(See Part 1, Part 2, Part 3 and Part 4. Also I am going to suspend the limit of three comments per post for this series of posts because it is a topic that benefits from back and forth discussions.)
It is time to finally get to the issue that triggered this series of posts and that is why some people think that consciousness plays a role in quantum mechanics.
When Einstein asked his friend Pascual Jordan whether he really believed that the moon exists only when he looked at it, he was undoubtedly being facetious. It is like asking if, when we enter a completely dark room and turn on the light and see all that is there, whether the furniture was not there before but only appeared because we observed it. It is not necessary that I must observe it, just that someone has observed it. In the case of macroscopic objects like the moon and room furnishings, the state had been observed before and thus it is no longer in a superposition of states. Thus the world of macroscopic objects is classical. The issue only arises when we talk about something that has not been observed before, such as the spin of a particle that has been created in a superposition of two states.
The big unanswered question is: What is it about a macroscopic object (the detector) that triggers the collapse of the wave function from a superposition of states to a single observable state? We have talked glibly about this interaction of the state with detectors somehow being the cause but we can also ask what makes something a detector. The detector could be something like a camera or a geiger counter or anything that macroscopically registers the state that the particle is found in so that we can know it. But if we believe that everything in the world is ultimately governed by the laws of quantum laws, which most physicists do, then the detector should also in principle be governed by quantum laws even if it is technically impossible to carry out the calculations.
This brings us unavoidably to the famous (or infamous) Schrodinger’s cat. This cat is perhaps the most famous cat in history, heard of even by people who have no idea who Schrodinger is or what the cat is supposed to have done. I have never quite understood the fascination with this story. It was created by Schrodinger because he intensely disliked the idea of a states being in a superposition and he felt that by making the state macroscopic, the absurdity of the idea of a cat being in both dead and alive states would be manifest and people would reject it. But his cat is not an argument for or against superposition and is thus an irrelevancy. This thought experiment uses the fact that radioactive decay is also a quantum phenomenon in which we do not know exactly when an atom will decay but can only assign probabilities that it will do so in a given time interval. So at the beginning, the atom will be undecayed but as time goes on, the probability that it will decay within that time interval increases. While the cat and the rest are in the closed box, since the atom is in a superposition of a decayed and an undecayed state, that must mean that the entire system must also be in a superposition of two states. One is the state of an alive cat and an undecayed atom. The other is a dead cat and a decayed atom. When the box is opened by us the superposition collapses and we see just one of those states. But we have not really learned anything new. The problem is that the cat, even if found alive, is unable to tell us whether it was in either or both of the two states before we opened the box. So this does not really solve the problem of how we know that there exists a superposition of states before the measurement. I actually find the whole cat paradox distracting and not helpful but I introduced it because everyone expects it to appear whenever we discuss the strangeness of quantum mechanics. To introduce the possible role of consciousness, I find it clearer to deal with the spin up and spin down particle and a detector. Here too we can discuss the situation in terms of a combined system of the detector and particle. This can be treated as a larger quantum system that consists of a superposition of two states: One state consisting of the detector that shows the result that the particle is spin up combined with a particle that is spin up, the other state consisting of the detector that shows the result that the particle is spin down combined with a particle that is spin down. Now when we make a measurement on this combined detector plus particle system, the wave function of this new enlarged state collapses to one of those two states, which is what we see. But this requires yet another detector/observer to act on the system of the original detector plus particle. You can see that by introducing a new detector, we are starting a regression, where now the new detector can also be combined with the earlier detector and particle to create a newer, larger, and more complicated superposition of states consisting of two detectors plus the particle. Now we need yet another detector in order to collapse this new enlarged superposition of states. And so on, with the quantum system becoming larger and larger, including more and more detectors, until it finally encompasses the entire universe. At this point the process must stop since there is no room for even a larger detector to serve as the external observer. So the system of the entire universe must be in an uncollapsed superposition of states. At this point, some physicists say the hell with it, that they have better things to do than worry about something that may not have any consequences in real life. They shrug their shoulders and stop with just the original particle in a superposition of states and a single macroscopic detector and are satisfied that that interaction somehow causes the particle’s wave function to collapse. It does not matter if we don’t know how or why it collapses, it just does, that is the way that the world