How is energy density calculated

[jimjohnson]

I understand how the Planck length (1.6 x E-33 cm) is calculated from the equation ,Gh/( 2πc3), but how is the Planck density calculated at E-5 gm/Planck volume (E93 to E94 gm/cm3). It is based on "energy jitters".
Also, is there an explanation for the vast difference between the observed cosmological constant (E-29 gm/cm3) and calculated value, a difference of E123? Thanks

 

[marcus]

the best discussion I have seen so far of the cosmological constant issue is this essay by a couple of quantum relativists.
Lambda naturally occurs as a curvature constant in the Einstein GR equation.
There is no reason to connect it with the gross QFT miscalculation of the vacuum energy density.

http://arxiv.org/abs/1002.3966
Why all these prejudices against a constant?
Eugenio Bianchi, Carlo Rovelli
(Submitted on 21 Feb 2010)
The expansion of the observed universe appears to be accelerating. A simple explanation of this phenomenon is provided by the non-vanishing of the cosmological constant in the Einstein equations. Arguments are commonly presented to the effect that this simple explanation is not viable or not sufficient, and therefore we are facing the "great mystery" of the "nature of a dark energy". We argue that these arguments are unconvincing, or ill-founded.
9 pages, 4 figures

 

[jimjohnson]

Great reference, who would think that this profound mystery (E120 difference)is "nonsense".
Also, I did find the equation for density in a sepatare reference, Density = c5/(h x G2). Thanks for your help.