Does Quantum Mechanics Disprove Causality?

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Discussion Overview

The discussion revolves around the relationship between quantum mechanics (QM) and the principle of causality. Participants explore whether QM disproves traditional notions of causality, examining determinism in both QM and classical mechanics, and the implications of probabilistic outcomes in quantum systems.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Exploratory

Main Points Raised

  • Some participants argue that QM modifies the traditional causal relationship, suggesting that event A determines a range of possible outcomes (B or C) rather than a single outcome.
  • Others assert that QM can be deterministic in the sense that it provides a range of values that results must fall within, despite being probabilistic in nature.
  • There is a contention regarding the definitions of "deterministic" and "cause," with some participants questioning the implications of these terms in the context of QM.
  • Some participants express skepticism about the existence of causes for apparently random behavior in QM, suggesting that the search for explanations should continue despite the statistical nature of quantum phenomena.
  • One participant highlights the historical resistance to accepting the statistical behavior of QM and the ongoing quest for deeper explanations of its randomness.
  • There are references to different interpretations of QM, including deterministic models and the role of measurements, indicating a variety of perspectives on how to reconcile QM with causality.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether QM disproves causality or how determinism should be defined in the context of quantum phenomena. Multiple competing views remain regarding the nature of causality and determinism in QM.

Contextual Notes

Discussions include varying interpretations of determinism, the implications of probabilistic outcomes, and the challenges of reconciling QM with classical notions of causality. Some participants express confusion over the terminology and concepts being discussed.

MetricBrian
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One commonly hears that Quantum Mechanics refutes or disproves the principle of causality.

and yet if this were the case, qm could not be used to build highly precise machines such as lasers.

the truth is that qm makes of use of a modified causality.

the normal causal relation is that event A necessarily determines event B

in qm, this relaton gets modified such that: event A necessarily determines result B or C.

thus event A necessarliy determines the the result will fall within the specified range.

qm is determistic in this sense.
 
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yeah, I'm not sure it would be science if it didn't have some determinism in it.

On the other hand, it doesn't necissarily mean the universe is deterministic.
 
The OP is equivocating what we mean by "deterministic" and "cause".
 
Moridin said:
The OP is equivocating what we mean by "deterministic" and "cause".

what is the difference?
 
Quantum mechanics (QM) is a deterministic theory. Let's compare to classical mechanics (CM) which everyone agrees is deterministic.

The classical state of a system of n particles in 3 dimensions is a vector of length 2n that contains the 3d position and momentum coordinates of each of the particles. Classically, this is all the information that is possible to know about the system. If the state of the particle is known exactly at time t, then using any formulation of mechanics that is equivalent to Newton's 2nd law we can predict with certainty the classical state of the system at any given time.

The only difference is that in QM the state of even a single particle is given by an infinite-dimensional vector. The Schroedinger time-evolution of such a state is perfectly deterministic.
 
Moridin said:
The OP is equivocating what we mean by "deterministic" and "cause".




Main Entry: de·ter·min·ism
Pronunciation: \di-ˈtər-mə-ˌni-zəm, dē-\
Function: noun
Date: 1846
1 a: a theory or doctrine that acts of the will, occurrences in nature, or social or psychological phenomena are causally determined by preceding events or natural laws
 
So, determinism does not require precise measurements?
That's good, because there QM is unavoidably probabilistic.
I'm happy it can be both deterministic and probabilistic.
It let's me sleep at night.
 
gendou2 said:
So, determinism does not require precise measurements?
That's good, because there QM is unavoidably probabilistic.
I'm happy it can be both deterministic and probabilistic.
It let's me sleep at night.

Certainly QM is deterministic in so far as an event determines a range of values that must fall within definite bounds.

But even a purely determistic theory can have probable outcomes which would be the case where we didn't know enough about the system to predict with accuracy. In the determistic model this is commonly called a margin of error.

The critical question is this: why are the results statistical?

I can't understand why people are so sure the failure to discover a cause proves that causes exist.
 
