomists and Giordano Bruno: “The absolute space which inspired the hexameters of Lucretius, the absolute space which that had been a liberation for Bruno, was a labyrinth and an abyss for Pascal.”[5] As for the scholars, they did not allow themselves to be discouraged by these moods and irresistibly moved towards the infinite universe.

The Descartes system of the world using vortices

The tendency toward the radical geometrization of an infinite space, initiated by Descartes, was consummated by the Englishman Isaac Newton (1642-1727). Newton postulated an absolute space, encompassing not only the background space of mathematics and the physical space of astronomy, but also that of metaphysics, since space was the “sensorium of God.” Physical space, finally identified with geometrical space, was necessarily Euclidean (the only one known at the epoch), without curvature, amorphous and infinite in every direction. At the heart of this immobile framework, Newton explained celestial mechanics in terms of the law of universal attraction, from now on considered responsible for gravitation and the large scale structure of the Universe. With Newton, cosmology took root for more than two centuries in the framework of an infinite Euclidean space and an eternal time.

Newton around 1700

All the problems are not resolved in Newtonian cosmology, far from it. On the question of the distribution of stars in space, for example, Newton believed that they must occupy a finite volume since, he argued, if they occupied an infinite space, they would be infinite in number, the force of gravitation would be infinite, and the universe would be unstable. Newton moreover supposed that the stars were uniformly spread within a finite mass|like a galaxy, for example. But a problem of instability remained: since each celestial body is attracted by every other one, at the least movement, at the least mechanical perturbation, all the bodies in the universe would fall towards a unique center, and the universe would collapse. Newton’s universe is therefore only viable if it does not admit motion on the large scale: its space is rigid and its time immobile. Continue reading

A Brief History of Space (2/4) : from Ptolemy to Galileo

Sequel of the preceding post A Brief History of Space (1/4).

The cosmology of Aristotle, as perfected by Ptolemy and reintroduced thanks to arabic translations and commentaries, was adapted to satisfy the demands of the theologians. Notably, that which is situated beyond the last material sphere of the world acquired the status of, if not physical, at least ethereal or spiritual space. Baptized “Empyrean”, it was considered to be the residence of God, the angels and the saints. The medieval cosmos was not only finite, but quite small: the distance from the Earth to the sphere of the fixed stars was estimated to be 20,000 terrestrial radii, because of which Paradise, at its edge, was reasonably accessible to the souls of the deceased. The Christian naturally found his place at the center of this construction.

In this medieval system of the world designed by Apianus in 1520, the whole universe is finite, bounded by a spherical layer containing the fixed stars, beyond which lies the Empyreum, the house of God and Saints.
In this medieval system of the world designed by Apianus in 1520, the whole universe is finite, bounded by a spherical layer containing the fixed stars, beyond which lies the Empyreum, the house of God and Saints.

A Hierachical universe according to Dante's Divine Comedy
A Hierarchical universe according to Dante’s Divine Comedy

 

Nicholas of Cusa
Nicholas of Cusa

This model of the universe imposed itself until the seventeenth century, without nevertheless impeding the resurgence of atomist ideas. After the rediscovery of the manuscript of Lucretius De rerum natura, the German cardinal Nicholas of Cusa (1401-1464) argued in favor of an infinite Universe, of a plurality of inhabited worlds, and of an Earth in motion. However, his arguments remained primarily metaphysical: the universe is infinite because it is the work of God, who could not possibly be limited in His works.

When the Polish canon Nicolaus Copernicus (1473-1543) proposed his heliocentric system, in which the Sun is at the geometric center of the world while the Earth turns around it and around itself, he kept the idea of a closed cosmos, surrounded by the sphere of fixed stars. Even if this is two thousand times further away than in the Ptolemeian model, the universe nevertheless remained bounded.

A romantic depiction of Copernicus
A romantic depiction of Copernicus and his new model of the universe

We must wait several decades more for the first cracks to appear in the Aristotelian edifice. In 1572, a new star was observed by the Dane Tycho Brahe (1546-1601), who showed that it was situated in the sphere of fixed stars, that is to say in the celestial region until then presumed to be immovable. In 1576, the Englishman Thomas Digges (1545-1595), a staunch Copernican, maintained that the stars were not distributed on a thin layer, at the surface of the eighth and last sphere of the world, but extended endlessly upwards. Digges nevertheless was not proposing a physical conception of infinite space: for him, the sky and the stars remained Empyrean, God’s realm, and in this regard did not truly belong to our world.

copernicus-diag Syst-Digges

An epistemological rupture[1] was triggered by two Italian philosophers. In 1587, Francesco Patrizi (1529-1597) produced Of Physical and Mathematical Space[2], where he put forth the revolutionary idea that the true object of geometry was space in itself, and not figures, as had been believed since Euclid. Patrizi inaugurated a new understanding of infinite physical space, in which it obeyed mathematical laws and was therefore accessible to understanding. But it is above all his contemporary Giordano Bruno (1548-1600) who is attributed with the true paternity of infinite cosmology. brunoThe first book of his De immenso is entirely dedicated to a logical definition of infinite space. Bruno argued from physical, and no longer exclusively theological, basics. His cosmological thought was inspired by the atomism of Lucretius, the reasoning of Nicholas of Cusa, and the Copernican hypothesis. From the latter, Bruno retained heliocentrism and the ordering of the solar system, but rejected the cosmological finitism. A precursor to Kepler and Newton, he also refuted the cult of sphericity and of uniform circular motion for describing celestial motion. His bold and original writings were not understood by his contemporaries, most notably Galileo. Above all they were firmly opposed by the Church. In fact, the true philosophical subversion of the end of the sixteenth century did not reside so much in the heliocentric affirmation of Copernicus as in that of the infinite multiplicity of worlds. Camped at the front ranks of the anti-Aristotelian battle, Bruno, carried away by his passion for infinity, refused to abjure and was burned at the stake in Rome.

Johannes Kepler (1571-1630), another great artisan of the astronomical revolution, tried at first to construct a universal model founded on the use of particular geometric figures: the regular polyhedra. He failed at this attempt; the ordering of planetary orbits as calculated did not correspond to the new experimental data collected by Tycho Brahe. After discovering the elliptical nature of the planetary trajectories, Kepler overturned the Aristotelian dogma of circular and uniform motion as the ultimate explanation of celestial movement. He nevertheless refused to follow Bruno in his arguments for the infinitude of the universe. He considered this notion to be purely metaphysical and, since it was not founded on Kepler_Epitomeexperiment, denuded of scientific meaning: “In truth, an infinite body cannot be understood by thought. In fact the concepts of the mind on the subject of the infinite refer themselves either to the meaning of the word `infinite,’ or indeed to something which exceeds any conceivable numeric, visual or tactile measurement; that is to say to something which is not infinite in action, seeing that an infinite measurement is not conceivable.”[3] Kepler supported his argument by expressing for the first time an astronomical paradox that seemed to be an obstacle to the concept of infinite space, and which would be extensively discussed: the “paradox of the dark night.” Just like the edge paradox, this problem would not be satisfactorily resolved until the middle of the nineteenth century, although by completely different arguments.

Starting in 1609, the telescope observations of Galileo (1564-1642) furnished the first direct indications of the universality of the laws of nature. On the question of spatial infinity, however, Galileo, like Kepler, adopted the prudent attitude of the physicist: “Don’t you know that it is as yet undecided (and I believe that it will ever be so for human knowledge) whether the Universe is finite or, on the contrary, infinite?” [4]

systemegalilee001

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[1] See Alexander Koyre, From the Closed World to the Infinite Universe, New York: Harper Torchbook, 1958.

[2] De spacio physico et mathematico ; See R. Brickman, “On Physical Space, Francesco Patrizi”, Journal of the History of Ideas, vol.4, 224 (1943).

[3] De stella nova, 1606. Unfortunately there is no English translation for this masterpiece.

[4] Letter to Ingoli, quoted in A. Koyré, From the Close World to the Infinite Universe, The John Hopkins Press 1957, p. 97.

A Brief History of Space (1/4)

This post is based on a chapter of my book  “The Wraparound Universe” but is much more illustrated.  The chapter is divided into 4 parts, here is the first one.

