December 23, 2019 0

Can we Predict Everything?

In our everyday world, we’re used to absolute,
deterministic predictions: throw a ball in the air, and it’ll fall along an ellipse;
leave your umbrella parked on the street, and when you come back, it’s still there,
just one umbrella. Quantum physics is not like this – because
quantum mechanics doesn’t allow us to make absolute predictions about the future. It
only predicts the likelihoods of different outcomes to happen, and doesn’t say anything
about which one will happen. “Well,” you might say, “that’s the same with the weather – the
weatherman only tells you what the chance of rain is; he can’t tell you whether or not
it will rain.” But maybe the weatherman just doesn’t have
good enough knowledge of exactly where all of the air and water molecules in the world
are, nor a good enough model of how they interact or a fast enough computer to simulate all
of their bajillion interactions. Maybe in principle, if he had enough data and a fast
enough computer, his weather model could tell you exactly where every raindrop would fall.
Right? This reasonable idea, that if you just had more data you could explain everything,
is the classical, deterministic view of the universe. And for a while, many physicists, including
Einstein, thought the same had to be true with quantum mechanics – maybe we just didn’t
have enough information to put into our quantum models; maybe there were classical variables
that were hidden from us and our experiments, inputs that explained everything perfectly
with no need for quantum mechanics and its “I’ll give you 50/50 odds on the cat being
dead” mentality. Except, it turns out that we can actually
test whether or not this sort of classical, underlying explanation of quantum physics
can exist even in principle. The details are a topic for another video, but the experiments
tell us… there is no classical, everyday, underlying description of quantum mechanics. And this means, Einstein, that the universe
is quantum mechanical whether you like it with a 50% chance, or not. ps, I’m excited to announce that MinutePhysics
is now supported by MinutePhysics t-shirts. Get yours now at and
don’t forget to be awesome.

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