# Tag Info

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The Bekenstein bound, $$S \le \frac{2\pi rE}{\hbar c},$$ is a limit on the natural log of the number of possible states (i.e., the information content) of a spherical region of space of radius $r$, containing mass-energy $E$. The mass of the hydrogen atoms in the observable universe is $\sim 10^{54}$ kg, and nonbaryonic dark matter is probably about 5 ...

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I didn't watch enough of the video to see the alleged claim, but I'm almost sure he is talking about the idea that the universe has different regions in which the "constants" of nature have different values, and only a few of those regions are hospitable to intelligent life, and we (of necessity) live in one of those, and that's why the constants here seem ...

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Classically, the CMB radiation would never completely disappear. It would just become more and more faint and redshifted. Quantum mechanically, if ΛCDM cosmology is correct, only finitely many CMB photons will reach us, so there will be a last photon. (edit: In general big bang cosmologies, there may be no last photon. I formerly said that the photon ...

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Light from recombination is not "constantly shining" and that's why you see it. At a given time in the universe's history (actually a slightly extended period but I'll keep things simple), and only at that time, photons decoupled from the ambient plasma and started travelling freely from all points in the universe. The photon background you see at any time ...

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