IM Egdall Posted January 31, 2015 Posted January 31, 2015 The BICEP2/Planck joint analysis is out. Evidence for "B-mode" polarized light in the Cosmic Microwave Background NOT confirmed. Too much interstellar dust in our galaxy - which can produce the same effect. Too bad. I don't know if there is a way around this dust problem with future instruments. (As I understand it, inflation -- the extreme expansion of the very early universe -- is theorized to produced gravitational waves. These in turn would produce a swirling B-mode polarization in the Cosmic Microwave Background. This is what the BICEP2 telescope in the South Pole was looking for.) Link: http://www.esa.int/Our_Activities/Space_Science/Planck/Planck_gravitational_waves_remain_elusive 1
imatfaal Posted February 1, 2015 Posted February 1, 2015 Will have to read up on that. Good spot - thanks
sunshaker Posted March 11, 2015 Posted March 11, 2015 The BICEP2/Planck joint analysis is out. Evidence for "B-mode" polarized light in the Cosmic Microwave Background NOT confirmed. Too much interstellar dust in our galaxy - which can produce the same effect. Too bad. I don't know if there is a way around this dust problem with future instruments. (As I understand it, inflation -- the extreme expansion of the very early universe -- is theorized to produced gravitational waves. These in turn would produce a swirling B-mode polarization in the Cosmic Microwave Background. This is what the BICEP2 telescope in the South Pole was looking for.) Link: http://www.esa.int/Our_Activities/Space_Science/Planck/Planck_gravitational_waves_remain_elusive I watched this on horizon yesterday, Planck analysis saying it was nearly 75-100% certain to be dust, But if there are gravitational waves, wouldnt the dust only highlight these waves? We use smoke to see aerodynamics in a wind tunnel/or dyes in water to see currents, surely the dust would show up these waves better than without dust?
imatfaal Posted March 11, 2015 Posted March 11, 2015 I watched this on horizon yesterday, Planck analysis saying it was nearly 75-100% certain to be dust, But if there are gravitational waves, wouldnt the dust only highlight these waves? We use smoke to see aerodynamics in a wind tunnel/or dyes in water to see currents, surely the dust would show up these waves better than without dust? This is a bit beyond my paygrade - but: No, I think not. The Gravitational waves are not still there ( I guess they would be attenuated to nothing and not in the right place); we were looking for the fossil evidence of past gravitational waves in the polarisation of the CMBR which is very ancient (just a few hundred thousand years after BB) - the dust however is very recent in comparison (ie the gravitational waves would gone before the dust was around). FYG - we cannot directly detect gravitational waves yet - we have tried and failed a few times; they are just too damned hard to resolve from the noise. But we are very good at detecting light and other EMR - so we look at the Cosmic Microwave Background and measure polarisation patterns. It was predicted that the squashing and stretching of space that is a gravitational wave (specifically that from the BB) would leave very specific patterns of polarisation - which BICEP2 claimed to have identified. 1
StringJunky Posted March 11, 2015 Posted March 11, 2015 This Caltech article on gravitational waves is illuminating, but what is the Strain parameter in the vertical axis of the gaph? 1
imatfaal Posted March 11, 2015 Posted March 11, 2015 strain is the fractional difference in displacement of two similar masses ( separated by a small distance in the direction of the wave) due to the passing of the gravitational wave - ie it is the net distortion due to the passage of a gravitational wave. if you have a field of free floating test objects perpendicular to the direction of the propagation of the wave: a. take the central point b. as the wave passes then objects will move towards/away from central point c. the ratio of distance moved / distance from central point is the "strain" d. (actually twice the ratio - but who is counting?) 2
StringJunky Posted March 11, 2015 Posted March 11, 2015 strain is the fractional difference in displacement of two similar masses ( separated by a small distance in the direction of the wave) due to the passing of the gravitational wave - ie it is the net distortion due to the passage of a gravitational wave. if you have a field of free floating test objects perpendicular to the direction of the propagation of the wave: a. take the central point b. as the wave passes then objects will move towards/away from central point c. the ratio of distance moved / distance from central point is the "strain" d. (actually twice the ratio - but who is counting?) Yep. Got it. Thanks.
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