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The IAP at 75: The early history of our Institute

The IAP at 75: The early history of our Institute

A grainy black-and-white photograph. A line of men stare into the camera. In the background, bare trees are outlined against the cold winter sky. The ground is thick with dead winter leaves. Four of the men are in suits and hats; three are labourers. One heavy-set man with a pencil moustache leans nonchalantly against a tree, another is there with his hands in his pockets. Behind them, a small truck is parked at an awkward angle. On the far left, one of the well-dressed men holds a pick in his hand. This man is Henri Mineur, who would in the following year become the first director of the IAP. The date is the 6 of January 1938: the date on which construction of the IAP started. Last Friday, we celebrated the institute’s 75th anniversary with a series of talks and presentations, and in addition a short film made by my friend Mr. Jean Mouette.

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Henri Mineur starts construction work  for the IAP

The IAP was created out of an urgent need for new structures to carry out scientific research. In the early part of the 20th century, astronomy was undergoing a radical transformation. With the arrival of new instrumentation and new telescopes it became possible for the first time to apply our knowledge of physics to understand astrophysical processes and observation: the science of “astrophysics” came into being. For centuries, astronomy had been concerned with the positions and movements of stars and other objects, but with the arrival of richly quantitative measurements such as spectroscopy, which can provide detailed information concerning the chemical make-up of very distant objects, it became clear that a new approach was possible. However, it was not clear where this kind of new astronomy could be done in France – certainly not at the Universities which were orientated uniquely towards teaching, and saw no place for research. The observatories, steeped in centuries of positional astronomy (and still labouring to accomplish immense tasks like the “Carte Du Ciel”) were not quite ready for the transition.

One man, Jean Perrin, saw the need for a new national institution to carry out astrophysical research – an institution which would not be part of any existing structures but would be independent. A left-leaning government had just arrived in Paris, le “Front populaire”, and they fully supported Perrin’s idea. Jean Zay, a minister at the time, signed a decree on the 30th of October 1936 which led to the creation of the Observatoire de Haute Provence (the OHP, in some ways the “observing station” of the IAP), and the IAP itself, initally designated as a centre of research which would analyse data arriving from OHP and devise new instruments for the telescopes. The IAP would be constructed on a patch of ground in the Jardin de L’Observatoire, which the government had requisitioned for this purpose (leading to tensions between the Observatoire and the IAP which persisted for decades). The front populaire was uniquely disposed to these ideas. In fact, Perrin’s visits to the minister Jean Zay’s office invariably resulted in him receiving all the funds he requested.

Construction of the IAP started soon afterwards, and the building’s skeleton was in place by 1940: the interior, however was unfinished, and with the arrival of the Vichy regime and the German occupation, the construction was halted. Nevertheless, as Daniel Chalonge tells us after the war, building work was carried on in secret. Certainly other concerns occupied the scientists. Some left, others remained. Neither Perrin or Zey would survive the war: Perrin left for New York, where he died in 1942. Jean Zey was arrested by the Vichy government and later assassinated. In Paris, two astronomers, Holweck and Solomon, were arrested and executed by the Nazis. Henri Mineur himself was briefly imprisoned, before being released: he spent the remainder of the war in the resistance. Even astronomers long-dead suffered: the statue of Arago on the place Ile-de-Seine, in front of the site of the observatory, was melted down for bullets and shells. But finally, in 1944, some staff moved to the IAP. The building would not be completed until 1952 (and in the 1980s a third floor would be added to create the building as we know it today).

From almost the beginning, both theoretical and observational subjects were investigated at the IAP: spectrophotometric observations of the sun, stellar atmospheres, and every aspect of physical processes in an astrophysical context. We heard how Evry Schatzmann, aided by a large number of students, investigated almost every kind of astrophysical phenomena, and contributed greatly to the international reputation of our institute (but it made life difficult for the students: as they were all working on different topics, none could help each other). At the same time, machine shops and mirror polishing facilities, together with facilities for numerical calculations has ensured that new observations from OHP and elsewhere could be fully exploited. Today at IAP there are no longer any machine shops, but the importance of computing in astrophysics at the IAP has only grown in the intervening years.

