Quantum Eraser and Its Implications

[Cthugha]

Okay... interesting... but if I got this right; the entanglement does not affect the outcome at D0 one bit, right? So what’s in fact is 'delayed' is the choice to measure "which path", or not, in "cloned twin beam", right?

If I understand this right, non-locality is not the crucial thing here, but a "clone copy" of the signal beam, right?

Well, entanglement has two main effects. One is that that the two entangled particles do indeed bahave like cloned copies (or shifted copies or whatever one likes to call it) with the main point being that you can tell what the entangled partner will do if you know what the first particle does. The second point in entanglement is that these properties are not imprinted from the beginning in a hidden variable-like fashion, but the state of both is fixed when the first measurement occurs which implies nonlocality. The latter is what is tested in Bell tests.

So for the experimental outcome it is in fact only the first property which matters. There is information that can only be accessed when detecting both entangled particles and "matching up". Non-locality does not really matter in terms of the outcome, but in terms of the interpretation of the results. For example the standard DCQE experiment could be changed such that the delay between detections of signal and idler becomes large and one could perform the measurements in such a fashion that Bell inequalities are tested.

Why do we get a mixture of interference/non-interference pattern in D0? What causes it? There’s no "flip-flopping gate" at the double slit, is it? I don’t get it? In a normal experiment we would get an interference pattern or no interference pattern, not both, right??

In a normal double slit experiment the pattern you will see depends on the geometry of your experiment. If your light source is for example not exactly centered between the two slits, you will get a slightly different pattern as the distances between the source and the two slits are now different. As you move the source around, you will get different patterns. So if you now place several light sources at different positions you will now get a superposition of all of these patterns. If you have enough sources the superposition will be no pattern at all. This is foe example the same reason why the interference pattern disappears in a common double slit experiment if you place your light source too close to the slits. It will then reappear as you increase the distance between the slits and the source.

Now in the DCQE you have a similar setting (I am referring to figure one in the paper by Kim, Kulik, Shih and Scully). You have two atoms A and B placed at the slits which could emit entangled photon pairs. This process is completely random and one cannot distinguish from which atom some certain phton pair comes (unless you have detections at D3/D4). However, the two atoms are not synchronized. The phase of the light fields emitted from the two atoms is pretty much random with respect to each other and it also fluctuates randomly. This is pretty much like having a like source emit a single photon in the common double slit experiment and then moving it somewhere else, emitting another photon, etc which will add up to no interference pattern at all. However, if you note the position of the source for each photon and afterwards just pick a subset of detections corresponding to the source being at the same position, you will find some pattern. If you pick a different subset corresponding to a different position, you will find some different pattern.

In DCQE the position of the peaks in the double slit pattern will depend on the relative phase between the fields emitted by the atoms, so you do not see a single interference pattern, but a superposition of many which add up to no interference pattern. However, you can find any of these interference patterns by just picking those detections that correspond to some phase difference between the fields. That picking is now done using the other entangled partner. Depending on the relative phase that partner is more likely to be detected at D1 or D2, so you get a fringe/antifringe pattern when the coincidence counts D0/D1 or D0/D2 are considered.

 

[DevilsAvocado]

One is that that the two entangled particles do indeed bahave like cloned copies
...
So for the experimental outcome it is in fact only the first property which matters.
...
Now in the DCQE you have a similar setting (I am referring to figure one in the paper by Kim, Kulik, Shih and Scully). You have two atoms A and B placed at the slits which could emit entangled photon pairs. This process is completely random and one cannot distinguish from which atom some certain phton pair comes (unless you have detections at D3/D4). However, the two atoms are not synchronized. The phase of the light fields emitted from the two atoms is pretty much random with respect to each other and it also fluctuates randomly. This is pretty much like having a like source emit a single photon in the common double slit experiment and then moving it somewhere else, emitting another photon, etc which will add up to no interference pattern at all. However, if you note the position of the source for each photon and afterwards just pick a subset of detections corresponding to the source being at the same position, you will find some pattern. If you pick a different subset corresponding to a different position, you will find some different pattern.

In DCQE the position of the peaks in the double slit pattern will depend on the relative phase between the fields emitted by the atoms, so you do not see a single interference pattern, but a superposition of many which add up to no interference pattern. However, you can find any of these interference patterns by just picking those detections that correspond to some phase difference between the fields. That picking is now done using the other entangled partner. Depending on the relative phase that partner is more likely to be detected at D1 or D2, so you get a fringe/antifringe pattern when the coincidence counts D0/D1 or D0/D2 are considered.

Yay! I think I’ve got it! Many THANKS!

I’ve been completely lost... (as you may have noticed). All the time I have assumed that an interference pattern is created already directly after the slits, that is "picked up" by the BBO to then be (randomly) 'transformed' into two entangled pair... god I’m stupid...

The distance is obviously too short for this to happen... the 'interference' is instead created by the random and relative phase (shift) in the photons emitted from the BBO. Please, tell me I got this right??

I was thinking... is it ever possible to move the BBO to be placed before the slits? And then use a (P)BS after the slits to separate signal & idler, and thereafter do "fancy measurements" on the two entangled twins?

Or is it already a dead end when hitting the BS??

 

[San K]

You’re welcome, hope it helped!

I see a problem right there; the idler twin photons don’t hit any "specific locations" (on the x-axis). It’s only a count of photon hits and timing, and depending on path you could tell/or not tell which slit it went thru. That’s it.

Sorry replace the concept "specific location" with detector. Once
Signal photon has stuck the detector the probability of idler hitting a particular detector is calculable (based on location of signal photon on the screen)

 

[Quaman]

Hi!
I have not finished reading through the whole thread, so please excuse me if I am asking something that was already covered. Here are my questions related to a DCQE setup:
1/a) If which-path information is observed (but not recorded!) by a non-human observer at D3 and D4, will or will not the interference pattern collapse at D0 when D0 is observed by a human?
1/b) If which-path information is observed and recorded by a non-human observer at D3 and D4, will the interference collapse at D0 when observed by a human? Let's assume that no human ever sees that record. It is clear that if the record later gets observed by a human, D0 will not show interference pattern.
1/c) What if the record made by a non-human observer at D3 and D4 is irrevocably deleted before any human can observe it? Will the interference collapse at D0 when D0 is observed by a human? If yes, why? I think it should not, because the entangled pair (idler) will never be observed.
2) In the same dcqe setup if which-path information is observed by Alice at D3 and D4, but does not have the possibility to tell Bob about it (eg. dies before she can do so), will Bob at D0 see interfence? This is somewhat similar to 1/c, but the difference is that the record was made by a human in this case and that record unfortunately also got 'irrevocably erased'.
I am pretty sure no-one has ever carried out experiment no. 2), as it is apparently against federal laws :) But I expect it should give the same results as 1/c, right?

If you know that an experiment was carried out before with any of the above or similar setup, I would be really glad if you could share the link to the paper (or at least to its abstract) here :) Thank you!

 

[Cthugha]

Same answer to all questions: The presence or absence of humans has absolutely nothing to do with the outcome. The meaning of observing in physics does not require any consciousness. Any irreversible interaction is sufficient.

 

[Ken G]

The meaning of observing in physics does not require any consciousness.

