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For centuries, the absolute time introduced by Newton was the fundament of theories in physics.
Without it, the structure of classical physics could not have been erected[1], p. 9:
" The criticism towards the Newton time term by Mach, Poincarè and Einstein therefore is not directed against the conception as such, but against the fact that the absolute time, as a mere construction of thought, does not directly appear in any experience accessible to us. The absolute time cannot be defined directly by any experiment and therefore is without practical value for the substantial description of physical processes."
The practical value of the absolute Newton time, moreover, is its univocal definition of term and that it, therefore, can serve as a „system of reference“ for any other time scales.Without reference to the Newton time, e. g., the relativistic Einstein time could hardly be comprehended.
Ernst Mach already demanded  to use only those terms in physics which have an immediate empirical meaning. His judgement on the Newton time was [1], p. 18:
"This  absolute time cannot be measured at any movement, it therefore has no practical and also no scientifical value, nobody is entitled to claim to know anything about it, it is an idle, "metaphysical" term."
Naturally, we must require, a time term which, according to Machs imagination, is accessible to direct experience, must also be able to explain the phenomena of nature as comprehensively as the Newton time.
So far, it could obviously not be achieved to reconcile both these premises (possibility to verify experimentally  and comprehensive capability of explanation) [1], p. 9:
"The new definition of a time term that suffices these requirements led to considerable physical, methodical and philosophical problems, which, until now, also could not be solved satisfactorily.”
Although, in the past decades, many scientists have intensively expounded the essence of time (see literature index),
the time term rather seems to have become more obscure.
Paul Davies remarks to this [2], p. 11:
"The conventional presentation of the time leaves us helpless to a chaos of mysteries and contradictions. In my estimation, the Einstein time is not suitable to explain the universe and our imagination of it fully.." And [2], p. 18: „Could it be that the Einstein time and the cosmic time are not identical? Is the flexible Einstein time simply not flexible enough to reach back to creation?"
His  upshot  finally is [2], p. 34:
"The revolution introduced by Einstein remains incomplete. We are still waiting for a complete understanding of the essence of time.”
 

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