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That which keeps quiet beyond everything, is this in fact simply what I name Space? . . . Space! An idea! A word! A breath!
Jean Tardieu

There is no space or time given a priori; to each moment in human history, to each degree of perfection of our physical theories of the Universe, there corresponds a conception of those fundamental categories of thought known as space, time, and matter. To each new conception, our mental image of the Universe must adapt itself, and we must accept that “common sense” was found lacking. For example, if space is limited by a boundary, what is there beyond it? Nothing? It is difficult to imagine that, by voyaging sufficiently far in a given direction, one could reach a point beyond which nothing more exists, not even space. It is just as troubling to think of an infinitely large Universe. What would be the meaning of any measurable, that is to say finite, thing with respect to the infinite?

A possible representation of Anaximander learning Pythagoras on his left, detail of Raphael's famous painting The School of Athens.
A possible representation of Anaximander learning Pythagoras on his left, detail of Raphael’s famous painting The School of Athens.

These types of questions were formulated in the sixth century BCE, in ancient Greece, where they rapidly became the object of controversy. The first schools of scholars and philosophers, called “presocratic” (although they were spread over two centuries and were quite different from each other), each attempted in their way to rationally explain the “world,” meaning the ensemble formed by the Earth and the stars, conceived as an organized system. For Anaximander, from the school of Miletus, the world where observable phenomena take place was necessarily finite. Nevertheless, it was plunged within a surrounding medium, the apeiron, corresponding to what we today consider as space. This term signifies both infinite (unlimited, eternal) and indefinite (undetermined). For his contemporary, Thales, the universal medium was made of water, and the world was a hemispheric bubble floating in the middle of this infinite liquid mass.

We meet up again with this intuitive conception of a finite material world bathing in an infinite receptacle space with other thinkers: Heraclitus, Empedocles, and especially the Stoics, who added the idea of a world in pulsation, passing through periodic phases of explosions and deflagrations.

Atomism, founded in the fifth century by Leucippus and Democritus, advocated a completely different version of cosmic infinity. It maintained that the Universe was constructed from two primordial elements: atoms and the void. Indivisible and elementary, (atomos means “that which cannot be divided”), atoms exist for all eternity, only differing in their size and shape. They are infinite in number. All bodies result from the coalescence of atoms in motion; the number of combinations being infinite, it follows that the celestial bodies are themselves infinite in number: this is the thesis of the plurality of worlds. The formation of these worlds is produced within a receptacle without bounds: the void (kenon). This “space” has no other property than being infinite and accordingly matter has no influence on it: it is absolute, given a priori.

Part of a fresco in the portico of the National University of Athens representing Anaxagoras.
Part of a fresco in the portico of the National University of Athens representing Anaxagoras.

The atomist philosophy was strongly criticized by Socrates, Plato, and Aristotle. Moreover, by affirming that the universe is not governed by gods, but by elementary matter and the void, it inevitably entered into conflict with the religious authorities. In the fourth century BCE, Anaxagoras of Clazomenae was the first scholar in history to be accused of impiety; however, defended by powerful friends, he was acquitted and was able to flee far from the hostility of Athens. Thanks to its two most illustrious spokesmen, Epicurus (341-270 BCE), who founded the first school that allowed female students and Lucretius (first century BCE), author of a magnificent cosmological poem, On the Nature of Things, atomism continued to flourish until the advent of Christianity. It was however marginalized over the course of the first centuries of the christian era, and would not again be part of mainstream science until the seventeenth century. Continue reading

Cosmogenesis (10) : A Modern Account

Sequel of the preceding post Cosmogenesis (9) : The Big Bang Discovery and End of the Cosmogenesis Series.

According to modern physics the universe has undergone a gradual process of expansion and cooling ever since the big bang; at the same time increasingly complex physical structures have evolved. The history of the universe can conveniently be divided into two main periods: the first million years (infancy) and the remaining 15 billion years (maturity).

The Infant Universe

The Bubble Theory of Cosmogenesis. According to some models constructed according to the laws of quantum physics, the observable universe is merely one of a multitude of ephemeral "bubbles" created by spontaneous fluctuations in the quantum vacuum. The universe as a whole is like a rapidly expanding foam, each "baby universe" giving birth to more "baby universes" and so on in an eternally self-reproducing system. Artistic view by S. Numazawa.
The Bubble Theory of Cosmogenesis. According to some models constructed according to the laws of quantum physics, the observable universe is merely one of a multitude of ephemeral “bubbles” created by spontaneous fluctuations in the quantum vacuum. The universe as a whole is like a rapidly expanding foam, each “baby universe” giving birth to more “baby universes” and so on in an eternally self-reproducing system.
Artistic view by S. Numazawa.

During the Planck era, time and the dimensions of space as we know them were so intimately linked as to be practically indistinguishable. Various speculative theories of “quantum cosmogenesis”, as yet in their infancy, attempt to explain how our universe emerged at the end of the Planck era. Some physicists refer to its “spontaneous emergence”, others to an infinite number of separate “cosmic bubbles” arising from the quantum vacuum like foam from the surface of the sea.

Between 10-43 and 10-32 seconds after the big bang the infant universe consisted of elementary particles bound by a primeval superforce. A few billiseconds later gravity separated itself from the surviving electrostrong force, which in turn, as the temperature fell to 1027 degrees, divided into the strong force and the electroweak force. Recent experiments in high energy physics suggest that these “symmetry breakdowns” had spectacular consequences: the appearance of strange objects; “topological defects” such as “cosmic strings”; even the onset of “inflation” – a very short period during which the universe grew immeasurably. The fundamental constituents of matter – quarks, electrons and neutrinos – also appeared at this time.

10-11 seconds after the big bang the temperature of the universe had dropped to 1015 degrees and the electroweak force split into an electromagnetic and a weak force, thus establishing the four fundamental forces  and fixing the physical conditions for the formation of complex structures.

10-6 seconds after the big bang all quarks were “linked” in threes by the strong force to form the first nucleons, i.e. protons and neutrons. By this time the temperature had fallen to a billion degrees as the universe continued to expand. As particles became more widely spaced, they collided less frequently but one hundred seconds or so later the crucial process of nucleosynthesis began. Neutrons and protons combined to form the simplest atomic nuclei: hydrogen, helium and lithium (in various isotopes). Most of the universe, however, remained as isolated protons, i.e. as hydrogen nuclei.

Nucleosynthesis took place only for a very short time: the universe was cooling so rapidly that there was only time for the lightest elements to form. These therefore constitute 99 per cent of the visible matter in the universe today (75% hydrogen and 24% helium). The remaining one per cent, consisting of heavier elements like carbon, nitrogen and oxygen, would not be created until billions of years later, when the stars were formed.

Nucleosynthesis. Scientists at the particle accelerator near Caen in France (known as GANIL — Grand Accélérateur National d'lons Lourds) have managed to fuse heavy ions by making them collide at high speed. These computer-generated images show the fusion of a lanthanum nucleus with a copper nucleus. Such experiments help scientists to understand the process of nucleosynthesis which, during the first few seconds after the big bang, caused the fusion of hydrogen ions and helium ions, creating the first lightweight elements. Nucleosynthesis is one way of testing big bang theory, whose predictions as to the quantity of each element in the universe can be compared with experimental results. Indeed they are remarkably similar: the universe does in fact comprise 75% hydrogen (in mass) and between 24 and 25% helium (in mass). There is an equally close correlation between the predicted and observed prevalence of deuterium and tritium. Other experimental results are valuable in limiting the possibilities open to those refining big bang theory. Montage by Philippe Chomaz (GANIL)
Nucleosynthesis. Scientists at the particle accelerator near Caen in France (known as GANIL — Grand Accélérateur National d’lons Lourds) have managed to fuse heavy ions by making them collide at high speed. These computer-generated images show the fusion of a lanthanum nucleus with a copper nucleus. Such experiments help scientists to understand the process of nucleosynthesis which, during the first few seconds after the big bang, caused the fusion of hydrogen ions and helium ions, creating the first lightweight elements. Nucleosynthesis is one way of testing big bang theory, whose predictions as to the quantity of each element in the universe can be compared with experimental results. Indeed they are remarkably similar: the universe does in fact comprise 75% hydrogen (in mass) and between 24 and 25% helium (in mass). There is an equally close correlation between the predicted and observed prevalence of deuterium and tritium. Other experimental results are valuable in limiting the possibilities open to those refining big bang theory.
Montage by Philippe Chomaz (GANIL)

Until it was 300,000 years old the universe remained opaque; in other words it emitted no radiation: the density of electrons prevented photons from moving freely. But the universe, consisting of a “soup” of particles and radiation, continued to cool and expand until, at 3,000 degrees, it became transparent and emitted its first electromagnetic signal in the form of what we now detect as cosmic background radiation.

