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Is machine learning good or bad for the natural sciences?

Posted in The Universe and Stuff with tags , , , , , , , on May 30, 2024 by telescoper

Before I head off on a trip to various parts of not-Barcelona, I thought I’d share a somewhat provocative paper by David Hogg and Soledad Villar. In my capacity as journal editor over the past few years I’ve noticed that there has been a phenomenal increase in astrophysics papers discussing applications of various forms of Machine Leaning (ML). This paper looks into issues around the use of ML not just in astrophysics but elsewhere in the natural sciences.

The abstract reads:

Machine learning (ML) methods are having a huge impact across all of the sciences. However, ML has a strong ontology – in which only the data exist – and a strong epistemology – in which a model is considered good if it performs well on held-out training data. These philosophies are in strong conflict with both standard practices and key philosophies in the natural sciences. Here, we identify some locations for ML in the natural sciences at which the ontology and epistemology are valuable. For example, when an expressive machine learning model is used in a causal inference to represent the effects of confounders, such as foregrounds, backgrounds, or instrument calibration parameters, the model capacity and loose philosophy of ML can make the results more trustworthy. We also show that there are contexts in which the introduction of ML introduces strong, unwanted statistical biases. For one, when ML models are used to emulate physical (or first-principles) simulations, they introduce strong confirmation biases. For another, when expressive regressions are used to label datasets, those labels cannot be used in downstream joint or ensemble analyses without taking on uncontrolled biases. The question in the title is being asked of all of the natural sciences; that is, we are calling on the scientific communities to take a step back and consider the role and value of ML in their fields; the (partial) answers we give here come from the particular perspective of physics

arXiv:2405.18095

P.S. The answer to the question posed in the title is probably “yes”.

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Three New Publications at the Open Journal of Astrophysics

Posted in OJAp Papers, Open Access, The Universe and Stuff with tags , , , , , , , , on May 25, 2024 by telescoper

After a very busy and unusual week, it’s time to get back to normal with the usual  Saturday roundup of business at the  Open Journal of Astrophysics. If you want to know how many papers we have published so far this year (Vol. 7), the answer is 42. The total published by OJAp is now 157. We’re still on track to publish around 100 papers this year, possibly more, compared to last year’s 50.

All the members of this week’s trio are in the folder marked Cosmology and Nongalactic Astrophysics, and indeed all three relate in one way or another to the topic of weak gravitational lensing.  All three were published on Wednesday 22nd May 2024.

First one up is “Joint constraints from cosmic shear, galaxy-galaxy lensing and galaxy clustering: internal tension as an indicator of intrinsic alignment modelling error” which is by Simon Samuroff (Northeastern U., USA), Andresa Campos (Carnegie Mellon U., USA), Anna Porredon (Bochum, Germany) and Jonathan Blazek (Edinburgh, UK).   A combined statistical approach to the identification of errors arising in cosmic shear analysis due to intrinsic alignments.

Here is a screen grab of the overlay, which includes the abstract:

You can read the paper directly on arXiv here.

The second paper to present is “A unified linear intrinsic alignment model for elliptical and disc galaxies and the resulting ellipticity spectra” by Basundhara Ghosh (Bangalore, India), with Kai Nussbaumer, Eileen Sophie Giesel & Björn Malte Schäfer (Heidelberg, Germany). It presents a discussion of the physical origin of intrinsic alignments of both elliptical and disk galaxies and the implications for cosmological studies

The overlay looks like this:

 

You can read this paper directly on the arXiv here.

The last paper of this batch is entitled “Neural style transfer of weak lensing mass maps”  and proposes a generative model for the mass-production of weak-lensing maps. The authors are Masato Shirasaki and Shiro Ikeda (both of the University of Tokyo, Japan)

Here is a screengrab of the overlay:

 

To read the accepted version of this on the arXiv please go here.
That’s all for now. I will do another update next week.

 

 

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Euclid Paper Day!

