Does stable mean that an isotope has a very long half life, for example xenon-124 has a half life of 1.8 x 10^22 years, or does it mean that fissure is theoretically not possible, or does it mean that the isotope has a very long half life, but the exact number is unknown?

Say I have a Lagrangian density with kinetic term $\mathcal{L}_{kin} = \phi \Box \phi$. To derive the equations of motion, I could integrate by parts to obtain $\mathcal{L}_{kin}' = - (\partial_{\mu}\phi)(\partial_{\mu}\phi)$, then apply the Euler-Lagrange equations to obtain $2\Box\phi=0$. (Corr...

I've recently started reading the book Biocentrism, by Robert Lanza and Bob Berman, which in its mind-blowing chapters, discusses the perceptions of reality, space, and time. Lanza states that: If one could travel at lightspeed, one would find oneself everywhere in the universe at once. This ind...

Suppose that we are dealing with the following matrix: $$A=\begin{bmatrix}a_{00} & a_{01} \\ a_{10} & a_{11}\end{bmatrix}$$ but I don't want to use matrix notation, insted I want to use tensor notation, so I write this matrix as: $$A^{\mu}_{\nu}$$ Question is: $A^0_1$ is equal to $a_{01}$ or $a_{...