So I have given my talk on the State of the Universe. It’s a bit intimidating giving a talk with Nobel Laureates in the audience, but I think it went OK.
The slides are here:
I’ll add a link to the recording when I have it. Here is a link to the event. The video is very long because of a lengthy introduction and discussion at the end so if I get time I’ll put an edited version of just the talk on my Youtube channel.
In the meantime here’s a picture of me looking weird during the presentation:
Just time for a quick reminder that I’m giving a talk on Wednesday (23rd June 2021). It’s at 4pm Paris Time which is 3pm Irish Time. See my original post here.
I had a sudden sense of dread that this Colloquium might clash with the Portugal-France game in the European Championship which takes place the same day but it turns out that won’t kick off until 9pm Paris Time which means that I should just about be finished before the football starts. I don’t think even I could overrun by 4 hours! Indeed I should finish before the earlier games that day, which kick off at 5pm Paris Time…
If you want to attend the Colloquium (via Zoom) you can register for it here.
Follow @telescoperThe Summer Solstice in the Northern hemisphere happens tomorrow, Monday 21st June 2021, at 04:32 Irish Time (03:32 UTC). Among other things, this means that tomorrow is the longest day of the year around these parts. Usually I post about the Solstices and Equinoxes close to the time that they occur, and on the same day, but because I don’t want to get up before 4.32am and few would be awake to read it then, I thought I’d do this one in advance.
Sunrise in the Dublin area is about 04:56 local time tomorrow and sunset is at 21:57: the interval between sunrise and sunset will be just about 1s longer on 21st June than today, 20th June, and 5 seconds longer than Tuesday 22nd June. The longest day will last 17 hours and 11 seconds (approximately) so make the most of it – it’s all downhill from now on!
Days will get shorter from tomorrow until the Winter Solstice in December, although this does not mean that sunset will necessarily happen earlier on 22nd than it does tomorrow. In fact it is a little later. This is because there is a difference between mean solar time (measured by clocks) and apparent solar time (defined by the position of the Sun in the sky), so that a solar day does not always last exactly 24 hours. A description of apparent and mean time was given by Nevil Maskelyne in the Nautical Almanac for 1767:
Apparent Time is that deduced immediately from the Sun, whether from the Observation of his passing the Meridian, or from his observed Rising or Setting. This Time is different from that shewn by Clocks and Watches well regulated at Land, which is called equated or mean Time.
The discrepancy between mean time and apparent time arises because of the Earth’s axial tilt and the fact that it travels around the Sun in an elliptical orbit in which its orbital speed varies with time of year (being faster at perihelion than at aphelion).
Using a rapid calculational tool (Google), I found a table of the local mean times of sunrise and sunset for Dublin around the 2021 summer solstice. This shows that the earliest sunrise was actually on 17th June and the latest sunset is on 24th.
If you plot the position of the Sun in the sky at a fixed time each day from a fixed location on the Earth you get a thing called an analemma, which is a sort of figure-of-eight curve whose shape depends on the observer’s latitude. Here’s a photographic version taken in Edmonton, with photographs of the Sun’s position taken from the same position at the same time on different days over the course of a year:
The summer solstice is the uppermost point on this curve and the winter solstice is at the bottom. The north–south component of the analemma is the Sun’s declination, and the east–west component is the so-called equation of time which quantifies the difference between mean solar time and apparent solar time. This curve can be used to calculate the earliest and/or latest sunrise and/or sunset.
P.S. A bit of light googling revealed to me that if you live in York then your sunrise on 21st June 2021 is at 4.32am, precisely the same time as the Solstice.
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The Irish Government has just produced its plan for A Safe Return to on-site further and higher education and research that outlines what is basically a full return to on-campus activity from September 2021.
I quote from the preamble to the document linked to above:
It is expected that the majority of the people over 18 in Ireland will have been vaccinated by September 2021, and so planning is proceeding on the basis that full resumption of on-site activity is possible, while ensuring that overall numbers attending on-site are monitored and controlled.
In the absence of regular updates about the progress of Ireland’s vaccination programme it is difficult to know whether the first sentence is accurate or not, especially since it appears that two vaccine doses are needed to protect against the Delta-variant. I think most teaching staff will have been immunized by September, but am not so sure about the student population.
I’m also mindful that we were optimistic in advance of the start of last academic year and things didn’t exactly go to plan then. Nevertheless there do seem to be reasonable grounds for believing that we can return to on-campus teaching in September and we will be planning on that basis until there is evidence to the contrary. I just hope we don’t have to do a rapid about-turn like we did last year.
The first step in this process for us here in Maynooth is that from 5th July staff and research students can return to their offices on campus – following the existing protocols on social distancing, sanitation and ventilation – without having to make a special case. Only a few people have been working inside the Department since the start of the year and I’d expect most to begin making their way back.
In fact some members of the Department of Theoretical Physics joined us only this academic year and have never actually been the building (or on campus) at all. I suppose I’ll now have to find office space for them, something that hasn’t been necessary while we have all been working from home!
