Is QM Deterministic in MWI and Time Reversible?

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    Determinism Mwi Qm
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Discussion Overview

The discussion explores the nature of quantum mechanics (QM) regarding its causal structure, determinism, and time reversibility, particularly in the context of the Many-Worlds Interpretation (MWI). Participants examine whether QM can be considered deterministic and how time reversibility relates to causality within various interpretations of quantum theory.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • Some participants question whether QM is causal and time reversible, suggesting that these concepts may not be directly related.
  • One participant asserts that quantum mechanics is causal but indeterministic, citing empirical evidence against time-reversal invariance in weak interactions.
  • Another participant argues that the interpretation of QM affects its classification as deterministic, noting that MWI is deterministic.
  • Several contributions emphasize that definitions of causality and determinism vary, with some suggesting that causality in QM could imply retrocausality.
  • Discussions include the idea that causality may be defined in terms of local time dependence, while others argue that causality is a broader principle that applies to all physical theories.
  • Participants discuss the implications of quantum gravity on determinism, with some suggesting that the lack of a complete theory may lead to stochastic descriptions of open systems.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the nature of causality, determinism, and time reversibility in QM. There is no consensus on whether QM is fundamentally deterministic or causal, and the discussion remains unresolved.

Contextual Notes

Limitations in the discussion include varying definitions of key terms such as causality and determinism, as well as the unresolved status of quantum gravity and its implications for the fundamental nature of quantum mechanics.

  • #31
vanhees71 said:
to find a consistent description of all phenomena (including a quantum description of gravity)
How could this ever be done without treating the universe as a quantum system?
 
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  • #32
We have a classical model of the universe without having ever observed it as a whole. There's also some philosophical debate, whether cosmology is really science since it assumes the Copernican principle without being ever able to test this hypothesis by observation or at least only to a certain extent.

That's why it is so complicated to get a clue about the quantum theory of gravitation: To get an idea, how to describe it, I think we'd need some phenomena related to it, and such phenomena are available to us only in a quite small piece of the universe, i.e., sufficiently close to us. Maybe we need strong gravitational fields to see deviations from classical behavior like better and better observations of black holes in our and other galaxies. Who knows?
 
  • #33
vanhees71 said:
We have a classical model of the universe without having ever observed it as a whole.
Therefore we can also expect to work successfully with a quantum model of the universe without having ever observed it as a whole. The thermal interpretation gives it a workable interpretation without weird, counterintuitive features.
 
  • #34
You are always referring to the "universe as a whole" not I ;-)).
 
  • #35
vanhees71 said:
You are always referring to the "universe as a whole" not I ;-)).
Sure, we can model the universe as a whole without having observed the whole universe.

We also model a univariate function as a whole already when we observed it only at a fairly small number of points. Otherwise we couldn't use the concept of a function in physics. Modeling an infinitely extended universe is not really different in principle from modeling an infinitely extended function.
 

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