Cosmological Constant - the Weight of the Vacuum

Recent cosmological observations suggest the existence of a positive cosmological constant $\\Lambda$ with the magnitude $\\Lambda(G\\hbar/c^3) \\approx 10^{-123}$. This review discusses several aspects of the cosmological constant both from the cosmological (sections 1-6) and field theoretical (sections 7-11) perspectives. The first section introduces the key issues related to cosmological constant and provides a brief historical overview. This is followed by a summary of the kinematics and dynamics of the standard Friedmann model of the universe paying special attention to features involving the cosmological constant. Section 3 reviews the observational evidence for cosmological constant, especially the…