is, and we should just accept it and move on. The immense success of quantum mechanics despite this big hole in our understanding suggests to them that knowing the answer to this particular question likely does not matter and that we should just use quantum mechanics to calculate observable quantities, something that it has been remarkably successful in doing in the microscopic world. As has sometimes been said, the attitude taken is “Shut up and calculate!” But others refuse to shut up. They think (and I tend to agree) that this is an interesting question in quantum theory that is worth addressing even if it may not have practical consequences in determining experimental results. But these attempts can lead, if we are not careful, to ideas that can open the door to woo territory. I am not saying that all the people who take these next steps are promoting woo but the fact is that some of these serious suggestions made by credentialed physicists have been exploited by woo practitioners (I am looking at you, Deepak Chopra) to make all manner of outlandish claims, and the introduction of consciousness into the discussion is one of those elements. Some people suggest that the reason we have the regression that eventually leads to a quantum system consisting of the universe as a whole is because all the detectors we have been talking about so far are inanimate and materialistic objects made up of atoms, and thus are subject to also being treated as quantum systems. They argue that to collapse the original wave function requires at some point the presence of a non-material entity that cannot be considered as a quantum system. They say a conscious observer satisfies this requirement because they claim that consciousness is something immaterial that is not governed by the laws of physics and thus cannot be made part of the ever-expanding detector system. Instead it can act on the system to collapse it. In other words, the presence of a Geiger counter or a camera or a bubble chamber does not collapse the wave function until a conscious observer notes what that detector has recorded. Until that point, the combined system of the detector and particle remains in a superposition of states, uncollapsed, with both options possible. So now we have consciousness as part of the mix and you can see why things can get wild because consciousness itself is a contentious issue quite apart from any role that it might have in quantum mechanics. Once you have introduced a non-material entity that lies outside the laws of physics but can act in the world as an autonomous agent, you are off to the races and pretty much anything goes. As a hard-core materialist myself, I do not view consciousness as a nonmaterial entity. I view it as an epiphenomenon, a byproduct of the workings of the brain, rather than as some kind of separate entity that can act independently and do things outside of the brain, like collapse the wave function. And since the brain is a material entity, it is subject to the same constraints as any other detector and thus can become part of a superposition of states, like the cat. So, for example, we can treated the particle and the conscious observer as being in a superposition of two states: one consisting of the particle being spin up and the brain registering it as spin up, the other with the particle spin down and the brain registering it as spin down. And so we are back to the regression to the universe issue. So, in my opinion, introducing consciousness into this discussion does not advance our knowledge and only invites people to include all manner of quasi-supernatural mysticism. But maybe that is what they want. As far as I am concerned, consciousness plays no special role in quantum mechanics. This ends my planned series of posts triggered by questions about the video of a discussion between physicist Bernard Carr and Robert Lawrence Kuhn about the role of consciousness in measurement. I hope that it answered at least some of people’s questions. This is a topic that has many subtleties and counter-intuitive ideas so I would not be surprised if it led to more questions, though I hope it did not lead to more confusion! I will be adding more posts to deal with any questions that come up that require extended responses. I already plan to add one on exactly what constitutes ‘objective reality’ and how we can tell if it exists, in response to a comment by bluerizlagirl.
up until this point it hadn’t really registered for me that physicists themselves would regard macroscopic things as behaving like the microscopic, as quantum systems. why should they have to be, to square quantum with classical physics? just try to get better ideas about what the “observer” is doing and draw that interaction between macro and micro scopic as the dividing line between things with and without this property. i can see how it’s a difficult, possibly impossible problem to solve, but i don’t see a useful solution in extending superposition up to the level of the cat.
at any rate, i’m with the people throwing hands up. if physics is your job and your interest, go nuts. but it’s neither of those things for me, so i’m good.
Regarding the bloody cat: the Geiger counter inside it is a macroscopic detector. It either goes off before you open the box, or it doesn’t. The cat is never in a superposition, any more than the Geiger counter is. The ‘problem’ is that the quantum state of a macroscopic object is far too complicated for us to evaluate.
The same sort of problem exists even in classical physics. The two-body gravitational problem is beautifully simple and solvable. But the stability of the Solar System can only be established theoretically over millions of years, rather than billions. Because it’s too bloody complicated.
(emphasis mine)
That’s what I still don’t get. How do we know that a particle didn’t have the state that we observe before we observed it? Why do we think that the observation is what caused the state?
