Saturday, June 1, 2013

Cosmological perturbations post-Planck (conference)

Helsinki, as it looked when the Planck data was released, less than three months ago. (Image credit: Samuel Flender's facbook photos)
Hello people reading this (present and distant future). Next week, we're hosting a conference here in Helsinki. On balance, I enjoyed covering the last conference I attended (it was demanding, but rewarding). So, I'll cover this one too. This means, each day I'll try to write a summary of what I found interesting during the day's talks.

The last conference was very observationally based. It was hosted by ESA and was the first scientific conference after ESA released data (measured by the Planck satellite) on the temperature fluctuations in the cosmic microwave background. The conference next week will be quite different. Next week, we'll mostly be theorists. Of course, there really isn't a cold, hard, dividing line between a "theorist" and an "observer", but nonetheless, this conference will be much more focussed on what the measurements from Planck (and other past and future experiments) mean for the universe and its laws. Whereas that last conference also focussed on what it is Planck actually measured (and how they measured it).

This is quite exciting. Planck's release was something of a bombshell, even if this was just because it seemed to strongly confirm the simplest cosmological model that was designed to fit all the previous data. People weren't (aren't?) so content with that model, and were hoping/expecting for something new that might show us where to look to replace it. However, even if theorists aren't, it seems that Planck is content with the model.

The theoretical cosmology community has now had three months, a quarter of a year, to digest these results. So this conference will be interesting, even just at the very least to see how the community is dealing with the shell-shock from March. However, it will be more interesting to see what models look good, which don't, and where people have adjusted their attentions from and to in this three month period. Should we still be interested in exotic particles potentially being present in the early universe? What about "monopoles" and "domain walls"? What inflationary models are still appealing and which are on their way out? Why is everyone suddenly talking about primordial magnetic fields? If the universe is a little asymmetric, what caused the asymmetry?

That's the sort of thing to be looking out for next week!

Take a look at the programme for the conference. Whether you are a member of the general public or another cosmologist, if there is anything you see that you are interested in let me know and I'll make sure to pay particular attention to that talk and summarise it here afterwards. Absent from reader's suggestions I will write about the things I generally find interesting, anything that might have some sort of human interest value and things that get a lot of discussion (either during the talk, or afterwards). The more you interact (whether you are an expert or a member of the public), the closer to what you find interesting my blogging will be.

Familiar faces

Helsinki, as it looks today. This year, winter in Finland went exceptionally late, and summer came relatively early. Spring did occur, for about fifteen minutes, sometime in early May. (Image credit, Samuel Flender, same source)
There are a number of people attending this conference who should be recognisable to regular readers of the blog:

For those on twitter, here is also a list of all the attendees I know who are on Twitter, who you should follow for cosmology related tweets and conversations (both during the conference, and after):

Active tweeters:

Not so active tweeters:

Real Time World War II (not a cosmologist, but Hitler is about to invade the Soviet Union. If you're on twitter and not following this account, you're really missing out)

Possible highlights
There's really no reason for this image, except to distract you and give your eyes a rest from the text. The Helsinki Institute of  Physics is one of the conference hosts.

One consequence of this being the first theory conference I've attended after the Planck release is that I actually don't know for certain what people are getting excited about. I know what I've been excited about and what others here in Helsinki and those whom I've been in email/skype contact with recently are excited about. But, the whole reason for having conferences like this is to share ideas and discover what everyone else in the community is getting excited about. So, stay tuned and we'll find out soon enough.

Having said that, I've had a look over the programme and some possible highlights are the following:

  • The CMB asymmetry. The "anomalies" in the WMAP/Planck data are polarising among the community. However, out of all of the anomalies, the apparent difference in the amplitude of fluctuations in the CMB along opposite directions in the sky seems like one of the more statistically significant ones. It is probably something real (i.e. not just a statistical fluke). The question is whether that something real is just residual foreground contamination in Planck's map of the CMB, or something more exotic. David Lyth will be talking about this on day one.
  • Small-scale perturbations. One of the sobering realisations every cosmologist has at some point, early in their career, is that all our measurements of the CMB and even of the large scale structure of the universe (i.e. the clustering of galaxies, the abundance of galaxy clusters, etc) constrains a very small range (of distance scales) of the perturbations in the early universe. Attempting to constrain the (much, much, wider) range of smaller scales is difficult because they've been so thoroughly messed up by gravity and all the other forces in the universe. Still, if we could measure/determine them, that would be wonderfully useful to learn about the early universe. Kazunori Kohri and Chris Byrnes will be speaking on aspects relating to this.
  • Magnetogenesis. This is a topic I don't know much about, but I've started to take a casual interest. The ordinary expectation is that inflation (the period early in the universe when the universe expanded exponentially and all fluctuations, exotic particles, curvature, etc, got diluted away) would leave the universe mostly absent of magnetic fields. Over time, the movement of charged particles would generate magnetic fields and we would then expect galaxies in the late-universe to have more magnetic fields than those in the earlier universe. From what I understand, there seems to be a much greater flux of magnetic fields in the early universe than expected. This is curious. Martin Sloth and Karim Malik will be speaking on topics relating to these magnetic fields, and their generation (i.e. "magnetogenesis").
  • The first day in general. On the first day (Tuesday), many of the talks have a title that looks something like "Some exotic model of early universe physics after Planck". If you've been wondering what the implications of Planck's measurements are for one of these exotic models, hopefully I can soon tell you!
It's only fair to have the logos of both hosts. This image is also mostly pointless. I will give a free glass of sparkling wine to the first person to guess correctly what the image in this logo is meant to represent.

Experts on...

