Category Archives: Sciences

The Rise of Big Bang Models (2) : Static solutions

Sequel of previous post :  From Myth to Science

In this series of posts about the history of relativistic cosmology, I  provide an epistemological analysis of the developments of the field  from 1917 to 2006, based on the seminal articles by Einstein, de Sitter, Friedmann, Lemaître, Hubble, Gamow and other main historical figures of the field. It appears that most of the ingredients of the present-day standard cosmological model, including the accelation of the expansion due to a repulsive dark energy, the interpretation of the cosmological constant as vacuum energy or the possible non-trivial topology of space, had been anticipated by Lemaître, although his papers remain mostly  unquoted.

The History of Relativistic Cosmology can be divided into 6 periods :

– the initial one (1917-1927), during which the first relativistic universe models were derived in the absence of any cosmological clue.

– a period of development (1927-1945), during which the cosmological redshifts were discovered and interpreted in the framework of dynamical Friedmann-Lemaître solutions, whose geometrical and mathematical aspects were investigated in more details.

– a period of consolidation (1945-1965), during which primordial nucleosynthesis of light elements and fossil radiation were predicted.

– a period of acceptation (1965-1980), during which the big bang theory triumphed over the « rival » steady state theory.

– a period of enlargement (1980-1998), when high energy physics and quantum effects were introduced for describing the early universe.

– the present period of high precision experimental cosmology, where the fundamental cosmological parameters are now measured with a precision of a few %, and new problematics arise (nature of the dark energy, topology of the universe, new cosmologies in quantum gravity theories, etc.)

Let us follow chonologically the rather hectic evolution of the ideas in the field. Continue reading

Black Hole Imaging (2) : Heads and Tails

 The thought experiments which have been described in my  previous post Back to the basics are more than an intellectual exercise, because if black holes really exist (and we have strong observational arguments to believe that), then there is a good chance that they will be illuminated by a natural light source. For a black hole or a planet the most obvious form of lighting is a star. This star could, for example, be bound to the black hole in a binary system. Although such systems are common throughout our Galaxy, the corresponding black holes would be impossible to detect by this effect, as their image  by reflected light would be drowned in the intense light of the direct image of the star itself.

A much more interesting situation from an observational point of  view is when the source of light comes from a series of rings of matter in orbit around the black hole.  It is believed that a number of black holes are surrounded by such structures, which are called accretion disks. Saturn’s rings are an excellent example of an accretion disk; they consist of amalgamated pieces of rock and ice which reflect the light of the distant Sun, whereas those of a black hole consist of hot gas brighting by itself (another important difference is that the accretion disk of a black hole is continually being supplied with gas, whereas that surrounding Saturn is the remnant of the primordial Solar System).

Planet Saturn and its rings. One can assume that a black hole accretion disc, although made of hot gas instead of rocks and ice, has a similar shape, namely circular thin rings.
Planet Saturn and its rings. One can assume that a black hole accretion disk, although made of hot gas instead of rocks and ice, has a similar shape, namely circular thin rings.

 The gases fall slowly into the black hole, like water in a whirlpool. As the gas falls towards the black hole it becomes hotter and hotter and begins to emit radiation. This is a good source of light: the accretion rings shine and illuminate the central black hole. One can then ask : what would be the apparent image of the black hole accretion disk ? Continue reading

The Cosmos As A Poem

As an astrophysicist and a poet, I am apparently well-prepared to talk about cosmic poetry. However it is not so obvious. During many years I conducted these two activities quite independently – I mean scientific investigation of the nature of the universe through the study of relativity, black holes, cosmology, topology, and poetic writing. I even refuted any relationship between these two ways of apprehending the world.

I began to publish poetry 30 years ago, at the same epoch when I also published my first scientific works, however my poetic works had nothing to do with astronomy. For me, poetry had to express feelings, emotions, and subjects that cannot not be reached by rational investigation, such as love, death, beauty, loneliness, despair, and so on.