And I'd like to interject one caveat that is seemingly picky but I think is actually quite important: meaning always requires consciousness. But your point, I believe, is that consciousness does not enter at the same physical level as the other elements of the experiment, the detector, the slits, etc., nor does it enter at the level of the theory, the Hilbert space or the operators, etc. So there is no "piece of the apparatus" we need to call conscious, and there is no term in the equation we might want to call the "effect of consciousness." All the same, I think quantum mechanics is one of the places where we are forced to come to terms with the fact that the "fingerprints" of our consciousness are all over what we are doing there. A universe without consciousness has no quantum mechanics in it at all, nor anything recognizable as physics, because as Bohr put it, physics is about what we can say about nature. And by "we", he means our consciousness/perceptions/intelligence, etc.. Not our measuring apparatus, which is quite mute.

. Any irreversible interaction is sufficient.

This provides me with a more concrete example of my point-- the fundamental interactions in physics are generally time reversible, so "irreversibility" is already a concept that appears, not in the physical interactions, but at the level of our mental processing of those interactions. Hence, there is no such thing as "irreversible" in the first place, without consciousness (and here I make no effort to parse between what it means to be conscious versus intelligent or able to perceive, as I don't think we have any kind of precise language to use to parse those notions).

 

[DevilsAvocado]

... A universe without consciousness has no quantum mechanics in it at all, nor anything recognizable as physics, because as Bohr put it, physics is about what we can say about nature. And by "we", he means our consciousness/perceptions/intelligence, etc.. Not our measuring apparatus, which is quite mute.

I don’t recall Bohr or the Copenhagen interpretation ever saying anything about consciousness... this sounds like the von Neumann/Wigner interpretation.

But I’m curious; exactly how do you explain the evolution of the universe and ΛCDM if consciousness has any crucial role in this evolution? For example red-shift of the CMB, in relation to "our consciousness", is something that you could describe in detail. Thanks.

I’m all ears!

 

[DevilsAvocado]

It's just an analogy, but I think it is a good one. The point is, if we stick to a "just the facts ma'am" approach, we have a bunch of events that led up to WWI, and we have a bunch of photons hitting detectors at various times. That's it, nothing more.

I don’t agree that "events that led up to WWI" could be compared to physics and the scientific model. If this analogy was ever to operate as a theory that is refutable, you need two things:

1. A mathematical description of the human mind, which we don’t have.
   
   
2. The ability to experimentally repeat "events that led up to WWI" as many times you like, which is impossible.

Ah, but the first half of your sentence has nothing to do with the second! The data never change, true, but whether or not the apple continues to fall is a description of what happened to the apple, it isn't data! Newton says the apple fell, Einstein says the apple ceased to be accelerated by the branch. A totally different story about what happened to the apple, both consistent with the data. So the data did not change when Einstein came along, but what "happened to the apple" certainly did change with Einstein! Because what happened is a construct, and changes in information, centuries later, can change that construct dramatically.

You are mixing apples and oranges. As I said Newton’s apple does not suspend itself in mid-air just because of Einstein, it will continue to fall the same way it always has, i.e. to the ground.

This is the empirical fact that no new theory could ever change - apples will not suspend in mid-air, period.

The explanation on why and how apples fall could of course change in the future.

 

[Cthugha]

And I'd like to interject one caveat that is seemingly picky but I think is actually quite important: meaning always requires consciousness. But your point, I believe, is that consciousness does not enter at the same physical level as the other elements of the experiment, the detector, the slits, etc., nor does it enter at the level of the theory, the Hilbert space or the operators, etc. So there is no "piece of the apparatus" we need to call conscious, and there is no term in the equation we might want to call the "effect of consciousness."

I have already stated elsewhere (was it inside this thread? I do not know) that one cannot rule out the influence of a human looking at some experiment with absolute certainty as there is no possibility to test this experimentally. You cannot find out what happens if you never find out what happens. However, this also makes it a non-scientific question for exactly the same reason. It is interesting from a philosophical point of view, though.

This provides me with a more concrete example of my point-- the fundamental interactions in physics are generally time reversible, so "irreversibility" is already a concept that appears, not in the physical interactions, but at the level of our mental processing of those interactions.

I doubt that. Irreversible interactions occur in every measurement. Whenever some superposition of states ends up in an eigenstate. Whenever entropy changes. In the context of my post you quoted I just wanted to point out that there is some difference between processes like inserting a wave plate in a light beam and rotating its polarization on the one hand and processes like absorbing a photon at one certain position. The first is reversible and does not constitute a measurement. The second is usually irreversible, collapses a wave function and constitutes a measurement.

Irreversibility shows up in entropy and such things as the arrow of time. While it is true that many underlying fundamental processes may be reversible, there is nevertheless a statistical prevalence for things to happen in a certain way (see Feynman's famous broken cup example) in the sense of statistical mechanics. I do not think that mental processing is a necessity for that concept from a physics point of view. Philosophical discussions are of course a different topic, bit from my point of view rather distracting when discussing real experiments.

 

[Maui]

But I’m curious; exactly how do you explain the evolution of the universe and ΛCDM if consciousness has any crucial role in this evolution? For example red-shift of the CMB, in relation to "our consciousness", is something that you could describe in detail. Thanks.

I’m all ears!

Something tells me a non-realist would not consider the CMB and the Big Bang the ultimate explanation of existence and reality. I am not sure they believe in reality at all(and that's not the craziest I've seen in the interpretations war)

 

[DevilsAvocado]

 

[San K]

I have already stated elsewhere (was it inside this thread? I do not know) that one cannot rule out the influence of a human looking at some experiment with absolute certainty as there is no possibility to test this experimentally. You cannot find out what happens if you never find out what happens. However, this also makes it a non-scientific question for exactly the same reason. It is interesting from a philosophical point of view, though.

I think there are (many simple) ways to rule out the influence of a human looking at an experiment.

By setting a series of processes, a cascade/chain of events (...like a domino effect).

One could still argue that the whole process happens when a human looks at it.

one of the arguments (and there are more) refuting that would be:

if you were to repeat the experiment say a hundred/thousand times...you could predict with exact certainty at what any particular point in time where the cascade of events would have reached...for each, and every, instance/run of the experiment.

another refutation would be:

that the series of events cannot happen in an instant, the moment a human looked at the other end of (or anywhere in-between) the series of events

another refutation would be:

even if you assumed multiple universes...you end up with infinite universes...for the more complex setups/experiment...

 

[Ken G]

I... this sounds like the von Neumann/Wigner interpretation. don’t recall Bohr or the Copenhagen interpretation ever saying anything about consciousness

Bohr said that physics is not about nature, it is about what we can say about nature. Last I checked, "we" were conscious.

But I’m curious; exactly how do you explain the evolution of the universe and ΛCDM if consciousness has any crucial role in this evolution?

How do "I" explain it? You mean using my consciousness, or not using my consciousness?

 

[Ken G]

I have already stated elsewhere (was it inside this thread? I do not know) that one cannot rule out the influence of a human looking at some experiment with absolute certainty as there is no possibility to test this experimentally. You cannot find out what happens if you never find out what happens. However, this also makes it a non-scientific question for exactly the same reason. It is interesting from a philosophical point of view, though.

There might not be such a "firewall" between what is scientific and what is philosophical. The point being, consciousnesses do both science and philosophy.

I doubt that. Irreversible interactions occur in every measurement.

