Press Conference on Major Discovery - primordial B modes?

[DevilsAvocado]

Andrei Linde is happy and hopes he is not tricked.

https://www.youtube.com/watch?v=ZlfIVEy_YOA
http://www.youtube.com/embed/ZlfIVEy_YOA

And now it's all over the news...

https://www.youtube.com/watch?v=UWEAtRrRLsg

https://www.youtube.com/watch?v=qun1L3HfQ7M

BBC Radio 4
Scientists 'expect' echoes of Big Bang

TELEGRAPH.CO.UK
http://www.telegraph.co.uk/science/space/10703721/Big-Bang-echo-scientists-find-signal-from-dawn-of-time.html

 

[Haelfix]

This is indeed a very important discovery, with far ranging implications that are (imo) quite a bit more important than anything that we have learned from Planck.

If true (and that's a big if and already being challenged by a number of colleagues) we will have essentially confirmed a number of remarkable properties about the early universe.

Moreover, the constraints on model building are absolutely staggering, with all sorts of popular models being ruled out. I recommend the following blog posts on the theoretical aspects of this discovery:

http://resonaances.blogspot.com/2014/03/curly-impressions.html

http://motls.blogspot.com/2014/03/bicep2-primordial-gravitational-waves.html

 

[bapowell]

Thanks and can this be done from the ground or does it need a space based mission?

It depends on how big $n_T$ ends up being. If we are looking at inflation, then from the consistency condition $r=-8n_T$, $n_T$ will be sufficiently small to require a high-precision experiment. I'm not sure whether there is a preference for space- vs. ground-based observations, but either one would need to be close to cosmic variance-limited in order to conclude with strong evidence (with a Bayes factor satisfying $2.5 < ln|B| < 5$) that the tensor spectrum is red.

 

[TrickyDicky]

Maybe someone can explain a little what the B-mode polarization is as opposed to the E-mode, and how it relates to the usual EM polarization, is the difference just the handedness(like in linear vs. elliptical EM polarization)?.

 

[skydivephil]

http://blankonthemap.blogspot.co.uk/2014/03/b-modes-rumours-and-inflation.html

 

[marcus]

Watched the YouTube part 1, could hear fine but video taken from too far from screen so slides not clearly visible.
Maybe if one had the downloaded paper, and or supplemental material in front of one , to consult, it would substitute for not being able to see the slides. Clem Pryke gave the second half of Part 1, on data analysis

 

[the_pulp]

In some places I am reading things like the following:

So, granting the context of inflation, the BICEP measurement tells us that inflation occurred around the GUT scale, just two orders of magnitude below the Planck scale. This is on the doorstep of quantum gravity. I will say more about this below.

For example here: http://motls.blogspot.com.ar/2014/03/bicep2-primordial-gravitational-waves.html#more

Where in the whole discovery is seen a connection with the scale at which inflation operated (10^16 Gev from what I see in the reviews). Is this energy value another output of the discovery? Why? Where?

Thanks!

 

[craigi]

Is there anything to suggest that this discovery favours or disfavours the eternal inflation variation on the inflation model?

 

[Tanelorn]

http://en.wikipedia.org/wiki/B-modes

In the reference above r the tensor-to-scalar ratio, can this be defined? Perhaps pictorially?

Could there by more than one stage of gravitational lensing on the cmbr at different distances which could explain this instead of inflation?

I am only aware of horizontal, vertical, and circular RF polarization. Does anyone have a pictorial description of b and e modes?

Useful links:
http://blankonthemap.blogspot.co.uk/2014/03/b-modes-rumours-and-inflation.html

http://blankonthemap.blogspot.co.uk/2014/03/first-direct-evidence-for-cosmic.html

 

[DennisN]

I tried your link, but could not get connection (may be overloaded).

Yeah, same here .
Hopefully a nicely recorded conference will pop up here: http://www.cfa.harvard.edu/news/conferences (it isn't up yet).
And thanks to everybody else in this thread for all links!

 

[lpetrich]

E-mode vs. B-mode is how the polarization direction is related to the fluctuation strength's gradients. E-mode is along the gradient or perpendicular to it, B-mode is 45d away from the gradient. This is an extension of the Stokes parameters for describing polarization.