A million years after the big bang the first atoms were formed, when electrons were captured by hydrogen and helium nuclei, and these atoms combined into molecules to create vast clouds of hydrogen, out of which stars would later emerge. Continue reading

Cosmogenesis (9) : The Big Bang Discovery

Sequel of the preceding post Cosmogenesis (8) : The Nebular Hypothesis

Star Clusters and Nebulae. This page from "Telescopic views of Nebulae and Clusters by the Earl of Rosse and Sir J. Herschel" (1875) includes a variety of drawings of nebulosities by different observers. There are star clusters and gaseous nebulae (now known to belong to our own galaxy) as well as other galaxies. Observational techniques of the time were unable to distinguish between these very different types of objects.
Star Clusters and Nebulae. This page from “Telescopic views of Nebulae and Clusters by the Earl of Rosse and Sir J. Herschel” (1875) includes a variety of drawings of nebulosities by different observers. There are star clusters and gaseous nebulae (now known to belong to our own galaxy) as well as other galaxies. Observational techniques of the time were unable to distinguish between these very different types of objects.

In the first quarter of the 20th century cosmology became a distinct scientific discipline, thanks in part to the theoretical advance made in 1915 by Einstein with his theory of general relativity and in part to the revolution in observational techniques which revealed the true extent of the universe. Having at last been able to measure the distance of certain spiral nebulae, Edwin Hubble could confirm in 1925 that there existed other galaxies like our own.

His colleague Vesto Slipher had previously discovered that the radiation from these galaxies was constantly shifting towards the red end of the optical spectrum, which suggested that they were moving away from us at great speed. This movement was not understood until scientists came to accept an idea based on the theory of general relativity and first proposed by Alexandre Friedmann in 1922 and independently Georges Lemaître in 1927: that space was constantly expanding and consequently increasing the distance between galaxies. This idea proved to be one of the most significant discoveries of the century[i].

Alexander Friedmann in 1922
Alexander Friedmann in 1922

In an article which appeared in 1922, entitled “On the Curvature of Space“, Friedmann took the step which Einstein had balked at: he abandoned the theory of a static universe, proposing a “dynamic” alternative in which space varied with time. For the first time the problem of the beginning and the end of the universe was couched in purely scientific terms. Friedmann suggested that the universe was several tens of billions of years old, much older than the earth (then estimated to be about one billion years old) or the oldest known celestial objects. It was a remarkable prediction, the most recent estimate for the age of the universe being between 10 and 20 billion years.

In 1927, in a seminal article entitled “A Homogeneous Universe of Constant Mass and Increasing Radius Accounting for the Radial Velocity of Extra-Galactic Nebulae“, Lemaître explained the observations of Hubble and Slipher by interpreting them, within the context of general relativity, as manifestations of the expansion of the universe. This expansion was taking place uniformly across the entire universe (which might be finite or infinite), not outwards from a particular point (in this sense the often quoted analogy of a balloon being inflated is misleading). It was not a case of matter moving within a fixed geometric framework, but of the framework itself dilating, of the very “fabric” of space-time stretching. Continue reading

Cosmogenesis (8) : The Nebular Hypothesis

Sequel of the preceding post Cosmogenesis (7) : The Date of the Creation

The Nebular Hypothesis

The ancient Babylonians had a different idea of how the world began. They believed that it had evolved rather than being created instantaneously. Assyrian inscriptions have been found which suggest that the cosmos evolved after the Great Flood and that the animal kingdom originated from earth and water. This idea was at least partially incorporated into a monotheist doctrine and found its way into the sacred texts of the Jews, neighbors and disciples of the Babylonians. It was also taken up by the early Ionian philosophers, including Anaximander and Anaximenes, and by the Stoics and atomists.

A portrait of Democritus (460-370 BC), the founder of atomistic theory.
A portrait of Democritus (460-370 BC), the founder of atomistic theory.

Democritus developed a theory that the world had originated from the void, a vast region in which atoms were swirling in a whirlpool or vortex. The heaviest matter was sucked into the center of the vortex and condensed to form the earth. The lightest matter was thrown to the outside where it revolved so rapidly that it eventually ignited to form the stars and planets. These celestial bodies, as well as the earth itself, were kept in position by centrifugal force. This concept admitted the possibility that the universe contained an infinite number of objects. It also anticipated the 19th century theory of the origin of the solar system, known as the nebular hypothesis, according to which a “primitive nebula” condensed to form the sun and planets.

The idea of universal evolution had a strong influence on classical thought and developed in various directions during Greek and Roman times. In the first century BC Lucretius extended the theories of atomism and evolution to cover every natural phenomenon[i] and argued that all living things originated from earth. Two centuries later, in his medical treatise On the Use of the Parts of the Body[ii], the Greek physician Galen (Claudius Galenus) expressed the essentially Stoic view that matter is eternal and that even God is subject to the laws of nature: contrary to the literal interpretation of the Genesis story, he could not have “formed man from the dust of the ground”; he could only have shaped the dust according to the laws governing the behaviour of matter. The Church Fathers, who insisted that the Creation was instantaneous, rejected any sort of evolutionary theory; to them the ideas of the Stoics and atomists were heretical.

In the second half of the 16th century the idea of universal evolution began to be incorporated into the new system of scientific thought resulting from the work of Copernicus, Kepler, Galileo, Descartes and Newton. According to Descartes, for example, space consisted of “whirlpools” of matter whose motion was governed by the laws of physics. Newton, with his theory of universal attraction, was accused of having substituted gravitation for providence, for having replaced God’s spiritual influence on the cosmos by a material mechanism[iii]. A new view of the world had nevertheless been established, whereby the workings of the universe were subject not to the whim of the Almighty but to the laws of physics – it was an irreversible step. Continue reading

Cosmogenesis (7) : The Date of the Creation

Sequel of the preceding post Cosmogenesis (6) : The Creation in the Renaissance

The Date of the Creation

None of the traditional myths gives a precise date for the Creation. The very idea of putting dates to the history of the world seems to have been foreign to the mentality of the ancients. For them the origin of the universe was simply a notion which helped them to understand the separation of reality into two regions: formless chaos and cosmic order. It was the Jewish/Christian preoccupation with time as a linear process which prompted the question: when was the Creation? From then on the greatest theologians (from Eusebius of Caesarea in the fourth century to James Ussher, Irish prelate and archbishop of Armagh, in the 17th century) and scientists (from Kepler to Newton) would attempt to provide the answer.

For centuries the only clues were to be found in the Bible, which was thought to be able at least to provide an upper limit to the age of the world. From studying the Bible, the vast majority of scholars put the date of the Creation at around 4000 BC, the most common method of calculation being to count the number of generations between Adam and Jesus. St Luke[i] and other commentators list 75 generations, which at approximately 50 years per generation make 4000 BC a plausible date. This reasoning was accepted until the 18th century, even though Ronsard ended his Hymn to the Sky of 1555 with the words: “Your beauty is such that I simply cannot believe / It is but four or five thousand years since your beginning.

More precise estimates gradually appeared. According to the theologian and historian the Venerable Bede in the eighth century and Vincent de Beauvais in the 13th, the Creation took place in the spring.

Depiction of the Venerable Bede from the Nuremberg Chronicle, 1493
Depiction of the Venerable Bede from the Nuremberg Chronicle, 1493

In his historical treatise Annales Veteris Testamenti, a Prima Mundi Origine Deducti (Annals of the Old Testament, Traced Back to the Origin of the World) of 1650, James Ussher attempted to determine precisely the dates of the great biblical events by checking them against historical facts and astronomical phenomena. According to his calculations the first day of the Creation was 23rd October 4004 BC (beginning at midday) and Adam and Eve were expelled from the Garden of Eden on Monday 19th November, Noah’s Ark went aground on the summit of Mount Ararat on 5th May 1491 BC, and so on.

Similarly, in 1642, the Vice-Chancellor of Cambridge University, John Lightfoot, an eminent Hebrew scholar, stated that “heaven and earth, centre and circumference, were created all together, in the same instant” and that “man was created by the Trinity on October 23, 4004 BC at nine o’clock in the morning.”[ii] Continue reading

Cosmogenesis (5) : The Order of the Creation

Sequel of the preceding post Cosmogenesis (4) : The Creator

The order of the Creation

“Order and Truth are born when Passion is aroused. From them is born Night and from Night the Ocean and its waves. From the Ocean’s waves is born the Year, which apportions Night and Day and governs all that the eye sees. The Creator gave shape first to the Sun and Moon, then to the Sky and the Earth, then to the Air and finally to Light.”
Rig-veda, X, 190.

