If you knew the quantum state of every particle in the universe, could you predict the future arbitrarily far out? - by Viktor T. Toth - Quora Question Review

This document contains a review of the answer by Viktor T. Toth on the question in Quora: "If you knew the quantum state of every particle in the universe, could you predict the future arbitrarily far out?"
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• The text in italics is copied from the article.
  
• Immediate followed by some comments
  

Contents

• 1. Answer Review

Reflection

• Reflection 1 - Question Review

1. Answer Review

If you had access to that information then yes, you would be able to predict the future quantum state of the universe.

The reality is you cann't know the position of all the particles in the world simultaneous. That means you can not calculate the positions of all these particle simulataneous for any specific moment.

The quantum theory itself is deterministic.

What does that mean?
Any way if you call the universe either deterministic or inderterministic, it does not help to answer the raised issue if you can predict the future positions. This is not possible. Anyway if you still do that your predictions can not be validated.

In particular, if this universe was a simulation, it could run on a deterministic computer with no random number generator, and the being(s) running the simulation could repeat the experiment, always getting the same results given the same initial conditions.

It is correct if you repeat a simulation of our solar system, using a set of initial conditions, and this simulation does not use any random number generator, you will always get the same results. But this has nothing to do with the actual evaluation of the movement of the planets.

But we do not live “outside” this universe, with full access to its quantum state.

What does that mean.

We are in this universe, and when we create models of things in this universe, we rely on measurement, which does not capture the full quantum state of the measured system.

It is impossible to measure the quantum state, specific you cannot measure the position of elementary particles.

Not to mention that we then predict not so much the quantum state of the system (which cannot be verified), but the result of future measurements of it.

Not clear.

The act of measurement confines the quantum system to an “eigenstate”, but with the information available to us, we can only predict probabilities of various outcomes.

You can calculate probabilities of positions of elementary particles, but these positions cannot be validated.

Well, this is the canonical theory anyway. In this view, the act of measurement, “wavefunction collapse”, is just a mathematical artifact, a simplification or approximation if you wish.

Don't use concepts like "wavefunction collapse", because it introduces uncertainties.

There are, however, alternative interpretations that treat wavefunction collapse as a physical process (“objective collapse”).

Please explain.

These theories are nondeterministic: if our universe works this way and it turns out to be a simulation, the computer doing the simulating would have to rely on a source of true random numbers (not just a pseudorandom generator, which is still deterministic) to mimic this behavior.

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