Not so, irreversibility is imposed by the analyst, as all the primitive happenings as described by classical physics are reversible. What's more, nothing ever actually reverses, it's just a mode of thinking that they could or could not. We judge the event to be irreversible based on assumptions we make about the constraints on the system. These judgements are useful, they are not mistaken or illusory, but they do come from our analysis. Nature never reverses itself, so nothing is actually reversible in nature. What's more, everything in nature happens only once, or at least that is a natural assumption to make that no experiment has ever refuted. Thus, the whole notion of "reversibility" comes from us, yet it has value in our physics, like so many of the other notions of physics that come from us. It's a little off topic though to get into thermodynamics!

Whenever some superposition of states ends up in an eigenstate.

I think you mean, whenever we choose to treat a system as changing from a superposition of states to an eigenstate. And we have good reason to do that, I don't dispute that, I'm just pointing out that it is we who are making that choice-- not nature. Such happenings do not actually occur in nature, none of those things actually exist. Quantum mechanics certainly doesn't claim they exist, the theory is perfectly clear on the fact that idealizations uphold that kind of language.

In the context of my post you quoted I just wanted to point out that there is some difference between processes like inserting a wave plate in a light beam and rotating its polarization on the one hand and processes like absorbing a photon at one certain position. The first is reversible and does not constitute a measurement. The second is usually

Yes, that is certainly true, I'm not trying to contradict the validity of that point. I'm saying something different-- as the thread is about the role of consciousness in physics.

While it is true that many underlying fundamental processes may be reversible, there is nevertheless a statistical prevalence for things to happen in a certain way (see Feynman's famous broken cup example) in the sense of statistical mechanics.

Not for things to happen that way, but there is certainly value in organizing our experiences around that way of thinking. In our consciousness.

I do not think that mental processing is a necessity for that concept from a physics point of view.

But it is, and just look at your own language: there is no "physics point of view", because physics doesn't have a point of view, that is the prerogative of consciousness.

Philosophical discussions are of course a different topic, bit from my point of view rather distracting when discussing real experiments.

In many situations in physics, yes, but not when the question is fundamentally about the role of consciousness in physics. In that situation, these other issues need to be raised, not in contradiction to what you were saying, but in addition to it.

 

[DevilsAvocado]

Bohr said that physics is not about nature, it is about what we can say about nature. Last I checked, "we" were conscious.

Okay, so how did you check this, with the help of "God"? Or, did you call 9-1-1?

I mean, according to you, everything is a wobbly fairy tale of "philosophical talk" and "(un)consciousness". So how could you ever check/prove that you are conscious?

Crucial, since most of your claims seem to be compatible to cranky unconsciousness.

[I know it’s hard for you to talk about anything that makes sense. Therefore, I’m going to help you with the most basic question:

– If nothing is real besides your (un)consciousness, how are you ever going to prove that your (un)consciousness is real, that it mean anything, except mumbo-jumbo?]

Please elaborate.

A universe without consciousness has no quantum mechanics in it at all, nor anything recognizable as physics

Unscientific nonsense and distortions of history... if you are claiming that Niels Bohr ever said anything like this stupidity, quote please.

This is what Niels Bohr actually said, as quoted in "The philosophy of Niels Bohr" by Aage Petersen (September 1963):

"There is no quantum world. There is only an abstract physical description. It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about nature..."​

And of course, the key word is quantum. Bohr never doubted the ontological reality itself, only the extent of our epistemic access to the real universe.*

You are distorting the words by Bohr as to "if we don’t talk about the universe, it will cease to exist" which is hilarious and completely absurd, and something that Bohr never said.

Niels Bohr is known as "The Man Who Talked".
Ken G is known as "The Man Who Spoke in Tongues".

How do "I" explain it? You mean using my consciousness, or not using my consciousness?

Well, it doesn’t seem to make much difference what "mode" you are in – nothing you say makes sense anyhow. But let’s not get stuck in tribulations between your ears; how about "fingerprints"?

All the same, I think quantum mechanics is one of the places where we are forced to come to terms with the fact that the "fingerprints" of our consciousness are all over what we are doing there.

Again, I will make it simple for you: – Are there, or are there not "fingerprints" of your (un)consciousness in the Cosmic Microwave Background, that has been red-shifted for ~13 billion years?

[If Yes, how was life at time of last scattering? Any "scattering parties"?]

So there is no "piece of the apparatus" we need to call conscious

Wow! I’m stunned! You are sure about this?? The apparatus need not to be conscious!?
If this will cause you any trouble, just send me a PM and I will talk to Harry Potter!


*Bringing the Human Actors Back On Stage; The Personal Context of the Einstein-Bohr Debate, David Kaiser, British Journal for the History of Science 27 (1994): 136-137.

 

[DevilsAvocado]

There might not be such a "firewall" between what is scientific and what is philosophical. The point being, consciousnesses do both science and philosophy.

Don’t know about the "firewalls" in your world, but on PF there are rules, and if you want to discuss philosophy or fuzzy personal speculations, you are in the wrong forum.

It's a little off topic though to get into thermodynamics!

No worries mate! We’re already as off topic one could get, wonderland here we come!

I'm just pointing out that it is we who are making that choice-- not nature.

Right, your brain has been controlling the universe from the beginning.

as the thread is about the role of consciousness in physics

Gosh, there must be something wrong with my browser... I have been searching OP for "consciousness"... and I just can’t find it...

In our consciousness

Go man, go!

that is the prerogative of consciousness

Yes!

fundamentally about the role of consciousness in physics

Yeah! YAY!

 

[Ken G]

Okay, so how did you check this, with the help of "God"?

Um, now you are disputing that we are conscious? I don't think you are interested in informative exchange. We'll just have to leave it that you are not understanding anything I'm saying, and not bother to try and place the blame. You are welcome to continue to imagine that the universe is just the universe, and our conception of it has nothing to do with how we conceive. I wouldn't try to tax you, my comments are for those willing to get past that.

Gosh, there must be something wrong with my browser... I have been searching OP for "consciousness"... and I just can’t find it...

Try post #55, or get a new browser. It's a long thread-- perhaps it has not occurred to you the thread has taken some twists and turns since the OP five pages ago. But as I said, you are not interesting in informative exchange, so that's fine, I'm willing to discuss these issues with those who are.

 

[DevilsAvocado]

Um, now you are disputing that we are conscious?

Of course not, I’m in the mainstream camp, consciousness is what it is, and as far as I know no one has yet defined it mathematically or proved that it can create universes, etc.

You are the one disputing reality, that nothing except your conscious is real. And the question is really simple: How do you prove that you are conscious if you live in a "bubble of self-creation", i.e. nothing outside your conscious is real?

By your "bubble-version-of-reality": It could all be a dream. [And I am your worst nightmare]

And there’s no way for you to prove or disprove this statement, right?

If there is; please let us know.

I don't think you are interested in informative exchange.

Sure I am, very much so. The problem is that when you face a question you can’t answer, you start to play games, and I think you just have to accept that I "play a little" in return. Fair enough, huh?

So, I’m going to give you one more chance to answer a serious question in a serious way. You seem not to like the Cosmic Microwave Background, so let’s talk stars instead (like our sun).

Could you please explain to me (and the readers): How intelligent life and consciousness could arise *before* any stars ignited in the universe? According to you, no evolution of gas clouds and formation of stars can ever take place, without a consciousness "making them real"?

[If you are refuting biological evolution as well, you’re definitely in the wrong place.]

