I just finished reading Jim Baggott’s new book Quantum Reality: The Quest for the Real Meaning of Quantum Mechanics – a Game of Theories. I was attracted to it due to this part of the description:
Although the theory quite obviously works, it leaves us chasing ghosts and phantoms; particles that are waves and waves that are particles; cats that are at once both alive and dead; and lots of seemingly spooky goings-on. But if we’re prepared to be a little more specific about what we mean when we talk about ‘reality’ and a little more circumspect in the way we think a scientific theory might represent such a reality, then all the mystery goes away.
Baggott begins by giving a basic primer on quantum mechanics, notably focusing on the measurement problem, the fact that quantum objects appear to behave like waves, until a measurement is made, then they behave like particles. (I gave a lightning primer on this a few weeks ago.) He then has a discussion about the philosophy of science, the demarcation problem, and scientific realism (as opposed to instrumentalism or anti-realism). He provides a number of “realist propositions”:
- There is such a thing as objective reality.
- Invisible entities such as photons and electrons really do exist.
- In quantum mechanics, the ‘base concept’ is the wavefunction.
- When deciding whether a theory or interpretation is realist or anti-realist, we ask ourselves what it encourages us to do.
The rest of the book is a discussion of various interpretations of quantum mechanics. He begins with the anti-real ones, but points out that, generally, these are anti-real only in the sense of rejecting proposition 3 above, not in terms of 1 or 2. In other words, these interpretations are not necessarily cases of idealism, or rejections of atomism, although they are sometimes assumed to be.
The main interpretation in this camp is the classic Copenhagen one with its wave function collapse. Others include Relational Quantum Mechanics, Information Theories, Consistent Histories, and QBism. It’d be a long post to describe all of these, but what they all have in common is in not claiming to provide a full understanding of the underlying physics, only our interaction with those physics. They all seem to say, “Move along, there’s nothing to see here,” or “Shut up and calculate!”
Personally, as an instrumentalist, I think the real vs anti-real distinction here is a red herring. In my view, Einstein was right, while pragmatically useful, what these theories are is incomplete. They fail to provide what we want from a scientific theory, a full framework to deduce, or at least explain, observations. The whole real vs anti-real designation just obfuscates this. My only beef with these interpretations is that the proponents often pretend that they’ve provided a final answer. In any case, once we’re willing to accept an incomplete account, I’ve never seen much benefit in moving beyond Copenhagen.
Baggott then moves on to the realist interpretations, such as deBroglie-Bohm pilot wave and various physical collapse theories. These interpretations at least make an attempt at explaining physical reality, although they all come with metaphysical costs, such as explicit non-locality in the case of pilot-wave. Baggott points out those costs, but notes that the approaches have the benefit of generating empirical investigation, something the anti-real ones aren’t good at doing.
There are a couple of discussions on decoherence. Decoherence is sometimes taken as an explanation of the wave function collapse, but it isn’t. While it describes how waves spread and become entangled into the environment, it never explains how the relation between the branches of the wave go from an and to an or, as in the particle going from being in a spin up and spin down state, to being in spin up or spin down, that is, the reduction to one reality.
In the penultimate chapter, Baggott gets to the idea of consciousness causing the collapse. John von Neumann in 1932, analyzing the dynamics, couldn’t find any mathematical reason for the wave function collapse, either at the measurement, in the measurement device, or in human sense organs. His explanation: something about the way the mind works causes it.
After expressing skepticism about the productiveness of this approach, Baggott then goes on a lightning tour of the consciousness debate, including citations of David Chalmers, Daniel Dennett, and others. It culminates in a discussion of Roger Penrose and Stuart Hammeroff’s theories about quantum consciousness. Baggott notes how aggressively speculative these concepts are, and discusses the issues that cause many in cognitive science and philosophy of mind not to take this approach seriously. Although I found his criticism here relatively gentle.
But the knives come out in the final chapter on the many worlds interpretation and its spin offs. I think it’s fair to say that Baggott detests this interpretation. He barely finishes a marginally fair description before attacking it. He goes on to discuss a number of increasingly speculative concepts, before finishing with a diatribe about multiverse theories. He groups them all together, seems to judge the lot by the most outrageous examples, then consigns all of them to hopeless metaphysics.
When I discussed Adam Becker’s book, I noted that Becker was often impatient with concerns about testability. I find the opposite vice in Baggott. He is often impatient with speculation. However, as I’ve noted before, science needs rigorous speculation to work. Baggott himself readily admits this, but doesn’t seem to apply it with theories he personally dislikes.