I = overall intensity
Q = horizontal - vertical
U = one diagonal - other diagonal
V = circular

I and V are essentially scalars, and are thus easy to specify for an area. However, Q and U are not, but they can be expressed as components of a symmetric traceless tensor:

L11 = Q, L12 = U, L21 = U, L22 = -Q

That gives a hint as to how to find Q and U as functions of a scalar quantity:

L_ij(E) = φ_,ij - (1/2)δ_ijφ_,kk
is the E mode
and
L_ij(B) = (1/2)(ε_ikL_jk(E) + ε_jkL_ik(E))
is the B mode

In components,

L(E) = {{(1/2)(φ_,11 - φ_,22), φ_,12}, {φ_,12, (1/2)(- φ_,11 + φ_,22)}}

L(B) = {{φ_,12, (1/2)(- φ_,11 + φ_,22)}, {(1/2)(- φ_,11 + φ_,22), - φ_,12}}

where φ is a scalar function.

I derived this for a flat surface, but one can extend it to a spherical one with the differential-geometry apparatus of general relativity.

 

[TrickyDicky]

Thanks for the link and the explanation, skydivephil and Ipetrich.

 

[Greg Bernhardt]

https://www.youtube.com/watch?v=ZlfIVEy_YOA

 

[DennisN]

Yeah, same here .
Hopefully a nicely recorded conference will pop up here: http://www.cfa.harvard.edu/news/conferences (it isn't up yet).
And thanks to everybody else in this thread for all links!

The conference is now up as a downloadable mp4 file (553 MB).
Page: http://www.cfa.harvard.edu/news/conferences
MP4 File:http://www.cfa.harvard.edu/pao/Bicep2_news_con.mp4

I'm downloading it right now, and will watch it later today .
EDIT: I looked at it briefly, and it seems it is excellent quality, both video, audio and slides.

 

[Paulibus]

This is indeed a very important discovery, with far ranging implications ...

.
For me, these implications include correcting my poor understanding of quantum mechanics,
and of its ‘vacuum state’, which I imagine as a label for probabilistic chaos in a seething,
fluctuating, unobservable turmoil of zero-point mass/energy. Perhaps the ultra-energetic state of
the nascent universe can also only be described in such probabilistic quantum-mechanical terms.
But I’ve wrongly thought of vacuum fluctuations as having real, observable consequences ( Casimir
effect, Van der Waals forces), and of fluctuations as rather less real entities — conveniently
imagined but unobservable constructs. However the observations made with BICEP2 pretty much
confirm that inflation indeed promotes vacuum fluctuations into the realm of directly observable
entities, and therefore strongly supports the accepted history in which vacuum fluctuations act as
seeds for gravitational condensation, and all the amazing complications that follow.

...this is a seriously big deal.

Informs about quantum mechanics and the 'reality' of the wave function as well!

 

[TrickyDicky]

I also agree about the importance of the discovery and its implications, though a little confused about the relative small response it has generated here compared to other recent discoveries with less implications.
Are people just being cautious? Maybe. Perhaps the experts learned their lesson from the infamous Opera neutrinos, but laymen?

 

[Haelfix]

Unfortunately many of the theoretical implications are laced with caveats, loopholes and mathematical subleties, which makes it rather difficult to present in a forum like this.

The arxiv is about to be flooded with careful discussion surrounding each one of these issues, so its prudent to not be too hasty and to actually listen to what the experts say.

All of this is assuming the experiment holds up to more scrutiny, which is far from a given. Science is mostly replete with examples of experiments that go away. To my naive non experimentalist eyes, this looks somewhat convincing (especially if what they say is true about the non-released data), but then there are some pretty knowledgeable and famous experimentalists who disagree strongly.

 

[TrickyDicky]

After reading the BICEP2 team paper and also lots of informed opinions on it I can say it looks like a very solid piece of work experimentally speaking.