According to Vedic tradition the Creation took place in a completely different order from that specified by the familiar Jewish/Christian story: on the first day God created matter and light out of chaos; on the second day He,  created the air by separating the sky from the waters; on the third day He divided the earth and the waters; on the fourth day He created the celestial bodies, on the fifth the fish and the birds and on the sixth the animals and man; finally, on the seventh day, God rested and contemplated his work.

According to Genesis the separation of light and darkness took place on the first day, the sun and moon not appearing until the fourth. The light which existed on the first day therefore did not come from the sun. Here the bible is perpetuating an ancient belief that light and darkness are independent of the sun, moon and stars, which exist not to provide light but merely to increase it, to distinguish between day and night, to mark the changing of the seasons, and so on. “We must remember that daylight is one thing and sunlight, moonlight and starlight another – the sun’s purpose is to give daylight additional brilliance,” wrote St Ambrose in his Hexameron.

This idea is clearly illustrated by the mosaics in St Mark’s cathedral in Venice and by the frescos in the baptistery in Florence and the basilica of St Francis at Assisi, all of which show the Creator placing in the sky two discs of equal size distinguished only by their colour or by an inscription.

The Creation of Light. The ceiling of St Mark's cathedral in Venice is adorned with a series of beautiful mosaics illustrating the story of Genesis. The pictures relating to the Creation, in the first cupola, were probably completed around 1220 and are modelled on the Cotton bible, a 5th or 6th century illuminated copy of an -ancient Greek manuscript.
The Creation of Light. The ceiling of St Mark’s cathedral in Venice is adorned with a series of beautiful mosaics illustrating the story of Genesis. The pictures relating to the Creation, in the first cupola, were probably completed around 1220 and are modelled on the Cotton bible, a 5th or 6th century illuminated copy of an -ancient Greek manuscript.

Whereas mythical and religious stories describe the creation of the world (by one or more gods), scientific “accounts” are concerned with the formation and evolution of the universe and its content. There are, however, many parallels between these two approaches.

The Creation of Heaven and Earth. The caption to this bible illustration reads: "The Creation of Heaven and Earth, of Trees, Plants, Stars and all the Animals". The engraving therefore represents the first five days of the Creation. God the Father is seen setting the sun and moon among the clouds and the stars; below are the creatures of the land (left) and the sea (right). Engraving by Jean Cousin, in Figures de la Bible, Paris, 1614.
The Creation of Heaven and Earth. The caption to this bible illustration reads: “The Creation of Heaven and Earth, of Trees, Plants, Stars and all the Animals”. The engraving therefore represents the first five days of the Creation. God the Father is seen setting the sun and moon among the clouds and the stars; below are the creatures of the land (left) and the sea (right). Engraving by Jean Cousin, in Figures de la Bible, Paris, 1614.

 

The Creation of the World According to the Nuremberg Chronicle Continue reading

Cosmogenesis (4) : The Creator

Sequel of the preceding post Cosmogenesis (3) : Time and Creation

The Creator

The fundamental theological question about the Creation is: who created the universe? The Christian doctrine of the Holy Trinity asserts that God comprises three Persons: the Father, the Son and the Holy Spirit. Some theologians have regarded God as the first Person of the Trinity, “the omnipotent Father”, Creator of heaven and earth. Others have focused on the image of the “Spirit of God moving upon the face of the waters” and envisaged the Holy Spirit as the Creator. Others again, in an attempt to reconcile these viewpoints, have maintained that the Holy Trinity itself created the world – a reminder of the Vedic belief in a supreme being incarnated as a single body (Trimurti) with three heads: those of Brahma, Vishnu and Siva.

The Hindu Triad. One of the central images of Indian mythology is the Hindu Triad (Trimurti) of Brahma, the creator, Vishnu, the maintainer, and Siva, the destroyer. In this picture they are shown combined into a single body with four arms. Album of paintings of Indian gods and rulers, 1831. Paintings with captions in Tamil and French. BNF, Manuscripts, Indian 744.
The Hindu Triad. One of the central images of Indian mythology is the Hindu Triad (Trimurti) of Brahma, the creator, Vishnu, the maintainer, and Siva, the destroyer. In this picture they are shown combined into a single body with four arms.
Album of paintings of Indian gods and rulers, 1831. Paintings with captions in Tamil and French. BNF, Manuscripts, Indian 744.

These different theological perspectives are reflected throughout the Middle Ages (in fact right up to the 18th century) in religious art, where one or other interpretation of the Genesis story is illustrated in mosaics, paintings, sculptures, stained glass windows, illuminations and engravings.

The most familiar image of the Creator is the patriarchal figure of the Father (the archetypal example being Michelangelo’s fresco on the ceiling of the Sistine Chapel).

God the Father Dividing the Light from the Darkness. In this 16th century engraving, which was clearly influenced by the work of Michelangelo, the Creator, in the form of the first Person of the Holy Trinity, God the Father, is dividing the light (represented by the sun) from the darkness (represented by the moon). Engraving by Raphael Sadeler, in Thesaurus Historia..., 1585
God the Father Dividing the Light from the Darkness. In this 16th century engraving, which was clearly influenced by the work of Michelangelo, the Creator, in the form of the first Person of the Holy Trinity, God the Father, is dividing the light (represented by the sun) from the darkness (represented by the moon).
Engraving by Raphael Sadeler, in Thesaurus Historia…, 1585
Young Christ as Creator. The wonderful fresco adorning the cupola of the baptistery of San Giovanni in Padua is the work of the Florentine artist Giusto Dei Menabuoi, who was active in the second half of the 14th century. It shows God the Son as Creator. Giusto Dei Menabuoi, [The Creation of the World], 14th century.
Young Christ as Creator. The wonderful fresco adorning the cupola of the baptistery of San Giovanni in Padua is the work of the Florentine artist Giusto Dei Menabuoi, who was active in the second half of the 14th century. It shows God the Son as Creator.
Giusto Dei Menabuoi, [The Creation of the World], 14th century.

As the Holy Spirit the Creator is represented by a dove (the ancient Christian symbol of the Divine Spirit) – in the work of Robert Fludd, for example – or by the Hebrew word “Jehova” surrounded by a symbol of fire (recalling the burning bush from which Moses received the word of God). In a few cases the Creator is shown as a young Christ figure – in the 13th century mosaics of the Basilica of San Marco in Venice and the 14th century frescos of Giusto Dei Menabuoi in Padua, for example. Continue reading

Cosmogenesis (3) : Time and Creation

Sequel of the preceding post Cosmogenesis (2) : Chaos and Metamorphosis

Time and Creation

In any discussion of the creation of the world the paradoxical and complex question of temporality inevitably arises. If the Creation is regarded as an event, it must have taken place at some point in time, on a specific date. If time is regarded as a linear phenomenon, as it is in the Western world, this necessarily raises the problem whether anything existed before the Creation and, if so, what. But if time itself existed before the Creation, it cannot be part of the world as we know it – something which is difficult to imagine…

A Treatise on the Hexameron. St Ambrose (c. 339-394), who was bishop of Milan, was a believer in "Platonic Christianity" and one of the first Church Fathers, along with Origen and St Basil, to deliver sermons on the six days of the Creation, which he collected into a treatise. His Hexameron (shown here in an 11th century manuscript copy) is more than an exegesis; it is a veritable encyclopaedia anticipating those of the Middle Ages: the third book is concerned with plants, the fifth with birds and fish, and the second part of the sixth book with the anatomy of the human body. Paris, BNF, Manuscripts, Lat. 1720.
A Treatise on the Hexameron. St Ambrose (c. 339-394), who was bishop of Milan, was a believer in “Platonic Christianity” and one of the first Church Fathers, along with Origen and St Basil, to deliver sermons on the six days of the Creation, which he collected into a treatise. His Hexameron (shown here in an 11th century manuscript copy) is more than an exegesis; it is a veritable encyclopaedia anticipating those of the Middle Ages: the third book is concerned with plants, the fifth with birds and fish, and the second part of the sixth book with the anatomy of the human body.
Paris, BNF, Manuscripts, Lat. 1720.