Anyway, it’s in the epilogue where we get something of a pay off on the promise of the book description. Here Baggott admits his sympathies with anti-real theories are growing. Many of the conundrums do seem to vanish with these approaches, but as I noted above, only because we’ve decided to make a virtue out of necessity and accept an incomplete account.
Baggott characterizes the many worlds approach as giving up, but I find this far more true with the explicitly anti-real interpretations. Maybe eventually we’ll have no choice but to live with an incomplete understanding. But I hope people never give up trying to move beyond it.
If you’re not familiar with quantum mechanics, or the interpretations in circulation, and would like a primer, this is a good book. One nice approach the book takes is to replace variables with pictures, making the quantum notation easier to deal with. Unfortunately, I think the book is marred by an unfair treatment of many worlds, but that’s not really unusual in this arena.
25 thoughts on “Quantum Reality”
First, a question. What, exactly, is an instrumentalist?
Second, this post involves a significant feature in philosophy, namely, ontology. You say “ Maybe eventually we’ll have no choice but to live with an incomplete understanding”, but this “maybe“ is an (almost) absolute “certainty”. I don’t know if the idea predates Kant, but he is the easiest to start with. He called it the “neumenon”, the thing in itself, as opposed to “phenomenon”, which is how we experience a thing. The standard paraphrase is: we can’t know what a thing *is*, we can only know what it *does*, and the “what it does” determines whether it exists. If it doesn’t do anything, we can’t know about it, so it doesn’t exist. [Sudden thought: maybe that’s a sufficient reason to say the multiverse doesn’t exist.]
So if we can’t know a “thing in itself”, what do we do? One possibility is to consign any ideas we find “hard” to it. (Hi panpsychism!). The other is to “never give up trying to move beyond it”, which I think of instead as digging down into it. We can keep digging down to find smaller parts, but at some point this effort will end because we will reach a point that to dig further will require more resources than exist. (Would you use half the galaxy to build the last collider?)
[FWIW: Relational QM is the best explanation I’ve seen so far.]
LikeLiked by 1 person
An instrumentalist, in my view, accepts that a scientific theory is not guaranteed to represent actual reality. It may only be a framework to predict observations, an a priori justification of a posteriori knowledge. (I should note that I always hope the theory represents reality, but I think we always have to be prepared for the possibility that it doesn’t.)
My issue with the interpretations labeled as “anti-real” isn’t their anti-realism. It’s that they are not a framework that predicts observations. They don’t provide that a priori justification for a posteriori knowledge, just posits some of them as brute facts. In other words, they do a lousy job at accounting for what things do.
I remember your attraction to RQM. If you’ll remember, my issue with it wasn’t the relational part, but the missing segments, a lack of accounting for what leads from one interaction to the next. You might assert that the missing accounting is noumena, but I don’t agree. What’s missing are accounts of what’s happening, a framework for accounting for why the phenomena occur.
Again, these accounts may be pragmatically useful, although I haven’t seen any more useful in that manner than plain old Copenhagen, but they’re not complete, even from an instrumental perspective.
For what it’s worth James, I also agree that Relational QM is the best model. There’s is nothing spooky, mysterious, wild or bizarre about RQM; it’s pretty straight forward. Mike’s criticism is unfounded because like any other model, RQM does not even attempt to address “causation”. Causation is still a mystery and will continue to be a mystery in the world of physics.
In the end, reality may just be what Mike finds objectionable, brute facts. To counter Mike’s criticism, RQM does an excellent job of accounting for what things do: (Stanford Encyclopedia of Philosophy)
The physical assumption at the basis of RQM is the following postulate: The probability distribution for (future) values of variables relative to S’ depend on (past) values of variables relative to S′ but not on (past) values of variables relative to another system S″.
If the objective reality of value being a brute fact at the center of power, a brute fact responsible for causation resulting in motion and form, then so be it.
I like this Jim Baggott guy. I suppose that you must have presumed as much given our similar “Many Worlds” stance. I recall Massimo Pigliucci talking favorably of him as well, or something which conforms with his “Nonsense on Stilts” book. Thus I was inspired to listen to their half hour 2014 rationally speaking podcast. http://rationallyspeakingpodcast.org/show/rs116-jim-baggott-and-massimo-on-farewell-to-reality.html
Even back then Baggott seemed to say things similar to what Sabine Hossenfelder has been saying in recent years. Of particular note is his skepticism for superstars who can’t easily be contacted given their fame. These people seem to use their enormous charismas to entrance people. I place Daniel Dennett here, and certainly the silky smooth many worlder Sean Carroll.
