Entropy in the Present and Early Universe and Vacuum Energy

It is demonstrated that entropy and its density play a significant role in solving the problem of the vacuum energy density (cosmological constant) in the Universe and hence the dark energy problem. Taking this in mind, two most popular models for dark energy - Holographic Dark Energy Model and Agegraphic Dark Energy Model - are analyzed. It is shown that the fundamental quantities in the first of these models may be expressed in terms of a new small parameter. Besides, the results obtained on the uncertainty relation of the pair 'cosmological constant - volume of space-time', where the cosmological constant is a dynamic quantity, are reconsidered and generalized up to the Generalized Uncertainty Relation (GUP).