The human machine: finely-tuned sensors

The previous post in this series can be found here.

All good machines need sensors, and we are no different. Everyone is familiar with the five classic senses of sight, smell, touch, taste, and hearing, but we often forget just how amazingly finely tuned these senses are, and many people have little appreciation of just how complex the biology behind each sense is. In this week's post, I hope to give you an understanding of how one of our senses, smell, functions and how, in light of recent evidence, is far more sensitive than we previously thought.

Microscopic sensors

The olfactory system is an extremely complex one, but it is built up from fairly simple base units. The sense of smell is of course located in the nose, but more specifically it is a patch of tissue approximately 3 square centimetres in size at the roof of the nasal cavity that is responsible for all of the olfactory ability in humans. This is known as the olfactory epithelium and contains a range of cell types, the most important of which is the olfactory receptor neuron. There are roughly 40 million of these cells packed into this tiny space and their job is to bind odorant molecules and trigger neuronal signals up to the brain to let it know which odorants they've detected. They achieve this using a subset of a huge family of receptors that I've written about before, the G protein-coupled receptors (GPCRs). These receptors are proteins that sit in the membranes of cells and recognise various ligands (i.e. molecules for which they have a specific affinity) and relay that information into the cell. There are over 800 GPCRs in the human genome and they participate in a broad range of processes, from neurotransmission to inflammation, but the king of the GPCRs has to be the olfactory family, which make up over 50% of all the GPCRs in our genome.

Preliminary: Cosmological impacts of BICEP2 + Planck

If anybody is interested, I'm currently drip-tweeting some of the constraints one can obtain from considering Planck and BICEP2 data together. BICEP2 did do a bit of this in their paper, but they only considered specific scenarios. They were also often a bit coy about the implications of the combined analysis. I'll try not to be ;-).

The results should only be seen as indicative, these aren't published, and never will be in this form (maybe they could be cited if used in a paper though!). They were provided to me by Sussex Uni's resident obtaining-cosmology-from-the-CMB expert Antony Lewis, after a hurried Tuesday adding the BICEP2 data to the Planck cosmology pipeline (i.e. CosmoMC) and may contain mistakes.

Antony has himself also made some of these results public at the Cosmo Coffee website.

Questions here, or on Twitter are most welcome. If you want to see specific cosmologies, I'll do my best to show them (if I have them), or ask Antony very nicely to provide them (no guarantees, of course).

You can find my Twitter account here: @just_shaun. Feel free to share!

Being a foreigner in Finland (Intro)

The major goal of this blog has always been to try to make fundamental research accessible to interested non-specialists.

Another worthwhile thing to do, from the "Trenches of Discovery", is to describe what life is like in those trenches.

One of the most notable aspects of the postdoctoral research lifestyle is that you get to spend 2-3 years living in a series of places you might not otherwise have chosen to live. I've just finished three years living in Helsinki, the capital of Finland. I can say with pretty firm confidence that, prior to landing that job, I had never seriously considered the prospect that I might one day live in Finland. I had also never been there.

I've moved now. This is sad and exciting. I'm now employed by the University of Sussex. I've spent the six weeks between living in Finland and living in Britain, back in New Zealand on a kind of small time-frame sabbatical type thing, visiting Auckland University. I wish I could live in three places at once.

While it is still fresh, I want to write here what life is like (for a foreigner) in Finland.

Nature, culture, day-length, work-day-length, an individual's mental state, whether some of Jesus' achievements can be considered to be miraculous or not, just about everything about life in Finland, is dictated by the seasons. So, I've decided to serialise this thing into four pieces, about life in each season, starting, in the next post, with winter. The rest of this post will be a more general introduction.

What is Finland?

The Finnish coat of arms. The Nordic countries' coats of arms kind of satisfy their stereotypes. Here, the Finnish lion, drunk, and drooling, in a field of summer flowers, has unfortunately stabbed itself in the eye with a rather randomly human fourth limb.

Finland is a pretty remote place (though some others are more remote) and it doesn't try hard to be noticed on the world stage. Unless you approach Finland, it probably won't approach you. Therefore, for many people, the extent of their knowledge about Finland is that it is that cold, dark, place between Russia and Sweden. This is more or less what my knowledge of Finland was in 2009.

Finland is indeed the cold, dark place between Russia and Sweden. This is actually quite a good description of Finland in a historical context as well (on a couple of levels). It is only very recently (1917) that Finland became an independent nation, it previously having been a part of either Russia or Sweden, depending on the year. The national identity is, thus, very new compared to most of the rest of Europe. The Finnish language is, also, not a part of the Indo-European language family and as such has no close relative in all of Europe, except Estonian (a very close relative) and Hungarian (only recognisably related if you're a linguist). It's like a small pocket of something else, kind of European, but a little bit different, sitting up in the corner there on the map. Of course, people are people wherever they are, so the individual people of Finland are themselves no different to individual people in France, Fiji or the Falkland Islands, but the collective culture can differ.

