Quantum Mechanics

[Polymath257]

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.


Again, our inability to gather and evaluate all the relevant causal factors does not mean they don't exist.

But we know such 'hidden variables' are NOT the explanation for what we see. There are actual experiments that have been done that exclude the probabilities being due to hidden information. Local realism is no longer a possibility. QM is a local, non-realist description.

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.

How about the violations of Bell's inequalities? Aspect's experiment? Here's a fun little article:

http://web.pdx.edu/~pmoeck/lectures/Mermin longer.pdf

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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And to a large extent I agree. I don't see quantum indeterminacy as relevant to consciousness at all.

 

[exchemist]

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.

Ho Ho! I shall have to gird my loins for this, I think.

Just to get the ball rolling, let me reiterate that a theory (model) in science has to make successful predictions about what observations of nature can be expected. QM predicts those aspects of nature it is designed to model triumphantly well. Prediction involves stating the effect of a given cause. So cause and effect still apply in QM. If they did not, it would be useless as a theory of science. However there are, for the first time in modern scientific theories, intrinsic limits to how much can be predicted (or even defined!), and with what degree of precision. And then we also have Heisenberg's famous principle of indeterminacy, which precludes certain combinations of properties from being exactly defined simultaneously.

In the Newtonian world, every interaction of every entity can be modelled with any desired degree of mathematical accuracy. This has led past philosophers to muse that the universe might be totally predetermined: if one had sufficient calculating power, every outcome of every process could be calculated, in principle, right through to the end of time.

QM demands we give up this strict, c.19th notion of determinism. If QM is right, and so far it has passed every test set for it, even the most bizarre, then at the atomic scale the outcome of an interaction can only be predicted as a probability rather than a certainty. This destroys the strict version of determinism at a stroke. (Which may give more hope to philosophers who subscribe to the idea of free will.)

What we were debating was whether destroying strict determinism also destroys cause and effect relationships. I have argued not, saying instead that in QM one has cause and probable, though not certain, effect. One does not in general have effects that are completely uncaused, though there are some circumstances where even this is possible, e.g. radioactive decay.

But there is - so I now read - a variety of views about this. For instance in this Wiki article on determinism Determinism - Wikipedia. there are nuanced versions of determinism such as "adequate determinism", embraced by people such as Hawking, that seem to treat determinism and cause and effect as synonymous, but then argue QM preserves a partial determinism at macro scales (i.e.on the scale of a large enough population of QM entities that expectation values of the probability distribution are what one observes.)

Will that do to open the batting?

 

[David T]

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.

Would we have understood a mechanical deterministic realitysay be for culture? I might say in Newtons time it would have seemed profoundly deep to see it mechanically like a clock.

 

[Bob the Unbeliever]

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.

I remember discussing this (electrons "moving" within their shells) way back in 1975-6.

Some among us were certain that the little electrons were buzzing around like little negatively-charged bees, simply being confined within their respective shells or manifolds.

Those of us who rejected that, loved to point out that some of the electron shells were not contiguous, and asked (rightfully) how the electrons managed the "jump" from one part to the other part, without traveling in-between where they were not "allowed" to be?

Of course, they could not answer.

My favorite analogy was that electrons were like frames in a movie: Each frame represented a quantum "time slice" wherein the electron wasn't moving at all-- and if we were to look for the electron, we'd find it somewhere within the manifold.

With each frame or quantum-blink, the electron would "appear" within that space-- it was not actually moving at all.... but blinking, not unlike phosphor dots on an old CRT screen, being excited by the electron beam behind it.

Of course, I realize that "quantum time" is pretty much bogus, and entirely invented. And it seems unlikely that electrons actually blink in and out-- for one thing, we have never detected when they were "out".

Perhaps they do blink-- but they blink from one place to the next, never actually not-existing, but always appearing within the probability manifold?

In fact, some postulated that they do not exist until they are interacted with-- then they "appear" or "resolve" within the expected space, but are only a potential prior to that. (and what does that mean? only a potential? )

Me? This is way, way above my pay-grade here... I'm just fascinated by it all.

 

[shunyadragon]

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

Who is they? Quantum level measurements are in Quanta.

 

[Brickjectivity]

I just got an app for android that is an introduction to quanta. It is an overview. Its called 'Quantum'. Its free, requires no extra permissions and I have seen no adverts. Its convenient. For questions about the formulas you will have to look more in depth, for example it does't explain the gamma factor but only mentions it. Its not a Physics education on toast. For me its nice.

 

[idav]

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.


Again, our inability to gather and evaluate all the relevant causal factors does not mean they don't exist.


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

.

Probability isn’t out of ignorance. The simple example is the double slit experiment. It isn’t a matter of determining which slit it went through, for all intents and purposes it goes through both. The universe is fundamentally not deterministic which effects everything.

 

[sayak83]

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.