Posted in Barcelona, Euclid, Maynooth, The Universe and Stuff with tags , , , , , , , , on May 24, 2024 by telescoper

This morning’s arXiv update brought the expected deluge of preprints from Euclid. You can find details of all fifteen of the new articles here. Ten of them relate to the Early Release Observations of which five were announced yesterday and five last November. These are essentially byproducts of the testing and calibration phase of the Euclid mission rather than the main cosmological survey. ESA is making a series of short videos about these results which I will share on here from time to time.

Of more direct relevance to cosmologists such as myself are the following five reference papers:

The overview paper, led by Yannick Mellier (Euclid Consortium Lead), giving a general description of the mission capabilities and science goals, will be the main reference paper and just about every active member of the Euclid Consortium is on the author list (including myself). That’s over a thousand people, not quite at the level of the Large Hadron Collider but getting there. I do think we need to find a better way of giving credit to work in large collaborations than through authorship, but until someone comes up with a workable scheme, and people responsible for hiring researchers adopt it, we’re stuck with what we’ve got. At least I can say that I’ve read that paper (which is 94 pages long, including the author list)

Papers II-IV are technical articles relating to Euclid’s instruments and their calibration, which will also be important references for the survey part of the Euclid mission. Paper V is about the Flagship simulations and the mock catalogues produced therefrom; I discussed these a while ago here. It is led by Francisco Castander of Institut de Ciencies de l’Espai, who organized the meeting I attended recently here in Barcelona.

These papers now now be peer-reviewed and, assuming they are accepted, published in a special issue of Astronomy & Astrophysics (A&A).

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New Results from Euclid

Posted in Euclid, Maynooth, The Universe and Stuff with tags , , , , on May 23, 2024 by telescoper

As it was foretold, exciting new results from the European Space Agency’s Euclid mission have now been released.

You can read more about these images here.

Together with the five images released last November that makes a total of ten Early Release Observations from the pre-survey phase of Euclid. It’s not all about the pictures, however. Today also saw the release of ten scientific papers to go with these images, as well as five reference papers for the main survey. You can find them all, with accompanying information here. They will be announced on arXiv tomorrow.

You might also be interested to read my Euclid piece on RTÉ Brainstorm which has just appeared. This is not just about the new images, but gives an update on what Euclid has been up to since launch, and what we can expect in the future. There’s also a version adapted for Maynooth University PR purposes here. It includes this quote:

Today’s release of new data and technical papers from Euclid is exciting in itself but also marks the start, after months of painstaking calibration and testing of the instruments, of Euclid’s main cosmological survey. We are on the threshold of a new era in cosmology. Maynooth is the only University in Ireland to be involved in this mission and it is very exciting to be at the forefront of such an important scientific development.

I’m also quoted in a piece in the Irish Times. You’ll probably find the article blocked by a paywall but my bit is:

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Two New Publications at the Open Journal of Astrophysics

Posted in OJAp Papers, The Universe and Stuff with tags , , , , , , on May 4, 2024 by telescoper

It’s Saturday morning in Barcelona, and time to post another update relating to the  Open Journal of Astrophysics.  Since the last update we have published two more papers, taking  the count in Volume 7 (2024) up to 32 and the total published by OJAp up to 147. There’s every chance we will reach 150 next week.

The first paper of the most recent pair – published on  Monday 29th April- is “Supernovae in 2023 (review): possible breakthroughs by late observations” by Noam Soker of Technion in Haifa, Israel. It presents  a discussion of observations of the aftermath of supernovae explosions, such as supernova remnants, and how these may shed light on the explosion mechanism. This one is in the folder marked High-Energy Astrophysical Phenomena.

Here is a screen grab of the overlay which includes the abstract:

 

You can click on the image of the overlay to make it larger should you wish to do so. You can find the officially accepted version of the paper on the arXiv here.

The second paper was published on Thursday 2nd May and has the title “ΛCDM is alive and well” The authors are: Alain Blanchard (Université de Toulouse, France), Jean-Yves Héloret (Université de Toulouse, France), Stéphane Ilíc (Université Paris-Saclay, France), Brahim Lamine (Université de Toulouse, France) and Isaac Tutusaus (Université de Genève, Switzerland). This one, which is in the folder marked Cosmology and NonGalactic Astrophysics, presents a review of  review of the alleged tensions between observations and the standard cosmological model.

