We report evidence from broadband dielectric spectroscopy that the dynamics of the primary α- and secondary Johari−Goldstein (JG) β-processes are strongly correlated in different glass-forming systems over a wide temperature T and pressure P range, in contrast with the widespread opinion of statistical independence of these processes. The α−β mutual dependence is quantitatively confirmed by (a) the overall superposition of spectra measured at different T−P combinations but with an invariant α-relaxation time; (b) the contemporary scaling of the isothermal-pressure and isobaric-temperature dependences of the α-and β-relaxation times as plotted versus the reduced variable Tg(P)/T where Tg is the glass transition temperature. These novel and model-independent evidences indicate the relevance of the JG relaxation phenomenon in glass transition, often overlooked by most current theories.

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