Finland is very far North. Helsinki, the capital, despite being on the south coast of Finland, is still further north than the tip of mainland Britain. For those elsewhere than Europe, Finland has a similar latitude to Alaska, which is further north than all other U.S. states and most of the places that Canadian people live. For people from the better hemisphere, no permanent settlements exist as far south as Finland is north. Some bits of Finland are as far north as some bits of Antactica are south. This means that the longest nights in Helsinki are long (about 21 hours or so) and the longest day is even longer (about two months or so). I'll try to let that sink in later. The summer is nice and warm, without (normally) getting uncomfortably hot. And the winter is cold, though no colder in its extremes than a city in the U.S midwest. It's hard to express how much this significant difference in season affects everything in Finland, but hopefully I can get a bit of it across in the next few posts.

Finland is quite big (bigger than Britain and New Zealand, for example), but relatively unpopulated (just 5 million people in the whole country). This means there is a lot of space. Finland is also the nation that has the greatest proportion of its surface covered by water. This means that a huge chunk of Finland is lake, with most of the rest being forest. This sounds a bit like pointless trivia, but this large quantity of open space, and preponderance of lake and forest does have a strong influence on culture and frame of mind. There are no mountains, although I wouldn't quite compare Finland to Denmark or The Netherlands; there definitely are hills.

Finally, despite being somewhat remote geographically, and not a particularly boisterous nation, modern Finland is far from remote from the rest of the world, culturally. I didn't learn to speak Finnish. I found by far that the most difficult part about trying to learn Finnish was not the language itself, but the fact that almost every single Finn speaks English fluently. I used to joke that the second most spoken language in Finland is Finnish. It didn't really go down that well.

What's to come...

In Finland, when someone is awarded a doctorate, they customarily buy a top-hat and a sword. That is a real sword. Hopefully  Finnish PhD graduates do a little better than that lion.

Experiencing Finland needs to be done (at least) twice for each season. You can appreciate moments more when you know what has lead to that moment and what that moment is leading to. I've found this particularly true for autumn, typically the most bittersweet of seasons anywhere. A Finnish autumn, in the moment, is delightful. There is a charge in the air, that, if you arrive for the first time in autumn, you notice right away. I didn't understand its origin the first time, but I came to associate it with an atmosphere left over from the vibrancy of a Finnish summer. And, the true poignancy of a Finnish autumn can only be experienced when you fully understood what the beginning of winter is like in Finland.

The darkness brought by the beginning of winter in Finland is oppressive. There is no point in hiding that. The second half of winter in Finland is wonderful, and easily one of my favourite things I've experienced, anywhere. But the beginning of winter can only be described as profoundly oppressive. This isn't necessarily an entirely bad thing. Witnessing anything extreme adds a sense of thrill and perspective. A Finnish winter definitely aids in quiet reflection. But it is only thrilling because it is extreme. Once the darkness breaks, however, winter turns into an almost literal wonderland, at least for a kiwi. You can walk on the sea. You can commute to work on skis (and some colleagues did). In one Finnish winter you see snow take thousands of forms and... apologies for geeking out... through these forms mimic many different kinds of rock, be they sedimentary, volcanic, granite, sand, or otherwise.

"Spring", in Finland, doesn't exist. Or, at least, it does, but what the rest of the world calls spring, happens for about fifteen minutes, at around 4pm, sometime late in May. Instead of spring, there is a long, ordinary length season, that would be more appropriately labelled "the thaw". This season is bleak and barren. Whatever got buried, under the snow, at the beginning of winter, be it leaves, grass, dog poo, bikes, cars, or even people, will emerge five months later, in April. The sterility of the cold and the snow passes, but what it leaves behind is the dead husk of the previous summer. None of any part of nature (plant, animal or human) will believe winter is over until it can be absolutely sure, so the city sits and it waits, continuing to wait long after the last snow has melted, and the tension builds.

Until summer arrives explosively. I'm only a little bit joking; you can see the grass grow in Finland in June if you sit and watch it. I've never been anywhere that feels more vibrant and full of life than Finland in the summer. August, in Helsinki, is my favourite thing in the world. I spent a significant chunk of each of my three Finnish Augusts wishing I'd had the chance to experience a Finnish August as a barefoot, lakeside, tree-climbing, berry-picking, lake-swimming, night-time book reading, eight year old. As it stands, I just got to be a sandal-wearing, seaside, tree-appreciating, berry-eating, sea-swimming, night-time book reading, 28 year old, which is still pretty good.

And then autumnn comes again. Nature, and the rest of Finland, prepares for rest, and the intensity of the summer gradually dissipates into winter.

[More in later posts...]

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Cosmological perturbations post-Planck - wrap up

Helsinki at midnight. OK, that's not Helsinki, and the photo wasn't taken at midnight. But it is in Finland (Kemiö) and was taken after 11:30pm. Image credit either Chris Byrnes or Michaela D'Onofrio, I'm not sure, although because I got it off facebook, I guess it belongs to Mark Zuckerberg now.