Try post #55, or get a new browser.

More games:

Same answer to all questions: The presence or absence of humans has absolutely nothing to do with the outcome. The meaning of observing in physics does not require any consciousness. Any irreversible interaction is sufficient.

And you take this as a justification to start a long harangue about consciousness and physics??

Ken G, some post of yours are very nice and very deep, and you know I have praised you for it, but then some post doesn’t follow any logic at all... it’s just n-u-t-s...

 

[Ken G]

Of course not, I’m in the mainstream camp, consciousness is what it is, and as far as I know no one has yet defined it mathematically or proved that it can create universes, etc.

Nor did I ever say it could. More straw men? Don't you ever get tired of misquoting me?

You are the one disputing reality, that nothing except your conscious is real.

More misquotes. Please don't refer to anything I say without quoting me, you never interpret it correctly.

And the question is really simple: How do you prove that you are conscious if you live in a "bubble of self-creation", i.e. nothing outside your conscious is real?

None of that has anything to do with anything I said. I'm am utterly uninterested in proving that I am conscious, this can be taken as an axiom or go have a discussion with someone who has some definition of the word where I am not it. What "conscious" means is like what a "point" means in geometry-- it must be held as axiomatic that we understand this, because defining it is fruitless for those who don't understand it already.

And there’s no way for you to prove or disprove this statement, right?

Correct, there is no way, and no need, to prove that life is not a dream. Science certainly does not require that we prove this, nor do I. Science does not care if you think life is a dream, or if you think there is absolute truth, or if you think our most naive notions of reality are absolutely true. Science doesn't need any of that baggage, nor do I-- all we do is make predictions, and form a sense of understanding, which together give us power over our environment and a sense of aesthetic order and beauty. That's it, that's what science does-- it is totally unimportant if you imagine it is a dream or if you imagine it isn't a dream, science just goes," huh? What difference does it make to me? I never had anything to do with your belief system."

The problem is that when you face a question you can’t answer, you start to play games, and I think you just have to accept that I "play a little" in return.

You are mistaken. When I face a question I can't answer, I look at why I can't answer it. You just pretend that you can, and when I point out the pretense, you start misquoting me. If you could really make a logical argument, you would not need to replace what I really say with caricatures about dream worlds that are not even wrong, they are simply irrelevant.

Could you please explain to me (and the readers): How intelligent life and consciousness could arise *before* any stars ignited in the universe? According to you, no evolution of gas clouds and formation of stars can ever take place, without a consciousness "making them real"?

More misquoting. I already answered this, but you didn't understand. Let me try again. First of all, I "like" the CMB just fine. But if you insist on repeating your same question for stars, I'll give you the same answer for stars. The word "star" is an invention of human intelligence. This is quite demonstrable, just pick up a dictionary or astronomy text, and look where it says "author". So, your question is, how could this word that we invented, to go with a concept that we formulated, not have existed before there were humans. Well, I'm sorry, but the only thing I can say is, how could either the word or the concept have arised before there where humans? Now, of course I know what you will say, you will say you are not talking about the word or the concept, you are talking about the actual thing. Um, just think about that for two seconds, please.

[If you are refuting biological evolution as well, you’re definitely in the wrong place.]

And the endless litany of misquotes go on and on. Maybe if I explain this one more time, you'll get it: there is nothing wrong with theory of evolution. It's fine, it's a wonderful theory, which means it is a wonderful way that human intelligence uses to organize and make sense of our sensory perceptions. That also means it is very good science. It also means it is a construct of human intelligence. That also means there is a role of consciousness in the theory of evolution. These are all just plain facts, I'm sorry that you cannot accept these facts, and feel the need to replace them with preposterous claims I never made in order to refute them. Maybe you just want to have a simplistic view of what science is, and don't like being asked to think in a more sophisticated way. I don't know why you feel the need to replace what I say with something else.

 

[DevilsAvocado]

You are the one disputing reality, that nothing except your conscious is real.

More misquotes. Please don't refer to anything I say without quoting me, you never interpret it correctly.

Feel free to blame me for anything, that’s totally okay. The real problem though, is the fluffy way you are expressing yourself, like the in following comment below, where one could only come to the conclusion that biological evolution "is a construct of human intelligence" solely, while you ignore raw data like bones and DNA. And if I would bring the that up, you would go on with something like "well, human [consciousness] got those bones out of the ground, no?", which is some sort of "kindergarten logic".

There’s only one "little" problem with these homemade personal cranky speculations of yours; you’re in a never ending recursive loop that leads to a catastrophic contradiction:

To discover [the theory of] evolution, one needs human intelligence and consciousness, and to get human intelligence and consciousness, one needs [biological] evolution.​

But you don’t have the capacity to separate facts from theory, and that’s why you end up in an intellectual Black hole, with no odds of ever getting out.

As you are clearly ignorant of terminology, process and the facts, here’s quote that should make everything clear (for any normal person):

Evolution is a theory. It is also a fact. And facts and theories are different things, not rungs in a hierarchy of increasing certainty. Facts are the world's data. Theories are structures of ideas that explain and interpret facts. Facts do not go away when scientists debate rival theories to explain them. Einstein's theory of gravitation replaced Newton's, but apples did not suspend themselves in mid-air, pending the outcome. And humans evolved from ape-like ancestors whether they did so by Darwin's proposed mechanism or by some other yet to be discovered. — Stephen Jay Gould​

[my bolding]

And the endless litany of misquotes go on and on. Maybe if I explain this one more time, you'll get it: there is nothing wrong with theory of evolution. It's fine, it's a wonderful theory, which means it is a wonderful way that human intelligence uses to organize and make sense of our sensory perceptions. That also means it is very good science. It also means it is a construct of human intelligence. That also means there is a role of consciousness in the theory of evolution. These are all just plain facts, I'm sorry that you cannot accept these facts, and feel the need to replace them with preposterous claims I never made in order to refute them. Maybe you just want to have a simplistic view of what science is, and don't like being asked to think in a more sophisticated way. I don't know why you feel the need to replace what I say with something else.

These are all just plain facts... Well, that goes straight down the intellectual Black hole...

I think you have to come up with a quote from On the Origin of Species where Charles Darwin clearly state; "Without my intelligent consciousness our ape-like ancestors would never have climbed down from the trees".

Or apologize for the extensive disinformation you are posting on PF.

[Please note: you added the words "theory of", where I originally used the phrase "biological evolution", in case you want to run the "misquote stunt" again.]


[my bolding]

More misquoting. I already answered this, but you didn't understand. Let me try again. First of all, I "like" the CMB just fine. But if you insist on repeating your same question for stars, I'll give you the same answer for stars. The word "star" is an invention of human intelligence. This is quite demonstrable, just pick up a dictionary or astronomy text, and look where it says "author". So, your question is, how could this word that we invented, to go with a concept that we formulated, not have existed before there were humans. Well, I'm sorry, but the only thing I can say is, how could either the word or the concept have arised before there where humans? Now, of course I know what you will say, you will say you are not talking about the word or the concept, you are talking about the actual thing. Um, just think about that for two seconds, please.

Thank you very much Ken, I understand if you are sorry, but I can’t remember when I laughed this hard. I have one last simple little question for you, which will end this remarkable discussion:

What came first, humans or our sun*?

*I don’t care how you define "sun", anything goes; word/concept/actual thing. I just want to hear you spell this out. If you need three alternative answers, that’s okay too.

