Archive for March, 2018

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The Weather and the LGBT Physical Sciences Climate Survey.

Posted in Uncategorized on March 3, 2018 by telescoper

I wrote this post on Thursday, after a long and busy day, in a hotel near Paddington station, having long since given up the possibility of returning to Cardiff today owing to the inclement weather conditions. Fortunately I had taken my overnight things and a change of clothes in anticipation of the likelihood of getting stranded.

Unfortunately the hotel WiFi crapped out and it seems it never got posted, so I’ve updated it and here it is now. I was in London for the launch event for the LGBT Physical Sciences Climate survey.

Before going on please let me wish you a belated Dydd Gŵyl Dewi Hapus, as Thursday was St David’s Day!

I rose at 5 o’clock on Thursday morning to get the 6.26 train to London to participate in this event. It was all going well until we reached Swindon (about halfway into the journey) but then we warned that Paddington station was closed and the train would be terminating at Reading. I was a bit surprised by this as there wasn’t really very much snow at all, but it turns out that the snowy conditions had made Paddington too slippery to be safe. That’s no doubt because of the shiny floors added at great expense but very little point when the station was refurbished some years ago. At no point on the journey into London did I see more than half an inch of snow. It’s truly pathetic that such total disruption of this major transport route resulted from such a small amount of snow.

I was advised by the GWR staff at Reading to turn forget about making it to London and instead to get on the train back to Cardiff, as no trains were going into out out of London and snow was heading for Cardiff making it unlikely I would get back this evening even if I did continue on my journey.

Eschewing this advice I found that trains were leaving from Reading to Ealing Broadway, so I got one of those and took the Central Line underground from there into town. I arrived about 11am at the Institute of Physics, about two hours later than planned but I had left early in anticipation of likely delays.

Anyway, the event itself seemed to go quite well. I gave a little introductory talk, followed by four other speakers, and then chaired a panel discussion. Here’s a few pictures:

The participants (from left to right) were: Dr Ashley Spindler, Dr James Claverley, myself, Niamh Kavanagh, and Professor Dave Smith. There then followed a little drinks reception and a group of us subsequently adjourned to a local pub for drinks.

Anyway, the main point is that the survey is now live and can be found here. That link also tells you who’s eligible to complete it.

The survey is open until the end of April so I’ll probably post a few reminders over the next few weeks…

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Back to Snowy Cardiff

Posted in Biographical, Bute Park, Cardiff on March 3, 2018 by telescoper

I made it back to Cardiff yesterday. The train I was on was about half an hour late, but that was understandable. The strange bit was that most of the delay resulted from us running very slowly through the Severn Tunnel. There certainly wasn’t any snow down there!

Cardiff city centre was virtually deserted and none of the roads had been cleared of snow. I’m guessing no buses were running, as I didn’t see any on the way, and there were few cars. Many shops were closed. The M&S in the station was open but had received no deliveries that day, and was just selling what it had from the day before. I bought some groceries, mostly at a reduced price.

It was snowing quite heavily and was very cold when I walked back to my house from the station, so I didn’t take many pictures, but I couldn’t resist this one of the River Taff, frozen over by the Principality Stadium:

This was the view towards Pontcanna Fields from near the cricket ground.

Fortunately I was wearing heavy walking boots, but I’d forgotten what hard work it is to walk through snow!

This morning there’s still a lot of snow around and no sign of any attempt to clear the roads.

I wonder if there’ll be anywhere open to buy a paper?

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Cosmic Dawn?

Posted in Astrohype, The Universe and Stuff on March 2, 2018 by telescoper

I’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.

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