Does Eternity have a Beginning? Yes
“Thus the cosmological proof, which this apostrophe addressed and which we are concerned with here, actually consists in the assertion that the principle of reason of becoming, or the law of causality, necessarily leads to a thought by which the law itself will be abolished and declared null and void. For one attains the first cause (the absolute) only by ascending from consequent to ground, via a series as long as you please. But in this series one cannot stop without annulling the principle of reason.”
(Excerpt From: Arthur Schopenhauer. “On the Fourfold Root of the Principle of Sufficient Reason and Other Writings.” Apple Books.)
Thus Schopenhauer, the greatest philosopher since Plato, declares that the idea of an absolute, or a first uncaused cause, is impossible since it abolishes the very concept of the law of causality. It’s a similar argument used for Zeno’s paradox of the dichotomy, that if I keep traveling by half steps I will never reach my destination for there are infinite operations of half-steps. The similarity between the two paradoxes is that there is an interaction between infinity and finitude — an infinite chain of causes can not have a beginning just as an infinite number of half-step operations cannot have an end.
Except we know with certainty that Zeno’s paradox can be solved using calculus, or the infinite operator. Can we say the same thing about the causal chain? The causal chain can possibly have an infinite number of causes, but surely in the same way we can arbitrate where the beginning and end of a infinite sum are, we can do for the causal chain.
Moreover, Schopenhauer himself places the law of causality as a specific incarnation of the Principle of Sufficient Reason as it applies to objects within complex empirical reality, which is differentiated and isolated from transcendental objects separate from our ability to perceive or cognize them.
Back to the original question of does eternity have a beginning? Another word for eternity, is timelessness and spacelessness, an object which is beyond the two most fundamental conceptions imaginable. Anything which belongs in this realm will by definition be eternal.
Now what can we compare this to? Imagine a programmer who is making a video game. He sets up variables which will govern the laws of space and time within his world. The variables themselves are real, but beyond space and time itself of that very world. Thus he has made something eternal, at a specific point in time. In other words, eternity is only contingently eternal, or there is an illusion around eternity, that that which is eternal was once a temporal thing, and so it applies to everything. Everything has its beginning within creations, only the Lord is eternal without beginning and without end.
There are levels to eternity, to timelessness, just as there are infinity of infinities.