I did a post recently relating to a Royal Society Meeting on this topic. The first version of this paper appeared on arXiv about two years ago but the final version is extensively modified.

Here is a screen grab of the overlay which includes the abstract:

 

 

You can click on the image of the overlay to make it larger should you wish to do so. You can find the officially accepted version of the paper on the arXiv here.

And that concludes this week’s update. More next week!

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Two New Publications at the Open Journal of Astrophysics

Posted in OJAp Papers, Open Access, The Universe and Stuff with tags , , , , , , , , , , on April 20, 2024 by telescoper

It’s Saturday, and it’s time to post another update relating to the  Open Journal of Astrophysics.  Since the last update we have published two more papers, taking  the count in Volume 7 (2024) up to 27 and the total published by OJAp up to 142.

The first paper of the most recent pair – published on  Tuesday April 16th – is “An Enhanced Massive Black Hole Occupation Fraction Predicted in Cluster Dwarf Galaxies” by Michael Tremmel (UCC, Ireland), Angelo Ricarte (Harvard, USA), Priyamvada Natarajan (Yale, USA), Jillian Bellovar (American Museum of Natural History, New York, USA), Ray Sharma (Rutgers, USA), Thomas R. Quinn (University of Washington, USA). It presents a  study, based on the Romulus cosmological simulations, of the impact of environment on the occupation fraction of massive black holes in low mass galaxies. This one is in the folder marked “Astrophysics of Galaxies“.

Here is a screen grab of the overlay which includes the abstract:

 

You can click on the image of the overlay to make it larger should you wish to do so. You can find the officially accepted version of the paper on the arXiv here.

The second paper was published on Wednesday 17th April and has the title “A 1.9 solar-mass neutron star candidate in a 2-year orbit” and the authors are: Kareem El-Badry (Caltech, USA), Joshua D. Simon (Carnegie Observatories, USA), Henrique Reggiani (Gemini Observatory, Chile), Hans-Walter Rix (Heidelberg, Germany),  David W. Latham (Harvard, USA),  Allyson Bieryla (Harvard, USA),  Lars A. Buchhave (Technical University of Denmark, Denmark),  Sahar Shahaf (Weizmann Institute of Science, Israel),  Tsevi Mazeh (Tel Aviv University, Israel), Sukanya Chakrabarti (University of Alabama, USA), Puragra Guhathakurta (University of California Santa Cruz, USA), Ilya V. Ilyin (Potsdam, Germany), and Thomas M. Tauris (Aalborg University, Denmark)

This one, which is in the folder marked Solar and Stellar Astrophysics, presents a discussion of the discovery of a 1.9 solar mass neutron star candidate using Gaia astrometric data, together with the implications of its orbital parameters for the formation mechanism.

Here is a screen grab of the overlay which includes the abstract:

 

 

 

You can click on the image of the overlay to make it larger should you wish to do so. You can find the officially accepted version of the paper on the arXiv here.

That concludes this week’s update!

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Challenging the Standard Cosmological Model

Posted in The Universe and Stuff with tags , , , on April 16, 2024 by telescoper

Some time ago I used the medium of this blog to plug a mini-conference at the Royal Society in London entitled Challenging the Standard Cosmological Model. Here’s a description of the meeting:

Is the universe simple enough to be adequately described by the standard ΛCDM cosmological model which assumes the isotropic and homogeneous Friedmann-Lemaître-Robertson-Walker metric? Tensions have emerged between the values of cosmological parameters estimated in different ways. Do these tensions signal that our model is too simple? Could a more sophisticated model account for the data without invoking a Cosmological Constant?

That conference is actually taking place this week (on 15th and 16th April, i.e. yesterday and today). I can’t be there, of course, because I’m here, but I can share the recording of the talks. Here is the first day’s worth. The recording is about 8 hours long so you probably won’t want to watch it all in one sitting. Let me point out the talk by Wendy Freedman, which starts at around 2:13.30 talking about the Hubble Tension largely from the point of view of stellar distance indicators and suggesting an answer of 69.1 ± km s-1 Mpc-1, which reduces the tension with Planck significantly.

