The paper proposes a model for holographic dark energy, suggesting that the short-distance cutoff is related to the infrared cutoff, specifically the size of the event horizon. The author, Miao Li, from the Institute of Theoretical Physics and the Interdisciplinary Center of Theoretical Studies at Academia Sinica, predicts that the equation of state of dark energy at the present time, given the cosmological constant ΩΛ = 0.73, should be characterized by w = −0.90. The cosmic coincidence problem can be resolved by inflation in this scenario, provided a minimal number of e-folds is assumed. The model addresses the cosmological constant problem, which has received significant attention due to observational evidence of a non-vanishing value. The author discusses the work of A. Cohen and collaborators, who suggested that a short-distance cutoff in quantum field theory is related to a long-distance cutoff due to the formation of black holes. However, this approach does not yield the correct equation of state for dark energy. To address this, the author proposes using the particle horizon or the future event horizon as the infrared cutoff. The future event horizon, defined as the boundary of the volume a fixed observer can eventually observe, is used to derive the dark energy density and its equation of state. The model predicts that the dark energy density scales with the universe's scale factor as \( \rho_\Lambda \propto a^{-2(1 + \frac{1}{c})} \), where \( c \) is a constant. For \( c = 1 \), the dark energy density approaches a constant in the far future, and the equation of state is \( w = -\frac{1}{3} - \frac{2}{3c} \). The author also discusses the causality issue associated with the event horizon and the connection between the Gibbons-Hawking entropy and holographic dark energy. The model is shown to be consistent with the standard big bang theory and does not affect the standard slow-roll inflation scenario. The cosmic coincidence problem can be resolved by assuming a minimal number of e-folds during inflation, which helps explain the current value of the dark energy density. In conclusion, the holographic dark energy model, with the infrared cutoff set by the event horizon, is viable and makes falsifiable predictions about the equation of state of dark energy.The paper proposes a model for holographic dark energy, suggesting that the short-distance cutoff is related to the infrared cutoff, specifically the size of the event horizon. The author, Miao Li, from the Institute of Theoretical Physics and the Interdisciplinary Center of Theoretical Studies at Academia Sinica, predicts that the equation of state of dark energy at the present time, given the cosmological constant ΩΛ = 0.73, should be characterized by w = −0.90. The cosmic coincidence problem can be resolved by inflation in this scenario, provided a minimal number of e-folds is assumed. The model addresses the cosmological constant problem, which has received significant attention due to observational evidence of a non-vanishing value. The author discusses the work of A. Cohen and collaborators, who suggested that a short-distance cutoff in quantum field theory is related to a long-distance cutoff due to the formation of black holes. However, this approach does not yield the correct equation of state for dark energy. To address this, the author proposes using the particle horizon or the future event horizon as the infrared cutoff. The future event horizon, defined as the boundary of the volume a fixed observer can eventually observe, is used to derive the dark energy density and its equation of state. The model predicts that the dark energy density scales with the universe's scale factor as \( \rho_\Lambda \propto a^{-2(1 + \frac{1}{c})} \), where \( c \) is a constant. For \( c = 1 \), the dark energy density approaches a constant in the far future, and the equation of state is \( w = -\frac{1}{3} - \frac{2}{3c} \). The author also discusses the causality issue associated with the event horizon and the connection between the Gibbons-Hawking entropy and holographic dark energy. The model is shown to be consistent with the standard big bang theory and does not affect the standard slow-roll inflation scenario. The cosmic coincidence problem can be resolved by assuming a minimal number of e-folds during inflation, which helps explain the current value of the dark energy density. In conclusion, the holographic dark energy model, with the infrared cutoff set by the event horizon, is viable and makes falsifiable predictions about the equation of state of dark energy.