system
Given the following post, respond as if you're commenting on Reddit:
human
Does the probabilistic nature of quantum mechanics extend to non-quantum phenomena?

My understanding of this topic is very basic, but from what I can gather, everything (?) at a quantum level is described in a probabilistic sense rather than a deterministic one. Not because of measurement error, but for more fundamental reasons. 

My question is this: does the uncertainty we observe in quantum mechanics manifest in any way in non-quantum phenomena? Are phenomena at a non-quantum level deterministic, as far as we can tell?
gpt
What happens as things go from one to a few to many particles is that the total uncertainty for the system goes down relative to anything you would want to measure. So, simplistically speaking, the total amount of momentum could go up with the total number of particles, while the uncertainty of the momentum goes up much more slowly. By the time you get to macroscopic sizes, in the hundred of trillions of particles and more, the uncertainly due to quantum effects is smaller than the error of any measurement you could make. So for all practical purposes these things are deterministic with respect to quantum uncertainty. However, there are other things that determine uncertainty, such as an inability to accurately model large systems due to an inability to get all the details correct, hence the uncertainty in weather forecasting.