As a matter of fact, since it’s a nice day and I’ve been on Teams all morning, I might take a walk onto campus myself this afternoon and visit my office in the Department for the first time in a month…
Follow @telescoperI recently came across a comprehensive review article on the arXiv and thought some of my regular readers might find it interesting as a description of the current state of play in cosmology. The paper is called Challenges for ΛCDM: An update and is written by Leandros Perivolaropoulos and Foteini Skara.
Here is the abstract:
A number of challenges of the standard ΛCDM model has been emerging during the past few years as the accuracy of cosmological observations improves. In this review we discuss in a unified manner many existing signals in cosmological and astrophysical data that appear to be in some tension (2σ or larger) with the standard ΛCDM model as defined by the Planck18 parameter values. In addition to the major well studied 5σ challenge of ΛCDM (the Hubble H0 crisis) and other well known tensions (the growth tension and the lensing amplitude AL anomaly), we discuss a wide range of other less discussed less-standard signals which appear at a lower statistical significance level than the H0 tension (also known as ‘curiosities’ in the data) which may also constitute hints towards new physics. For example such signals include cosmic dipoles (the fine structure constant α, velocity and quasar dipoles), CMB asymmetries, BAO Lyα tension, age of the Universe issues, the Lithium problem, small scale curiosities like the core-cusp and missing satellite problems, quasars Hubble diagram, oscillating short range gravity signals etc. The goal of this pedagogical review is to collectively present the current status of these signals and their level of significance, with emphasis to the Hubble crisis and refer to recent resources where more details can be found for each signal. We also briefly discuss possible theoretical approaches that can potentially explain the non-standard nature of some of these signals.
Among the useful things in it you will find this summary of the current ‘tension’ over the Hubble constant that I’ve posted about numerous times (e.g. here):
I see that the press interest in the recent Dark Energy Survey results (to which I referred in a post here) has extended to a cartoon in the latest Private Eye…
The Coronavirus pandemic has not only changed the nature of conferences but also changed the nature of conference photographs. Here’s the group picture of the Euclid Consortium Conference that took place via Zoom at the end of May. I’m actually in it, though I wasn’t paying attention at the time and am therefore not looking at the camera. Moreover, there are some other people who are in it several times!
I’ve a very busy morning this morning but I’ve just got time to share this stunning picture of the partial solar eclipse happening between about 10.00am and 12.20pm across Ireland, as seen from Maynooth.
I’ll post more exciting images if and when the sky ceases to be eclipsed by clouds.
Time to announce another publication in the Open Journal of Astrophysics. This one was actually published on Friday actually, but I didn’t get time to post about it until just now. It is the fourth paper in Volume 4 (2021) and the 35th paper in all.
The latest publication is entitled The local vertical density distribution of ultracool dwarfs M7 to L2.5 and their luminosity function and the ultracool authors are Steve Warren (Imperial College), Saad Ahmed (Open University) and Richard Laithwaite (Imperial College).
Here is a screen grab of the overlay which includes the abstract:
You can click on the image to make it larger should you wish to do so. You can find the arXiv version of the paper here. This one is in the Astrophysics of Galaxies section but it also has overlap with Solar and Stellar Astrophysics.
Over the last few months I have noticed that it has taken a bit longer to get referee reports on papers and also for authors to complete their revisions. I think that’s probably a consequence of the pandemic and people being generally overworked. We do have a number of papers at various stages of the pipeline, so although we’re a bit behind where we were last year in terms of papers published I think may well catch up in the next month or two.
I’ll end with a reminder to prospective authors that the OJA now has the facility to include supplementary files (e.g. code or data sets) along with the papers we publish. If any existing authors (i.e. of papers we have already published) would like us to add supplementary files retrospectively then please contact us with a request!
There is a rather provocative paper on the arXiv by Jeroen van Dongen with the title String theory, Einstein, and the identity of physics: Theory assessment in absence of the empirical. I thought I’d share it here because it sort of follows on from yesterday’s post.
The abstract is:
String theorists are certain that they are practicing physicists. Yet, some of their recent critics deny this. This paper argues that this conflict is really about who holds authority in making rational judgment in theoretical physics. At bottom, the conflict centers on the question: who is a proper physicist? To illustrate and understand the differing opinions about proper practice and identity, we discuss different appreciations of epistemic virtues and explanation among string theorists and their critics, and how these have been sourced in accounts of Einstein’s biography. Just as Einstein is claimed by both sides, historiography offers examples of both successful and unsuccessful non-empirical science. History of science also teaches that times of conflict are often times of innovation, in which novel scholarly identities may come into being. At the same time, since the contributions of Thomas Kuhn historians have developed a critical attitude towards formal attempts and methodological recipes for epistemic demarcation and justification of scientific practice. These are now, however, being considered in the debate on non-empirical physics.
You can find a PDF of the full paper here.
As always, proper comments are welcome through the box below.
P. S. The answer to the question posed in the title is of course that a proper physicist is a physicist who’s at rest in the laboratory frame.
In the Dark 