How survey astronomy began, part I: An international conference is held

How survey astronomy began, part I: An international conference is held

It’s time to get this blog back on track and talk about SCIENCE (….”Mr. White”, if you understand the reference). It’s been too long.

Last weekend (14th-15th of September) was “Journée du patrimoine”, that wonderful day in which buildings normally closed are open to the public. I’ve seen any number of interesting things in Paris over the years. However, this year, I decided it was about time I was on the other side, so to speak, and I volunteered to assist at that august institution the IAP shares its grounds with, the “Observatoire de Paris”. The IAP is the oldest CNRS lab in France, and this year we are celebrating our 75th anniversary, but the Observatoire is much older — it was founded in 1667. It is probably one of the oldest Observatories in the world and probably one of the only ones in which there are still real astronomers doing real research. All the other institutions from that distant epoch have been either demolished or converted to museums and their staff shuttled off to unhappy ugly concrete buildings in the suburbs. So you may imagine what a rich heritage of science and learning there is to talk about when considering Paris Observatory (and how much Paris has transformed itself around the site of the observatory in the last three and half centuries, but that is another story).

There are so many interesting stories concerning the Observatory, but perhaps the most fascinating for me is the “Carte du Ciel” project — because it is no underestimate to say that with this undertaking modern international survey astronomy really began. There is a direct link between the Carte du Ciel and the Euclid project I’m involved in.

Modern survey astronomy started here !

But let’s take a step back. You have just left the IAP and are crossing the observatory gardens. On your left you see two small, rusted domes. The paint is peeling off. These are the domes of the “carte du ceil” observatory. Open the door, and inside the left dome, you can see a small refracting telescope. There is a large square metal box just below the eyepiece. Now take a step even further back. It’s end of the 19th century. Paris under the second Empire. Only a few years previously, in 1882, astronomers in the Cape of good hope, took some of the first images of the heavens with photographic plates — Halley’s comet — and they were astonished to see many, many stars on each plate. The image below shows of one of these first “deep sky” images made with photographic plates (by a Dr. David Gill). I found a scan of this plate (from H. H. Turner’s “Astronomical discovery” and have included it below):

The first deep sky image of all time ! 

It became clear very quickly that the information gathering capacity of photographic plates surpassed anything which was available before then. Moreover, photographic measurements had the great promise of being objective, unlike hand-drawn sketches and notes (think of those “canals” on Mars). Now the only thing missing was a telescope optimised for photographic measurements.
In Paris two opticians, the Henry brothers, working out of their garden shed (as far as I could tell) had a design for a refracting telescope which could provide a wide field of view, 2 degrees on a side. A second-Empire start-up! Admiral Mouchez, the director of the Paris observatory, impressed by their successes, ordered the construction of a much larger telescope with an objective of 34 centimetres. This would later become the first telescope of the “carte du ciel project”. Photographic plates attached this instrument could easily reach stars of V~12 or 13 magnitudes, unheard of at the time, and on each plate hundreds of stars were visible.

Such an instrument would be perfectly optimised to realise a modern survey of sky using photographic detectors. These was one problem — from Paris, only a small fraction of the heavens are visible. To survey the entire sky, observatories would be needed in the four corners of the world. Everyone would have to agree on what parts of the sky they would survey and what instruments they would use. To make progress… there would be to have a meeting. So an international conference in was held in April 1887 in Paris Observatory, under the instigations of the paris Academy of Science (suggested by Mouchez) — “The international astrophotographic congress”. It started on Saturday, 16th of April 1887, at 14:00, (so I should really not complain about meetings starting on Sunday). Was this the first international astronomy meeting? It was certainly the first international meeting to whose principal objective was a sky survey.

