I’m told that there are pubs in which people don’t sit around discussing antimatter and time reversal by sketching Feynman diagrams on seasickness bags, but who would want to drink in one those?
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Public House Outreach
Posted in Education, The Universe and Stuff with tags Antimatter, Feynman Diagrams, Particle Physics, sick bag, time reversal on April 10, 2018 by telescoperRemembering Clover
Posted in Biographical, Science Politics, The Universe and Stuff with tags 9th April 2009, B-mode, Bicep2, Clover, Cosmic Microwave Background, Cosmology, Polarization, Science and Technology Facilities Council on April 10, 2018 by telescoperI was tidying up some papers in my desk yesterday and came across a clipping dated April 9th 2009, i.e. exactly nine years ago to the day. Amazed by this coincidence, I resolved to post it on here but was unable to work out how to use the new-fangled scanner in the Data Innovation Institute office so had to wait until I could get expert assistance this morning:
Sorry it’s a bit crumpled, but I guess that demonstrates the authenticity of its provenance.
The full story, as it appeared in the print edition of the Western Mail, can also be found online here. By the way it’s me on the stepladder, pretending to know something about astronomical instrumentation.
I wrote at some length about the background to the cancellation of the Clover experiment here. In a nutshell, however, Clover involved the Universities of Cardiff, Oxford, Cambridge and Manchester and was designed to detect the primordial B-mode signal from its vantage point in Chile. The chance to get involved in a high-profile cosmological experiment was one of the reasons I moved to Cardiff from Nottingham almost a decade ago, and I was looking forward to seeing the data arriving for analysis. Although I’m primarily a theorist, I have some experience in advanced statistical methods that might have been useful in analysing the output. It would have been fun blogging about it too.
Unfortunately, however, none of that happened. Because of its budget crisis, and despite the fact that it had already spent a large amount (£4.5M) on Clover, the Science and Technology Facilities Council (STFC) decided to withdraw the funding needed to complete it (£2.5M) and cancel the experiment. I was very disappointed, but that’s nothing compared to Paolo (shown in the picture) who lost his job as a result of the decision and took his considerable skills and knowledge abroad.
We will never know for sure, but if Clover had gone ahead it might well have detected the same signal found five years later by BICEP2, which was announced in 2014. Working at three different frequencies (95, 150 and 225GHz) Clover would have had a better capability than BICEP2 in distinguishing the primordial signal from contamination from Galactic dust emission (which, as we now know, is the dominant contribution to the BICEP2 result; see thread here), although that still wouldn’t have been easy because of sensitivity issues. As it turned out, the BICEP2 signal turned out to be a false alarm so, looking on the bright side, perhaps at least the members of the Clover team avoided making fools of themselves on TV!
P.S. Note also that I moved to Cardiff in mid-2007, so I had not spent 5 years working on the Clover project by the time it was cancelled as discussed in the newspaper article, but many of my Cardiff colleagues had.
Follow @telescoper‘Stephen Hawking RIP’ by Ella Baron
Posted in Art, The Universe and Stuff with tags Ella Baron, Stephen Hawking, Times Literary Supplement on April 5, 2018 by telescoper
I just saw this lovely illustration (by Ella Baron) and thought I would share it here.
It appears in the March 23 of the Times Literary Supplement which arrived in Maynooth while I was away and I’ve just found time to read it. I subscribe to the TLS primarily because I like the crossword..
The ‘cartoon’ is accompanied by an excerpt from A Brief History of Time:
Follow @telescoperIf a pulse of light is emitted… then as time goes on it will spread out… like ripples on the surface of a pond when a stone is thrown in…
EWASS in Liverpool
Posted in Football, The Universe and Stuff with tags astronomy, EWASS, EWASS2018, Liverpool, National Astronomy Meeting, Royal Astronomical Society on April 4, 2018 by telescoperI’m back in Maynooth with teaching to do after the Easter recess. The Flybe schedule having just changed for the summer, I took a 7am flight from Cardiff to Dublin this morning, which meant getting up at stupid o’clock, but I got here safely enough to Maynooth at about 9.40am.