“the Geiger counter inside the box” is what I meant. No cat I’ve known would stand for such a thing being inserted into it.
billseymour @3:
At the risk of sounding like a broken record, because of the Kochen-Specker theorem. I regret that there is no simple explanation for that.
billseymour @#3,
I will give a shot at explaining it in a post next week that will be an addition to this series.
consciousness = plogiston = luminiferous ether = strings 🙂
Bébé @#1,
My response to your question is what I said in the first post in this series. We (i.e., physicists) think that there is just one world and it should be describable by just one set of laws. The idea of having a macroscopic world obeying classical laws and a microscopic world obeying quantum laws just does not sit well, especially since there is no clear dividing live between the two worlds.
So either the quantum world applies everywhere or the classical world applies everywhere. The second option does not work because we know that the classical laws fail at the microscopic scale. Quantum theory works at the microscopic level and there seems to be no theoretical reason why it should not also work at the macroscopic world, especially since the sizes of entities in the microscopic world that have been found to obey quantum theory have been slowly increasing.
Of course, a third option is that neither classical or quantum laws are correct and we need a new theory that bridges both. Sucha theory has not yet been found.
or neither does and we need a completely new theory.
Mano @8:
It sits just fine with me. Two radically different scales can appear to be governed by different laws. The laws at one scale can be seen as emerging from those at another. As an example, what is the clear dividing line between particles bouncing around in a box, and the macroscopic concepts of pressure and temperature? We’ve largely worked those out. Quantum physics is just more complicated.
total baby know-nothing over here but @9 makes sense to me too. like, taking this pre-scientific philosophical, going subatomic is going to the edge of what it even means to exist, so it’s easy to imagine how existing itself could work differently there.
nonetheless, i dip. this is way above my pay grade. i’ll have an article up tomorrow about why i asked in the first place, with an appropriate link back to your series.
@ 3 billseymour
I can only vaguely recall from years ago when I became infatuated with quantum physics as a layperson and tried my best to understand it:. I believe it is possible to design an experiment such that the results will be statistically different depending on whether a) a particle has a definite spin that is simply unknown until we detect it, or b) the particle has no definite spin until we detect it. The name Bell rings a (ahem) bell, and I think this wikipedia article may be relevant -- https://en.wikipedia.org/wiki/Bell_test -- but it’s too full of physics jargon (“local hidden variables”) for me to give a meaningful synopsis.
So we must await Mano’s lucid explanation. But for now I think the short answer to your question is that experimental results are uniformly consistent with superposition states and inconsistent with unknown definite states.
@ 9 Grigjanis
What a silly analogy! The macroscopic phenomena are what we would expect given an understanding of excited particles. There is no discontinuity.
But macroscopic objects in closed systems (composed of subatomic particles) do not behave as we would expect from the behaviour of subatomic particles. There is a discontinuity. That was Schrodinger’s entire point. His cat thought experiment was a reductio ad absurdum showing that there is an unexplained discontinuity between the subatomic and macroscopic
We get you’re a “shut up and calculate” guy who shrugs and moves on devoid of curiosity, but it’s not addressing the point to simply say “the equations are too hard” or “the Geiger counter is macroscopic”. That’s side-stepping Schrodinger’s point. Why different rules for the macroscopic, and what is “macroscopic” anyway except “lots of subatomic”?
I agree with Mano that consciousness is an emergent phenomenon of biology and electical activity in the brain. But I think many people strongly resistant to a role of consciousness in the collapse of the wave function misunderstand the claim. They seem to think the claim is that we “will” the universe into existence.
This ignores that the collapse is probabilistic, and consciousness doesn’t “control” the possibilities.
Physicists like John Wheeler were not Deepak Chopra!
If there is, for example, a 50/50 probability of seeing a live/dead cat opening the box and recording the information in your consciousness; that does not mean you can conjure up a live cat by force of will. It means the cat is in a superposition state until observed (observation requiring consciousness) but the outcome is random like the toss of a coin.
Physicists like Wheeler didn’t think consciousness was involved because of some magic property of minds, but because of information theory. It was the storage of information that was (somehow) fundamental to physics.