So according to Baggott, it’s effective to put me in the “antirealist” camp? Well I guess that’s okay as long as it’s noted that we don’t claim that nothing is real, but rather just that we’re unable to figure out what’s real. I still like the idea that one or more dimensions might exist beyond time and space that are essentially just detected at the quantum scale. I’ve got no need for locality or temporality given that these are essentially dimensions of existence which thus could be subverted to us with others that we don’t otherwise detect. I don’t know if anyone formally states this position. Of course string theorists get into extra dimensions, though not regarding QM that I know of.
One thing that I didn’t quite catch from your post, is Baggott’s QM interpretation. Or is his essentially just mine?
LikeLiked by 1 person
Baggott is definitely in the skeptic camp with Hossenfelder and Peter Woit. (Although lately Hossenfelder has made some posts that indicate her skepticism is pretty selective.) I don’t remember that Rationally Speaking episode, but I reviewed Baggott’s earlier book, Farewell to Reality, back in 2014. At the time I accepted all his stances as face value, although I now think at least some of them are a bit closed minded. For instance, I suspect Baggott would have an issue with your extra dimensions speculation.
As I noted in the post, I’m an instrumentalist myself, which is often considered synonymous with anti-realism. There is something to be said for being epistemically cautious, as long as we don’t pretend we have the final answer, which can easily harden into a dogma that freezes progress.
On formally stating your position and string theory, you’re actually taking the initial steps that can lead to things like string theory. One dimensional strings are what replace elementary particles in classic string theory. Although I have no idea if string theory ever gets into the measurement problem. It’s usually more presented as trying to reconcile QM and general relativity.
Baggott doesn’t express a specific QM interpretation. He actually doesn’t even definitively commit to anti-realism. He merely expresses doubts about his third realism proposition. He’s become wary of the metaphysical “costs” of realism theories.
Personally, I think the costs are irrelevant. Reality is reality. We should follow it wherever it leads, and deal with whatever “costs” arise. Worrying about those types of “costs” is what delayed acceptance of Copernicanism for several decades, and why people still resist evolution.
LikeLiked by 1 person
Wow Mike, so much conformity in our perspectives lately. We must be affecting each other.
LikeLiked by 1 person
I beg to differ. First off, technically, it is possible to view the whole process as “one reality”, namely the wavefunction. But if I read what you meant instead of what you wrote, the question is why do we stop observing and “and”-like state and start observing an “or”-like state. And decoherence explains that beautifully – as long as you use an appropriately probabilistic notion. It’s not absolutely certain that we will *either* collide with a quantum physicist running down the hall crying “Eureka, my quantum experiment worked” *or* not collide with him. It’s just really really (repeat lots of reallys) unlikely that we will experience a detectable superposition of those two states. And the list of “reallys” before “unlikely” rapidly gets longer, the more entangled with the environment that quantum experiment becomes.
LikeLiked by 1 person
Your reply presupposes the many-worlds interpretation. Under it, I agree with everything you said. In that interpretation, the and never becomes an or except relative to a version of the experimenter on one of the branches.
But decoherence by itself, sans any particular interpretation, doesn’t provide the and to or accounting.
Actually I think a lot of other interpretations could make decoherence do similar work for them. But I’m too lazy to work it out myself. I do admit that some Objective Collapse interpretations would be contrary to what I said.
LikeLiked by 1 person
From your intro, and the fact that Baggott has sneaked in an axiom – “In quantum mechanics, the ‘base concept’ is the wavefunction” – under the guise of a definition, I thought that he was going to end up endorsing the many worlds interpretation. As it is, he doesn’t seem to endorse any view. Do you think the book in any way lives up to the claim in its description that “then all the mystery goes away”?
LikeLiked by 1 person
I think he introduces the propositions to make clear where the anti-realism is purported to be. Don’t worry, he seems to be saying, it’s not like the quantum antirealists are calling all of reality into question, only this little part of it. But by calling it into question, it enables them to avoid the metaphysical costs. Whether the book delivers on its promise depends on how you feel about that move.
Myself, I’m an instrumentalist. I think we always have to be prepared that a scientific theory isn’t really representing reality. But it feels like cheating to depend on that antirealism, or to cherry pick it, only to avoid implications we don’t like. It only feels like a valid move if there is evidence, or at least clear logic, contradicting those implications.
In regards to many-worlds in particular, I found this snippet from the end of the final chapter revealing:
As you know, I’m pretty thoroughly aligned with Baggott, especially when it comes to MWI, but I have nothing new to add to an old discussion.
