# Tag Info

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Ever heard of the cosmic microwave background? The CMB is a relic from when the universe became "opaque" - when, as Wikipedia says, protons and electrons combined to form neutral atoms. These atoms could no longer absorb the thermal radiation, and so the universe became transparent instead of being an opaque fog. So photons decoupled and the CMB was ...

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I've found this paper: Cosmological quantum entanglement, of E. Martin-Martinez and N. C. Menicucci. (last revised 19 Oct. 2012) Abstract We review recent literature on the connection between quantum entanglement and cosmology, with an emphasis on the context of expanding universes. We discuss recent theoretical results reporting on the ...

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To my mind, the Big Bang doesn’t refer to a distinct event but to a cosmogonic theory as a whole, that “predicts” ( should we say “retrodicts”?) many different events of the deep past. For example, there is such established term as “Big Bang nucleosynthesis” that describes an epoch several seconds past the Beginning of Time. The Beginning of Time in the ...

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So I've done some further research into this question and the result I found is quite surprising. There truly is no set definition. Some cosmologists will tell you (as John Rennie mentioned) to avoid using the term "Big Bang" unless you absolutely have to. However, that is a luxury not afforded to all cosmologists. The more surprising thing is that among ...

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All statements like "when the universe was the size of a grapefruit" refer to the currently observable universe. As the universe has a finite age and light travels at a finite speed (and there is nothing infinite going on with expansion), the observable universe is a finite patch. I discussed some of the different notions of horizons in answering another ...

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If I understand correctly your question, you are essentially asking why is it, that we always see a potential of this form: Rather than a, say $V=-\phi^2 +\lambda \phi^4$ graph. Where in the first case the coordinate can roll-down only one direction, whereas in the other case it can roll down the other direction as well. It doesn't matter which you ...

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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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