Silentbob @11:
You missed the next sentence -- “We’ve largely worked those out.” But it took more than a hundred years, from Bernoulli’s primitive version of the kinetic theory of gases, to the work of Maxwell, Boltzmann and Gibbs, to establish statistical mechanics.
Please do explain how we expect a system of on the order of 10^23 subatomic particles to behave based on the behaviour of a few subatomic particles, and how that differs from what we do observe.
Is that the royal ‘we’?
PS it’s just about 100 years since the Schrödinger equation was first written.
Doesn’t decoherence do a pretty good job of handling the “transition” from micro to macro? That’s always felt to me to be kind of an entropic solution.
So, on one hand, the “observer” in the S.-cat setup is the Geiger counter. If the counter pings, the cat dies. If we open the box without a ping, the cat is alive? But if the radioactive particle missed the detector, the cat would still be superpositioned until we opened the box, at which point our observation would collapse that, with either live or dead being equally possible. So the Geiger observer can only yield one result, while a human observer could yield either. Not really sure where I was going with that, just that it has always bugged me that the setup assumed a magical counter that would necessarily record the quantum event of the radioactive decay, which is not predictably unidirectional. 🙂
I had thought some physicists held that interaction with another subatomic “particle” would suffice to collapse a superposition. Nicht war? (Somebody needs to explain why Germans happened to figure out all this in the 20th century!)
Personally, I settle for a flawed metaphor: the unresolved state is like a spinning coin, the “observation” is the table that coin lands on.
As for consciousness, that strikes me as a variable. If the “observation” (of a relevant instrument) settles the question, surely it matters whether the observer is a Singham or Grigjanis who whom the reading means something or the observer understands it no better than me or the cat.
Fortunately, xkcd also explains Wavefunction Collapse.
Consciousness is only pertinent to quantum collapse in that all quantum experiments to date have been set up by purported consciousnesses…
… which brings up an unaddressed observation. (Not that I want this comment to prematurely collapse, so please read on.) The experimental apparatus that is consciously set up to emit particles with indeterminate wave functions does so seemingly without becoming part of the uncollapsed superposition of states. If the detector is part of the superposition of states, then how is the emitting apparatus not also in that regression of states?
Thanks for the set of posts , I enjoyed them -- I still dont understand quantum mechanics -but thats all me , not you! With Quantum Mechanics I think its even worse because a lot of times I cant even figure out what question to ask , much less understand the answer.
Sure. But are we both observer and the observed ? If say our brain internally makes a decision to like/dislike someone , but never express it out loud , what happened here -- do separate portions of our brain count as same or different ? You dont need to believe in anything supernatural to wonder what is happening.
Unrelated -- Do you not re-evaluate your definition of free will (if we were to reset to a point , we can only make the same decision ) given all this quantum probabilistic stuff -- which doesnt guarantee the same outcome.
SilentBob @11
We get you’re a “shut up and calculate” guy who shrugs and moves on devoid of curiosity
Hope that made you feel better. I guess Rob makes a better target for your frustration than the uncaring universe that moves on devoid of curiosity.
A more charitable description of Rob’s perspective is “you can’t argue with the math.” I like Rob’s comments because he functions as a hard reality check lest we all start talking woo. It’s very tempting for the ignorant to talk woo, I should know.
file thirteen @20: Thanks for that.
i don’t think consciousness plays any role in QM.
first because: what is consciousness? there is no good definition of it. we don’t know how brains work. i think most people would say humans are conscious. are primates? cats and dogs? mice? octopi? sea cucumbers? ants? planarians? tardigrades? slime molds? amoeba? bacteria? carbon atoms? where do you draw the line for what is consciousness--and why do you draw the line there? i don’t think such an ill defined concept as consciousness is useful to do science.
second because: for the first 380,000 years or so, there were no stable atoms, until Recombination when hydrogen formed. i think it’s safe to say no observers were around to collapse wave functions. so, did the universe exist only in quantum superposition of 10^80 particles back then?
today we can detect and map photons from that era to get maps of the CMB. did Penzias and Wilson collapse the wavefunction of the universe at Recombination by being the first observers to detect photons from that era? if so, was everything in the universe in a superposition until they made their first detection in 1964, or did it collapse 380,000 years ago when Recombination began?
if they collapsed the wavefunction at 380,000 years, it was quite a non-local measurement. billions of light years away, billions of years ago.
if they collapsed it in 1964 with their first detection, we should ask anyone who was alive in 1964 what it is like being in a superposition.
all those suppositions seem rather silly. but might make for a good sci-fi novel…
there must be some way wave functions collapse naturally, without any consciousness involved.