This paradox was pondered by Medieval scholars, who were forced to conclude that the world and time were created simultaneously. In the fourth century the Bishop of Milan, St Ambrose, wrote in his Hexameron: “In the beginning of time, therefore, God created heaven and earth. Time proceeds from this world, not before the world.”[1]. In the early 13th century the French philosopher and theologian William of Auvergne (also known as William of Paris) pursued a similar line of reasoning in his thinking about time: “Just as there is nothing beyond or outside the World, since it contains and includes all things, so there is nothing before or preceding time, which began with the creation of the World, since it contains all the periods of which it is comprised. This poses the question: What was before the beginning of time? or, since the word ‘before’ implies the existence of time, In the time preceding the beginning of time, did anything exist?”[2]

The same questions continue to be asked today, and scientists who are asked to give public lectures on big bang theory and the expansion of the universe commonly face two kinds of questions: “What was there before the big bang?” and “What is there for the universe to expand into?” – in other words “Did time exist before time began?” and “Is there space beyond the limit of space?” The solution of modern physics to these paradoxes is that the universe consists of space-time and therefore the creation of the world cannot be regarded as a temporal phenomenon. Continue reading

Cosmogenesis (2) : Chaos and Metamorphosis

Sequel of the preceding post Cosmogenesis (1) : From Myth to Myth

Chaos and Metamorphosis

 

The ancient Greeks had a great variety of myths relating to the history of the world. Although they all shared a language and a culture, each village, each tribe had its own beliefs, its own version of the Creation story and its own gods who were responsible for cosmic order.

213 The Birth of the Gods According to Hesiod's Theogony (8th-7th century BC) is a history of the gods. It begins with Gaea, goddess of the Earth, the primordial element from which all the deities emerged. By herself she gave birth to the sea and the sky as well as to the gods Uranus and Pontus; by Uranus she then mothered numerous other deities: the Titans (including Cronos) and Titanesses, the Cyclops and the Giants. The work continues with an account of how Zeus became lord of the universe after decisive battles against the Titans and against the monster Typhoeus. This story of the creation of the world out of the struggle between the forces of order (cosmos) and the forces of disorder (chaos) had a strong influence on Greek cosmological thinking. In this illustration by Georges Braque, Hesiod is seen receiving the torch of Hebrew tradition from Moses. Hesiod, Theogony, Paris, Maeght, 1955.
The Birth of the Gods According to Hesiod’s Theogony (8th-7th century BC) is a history of the gods. It begins with Gaea, goddess of the Earth, the primordial element from which all the deities emerged. By herself she gave birth to the sea and the sky as well as to the gods Uranus and Pontus; by Uranus she then mothered numerous other deities: the Titans (including Cronos) and Titanesses, the Cyclops and the Giants. The work continues with an account of how Zeus became lord of the universe after decisive battles against the Titans and against the monster Typhoeus. This story of the creation of the world out of the struggle between the forces of order (cosmos) and the forces of disorder (chaos) had a strong influence on Greek cosmological thinking.
In this illustration by Georges Braque, Hesiod is seen receiving the torch of Hebrew tradition from Moses.
Hesiod, Theogony, Paris, Maeght, 1955.

Hesiod’s Theogony (8th-7th century BC) was the first attempt to synthesize these traditions, which probably dated back to the Assyrian and Babylonian civilizations. In recounting the stages in the emergence of the gods from primordial chaos Theogony offers an answer to the eternal questions of cosmogony: who created the world; what were the basic materials from which it was made; which came first, the gods, the stars or the elements?

Not only did Theogony have a strong influence on Greek thought, it also anticipated in many ways today’s theories of the origin of the world – particularly the idea of primordial chaos. Since the universe appears to have an ordered structure (albeit an imperfect one), it seems logical to regard the state which preceded the Creation as one of disorder and confusion. This notion has provoked greater controversy than almost any other in the history of cosmogony.

Ovid’s Metamorphoses also trawled Greek mythology, as well as Roman legend, in attempting to reconstruct the series of metamorphoses the world had undergone between the original state of Chaos and Julius Caesar’s supposed transformation into a star:

“Before the sea and the lands and the sky that covers all,
there was one face of nature in her whole orb
(they call it Chaos), a rough unordered mass,
nothing except inactive weight and heaped together
the discordant seeds of unassembled things.” [i] Continue reading

Cosmogenesis (1) : From Myth to Myth

Introduction

Every society has a story, rooted in its most ancient traditions, of how the earth and sky originated. Most of these stories attribute the origin of all things to a Creator -whether god, element or idea.

In the Western world all discussions of the origin of the world were dominated until the 18th century by the story of Genesis, which describes the Creation as an ordered process that took seven days. The development of mechanistic theories in the 18th century meant that the idea of an organized Creation gave way to the concept of evolution, and in the 19th century astrophysicists discovered that stars had their origin in clouds of gas. Big bang theory, conceived at the beginning of the 20th century, was subsequently developed into a more or less complete account of the history of the cosmos, from the birth of space, time and matter out of the quantum vacuum until the emergence of life.

Today sophisticated telescopes show us how the first galaxies were formed, how clouds of hydrogen gave birth to stars and how the planets emerged from swirling dust. We now know that creation is still going on in our universe but the origin of life remains an enigma. How did life forms appear? The universe’s best kept secret continues to baffle scientists.

From Myth to Myth

What are the origins of the universe, of the sky, of the earth, of life, of man? These questions have given rise to many different myths and legends and continue to be the subject of intensive research by astrophysicists, biologists and anthropologists. What were once fanciful stories are now scientific models but, whatever form they take, ideas about the origins of the universe both reflect and enrich the imagination of the people who generate them. Every society has developed its own stories to explain the creation of the world; most of them are ancient myths rooted in religion.

Whereas in monotheistic religions God is believed to have existed before the Creation, in most other kinds of religion the gods themselves are thought to originate from a creative element such as Desire, the Tree of the Universe, the Mundane Egg, Water, Chaos or the Void.

Babylonian Gods. An inscription on the back of this stone carving tells us that it was a gift from the Kassite king Melishishu II to his son. The picture shows the symbols representing the gods carved on the front. On the right the principal deities -Anu, god of the sky, and Enlil, god of the atmosphere - are each shown as a sort of tiara standing on a plinth. Next a ram's head above a creature half-goat half-fish represents Ea, god of the Waters of the Abyss. The symbol on the left might be for the goddess Ninhursag. Above these are the three celestial divinities: a crescent for Sin, god of the moon, a star for Ishatar and an image of the sun for Shamash. Stone from Kassite era (1202-1188 BC). Paris, Louvre.
Babylonian Gods. An inscription on the back of this stone carving tells us that it was a gift from the Kassite king Melishishu II to his son. The picture shows the symbols representing the gods carved on the front. On the right the principal deities -Anu, god of the sky, and Enlil, god of the atmosphere – are each shown as a sort of tiara standing on a plinth. Next a ram’s head above a creature half-goat half-fish represents Ea, god of the Waters of the Abyss. The symbol on the left might be for the goddess Ninhursag. Above these are the three celestial divinities: a crescent for Sin, god of the moon, a star for Ishatar and an image of the sun for Shamash.
Stone from Kassite era (1202-1188 BC). Paris, Louvre.
The Chinese giant Pangu
The Chinese giant Pangu

Ideas like these appear in the Rig-veda, one of the four sacred books of the Brahmins and the oldest surviving written record of Indian culture which were compiled between 2000 and 1500 BC. The Tree of the Universe, symbol of the outward growth of the world and of its organic unity, is mentioned in ancient Indian legends as well as in those of the Babylonians and Scandinavians (who call it Yggdrasil). The anthropomorphic symbol of Desire was invoked by the Phoenicians and by the Maoris of New Zealand. The Mundane Egg, from which the Hindu Prajapatis (lords of all living things) emerged, also gave birth to the gods Ogo and Nommo, worshipped by the Dogon of Mali, and the Chinese giant Pan Gu as well as constituting the celestial vault in the legend of Orpheus.

Birth of Gods and Cosmic Egg according to the Upanishad
Birth of Gods and Cosmic Egg according to the Upanishad

A belief in some such primordial element, of which there are traces in every culture, underlies man’s thinking about the history of the cosmos like a primitive universal symbol buried in the collective subconscious. This may explain the vague links which can always be discerned between this or that creation myth and modern scientific descriptions of the origin of the universe – for example, big bang theory. There is therefore nothing mysterious or surprising about these correspondences other than that certain ways of thinking about the world should be so ingrained in the human mind. Continue reading

The Warped Science of Interstellar (6/6) : the final equation

Sequel of the preceding post The Warped Science of Interstellar (5/6)

In november  2014, the Hollywood blockbuster and science-fiction movie Interstellar was released on screens and  much mediatic excitation arose about it.
This is the last one of a series of 6 posts devoted to the analysis of some of the scientific aspects of the film, adapted from a paper I published last spring in Inference : International Review of Science.