And here is Day 2:

You can find more information about the meeting, including a full list of the talks here.

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Presentation of the BAO DESI results at ICCUB Uni Barcelona – by Licia Verde & Héctor Gil Marin

Posted in The Universe and Stuff with tags , , , , on April 8, 2024 by telescoper

Last week, when I wrote about the new results from the Dark Energy Spectroscopic Instrument (DESI) I mentioned that there would be a seminar here at ICCUB about that very topic. Well, the seminar, by Licia Verde & Héctor Gil Marin, was recorded and here it is:

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Cosmology Talks: Cosmological Constraints from BAO

Posted in The Universe and Stuff, YouTube with tags , , , , , , , , , on April 5, 2024 by telescoper

Here’s another video in the Cosmology Talks series curated by Shaun Hotchkiss. This one very timely after yesterday’s announcement. Here is the description on the YouTube page:

The Dark Energy Spectroscopic Instrument (DESI) has produced cosmological constraints! And it is living up to its name. Two researchers from DESI, Seshadri Nadathur and Andreu Font-Ribera, tell us about DESI’s measurements of the Baryon Acoustic Oscillations (BAO) released today. These results use one full year of DESI data and are the first cosmological constraints from the telescope that have been released. Mostly, it is what you might expect: tighter constraints. However, in the realm of the equation of state of dark energy, they find, even with BAO alone, that there is a hint of evidence for evolving dark energy. When they combine their data with CMB and Supernovae, who both also find small hints of evolving dark energy on their own, the evidence for dark energy not being a cosmological constant jumps as high as 3.9σ with one combination of the datasets. It seems there still is “concordance cosmology”, it’s just not ΛCDM for these datasets. The fact that all three probes are tentatively favouring this is intriguing, as it makes it unlikely to be due to systematic errors in one measurement pipeline.

My own take is that the results are very interesting but I think we need to know a lot more about possible systematics before jumping to conclusions about time-varying dark energy. Am I getting conservative in my old age? These results from DESI do of course further underline the motivation for Euclid (another Stage IV survey), which may have an even better capability to identify departures from the standard model.

P.S. Here’s a nice graphic showing the cosmic web showing revealed by the DESI survey:

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DESI Year 1 Results: Baryon Acoustic Oscillations

Posted in Barcelona, Euclid, The Universe and Stuff with tags , , , , on April 4, 2024 by telescoper

There has been a lot of excitement around the ICCUB today – the press have been here and everything – ahead of the release of the Year 1 results from the Dark Energy Spectroscopic Instrument (DESI). The press release from the Lawrence Berkeley Laboratory in California can be found here.

The papers were just released at 5pm CEST and can be found here. The key results pertain to Baryon Acoustic Oscillations (BAOs) which can be used to track the expansion rate and geometry of the Universe. This is one of the techniques that will be used by Euclid.

There’s a lot of technical information to go through and I have to leave fairly soon. Fortunately we have seminar tomorrow that will explain everything at a level I can understand:

I will update this post with a bit more after the talk, but for the time being I direct you to the high-level cosmological implications are discussed in this paper (which is Paper VI from DESI).

If your main interest is in the Hubble Tension then I direct you to this Figure:

Depending on the other data sets included, the value obtained is around 68.5 ± 0.7 in the usual units, closer to the (lower) Planck CMB value than the (higher) Supernovae values but not exactly in agreement; the error bars are quite small too.

You might want to read my thoughts about distances estimated from angular diameters compared with distances measured using luminosity distances here.

If you’re wondering whether there is any evidence for departures from the standard cosmology, another pertinent comment is:

In summary, DESI data, both alone and in combination with other cosmological probes, do not show any evidence for a constant equation of state parameter different from −1 when a flat wCDM model is assumed.

DESI 2024 VI: Cosmological Constraints from the Measurements of Baryon Acoustic Oscillations

More complicated models of time-varying dark energy might work, but there’s no strong evidence from the current data.

That’s all from me for now, but feel free to comment through the box below with any hot takes!

UPDATE: As expected there has been quite a lot of press coverage about this – see the examples below – mostly concentrating on the alleged evidence for “new physics”. Personally I think the old physics is fine!

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