Gosh! This is so exciting! :!)

 

[Ken G]

As I said, you cannot understand. If what I said was what you thought I said, it would be pretty silly, that much is true. I guess that's just the best we're going to do. I will just point out one of your logical mistakes, there are too many others to count:

There’s only one "little" problem with these homemade personal cranky speculations of yours; you’re in a never ending recursive loop that leads to a catastrophic contradiction:
To discover [the theory of] evolution, one needs human intelligence and consciousness, and to get human intelligence and consciousness, one needs [biological] evolution.

This logical error is quite well known by people who understand epistemology, it is called a classic "category error". You have confused the way we understand the way our intelligence appeared (whatever our intelligence is in the first place, which we currently have little understanding of), with however our intelligence actually appeared, what our intelligence actually is, and what "appearing" actually means, none of which do we have anything but effective concepts to deal with. The correct statement of what you were trying to say, on the other hand, clearly reveals the absence of any logical paradox, goes like this:
"To create the theory of evolution, and discover its success, humans needed intelligence. The way they obtained that intelligence is explained, to humans, by their theory of evolution."
Anyone who sees a logical inconsistency in that doesn't understand the very first thing about either science or logic.

 

[Len M]

What came first, humans or our sun*?

*I don’t care how you define "sun", anything goes; word/concept/actual thing. I just want to hear you spell this out. If you need three alternative answers, that’s okay too.

Gosh! This is so exciting! :!)

There is a perfectly legitimate philosophical perspective that says neither came first – its called idealism.

From my perspective, mind independent reality does not lie within space and time; I see those as constructs of our mind. So there is no historical time line of past events as having existed outside of our reality; they are constructions that we make as if there was a hypothetical human present along that time line. That’s not to say that I consider our reality an illusion, it is simply the case that our reality plays out as it plays out – nothing more than that. We think of the separation of subject and object, space and time, as being some kind of bedrock of the universe independently of us, but why on Earth should we think that to be a universal truth?

From all of this I see physics as exploring the mix that constitutes our reality – our minds, our consciousness and our perceptions. That exploration is objective because it utilises the agreement that exists between us all concerning the physical world – we all perceive the apple fall to the ground. That intersubjective agreement gives us mathematical predictive models that work for everybody and that is the scientific method. Intersubjective agreement works at the quantum level as well, but here the subject/object separation becomes distinctly uncomfortable, the separation breaks down in a manner that is just not apparent at the macroscopic level.

We have the scientific method and the mathematical predictive models that are true to everyone, but that’s as far as I would take that “truth”. In terms of extrapolating the models to mind independent reality, that is a philosophical quest, and we can all take our own philosophical stance on that from strong realism to radical idealism. There is nothing in science that can remove the mind from our reality and create a “God’s eye” perspective, thus the objectivity within science, whereby we “separate” the subject from the object is not a proven absolute separation - the true nature of that separation is a philosophical question. From my philosophical stance, it is a separation in appearances only, not an absolute separation and is part of the “whole” that constitutes our minds, our consciousness and our perceptions. I consider (philosophically) that our minds, consciousness and perceptions “emerge” from a mind independent reality that will forever be outside of the scientific method, simply because the scientific method requires that separation. Those who dispute this will have to tell me how we can step outside of our reality without using our minds.

So that’s just my philosophical opinion, of relevance only to me and no more or less valid than any other philosophical stance. I see no reason to state as a universal truth a notion that the sun (as it plays out in our reality) exists outside of our reality with its human time line in anything like our intuition suggests it does. The historical time line is there hypothetically, in the sense that we can establish the physics of a time line that is based on a hypothetical observer, but none of that constitutes a universal truth that that timeline exists independently of our reality. But what always seems to be the case is that physics does not seem to easily divide between philosophical thought and physical models when considering ontology. Some physicists such as Bernard d’Espagnat (his books, “conceptual foundations of Quantum Mechanics”, “Veiled Reality” and “On Physics and Philosophy” along with Ken G on this forum provide a framework in which to make the distinction, and it is a framework for which I am most grateful to follow, but others seem to (naively in my opinion) consider that the scientific method can penetrate mind independent reality. All we will ever have for that task is philosophical thought.

 

[Ken G]

(Waiting for the predictable reaction whenever naive scientific thinkers are told they need to use philosophy to understand their science.)

 

[Cthugha]

There might not be such a "firewall" between what is scientific and what is philosophical. The point being, consciousnesses do both science and philosophy.

Sure, there is. The minimum requirement for a theory to be scientific lies in the possibility to falsify it. And yes, I am aware that this definition places small parts of todays high energy physics theory in the realm of philosophy. And, yes, I am aware that "falsifying" is also a human concept.

Thus, the whole notion of "reversibility" comes from us, yet it has value in our physics, like so many of the other notions of physics that come from us. It's a little off topic though to get into thermodynamics!

I do not think it is off topic. If you look at the historical development, the concept of entropy in thermodynamics is closely linked to Shannon's measure of entropy in information theory which gives a good starting point to identify reversible or irreversible interactions.

I think you mean, whenever we choose to treat a system as changing from a superposition of states to an eigenstate. And we have good reason to do that, I don't dispute that, I'm just pointing out that it is we who are making that choice-- not nature. Such happenings do not actually occur in nature, none of those things actually exist. Quantum mechanics certainly doesn't claim they exist, the theory is perfectly clear on the fact that idealizations uphold that kind of language.

Here you lost me. Are you trying to say that "superposition" and "measurement" are just names and theoretical processes describing the "real" thing. If so, sure. That is what science is about. However, this topic was at the point discussing whether it makes a difference for the outcome of an experiment whether you place a photo diode somewhere and record some detections automatically or whether you place a human there who (exaggerating) shouts once every time a photon passes by him. Taking this completely to epistemology is somewhat like cracking a walnut using a sledgehammer to me.

Yes, that is certainly true, I'm not trying to contradict the validity of that point. I'm saying something different-- as the thread is about the role of consciousness in physics.

As stated above I do not think that is the case. The question was about the outcome of one certain experiment when people are watching, not about the role of science in developing a human language and concepts describing reality. While I understand it is a process of abstraction, talking about the terms used in science being different from the things they describe, does not really help much when discussing this special issue from the scientific (experimentally testable) point of view and tends to make readers think that there is some deeper role of consciousness in QM as these discussions turn up again and again. In fact, this is not so. Any argument you offer is valid for any scientific discipline. I see no reason to highlight this point especially when discussing QM.

 

[Ken G]

Sure, there is. The minimum requirement for a theory to be scientific lies in the possibility to falsify it. And yes, I am aware that this definition places small parts of todays high energy physics theory in the realm of philosophy. And, yes, I am aware that "falsifying" is also a human concept.

Then look at Len M's last post, to see the necessity of philosophy in science-- if one's goal is to understand one's science. Of course, if one is a "shut up and calculate" type, then that is the only time one can place a firewall successfully between physics and the philosophies that invented physics. But frankly, I've met many who claimed they believed in "shutting up and calculating", but none who ever really did. We all want to understand our calculations.

I do not think it is off topic. If you look at the historical development, the concept of entropy in thermodynamics is closely linked to Shannon's measure of entropy in information theory which gives a good starting point to identify reversible or irreversible interactions.