Formules

The final equation

At the very end of the film, the scientist’s character called Murph begins to write an equation aimed to solve the problem of the incompatibility between general relativity and quantum mechanics. We can see blackboards covered by diagrams and equations supposed to be a possible way to the « ultimate equation » of a so-called « Theory Of Everything ». If discovered by the scientists, it would eventually help to solve all the problems of humanity. I will not discuss the naivety of such a view, but briefly discuss the question whether the equations on the screen have any meaning.

The complete unification of the four fundamental interactions can be achieved only at very high energy, conditions which prevailed in the very early universe during the so-called « Planck era ».
The complete unification of the four fundamental interactions can be achieved only at very high energy, conditions which prevailed in the very early universe during the so-called « Planck era ».

At first sight we can doubt because the unification of general relativity and quantum mechanics remains unsolved – even if various approaches, such as the loop quantum gravity[1], the string theory[2] (of which the Randall-Sundrum model referred above is a very particular solution) or the non-commutative geometry[3], are intensively explored by theoretical physicists all around the world. Continue reading

The Warped Science of Interstellar (5/6) : Time machine and Fifth Dimension

Sequel of the preceding post The Warped Science of Interstellar (4/6)

In november  2014, the Hollywood blockbuster and science-fiction movie Interstellar was released on screens and  much mediatic excitation arose about it.
This is the fifth of a series of 6 posts devoted to the analysis of some of the scientific aspects of the film, adapted from a paper I published last spring in Inference : International Review of Science.

TIME TRAVEL INSIDE GARGANTUA

Interstellar-FLprStills16-2nd-Batch

In the last part of the film, the main character, Cooper, plunges into Gargantua. There, beware the tidal forces breaking anything up ! Indeed in the Schwarzschild geometry, the tidal forces become infinite as r -> 0 ; so, even for a supermassive black hole like Gargantua, once past safely the event horizon and approaching the central singularity, everything will be ultimately destroyed. Happily for the continuation of the story, Gargantua has a high spin, and its lethal singularity has the shape of an avoidable ring. Thus the space-time structure allows Cooper to use the Kerr black hole as a wormhole ; he avoids the ring singularity and transports to another region of space-time. In the movie he ends up in a five-dimensional universe, in which he will be able to go backwards in time and communicate with his daughter by means of gravitational signals.

Inner structure of a rotating black hole with a ring singularity
Inner structure of a rotating black hole with a ring singularity

A lot of research has been done on whether the laws of physics permit travel back in time or not. Black hole physics gives interesting results but no firm answers. As seen in the post The Warped Science of Interstellar (1/6), according to Penrose-Carter diagrams a rotating black hole could connect myriads of wormholes to different parts of the space-time geometry. Since two events can differ in time as well as in space, it would be possible to pass from one given position at a given time, along a carefully chosen trajectory, through a wormhole, and arrive at the same position but at a different time, in the past or future. In other words, the black hole could be a sort of time travel machine.

Noneless a journey back through time is an affront to common sense. It is difficult to accept that a man could travel back through time and kill his grandfather before he has had the time to produce children. For the murderer could not have been born, and could not have murdered him, and so on… Such time paradoxes have been pleasantly presented in the celebrated series of movies Back to the future.

Continue reading

The Warped Science of Interstellar (4/6) : Time dilation and Penrose process

Sequel of the preceding post The Warped Science of Interstellar (3/6)

In november  2014, the Hollywood blockbuster and science-fiction movie Interstellar was released on screens and  much mediatic excitation arose about it.
This is the fourth of a series of 6 posts devoted to the analysis of some of the scientific aspects of the film, adapted from a paper I published last spring in Inference : International Review of Science.

A HUGE TIME DILATION

The elasticity of time is a major consequence of relativity theory, according to which time runs differently for two observers with a relative acceleration – or, from the Equivalence Principle, moving in gravitational fields of different intensities. This well-known phenomenon, checked experimentally to high accuracy, is called « time dilation ».

The celebrated "smooth watches" by Salvador Dali are a nice metaphor of time elasticity predicted by Einstein's relativity theory.
The celebrated “smooth watches” by Salvador Dali are a nice metaphor of time elasticity predicted by Einstein’s relativity theory.

Thus, close to the event horizon of a black hole, where the gravitational field is huge, time dilation is also huge, because the clocks will be strongly slowed down compared to farther clocks. This is one of the most stunning elements of the scenario of Interstellar : on the water planet so close to Gargantua, it is claimed that 1 hour in the planet’s reference frame corresponds to 7 years in an observer’s reference frame far from the black hole (for instance on Earth). This corresponds to a time dilation factor of 60,000. Although the time dilation tends to infinity when a clock tends to the event horizon (this is precisely why no signal can leave it to reach any external observer), at first sight a time dilation as large as 60,000 seems impossible for a planet orbiting the black hole on a stable orbit.

As explained by Thorne in his popular book, such a large time dilation was a « non-negotiable » request of the film director, for the needs of the story. Intuitively, even an expert in general relativity would estimate impossible to reconcile an enormous time differential with a planet skimming up the event horizon and safely enduring the correspondingly enormous gravitational forces. However Thorne did a few hours of calculations and came to the conclusion that in fact it was marginally possible (although very unlikely). The key point is the black hole’s spin. A rotating black hole, described by the Kerr metric, behaves rather differently from a static one, described by the Schwarzschild metric. The time dilation equation derived from the Kerr metric takes the form:

1 – (dτ/dt)2 = 2GMr/c2rho2, where rho2 = r2 + (J/Mc)2cos2θ.

Continue reading

The Warped Science of Interstellar (3/6) : Accretion Disk and Tidal Stress

Sequel of the preceding post The Warped Science of Interstellar (2/6)

In november  2014, the Hollywood blockbuster and science-fiction movie Interstellar was released on screens and  much mediatic excitation arose about it.

This is the third of a series of 6 posts devoted to the analysis of some of the scientific aspects of the film, adapted from a paper I published last spring in Inference : International Review of Science.

VISUALISATION OF THE ACCRETION DISK

Since a black hole causes extreme deformations of spacetime, it also creates the strongest possible deflections of light rays passing in its vicinity, and gives rise to spectacular optical illusions, called gravitational lensing. Interstellar is the first Hollywood movie to attempt depicting a black hole as it would actually be seen by an observer nearby.

For this, the team at Double Negative Visual Effects, in collaboration with Kip Thorne, developed a numerical code to solve the equations of light-ray propagation in the curved spacetime of a Kerr black hole. It allows to describe gravitational lensing of distant stars as viewed by a camera near the event horizon, as well as the images of a gazeous acccretion disk orbiting around the black hole. For the gravitational lensing of background stars, the best simulations ever done are due to Alain Riazuelo[i], at the Institut d’Astrophysique in Paris, who calculated the silhouette of black holes that spin very fast, like Gargantua, in front of a celestial background comprising several thousands of stars.

BH_LMC_APOD-BR
Gravitational lensing produced by a black hole in a direction almost centered on the Large Magellanic Cloud. Above it one easily notices the southernmost part of the Milky Way with, from left to right, Alpha and Beta Centauri, the Southern Cross. The brightest star, close to the LMC is Canopus (seen twice). The second brightest star is Achernar, also seen twice. © Alain Riazuelo, CNRS/IAP

But perhaps the most striking image of the film Interstellar is the one showing a glowing accretion disk which spreads above, below and in front of Gargantua. Accretion disks have been detected in some double-star systems that emit X-ray radiation (with black holes of a few solar masses) and in the centers of numerous galaxies (with black holes whose mass adds up to between one million and several billion solar masses). Due to the lack of spatial resolution (black holes are very far away), no detailed image has yet been taken of an accretion disk ; but the hope of imaging accretion disks around black holes telescopically, using very long baseline interferometry, is nearing reality today via the Event Horizon Telescope[ii]. In the meanwhile, we can use the computer to reconstruct how a black hole surrounded by a disk of gas would look. The images must experience extraordinary optical deformations, due to the deflection of light rays produced by the strong curvature of the space-time in the vicinity of the black hole. General relativity allows the calculation of such an effect. Continue reading

The Warped Science of Interstellar (2/6)

Sequel of the preceding post The Warped Science of Interstellar (1/6)

One year ago, in november  2014, the Hollywood blockbuster and science-fiction movie Interstellar was released on screens and  much mediatic excitation arose about it.