Looking through the participant list I see that there are a few topics/fields which will have a high concentration of experts present next week. I'll list the ones I've noticed here. If you are interested in any of these topics, then ask me a question (in the comment field, via email, or via twitter) and I'll pass on the question and return with an answer. If you ask enough questions, I might even post a pseudo-interview with one of the experts. Obviously, I'm aiming this request at semi-knowledgeable members of the public, but if instead you are another cosmologist, or someone who knows nothing of cosmology, feel free to ask a question also. I will pass on any question asked (even if that question is just "what is a curvaton?").

  • the curvaton
  • reheating at the end of inflation
  • Higgs inflation
  • warm inflation
  • topological defects
  • primordial non-Gaussianity
  • cosmological backreaction


As I wrote at the beginning, if there is anything you want me to cover, or any question you wish to ask, let me know. Read the programme, and write a suggestion or question in the comments (or via email, or via twitter). If you want to engage with conference attendees directly, follow those of us who are on Twitter. You can ask us questions and we'll try to discuss/respond. Twitter is great for that. Otherwise, I will be covering the stuff I find interesting, the stuff that has a good human interest story behind it and the stuff that gets lots of discussion during the conference (due to interest or controversy).

Interacting with me here while I do this is good (even if you're another conference attendee, or TToD blogger). It helps me understand what I should be covering. It shows me what our readers find interesting so that I can cover that more in the future. "Live-blogging" an event like this is demanding, so if you do interact it makes it feel much more worthwhile for me. If you are a conference attendee, or other expert, feel free to read the comments and help answer people's questions. Also, please do clarify the things that I write if they are wrong or misleading. This is my favourite type of comment. If I write something wrong here it means I have a misconception. I don't want to have misconceptions.

Finally, if you do enjoy these mid-conference posts, then even just writing a comment saying "thanks dude, keep it up" is remarkably helpful in keeping up my posting enthusiasm during the week. And, of course, if you really enjoy these mid-conference posts, feel free to share them and let people know I will be writing them...

See you on Tuesday!

In the meantime, I'll leave you with the following... it's by far my favourite talk from the recent TedxCERN event. It is by Becky Parker, a living legend and a high-school physics teacher in England. She spoke last at the event and went way over-time. That didn't matter because her talk was awesome, infectious, and fascinating. I wish she'd gone more over-time. An example of how awesome her talk is, she spends some of it talking about her school's space-programme (I mean that literally... her school has an actual, active, space-programme). I know the talk is long, so don't commit to watching all of it, just watch the first 2-3 minutes, they're good enough. If you find it boring, you've only wasted two minutes. If Becky's enthusiasm overcomes you, you're welcome; share the video with your friends.

Twitter: @just_shaun


  1. I am looking forward to your conference coverage and thank you for soliciting questions.
    While this is all very much over the head of this casual observer I would be interested to learn how any of this data plays into Brane Theory and perhaps how proponents of the same view these developments.
    At any rate, thank you for bringing us Becky's enthusiastic TedxCERN offering - She is quite a motivational visionary.
    Best wishes for a productive conference!

    1. Hi Masodo, thanks for the comment and question.

      Do you mind if I ask what exactly you mean by "Brane Theory"? In some conversations "brane theory" would be almost synonymous with string theory, but it could also mean some other models potentially unrelated to string theory where we live on branes.

      I'd rather not answer a different question to what you're actually wondering about, so I thought it important to clarify.

      Thanks for the wishes! It's almost too hot here (>27 celsisu, in Helsinki!), but otherwise the conference is going well so far.

    2. Fair enough...
      To me "Brane Theory" in this context suggest the "Big Splat" as opposed to the "Big Bang/Inflation" cosmological model of astrophysicists.
      Sorry for the late reply. Thanks for asking...

    3. I see. I might get back to you on this then in more detail. I would argue that the consequences for a "Big Splat" type theory from Planck's data is similar to that for the curvaton (see my later posts). The new evidence doesn't favour it, but this doesn't rule it out.

      The theory itself does have conceptual problems, these problems are (to me) more problematic than inflation's problems. Therefore, in the absence of evidence favouring one or the other, inflation seems the more likely.

      The proponents of the "Big Splat" theory have written papers recently claiming that Planck strongly favours their models; however nobody else in the cosmology community agrees with their arguments. I can try to elaborate more on this if you want.

    4. Glad to get your perspective Shaun.

      I was curious to know if this theory was even bandied-about at the conference and if the new data would have any impact on it's acceptance or rejection within the community of cosmologists.

      I appreciate your comment regarding the conceptual problems of the "Big Splat" (while at the same time pointing out that inflation is not without problems of its own.)

      Knowing that proponents of "Big Splat" (can we call this "BS" for short?) have written papers in light of Planck I will seek out their finding to see what they are claiming/thinking. I will keep in mind your observation that they are not "converting souls" with their arguments.
      Thanks a lot!

  2. Look forward you to get your opinion on David Lyths talk. I was a bit stunned how he listed the asymmetry as being detected, and put it on a par with the COBE detection of perturbations. Does he really believe its detected and real in the sense of cosmological? May well ask him myself

    1. Just about to start writing some thoughts now... I was a bit surprised too that he listed it as "detected"... though if it genuinely is detected I would put it on a par with the COBE detection (assuming it has a non-foreground-related explanation, of course).

      However, my feeling is that his comparison to COBE's detection of the perturbations in his introduction was mostly just salesmanship.

      Having said that, one of the things I'm going to mention is the small-scale-asymmetry, which Lyth didn't go into, but to me seems to be something of an elephant in the room - Planck didn't supply a statistical significance, but it looks extremely large. I'm confused that a bigger deal isn't being made of it? I wonder whether I'm missing something...


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