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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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Jueves Santo

Posted in Barcelona with tags , , , on March 28, 2024 by telescoper

Today, Jueves Santo (Holy Thursday, aka Maundy Thursday), is a public holiday in many parts of Spain but not here in Catalonia, where all the shops have been open. I mentioned that Barcelona is not the most religious city in Spain and this is another demonstration of that. I am glad the shops were open because I used the occasion to stock up for the approaching long weekend.

Nice weather having resumed, the tourist areas of Barcelona were extremely busy today. I’m not sure what the Spanish or Catalan words are for Chuggers but they were out in force. One guy stepped right in front of me and I couldn’t avoid bumping into him. As someone who is often very nervous in large crowds I find this sort of thing very irritating. I gave him an earful (in English) and walked on. I still don’t know what he was plugging.

Like everywhere I’ve stayed during this sabbatical, the apartment I’m on is equipped with a Nespresso machine. This one, however, is different from the usual type and takes larger capsules like those shown above. While you can get standard Nespresso pods in supermarkets and other stores, these funny hemispherical pods have to be purchased in a Nespresso shop. There are plenty of these shops around – there’s one just over the street from my apartment – but it’s quite hard work just buying the capsules at them. You can’t just pick up a box of capsules and take it to a till: you have to queue to see one of the assistants who will try to sell you some sort of subscription. On the other hand, they also offer you a coffee to taste if you don’t know which of the myriad types you want. You can also recycle used capsules there. Anyway, despite my broken Spanish, I did succeed in buying what I wanted and will be sufficiently caffinated for the next few weeks.

P.S. As well as the ceremonial purchase of coffee, one of the other rites performed on Jueves Santo is the Lavatorio de Pies which means “the washing of the feet” and has nothing to do with lavatories or pies.

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L’aigua no cau del cel

Posted in Barcelona, Biographical with tags , , on March 26, 2024 by telescoper

It has rained more in the past 24 hours in Barcelona than it did in the three months I spent here before Christmas. In fact it rained so hard last night that it woke me up. More precipitation is forecast in the next few days too, but it will take a lot more than a few days of rain to fill up the empty reservoirs. The drought emergency is still a thing and water restrictions are still in force.

I’m doing my bit for the situation by only drinking wine.

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Diumenge de Rams

Posted in Barcelona, Biographical with tags , , , on March 24, 2024 by telescoper

Walking about yesterday I noticed that, not far from my apartment, on the Rambla de Catalunya, there was a street market offering a variety of curious merch. I was a bit confused until I realized that today is Palm Sunday, which is Domingo de Ramos in Spanish or Diumenge de Rams in Catalan; both mean “Sunday of Branches”. The long branches, some festooned with sweets and/or ribbons, are meant to be held by boys, while girls carry the smaller stems with intricate woven crosses. There is a procession called La Borriquita (“The Little Donkey”) which goes around the town today. It involves a statue rather than a real donkey, in case you were wondering.

Palm Sunday marks the start of Holy Week (Semana Santa), leading up to Easter Sunday, which lies on March 31st this year. There are no lectures for students next week at the University of Barcelona, though I believe the Faculty of Physics will remain open up to Thursday; Good Friday (Viernes Santa) is a public holiday, as is Monday. I think these holidays are more strictly observed here than in Ireland; most stores are closed on Sundays anyway, and this will be even more the case on Easter Sunday. Having said that, Barcelona is by no means the most religious Spanish city. I have been in Spain at Easter a few times before, and the ceremonies vary considerably from place to place, some sombre and some celebratory.

In practical terms this all means that I have to remember to get some serious shopping in on Thursday. Although stores will be open on Saturday, I think they will be very busy!

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A Casa a Barcelona

Posted in Architecture, Barcelona, Biographical with tags , , on March 23, 2024 by telescoper

It’s Saturday morning, and this week has been very busy and stressful, mostly for reasons that I can’t blog about, but it helped yesterday to come back to my very pleasant top-floor apartment on the Rambla de Catalunya to have a glass or several of wine on the terrace and enjoy the lovely weather. It reached 22°C yesterday afternoon, and my flat gets the sun most of the day.