Yes, and that's exactly what I'm talking about. Shannon entropy is about information, and information is very much in the mind of the physicist. That is the path for seeing how closely connected is the whole concept of entropy, and the way we process information.

I'll give you a classic example. Imagine someone with a very neat office, everything alphabetized. Then a tornado hits. Afterward, we'd say the entropy has risen-- we'd say that something irreversible happened. But all that really happened was the office went from one state to one other state, out of all the possibilities. The only thing that makes that irreversible is our assumptions about the context-- we group all the neat offices together in a bin with few entries, and all the messy offices in a bin with zillions of entries, and we know that a tornado is much more likely to choose the latter bin. But these are our groups, our classifications, related to our goals and how we think. Reality itself might not give a hoot if the papers were alphabetized or stacked neatly, every state of the office is just one state to the reality. This is not to say that irreversibility is a bogus concept, it's a very useful concept-- but it is useful to us, to how we think, to what our goals are. Our consciousness is all over the concept of irreversibility-- an unconscious universe wouldn't give a hoot about the entire issue, it would have no idea what we mean by reversibility because reality never reverses anyway.

Here you lost me. Are you trying to say that "superposition" and "measurement" are just names and theoretical processes describing the "real" thing.

And even more than that, I mean that the whole concept of a "system" that could be in an eigenstate in the first place is an idealization of our conscious minds. We have chosen what we care about, and found a way to predict it, but reality would have to see what we are doing as hopelessly naive. Adopting a highly realist attitude and tacking on some anthropomorphism to boot, we must still admit that reality would need to be tracking so much vastly more information than we talk about with our "eigenstates of a subsystem" construct, it would be almost laughable to it what we call quantum mechanics. Like you said, that's what science is about.

However, this topic was at the point discussing whether it makes a difference for the outcome of an experiment whether you place a photo diode somewhere and record some detections automatically or whether you place a human there who (exaggerating) shouts once every time a photon passes by him.

That's where it started, and you answered that already. I'm saying that if we are going to talk about the role of consciousness in quantum mechanics, writ large, we must go beyond the simple issue of whether there is a human looking at the detector or not. I'm talking about the very meaning of "a detector", including whether or not there is any such thing as a detector when there are no consciousnesses around to decide what that is. I'm saying that quantum mechanics is done by conscious physicists, and they give meaning to terms like "detector" and "measurement", not reality itself (much like the concept of entropy above).

So that is the sense that I am saying there is a crucial role of consciousness in quantum mechanics-- there simply is no such thing as quantum mechanics without it. But I agreed with you that if we are just talking about whether or not a human mind is registering a particular detector reading, that is not anything of importance to the theory of quantum mechanics

While I understand it is a process of abstraction, talking about the terms used in science being different from the things they describe, does not really help much when discussing this special issue from the scientific (experimentally testable) point of view and tends to make readers think that there is some deeper role of consciousness in QM as these discussions turn up again and again. In fact, this is not so. Any argument you offer is valid for any scientific discipline. I see no reason to highlight this point especially when discussing QM.

That is a valid objection, but I can answer it. I do feel there are analogs in other areas of science, like entropy in thermodynamics. But the problem is never as central as it is to quantum mechanics, because quantum mechanics has a formal evolution that is unitary, which leads to things like interfering wavefunctions, but experiments show nonunitary outcomes, like individual photon counts and decoherence in general, any time one particular outcome is perceived out of all the possible ones. Someone curious about how two-slit experiments can work this way, and what is wave/particle duality, are going to have to encounter the role of the conciousness that says a photon has been detected. That's because formal quantum mechanics (the Schroedinger equation in closed systems) doesn't even allow such a thing to happen, and indeed some interpretations of it assert that it does not in fact happen, it's just a kind of illusion that it happens.

I'm pointing out that the fundamental weirdnesses associated with two-slit experiments are fundamentally about the role of the consciousness, for the simple reason that only a conscious being can perceive a nonunitary outcome. Without the need to explain that perception, quantum mechanics works just fine treating everything as a superposition-- it's only a question of how large the closed system is.

 

[Cthugha]

Then look at Len M's last post, to see the necessity of philosophy in science-- if one's goal is to understand one's science. Of course, if one is a "shut up and calculate" type, then that is the only time one can place a firewall successfully between physics and the philosophies that invented physics. But frankly, I've met many who claimed they believed in "shutting up and calculating", but none who ever really did. We all want to understand our calculations.

Understanding in the meaning you use is not the task of science. It is the task of mapping (intersubjective) experimental results to a predictive model of how stuff works and minimizing the number of false predictions. Of course many want to "understand" the meaning at a deeper level. This is, however, a philosophical question, not a scientific one and it is good practice to keep this difference in mind.

Yes, and that's exactly what I'm talking about. Shannon entropy is about information, and information is very much in the mind of the physicist. That is the path for seeing how closely connected is the whole concept of entropy, and the way we process information.

Your tornado example is a classical one. Entropy is clearly more important in a scenario where a system having one state is linked to a system having many degenerate states of the same energy (like an excited atom and the vacuum).

And even more than that, I mean that the whole concept of a "system" that could be in an eigenstate in the first place is an idealization of our conscious minds. We have chosen what we care about, and found a way to predict it, but reality would have to see what we are doing as hopelessly naive.

Does it? To be honest I do not really care. As long as the predictions are ok, the physics is ok, too. By the way I also feel pretty bored by the constant discussions whether CI, MWI, BM, Ithaca or any interpretation of qm is better than the other. As long as the predictions do not differ, that is not a scientific question. I see the point that some people may get some inspiration from one certain interpretation and that is fine. However, I do not see any scientific importance beyond that.

That's where it started, and you answered that already. I'm saying that if we are going to talk about the role of consciousness in quantum mechanics, writ large, we must go beyond the simple issue of whether there is a human looking at the detector or not.

One can discuss that. But I doubt that was really the question asked in this thread. I think the question was indeed simply whether a human looking at a detector makes a difference. Nothing else.

That is a valid objection, but I can answer it. I do feel there are analogs in other areas of science, like entropy in thermodynamics. But the problem is never as central as it is to quantum mechanics, because quantum mechanics has a formal evolution that is unitary, which leads to things like interfering wavefunctions, but experiments show nonunitary outcomes, like individual photon counts and decoherence in general, any time one particular outcome is perceived out of all the possible ones.

If you take your position seriously then it will apply to any field of science. There are not even simple things like tennis balls, but just our perception of it. It is just more puzzling in qm.

I'm pointing out that the fundamental weirdnesses associated with two-slit experiments are fundamentally about the role of the consciousness, for the simple reason that only a conscious being can perceive a nonunitary outcome. Without the need to explain that perception, quantum mechanics works just fine treating everything as a superposition-- it's only a question of how large the closed system is.

I still doubt that the role is fundamental in physics. It can be fundamental in philosophy, but physics is indeed "shut up and calculate". Of course many people are interested in areas beyond physics, but imho things are much clearer if you keep the dividing line clear.

I agree that philosophy had influence on the development of physics and science in general like developing falsifyability (is that a word? hmm) as a criterion to distinguish between scientific and other theories. But apart from that I really vote for keeping the physics part "shut up and calculate" and taking all other issues to philosophy.

 

[Ken G]

Understanding in the meaning you use is not the task of science. It is the task of mapping (intersubjective) experimental results to a predictive model of how stuff works and minimizing the number of false predictions. Of course many want to "understand" the meaning at a deeper level. This is, however, a philosophical question, not a scientific one and it is good practice to keep this difference in mind.