I'm very sorry. As I wrote last week, we just hosted a conference here in Helsinki. I wanted to cover it as the conference happened and I just didn't have the combination of time and mental energy to do so. I won't be covering it in any detail retrospectively either because I need to get on with research. Nevertheless, this blog is slightly more than a hobby for me, it is also slightly ideological, so I will try to work out how to do it all better next time and try again then (this will be the annual theoretical cosmology conference "COSMO" in early September).

Here's a summary of some of the more interesting aspects that I'll quickly write up, starting with some closure concerning the topic I was halfway through in my last post...

David Lyth, the curvaton and the power asymmetry

David Lyth receiving the Hoyle Medal. David's the one in the photo who doesn't already have two medals. From this photo it seems that the guy on the left is graciously donating one of his many medals to David. I got this image from Lancaster University.

Where I left my last post I was describing David Lyth's talk about explaining the possible asymmetry in the amplitude of fluctuations on the sky (as seen through the temperature of the CMB). It's a small effect, the sky is almost symmetric; but it could be a real effect, the sky might be slightly asymmetric.

The possible asymmetry was seen before Planck and one candidate explanation involves quite large super-horizon fluctuations in some of the properties of the universe. "Super-horizon" here means fluctuations whose characteristic scale is bigger than the currently observable universe, i.e they are outside of our observable horizon. Such a fluctuation would be seen by us, within the observable universe as a smooth gradient in the fluctuating observable. Put simply, the idea is to have a smooth gradient in the amplitude of the measured temperature anisotropies. This would quite naturally result in a bigger amplitude in one direction, than another.

It seems that simple inflation can't achieve this without making the fluctuations in the universe significantly non-Gaussian. However, the curvaton can do it (according to David and a paper he is working on). Quite nicely, there is a relationship that David discussed that occurs between the amplitude of the asymmetry and the amount of deviation from a Gaussian distribution one would expect in both an inflation model and a curvaton model. For inflation, the deviation is too big, but for the curvaton it is small but not insignificant. This is nice because, according to David, if this asymmetry is real and the curvaton is responsible for it, then the fluctuations will be measurably non-Gaussian.

This means we can either rule this mechanism out as the cause of the apparent asymmetry, or even better, get evidence supporting it and thus supporting both the curvaton model and the real-ness of the asymmetry. So, watch this space...

CPPP II

This is a continuation of posts about the Cosmological Perturbations post-Planck conference being held in Helsinki this week. You can see my introduction post here and my first post from the conference here. If you're a member of the general public and want to understand more, please ask. If you're a cosmologist and want to add anything to what I've written, please add a comment.

The Curvaton

Yesterday I tried to introduce what the curvaton is. We had a few talks yesterday that related to this particular framework for generating the initial perturbations in the density of the universe (the curvaton is named the "curvaton" because, in this framework it is responsible for perturbations in the curvature of space-time). Prior to the Planck release, the curvaton had become quite a popular model because it would be capable of producing a distribution of density perturbations that was almost, but not quite Gaussian. This is quite a technical sounding term, non-Gaussian. To hopefully simplify it a little, I'll say that a Gaussian distribution is the familiar bell-shaped curve of a normal distribution. There is no a priori reason to expect that the distribution of the primordial density perturbations has to be Gaussian, but in many aspects of physics (and statistics in general) a Gaussian distribution does turn out to be the default.

However, even before Planck, we knew that the distribution of primordial density perturbations was close to Gaussian. Planck was going to be capable of measuring this distribution even more accurately and thus would be sensitive to even more subtle deviations from a Gaussian distribution. Ordinary inflation predicts a deviation from a perfect Gaussian distribution that would have been too small to detect with Planck. And, the WMAP satellite's measurements of the CMB provided a small amount of evidence that the perturbations did deviate from being Gaussian. This would have been fascinating to discover, and if WMAP's best-fit distribution had been true, Planck would have detected it beyond "all reasonable doubt".

Unfortunately, as we all know now, Planck found that WMAP's evidence was (probably) a statistical fluke (they do happen). So where, does that leave the curvaton?

David Wands gave a talk addressing precisely this question. I suppose the spirit of this talk (and a few others so far) could be summed up by one sentence on one of David's slides: "absence of evidence is not evidence of absence". This sounds like a cop-out, and of course to a certain degree it is. I'm certain David would have preferred to have been giving his talk in the context of a definitive detection of a slightly non-Gaussian distribution of density perturbations. He could tell us which specific curvaton models are favoured, which are ruled out, what needs done to tell the curvaton apart from other mechanisms that can generate non-Gaussianity, etc. On the other hand, the quoted sentence is also true. While the curvaton could generate detectably non-Gaussian perturbations, it could also generate perturbations that Planck wouldn't have distinguished from Gaussian ones.

However, the situation now is that there is no (strong) observational evidence that prefers a curvaton type mechanism to simple inflation. It is customary in this sort of situation to appeal to Occam's Razor and say that, in the absence of evidence that distinguishes between them, the simpler model should be preferred. In the case of the curvaton, I think this is probably going to be the community's consensus, for now (though if you're in the community and you disagree, speak up!).

