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Here are some BICEP2 details to augment Chris White's answer: BICEP2 accomplishes the task of measuring angular variations in polarization by converting those angular variations to a time domain signal. It does so by scanning its telescope across the sky at a constant rate. Specifically, the telescope scans at a fixed rate of $2.8^\circ$/ second in ...

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The F(L)RW metric comes with very few assumptions, though these are fairly strong: Spacetime is homogeneous. Spacetime is isotropic. Or, in other words, the cosmological principle is assumed. Philosophically this is very desirable, as the notion that there are preferred locations or directions in the Universe is, from a modern point of view, somewhat ...

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We don't think the FLRW metric is valid throughout the entire history of the universe. If we take a metric of the form: $$ds^2 = -dt^2 + a^2(t) d\Sigma^2$$ then we expect this to be valid throughout the history of the universe as long as the universe is isotropic and homogenous. However we need to find the equation for the function $a(t)$, and this is ...

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Since the original BICEP2 publication there has been increasing suspicions that what they had seen was actually just a signal from interstellar dust. We've been waiting for data from the Planck experiment on the dust signal, and that data has just been released. Sadly it looks as if BICEP2 did indeed just see dust and not signals from gravitational waves. ...

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How do we know that space expanded faster than a speed of light in inflation? Let us start from the beginning, on the reason that the Big Bang theory was proposed as a model for the universe. The reason was the observations that all clusters of galaxies were receding from each other. This is what happens from an explosion at the center, in three ...

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Inflation does not violate any local speed of light physics and there is no global prohibition in general relativity against spacetime points that are moving away from each other faster than the speed of light. Such spacetime points are simply not causally connected, i.e. there is no physical way to communicate between them (since light signals from one can ...

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