Background = Most Pervasive = Resonnace

This is the resonance of the electromagnetic dipole not of free space

The cosmic microwave background radiation spectrum peaks at 160.2 GHz, corresponding to a wavelength of 1.9 mm.  If we model space as light springs, then we can expect this frequency to be the resonance frequency of free space.  It is at this frequency that radiation losses are less and so will exhibit as a peak in the spectrum.  The resonance frequency formula,

${ f }_{ res }=\cfrac { 1 }{ 2\pi  } \sqrt { \cfrac { k }{ { m } }  }$

is still valid if we redefine m as ${ \Delta m }$ a small mass element of space.

${ f }_{ res }=\cfrac { 1 }{ 2\pi  } \sqrt { \cfrac { k }{ { \Delta m } }  }$

from which we refine to

${ f }_{ res }=\cfrac { 1 }{ 2\pi  } \sqrt { { k }_{ space } }$  and

${ k }_{ space }={ (2\pi { f }_{ res }) }^{ 2 }$

where  ${ k }_{ space }$ is defined as spring constant per unit mass
${ k }_{ space }=1.0131757\times { 10 }^{ 24 }{ s }^{ -2 }$

$K_space$ is still valid but it is of the dipole that carries electromagnetic waves.