This is the second of a series of 6 posts devoted to the analysis of some of the scientific aspects of the film, adapted from a paper I published last spring in Inference : International Review of Science.

THE FAST-SPINNING BLACK HOLE « GARGANTUA »

Once on the other side of the wormhole, the spaceship and its crew emerge into a three-planets system orbiting around a supermassive black hole called Gargantua. Supermassive black holes, with masses going from one million to several billion solar masses, are suspected to lie in the centers of most of the galaxies. Our Milky Way probably harbors such an object, Sagittarius A*, whose mass is (indirectly) measured as 4 million solar masses (for a review, see Melia[i]). According to Thorne, Gargantua would be rather similar to the still more massive black hole suspected to be located at the center of the Andromeda galaxy, adding up 100 million solar masses[ii]. Its size being roughly proportional to its mass, the radius of such a giant would encompass the Earth’s orbit around the Sun.

CGal_IR_1al
A view of the Galactic Center in X-rays

CGal_*Keck
The analysis of trajectories of stars orbiting around the Galactic Center leads to estimate the mass of the central black hole at about 4 millions solar masses.

m31
The Andromeda Galaxy (M31), located at 2.2 million light-years

coeurM31_HST
Detailed image of the core of Andromeda Galaxy by the Hubble Space Telescope. The central black hole would have 100 million solar masses.

Such enormous black holes are not a science-fiction exaggeration, since we have the observational clues of the existence of « Behemoth » black holes in faraway galaxies. The biggest one yet detected lies in the galaxy NGC 1277, located at 250 million light-years ; its mass could be as large as 17 billion solar masses, and its size would encompass the orbit of Neptune[iii]. Continue reading

The Warped Science of Interstellar (1/6)

One year ago exactly, in november  2014, the Hollywood blockbuster and science-fiction movie Interstellar was released on screens and  much mediatic excitation arose about it.

This is the first of a series of 6 posts devoted to the analysis of some of the scientific aspects of the film, adapted from a paper I published last spring in Inference : International Review of Science.

interstellar-posterInterstellar  tells the adventures of a group of explorers who use a wormhole to cross intergalactic distances and find potentially habitable exoplanets to colonize. Interstellar is a fiction, obeying its own rules of artistic license : the film director Christopher Nolan and the screenwriter, his brother Jonah, did not intended to put on the screens a documentary on astrophysics – they rather wanted to produce a blockbuster, and they succeeded pretty well on this point. However, for the scientific part, they have collaborated with the physicist Kip Thorne, a world-known specialist in general relativity and black hole theory. With such an advisor, the promotion of the movie insisted a lot on the scientific realism of the story, in particular on black hole images calculated by Kip Thorne and the team of visual effects company Double Negative. The movie also refers to many aspects of contemporary science, going from well-studied issues such as warped space, fast-spinning black holes, accretion disks, tidal effects or time dilation, to much more speculative ideas which stem beyond the frontiers of our present knowledge, such as wormholes, time travel to the past, extra-space dimensions or the « ultimate equation » of an expected « Theory of Everything ».

It is the reason why, beyond the subjective appreciations that everyone may have about the fiction story itself, many people – physicists and science journalists – have taken the internet to write articles lauding or criticizing the science shown in the movie. Kip Thorne has written a popular book, The Science of Interstellar [i], to explain how he tried to respect scientific accuracy, despite the sometimes exotic demands of Christopher and Jonah Nolan, ensuring in particular that the depictions of black holes and relativistic effects were as accurate as possible.

The aim of this article is not to write a (inevitably subjective) review of Interstellar as a fiction story, but to decipher some of the scientific notions, which support the framework of the movie.

AN ARTIFICIAL WORMHOLE IN THE SOLAR SYTEM ?

 In the first part of the film, we are told that a « gravitational anomaly », called a wormhole, has been discovered out near Saturn several decades ago, that a dozen habitable planets have been detected on the « other side » and a dozen astronauts sent to explore them. In particular, one system has three potentially habitable planets, and it is now the mission of the hero, Cooper, to pilot a spaceship through the wormhole and find which planet is more suitable for providing humanity a new home off the dying Earth. Continue reading

My books (2) : Glorious Eclipses

Until now I published as an author 30 books in my native language (French), including 14 science essays, 7 historical novels  and 9 poetry collections (for the interested reader, visit my French blog  here.
Although my various books have been translated in 14 languages (including Chinese, Korean, Bengali…), 4 of my essays have been translated in English.

The second one was :

Glorious Eclipses : Their Past, Their Present, Their Future

Translated from French by Storm Dunlop
Cambridge University Press, 2001 -ISBN 0 521 79148 0

GEclipsesThis beautiful volume deals with eclipses of all kinds – lunar, solar and even those elsewhere in the Solar System and beyond. Bringing together in one place all aspects of eclipses, it is written by the perfect team : Serge Brunier is a life-long chaser of eclipses, and internationally-known astronomy writer and photographer, whilst Jean-Pierre Luminet is a famous astrophysicist with a special interest in astronomical history. Lavishly illustrated throughout, Glorious Eclipses covers the history of eclipses from ancient times, the celestial mechanics involved, their observation and scientific interest. Personal accounts are given of recent eclipses – up to and including the last total solar eclipse of the 20th century : the one on August 11th 1999 that passed across Europe, Romania, Turkey and India. This unique book contains the best photographs taken all along its path and is the perfect souvenir for all those who tried or wished to see it. In addition, it contains all you need to know about forthcoming eclipses up to 2060, complete with NASA maps and data.

 

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EXCERPT : FOREWORD

Why should a theoretical astrophysicist, who has rarely peered through the eyepiece of a telescope, preferring to speculate on the invisible architecture of space-time by means of dry equations, be interested in eclipses, to the extent of writing a book about them?

It is true that Einstein’s general theory of relativity, which has been a constant intellectual delight for me over so many years, was first proved experimentally thanks to a ‘simple’ solar eclipse. That was on 29 May 1919. But such an argument satisfies only the intellect. When it comes to the soul, it demands a greater spectacle, a more tangible emotion.

I was not yet ten on 15 February 1961, when a total eclipse of the Sun crossed the Provence where I was born. All I can recall is preparing smoked glass under the watchful eye of our schoolmistress. Clouds over Cavaillon probably spoilt the spectacle, because I have no memory of the eclipse itself…

Then… then I waited nearly forty years before finally seeing a total eclipse of the Sun. That was on 26 February 1998, in the Sierra Nevada de Santa Maria, in the north of Colombia. Serge Brunier and a few other colleagues, genuine eclipse chasers, had finally convinced me that any astrophysicist worthy of the name should not ‘die a fool’! It is true that, obviously, such a recurrent and ‘nearby’ astronomical event might seem somewhat prosaic to someone who spends his life in abstract research on models of the Big Bang, black holes, and the realms of space-time.

On that day, however, between 10:59 and 11:03, I experienced what John Couch Adams described so well, some 150 years before. The English mathematician-astronomer, less accustomed to handle telescopes than complex equations of celestial mechanics – he predicted the existence of the planet Neptune through calculation – witnessed a total eclipse of the Sun for the very first time in his career during the summer of 1846. He subsequently described the extraordinary emotions he felt as an astronomer – and, moreover, an experienced one – who realized that he was a novice when he discovered this astounding cosmic drama for the very first time.

The darkness that descends suddenly in the very middle of the brilliance of the day; this new light that arises from the obscurity; the planets aligned like a necklace of pearls in a configuration that is never seen by night; and the Sun’s flamboyant corona…

These few minutes in which time seems suspended, create the almost palpable feeling of being, transiently, part of the invisible harmony that rules the universe. It is as if a sudden opening in the opaque veil of space allows our inner vision to reach into the otherwise hidden depths of the cosmos, giving us humans – mere insignificant specks of dust – an all-too-brief instant to see the other side of the picture.