But section 11.3 that enters into theoretical asides leaves me a bit intrigued. They acknowledge the constraints set by Planck that are in accordance with the LCDM model are in tension with their interpretation of the B-modes measures as tensors in the context of primordial gravitational waves imprint on the CMB.
And to avoid this tension they tentatively propose a modification of the model, specifically of the spectral index parameter n_s that measures the slight deviation from scale invariance predicted by inflation, and that according to inflation must be approximately constant. But the modification they propose is that n_s is no longer a constant but a "running parameter".
Wouldn't this theoretical modification prevent the interpretation of the B-modes as cosmic inflation related?

 

[exponent137]

Can this measurement give any new information on quantum gravity theory (QG)? Are probabilities for correctness of theories of QG at the same ratio, as before?

I saw link
http://iopscience.iop.org/1742-6596/484/1/012060/pdf/1742-6596_484_1_012060.pdf

 

[exponent137]

Gravitational waves stretch and shrink space. Does this means that light in stretched space travel more time and in shrunk space it travel shorter time?

p.s. It is annoying to me, that everyone speak about bilionth of bilionth .. part of the second, why not simple 10^34 and so on?

 

[exponent137]

Gravitational waves stretch and shrink space. Does this means that light in stretched space travel more time and in shrunk space it travel shorter time?

p.s. It is annoying to me, that everyone speak about bilionth of bilionth .. part of the second, why not simple 10^34 and so on?

 

[cristo]

Can this measurement give any new information on quantum gravity theory (QG)? Are probabilities for correctness of theories of QG at the same ratio, as before?

I saw link
http://iopscience.iop.org/1742-6596/484/1/012060/pdf/1742-6596_484_1_012060.pdf

The article you link to is regarding loop quantum cosmology -- a cosmology derived from a candidate 'quantum gravity' theory. I haven't followed this literature, but a few years ago the statement was that LQC predicted a tensor spectrum with a large blue tilt which is unobservable on large scales. However, this paper seems to now include a tuneable parameter (k_*) which can give you any spectrum of gravity waves. I don't know how this parameter is obtained, but there will likely now be an allowed value that can be determined by the data which hopefully then has other observable consequences.

 

[marcus]

Can this measurement give any new information on quantum gravity theory (QG)? Are probabilities for correctness of theories of QG at the same ratio, as before?

I saw link
http://iopscience.iop.org/1742-6596/484/1/012060/pdf/1742-6596_484_1_012060.pdf

We may be able to get you a link to a more comprehensive and up-to-date paper.
What you link to is in the proceedings of a conference given in 2011. It is not especially up-to-date. The talk given by Julien Grain has numerous references "for details" to a 2010 paper by Grain's thesis advisor Aurelien Barrau, Grain himself, and a couple of other collaborators. So what is presented basically reflects the status of the field as of 2010.

The same four authors also have a 75-page INVITED REVIEW, published February 2014 in Classical and Quantum Gravity, which is probably overall a better source. Here are several links:
http://arxiv.org/pdf/1309.6896.pdf
http://arxiv.org/abs/1309.6896
http://inspirehep.net/record/1255638?ln=en



In case it's needed, here's an alternate link to the conference talk given by Grain you linked to:
http://arxiv.org/abs/1206.1511
Here are the proceedings of the December 2011 ICGC conference where it was presented:
http://iopscience.iop.org/1742-6596/484/1
Here's the more complete 2010 paper it is based on:
http://arxiv.org/abs/arXiv:1011.1811
Observing the Big Bounce with Tensor Modes in the Cosmic Microwave Background: Phenomenology and Fundamental LQC Parameters
J. Grain, A. Barrau, T. Cailleteau, J. Mielczarek

 

[cristo]

We may be able to get you a link to a more comprehensive and up-to-date paper.
What you link to is in the proceedings of a conference given in 2011.

I only looked at the date of publication, and didn't realize this was from a talk a few years back.

Without digging into the literature (which I don't have the chance to at the minute) do you have an idea how much that prediction has changed since 2011? Has this k* parameter been constrained by other observations to make a meaningful prediction of B mode spectrum, or is it the case that the spectrum can be fit by choosing a value of this parameter?

 

[marcus]

... do you have an idea how much that prediction has changed since 2011? Has this k* parameter been constrained by other observations to make a meaningful prediction of B mode spectrum, or is it the case that the spectrum can be fit by choosing a value of this parameter?

