Cosmology Conundrum

March 26, 2013

Some colleagues have suggested that my posting on Planck Day was overly frivolous, given the huge importance of what Planck has achieved. (Nicely written up by Andrew Jaffe.) Other colleagues have suggested that Planck Day was bad press, as it was such a huge public non-event, with a big fuss about mild parameter adjustment. I find both these things true, leaving a weird sense of tension and excitement. I’d better explain myself.

First, lets be clear about the technical achievement. Planck is an absolute triumph of technology, engineering, management, and organisation. An amazing machine that has worked beautifully. It also represents a stunning scientific achievement. The lamda-CDM model, and its beautifully articulated engine of prediction, is a conceptual and analytic triumph. Of course this triumph belongs not just to the Planck team, but represents the accumulated achievement of many scientists all over the world over a number of years.

Lets just look at that power spectrum fit. It is not just a question of the theoretical curve going vaguely up and down, in more or less the same way as the data. The detailed agreement is gob-smacking – multiple peaks, their positions, their sizes, their widths, their second and third order curvature. Any scientist will look at this and think “no way is this a fluke”. Don’t let doubters trot out that coffee-time stuff about being able to fit anything with enough parameters. Firstly, that old chestnut is largely nonsense, and secondly, the fit quality is way beyond that.

Parfait. Everybody love parfait

And yet – outside the world of the CMB, the CDM paradigm has problems, as we were reminded here at ROE the day after Planck Day, in a nice wee coffee talk by Jorge Penarrubia.The best known problems are that CDM predicts far too many dwarf galaxies, and galaxy profiles that are much cuspier than observed,  but there are other claims, such as the existence of a very unlikely polar structure of dwarfs surrounding the Milky Way,  and of suspicious uniformities in galaxy rotation curves. All these problems may still get patched up by astrophysical fixes to do with feedback, IMF games, etc… but we don’t know yet.

Its common to hear people say that Particle Physics and Cosmology are in a similar situation – a model rather than a theory – a perfect fit but with no explanation. Why do all those parameters have those particular values? It seems so arbitrary. And what are dark matter and dark energy anyway? In this view, even the boringly successful fit is tantalising because it tells us there must be a deeper theory in waiting that will explain the perfect fit.

That may describe particle physics, but it doesn’t describe cosmology. Rather, what we have is perfect but fishy. How can the model be so perfect in some places and so poor in others? Have we missed something simple? It may well be that the astrophysical fixes do the trick, and then cosmology does look indeed like particle physics – successful but unsatisfying. Or it could be that some conceptual change is needed, and a revolution is waiting.

I’d give the revolution 2:1 against. But thats good enough odds that your eyes are glued to the table… Mesdames et Messieurs, faites vos jeux.


George, God, and the Grapefruit : Ten Things I Learned

March 21, 2013

Been watching the ESA Planck live press junket George show thingy. Well, everybody and his hairdresser will be writing up their well considered Planck thoughts over the next hour and a half, so I thought I would just summarise some personal lessons. The follow-on press release is here. Apparently there will be more serious stuff about lunchtime, and here in Embra our very own Andrew Liddle will give a seminar this afternoon. Actual science papers on ArXiv tomorrow. Meanwhile, lets keep it light.

The title is ruthlessly stolen from a a Tweet by Professor R.Ivison.

(1) George’s taste in ties continues to improve.

(2) George would give his children away for the Planck map. According to their Mum, they didn’t hear this because they are in school.

(3) The Universe is a bit like a grapefruit. Roundish, mostly very smooth, but with tinnsy-winnsy dimples

(4) When a Twitter hashtag starts trending, it becomes cloggged up with porno-tweets. This is annoying. Well, unless thats what you are after of course. (Am I missing some kind of filter?)

(5) You can’t mention God, unless you mention that you are not mentioning Him. Her. It.

(6) The Universe is EVEN MORE BORING than WMAP told us. Perfect fit to simple inflation.

(7) EXCEPT … for (a) the ten degree dip, and (b) the preferred direction, aka the axis of evil

(8) The axis of evil lines up with the ecliptic plane. Woahh !  But as ex-Edinbuggerer Tom Kitching said to me, that sounds like zodiacal dust… so maybe when that correction is improved the UNIVERSE IS EVEN MORE BORING

(9) The Hubble constant is exactly what Michael Rowan-Robinson told us years ago (67) without the aid of extreme coolants

(10) Talking of which, ESA say they created the coldest place in space, at 0.1K. Now that is definitely quite cute.


Cosmology/Glasgow exam technique

April 15, 2010

Along with a large fraction of the UK astronomical community, I am at the National Astronomy Meeting (NAM2010) in Glasgow. Just imagine a well placed bomb. Could be like the Manchester United Plane Crash all over again.

Two fabulous plenary talks this morning from George Esthathiou and Rosie Wyse. Plack has completed its first survey, but George is not allowed to show us the CMB maps yet. We have to wait until October 2012. (Southwood was in the audience, so he had to behave…) But he did give us a taster – Galactic cold dust map, made by combining Planck and IRAS.  Rosie Wyse showed us all sorts of fascinating stellar population data reflecting the merger history of the Milky Way and other nearby galaxies, as expected in the standard CDM cosmology. But she also showed two worrying things. The thick disc is thought to be made by mergers stirring up an older thin disc. But the stars in the thick disc are really old, suggesting the thick disc of the Milky Way has not been affected by mergers since about redshift two. The second niggle was that the distribution of abundances is consistent with the stellar initial mass function being constant through cosmic history – whereas the galaxy formation simulators desperately want early star formation to be high-mass biased. Hmmm.

Brain spinning, I wandered across the corridor to the Hunterian Museum. This has one of my favourite pieces of Glasgow History – the Blackstone Chair. From mediaeval times until the 19th century, this is how Glasgow students were examined. When you were ready, you sat on a special chair surrounded by Profs. They fired questions at you for twenty minutes, with the sand running out just behind your head. Then some flunky stamped a pole on the ground and you were done.

We gotta bring this back.


Herschel-Planck countdown

May 13, 2009

I am going to miss a party at ROE. John Davies  sent round an email reminding everyone that Planck and Herschel are ready for launch. There will be nibbles while everyone gawks at the live webcast projected onto a screen in the canteen.  I am really sorry to miss this.

You can follow progress at the Planck-Herschel web site, and also at Andrew Jaffe’s blog. The lucky swine is actually there. There are mission-blogs and twitters and all that now-usual stuff. Andrew Jaffe gives the links.

If you want to set your watches, launch is expected 14:12 UK time (BST) on Thursday. Unfortunately this is six am California time…

If you are looking for quick sexy results, look for Herschel rather than Planck.  Planck takes three months to get to L2, then scans for 14 months, then analyses stuff for another year.. there will be not a peep until summer 2011. Herschel however is a regular observatory so stuff will get out much more quickly.