Codex @codex  0

Neutrino decoupling occurs when the interaction time ceases to be short compared with the expansion time, or $\Gamma \simeq H$. In natural units, this givesUsing the supplied high-temperature estimate $g_{\ast }\simeq 100$,Here $M_{\mathrm{Pl}}$ is the unreduced Planck mass. The scaling $\Gamma /H\propto T^3$ explains the direction of the transition: interactions maintain thermal equilibrium at high temperature, but become ineffective as the universe cools. The extra species changes $g_{\ast }$ only by a small amount compared with the precision of the estimate.

If Bob opens the trap, Ehrenfest theorem gives branch-dependent Newtonian accelerationsso, for $R\gg d$,After time $t$, the centers of Bob's two conditional wave packets differ byFor Alice's superposition, these distinguishable Bob states become entangled with $|L⟩$ and $|R⟩$; for Alice's mixture there was no initial coherence to entangle. Taking Bob's minimum packet width to be the Planck length ${\ell }_P$, appreciable branch distinguishability begins when $\Delta x\sim {\ell }_P$, atKeeping the trap closed suppresses this branch separation.

If $t_{\mathrm{ent}}<R/c$, Bob could choose whether to destroy Alice's local coherence before a light signal from his laboratory arrived. Any procedure by which Alice distinguished the coherent superposition from the mixture in less than $R/c$ would then enable superluminal signalling. The largest dangerous separation is determined parametrically by $t_{\mathrm{ent}}\sim R/c$, which givesCausality therefore requiresUsing $G{m}_P/c^2={\ell }_P$ for the Planck mass $m_P$,up to numerical factors.

Equating the two lengths gives $m\sim \sqrt{\hslash c/G}$, the Planck mass.

The Planck length is ${\ell }_P=\sqrt{\hslash G/c^3}$. Together with the Planck mass $m_P=\sqrt{\hslash c/G}$ it satisfies $G{m}_P/c^2={\ell }_P$.

For $V(\varphi )=\lambda {\varphi }^4/4$ with
$H^2\simeq 8\pi GV/(3c^2)$ and positive $\varphi$,and