On the claim of the "eternal now" as the only existing time, as opposed to the past or the future, I opine:
True: The past is gone and the future is yet to be, so the only living‒and malleable‒time is contained within the present. And yet, what was, is; what is, will be. The present is (was) built upon the past and the future is (being) built upon the present. What was has led here and here is whence what follows stems. Each moment, however alive, passes quickly, merging with the past, a time that once was and used to be the "now". What is now is a remnant of what was and a vision of what will be. Yesterday is a now in retrospect, tomorrow is a now in prospect. Thus, the now is not only now ‒ spanning over past and future times in constant parallels, the only time known to man to be alive, it lies in eternity.