My postulation that identical Universes will evolve differently has engendered some discussion, most of which disagrees with my answer. I want to highlight two points of contention. The first concerns the distinction between outcomes and their predictability. Marcus Geduld writes:
You rephrased the question as “What you are asking is if you take an infinite number of Universes all starting from exactly the same initial condition, will they all evolve in identical ways?” And you answered no.
Why not? How can you be so sure?
I feel like there was a very subtle slippage in meaning in your (otherwise) fantastic answer. I see this same slippage a lot, in Scientific and Philosophical discussions, so it’s very possible (likely) that I’m the one who is slipping. But I’ll go ahead and explain my objection, anyway.
There’s a difference between what we can predict and what winds up happening. I agree we can’t make PREDICTIONS about whether universe A will behave identically with universe B, given the same initial conditions”¦event X at time 
A second contributor, Andre Parsa, tells me I’m flat out wrong. He answers the question of whether the future of all particles was set after the Big Bang by writing:
Yes. The result or apparent behavior of a system is the sum of its past. This comes out of several points including:
- A system in physics, in the broadest sense of the term is the sum of states of its parts, and whatever rules govern those parts. Basically all matter, in the specific states of energy each individual smallest part is in and whatever rules govern all possible interaction this smallest part may have with other parts in the system.
- The issue of “quantum mechanical uncertainty” has nothing to do with this. The “uncertainty” of the concept is that we are unable to obtain absolute knowledge of particles in a quantum system (at the quantum level), in other words, to know in what state the particle is in. But each particle does have its own absolute state, a position and velocity etc. The mistake in using it here is that concept only explains that humans cannot measure these values because we affect them when we do, if we leave the particle alone, it has an actual and concrete state. Radiation may be released at rather random points in time from a mass, but is released at a concrete time nonetheless. Radioactivity is not random it only difficult to measure this is a concept chemists understand not physicists.
To me, the first critique can be answered with a clarification while the second assumes a philosophy I don’t believe best fits the data physicists currently possess. In future posts I will use our knowledge of the weird and wacky quantum mechanical wavefunction to justify my answer of “No, the Universe’s future is not locked in stone.”
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