[colordrops]

Quantum mechanics demonstrating non-determinism in the realm of the very small necessarily means that the macroscopic realm is also non-deterministic. A non-zero percentage of events occur in which that one particle appearing in one place rather than an is just enough to cause the macroscopic object to take a materially different path. In fact a simple thought experiment shows that a system could be engineered to demonstrate this. Add a sensor that reads which way a particle goes in a double slit experiment and based on the direction, flip a switch that makes a train go east or west based on the sensor read out.

[eridius]

Adding a sensor to the double slit experiment to measure which slit the particle goes through removes the quantum effects from the experiment.

[colordrops]

Not sure what you mean. Quantum effects don't "disappear". They are physical laws. Which slit the particle enters after the wave decoheres is precisely a non-deterministic element of quantum mechanics.

[bouncycastle]

But wouldn't measuring something also alter the outcome? Ie. Observer Effect https://en.m.wikipedia.org/wiki/Observer_effect_(physics)

[colordrops]

It doesn't alter the outcome. It causes it to decohere into a particular outcome. There is no way to force a particular outcome, hence it being non-deterministic.