Anyway, had I not known that I would be here in Ireland I would probably have planned to visit the English Midlands in order to attend EWASS (European Week of Astronomy and Space Science) which takes place this week in Liverpool. This meeting, which is in a different country each year, this time incorporates the Royal Astronomical Society’s annual National Astronomy Meeting making it one of the biggest astronomy conferences ever held in the UK.
Sadly my teaching commitments meant I couldn’t attend EWASS2018, but I thought I’d take this opportunity to wish everyone there all the best for an enjoyable and productive week.
I’ll also mention that various short videos of press briefings etc are coming out on Youtube with little snippets from the conference, including this one about Ariel (which I blogged about recently):
You can find other videos by searching for EWASS on Youtube. I’m sure more will emerge over the next couple of days!
P.S. The event in Liverpool has clearly been planned with football fans in mind: Liverpool play Manchester City tonight, in Liverpool, in the UEFA Champions League..(UPDATE: the match finished 3-0 to Liverpool, which presumably pleased the locals).
Follow @telescoperIs the Cosmological Flatness Problem really a problem?
Posted in Bad Statistics, The Universe and Stuff with tags arXiv:1803.05148, Cosmological Flatness Problem, Marc Holman on March 26, 2018 by telescoperA comment elsewhere on this blog drew my attention to a paper on the arXiv by Marc Holman with the following abstract:
Modern observations based on general relativity indicate that the spatial geometry of the expanding, large-scale Universe is very nearly Euclidean. This basic empirical fact is at the core of the so-called “flatness problem”, which is widely perceived to be a major outstanding problem of modern cosmology and as such forms one of the prime motivations behind inflationary models. An inspection of the literature and some further critical reflection however quickly reveals that the typical formulation of this putative problem is fraught with questionable arguments and misconceptions and that it is moreover imperative to distinguish between different varieties of problem. It is shown that the observational fact that the large-scale Universe is so nearly flat is ultimately no more puzzling than similar “anthropic coincidences”, such as the specific (orders of magnitude of the) values of the gravitational and electromagnetic coupling constants. In particular, there is no fine-tuning problem in connection to flatness of the kind usually argued for. The arguments regarding flatness and particle horizons typically found in cosmological discourses in fact address a mere single issue underlying the standard FLRW cosmologies, namely the extreme improbability of these models with respect to any “reasonable measure” on the “space of all space-times”. This issue may be expressed in different ways and a phase space formulation, due to Penrose, is presented here. A horizon problem only arises when additional assumptions – which are usually kept implicit and at any rate seem rather speculative – are made.
It’s an interesting piece on a topic that I’ve blogged about before. I think it’s well worth reading because many of the discussions of this issue you will find in the literature are very confused and confusing. Apart from mine of course.
Follow @telescoperAriel to Fly
Posted in The Universe and Stuff with tags Ariel, Cardiff University, ESA, European Space Agency, exoplanets on March 23, 2018 by telescoperAll hail, great master! Grave sir, hail! I come
To answer thy best pleasure. Be ‘t to fly,
To swim, to dive into the fire, to ride
On the curled clouds, to thy strong bidding task
Ariel and all his quality.The Tempest, Act I, Scene 2.
It’s nice to be able to pass on a bit of good news for the good folk of the Astronomy Instrumentation Group here in the School of Physics & Astronomy at Cardiff University.
The ARIEL mission has been given the green light by the European Space Agency and will launch sometime around 2028. It will produce the first ever large-scale survey of the atmospheric chemistry of planets outside our solar system. Ariel will extract the chemical fingerprints of the gases in the atmospheres of over 1000 exoplanets, as well as capturing information about the temperatures and pressures in their atmospheres and the presence of clouds.
Whenever I read of exciting news from the field of exoplanet research – which happens quite frequently nowadays – it reminds me that when I started my graduate studies (in 1985) the field didn’t really exist. Now it’s one of the biggest and most active areas of astronomy! Another thing that makes me feel a bit of a dinosaur is that when Ariel actually launches I’ll be 65…
As with all such missions, a large international collaboration will be involved in Ariel, and much of the detail of who will do what is yet to be worked out, but Cardiff scientists will be providing detailed computer simulations of the Ariel satellite and its instruments, ensuring that the scientific observations can be carefully planned and the resulting data can be analysed correctly. The team will also be involved in the ground segment after launch, interpreting the data from the observations to characterise the atmospheres of the exoplanets. The Principal Investigator of the whole mission is Professor Giovanna Tinetti of University College, London, who I see regularly at dinner with the RAS Club.