So.. I skipped the entire classical physics part and learnt and used QM directly. I think of macro reality as averaged out appx. based on statistical mechanics. Thus I don't find QM weird.

 

[sayak83]

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.


Again, our inability to gather and evaluate all the relevant causal factors does not mean they don't exist.


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

.

No. In QM mechanics its been proved that probabilities are intrinsic and don't arise out if ignorance (Bell theorem, EPR and current advancements rule out any ignorance or hidden effects causing probabilities to occur. )

https://www.newscientist.com/articl...roved-real-in-first-loophole-free-experiment/

Let's not discuss human mind. One non-trivial subject per thread is enough.

 

[Polymath257]

So.. I skipped the entire classical physics part and learnt and used QM directly. I think of macro reality as averaged out appx. based on statistical mechanics. Thus I don't find QM weird.

I didn't exactly skip over classical theory, but I did QM early enough that the classical intuitions hadn't gelled yet. Similarly for relativity. So there are a lot of aspects of the quantum world that don't seem to strange to me but seem strange to others.

On the other hand, the way angular momentum works is often pretty strange.

 

[Polymath257]

What we were debating was whether destroying strict determinism also destroys cause and effect relationships. I have argued not, saying instead that in QM one has cause and probable, though not certain, effect. One does not in general have effects that are completely uncaused, though there are some circumstances where even this is possible, e.g. radioactive decay.

I also ponder the situations where a single type of particle, say a tau particle has several different decay modes, each with a different half-life. So, two tau particles that are otherwise the same in all characteristics might have one decay into a muon and associated neutrinos or a pion with associated neutrinos. In fact, there are several dozen different decay modes for a tau particle. In what sense are the decay products 'caused' by the initial tau particle?

My difficulties are as much in how to define the terms 'cause' and 'effect' as anything else. OK, we set up initial conditions and call them the 'cause' and see what happens and call that the 'effect'. So, is causality simply one event (or collection of events) happening before a different event (or collection of events)?

Is being able to predict probabilities enough to say there is causality?

But there is - so I now read - a variety of views about this. For instance in this Wiki article on determinism Determinism - Wikipedia. there are nuanced versions of determinism such as "adequate determinism", embraced by people such as Hawking, that seem to treat determinism and cause and effect as synonymous, but then argue QM preserves a partial determinism at macro scales (i.e.on the scale of a large enough population of QM entities that expectation values of the probability distribution are what one observes.)

Will that do to open the batting?

I interpret the macroscopic causality as being an averaging process over the probabilities from the lower levels. A trivial example is to imagine a coin. Flip it one time and you have a 50/50 chance of a head or a tail, with little predictability (well...this is a classical system, so...). But, if you flip a trillion coins, the number of heads will be very close to 50%. Yes, there is a spread, but as a percentage that spread is small.

If you have Avagadro's number of coins to flip, that 50% is accurate to within our ability to measure. And for macroscopic measurements, we are always dealing with an average over many, many quantum particles. So the predictability is very high. And that is why classical causality works for macroscopic objects.

yes, good contribution!

 

[Thief]

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.

so.....plan A gets a smoothie into plan B......

and God gets left out?

 

[blü 2]

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

Depends how long you've been at it. Some of the things I read twice or more when first encountering them were uncaused causes like the Casimir effect, faster-than-light information transfer in entanglement, the reasoning and implications of Bell's theorem; they're weird. (And I wasn't the one who coined 'spooky action at a distance'.)

Only afterwards did I get used to them. Well, as used to them as I am now, anyway.

 

[blü 2]

My difficulties are as much in how to define the terms 'cause' and 'effect' as anything else. OK, we set up initial conditions and call them the 'cause' and see what happens and call that the 'effect'. So, is causality simply one event (or collection of events) happening before a different event (or collection of events)?

One definition of 'cause' proposed for physics is 'the movement of energy from a region of higher energy to a region of lower energy, 'effect' being the change that results. (Other less committal words than 'energy' have been suggested too.)

As I understand it, this doesn't describe quantum fluctuations hence doesn't describe the consequences of quantum fluctuations.

So QM cases may require a different vocabulary.

 

[Sunstone]

First, I want to thank everyone participating in this excellent thread for such an interesting discussion, and especially @Polymath257 for starting the thread.

Second, you're all such morons for failing to grasp even on the most rudimentary level, as I myself have, the simple fact that quantum mechanics proves beyond doubt aliens are visiting us in order to conduct anal probes on fans of Country and Western music!!!!!

Actually, I don't believe that even for a nanosecond. You pretty much all seem knowledgeable to me. But this is RF, and you were having a civil discussion, so I was alarmed that something might be wrong -- terribly wrong -- here. Hence, my obligatory ignorant and arrogant outburst.

Next, and more seriously, I must honestly apologize for my own ignorance of quantum mechanics, and for the fact I might be asking some dumb questions now or later on -- if and when I'm not merely lurking.