I chose the angle for the second pic carefully, as a lady on the side of the street had obviously done her laundry recently and hung the smalls out to dry. I thought it would be indelicate to photograph them.

When the apartment was refurbished recently they took down the ceiling to reveal some interesting brickwork with the distinctive red clay that features in many buildings; the bricks are often covered with decorative ceramic tiles in a style called Bóveda Catalana in Spanish (Volta Catalana in Catalan), but along with the bare brickwork on the wall, this is a much plainer look.

You can see the mortar which attached the false ceiling removed during the refurbishment.

Anyway, if you want to know roughly where I am, it is just one block away from the Casa Batlló. I took the picture on the left last September but the crowds outside queuing to get in are apparently a perennial feature as you can see from the picture on the right I took today.

Casa Batlló from outside, September 30th 2023
Today, March 23rd 2024

Anyway, I’m determined to relax today so will now go for a stroll, and do some shopping in preparation for cooking dinner tonight.

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The Vernal Equinox 2024

Posted in Barcelona, The Universe and Stuff with tags , , on March 20, 2024 by telescoper

Loughcrew (County Meath, Ireland), near Newgrange, an ancient burial site and  traditional place to observe the sunrise at the Equinox

Just a quick note to mention that the Vernal Equinox, or Spring Equinox, (in the Northern hemisphere) took place today, Wednesday 20th March 2024, at 3.06 UTC (which was 4.06am CET, where I am at, though I was sound asleep at the time). Many people in the Northern hemisphere regard the Vernal Equinox as the first day of spring; of course in the Southern hemisphere, this is the Autumnal Equinox.

The date of the Vernal Equinox is often given as 21st March, but in fact it has only been on 21st March twice this century so far (2003 and 2007); it was on 20th March in 2008, has been on 20th March every spring from then until now, and will be until 2044 (when it will be on March 19th). This year the equinox happened before dawn, so sunrise this morning could be taken to be the first sunrise of spring. It felt more like summer, sipping coffee on my terrace in Barcelona:

This reminds me of a strange conversation I had on a plane recently. I was chatting to the person sitting next to me, who happened to be British. When he asked what I did for a living, I replied that I was an astrophysicist. He then complained that he preferred the old days when the Spring Equinox was on March 21st, and that now that Britain was out of the European Union he hoped it would change back…

Anyway, people sometimes ask me how one can define the `equinox’ so precisely when surely it just refers to a day on which day and night are of equal length, implying that it’s a day not a specific time?

The answer is that the equinox is defined by a specific event, the event in question being when the plane defined by Earth’s equator passes through the centre of the Sun’s disk (or, if you prefer, when the centre of the Sun passes through the plane defined by Earth’s equator). Day and night are not necessarily exactly equal on the equinox, but they’re the closest they get. From now until the Autumnal Equinox, days in the Northern hemisphere will be longer than nights, and they’ll get longer until the Summer Solstice before beginning to shorten again.

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Not in Not-Barcelona

Posted in Barcelona, Biographical with tags , on March 18, 2024 by telescoper

So here I am, after far too long an absence, back in Barcelona. I had to get up at silly o’clock (i.e. 3am) to get the bus to Dublin Airport to get a flight this morning. If that weren’t bad enough, the airport was littered with people clearly the worse for wear after Paddy’s Day yesterday. Today is a public holiday in Ireland, but some folks decided to travel rather than recuperate.

There was some drama on the flight too. About halfway through, the cabin crew asked if there was a doctor or a paramedic on board. I feared that someone had been taken seriously ill, but it seems it was just someone suffering the aftermath of yesterday’s indulgence. I didn’t see what happened as it was at the rear of the aircraft, and I was in row 10.