The more I think about it, the more I think decoherence explains everything except why the wave-function selects where it interacts, which is what I see as the core of the measurement problem. Why does the photon interact with this electron and not that electron. It appears to be the one truly random thing in reality. (Which, if so, would be fine with me. More than fine; I prefer a bit of randomness to reality.)
Once the interaction does occur, decoherence explains everything that happens (including why MWI has to be false, BTW). The photon’s wave-function is smeared among the wave-functions of all the particles local to the interaction — and spreads to other particles throughout the measurement device.
In the case of a photon, the photon is absorbed by the electron, so it’s wave-function essentially ends. In cases where the “particle” (a term we should always put in quotes because there are no such things as quantum “particles”) remains, its wave-function extremely rapidly decoheres by interacting with the surrounding particles.
There really is no mystery to any of that. The mystery is why this location and not that location. It’s possible that one may not have an answer.
LikeLiked by 2 people
I think you’d find a lot to cheer in Baggott’s final chapter. It’s pretty similar to his assessment in Farewell to Reality, albeit possibly more strident.
Definitely decoherence in and of itself doesn’t really help with the measurement problem. This fits when you remember that Zeh originally researched it to find support for the pilot-wave interpretation, which has no collapse. And since MWI is pilot-wave minus the particle, decoherence ended up supporting it as well.
I’m curious how see decoherence explaining why MWI must be false. Usually decoherence is seen as explaining why the branches of the wave evolve to no longer be able to interfere with each other, which seems like a major support of MWI (or pilot-wave if we want to go that way, although given your remarks about particles, probably not).
Definitely, the central mystery is why we get one result instead of multiple. Maybe we’ll never know. It might be that quantum entities are something so far out of the scope of what our minds evolved to process that we can never comprehend them. That seems to be the take of the explicitly anti-real approaches (Copenhagen, RQM, etc). It’s a pragmatic approach that has its virtues. But it goes against history to assume something is permanently unknowable.
“Definitely decoherence in and of itself doesn’t really help with the measurement problem.”
No, and you touched on another view of it when it comes to superposition. Why we measure a “particle” as having spin up (rather than down) seems entirely random. Likewise why a photon goes through a half-silvered mirror (or not).
I suspect, as with which electron a photon “selects” to interact with, these may be truly random events. There is also the mystery of non-locality in these selections. In the case of measuring spin, there is what happens with entangled particles separated by distance. In the case of “particles” interacting, the wave-function appears to collapse FTL.
Perhaps the mystery of non-locality and apparent randomness are related. It seems we’re gonna need a bigger theory. (Cue the Jaws music.)
As I think you know, I’m firmly on the realist side, so I think there is a theory we can discover, although I’m sure we’ll end up accepting that some kind of weirdness is just the way things are.
I suspect MWI involves a kind of mental “switch” that gets thrown one way or the other when one really digs into it. For some (e.g. Carroll), the idea is attractive and seems simple. For others (e.g. Baggott and I), the idea seems so without foundation it’s hard not to get strident.
It might be summed up in what I’ve said before about the requirements for the Big Bang creating a universe versus the idea that detecting a photon creates new universes so easily. How can a single photon have that kind of power? A while back I showed you the equation Everett based his ideas on, and that equation assumes the wave-function of the measured “particle” becomes a significant portion of the measuring device. That seems, to me, a huge assumption, and one without real justification or evidence.
So why decoherence seems to me to falsify MWI is my view that the wave-function of a single photon is utterly and completely swamped by the combined wave-functions of the detector. The phase information of the photon is absorbed and distributed such that it’s completely diluted and effectively lost.
On some level, its wave-function does become a part of the combined wave-function of the measurement device, but the wave-function contribution is minuscule. The energy the particle contributes is what the measurement device seeks to amplify to a detectable level.
If we’re going to go non-local in realist mode, then it seems like we need an actual theory of non-locality, on exactly how it would work. And it would have to be reconciled with special and general relativity. Maybe we’ll eventually have to go there, but I can understand why Einstein wasn’t wild about that option.
I don’t buy the version of MWI where a whole universe instantly comes into being either. I know some physicists try to sell that version, but I think it weakens their case. The version I find more plausible is the one where each branch starts at the site of the interaction and spreads from there. That might be instrumentally the same as a whole universe coming into being, but if we’re sticking with realism, then they’re not the same.
On a single photon and the detector, remember that as a system of quantum objects constantly interacting with each other, the detector is perpetually branching anyway. (As is, for that matter, a rock, or a person.) So the arriving photon isn’t doing anything every boson exchanged between the detector’s elementary particles aren’t already doing, although photon’s addition does further multiply the number of branches.
