Usually arguments like those tend to draw on recent development in physics, especially those dealing with quantum mechanics. The most basic argument is that Determinsim's foundation rests in Newtonian physics, ergo it is no longer an accurate stance.
Most lose sight of the fact that Determinism is not solely based on Newtonian physics, but on the idea that absolute principles exist which guide all natural events. This does not preclude the idea of "apparent randomness" or causation on a scale too small or remote to be directly observed. Part of the soundness of Determinism is that it has roots in basic science and common sense; all explanations in science rely on causation which in turn implies Determinism. Even Hume admitted that causation cannot be directly observed on a macroscopic level but only implied through actions between entities, yet it seemed to be the most logical explanation based on the available evidence.
Quantum particles behave in ways which are inconsistent with objects more easily observed by the human eye, yet their seemingly erratic behavior does not preclude causation. It merely challenges our current understanding of it. Even Bell was not certain that Determinism had been avoided because of his understanding of quantum physics, being unable to completely rule out the loophole of superdeterminism.
Hmm, so let's say, in the case of parallel timelines, could quantum indeterminancy be used as a justification for variations between the different timelines? Like say, if events don't necessarily occur in a causal manner but sometimes in a random manner, than if events were to start from point zero and be repeated in every single parallel timeline, then given the random nature of it they don't necessarily have to proceed into the same set of events in each timeline, accounting for variations?
So in other words randomness begets randomness?
The idea behind quantum indeterminancy as I understand it is that causation at quantum level simply does not exist and that this in turn has an impact on macroscopic events. The problem with this is that it implies a certain absolute knowledge of quantum events, which is improbable. It is highly unlikely that we already possess the range of knowledge and capability to observe all that determines things at a quantum level. Or to put that another way, saying that an apparent lack of the quantum physics equivalent of a pool stick to a cueball doesn't preclude the former's existence.
Because the limit of human perception is just that - limited, it's difficult to show true lack of causation when it appears to be everywhere in life, and is the very foundation of how we explain things as well. No one would ever argue that because bacteria was unable to be detected in the early centuries, it did not exist as a causal factor in sickness and disease nor would anyone argue that data is not existant on a hard drive simply because no computer is present to read it.
The bottom line is that quantum indeterminancy is a theory based on an apparent lack of evidence as opposed to a sound showing of determinist failing. It's no better than pure atheism's answer to religion.
