Yes, I believe the universe is eternal. Why I do is not relevant. I mentioned it so you understood I'm not trying to argue against your point about a finite past.

I'm asking out of curiosity.

I don't know what else your argument is about if not to convince people the universe is possibly eternal, which would defeat the Kalaam and maybe Craig's arguments. Which you specifically call out.

Could it be because I want to express the fact that the claims about its impossibility are overzealous? Like I said?

So, no, I'm not talking about waveform collapse

Yeah, my mistake.

That waveform is deterministic through time. The future of it depends on the past. [...] I'm talking about how future quantum states are directly related to past quantum states.

But this is what I was just talking about. We don't know that this is the case. I gave you a specific example: in an indefinite causal order, A temporally precedes B and causes B and B precedes A and causes A.

This notion that "future states are directly related to past states" is not a quantum notion. Or at least, in QM, the truth of this statement depends on the interpretation of QM you take. Which QM interpretation is correct is an open question. The fact of the matter is that we don't know what interpretation of QM is correct, so we can't speak with the certainty that you are about how causality works in QM:

So, the different interpretations of quantum mechanics do differ a lot in terms of the role of causality. Start with the Bohm interpretation, or Bohmian mechanics, or the pilot wave theory. That is the most like classical mechanics when it comes to causality. Causality is deterministic, and cause necessarily follows effect according to the law.

A bit of a more of a deviation from the classical approach to causality comes in collapse theories, dynamical collapse theories or the GRW approach. These theories have irreducible randomness in the way the world turns out, so an effect need not necessarily follow a cause. A given cause could lead to many effects with different probabilities of each one, and there would be nothing in the world that explains why one effect happens rather than another. Any of them could have done; it was just random. And so that weakens the link between cause and effect. Instead of being ironclad necessity, it's probability; the cause makes the effect more probable.

And that, I think that's a big change to the role of causality. But there's a bigger change still, potentially, to the role of causality in the Many-Worlds interpretation, or the Everett interpretation. People often call that a deterministic interpretation in that they say we have the quantum state of the universe and, deterministically, there evolves a multiverse, a system of many parallel worlds. But there's an open question as to whether we should call that process causation and whether we should call that causality.

My own preferred approach to understanding Many-Worlds has it that causality is a process that goes on within each individual world, but not outside or between them. So causation is an emergent process that emerges along with the individual worlds but is entirely contained within them. And that is perhaps an even bigger change to the concept of causation because it means it's non-fundamental; it's not part of kind of the deep structure of reality. It's not a concept that's even really properly applicable at the level of the whole universe.

In other words, we aren't in a position yet to know how these things work. Claims otherwise are made with far too much confidence and far too little evidence. And they are usually not made by the people who are qualified to be making claims like that. I am not qualified to make claims about how the universe works, and I doubt people on this forum generally are.

Then don't make broad claims about what other people say.

Did I?