After that we were delayed landing by about 20 minutes as there was fog at Barcelona Airport that had slowed operations down; we circled for a while waiting for the mist and the backlog to clear. When we did land the fog was barely perceptible. The rest of the day has been very nice – a mild 19 degrees and sunny.

I made my way by bus from the Airport and thence on foot to the apartment in which I’ll be spending most of the time until the summer. It’s very nice, in a central location on Rambla de Catalunya. I’m on the top (6th) floor, with a nice terrace overlooking the street. I’m only 2 minutes from the Metro station at Passeig de Gràcia and Gaudi’s Casa Batlló; there was a crowd outside this afternoon as there has been every time I passed this place!

Anyway, I found my way back to the same office I was in last semester, where I await yet another Zoom call*. After that I’ll get a few essentials for the flat and have an early night. I’m looking forward to not travelling for the next several weeks.

*More excitement – the fire alarm went off, so we had to evacuate the building, but it seems to have been a false alarm.

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Travel Travails

Posted in Barcelona, Biographical with tags , , , on March 13, 2024 by telescoper

I’m sitting in Heathrow Airport Terminal 2 waiting for a flight to Dublin to complete the return home from Phoenix. The transatlantic part of this journey went pretty well despite an unpromising start. The terminal at Phoenix was incredibly crowded, and the gate area far too small to accommodate the number of passengers on the flight. The Club World lounge was completely full and operating a wait list just to get in. I waited for 30 minutes to enter and then gave up without succeeding. Had I actually paid a business class fare I would have been very angry about that. The general overcrowding led to my flight taking off about 30 minutes late, but at least that didn’t get significantly worse and I got to Heathrow with plenty of time to make my connection.

I have to admit that the fatigue and disorientation resulting from the excessive travel I’ve been doing over the past few weeks is getting to me a bit. I don’t think I’m cut out for the jet set! It’s not quite over yet, either. After flying back to Dublin I will spend a few days in Maynooth to recover and celebrate the (predicted) success of a PhD student whose examination is tomorrow, then fly back to Barcelona. Fortunately that’s just a short-haul flight and then I’ll be able to settle there until at least July.

Update: I got back to a very rainy Maynooth safely and ahead of time: I managed to get a Hopper bus I should have missed, but which was 10 minutes late!

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Hasta la vista, Barcelona!

Posted in Barcelona, Biographical with tags , , , , on December 22, 2023 by telescoper

I’m reliably informed that Spanish people don’t really say “hasta la vista” very often, but it seemed an appropriate title. I’m writing this post in the Departure Lounge at Barcelona Airport, having got here in very good time for my flight. Last time I checked in here the check-in staff were so slow that it took two hours to drop my bag at the desk and I only just made it to the gate in time for my flight. This time I arrived three hours ahead of time and it only took about 15 minutes to get processed so now I’ve got ages until I leave.

Yesterday, my last day in the office, we had a “Christmas Toast” in the foyer of the Physics Faculty building which consisted of a couple of inaudible speeches, followed by drinks and snacks in the company of a Grubb Telescope, an Atwood Machine, and many physicists.

This morning I said goodbye the flat I’ve been in for most of the past three months. I’ll be back in Barcelona in 2024, of course, but I’ll be in a different apartment when I return. Although my time in Barcelona is not over, I’d like to thank my hosts – especially Licia and Raul – for what has been a very enjoyable stay so far.

I’ll be back!

P.S. The last arXiv mailing before Christmas brought news of the accepted version of a paper for the Open Journal of Astrophysics, so I’ve just made the overlay and published the paper. That means that we finish 2023 with a half-century of articles in Volume 6. Roll on, Volume 7 (2024)!

UPDATE: I arrived safely in not-Barcelona and am looking forward to spend the next couple of weeks very lazily.

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Merry Christmas from Barcelona!

Posted in Barcelona on December 19, 2023 by telescoper
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Merry Christmas from Barcelona!

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