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Quantum Mechanics

Polymath257

Think & Care
Staff member
Premium Member
This thread is to discuss quantum mechanics and its impact on our ideas of causality, reality, and such. it is an outgrowth of the discussion at Why it's easier to be a creationist than an atheist. Specifically, @exchemist is invited to discuss!

One question is how our classical ideas of causality have to be modified in light of the discoveries of quantum theory. In particular, the fact that initial conditions do NOT determine later states means that the classical concept of causality needs at least some massage.
 

suncowiam

Well-Known Member
This thread is to discuss quantum mechanics and its impact on our ideas of causality, reality, and such. it is an outgrowth of the discussion at Why it's easier to be a creationist than an atheist. Specifically, @exchemist is invited to discuss!

One question is how our classical ideas of causality have to be modified in light of the discoveries of quantum theory. In particular, the fact that initial conditions do NOT determine later states means that the classical concept of causality needs at least some massage.

Can you give me an example of how initial conditions do not affect later states?

Also, how does entanglement affect causality?

Thanks
 

Polymath257

Think & Care
Staff member
Premium Member
Can you give me an example of how initial conditions do not affect later states?

Also, how does entanglement affect causality?

Thanks

Well, for most quantum systems, the initial state only determines *probabilities* of later measurements, not the measurements themselves. In classical physics, the dynamics were deterministic and knowing the initial state would completely determine all later states.

So, in the double slit experiment, there is no way ahead of time to determine the result of any one electron going through the slits. It is only the built up probabilities that are determined.

Entanglement is a different story. The probabilities are shared. So, there might be a 50/50 probability for each to show an 'up' spin. But if one side shows 'up', the other shows 'down'.
 

shunyadragon

shunyadragon
Premium Member
This thread is to discuss quantum mechanics and its impact on our ideas of causality, reality, and such. it is an outgrowth of the discussion at Why it's easier to be a creationist than an atheist. Specifically, @exchemist is invited to discuss!

One question is how our classical ideas of causality have to be modified in light of the discoveries of quantum theory. In particular, the fact that initial conditions do NOT determine later states means that the classical concept of causality needs at least some massage.

I very much disagree concerning what you describe as the ramifications of Quantum Mechanics, and will comment further.

The concept of how initial conditions determine later states or outcomes of cause and effect, and influence of chaos theory on outcomes only applies to the macro world beyond the Quantum world. The Macro World has natural laws not common to the Quantum World like the Law of Gravity, and not necessarily the Laws of Thermodynamics.

The Quantum World is the foundation, and relates to the behavior of the basic particles of matter and energy. After the basic particles of energy and matter form atoms and molecules on the larger scale the Laws of Nature dominate with natural determinism.
 
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shunyadragon

shunyadragon
Premium Member
Well, for most quantum systems, the initial state only determines *probabilities* of later measurements, not the measurements themselves. In classical physics, the dynamics were deterministic and knowing the initial state would completely determine all later states.

So, in the double slit experiment, there is no way ahead of time to determine the result of any one electron going through the slits. It is only the built up probabilities that are determined.

Entanglement is a different story. The probabilities are shared. So, there might be a 50/50 probability for each to show an 'up' spin. But if one side shows 'up', the other shows 'down'.

Ok post, but to clarify the deterministic outcome of cause and effect relationships in the macro world are subject to a range of outcomes with fractal relationships based on chaos theory.
 

Polymath257

Think & Care
Staff member
Premium Member
I very much disagree concerning what you describe as the ramifications of Quantum Mechanics, and will comment further.

The concept of how initial conditions determine later states or outcomes of cause and effect, and influence of chaos theory on outcomes only applies to the macro world beyond the Quantum world. The Macro World has natural laws not common to the quantum Would like the Law of Gravity, and not necessarily the Laws of Thermodynamics.

The Quantum World is the foundation, and relates to the behavior of the basic particles of matter and energy. After the basic particles of energy and matter form atoms and molecules on the larger scale the Laws of Nature dominate with natural determinism.

First of all, Chaos theory has almost nothing to do with QM. It is an aspect of purely classical, deterministic equations where small changes in initial conditions lead to large changes later on. But the systems themselves are deterministic.

