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By relaxing the constraint of adiabatic universe used in most cosmological models, we have shown that the new approach provides a better fit to the supernovae Ia redshift data with a single parameter, the Hubble constant H0, than the standard ΛCDM model with two parameters, H0 and the cosmological constant Λ related density, ΩΛ. The new approach is compliant with the cosmological principle. It yields the H0 = 68.28 (±0.53) km s−1 Mpc−1 with an analytical value of the deceleration parameter q0 = −0.4. The analysis presented is for a matter-only, flat universe. The cosmological constant Λ may thus be considered as a manifestation of a nonadiabatic universe that is treated as an adiabatic universe.