Head Irishman of the School, Matt Griffin, who will himself is quoted in the news item as saying
The decision to select the Ariel mission demonstrates the scientific vision and ambition of ESA, and it’s the start of a great adventure for everyone involved. This is a mission that will hugely advance our understanding of the nature of planets and of our place in the Universe, and at Cardiff we are very much looking forward to our participation in the project.
The launch date of 2028 is some way off but space missions are exceedingly complicated things and there’s a lot to do in the next decade or so until Ariel finally flies. Hopefully neither swimming, nor diving into fire nor riding on the curled clouds will be involved, but the scientific quality is something of which we can be very confident.
Congratulations to everyone involved in getting this mission selected and best wishes to all those involved in Cardiff and elsewhere!
Follow @telescoperEquinoctial Molehills
Posted in Biographical, Bute Park, The Universe and Stuff with tags astronomy, molehills, moles, Vernal Equinox on March 20, 2018 by telescoperVery busy today, what with a return to lecturing in Cardiff and so on, so I’ve just got time for a quick post to mark the fact that the Vernal Equinox in the Northern Hemisphere took place today, Tuesday 20th March 2018, at 16.15 UTC (which is 16.15 GMT). This means that the Sun has just crossed the celestial equator on its journey Northward. Some people regard this as the first day of spring, which is fair enough as it does correspond fairly well to the end of the Six Nations rugby.
It wasn’t exactly spring weather when I walked into work this morning, as there are still bits of snow around in Bute Park.
More significantly, a huge number of molehills have appeared. Not quite a mole of molehills, but still quite a few. I’m not sure of the reason for all this molar activity. Perhaps moles have special rituals for marking the Vernal Equinox?
Incidentally I was dismayed to see that my Royal Astronomical Society diary gives the time of the 2018 Vernal Equinox as 16.16 GMT while the wikipedia page I linked to above gives 16.15 GMT. I find a discrepancy of this magnitude extremely unnerving. Or am I making a mountain out of a molehill?
Follow @telescoperR.I.P. Stephen Hawking (1942-2018)
Posted in Books, Talks and Reviews, Television, The Universe and Stuff with tags Stephen Hawking on March 14, 2018 by telescoper
I woke today to the sad news of the death, at the age of 76, of theoretical physicist and cosmologist Stephen Hawking. We all knew he had to pass away one day, but having been diagnosed with Motor Neurone Disease and given just a couple of years to live at the age of 22, I think we had all come to regard him as indestructible, so news of his death still came as a shock.
Stephen’s immense contributions to physics, including but not restricted to cosmology, are remarkable in their own right, but made even more remarkable that has done so much after having been stricken by such a debilitating disease when he was only in his twenties. Hawking was undoubtedly a brilliant and inspirational mind, but his courage and physical endurance in the face of difficulties that others might have found unbearable have provided inspiration for many far beyond the field of physics.
To give an example of his scientific work, here is an equation which I think would serve as a memorial to Stephen Hawking as it brings together quantum mechanics, gravity and thermodynamics in giving the entropy of a black hole in terms of its surface area and fundamental constants:
I’ve talked and written quite a lot about Stephen Hawking over the years. In particular I have in the past gone on record, both on television and in print, as being not entirely positive about the `cult’ that surrounds him. I think a number of my colleagues (and some some people at the University of Cambridge) have found things I have said insufficiently reverential or perhaps even disrespectful. This is not the time to go over these things. For the record I’ll just say (yet again) that, while I stand by everything I have said, I do – and always will have – enormous respect for Hawking the physicist, as well as deep admiration for his tenacity and courage.
I may post a longer reflection on Stephen Hawking’s life and work in due course, but for now let me just offer my condolences to his family, friends, and colleagues. He was one of the most celebrated public intellectuals of his day as well as a courageous and determined human being. He is irreplaceable.
Follow @telescoperCosmic Dawn?