The hemispherical power asymmetry

Having said that, David Lyth spoke yesterday about one of the infamous WMAP anomalies that Planck confirmed. David's choice of anomaly was the "hemispherical power asymmetry". This anomaly comes from the fact that the amplitude of the fluctuations in the temperature of the CMB along one particular line of sight seems to be systematically slightly larger than the amplitude in the opposite direction. I say "systematically" because this larger amplitude seems to persist when you average the CMB over a range of angular scales. Obviously, for any single angular scale there will be a direction of maximum asymmetry, but it wouldn't be expected that this direction of maximum asymmetry would be the same for other angular scales. The anomaly is then a combination of the fact the magnitude of this asymmetry is unlikely in the standard cosmology and the fact that all angular scales seem to have the same maximal direction of asymmetry.

I want to pause for just a moment to stress something for the people outside of the cosmology community who like to dwell on anomalies like this to claim that cosmology needs to be over-turned. This asymmetry is small (of the order of a few percent). The thing is though that Planck (and WMAP before it) has measured the CMB so incredibly accurately that even very small effects can now be noticed with quite strong statistical significance. Therefore, even if it turns out that this hemispherical asymmetry is more than a statistical fluke, this doesn't mean that the universe is very asymmetric. The universe would be almost symmetric, with a small perturbation away from perfect symmetry. It is certainly conceivably possible that some other, very different, model, will replace the current model (many cosmologists desperately hope for this); however whatever this model is it will still describe an almost perfectly symmetric universe, because that's not a theoretical prejudice, that's observed fact!

Back to David Lyth's talk. David started by making a somewhat over the top proclamation (mentioned in a comment in an earlier post about the conference) that the detection of this asymmetry was as important as the detection of the fluctuations in the CMB themselves (by COBE). I would probably back David up that if the asymmetry is not a statistical fluke and is primordial in origin, that it does rank as highly in importance; however, it is not unlikely enough to rule out the possibility that it is a fluke, yet. However, that wasn't the main point of David's talk. He's a theorist so he wanted to explain where the asymmetry might have come from (and in the process try to make a prediction for how to check whether this explanation is true).

Here, fans of the curvaton might have had their interest piqued, because David's explanation needs the curvaton to work. The method he described was originally proposed by Adrienne Erickcek, Mark Kamionkowski and Sean Carroll (EKC). Thankfully, Sean is also a blogger and has written a blogpost about this method. You should check it out.

I will try to give my own description later, but David did have a clear consistency relationship that would be satisfied if the curvaton and EKC method was responsible for the asymmetry...

The final post of the conference now appears here...

Twitter: @just_shaun

Cosmological perturbations post Planck (CPPP) I

This week Helsinki is hosting a conference on the theoretical implications of the recent results from the Planck satellite. The official theme of the conference is cosmological perturbations post Planck. This is alluding to the fact that on large distance scales and at early times, the universe is very homogeneous (it is almost the same everywhere) but has small perturbations in things like its temperature and its density. Planck measures the temperature of the cosmic microwave background (CMB) today, which is an almost direct measurement of the density of the universe soon after the big-bang. This is because the CMB that came from the more dense bits of the universe lost a bit of energy climbing away from that little bit of extra matter and vice versa, the CMB gained energy falling out of less dense regions. Therefore, Planck has made an accurate measurement of the perturbations of the density of the early universe.

But what, are (some of) the implications of this measurement..? Hopefully this conference will elucidate that a little.

I'm going to do my best to describe what is said as the conference proceeds...

Planck's results

The conference started this morning with Helsinki's Mr Planck, Hannu Kurki-Suonio giving an overview of specifically what Planck found in its measurements. If you want a more detailed summary of this you can read some of my posts from when the data was released. The essence is, however, that the standard cosmological model, which had been settled on by most of the community as the simplest model that fits all the pre-Planck data works very, very well in a post-Planck world. There are a number of things about this model that are uncomfortable from a theoretical perspective, but it fits the data we measure extremely well.

But, there are some anomalies (which Hannu ran out of time to cover), which means there are some aspects of the data that aren't predicted by this simplest cosmological model. The anomalies are anomalies because they aren't overwhelmingly statistically significant. This simplest cosmological model only predicts the statistical properties of the perturbations in the universe and all of these anomalies are technically possible, they're just somewhat unlikely. They also don't have obvious explanations from well-motivated new physical effects. They could be statistical flukes. If you have a big enough set of data and look at it in enough different ways you will find anomalies, that's just what noise is. There are two questions that need asked when considering these anomalies:

• Are there actually more anomalies than we would expect?
• For each anomaly, is there a well-motivated model that can generate the effect seen without changing all of the many other things that aren't anomalous (either by completely replacing this simplest cosmological model, or by tweaking it in some way)?

The first question is almost impossible to answer. There are too many ways of looking at a data set this big and it's just too hard to quantify all the ways in which is isn't anomalous. This leaves us with just the second question. The reason why these anomalies are called anomalies is that we weren't expecting things like this and the reason for that is that none of the things we thought were well-motivated deviations from the simplest cosmological model predicted these things.

That's the playing field at the beginning of the conference.

The Curvaton

Many of today's talks were on the topic of the curvaton.