To me, the invisible is not restricted to dark objects that our telescopes cannot detect. It is also, and in particular, the secret architecture of the universe, the insubstantial framework of our theoretical constructs. I have always been moved by black. Not black as in absence, but rather black as revealing light. According to the painter Francois Jacqmin ‘Shadow is an insatiable star-studded watchfulness. It is the black diamond that the soul perceives when the infinite rises to the surface.’ Astrophysics and cosmology team with examples where black is all-important. It is in the black of the night that one sees stars, or, in other words, that one perceives the immensity of the cosmos. This same night-time darkness reveals the whole evolution of the cosmos, and the finite nature of time. The mass of the universe is largely dominated by dark matter; massive, non-luminous objects, which through their gravitational attraction govern the dynamics of the cosmos. As for black holes, the epitome of invisibility, they are perhaps secret doorways opening onto other regions of space-time.

Another aspect of eclipses enthrals me: their historical and cultural dimension. I have always been attracted by the way in which different forms of human invention interact. Science, despite being an effective and rational approach to truth, nevertheless remains incomplete. Art, philosophy, and the comparative study of traditions, myths and religions, are all complementary approaches that are indispensable for anyone who wants to gain a greater insight into where they fit in the cosmic scheme of things.

In unfolding the story of people, their civilizations, and their relationships with heavenly phenomena, one cannot but be fascinated to see how past eclipses have influenced their course. The impression of a supernatural power engendered by the sudden disappearance of the Sun or the Moon has often struck human beings, frightened by an apparently hostile and incomprehensible nature, to the extent of changing their behaviour.

That’s enough. My colleague, Serge Brunier, and I decided to write a book that alternated between these ‘two voices’. After all, the various types of eclipses are created by the Earth and the Moon taking it in turn to pass in front of each other beneath the blazing Sun…

Eclipses are a benign contagious virus, which once it has infected you, recurs at intervals. Which is why, for the eclipse of 11 August 1999, I went deep into the Iranian desert, to be (almost) certain of finding a sky devoid of clouds.

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PRESS REVIEWS

An extrordinarily beautiful book, Glorious Eclipses guides us elegantly through the history of obscurations of the sun and moon – from the ancient Chinese belief that a dragon was devouring the daytime star through current theories and on to celestial events forthcoming in the next six decades. Some of the most startling images come from the days when photography was in its infancy and astronomers still made drawings of eclipses.

Scientific American, June 2001


Darkness at noon

At first sight, this is the ultimate eclipse book. Oversize, well-produced photographs in a large-format book are accompanied by interesting text covering a wide variety of eclipses phenomena. The partnership of an astronomer writer/editor and a professional astronomer, albeit a cosmologist, successfully brings the beauty of total solar eclipses to the fore.

Although the writers alternate, the difference is not jarring, perhaps thanks to the expert translator, Storm Dunlop. In a chapter entitled “The great cosmic clockwork”, Serge Brunier, long-time editor of the French popular astronomy journal Ciel et Espace, discusses the many kinds of eclipses and occultations (when one astronomical body occults, or hides, another). He even includes the eagerly awaited 2004 transit of Venus – the passage of Venus across the face of the Sun. This will be the first transit of Venus visibe from Earth since 1882.

The reproduction of photographs in 25 cm x 35 cm format on heavy stock is outstanding. For example, we see Saturn’s rings extending across a double page for almost half a metre in a Hubble Space Telescope image. The authors justify using this image, which shows the shadow of Saturn’s satellite Titan on Saturn’s clouds, by pointing out that it corresponds to an eclipse of the Sun by Titan as seen from Saturn. It’s a pity, though, that Brunier calls himself an “eclipse chaser” – that common but misleading phrase seemps to imply that people can outrun, or even outfly, eclipses, which has never been done.

Brunier is responsible for some of the most magnificent photographs, such as one from the 1991 total solar eclipse visible from the Mauna Kea Observatory in Hawaii, with a few telescopes in the foreground. But the image I found most arresting is not one of this; it is a wide-angle shot of the 1991 eclipse viewed through a hole in the clouds and showing the front of Reims Cathedral in the left foreground.

In his chapters on the history and cultural significance of eclipses, Jean-Pierre Luminet reproduces a remarkable set of historical images related to solar and lunar eclipses from around the world. These are no doubt related to his work on an exhibition of astronomical atlases held in Paris at the Bibliothèque Nationale in 1998.

It was good to read about myths that cast eclipses in a favourable light rather than as evil omens. Luminet also describes the history of scientific discovery through observations of solar eclipses. One example is the discovery at the 1868 total solar eclipse of the spectrum of the solar chomosphere – the layer of the Sun just above the surface that becomes briefly visible at the beginning and end of totality. The element helium was also discovered at this eclipse.

There is much that is excellent in the book. The charts of future eclipses at the end of the book are redrawn at the highest quality. Lunar eclipses are included in the text, photos and charts, looking almost as dramatic on the page as the solar ecipses, even though they are much less so in reality. As a book of history, myth, literature, photography and expeditionary experiences, Glorious Eclipses is outstanding, despite its omission of the solar research carried out at recent eclipses.

Jay Pasachoff, Nature, vol. 410, 29 march 2001.


Wonder of day turned into light

A total eclipse of the Sun is about as astonishing a treat as nature provides. For a few minutes, the Moon exactly covers the Sun, making night from day and displaying the otherwise invisible solar atmosphere. This book celebrates eclipses of both Sun and Moon (the rather less spectacular sweeping of Earth’s shadow across the lunar surface) from many directions, including the complex history of eclipse observations and their declining but still real scientific value.

Serge Brunier and Jean-Pierre Luminet are respectively a science journalist and photographer, and a senior astronomer. This book, well translated from French by Storm Dunlop, makes the most of their strengths. It displays a deep understanding of history, some gripping science and a wealth of images, both of eclipses and of the many ways in which they have been represented over the years.

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If you want to take up eclipse chasing, the book’s maps of future eclipses will tell you when and where to be, and its illstrations will tell you what to expect and how to observe in safety. There are explanations of the eclipse cycle, or Saros, and of the fact that in the far future, there will be no more solar elipses as the Moon’s distance from the Earth increases.

The book also provides generous coverage of lunar eclipses and of related events such as occultations and transits. There is even space to reveal how planets in other solar systems are being detected as they eclipse their own star as seen from Earth. Eclipses still make cutting-edge science thousands of years after they first caused dismay to our ancestors.

Martin Ince, Deputy Editor, The Times Higher, March 9 2001.


Not in the shade

This attractive and beautifully illustrated book, by two Paris astronomers and dedicated eclipse-chasers, was originally published in French under the title Eclipses, Les Rendez-vous Celestes (Larousse-Bordas/HER, 1999). The present English translation is by Storm Dunlop. This book is a veritable mine of information on eclipses and is suitable for anyone who has an interest in eclipses, be they amateur or professional astronomer, photographer or historian.

The scene is set in the first chapter, which captures much of the appeal of total solar eclipses and leaves the reader in no doubt as to why eclipse chasers will travel vast distances to witness a few minutes of totality.

In chapters two and three, the historical and literary aspects of both solar and lunar eclipses are discussed. Although there is some sound history in the first of these chapters, there is also much speculation – especially with regard to such torical and literary aspects of both such diverse matters as Stonehenge, Thales, and the date of the Crucifixion of Jesus. Regrettably, there are several serious errors. Thus the “Assyrian tablet dating from the

2nd century BC” (p40) is in fact from Babylonia, several centuries after the demise of Assyria. Thucydides reports three eclipses, not just two (p43). “According to the Evangelists,” Jesus was not “crucified on a Thursday,” (p44). Chapter three contains some intriguing literary allusions to eclipses in prose and poetry – both ancient and modern.

Chapters four to seven provide the main substance of this book and are both fascinating and informative. They deal respectively with: the cause of both lunar and solar eclipses; lunar and planetary occultations and also Mercury and Venus transits; total solar eclipse phenomena; and the famous or infamous (depending on the wearher) 1999 eclipse. In particular, it is gond to see a discussion of occultations and transits – which, in a sense, are eclipses in their own right.

The final chapter contains helpful hints for observing and photographing eclipses and also a series of attractive maps showing the visibility of future solar and lunar eclipses – with special emphasis on those over the next 20 years. Unfortunately many of the individual solar eclipse maps (p156–69) are confusing; in each case the maps show “Total eclipse begins at sunrise”, “Path of totality” and “Total eclipse ends at sunset” whether the eclipse was annular or total.

Overall, this is a splendid hook, profusely illustrated.

F Richard Stephenson. Astronomy & Geophysics, 2001 December (Vol.42), 6.33

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