# What does electroweak vacuum lifetime refer to?

I just read an article about the correlation between the Higgs boson mass and the stability (or metastability) of vacuum, so I want to ask to someone this:

When someone is talking about the electroweak vacuum lifetime, does it refer to a certain region of space, the time needed for quantum tunnelling to occur once in the whole vacuum, the lifetime of the entire vacuum or something else?

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In the real Universe, the volume where a dangerous decay may start is proportional to $c^3\tau^3$ where $\tau$ is the lifetime. So if the probability of the nucleation of a "bubble of the new vacuum" is $$\gamma=\frac{dP}{d\Omega} = \frac{dP}{dt\cdot dV}$$ per unit spacetime four-volume, I believe that by the lifetime, people just mean $$\tau =\left({\gamma}{c^3}\right)^{-1/4}$$ up to number-one prefactors that are not specified and it's somewhat likely that the normalization is exactly as I wrote it. Note that $\gamma$ has units of ${\rm m}^{-3}{\rm s}^{-1}$ which gets converted to ${\rm s}^{-4}$ with the multiplication by $c^3$.