The Harvard-Smithsonian Center for Astrophysics (CfA) will host a press conference at 12:00 noon EDT (16:00 UTC) on Monday, March 17th, to announce a major discovery.
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,
skydivephil said:So I am guessing theyv'e found evidence for the b mode polarisation of the CMb.
If so , how much can we learn from a ground based detector? Do we need a space based project like CORE, PRISM or EPIC?
Only from space can one reliably detect the very low-l B-modes due to the re-ionization bump. Because of its broad frequency coverage and extreme stability, PRISM will be able to detect B-modes at 5sigma for r = 5 exp -4;even under pessimistic assumptions concerning the complexity of the astrophysical foreground emissions that must be reliably removed. Moreover, PRISM will be able to separate and filter out the majority of the lensing signal due to gravitational deflections. Hence PRISM will perform the best possible measurement of primordial CMB B-mode polarization, and hence the best possible measurement of the corresponding inflationary tensor perturbations achievable through CMB observations.
Drakkith said:What would evidence for B mode polarization of the CMB indicate?
cristo said:A detection will indicate several things, as touched upon in the above blog post:
(i) it will be the first detection of gravitational waves, in itself a big milestone
(ii) the B mode is often called the 'smoking gun' test of inflation, since other mechanisms predict a very small signal
(iii) it's also evidence for quantum gravity, through the quantum fluctuations of the tensor gravitational mode during inflation
(iv) the size of the signal (called the tensor to scalar ratio for the inflationary model) will help rule out different classes on inflation models.
Perhaps most interestingly, though it's somewhat model-dependent, the level of primordial B modes serves as a measurement of the energy scale of inflation.cristo said:A detection will indicate several things, as touched upon in the above blog post:
(i) it will be the first detection of gravitational waves, in itself a big milestone
(ii) the B mode is often called the 'smoking gun' test of inflation, since other mechanisms predict a very small signal
(iii) it's also evidence for quantum gravity, through the quantum fluctuations of the tensor gravitational mode during inflation
(iv) the size of the signal (called the tensor to scalar ratio for the inflationary model) will help rule out different classes on inflation models.
DennisN said:Very interesting! I will try to tune in on Monday for this. According to the spaceref page the conference will be streamed here: http://www.cfa.harvard.edu/news/news_conferences.html
I think it started closer to 11:00 Eastern. I caught the latter half. Bottom line: r=0.20+0.07-0.05, r=0 disfavored at 7.0/5.9 sigma. This implies GUT-scale inflation, too. Far out.marcus said:It was scheduled for noon Eastern, so should have started 20 minutes ago. I tried your link, but could not get connection (may be overloaded).
Anybody have another suggestion? Some other link to try later, for summary report or written statement?
DennisN said:Very interesting! I will try to tune in on Monday for this. According to the spaceref page the conference will be streamed here: http://www.cfa.harvard.edu/news/news_conferences.html
marcus said:I actually got connected on that link and was able to watch. It just took a while. They also said that the news conference would be archived at the harvard website, so could be watched later.
Statements by Mark Kamionkowski and Clem Pryke were especially clear and articulate. The questions from the audience were worthwhile (I thought) and so some of the responses were enlightening. Alan Guth and Andrei Linde were in the audience and took the mike several times to talk up the "multiverse". Their argument was essentially that it was possible to make models of inflation that do NOT lead to eternal inflation and that kind of multiverse, but that it was HARD to construct models in which adequate inflation occurred and stopped in some cases without generating a lot of unsatisfactory cases as well. Thanks to the other posters who just now provided what look like very helpful links! I'll be checking some out this morning.
Just glanced at the main BICEP release paper that Skydive linked to
http://bicepkeck.org/b2_respap_arxiv_v1.pdf
full of technical detail, very thorough, see Figure 13 on page 17, which kind of sums it up. r is the strength of the signal confirming direct evidence of gravitational waves have been seen. The find r = 0.2 and they regard that as very strong, higher than they thought could be the case based on rough back-of-envelope estimates.
They say they now have a handle on the energy density of the very early universe, and with further observations will be able to plot how it changed.
bapowell said:Yes, now we need to measure the tilt of the tensor spectrum. Shameless plug, but a while back I studied how well we can expect future experiments to distinguish between the competing models:
http://arxiv.org/abs/arXiv:1106.5059
skydivephil said:..., but what about the issue of red tilt versus blue tilt in the primordial gravity wave spectrum? Can that/has that been addressed by BICEP 2 data or not?