Euclid 2018: Day 3

It’s the morning after the conference dinner the night before, so as Day 4 of the Euclid Consortium meeting gets under way I’ve just got the time and bandwidth to do a brief post about the events of yesterday. First of all, the conference photo arrived and is shown above. You’d be hard pressed to spot me in it, as there are a lot of people in it (and bear in mind that only about a quarter of the membership of the Euclid Consortium are actually present here in Bonn).

Yesterday I went to splinter meetings related to the working groups on cross-correlating Euclid with cosmic microwave background data (morning) and clusters of galaxies (afternoon). The latter session produced the following diagram, which makes everything clear:

After the day’s work was done I took a walk down to the western bank of the Rhine (just about 15 minutes’ walk from my hotel), on the way to the conference dinner at the . Sadly, I didn’t see any Rhine Maidens or find any gold to make into a ring.

Anyway, the dinner was at the splendid Rhein Hotel Dreesen and I had the good fortune to sit with some Italian friends from way back – by which I mean over 20 years!

Fortunately I didn’t have far to go to get back to my hotel after the festivities!

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9 Responses to “Euclid 2018: Day 3”

  1. Robert Lacey Says:

    I hadn’t come across your site before but I find the combination of physics and culture quite compelling. I’ll definitely be back. I see you enjoyed a piece by Messiaen recently – I’m sure you would also enjoy his Quatuor pour la fin du temps. As you are at Euclid 2018 I thought you might be interested in the following:

    The Euclid Collection

    The National Library’s collection of works ascribed to Euclid contains more than 300 volumes, representing 270 editions,[79] and is considered to be an important reference point for Euclidean bibliographical studies.[14][84] The collection has been developed through additions to the initial thirty-nine volumes of early editions of the Elements that Sir Charles Thomas-Stanford donated in 1927,[14][79] including further eleven volumes from Sir Charles in 1928.[79] With the subsequent additions the collection covers all of Euclid’s works, including Data, Phaenomena, Optica and Catoptrica along with numerous editions of the Elements, in many languages. There are two incunabula (Erhard Ratdolt, Venice, 1482 and Leonardus de Basilea & Gulielmus de Papia, Vicenza, 1491) in the collection, as well as seventy-three volumes from the sixteenth century, including the first English (Reynold Wolfe, London, 1551) and Arabic (Typographia Medicea, Rome, 1594) editions.[79][85]

    I’m Head of Collection Development at the National Library of Wales
    Robert Lacey

  2. Robert Lacey Says:

    A rather shameless and tenuous plug admittedly!

  3. Shantanu Says:

    Peter: one sales pitch for stage IV dark energy experiments such as Euclid is to check if cosmic acceleration is caused by modified gravity or dark energy. However if you talk to anyone who works on strong field gravity or a string theorist, they will tell you that all these models of modified gravity which dispense with dark energy such as f(R) gravity, Hordensky gravity etc are very contrived, have issues with stability, etc. (see for eg Gia Dvali’s comments after Luca Amendola’s talk at LMU a few years back https://cast.itunes.uni-muenchen.de/clips/hanaXU9e7Q/vod/high_quality.mp4) Plus after the LIGO results from GW170817, most of them are ruled out or severely constrained. So why do cosmologists continue to work on these models or try to repeat the buzzword “modified gravity”.

    • Because not all of them are ruled out.

      Personally, I would bet on MOND (not generally seen as part of the modified-gravity camp) and/or dark matter (maybe Khoury’s combination of the two). However, it is always good to have a few people working on the dark horses, as long as they are not ruled out.

      The observation of a gamma-ray burst associated with a gravitational-wave event does rule out many theories: trivially for those which have a different speed of propagation for gravitational waves and electromagnetic radiation, but more subtly for several others. Watch this space.

      • Shantanu Says:

        Here I am only talking about modified theories of gravity which emulate dark energy (not dark matter). That’s always an argument given for stage IV dark energy experiment.

    • telescoper Says:

      Perhaps it’s better to rule models out using observational data than the opinions of string theorists.

      • Shantanu Says:

        Fair enough, but their point is that they already run into problems with stability of neutron stars (see Dvali’s comment on Armendola’s talk) etc, so in some sense they are practically ruled out. and its not just string theorists objecting to these theories. Any pure GR person will object to these. You will hardly ever see a paper on these theories by people from the GR community.

      • True, but that’s like saying that few bluegrass musicians play Wagner, or vice versa. Obviously, someone working on modified gravity is, pretty much by definition, not a GR person.

  4. Shantanu Says:

    Long before we had evidence for accelerating universe, there was lot of work on defining & testing alternate theories of gravity by folks such as Cliff Will, Stan Deser, Brandon Carter, Thibault Damour, Ken Nordtvedt, Jim Hartle etc. You will rarely ever see any paper from such folks constructing modified gravity theories which dispense with dark energy. One exception I am aware is that in sometime in 2006 or so, Bob Wald and his student Mike Seiffert showed that sun will evaporate in 10^-36 seconds in some of the f(R) gravity theories constructed then.

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