It's going to be hard for me to describe to you what the curvaton is given that I haven't ever properly told you what the inflaton is, but I'll give you a quick whirlwind introduction of both. The inflaton is the field that drove something called inflation. Inflation is a (hypothetical) period early in the history of the observable universe when the universe's expansion accelerated. This period is thought to have happened because it would have smoothed out any pre-exisiting inhomogeneities in the universe (in its density, in the curvature of space-time, in the number density of exotic types of matter, etc). There are issues with this because inflation needs the universe to be somewhat homogeneous even to get started, but despite that inflation still definitely leaves the universe more homogeneous than it found it, so at the very least it helps.

But, the thing that is most interesting about this potential inflationary period is that it would also seed very small perturbations in the otherwise homogeneous universe it left behind. This doesn't sound like much of a gain. Without inflation the problem was that there might be too much inhomogeneity, why should we celebrate this small amount of inhomogeneity inflation leaves behind? The answer to that is that, for a given inflationary model we can actually predict the statistical distributions of these post-inflation perturbations. This gives us something to measure and then compare to theory. In other words, we can gain evidence for or against inflation through observation. There may have been inhomogeneities around in the universe before inflation but we have (almost) no way of predicting them. Inflation lets us make predictions and test them.

So, what is the curvaton in all of this? Well, in the simplest models of inflation there is only one thing other than space-time that is around during inflation. This is the inflaton, the field driving this accelerated expansion. In a curvaton model, there is still an inflaton driving this expansion, but there is also as least one other thing around, the curvaton. And, in these models, it is the curvaton that produces the perturbations that we observe today. The inflaton still produces perturbations, but they decay over-time and the curvaton's don't (as quickly).

Why is this interesting? Why should one study a curvaton model?

That's a very good question. The first, not-quite-completely-joking answer I can give is because you can. It is a possible reality for the universe. This is what theoretical physics is about, thinking about what is possible and exploring the observational consequences if the possible were real. So, from that perspective, why just assume that, if inflation occurred, that a curvaton field wouldn't be present? The counter to this perspective is that it adds complexity to inflationary models.

 Unfortunately, it is now past midnight. More to come tomorrow...

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.

The universe as seen by Planck - Days Three and Four II

[Continued from yesterday...]

In the first piece of this post I covered the implications of Planck for the paradigm of inflation. This piece covers the rest.

The anomalies

This is what the CMB would look like in an unphysical Bianchi universe. A worry for our physicality is that this unphysical Bianchi universe seems to fit the data better than a physical \(\Lambda\)CDM universe.

It would be impossible to provide an overview of this conference without mentioning the features and anomalies that Planck has chosen to draw significant attention to. I have a bunch of notes that I've written down that I might one day turn into a new blog post, but I'm not going to delve into them now.

These features and anomalies are clearly going to become a contentious issue in cosmology for the next few years. In fact, the words believer, atheist and agnostic were even being used by speakers during talks regarding whether the anomalies are real or statistical effects. Each time someone declared themselves an anomaly atheist or anomaly agnostic, someone in the audience inevitably spoke up and passionately defended the significance of the questioned anomaly.

The list of potential anomalies is long. There is the cold spot, the anomalously low quadrupole, the hemispherical asymmetry, the statistical difference between the odd and even multipoles at large scales, there is the dipole modulation, there is the general lack of power at large scales, there is the feature in the temperature power spectrum at small scales, the fact that the universe seems to be in an unphysical Bianchi model and there is the "axis of evil" (to name a few).

Pick your side. Atheist, believer or agnostic. The great anomaly wars of cosmology are about to begin (another inevitable consequence of an observational, rather than experimental science, I suppose - i.e. there is only a finite quantity of information available to us, so for some observables we can't just do the experiment again to check who is right).

What should we make of Planck vs SPT and Planck vs the local universe?

The universe as seen by Planck - Days Three and Four I

Sorry for the delay on this. I was pretty tired on Friday, travelling home on Saturday and doing physics on Sunday. I figured it would be better to write something with a little more care today.

Those who were following last week will know that on March 21 ESA finally released some cosmological results from the measurements they were taking with the Planck satellite. And, last week, they had their first scientific conference. I decided to blog about this. I had the initial ambition of one post for each day, but the conference dinner on Thursday beat me and all I got out was a brief teaser post. This post now will be comprised of a summary of what I found interesting on both Thursday and Friday, along with a summary of the whole conference at the end.

I hope you enjoy it (and thanks for the feedback during the week).

Highlights

• What has Planck told us about inflation?
• What should we make of Planck vs SPT and Planck vs the local universe?
• What is next for CMB science?

• Some final thoughts

What has Planck told us about inflation?

Slava Mukhanov. Cosmology can do what it wants, but Mukhanov's  predictions for inflation will remain unchanged. Somehow cosmology always seems to come back to him in the end. Will that last missing piece show up? Will primordial gravitational waves one day be detected? It's starting to look like a "no", but Mukhanov's heard that talk before. Time will tell...