We know that quantum particles are subject to gravity, for example. In fact, measurements on how fast different particles fall is an interesting test for our ideas about gravity.

Thermodynamics actually arises naturally out of QM via Statistical Mechanics. The large number of particles in any macroscopic system is part of why Stat Mech is so useful.

One question (not too difficult to answer, by the way) is how the probabilistic aspect of the low levels leads to so much determinism at the upper levels.

But the low levels are still NOT deterministic. And that can have relevance in many cosmological situations, especially in the early universe.
 

Polymath257

Think & Care
Staff member
Premium Member
Ok post, but to clarify the deterministic outcome of cause and effect relationships in the macro world are subject to a range of outcomes with fractal relationships based on chaos theory.

One interesting research question is to take a classical system that shows chaos and see what the corresponding quantum system does. I've seen some preliminary work and the fractal aspect seems to be maintained to some extent, but is 'fuzzed out' and expands over time. This isn't too surprising since the classical chaotic system is sensitive to initial conditions and the probabilistic aspect of QM guarantees a spread of initial conditions.

So, in a case where chaos is relevant, at what point do quantum effects become significant in the dynamics? Does the indeterminacy of the quantum level translate into a greater indeterminacy of the chaotic system? I don't know.
 

shunyadragon

shunyadragon
Premium Member
First of all, Chaos theory has almost nothing to do with QM. It is an aspect of purely classical, deterministic equations where small changes in initial conditions lead to large changes later on. But the systems themselves are deterministic.

Clarification., I never claimed Chaos Theory applies to Quantum Mechanics. In fact I made it clear by our present knowledge it applies only to the macro world as far as we know. There is a fuzzy boundary here between Quantum behavior at the micro scale and Classical behavior in the macro world.

We know that quantum particles are subject to gravity, for example. In fact, measurements on how fast different particles fall is an interesting test for our ideas about gravity.

Quantum particles may be subject to gravity, but beyond this I believe a form Quantum Gravity(?) applies.

Thermodynamics actually arises naturally out of QM via Statistical Mechanics. The large number of particles in any macroscopic system is part of why Stat Mech is so useful.

I agree, but it remains uncertain as to how the Laws of Thermodynamics apply within the Quantum world.

One question (not too difficult to answer, by the way) is how the probabilistic aspect of the low levels leads to so much determinism at the upper levels.

But the low levels are still NOT deterministic. And that can have relevance in many cosmological situations, especially in the early universe.

Agreed.
 

suncowiam

Well-Known Member
Well, for most quantum systems, the initial state only determines *probabilities* of later measurements, not the measurements themselves. In classical physics, the dynamics were deterministic and knowing the initial state would completely determine all later states.

So, in the double slit experiment, there is no way ahead of time to determine the result of any one electron going through the slits. It is only the built up probabilities that are determined.

Entanglement is a different story. The probabilities are shared. So, there might be a 50/50 probability for each to show an 'up' spin. But if one side shows 'up', the other shows 'down'.

Thanks.

This could be just semantics but isn't probability an expression of how deterministic something is?
 

sealchan

Well-Known Member
This thread is to discuss quantum mechanics and its impact on our ideas of causality, reality, and such. it is an outgrowth of the discussion at Why it's easier to be a creationist than an atheist. Specifically, @exchemist is invited to discuss!

One question is how our classical ideas of causality have to be modified in light of the discoveries of quantum theory. In particular, the fact that initial conditions do NOT determine later states means that the classical concept of causality needs at least some massage.

There are two kinds of people in this world, my friend...those that still think in classical physics terms and those that go a bit far and favor all the weirdest stuff in quantum mechanics and seek to make it a proof (when it is really "only" a metaphor) for more speculative ideas about our reality.

That said, quantum mechanics challenges the set of metaphors we might knowingly or unknowingly use to make sense of the world we live in...which makes this topic appropriate for a religion forum.
 

shunyadragon

shunyadragon
Premium Member
There are two kinds of people in this world, my friend...those that still think in classical physics terms and those that go a bit far and favor all the weirdest stuff in quantum mechanics and seek to make it a proof (when it is really "only" a metaphor) for more speculative ideas about our reality.

