Cardy-Verlinde formula and holographic dark energy

If we separate energy in a holographic theory into an extensive part and an intrinsic part, where the extensive part is given by the cosmological constant, and assume entropy be given by the Gibbons-Hawking formula, the Cardy-Verlinde formula then implies an intrinsic part which agrees with a term recently proposed by Hsu and Zee. Moreover, the cosmological constant so derived is in the form of the holographic dark energy, and the coefficient is just the one proposed recently by Li. If we replace the entropy by the so-called Hubble bound, we show that the Cardy-Verlinde formula is the same as the Friedmann equation in which the intrinsic energy is always dark energy. We work in an arbitrary dimension. (C) 2004 Elsevier B.V. All rights reserved.