Michel Haar, referring to Heidegger's catastrophic prediction in "Overcoming Metaphysics", writes:
In this extreme hypothesis, the other history would effectively be chronologically posterior. Most of the texts leave one to think that, on the contrary, the other history would be a secret history, parallel to that of the technical world which would follow its path without one being able to assign to it visible external events. This would be the secret history of the Ereignis that is rather outside of history, non-historical, or in any case outside of the epoch. The Ereignis is this event of thought by which such an elementary constatation appears as a momentary glimpse that humankind belongs to Being and Being belongs to humankind, that there is a coappropriation which is older than history and rules over all of its phases. It appears that the emergence of the Ereignis and of the new beginning depend on our own initiative, or at least in the texts of 1936-38 they arise out of a human decision: "We are standing before the decision between the end (and its running out, which may still take centuries) and another beginning, one which can only be a moment, but whose preparation requires the patience 'optimists' are no more capable of than 'pessimists.'
The essential term in this passage, a moment, belongs to the vocabulary of Being and Time where the moment (Augenblick) is, in contrast to a given now, the moment of the resolute decision where temporality, reassembled into a project, both anticipates the extreme finitude of the future and takes up again the constancy of a possible past. A decision is possible only if we are authentically open to an extreme future and capable of repeating an essential past. Here the essential past is the first beginning, that of the greeks. We must, says Heidegger, appropriate it for ourselves to put it behind ourselves, and prepare for the second beginning.
P. 161