Is The Future Predetermined By Quantum Mechanics?

**SPEAKER_1** (0:00)
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**SPEAKER_2** (0:30)
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**Matt O'Dowd** (1:00)
Einstein's special theory of relativity combines space and time into one dynamic unified entity, space time. But if time is connected to space, can the universe be anything but deterministic? And does that mean that the future is predestined?
In the last episode, we saw that we could think of the unified space-time in terms of the block universe. An atemporal entity that sort of just exists. In a block universe of Einstein's relativity, there's no way to cleanly define the present, and so no way to cleanly separate the future from the past. The notion of the present is relative. To us, it looks like a particular slice through the block universe. But different observers will slice the block at different angles that depend on their velocities. That means that for every observer it's possible to imagine another observer who lives in their definition of the present, but for whom your future is already the past, or for whom your past is their future.
But how does this give us a deterministic universe? If we accept a unique reality for those other observers in our present, and we accept that their perception of the present is as valid as ours, then all of the future is defined. That seems to support the philosophical stance of eternalism. The idea that all space and time exist from a sort of god's eye view from outside of both space and time. And it suggests a deterministic universe where every slice through the block universe is completely determined by every other slice, either behind it or ahead of it. They are connected by the unalterable laws of physics. So here's the big question. Given that relativity is definitely a good description of space and time, what would it take for our future to remain undefined?
It seems we have two options. Either the entire block universe is defined past, present and future, or everything outside our past light cone is undefined, including other observers and the room around you in what you would normally think of as the present, and the only aspect of the present that exists is a vanishingly small patch of space-time around your own brain. In order to even try addressing which of these options is right, we need to take into account something we've totally ignored so far.
Where relativity is the key to understanding the universe of the large and the very fast, we also need to understand the universe of the very tiny. We need to see what quantum mechanics says about determinism and how it plays with relativity and the block universe. According to quantum mechanics, physical systems, parts of the universe, evolve as wavefunctions, not as well-defined reality, but rather as distributions of probability that describe all possible states that.

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