MetricBrian said:
Certainly QM is deterministic in so far as an event determines a range of values that must fall within definite bounds.

But even a purely determistic theory can have probable outcomes which would be the case where we didn't know enough about the system to predict with accuracy. In the determistic model this is commonly called a margin of error.

The critical question is this: why are the results statistical?

I can't understand why people are so sure the failure to discover a cause proves that causes exist.

I strongly agree.
However, I cannot shake the curiosity that maybe there is an explanation for the apparent randomness of the QM world.
Einstein's god dice haunt me.
 
  • #10
gendou2 said:
I strongly agree.
However, I cannot shake the curiosity that maybe there is an explanation for the apparent randomness of the QM world.
Einstein's god dice haunt me.

I don't see why not. Why are people so sure that causes must not exist. I don't get it.
 
  • #11
MetricBrian said:
Why are people so sure that causes must [sic] exist? I don't get it.

Science attempts to explain how the world works.
There seem to be limits on what we can and can't explain.
It takes years of training to quickly distinguish between the two.
The lay-person sometimes demands that science to explain every detail in a way they can immediately understand.
When this cannot be done, the expectably common result is frustration and disbelief.
The goal of a science educator is to present the explanation of nature in a way that is congenial to the public.
This is a very hard job.
 
  • #12
gendou2 said:
Science attempts to explain how the world works.
There seem to be limits on what we can and can't explain.
It takes years of training to quickly distinguish between the two.
The lay-person sometimes demands that science to explain every detail in a way they can immediately understand.
When this cannot be done, the expectably common result is frustration and disbelief.
The goal of a science educator is to present the explanation of nature in a way that is congenial to the public.
This is a very hard job.

i'm a little confused. are we talking about the same thing?

i think i mistyped.

my question was really: why are people so sure that causes don't exist for apparently random behavior?

is that the question you were answering?
 
  • #13
Crosson said:
Quantum mechanics (QM) is a deterministic theory. Let's compare to classical mechanics (CM) which everyone agrees is deterministic.

The classical state of a system of n particles in 3 dimensions is a vector of length 2n that contains the 3d position and momentum coordinates of each of the particles. Classically, this is all the information that is possible to know about the system. If the state of the particle is known exactly at time t, then using any formulation of mechanics that is equivalent to Newton's 2nd law we can predict with certainty the classical state of the system at any given time.

The only difference is that in QM the state of even a single particle is given by an infinite-dimensional vector. The Schroedinger time-evolution of such a state is perfectly deterministic.

That's not what we mean when we use the term "deterministic". Determinism here means "events could not have preceded differently if replayed".
 
  • #14
MetricBrian said:
why are people so sure that causes don't exist for apparently random behavior?

A good scientist will always look for patterns in the chaos.
If, however, no explanations can be found after much effort, one looks for order elsewhere.
The statistical behavior of quantum mechanics was not accepted easily.
It has been made clear that there is no avoiding the "apparently random behavior" of nature.
This was done by careful argument, and has been verified time and time again in experiment.
This is no reason to stop looking and give up!
Neither is it a reason for everyone to focus on this one illusive problem.
A sensible distribution of effort would allow for the occasional brave physicist to research new explanations for the "apparently random behavior" of the quantum world.
So far, no tied and proved theory has arisen from this line of research, to my knowledge.
Personally, I wish someday this could all be explained, but I don't expect it will.
 
  • #15
Moridin said:
That's not what we mean when we use the term "deterministic". Determinism here means "events could not have preceded differently if replayed".

that's fine, but it is determinstic insofar as an Event necessarily determines a result that must fall within a specifed range - if you replay the experiment, the result will always fall within the range. It's sort of a restricted casually determined relation
 
  • #16
Crosson said:
The Schroedinger time-evolution of such a state is perfectly deterministic.
What are you doing with measurement ? Are you advocating Rovelli's interpretation ?

Basically, the OP describes t'Hooft deterministic QM. This does take into account measurements by equivalence classes.
 

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