Dark energy density is not back from the future Unruh advanced Wheeler-Feynman black body radiation

The black body radiation density ~ T^4

but T ~ /\^1/2

Therefore the Unruh radiation density back from our future cosmological horizon is Lp^2/\ too small compared to the actual dark energy density.

That is, the Unruh acceleration effect energy density is  hc/\^2 

The observed dark energy density is hcLp^-2/\

from Einstein's GR field equation

/\ ~ (G-string tension)^-1(vacuum energy density)

G-string tension = hc/Lp^2

where /\ = 1/(area of future horizon)