The first talk on Thursday was about inflation, by another one of the scientists who helped found it. This was by Slava Mukhanov, another old-school Russian physicist. Mukhanov was one of the first to realise that inflation wouldn't just cause the universe to expand dramatically and to make it more homogeneous, it would also seed new fluctuations with a very small amplitude. These new, small, fluctuations arise from the stretching (and eventual amplification) of quantum fluctuations in the field driving inflation. This type of realisation was what took inflation from an interesting concept to a testable paradigm.

The universe as seen by Planck - Day Three (two rumours)

The conference dinner here is about to start (has already started), so I don't have time for a proper post. However, there were some very interesting rumours/revelations today so I'll write them down super-quickly. In increasing order of potential interest (note this post might be a bit technical, I'll explain all of this before the end of the weekend):

The feature at l=1700

A senior Planck figure gave a talk today on the features in the Planck angular power spectrum. Much of his talk was devoted to the apparent feature at \(l\simeq 1700\). In the 15 months worth of data that Planck has used to generate the cosmological results shown in their released papers, the statistical significance of this feature (when any feature is looked for) was \(\sim 3\sigma\). This was with a look elsewhere effect that took into account the possibility of the feature occurring at another \(l\) value.

What he let slip was that, when they analyse this same feature with the full temperature data set, the significance of the feature drops to \(\sim 2\sigma\).

Of course, not too much should be read into this because the additional data isn't quite as well understood as that first 15 months; however, its the same telescope looking at the same sky and foregrounds, so there shouldn't be too many complications. Note that this feature is out of the resolution range of Planck's polarisation capabilities, so the new temperature data is the only additional data we will get in the next data release.

Planck's data analysed on the SPT sky

One of the curiosities of the Planck release was that it seems to give cosmological results that are slightly discrepant with what the South Pole Telescope was giving. If Planck disagrees with BAO or supernovae, or galaxy clusters this is all interesting, but potentially the result of Planck and/or one of those other analyses getting it wrong. However, SPT is another CMB experiment, the fact that Planck and SPT are a bit discrepant is very confusing.

Perhaps SPT made a mistake and the CMB they measured is not the correct CMB?

The obvious way to test this is to analyse the Planck data on the same part of the sky that SPT measured. I overheard a conversation between lead figures in Planck, WMAP and SPT and it seems this is exactly what SPT have done (in unpublished work).

The result is striking.

They found a cosmology that agrees with SPT.

If true, this means that it isn't just Planck and SPT that are slightly discrepant, but different regions of Planck's sky.

What this means cosmologically is unsure. I'll speculate a bit tomorrow.

Power asymmetry

There was quite a bit of excitement over a plot that showed power asymmetry in different directions of the sky. I was going to write about it, but upon reflection, the excitement seems confusing. I'll try to explain the excitement and background before the end of the week.

[The final summary is now available here]

The universe as seen by Planck - Day Two

The cosmic microwave background (CMB) is the best probe we've yet found to study the early universe. The CMB's temperature is very nearly uniform. However this temperature does have very small anisotropies that can be used to study sound waves that existed in the primordial universe. The Planck satellite (an ESA funded experiment) has mapped these temperature anisotropies over the entire sky with the best resolution to date. Last month, Planck released its data and it immediately became the new benchmark for the testing of cosmological models and the measurement of cosmological parameters.

This week ESA is hosting the first conference since Planck released its data. The conference is at ESTEC in the Dutch town of Noordwijk. I am attending this conference and will be doing my best to write updates about what was discussed during the week.You can read my introductory post where I give my motivation for doing this, here.

The CMB is not just useful for studying the primordial universe. As soon as the CMB forms, everywhere in the universe, it travels freely, in every direction, at the speed of light. This means that, in every direction, the CMB we measure here on Earth today has travelled to us from a point billions of light years away. In principle, this makes the CMB not just a really good probe of the state of the universe where and when it was emitted, but also of everything it passed on its way to us.

This secondary use for the CMB turns out to be very useful and many of the highlights from Planck relate to the way in which the CMB interacts on its way to us. The existence of matter in the universe affects the CMB gravitationally. This causes the CMB to bend towards regions of over-density and away from regions of under-density. It also causes the CMB's temperature to shift as it falls into and out of over and under-dense regions. This first effect is known as lensing and one of Planck's most impressive results is a map of the locations of matter in the universe through this lensing effect. The second effect is known as the Sachs-Wolfe effect, something I've written about in some detail.

There is a third way that the CMB is significantly affected by the intervening universe. Within clusters of galaxies there is a lot of hot gas. If the CMB passes through a cluster it can scatter off electrons in this hot gas. The effect of this scattering on the CMB is known as the Sunyaev-Zeldovich (SZ) effect. Therefore, we should be able to use the CMB to detect the lines of sight along which the most massive clusters lie.

We can. And Planck has.

The universe as seen by Planck - Day one

 I am currently attending the ESA run conference "The Universe as seen by Planck". I will be trying to write a summary each day of what I found interesting. To read about my motivation for this, please read yesterday's post. Below is the summary of the first day's talks. I apologise if the posts this week are overly technical. I don't have much time for writing these and this is the best I can do given the constraints. As always, if you don't understand, just ask questions in the comments.