You see, the fact is, QM never interested me until quite recently in life, except for my early on interest in QM as an obvious and exciting means of picking up babes in bars (e.g. "So...is it 'Lisa'?...so Lisa, shall we go to my apartment, have a little more wine, and then discuss 'entanglement' in the privacy of my bedroom? Or would you prefer to entangle on my kitchen table where you'll find even more cheese than in my pick-up lines?"). Hence, I have only recently gotten interested in it, and that mainly for its philosophical implications.

Having said all that, please allow me now to ask two questions.

1) Does the fact (as indeed I understand it to be a fact) that in QM some effects are completely uncaused (e.g. radioactive decay) imply that the universe itself might have been a completely uncaused effect?

2) And, more broadly, if there can be uncaused effects, does that decisively sink once and forever the ancient notion that, "Something cannot come from nothing"?

Thanks for your patience.

 

[exchemist]

I remember discussing this (electrons "moving" within their shells) way back in 1975-6.

Some among us were certain that the little electrons were buzzing around like little negatively-charged bees, simply being confined within their respective shells or manifolds.

Those of us who rejected that, loved to point out that some of the electron shells were not contiguous, and asked (rightfully) how the electrons managed the "jump" from one part to the other part, without traveling in-between where they were not "allowed" to be?

Of course, they could not answer.

My favorite analogy was that electrons were like frames in a movie: Each frame represented a quantum "time slice" wherein the electron wasn't moving at all-- and if we were to look for the electron, we'd find it somewhere within the manifold.

With each frame or quantum-blink, the electron would "appear" within that space-- it was not actually moving at all.... but blinking, not unlike phosphor dots on an old CRT screen, being excited by the electron beam behind it.

Of course, I realize that "quantum time" is pretty much bogus, and entirely invented. And it seems unlikely that electrons actually blink in and out-- for one thing, we have never detected when they were "out".

Perhaps they do blink-- but they blink from one place to the next, never actually not-existing, but always appearing within the probability manifold?

In fact, some postulated that they do not exist until they are interacted with-- then they "appear" or "resolve" within the expected space, but are only a potential prior to that. (and what does that mean? only a potential? )

Me? This is way, way above my pay-grade here... I'm just fascinated by it all.

As a chemistry undergraduate I became used to thinking of electrons and photons as predominantly waves, but which could only interact in quantised "units", corresponding to one photon at a time or one electron a time. This picture helps a lot to overcome primitive Bohr-model thinking about atomic transitions, for instance, with its rather absurd ad-hoc requirement for "discontinuous" jumps and all that.

But I think in the end we all have to manage a degree of of cognitive dissonance in dealing with quantum phenomena when we try to visualise them. (At university, one thing I briefly glimpsed was the nirvana in which the mathematics becomes so familiar that one no longer thinks in terms of pictorial models. That is the real breakthrough to a new level of understanding, but sadly it is hard to sustain, unless one does theoretical science for a living.)

For the rest of us, sometimes a wave picture fits and sometimes a particle* picture. My own view is that this should not shock us, actually. We do this all the time in science, e.g. Newtonian gravitation vs general relativity, valence bond vs. molecular orbital models of chemical bonding, etc. Even the achingly trendy Casimir effect can be modelled either as a (potentially woo-laden) quantum fluctuations model or as good old van der Waals forces!

Finally, in deference to the religious nature of this forum, I offer the personal observation that I sometimes think my Catholic upbringing has made it easier to for me to accept the cognitive dissonance between different models: the notion that reality itself remains something of a mystery, which we mere mortals glimpse and make approximate sense of, via more or less inadequate analogies. Maybe this too is why I am comforted by the message of QM that we cannot know it all!

"For now we see through a glass, darkly" as St Paul has it.


* It sometimes occurs to me that the Newtonian idea of a "particle" is fairly ridiculous: a thing with no spatial extent but nevertheless with mass, charge etc. But we are all brought up with it and never question it!

 

[JoshuaTree]

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.


Again, our inability to gather and evaluate all the relevant causal factors does not mean they don't exist.


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

.

What about "quantum robin" supposedly using quantum entanglement for migration?

http://www.physicscentral.com/explore/action/pia-entanglement.cfm

 

[JoshuaTree]

What about "quantum robin" supposedly using quantum entanglement for migration?

http://www.physicscentral.com/explore/action/pia-entanglement.cfm

...and then there are the lemmings lol.

 

[james blunt]

Quantum entanglement, try the minds entanglement with the Universe, you will understand once you couple your mind with the Universe.

 

[shunyadragon]

so.....plan A gets a smoothie into plan B......

and God gets left out?

As far as science for the sake of science goes it is very fortunate that that ancient mythical beliefs of God are left out, because these ancient mythical views tend to mess with science . . .

, , , but God is not left out, because the sciences simply see how God Created our physical existence.