Now, today, in the 21st Century, everything has been virtualised … and I found, digging around just a little bit, the conference proceedings for this meeting. Well, not exactly: it is an account of the meeting written by a one A. G Winterhalter, who represented the American Academy of Sciences (and is published here as an annex to the 1887 proceedings of the United States Naval Observatory’s). Steam-ships and trains, natural products of the industrial revolution, meant that such an international conference could take place for the first time (Winterhalter writes in his introduction that his steam-ship voyage from New York to Cherbourg takes 11 days, and during the trip he met another astronomer who was attending the same conference – so nothing changes there!). There is a table listing attendance at the conference, broken down by country:

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Who attended the first international astronomy conference

Winterhalter notes that “the proceeds were conducted entirely in the French language”. Hey, those were the days (sorry, French colleagues)! It’s interesting to read Winterhalter’s account of the meeting: a large part of the proceedings is concerned with finding the best possible technical solutions and fixing the parameters of they survey (to which everyone had to agree to). At the meeting, everyone agreed to use the Henry brothers’ telescope, paired with a standard photographic emulsion.
One important question which had to be addressed was: what would be the limiting magnitude of the survey? It was already clear at the outset that this would be a massive undertaking, because at the faintest limits accessible by the Henrys’ telescope there would be an overwhelming number of stars. Millions and millions. How could catalogues be made on paper containing all those stars? The could never be printed, they would simply be too large.

A compromise solution was adopted: the survey would be in two parts: a catalogue release containing all stars to V < 11 and an “imaging data release” which would consist of reproductions of the plates themselves and reach fainter magnitudes – down to V< 14.

Well, that was the plan… More coming up in the second post..

George Ellis and the Multiverse

George Ellis and the Multiverse

Last Friday’s IAP “blockbuster” seminar speaker was the renowned cosmologist George Ellis. Ellis talked to us about the “multiverse”,  a topic which has gained an enormous amount of coverage in the popular press. Countless books have been written about it: during his talk he gave us a healthy selection of quotes from many of these texts.

The “multiverse” idea is essentially that the the Universe we observe is really only a universe, with a small u, and that outside the bubble of our past “light cone”, those photons which can reach us within the lifetime of the Universe, there are in fact an infinite number of other Universes. And, this is the important part, these Universes many not resemble anything like our own Universe at all: they could be Universes completely different. Radically different, with a different set of physical parameters, leading to them being utterly barren of planets, stars and structures. God does not only play dice, but he does it with the whole Universe, infinite numbers of times. There could be a Universe exactly like the one we are living in with the only difference being that my espresso this morning was slightly stale. The reason this idea is attractive is that helps us to explain why there are complex structures like human beings and stars — we just happen to live in one of these multiverses where everything was tuned just the right way. Otherwise, of course, we wouldn’t be around to observe any of it — the anthropic principle.

Or, does it really explain anything at all? The point is that we can never, ever observe any of this. Since the multiverse are too far away from us, photons from these Universes can never reach our Universe. They are in a region of space which is not casually connected to our own (or maybe — Ellis talked about the mind-bending idea that Multiverses could actually collide — if that happened in our Universe it would lead to the formation of a ‘ring’ on the cosmic microwave background. No rings have been spotted so far ;- ).

And that is really his criticism — multiverse theories aren’t really science. One of the most important aspects of any scientific theory is that it should falsifiable, which is to say that there must be some observation which you can make to exclude the theory. Since there is no casual link between these other universes and our own there is no way we could ever make an observation to rule out the theory.  It’s not testable: these universes don’t ever interact with our own.  But, it is certainly presented as a scientific theory by its practitioners. Fair enough — to me, as someone who spends a lot of time on  galaxy surveys and observations, I appreciated very much his blast of Popperian realism, which is something sometimes you don’t get too much of in the more speculative branches of cosmology (I think all most of my observer colleagues would agree with Ellis).  And, warned Ellis, once you accept the theories of the multiverse as a real scientific theory, the gates are soon opened to all other kinds of questionable theories…

Is this really any different from what has happened before? In the past, there have been lots of crazy theories which either turned out to be consistent with observations and not falsifiable (quantum mechanics is a pretty good example of that — the theory is so counter-inutitive, and people have gone to enormous lengths to try to “catch the universe out”, like Serge Haroche with his single atom traps — but no-one has succeeded so far).  Or,  they have been ruled out by observations, like the “luminiferous aether”, instantly killed by Michelson and Morley and their interferometer experiment. These “bad” theories just fall away, because they don’t help us understand the Universe any more. However, the difference with the ideas around the “multiverse” is that they have a strong philosophical attraction to us — they claim to provide (at least a partial) answer the question, “why are we here?”.  But, for the moment, they’re not science.

Reflecting on this I see one possible course of action for the multiverse practitioners — start a church!