That said, quantum mechanics challenges the set of metaphors we might knowingly or unknowingly use to make sense of the world we live in...which makes this topic appropriate for a religion forum.

Disagree, Quantum Mechanics is a science topic and discussion. Quantum Mechanics is not 'weird' nor weirded stuff.'
 

David T

Well-Known Member
Premium Member
This thread is to discuss quantum mechanics and its impact on our ideas of causality, reality, and such. it is an outgrowth of the discussion at Why it's easier to be a creationist than an atheist. Specifically, @exchemist is invited to discuss!

One question is how our classical ideas of causality have to be modified in light of the discoveries of quantum theory. In particular, the fact that initial conditions do NOT determine later states means that the classical concept of causality needs at least some massage.
That old idea of causality was really a development of Newtonian mechanics if I am not mistaken . Is that correct poly ?.
 

sealchan

Well-Known Member
Disagree, Quantum Mechanics is a science topic and discussion. Quantum Mechanics is not 'weird' nor weirded stuff.'

What I meant was in the spirit of what Richard Feynman says...

If you think you understand quantum physics you don't

In my studies of human cognition I am fairly convinced that concepts we hold in the mind are built up from metaphors from our experience of having a body in a (classical) three dimensional world moving through time. As such quantum mechanics presents us with "truths" which are either hard to or impossible to understand via such embodied concepts.

In short, quantum mechanics is weird...even if it is concisely described by mathematics.
 

Polymath257

Think & Care
Staff member
Premium Member
That old idea of causality was really a development of Newtonian mechanics if I am not mistaken . Is that correct poly ?.

Yes, at least in part. The equations of Newtonian mechanics are deterministic: if you know the exact state of your system at one time, then the state at any other time is determined. So, we say the initial conditions cause the later state of the system.

In quantum mechanics, that is no longer the case. In fact, the 'exact sate' only determines the probabilities of later measurements, not the the values of the measurements themselves (although the values can be restricted).

So, if you have two quantum systems that are *exactly* the same at one time, they may not be the same at later times. For example, if you have two uranium-238 nuclei, they can be in exactly the same state and one will decay now while the other doesn't decay for another 5 billion years.
 

Polymath257

Think & Care
Staff member
Premium Member
Disagree, Quantum Mechanics is a science topic and discussion. Quantum Mechanics is not 'weird' nor weirded stuff.'

It's weird if you insist on looking at it from a classical perspective. There can *appear* to be backwards causality, effects from particles that aren't there, etc. In actuality, these claims are hyped and are mostly the results of interference and the fact that spin acts like polarization.

But people manage to get themselves tied into all sorts of knots because they insist on thinking of electrons as taking a definite path or having definite properties at all times.
 

sealchan

Well-Known Member
Yes, at least in part. The equations of Newtonian mechanics are deterministic: if you know the exact state of your system at one time, then the state at any other time is determined. So, we say the initial conditions cause the later state of the system.

In quantum mechanics, that is no longer the case. In fact, the 'exact sate' only determines the probabilities of later measurements, not the the values of the measurements themselves (although the values can be restricted).

So, if you have two quantum systems that are *exactly* the same at one time, they may not be the same at later times. For example, if you have two uranium-238 nuclei, they can be in exactly the same state and one will decay now while the other doesn't decay for another 5 billion years.

What about the three-body problem in classical mechanics? There is perhaps a sort of continuum one might intuit running from the three-body problem through chaotic systems through quantum probability. A system's initial conditions are knowable to a limited precision, future states require infinite precision to track accurately and then finally future states are probabilistic and cannot be predicted precisely at all without actually observing the outcome.

Taken at face value one could argue for the uselessness of mathematical science if one wasn't surrounded by the overwhelming argument of technological development based on the mathematics of science.
 

Polymath257

Think & Care
Staff member
Premium Member
What about the three-body problem in classical mechanics? There is perhaps a sort of continuum one might intuit running from the three-body problem through chaotic systems through quantum probability. A system's initial conditions are knowable to a limited precision, future states require infinite precision to track accurately and then finally future states are probabilistic and cannot be predicted precisely at all without actually observing the outcome.