I agree completely, except I view "the task of science" as having a broader mission. Indeed, if you go into any classroom where science is being taught, you will find the philosophical version there far more often than the strict predictive model version! It's a lot to ask a high school science teacher to say "now we will leave the formal realm of what science is and begin to address the philosophical ramifications" every time they want to say "forces cause acceleration" or some such. So I think we do better by tracking the difference you speak of, but not imagining that science comes equipped with a firewall between them. Science, in practice, is more like an amalgamation of those two very different goals.

Your tornado example is a classical one. Entropy is clearly more important in a scenario where a system having one state is linked to a system having many degenerate states of the same energy (like an excited atom and the vacuum).

Yes, I am using a classical theory there.

Does it? To be honest I do not really care.

A self proclaimed "shut up and calculate" type. More power to you, but as I said, many times I have seen that claim but few times have I seen it held to, the lure is just too great.

One can discuss that. But I doubt that was really the question asked in this thread. I think the question was indeed simply whether a human looking at a detector makes a difference. Nothing else.

I suspect you're right. But sometimes the questioner does not know what question to ask to get to the answer they need. We have to guess a little.

If you take your position seriously then it will apply to any field of science. There are not even simple things like tennis balls, but just our perception of it. It is just more puzzling in qm.

Yes, that is true. Indeed I'd say it's pretty clear that "tennis ball" is not a strict ontological concept, it is an effective ontological concept, like all in science. Effective ontology is all you need, so that should be fine with you (and me also), my issue is with those who demand absolute ontology.

I still doubt that the role is fundamental in physics. It can be fundamental in philosophy, but physics is indeed "shut up and calculate".

Not in those high school science classes-- it just isn't.

Of course many people are interested in areas beyond physics, but imho things are much clearer if you keep the dividing line clear.

I don't disagree, it's important to maintain that division, even though both end up being part of the mission of science.

I agree that philosophy had influence on the development of physics and science in general like developing falsifyability (is that a word? hmm) as a criterion to distinguish between scientific and other theories. But apart from that I really vote for keeping the physics part "shut up and calculate" and taking all other issues to philosophy.

That is certainly a logically sound proposition. It does make philosophy more important to scientists though!

 

[RalkoCzez]

Isn't the Quantum Eraser a Fourier Transform in action?

 

[Cthugha]

I agree completely, except I view "the task of science" as having a broader mission. Indeed, if you go into any classroom where science is being taught, you will find the philosophical version there far more often than the strict predictive model version! It's a lot to ask a high school science teacher to say "now we will leave the formal realm of what science is and begin to address the philosophical ramifications" every time they want to say "forces cause acceleration" or some such. So I think we do better by tracking the difference you speak of, but not imagining that science comes equipped with a firewall between them. Science, in practice, is more like an amalgamation of those two very different goals.

Why should one say such? Saying "forces cause acceleration" is perfectly within the realm of science. Every student should be taught a lesson about scientific theory and method once during school time, maybe adressing questions of intersubjectivity, a bit of Popper, qualia problems and such, but that is enough. As soon as that framework is established, forces and accelaration are perfect scientific concepts. There is no need address any philosophiocal implications.

Yes, I am using a classical theory there.A self proclaimed "shut up and calculate" type. More power to you, but as I said, many times I have seen that claim but few times have I seen it held to, the lure is just too great.

Taken by your above quote you have a very strange concept of what shut up and calculate should be. Forces and accelerations are "shut up and calculate". The question, what a force is microscopically and how it creates accelerations might not be, but is usually not considered in classrooms.

Not in those high school science classes-- it just isn't.

Taking the very rough models that are usable in classrooms into account, high school physics is very much shut up and calculate. What the guys in school expect, however, is often something different.

Isn't the Quantum Eraser a Fourier Transform in action?

That short comment is way too short to judge whether you understood the concept or not. All in all, it is not that easy.

 

[Ken G]

Why should one say such? Saying "forces cause acceleration" is perfectly within the realm of science.

The reason I view that as a philosophical statement (and one on rather shaky ground, actually), rather than a scientific statement, is that it certainly does not fall within the narrow realm of empirical demonstrability that you referred to earlier. It is a statement that certainly has its purposes, and in fact I use it all the time, but I also recognize when I do that it does not stand up to the standard of what is scientifically correct. The reason I object to saying that statement is scientifically justified in any absolute sense is twofold:

1) It asserts a particular type of causation, which actually stems from how we think about the phenomenon rather than anything that is demonstrably happening there. Instead of saying what is accurate, that we can understand acceleration better by imagining that it is caused by forces (similar to how we gain conceptual understanding of everyday life by imagining cause/effect relationships rather than simple temporal correlations which would suffice to get power over our environment), we just say that acceleration is actually caused by forces. By removing our responsibility from drawing that conclusion, we can imagine we have stated some absolute truth, around the true existence of forces, and the true presence of a causal relationship. Yet neither of those claims are scientifically demonstrable, a force is not an ontological entity (it is even defined by its effects, not by what it is), and is not even needed in some versions of classical physics. And causation is also not present in any theory-- when we say F=ma, we can imagine the causal relationship a comes from F/m, but we can just as easily imagine the causal relationship that F comes from ma. (The latter would be how forces are derived from Lagrangian mechanics, for example.)

2) The statement sounds highly ontological, yet does not identify the true sources from which the ontological elements are borrowed. As I said already, forces are scientifically defined by their effects, not by what they are, so it is already a bit scientifically imprecise to say that these things we call forces can cause anything (they are defined by what we imagine them causing, so that's quite circular). A more accurate statement is that accelerations can be organized in very useful ways by attributing them to forces, where forces are nothing more than the patterns by which the accelerations can be organized. This core circularity causes no problems when no ontological claims are made surrounding it. Such claims are just a convenience, that we all use but can create misconceptions very easily-- especially if we ourselves lose track of what semantic conveniences we have invoked.

Taken by your above quote you have a very strange concept of what shut up and calculate should be. Forces and accelerations are "shut up and calculate".

No-- not when forces are said to cause acceleration. That is not shut up and calculate-- it is an ontological claim on reality that is not scientifically justified. It's OK to say it, we're not going to make sure everything that we say is fundamentally scientifically correct, but we should be aware when we are leaving the realm of what can be scientifically demonstrated (the shut up and calculate realm), and have entered the philosophical realm of using language to understand our calculations. If I can do the calculation without believing that forces cause acceleration (which I can), then how can that statement be part of the calculation?

The question, what a force is microscopically and how it creates accelerations might not be, but is usually not considered in classrooms.

It's not an issue of detail. There is no such thing as a force, not at any scale or in any level of detail, that is not simply a non-unique, contextual, and goal-oriented concept borrowed from some formal mathematical structure (here a structure along the lines of classes of potential energy functions). We are fundamentally talking about patterns of accelerations, and how to group and quantify those patterns, and we generate the force concept to unify and simplify that task. There is never any reason to imagine that forces actually exist, or that they cause anything, but it is certainly a useful fantasy when we go to picture what our calculations are saying. Some might find the concept useful in actually carrying out the calculation, some might prefer to use a different approach that never references forces at all. Yet how many students are going to recognize these facts when they are told "the cause of an acceleration is a force"?

