Archive for Post-Planck Cosmology

Post-Planck Cosmology: Day 4

Posted in Talks and Reviews, The Universe and Stuff with tags , on October 12, 2017 by telescoper

So here we are at the end of the meeting, after a fourth and final day of wide-ranging cosmology talks. I did the first presentation at 9am. I won’t summarize my own lecture because you can find the slides here:

Here are two pictures of me in action:

me_2

me_1

After that we had, amongst others, invited talks by Subhabrata Majumdar on the eROSITA all-sky X-ray survey and Somak Raychaudhury (Director of IUCAA) on large-scale structures in the local universe, Kandu Subramanian on primordial magnetic fields and Anvar Shukurov on Probabilistic Topology and Morphology (a change to the advertised title). There were also a number of shorter talks of diverse nature mainly on the subject of large-scale structure and galaxy formation.

I have known Kandu Subramanian since I was a student at Sussex and he was a postdoc there. At that time he was working mainly on gravitational lensing. I haven’t seen him for quite a long time and was surprised to see that now his hair has gone completely white. That’s what happens to you if you work on primordial magnetic fields.

The afternoon session overran and I had an appointment for Skype call so I had to leave before the closing remarks, so let me take this opportunity to thank the conference organisers for putting together such an interesting meeting and especially for inviting me back to Pune after all this time. It has been very enjoyable.

Many of the conference guests have already left and some are leaving tomorrow. I am staying in India for a few more days, however. Tomorrow morning I’m going to Mumbai to give a talk at the Tata Institute for Fundamental Research. I have to get up early tomorrow for that trip so I think I’ll take an early night.

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Post-Planck Cosmology: Day 3

Posted in The Universe and Stuff with tags , , , , on October 11, 2017 by telescoper

Before carrying on with my daily updates from this meeting on Post-Planck Cosmology I’ll just remark that this is a great venue: it has all the facilities necessary to keep a group of cosmologists happy…


At the tea break this morning I managed to find a shot that included all four of the statues in the main quadrangle too:

This morning kicked off with Roy Maartens discussing the cosmological potential of the Square Kilometre Array and other future galaxy surveys, one of his main points being the benefit of using multiple tracers to beat down some of the problems with single surveys.  The first phase of this project, SKA1,  will deliver 10 million redshifts with z<0.6. With SKA2 that will go up to 1 billion galaxies out to z<2, but many things can be done without redshifts using intensity mapping. SKA1 is some way off, but the precursor `Meerkat' consisting of 64 × 13.5 metre dishes will be hopefully starting next year in South Africa.

We then had a series of talks about reionization and the formation of the first stars, an epoch usually referred to as `Cosmic Dawn' or `First Light', taking us into lunch.

In the afternoon we had talks loosely grouped around the theme of `classical cosmology' – using geometric or other probes to study the expansion history of the Universe. This session included a talk by Chris Messenger of the LIGO collaboration about the beginnings of gravitational wave cosmology, though as the current generation of detectors is only sensitive to relatively nearby sources for the time being the main effort will be devoted to distance scale measurements, attempting to measure the Hubble constant directly without the need for the traditional distance ladder.

The last part of the day was devoted to a panel discussion, chaired by Francois Bouchet that was interesting and wide-ranging but largely motivated by responses to Paul Steinhardt's talk last night.

Now, no conference dinner to tear me away tonight – but I do have to finish my talk, which is at 9am tomorrow – so that will have to do for now. Toodle-pip!

Post-Planck Cosmology: Day 2

Posted in The Universe and Stuff with tags , , on October 10, 2017 by telescoper

Just finished the last session of the day and it’s only half an hour before the conference dinner begins, so I’ll just do a brief summary.

The weather in Pune continues to be `interesting’:

It’s pouring down at the moment, in fact. The session I chaired started late because we had to postpone the conference photograph because of inclement weather.

Anyway, this morning’s talks were primarily about the difficulties of measuring B-mode polarization in the cosmic microwave background. Carlo Baccigalupi gave a perspective on foregrounds from Planck and Zeeshan Ahmed updated us on Keck/BICEP progress. There are no new results from the latter – we’ll have to wait for data from the extra 220 GHz channel – but Zeeshan also spoke about a proposal for the next generation ground-based experiment, glamorously named CMB-S4 – details of which can be found here.

The afternoon was largely devoted to early universe physics, including inflation. We’re only two days in to the conference but already several speakers have showed this plot (from here), which shows the extent to which current cosmological data disfavours various inflationary models:

Some are disfavoured, but clearly there are still lots of viable models! Too many!

For the final session of the day we were joined by Paul Steinhardt via Skype from the USA. He gave a very cogent and stimulating talk arguing that the prevailing paradigm (i.e. inflation) was about to be overturned. I don’t have time to do a full summary of his contribution, but you can check out a previous post about some of the issues he raised, and here’s a picture of the last slide of his presentation:

Anyway, that will have to do. The conference dinner beckons.

Post-Planck Cosmology: Day 1

Posted in The Universe and Stuff with tags , , , on October 9, 2017 by telescoper

Well, I’m just back to my guest flat from a pleasant birthday party for one of the conference organizers, Tarun Souradeep, is now in the same decade as me! I don’t have time to write about all the talks today so apologies to anyone I don’t mention by name. I also got called away to have tea with an old friend so missed the final session and consequently missed the last session. I can’t do that again tomorrow as I’m chairing the last session tomorrow (including a presentation from Paul Steinhardt via Skype).

Also, I forgot to take my camera to today’s session so here are a couple of pics that I’ve stolen without permission from the Director of IUCAA, Somak Raychaudhury showing Francois Bouchet and Jacques Delabrouille who gave the first two talks.

Here are some brief notes.

Francois Bouchet delivered an expert summary on the state of cosmology up to and including the Planck mission. He started by saying out that before the discovery of the cosmic microwave background, cosmology was a `semi-crackpot subject’ and went on to show how much the field has moved on: there are no longer any semi-crackpots in cosmology. Three particularly interesting points he made on his grand tour were: (i) that the `inflationary prediction’ that the spectral index of primordial density fluctuations is not that n=1 (which was argued for before inflation by Harrison and Zeld’dovich) but n=0.96, and that the difference between these numbers is very significant; (ii) there aren’t enough independent modes in the (2D) CMB to improve current limits on non-Gaussianity by much so we will have to use (3D) galaxy clustering data; and (iii) the apparent `tension’ in measurements of the Hubble constant is not solely a problem with the CMB (he mentioned this paper in particular.

Next up, Jacques Delabrouille spoke about future CMB space missions. Unfortunately none of the three putative missions currently on the table (LiteBIRD, CORE and PIXIE) has been selected for Phase A by the relevant space agencies. Although not officially dead, any of these will need to find international partners to proceed, and none will be launched for at least a decade. The current generation of CMB scientists will therefore probably have to rely on ground-based data for the immediate future. However, he was ambitious in the science goals for future missions: `we want to measure it all!’

We then had a series of talks about various matters, including the resurgence of interest in spectral distortions of the CMB that I blogged about recently.

Anyway, that will do for this evening. I’ll try to post about Day 2 tomorrow, though it is the conference dinner in the evening so I may not be in a fit state!