Griph NoirSoleil
Iti lanature

Continue reading

Black Hole Imaging (1/3): Back to the basics

The centre of the black hearth,
of setting suns on the shore :
ah ! well of magic
Arthur Rimbaud (Illuminations)

As probably all of you already know, the Interstellar movie tells the adventures of a group of explorers who use a wormhole to cross intergalactic distances and find potentially habitable exoplanets to colonize. For the scientific part, the film director, Christopher Nolan has collaborated with a colleague of mine, the famous physicist Kip Thorne, a specialist in general relativity and black hole theory.

With such a scientific consultant, the promotion of the movie insisted a lot on the realism of the black hole images calculated by Kip Thorne and the team of visual effects company Double Negative. The most striking one shows a glowing accretion disk appearing above, below  and in front of the black hole.

The simulation of a black hole with thin accretion disk as shown in the Interstellar movie

As soon as the movie was displayed on the screens, a lot of physics blogs have commented in details the “Science of Interstellar”. Kip Thorne himself has published a such entitled popular book, to explain how he tried to respect scientific accuracy despite the sometimes odd demands of Christopher Nolan, ensuring in particular that the depictions of black holes and relativistic effects were as accurate as possible.

destinSince, as soon as 1979, I was the first researcher to perfom numerical calculations and publish the simulated image of a black hole surrounded by a thin accretion disk (you can upload the technical article here), to inaugurate this new blog I’ll devote a series of 3 posts to the basics of black hole imaging. A good part is adapted from a chapter of one of my books, published in French in 2006, Le destin de l’univers – unfortunately not yet available in English. Continue reading

The Rise of Big Bang Models (1) : from Myth to Science

In this series of posts about the history of relativistic cosmology, I’ll  provide an epistemological analysis of the developments of the field  from 1917 to 2006, based on the seminal articles by Einstein, de Sitter, Friedmann, Lemaitre, Hubble, Gamow and other main historical figures of the field. It appears that most of the ingredients of the present-day standard cosmological model, including the accelation of the expansion due to a repulsive dark energy, the interpretation of the cosmological constant as vacuum energy or the possible non-trivial topology of space, had been anticipated by Lemaitre, although his papers remain mostly  unquoted.

 From Myth to Science

What are the origins of the universe, of the stars, of the earth, of life, of man? These questions have given rise to many different myths and legends, and today they are more than ever 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; all 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.

Tiamat-Marduk
Marduk slays the chaos dragon, Tiamat, in the Babylonian creation epic (British Museum, London)

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 that 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.

An interesting approach, by the scientist and philosopher Wolfgang Smith (published in 2012)
An interesting approach, by the scientist and philosopher Wolfgang Smith (published in 2012)

In fact scientific and mythical explanations of the origins are neither complementary not contradictory; they have different purposes and are subject to different constraints. Mythical stories are a way of preserving collective memories, which can be verified neither by the storyteller nor by the listener. Their function is not to explain what happened at the beginning of the world but to establish the basis of social or religious order, to impart a set of moral values. Myths can also be interpreted in many different ways. Science, on the other hand, aims to discover what really happened in historical terms by means of theories supported by observation. Often considered to be anti-myth, science has in fact created new stories about the origin of the universe: big bang model, the theory of evolution, and the ancestry of mankind. It is therefore hardly surprising that the new creation stories developed by scientists tend to be regarded by the general public as modern myths.

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Welcome on e-luminesciences

I like to share my various interests for science, art, literature and many other fields. As there are already a lot of excellent blogs devoted to astrophysics, physics, general relativity, cosmology, etc., this one  will be more specifically devoted to « scientific culture », trying to cover some of my fields of interest and activity at the intersection of science, history, literature, art, philosophy.

This anglophone blog, « e-luminesciences », is NOT a translation of my francophone blog «luminesciences» (https://blogs.futura-sciences.com/luminet/, that I recommend to all the lovers of French culture), since it will present original posts as well as some ones adapted from their French version.

Have a nice time !

Quote by Tsiolkovsky

To set foot on the soil of the asteroids, to lift by hand a rock from the Moon, to observe Mars from a distance of several tens of kilometers, to land on its satellite or even on its surface, what can be more fantastic? From the moment of using rocket devices a new great era will begin in astronomy: the epoch of the more intensive study of the firmament. ­

Konstantin E. Tsiolkovsky, Father of Russian Astronautics, 1896