It's a good question! I don't know. I'll take a look at the recent invited review paper by those same authors. With luck they will mention that k parameter and give us some larger context.

http://inspirehep.net/record/1255638?ln=en
Observational issues in loop quantum cosmology
A. Barrau (LPSC, Grenoble & IHES, Bures-sur-Yvette) , T. Cailleteau (Penn State U., University Park, IGC) , J. Grain (Orsay, IAS & Orsay) , J. Mielczarek (Jagiellonian U. & Warsaw, Inst. Nucl. Studies)
Abstract: Quantum gravity is sometimes considered as a kind of metaphysical speculation. In this review, we show that, although still extremely difficult to reach, observational signatures can in fact be expected. The early universe is an invaluable laboratory to probe "Planck scale physics". Focusing on Loop Quantum Gravity as one of the best candidate for a non-perturbative and background-independant quantization of gravity, we detail some expected features.
75 pages, invited topical review for Classical and Quantum Gravity

The relevant passages start around page 56 (and the 2010 paper does NOT seem to have been outmoded! It is reference [76] and they often cite that reference "for details".) My concern to get an up-to-date source does not, in this case, seem to matter. Sometimes it makes a difference but maybe in this instance it doesn't.

I'll quote some, starting on page 56.
==review paper Feb. 2014 Classical and Quantum Gravity==
The primordial component of the B-mode angular power spectrum is determined by the five following parameters: k_*, R, n_T, T/S and the reionization optical-depth τ. This set of parameters will be denoted θ_i hereafter. There values are not fixed as this is precisely those parameters that can be constrained by a potential observation of the B-modes. The other cosmological parameters will be fixed to the WMAP 7-yr best fit, and the lensing-induced B-modes will be fixed to the standard prediction. The case of τ should be briefly discussed. Its value is already constrained by measurements of the TT, TE and EE angular power spectra. However, this parameter is potentially degenerated with the other cosmological parameters, k_*, R, n_T, T/S. It is therefore worth letting this parameter free from the perspective of exploring its degeneracies with e.g. k_* and R and evaluate how such degeneracies could affect the estimation of k_* and R from CMB measurements.

When compared to standard cosmology, the set of cosmological parameters is therefore enlarged by adding two phenomenological parameters, k_* and R, parametrizing the LQC-induced distortions of the primordial power spectrum. The parameters k_*, R, n_T, T/S encode all the physics taking place in the primordial universe. They allow for a phenomenological description of the primordial power spectrum. The constraints that one can set on those four parameters can finally be translated into constraints on fundamental parameters of the model using:

[Here are given 4 equations (176) thru (179) determining those 4 quantities in terms of model parameters]
==endquote==
The following paragraphs look interesting. I'll look the over some more and post again later today.

 

[Haelfix]

What that means is they don't have enough control of their theory to output a prediction, there are more free parameters than unknowns. In short there is no value of r or n that will either confirm or falsify Lqc at this time.

As I said in another thread the problem is that Lqc is like multi bout models of inflation. The first super bounce is followed by a standard bout of inflation. But the latter can effectively wipe out all traces of the former (this corresponds in their language to kstar < khubble), but you can't know that without making assumptions about the inflaton to begin with.

 

[exponent137]

Please, more simply for the beginning. I am not an expert.
Is Linde's theory probably based on some quantum gravity premises? What they are?

Isham wrote something about quantum gravity, as http://arxiv.org/abs/gr-qc/9310031.
If we suppose that BICEP2 is correct, can it tells something about Isham?

McAllister wrote something about quantum gravity.
http://motls.blogspot.com/2014/03/b...tational-waves.html?showComment=1395081102056
(I hope that this will not be deleted.)
He wrote more about superstrings. Is it possible to write something about quantum gravity, not connected to specific QG theories, like Isham.

Feynman's approach to quantum gravity has the problems, because of nonrenormalizability. Why this is the problem if we assume that spacetime is grained? Why we need strings, why grained spacetime is not enough?

 

[cristo]

Thanks for the info marcus.

What that means is they don't have enough control of their theory to output a prediction, there are more free parameters than unknowns. In short there is no value of r or n that will either confirm or falsify Lqc at this time.

