The concept of eternal life (whether qualitative or quantitative) is one based on a simple maxim – that what we see, hear, feel and touch here is not all that there is. The very idea defies proof or disproof because it is an allegation that there is more, that the dimension that we think we know such a lot about is only a tantalizing prelude to something else. The idea of “feasibility” therefore, belongs to this life – it is an inappropriate question here, precisely because eternity is, well, its something else.
So eternal life is feasible because it is not unfeasible. It is arguable because it simply does not belong to the concepts, laws and ideas that we feel we can prove or disprove. We are beginning to know what causes “finite-ness” and though we cannot fix it or stop the process of decay and death, it is becoming possible to at least imagine a universe or a dimension where those laws did not apply.
Feasibility is based on the application of known laws. Bridges are feasible, landing on Mars is feasible, and vaccines are feasible, because they obey laws that we can harness. Eternity simply does not bow down to any laws. God as the creator of all realities (plural) has created another reality that doesn’t bend to the rules we see. This is God, the one who always was, even before and beyond measurable time. Even modern physics is starting to grasp that idea.
The Christian belief is of “a new heaven and new earth”, of creation reborn (Revelation 21:1-4). This is a reality that is reborn according to new “rules” as Jesus’ resurrected body was remade. But we can never explain it, not here, not now. When God says, “my thoughts are not your thoughts” He means something very profound. This is saying that there is nothing whatsoever in all our exocrine or reason that can fully prepare us for Him. While we must use our brains and our reason, nothing is “unfeasible” for him (Matthew 19:26) because if it were, He would not be God at all.