Overall summary

Today was mostly about introducing the Planck experiment and its data. This is the first conference ESA has held since the data was released and in fact the first conference about Planck open to non-Planck scientists like myself at all. Therefore today was actually the first chance for the Planck collaboration to be honest about what their telescope has and has not been able to do. As a result, many of the talks that can lead to the most speculation will not come until tomorrow and Thursday. Still, there were some interesting things to come out of today. For example:

• The reasons why no polarisation data from the CMB were used in likelihood analyses this time
• (Not mentioned in a talk, but overheard from reliable sources) The reason no constraints on "\(g_\mathrm{NL}\)" were released this time
• The existence of two "features" in the temperature power spectrum and many "features" in the temperature bispectrum
• A few other curiosities

Here are, in no particular order, the things I found interesting today...

The missing data feature

People who watched the data release conference in March might have been a bit startled by the set of CMB maps that looked like the one below. I was. The particularly startling thing about these maps is the band slightly greyer in colour that persists right in the middle of the image and in the bottom left. The rest of the map looks quite similar to a typical map of the microwave radiation measured on the sky.

The universe as seen by Planck (conference)

The 47th ESLAB symposium. All the cool kids will either be there, or watching it live on the webcast. Are you one of the cool kids?

This week I will be at a scientific conference, organised by ESA. In ESA's words, this conference is "An international conference dedicated to an in-depth look at the initial scientific results from the Planck mission". The conference is taking place in the small Dutch down of Noordwijk. At this conference there will be many people from within the Planck collaboration, who I'm sure will be delighted to finally be able to talk about their work and many people like myself who have spent the last few years eagerly anticipating the Planck collaboration's results.

The conference will have a live webcast here, you should watch some of it.

I will also be blogging during the conference. My goal is to try to write a new post here each day summarising the most interesting talks and discussions from the conference that day.

Why am I doing this?

An absolutely wonderful image showing how the various all sky images of the CMB anisotropies have improved each decade.

This won't be an easy task. The conference goes quite late each day and many topics will be covered, but I want to do this anyway. To understand why, first go watch my new favourite video on the internet. Brady Haran makes science videos and if you've never seen them, you should go check them out. I felt like Brady was taking the words out of my mind when I saw that video. One day the utopia that Brady and I envisage will exist and a Planck conference like this will be besieged by legions of fans. One auditorium will be fill of fans of non-Gaussianity and fans of Gaussianity, on opposite side, cheering their preference on. Another auditorium will be filled with fans of dark radiation, cheering their team on. Yet another will be filled with fans of the cosmological constant shouting their favourite chants at their mortal enemies, the quintessence crowd. But that day is not today.

Highlights from Beijing: COSMO 2012

The obligatory conference photo. The photographer spoke to us in Mandarin. I think what he was trying to say was "more intensity".

Just over a week ago I was at the annual COSMO conference. This year's host was Beijing. I had originally intended to live blog this event, but the Great Wall of China (alternative link) managed to prevent that entirely.

What follows are some reflections on the scientific bits and pieces people presented at the conference that I happened to find interesting. It might be a bit technical, but please ask questions if I use jargon you don't understand. Also, if you're an expert and I write something you want to comment on, please do (especially if something I write is misleading or just plain wrong).

The topics I've chosen below just happen to be what I found memorable. I made no attempt to choose these topics by any sort of theme. I apologise if I've missed anything particularly interesting. Perhaps if you were there and think I missed out something interesting you can either mention it in the comments or write a guest post for us.

Neutrinos and precision cosmology

One of the first images captured by the Dark Energy Survey. The more interesting images it will take will be of very distant galaxies and won't look anywhere near as nice. This one is just for people to put in their blogs.

Jan Hamann gave a talk on the future constraints that cosmology will provide for neutrino physics. I was pleasantly surprised by the power of large scale structure probes, such as Euclid.

We know from particle physics experiments that the difference between the masses of two of the neutrinos is more than 0.06 electron volts. This means that the heaviest neutrino must be heavier than 0.06 electron volts.

The ISW mystery II: Trying to see the invisible

[Note: I'm travelling at the moment and haven't had time to write as substantial a post this time around as I'd hoped. We're all new to this blogging business, so next time I'm travelling for this long I'll plan further ahead and have the post ready in advance, or something. Anyway, enough excuses from me... I'll be back in Helsinki in a few weeks and will hopefully then be able to write something more substantial...]

In my last post I introduced something known as the integrated Sachs-Wolfe (ISW) effect. You'll probably get more out of today's post if you've read that one. However, I've tried to make today's post as self-contained as possible, so don't fret if you're new to the blog or have forgotten things over the last six weeks.

Put most simply, the ISW effect is the very subtle heating and cooling of light as it travels through structures in the universe. In the standard model for the universe's history this ISW effect grows with time and is most significant when dark energy starts to dominate the universe late in its history. The effect occurs because the energy gained or lost by light as it climbs into or falls out of structures becomes smaller with time. Therefore light receives an overall change in energy when it travels through these structures.