Deepak @#19,
The lack of free will does not guarantee the same outcome because of the quantum indeterminacy. Different initial states can produce different outcomes.
But that does not mean that there is free will. ‘Will’ implies the ability to control events in specific ways. When we have indeterminacy, we cannot choose what outcome to get, so we are not in control. We are subject to randomness.
@mano @23
I may be mistaken , but I believe that in one of your previous posts on free will , you did also use the if we could reset the world to a point in the past , we would make the same choices (= no free will).
Deepak @#24,
You must be mistaken because classical determinism (which is what you are describing) is not compatible with quantum mechanics.
@mano @25
Ah I see I may have misunderstood your words but perhaps not entirely
https://freethoughtblogs.com/singham/2023/11/17/on-free-will/
I believe you do classify yourself as a ” thoroughgoing materialist”
What I meant by that is that the decision that was made at that moment could not have been willed to be something different. In other words, if I pick up a cup, it is not the case that I could have decided not to pick up the cup, which is the alternative decision. I had no control over that particular decision.
What made me pick up the cup is a combination of historical factors, environmental factors, and randomness due to quantum theory. I could not have willed it to be something else.
Mano @ 27
All we have available to us for sensing and decision making are photons and electrons, and none of them in our biology are in any configuration that could create a superposition of states to influence decisions nor detect outside sources of quantum phenomena to influence decisions. There is too much macroscopic meat for random quantum events in our decisions. A cosmic ray interacting with atoms within our eye causing us to see a flash of light while driving down the road and we crash is no more a quantum event than a lightning strike causing a tree limb to fall in front of our car and we crash. Our biology cannot detect the whether the cosmic ray had up or down spin, in both cases it is history and environment all the way down.
I much prefer that all my decisions are a puppet show of my environment and history and that I enjoy all the meals I eat rather than some random quantum events make me end up at Chick-fuck-a or in front of a bowl of Cap’n Crunch cereal.
@ 22 Robbo
It is indeed a part of the participatory anthropic priciple that observations in the present select histories. It is not that the present determines the past, but that there are many possible pasts, one of which corresponds with observations in the present.
https://en.wikipedia.org/wiki/Anthropic_principle
You sound like Einstein who simply couldn’t accept a probabalistic universe. He was convinced there must be determinsm at base. He thought the alternative was “rather silly” and “might make for a good sci-fi novel”. He was wrong. “Common sense” can lead you astray when it comes to things far outside the realm of common experience.
Also, consciousness is “natural”. You propose a false dichotomy.
By the way, I don’t think it’s commonly appreciated just how fundamental to our reality the probabilistic nature of the universe is. If Einstein were right -- your computer wouldn’t work! X-D This website wouldn’t exist.
Solid-state electronics absolutely depends on particles having no fixed position and momentum at the same time. Integrated circuits absolutely depend on particles behaving in ways that would be completely impossible in a deterministic universe. Your computer, your smartphone, anything with a chip or a transistor in it only works if particles exist in probable states, not definite states.
Quantum physics isn’t just some interesting nerd thing to think about -- you rely on it practically every day of your life. Just sayin’.
@ file thirteen
To use a physics metaphor, you assume my determination of Grigjanis’s position and momentum was based on a single observation. Not so. The more observations, the more the probabilities are constrained, and the more definite we can be. My observations span years.
X-D
(In plain English, Grigjanis has form.)
To use a physics metaphor, you assume my interpretation of your determination of Grigjanis’s position and momentum was based on a single observation. Not so. The more observations, the more the probabilities are constrained, and the more definite we can be. My observations also span years, or didn’t you think of that possibility? Do you believe only your observations matter?
X-|
(In plain English, think before you write.)
Mano,
If you’re taking requests I would be interested in some commentary on so-called “quantum eraser” experiments.
That is, experiments where although the position of a particle is detected, the experiment is designed such that the information cannot be recovered -- by say, recombining separate paths -- and then an interference pattern is observed.
The implication being that it is not detection that collapses the wave function, but whether information on a particle’s path can be recovered.
https://en.wikipedia.org/wiki/Quantum_eraser_experiment