Unruh Effect

When an accelerating detector moves through empty space it will detect a gas of particle with a temperature linear in the acceleration. The acceleration can be easily estimated from dimensional analysis. Since this is a quantum effect, the relevant constants are Planck's constant $h$ and the speed of light $c$. In order to convert energy to temperature we also need the Boltzmann constant $k$. The relation between the acceleration $a$ and the temperature $T\,$ is, up to a numerical constant,

$k T = h \frac{a}{c}$

The acceleration that corresponds to 1 kelvin is 6e18 m/s^2