Unfortunately, the ISW effect is tiny. It will happen to any light travelling anywhere through the universe, but it is really, really tiny. This means that, for almost every light source in the universe (galaxies, stars, supernovae, etc), we just don't know the initial light source well enough to be able to tell if it has changed by the tiny amount we expect from the ISW effect. But, there is one source for which we have a very clear, very precise prediction. This is the cosmic microwave background, or CMB (note: I introduced the CMB in this post). As regular readers of the blog might be starting to appreciate, the CMB is more or less every cosmologist's favourite data source.

Unfortunately even the CMB has tiny fluctuations in it. These arise because the source of the CMB, a plasma of hydrogen that once permeated the entire universe, was not uniform (I explained the shape of the fluctuations in the CMB in an earlier post). And, most unfortunately, even these tiny fluctuations, fluctuations so small that Nobel prizes were awarded for their detection, are bigger approximately the same size as [Edit: 16/3/2012] the predicted size of the ISW effect. I have to admit that I find this irony amusing. The ISW effect is so small that one of the most significant measurements humanity has ever made is just annoying noise in the quest to detect it.

Alas! So it seems that we can't even see the ISW effect in the CMB?

Not quite...

The ISW mystery I: Introduction

Looks nice Roger, but what are the industrial applications?

Making science a spectator sport

A huge part of the motivation for us starting this blog, if not the main motivation was to present new research as it is being done. In other words, to present the view of new research from the very trenches where the discoveries are made. I still intend (at some point in that mythical, utopian, land called later) to write a more thorough “motivation for the blog” post; however, the main motivation for presenting new research now, rather than waiting for Brian Cox to make a documentary about it, is this: it allows everyone in society to feel involved in scientific research. The hope is that science will then go beyond being just what those guys with beards in white coats do that we, everyone else, don't understand and instead becomes something that society as a whole gets behind and becomes fascinated by and talks about excitedly during their lunch-break.

You might think this is over-ambitious (though possibly not if you're reading this blog). But, meh, I think you are wrong. The public response to scientific discoveries/announcements last year like this and this tells me that people do care and are immensely fascinated by what scientists do. If society is not talking about science at the water-cooler it is because we, the scientists, are not collectively trying hard enough to involve society in science. There are numerous hard working and successful exceptions of course. The fact that they are exceptions is the problem.

Some scientists reading this might wonder why we even want society talking about science at the water-cooler. Mightn't science become corrupted by such base chatter? Think about this again the next time you are applying for some grant money and have to bend over backwards trying to come up with possible industrial applications for your work. Especially when later that evening you could watch a sportsman get paid millions for doing what he or she chooses to do. I doubt Nike have ever asked Roger Federer to come up with potential industrial applications for his backhand. Sportsmen are paid simply because people like watching them play and think they are cool. But people also want to keep track of scientific progress and they definitely also think it is cool. This latent popularity isn't a bad thing and it isn't being utilised enough by science.

In this sense this blog, and others like it, could be described as attempts by scientists to start making science a spectator sport. Hopefully we'll get better with time.

So, with that unnecessarily long introduction out of the way, let me finally (from the perspective of both this post and the blog itself) start telling you about some of my own research...

Snapshots from the trenches: Stockholm clusters workshop

As a part of contributing to this blog, I am going to try to write quick-ish summaries of any papers I co-author and any conferences or workshops I attend. Though, unlike the commitment to a new post every six weeks, I make no promises about how well I'll keep to this particular aim. These posts will inevitably be the most technically demanding of my posts, but also, potentially the most rewarding. They will be demanding because I won't choose to spend a lot of time writing them, but, more importantly, because the physics I will be discussing will be fresh off the press. As a result, it will not be written in a coherent, packaged, easily understood, form.

But, here's the thing, research is never in that form, even for those who are immersed in the field. It is only when we look back on past research with the benefit of time that we can see it in a form that can be packaged in a complete and coherent picture (the galaxy clusters stuff I wrote last week took physicists more than decades to properly understand). By this time it is no longer 'research', but simply 'past results'.

Often scientific knowledge is only popularised for the consumption of those outside of the field once it has reached this final, 'packagable', state. This is great, but the awesome thing about a blog like this (and the many other similar blogs) is that we can also give you a real-time view inside the research trenches. We can discuss what people are working on, thinking about and discovering, right now. It may be more difficult to follow than a coherent look back, but it should be more exciting to follow, and, as other blogs have shown, it is definitely possible to do. You don't have to follow every line of every calculation, to be pointed to a final number, or final figure in a paper and, when given the context, use that to reach the same conclusions as the authors. Yes, even in the actual, raw, unadulterated, not fit for the eyes of the young and innocent, scientific, papers! That's the goal, at least.

It shouldn't end up being too much more difficult than keeping track of various sports teams and players during a season of professional sport.

I think that giving this view from inside the trench is really important. Popularising scientific results in neat packages isn't a bad thing, it is great to help us all understand what is known and what has been achieved. The problem is when it is only the final package that the public ever sees. Then what is hidden from view is how we know the result and what we did to learn it. When it is only ever the final result that is seen it gives a skewed perception of how science proceeds, which I think can be damaging.