Posted in Astrohype, The Universe and Stuff on March 2, 2018 by telescoperI’m still in London hoping to get a train back to Cardiff at some point this morning – as I write they are running, but with a reduced service – so I thought I’d make a quick comment on a big piece of astrophysics news. There’s a paper out in this week’s Nature, the abstract of which is
After stars formed in the early Universe, their ultraviolet light is expected, eventually, to have penetrated the primordial hydrogen gas and altered the excitation state of its 21-centimetre hyperfine line. This alteration would cause the gas to absorb photons from the cosmic microwave background, producing a spectral distortion that should be observable today at radio frequencies of less than 200 megahertz1. Here we report the detection of a flattened absorption profile in the sky-averaged radio spectrum, which is centred at a frequency of 78 megahertz and has a best-fitting full-width at half-maximum of 19 megahertz and an amplitude of 0.5 kelvin. The profile is largely consistent with expectations for the 21-centimetre signal induced by early stars; however, the best-fitting amplitude of the profile is more than a factor of two greater than the largest predictions2. This discrepancy suggests that either the primordial gas was much colder than expected or the background radiation temperature was hotter than expected. Astrophysical phenomena (such as radiation from stars and stellar remnants) are unlikely to account for this discrepancy; of the proposed extensions to the standard model of cosmology and particle physics, only cooling of the gas as a result of interactions between dark matter and baryons seems to explain the observed amplitude3. The low-frequency edge of the observed profile indicates that stars existed and had produced a background of Lyman-α photons by 180 million years after the Big Bang. The high-frequency edge indicates that the gas was heated to above the radiation temperature less than 100 million years later.
The key plot from the paper is this:
I’ve read the paper and, as was the case with the BICEP2 announcement a few years ago, I’m not entirely convinced. I think the paper is very good at describing the EDGES experiment, but far less convincing that all necessary foregrounds and systematics have been properly accounted for. There are many artefacts that could mimic the signal shown in the diagram.
If true, the signal is quite a lot larger than amplitude than standard models predict. That doesn’t mean that it must be wrong – I’ve never gone along with the saying `never trust an experimental result until it is confirmed by theory’ – but it’s way too early to claim that it proves that some new exotic physics is involved. The real explanation may be far more mundane.
There’s been a lot of media hype about this result – reminiscent of the BICEP bubble – and, while I agree that if it is true it is an extremely exciting result – I think it’s far too early to be certain of what it really represents. To my mind there’s a significant chance this could be a false cosmic dawn.
I gather the EDGES team is going to release its data publicly. That will be good, as independent checks of the data analysis would be very valuable.
I’m sorry I haven’t got time for a more detailed post on this, but I have to get my stuff together and head for the train. Comments from experts and non-experts are, as usual, most welcome via the comments box.
Follow @telescoperA Guest Paradox
Posted in Cute Problems, The Universe and Stuff with tags electrostatics, Gauss' Theorem, general relativity, Physics on February 9, 2018 by telescoperHere’s a short guest post by my old friend Anton. As usual, please feel free to discuss the paradox through the comments box!
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I thought of a physics paradox the other day and Peter has kindly granted me a guest post here about it, as follows. Consider a homogeneous isotropic closed universe as described by general relativity. Let it contain a uniform density of a single species of electrically charged particle, so that this universe has a net charge. The charged particle density is sufficiently low, however, that the perturbation from the regular uncharged metric is negligible. Since this universe is homogeneous and isotropic the electric field in it is everywhere zero. BUT if I consider a conceptual 3-dimensional sphere, small enough for space-time curvature to be neglected, then it contains a finite amount of electric charge, and therefore by Gauss’ theorem a nonzero electric field points out of it at every point on its surface. This contradicts the zero-field conclusion based on the metric.
Here are three responses (one my own) and my further responses to these, in brackets:
- In a closed universe it is not clear what is the outside and what is the inside of the sphere, so Gauss’ law is not trustworthy (tell this to a local observer!);
- the electric field lines due to the charges inside this (or any) conceptual sphere wrap round the universe an infinite number of times (this doesn’t negate Gauss’ theorem!);
- the curved rest of the Universe actually adds a field that cancels out the field in your sphere (neither does this negate Gauss’ theorem!)
In the Dark 