The Smoking Gnu

Today the cosmology community is full of chatter about an impending announcement – I heard the story from people on three continents. Moreover, the Center for Astrophysics at Harvard has scheduled a media conference on Monday with the promise of a major discovery, so there is some substance to the stories.

As always though, rumours run beyond the available facts, starting with the claim that the discovery was made by BICEP2, a telescope at the South Pole. BICEP2 is one of a number of instruments around the world that are dedicated to observations of the microwave background, the afterglow of the Big Bang. The word is that the BICEP team will announce evidence for a primordial B-mode – a delicate twist in the polarisation-pattern of the microwave sky,

Unlike the dark matter and dark energy that dominate the cosmos today, a B-mode would be a tiny pinch of spice that adds an oh-so-subtle flavour to the recipe of the universe. What makes a B-mode interesting (at least to a theorist) is how it gets there. Most realistic cosmological models rely on inflationa hypothetical period of accelerated growth, to solve “initial conditions problems” that plague simple models of the Big Bang. During inflation, quantum ripples in spacetime are stretched until they span the visible universe. It is these ripples, or gravitational waves, that would induce a B-mode in the microwave sky. Conversely, the B-mode predicted by competing solutions to the initial conditions problems is unobservably small, making the B-mode a “smoking gun” for inflation. So if the rumours hold up, BICEP could have detected a “signal”  that confirms a key tenet of modern cosmology and which was written into the sky a trillion, trillion trillionth of a second after the Big Bang. And that would be a very big deal indeed. 

When it comes to the details, the stories diverge. Some claim a (relatively) large B-mode that could be hard to square with other datasets, or would imply that the early universe is weirder than we imagine. Other rumours tell of a signal that is consistent with everything else we know, but might permit only a more tentative detection. (And not all possible B-modes match the predictions of simple inflationary models: a big B-mode that was not an inflationary B-mode might be the most astonishing outcome of all.)

This is a blog about a rumour and what it would mean if the rumours are correct (and the results then stand the test of time). It may be that rumours are wrong and the announcement is about something entirely different but at Noon, Eastern Daylight Time on March 17th we will know. 


Rare footage of the cosmology rumour mill in action 

PS For a Smoking Gnu look at the Discworld — which is certainly a fascinating cosmology, even if it is not the universe we actually inhabit. 

Planck Live Blog

RELOAD FOR UPDATES [Lo-tech live blogging!]

THE DAY AFTER:  t work, digesting the Planck data.    The commentary below ran a bit technical; once I have my own thoughts together I will write them down…

12:49 AM NZST oo distracted to update the live blog after downloading the key papers.  They are a thing of beauty and a joy to behold. Huge kudos to the Planck team. Quick reactions, and then time to turn in (nothing like a global twitterfest to confirm that the world is round, I guess.)  

  • Firstly, the Hubble constant result from Planck really is quite low when compared to direct measurements. The parameters paper digs into the error budget here, and you can expect to see a good deal of effort going into improving the lowest rungs in the cosmic “distance ladder” in the next little while.
  • Neutrino physics results are in broad agreement with expectations from particle physics — three kinds of neutrinos, with a small overall mass.
  • The analysis of inflation is lovely (although I am bound to say this, as parts of it are influenced by a paper I wrote with Hiranya Peiris, a member of the Planck collaboration) — simple single-field, slow-roll models are still alive and kicking.
  • Speaking of which, non-Gaussianity is not detected, and constraints are significantly tightened.
  • People who like a simple universe will be happy.
  • If you were hoping that Planck would expand the fundamental set of parameters n the concordance model, looks like you were out of luck.
  • One elephant in the room is that there is no use of polarization data — this is being worked on, but it will make a big difference when it becomes available.
  • Finally, the emphasis on “anomalies” in the media conference and press release seems like headline-bait to me. By and large these were already known from the WMAP data, and are at large angular scales — where Planck and WMAP should overlap with one another.  Any dataset has anomalies and by stressing these, the ESA media-monkeys detract from the huge advance this dataset represents. Planck has provided us with a picture of the early universe with unprecedented clarity and precision, and every cosmologist in the world will have to do their job differently on the strength of it.  Working out what it tells us may take years, but it is going to be fun. 


10:56 PM NZST  tarting to think there is no big discovery to be announced.  But beautiful measurement of the early universe.  

10:51 PM NZST  old us that there are 3.2 ± .2 species of neutrinos — confirms predictions of particle physics.  Nothing about their mass so far. 

10:48 PM NZST  akeaway so far, inflation seems to be in good shape as a theory of the early universe.  Anomalies discussed were mostly seen in WMAP data, but now confirmed at higher precsion by Planck.

10:45 PM NZST Stunning accuracy in results for “standard’ cosmological parameters. Hubble’s constant lower than expected, universe a little older.   ots of time being spent on “anomalies”; wonder what will be said next.  

10:27 PM NZST  Foreground subtraction. #planck has 9 frequency bands — foregrounds have differnt freq. dependence from CMB, subtracted away. 


10:12 PM NZST  George Efstathiou about to take the stage. 

10:16 PM NZST Giving a quick overview of CMB physics…  Electrons and protons join to form atoms 380000 years after the big bang — CMB decouples from the matter, and largely unchanged since then.  ives us a baby photo of the universe.

10:07 PM NZST  Super choppy video. Promise of an “almost perfect” universe. Planck detectors cooled by liquid helium until they are a fraction of a degree above absolute zero — much colder than the CMB [microwave background] itself.

9:41 PM NZST  New Zealand is currently 12 hours ahead of Paris.  Press conference starts in 15 mins, but the actual papers go live at 12pm apparently.  Worry the ESA server will look this ery shortly afterwards, but suspect they can handle it. 

:40 PM NZST ooking at astrophysicists on facebook, the East Coast of the US appears to be waking up (or never went to sleep).  

3:50 PM NZST  Planning to live blog the lanck live blog data release tonight.  In the meantime, read Renee Hlozek and Shaun Hotchkiss‘s blogposts which give good discussions of what is at stake, or watch Ed Copeland giving a quick survey of cosmology. For my part, I am enormously curious to understand how Planck tightens constraints on the inflationary phase in the early universe, whether it confirms the existence of possible “glitches” in the early universe (and it will almost certainly provide new candidates, even if it rules out the old ones), the results for non-Guassianity, and the implications of Planck for neutrino physics. All this and more will be explained in a few hours. The webcast starts at 10am in Paris — 10pm in New Zealand, with the technical papers scheduled to become available at noon. 

And the European Space Agency says that #askplanck is the official hashtag for questions.