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Was the announcement that BICEP2 has detected Inflation Gravity Waves premature?

  1. Nov 21, 2014 #1

    Garth

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    Constraint on the primordial gravitational waves from the joint analysis of BICEP2 and Planck HFI 353 GHz dust polarization data
    It seems that the contamination of the BICEP2 signal by B Mode polarised light from galactic dust lanes might explain all the polarisation detected. I was at a lecture the other night by Professor Jo Dunkley of Oxford University who is working on the problem. She is now working on a balloon experiment to be launched in two years time to see if there is an Inflation Gravity Wave signal hidden behind the dust signal detected by BICEP2.

    In any case the BICEP2 team's announcement in March that they had 'detected Inflation' seems embarrassingly premature given that they did so before their paper had been peer reviewed and published.

    Garth
     
    Last edited by a moderator: Jan 30, 2015
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  3. Nov 21, 2014 #2

    Chronos

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    I think they were mainly guilty of unbridled enthusiasm. But, who wouldn't be a little tight under the circumstances?
     
  4. Nov 21, 2014 #3

    Garth

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    Yes, but so were the Cold Fusion crowd!

    Garth
     
  5. Nov 21, 2014 #4

    Chalnoth

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    The cold fusion crowd wasn't just mistaken. They fabricated data. The BICEP2 team was just a bit overly-enthusiastic, which is far more understandable.
     
  6. Nov 21, 2014 #5

    Garth

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    That as maybe, the point I was making was that the BICEP2 team, and the cosmological community, went very public, with news reports around the world, about a result that had not even been published and peer reviewed.

    It may well be that there is no B mode polarisation signal from primordial Inflation induced gravity waves, and Inflation may be just a complicated attempt to "save the phenomena"; yet the whole world thinks such a signal had been received. I haven't yet seen a retraction as public as the original announcement.

    Perhaps there may be in two years time, or on the other hand, there may then be a confirmation that under the dust induced signal there is a faint priordial signal.

    We wait and see!

    Garth
     
  7. Nov 21, 2014 #6

    Chalnoth

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    I still think there's a gigantic difference between getting overly-enthusiastic and putting the news out too soon than outright fabricating data.

    No doubt that they should not have gone for the sensationalist approach, but I still think the comparison to cold fusion is unfair.
     
  8. Nov 21, 2014 #7

    Garth

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    Okay maybe a bit unfair!

    Garth
     
  9. Nov 21, 2014 #8

    Chronos

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    The unfortunate aspect of the BICEP2 incident was the drama fueled by Harvard CFA. I have the suspicion the research team was not necessarily all in with that. It could have been done in less grandiose fashion with less egg spatter.
     
  10. Nov 22, 2014 #9

    Vanadium 50

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    BICEP looked at a region of sky that they had reason to believe would minimize the effect of dust. As it happens, it was not as good as they thought. The paper was very clear about what they did and what assumptions they made. What more should they have done?
     
  11. Nov 22, 2014 #10

    Chronos

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    Make cfa read the entire study before embarrassing everyone involved.
     
  12. Jan 30, 2015 #11
  13. Jan 31, 2015 #12

    Garth

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    Thank you Greg!

    Note this topic has appeared in three current threads, this one, You think there's a multiverse? Get real and A Rough Guide to Spotting Bad Science.

    The more this detraction of the "Inflation evidence discovery" appears in the popular press, rather than just academic papers, then the more the confusion in the public eye may be resolved.

    There is still "wriggle room!" in the error bars of the Planck data for a tiny gravitational wave signal to hide in the dust signal - that is why we must wait for BICEP3 and the balloon experiments that will be ready in a few years time.

    Garth
     
    Last edited: Jan 31, 2015
  14. Jan 31, 2015 #13

    Chalnoth

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    Not necessarily even that tiny. Planck wasn't really designed to be great for detecting B-mode polarization. The only reason why it's able to weigh in on the BICEP2 results at all is because BICEP2's claimed signal was so huge. It was always expected that we'd have to get incredibly lucky to detect primordial B-modes with Planck.

    The most we can say at this point is that the B-mode signal isn't gigantic, which is definitely a step up from before, when we really didn't have much of any constraints on the signal at all.
     
  15. Jan 31, 2015 #14

    Garth

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    Okay, a possible hidden signal may not be that tiny at the present status of the analysis of the available data.

    However "The most we can say at this point is that the B-mode signal" has not been detected.

    From this week's Nature Gravitational waves discovery now officially dead :

    At least they all agree with my OP - they were premature in the announcement.
    However all might not be lost:
    Garth
     
  16. Feb 1, 2015 #15

    Chalnoth

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    Unfortunately, it's really really difficult to do observations across a wide range of frequencies without going into space. While there are a number of good experiments in the works for detecting polarization of the CMB from balloons and ground-based telescopes, there are only so many relevant frequencies where our atmosphere is (mostly) transparent.

    There have been some proposals for a CMB satellite with a focus on polarization, but so far nobody has taken one of the proposals up.

    The real trick here is having a telescope design which minimizes systematic errors in polarization. Planck really wasn't designed for polarization (support for polarization was tacked-on later in the development of the satellite), and this meant that the systematic errors in polarization were really difficult to eliminate. This is why it took so long for the Planck collaboration to release polarized maps.

    Edit:
    For example, this is one proposal of a future satellite for measuring CMB polarization:
    http://www.core-mission.org/
     
  17. Feb 1, 2015 #16

    Garth

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    Thank you Chalnoth, Cosmic Origins Explorer certainly looks interesting for about ten years time, (if it gets off the ground).

    However I believe SPIDER has just finished its two week observing run circling the Antarctic continent, carried by a balloon and driven by the polar winds. Do we know when any results may be known, and may they give a clearer picture?

    To elaborate on the "wriggle room" for Gravitation Wave Background (GWB). From Peter Coles' blog: In the diagram below the black dots with error bars show the original BICEP/Keck “detection” of B-mode polarization which was assumed to be due to primordial gravitational waves, while the blue dots with error bars show the results after subtracting the correlated dust component. On top of which the red curve shows the known B-mode polarization signal that is generated by gravitational lensing.


    cross-correlation.jpg

    Note there’s a slight, not statistically significant, hint of a GWB excess over the red curve at multipoles of order 200, where the error bars are larger.

    Garth
     
    Last edited: Feb 1, 2015
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