Taken at face value one could argue for the uselessness of mathematical science if one wasn't surrounded by the overwhelming argument of technological development based on the mathematics of science.

The problem in the three body problem is that there is no *analytic* description of the motion of the three particles. It is still determined by the initial conditions if perfectly known.

But you are also correct, the initial conditions cannot be perfectly known and divergence of close paths is part of what makes a deterministic system chaotic.

The nature of QM is different, though. In QM, we don't even have determinism of the chaotic sort. The probability description in QM is inherent in the model. Furthermore, we know it isn't just a matter of finding 'hidden variables' to make things deterministic (even if chaotic).
 

sealchan

Well-Known Member
It's weird if you insist on looking at it from a classical perspective. There can *appear* to be backwards causality, effects from particles that aren't there, etc. In actuality, these claims are hyped and are mostly the results of interference and the fact that spin acts like polarization.

But people manage to get themselves tied into all sorts of knots because they insist on thinking of electrons as taking a definite path or having definite properties at all times.

They insist on what their entire framework of ideas is based on...human scale (classical) physics.

Now you or I might study the topic enough to get a sense of familiarity...I've done some textbook problems in relativity (at the algebra level) for instance...but unless you are talking to such people, I would expect people will use such words as crazy, weird, bizarre, etc...

So to me I find that classical mechanics is the language of our experience of reality and the new quantum mechanics comes in from a more remote and rare experience of a reality heavily filtered through mathematics and the science lab. We can't expect human culture at large to digest this sort of experience in a general way.
 

sealchan

Well-Known Member
There is also the challenge for non-scientists to understand that although science has given us substantial new ways of relating to reality it also has developed a precise sort of self-deprecation as to the scope of its knowledge. This self-deprecation is often abused by those who wish to counter the scientific consensus (which I generally find authoritative) as weakness and taken out of context used to show the uselessness of scientific ideas.

So understanding how a more general knowledge of causality is to be communicated from science to the broader public requires the difficulty of getting the public to understand anything mathematical that science is basing its truth on and then going the one step deeper of getting the public to then understand and accept the limitations of knowledge.

I say all this because science is moving us from the paradigm of the clockwork universe towards something much less mechanistic. Ironically, however, most people don't engage the world as if it were a simple machine but as something more alive and complex. In this sense, some of these exceptions to a simple causality might actually chime in with simple truths that most people hold such as "no one is perfect" and "you never know what will happen". I've even experienced on many occassions in my experience with computers that the truism of "doing the same thing repeatedly and expecting different results" is really not that true in many situations.

Now when we can yield new quantum technologies that impact the consumer market, then we might get to see where the rubber hits the road as far as how quantum mechanical understanding will impact our human understanding of causality.
 

Skwim

Veteran Member
Well, for most quantum systems, the initial state only determines *probabilities* of later measurements, not the measurements themselves. In classical physics, the dynamics were deterministic and knowing the initial state would completely determine all later states.
As has always been the case, probabilities arise out of ignorance. Because we don't know enough about the governing conditions to nail down a future event---whether it will happen or not---we are left to to construct likelihoods: probabilities. Of course, this does not mean such an event is uncaused.

So, in the double slit experiment, there is no way ahead of time to determine the result of any one electron going through the slits. It is only the built up probabilities that are determined.
Again, our inability to gather and evaluate all the relevant causal factors does not mean they don't exist.

the fact that initial conditions do NOT determine later states means that the classical concept of causality needs at least some massage.
Says who? If initial conditions don't, then it must be the case that some kind of absolutely random uncaused event intervened. Got any unequivocal evidence for such an intruder?

Honestly, I'd be extremely interested to see the evidence for such an event. And just as an fyi, things like quantum tunneling and beta-particle emissions have yet to qualify.



As a side note, even if it was shown that some quantum events are absolutely uncaused, they would have no impact on the deterministic nature of human events. As physicist Max Tegmark observed: "quantum states in the brain would decohere before they reached a spatial or temporal scale at which they could be useful for neural processing. Based on his calculations, Tegmark concluded that quantum systems in the brain decohere quickly and cannot control brain function."
Source: Wikipedia

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