 

[StevieTNZ]

If we place detectors behind the slits in Scully et al delayed choice quantum eraser experiment, could we open the shutters at the same time and 'erase' the which-way information? If we describe the whole situation using the Scrodinger equation, everything is in superposition.

Also, with Bohm Mechanics, wouldn't we expect clicks EVERY TIME we open both shutters at the same time? That would be because there'd be a definite particle in either cavity each time.

 

[Cthugha]

1) It asserts a particular type of causation, which actually stems from how we think about the phenomenon rather than anything that is demonstrably happening there. Instead of saying what is accurate, that we can understand acceleration better by imagining that it is caused by forces (similar to how we gain conceptual understanding of everyday life by imagining cause/effect relationships rather than simple temporal correlations which would suffice to get power over our environment), we just say that acceleration is actually caused by forces. By removing our responsibility from drawing that conclusion, we can imagine we have stated some absolute truth, around the true existence of forces, and the true presence of a causal relationship. Yet neither of those claims are scientifically demonstrable, a force is not an ontological entity (it is even defined by its effects, not by what it is), and is not even needed in some versions of classical physics. And causation is also not present in any theory-- when we say F=ma, we can imagine the causal relationship a comes from F/m, but we can just as easily imagine the causal relationship that F comes from ma. (The latter would be how forces are derived from Lagrangian mechanics, for example.)

I disagree with most of that. I agree that forces are not ontological entities. However, the same is true for accelerations. The point I really disagree with is "By removing our responsibility from drawing that conclusion, we can imagine we have stated some absolute truth". Any kind of absolute truth is not the job of science Determining what is really happening is also not the job of science. The job of science is to create models that correlate with experimental outcomes and have predictive power. And any theoretical scientific statement should be understood as an explanation of the model, whether "forces cause accelerations", "our universe started from the big bang" or "global warming is related to the decrease of pirate activity". These models are to be tested against our perception of reality via experiments. That is not the same as comparing it to reality, but anyway the closest we can get.

2) The statement sounds highly ontological, yet does not identify the true sources from which the ontological elements are borrowed. As I said already, forces are scientifically defined by their effects, not by what they are, so it is already a bit scientifically imprecise to say that these things we call forces can cause anything (they are defined by what we imagine them causing, so that's quite circular).

No scientific term is defined by what it is, but by its effects.

If I can do the calculation without believing that forces cause acceleration (which I can), then how can that statement be part of the calculation?

Sure you can believe that forces do not cause acceleration. That is a different model. There is no need to find a single model. And that is (also) the meaning of "shut up and calculate": Stopping at the level where one may have different models of the same situation which are equally good and predictive without having one better or more real than the other. All scientific statements similar to "forces cause accelerations" should always be understood in the framework of the model used.

Some might find the concept useful in actually carrying out the calculation, some might prefer to use a different approach that never references forces at all. Yet how many students are going to recognize these facts when they are told "the cause of an acceleration is a force"?

I do not know. Maybe many people are not aware of that. Anyway, they should be. On the other hand many students encounter for example both Newtonian and Lagrange/Hamilton mechanics and often the role of science is clarified while these topics are discussed. However, I obviously cannot say how usual this is around the globe.

Do you mind if we stop the discussion here or move it to a different topic? While the discussion was somewhat fitting in the beginning, I somewhat feel like we are hijacking the topic.

@StevieTNZ: I have to reread the original Scully paper again before I can comment on that.

 

[Ken G]

I disagree with most of that. I agree that forces are not ontological entities. However, the same is true for accelerations.

And for every single concept used in physics, yes. But accelerations have a mathematical definition as the rate of change of the rate of change of position-- the problem is more generally with the ontological baggage attached to the concept of position.

The point I really disagree with is "By removing our responsibility from drawing that conclusion, we can imagine we have stated some absolute truth". Any kind of absolute truth is not the job of science Determining what is really happening is also not the job of science.

Then you don't disagree at all-- that's what I'm saying. I'm merely noting that the sentence "forces cause acceleration" has an ontological character, which means that it is very often interpreted as a statement of what is really happening-- exactly what you say science is not trying to do.

The job of science is to create models that correlate with experimental outcomes and have predictive power.

As I said before, that is not the sole job of science, and what happens in any science classroom demonstates that very clearly. Science is not just taught "here is the model and here is its predictive power," it is taught "this is what science tells us is the truth of our reality." There is no question that science is taught that way, more often than the way you describe. If you doubt that, sit in on any astronomy lecture the day they say why the Earth isn't the center of the solar system but the Sun is, or that the Sun doesn't go around the Earth but the Earth does go around the Sun.

And any theoretical scientific statement should be understood as an explanation of the model, whether "forces cause accelerations", "our universe started from the big bang" or "global warming is related to the decrease of pirate activity". These models are to be tested against our perception of reality via experiments. That is not the same as comparing it to reality, but anyway the closest we can get.

I couldn't have said it better myself. All that isn't clear to me is why you think that disagrees with what I just said above!

No scientific term is defined by what it is, but by its effects.

You are saying that all science is epistemic rather than ontological. That is what I keep saying! Yet there are many threads going on right now about the PBR theorem and how it proves the ontological character of quantum mechanics, and another thread where Jaynes is quoted as saying that people are entering into logical fallacies if they won't admit that atoms are real. Is an atom defined by what it is, or what the effects of the concept are? If the latter, how can anyone hold that good science must assert that atoms are real?

Sure you can believe that forces do not cause acceleration. That is a different model. There is no need to find a single model. And that is (also) the meaning of "shut up and calculate": Stopping at the level where one may have different models of the same situation which are equally good and predictive without having one better or more real than the other.

I would say that shut up and calculate involves stopping even short of that-- it stops at saying that all models are just concepts we use for their effectiveness, with no ontological character except what we bring to them-- provisionally, conceptually, and in a goal-oriented way. That's also what I have been saying.

All scientific statements similar to "forces cause accelerations" should always be understood in the framework of the model used.

I agree, yet the same cannot be said generally. Have you seen the threads where the existence or non-existence of virtual particles is being hotly disputed? Why can't those on both sides of that debate just allow that the existence of virtual particles should always be understood in the framework of the model used? The problem is, some models are better than others, and so people tend to say that one particular model is the "right one" to talk about virtual particles, but someone else talks about them by modeling them in a different way. Different subdisciplines of physics even have their own particular slant, yet still the argument rages, no one is saying that none of these concepts actually exist outside of the mathematical structure that they are borrowed from.

I do not know. Maybe many people are not aware of that. Anyway, they should be.

There are probably a dozen active threads right now in which it is clear that many people are not aware of this. Indeed, on one thread I find myself being ridiculed for suggesting that even the ontological elements of quantum mechanics are provisional, contextual, and dependent on the goals of the physicist-- not just the ontological elements of ancient discarded theories. I'm branded a non-realist for noticing that human intelligence plays a role in choosing the mathematical structures from which we borrow our ontological elements in our theories!

Do you mind if we stop the discussion here or move it to a different topic? While the discussion was somewhat fitting in the beginning, I somewhat feel like we are hijacking the topic.

Yes, I don't want to be accused of hijacking. However, I feel that the basic issue we are discussing is at the heart of a very large number of threads on here-- including this one. Now I'll step back and let the delayed-choice ontological haggling go on without the recognition of how unnecessary it is to the way science actually works!