That's exactly what I suspected.

 

[TrickyDicky]

Can anyone clarify if having a running spectral index n_s is compatible with primordial gravitational waves within the inflationary scenario?
I guess it depends on how much it tilts the spectrum, but I was under the impression that a certain amount of scale invariance is needed simply to observe coherently the primordial spectrum fluctuations (coherent acoustic peaks, etc)and in any case inflation predicts a gravitational waves spectrum almost scale invariant, how would the introduction of a running tilt affect this?

 

[exponent137]

Some things are not clear enough:
Quantum fluctuactions cause gravitational waves and these waves cause polarization of the electromagnetic waves. Does this means: any gravitational waves could produce D-mode, even not caused by Quantum fluctuations?
Does Quantum fluctuations built some different gr. waves as the classical gravitational waves?

 

[marcus]

What that means is they don't have enough control of their theory to output a prediction, there are more free parameters than unknowns. In short there is no value of r or n that will either confirm or falsify Lqc at this time.
...

In fact there are several lines of development in LQC, and results on r appear to be helping to distinguish and sort them out (assuming the observed values are confirmed).
for instance, one line of LQC development is teleparallel--Jaume de Haro is the main person on that one:
http://arxiv.org/abs/1403.6396
Viability of the matter bounce scenario in Loop Quantum Cosmology from BICEP2 last data
Jaume de Haro, Jaume Amorós
(Submitted on 25 Mar 2014)
The CMB map provided by the Planck project constrains the value of the ratio of tensor-to-scalar perturbations, namely r, to be smaller than 0.11 (95% CL). This bound rules out the simplest models of inflation. However, recent data from BICEP2 is in strong tension with this constrain, as it finds a value r=0.20^+0.07_−0.05 with r=0 disfavored at 7.0σ, which allows these simplest inflationary models to survive. The remarkable fact is that, even though the BICEP2 experiment was conceived to search for evidence of inflation, its experimental data matches correctly theoretical results coming from the matter bounce scenario (the alternative model to the inflationary paradigm). More precisely, most bouncing cosmologies do not pass Planck's constrains due to the smallness of the value of the tensor/scalar ratio r≤0.11, but with new BICEP2 data some of them fit well with experimental data. This is the case with the matter bounce scenario in the teleparallel version of Loop Quantum Cosmology.
4 pages, 1 figure

 

[skydivephil]

Ive often seen "matter bounce" suggested as an alternative to inflation. However in standrad LQc you go form bounce to super inflation to inflation and so on. So in this standard scenario, is it different to the phrase "matter bounce" are there different types of bounces?

 

[bapowell]

Can anyone clarify if having a running spectral index n_s is compatible with primordial gravitational waves within the inflationary scenario?
I guess it depends on how much it tilts the spectrum, but I was under the impression that a certain amount of scale invariance is needed simply to observe coherently the primordial spectrum fluctuations (coherent acoustic peaks, etc)and in any case inflation predicts a gravitational waves spectrum almost scale invariant, how would the introduction of a running tilt affect this?

Yes, sure -- they are determined by different aspects of the inflationary dynamics: GW's by the energy density and running by the shape of the potential (mostly by the third derivative, V''').

The scalar perturbation is decidedly *not* scale invariant: $n_s = 1$ is ruled out at several sigma.

 

[bapowell]

Ive often seen "matter bounce" suggested as an alternative to inflation. However in standrad LQc you go form bounce to super inflation to inflation and so on. So in this standard scenario, is it different to the phrase "matter bounce" are there different types of bounces?

Yes, you can have noninflationary matter bounces. In these scenarios, the perturbations are set up during the contracting phase (pass outside the shrinking horizon) and carry through the bounce. The problem is how to keep the calculation under control through the bounce which, depending on the model and perturbation variable, can become singular.

 

[bapowell]

Some things are not clear enough:
Quantum fluctuactions cause gravitational waves and these waves cause polarization of the electromagnetic waves. Does this means: any gravitational waves could produce D-mode, even not caused by Quantum fluctuations?
Does Quantum fluctuations built some different gr. waves as the classical gravitational waves?

Primordial gravitational waves produced by inflation behave just like classical gravitational waves.