As you note, the detector is designed to magnify the energy effects of the photon. And this alters the state of the portion of the detector’s branches where the photon hit. All of those branches cascade into the environment, including to any observers, who will then have branches where the photon hit the detector and where it didn’t, and all variations thereof.
I agree our putative theory would have to account for non-locality. FWIW, back in high school I had the metaphor of a fish in water seeing the apparently unrelated finger tips of a human sticking their hand in the water. To the fish, there would seem no correlation.
So a realist theory of non-locality might involve something that turns our notions of spacetime on its head and allows for non-local points to be, in some regard, local. It may turn out our 3D reality is a projection of some deeper reality. (I’m askance at holographic theory, which applies to AdS space anyway, but something along those lines.)
The idea that an event seeds a new reality that expands… Seems like Bell’s Inequality experiments would rule that out, or that the spreading would otherwise be apparent somehow. I still need some kind of explanation of where the energy comes from. How does E=mc^2 go on working?
“On a single photon and the detector, remember that as a system of quantum objects constantly interacting with each other, the detector is perpetually branching anyway.”
By “branching” are you assuming MWI? As I see it, the particles of the detector, due to all those interacts, have no coherence. Any coherent states are lost in times brief enough to have no name.
That’s not to say each particle doesn’t have a quantum state, but its phase information is constantly shifting in that ultra-short time frame. When we speak of “decoherence” we just mean from our perspective — the particles always have a definite phase, but a constantly and very rapidly evolving one.
But I quite agree the incoming particle, as you say, isn’t doing anything that isn’t already going on at a much higher scale. Which is exactly why MWI has to be false. The incoming particle’s phase has no real effect on the combined quantum state of the detector.
“And this alters the state of the portion of the detector’s branches where the photon hit.”
Agreed. But I disagree there is a reality in which the detector wasn’t affected. I think there is just one reality where things happen or don’t happen.
On non-locality, reading your remarks, I’m starting to see the motivation some physicists have for wondering if time, space, or both don’t exist. If they can be eliminated, then the locality issue seems to go out the window. Of course, if we’re going to make that move, we then have to explain why time and space certainly seem to be present, or how they emerge. Hmmm.
“By “branching” are you assuming MWI?”
Yes, I was describing things under the MWI. Certainly if MWI is false, then all those quantum entities in the detector are constantly collapsing into a localized state before they ever get started. But if MWI is true, then they’re only constantly decohering without the collapse, leading to ongoing branching.
Importantly, we have to evaluate the effects of the photon either under MWI or not under it. If MWI is false for the detector, we can’t expect the photon by itself to make it true.
LikeLiked by 1 person
One of my favorite philosophers, Jenann Ismael, discusses a fish metaphor for the same underlying idea of events that span hidden dimensions. Only instead of the fish looking at human fingertips, it’s a human viewing two camera images of one fish in an aquarium. One camera views from the north, and one from the west, so if the fish faces north we see a frontal view on the first camera and a side view on the second. As the fish swims around, “spooky action at a distance” correlations are observed on the two screens. (Bohm came up with the metaphor.)
LikeLiked by 2 people
Interesting idea! What would the two cameras be in this case?
For Bohm I think the camera affecting the screens would be the wavefunction guiding the particles. For Ismael, I think she’s deliberately leaving it open, but any QM interpretation that takes the wavefunction to be real would fit her point about high-dimensional underlying reality.
It sure seems like we need some sort of extended definition of spacetime.
(Sounds like a Matt O’Dowd closing line. 😀 )
“For some (e.g. Carroll), the idea is attractive and seems simple.” For me, the idea initially seemed grossly complex. Then an advocate said “wavefunctions never collapse”. Then my objection became: why don’t I ever run into a partial physicist running down the hall crying “Eureka, my quantum experiment worked!”? And besides, the handshake interpretation is so much cooler.
But then I read the Wiki on decoherence, and while most of the math went beyond my comfort zone, I could see that the partial-physicist problem was imaginary. And then MWI looked a lot more reasonable.
LikeLiked by 1 person
I went the other way with MWI. It seemed reasonable at first, but the more I thought about it, the less sense it made. In my view, the wave-function of a single photon simply does not have the ability MWI ascribes to it (to alter the vastly more complex composite wave-function of the detector)..
Hmm, I think we’re already stuck with tiny things affecting big ones. Butterfly flaps and hurricanes.
But which require vast amounts of input power to amplify into a storm.