# Tag Info

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All we can do precisely is give a probability for some physical quantity to have its observed value. For example (subject to various assumptions!) the probability of the cosmological constant having it's observed value is around 1 in $10^{120}$. Since this is absurdly low we say it's fine tuned. But where you draw the line between fine tuned and not fined ...

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The argument for fine tuning is far broader than just the Higgs. For example it's argued that the existance of any elements heavier than lithium relies on a fine tuned resonance in the carbon 12 nuclues that allows three helium nuclei to stay together long enough to form a carbon nucleus. There are lots of books that explore these ideas. A good start would ...

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The hierarchy problem is not only about big numbers, such as $M_{pl}/M_{EW}$, per se'. In fact in QCD there is no hierarchy problem associated to the ratio $M_{pl}/\Lambda_{QCD}$. The problem is actually about the quantum numbers of certain operators in a Wilsonian EFT. The point is that we understand the SM as an effective low-energy description of the ...

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It's the same problem because the low scale matches in both definitions; and the high scale matches in both definitions, too. Both problems are the puzzle why the two scales are so much different. First, the low scale. In the Higgs fine-tuning, you define the low scale as the Higgs mass. But the Higgs mass can't be parameterically greater than the Z-boson ...

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To me, it seems like there are 3 different concepts being discussed: (1) fine-tuning, (2) wanting unitless constants to be of order unity, and (3) wanting theories to have a simple form. The WP link defines "naturalness" as #2, although I don't think that's universally understood. A very old example of #3 would be the history of models of the solar system, ...

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1) The cosmological constant in the context of quantum field theory is a set of calculations and leads to a sum that will look something schematically like this cc = 3-5+22-120+3042-50242+... +O(M^4) where M is some heavy mass scale The problem is we don't know the exact numbers in the sum, we can only calculate a few of them and the best we can do is ...

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Analogously to the use of SU(2) instantons for describing tunelling between topologically distinct vacuum sectors, I've heard people talk about gravitational instantons as describing a tunneling process connecting "nothing" with an expanding Minkowski signature universe. People talk heuristically of a universe having emerged by tunnelling from "nothing". ...

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