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Here's a partial answer. I hope it helps. Are there galaxies in the observable universe that are too far away to be detected? Yes and no. By definition, all the objects in the observable universe can be detected. However, the observable universe does not encompass the entire universe (we think!), and so there are probably many more galaxies out there. ...


1mol of protons is $6\times10^{23}$ particles. If proton decay has a half life of $6\times10^{33}$ years, then there should be one proton decaying per year per $10^{10}$mol. Since one mol of protons weighs one gram, that's a mere $10^7$kg of protons. Even at the density of liquid hydrogen (70kg/m$^3$), that's only $1.4\times10^6$m$^5$ of liquid volume. Take ...

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