Interview with Astrophysicist Adam Becker
Adam Becker is an astrophysicist and science writer whose first book “What Is Real?: The Unfinished Quest for the Meaning of Quantum Physics” just hit the bookshelves!
Table of Contents
Give us some background on how you got interested in physics and some experiences in youth/school that were formative.
I don’t remember a time when I wasn’t interested in science—some of my earliest memories are of going to the American Museum of Natural History in Manhattan and staring at the dinosaurs. Like a lot of little kids, I was obsessed with dinosaurs, but when I was six years old, a switch flipped. By that time, I’d read most of the dinosaur books in my elementary school library, and the shelf with the space books was right next to the shelf with the dinosaur books, so I tried one of the ones about space, and that was it—dinosaurs were out and space was in. (Though I still think dinosaurs are pretty cool.) My parents and my first grade teacher were very supportive, and helped me find more things to read. (My first grade teacher also set me on the path to become a science communicator by having me do a presentation in front of her class about the solar system — I talked about this on a Story Collider podcast, which you can listen to here: https://www.storycollider.org/stories/2016/12/30/adam-becker-the-solar-system)
I read absolutely everything I could get my hands on about space (a book called From Quarks to Quasars made a big impression, as did Tyson’s Universe Down To Earth). As I learned more about space, I learned more about physics too, and my interests slowly shifted to physics more generally as I got a little older. I taped the old Timothy Ferris PBS special “The Creation of the Universe” and practically wore out the VHS tape from rewatching it so many times. I watched Carl Sagan’s Cosmos, of course, and read the book too; that introduced me to the idea of a history of science, science as a process, ideas that people pieced together over time, rather than a monolithic set of facts. Similarly, Kip Thorne’s excellent book Black Holes and Time Warps brought to life some of the personalities behind the great scientific discoveries of the 20th century. By the time I was in high school, I knew I wanted to do physics—and I wanted to know more about the people who did physics.
Tell us a bit about what readers will find in your new book “What is Real?“
What is Real? is about the unfinished quest for the meaning of quantum physics. We have this beautiful theory, quantum mechanics, and it’s astonishingly accurate. But it’s not at all clear what that theory is saying about the nature of the world around us. It must be saying something about that world—there must be something in nature that resembles the mathematics of quantum mechanics, otherwise why would the theory work so well? But there’s no clarity or consensus among physicists about what, exactly, quantum physics is saying about reality. This is very strange, especially given that quantum mechanics is over 90 years old.
Even worse than that, there’s a problem at the heart of quantum physics that doesn’t have a generally accepted answer: the measurement problem. The Schrödinger equation does a beautiful job of describing what wave functions do when nobody’s looking, but when we do look, suddenly the Schrödinger equation is suspended and we have to use the Born rule instead. Why? How does that work? And what counts as a “measurement” anyhow? “What exactly qualifies some physical systems to play the role of ‘measurer’?”, John Bell asked in 1989. “Was the wavefunction of the world waiting to jump for thousands of millions of years until a single-celled living creature appeared? Or did it have to wait a little longer, for some better qualified system…with a PhD? If the theory is to apply to anything but highly idealized laboratory operations, are we not obliged to admit that more or less ‘measurement-like’ processes are going on more or less all the time, more or less everywhere? Do we not have jumping then all the time?”
The closest thing we have to a consensus about any of this is the Copenhagen interpretation. But the Copenhagen interpretation isn’t really a single coherent set of ideas about quantum mechanics—it’s a family of mutually-contradictory ideas, none of which adequately solve the measurement problem or answer the other questions at the heart of quantum theory. This is all the more strange given that reasonable alternatives to Copenhagen have existed for decades.
What is Real? is the history behind all of this—the history of quantum foundations. How did we end up with the Copenhagen interpretation? Why were superior alternatives ignored for so long? Why is the Copenhagen interpretation less popular than it once was? My book picks up where other books on the history of quantum physics leaves off—it starts with the Bohr-Einstein debates and goes all the way to the present day. What Is Real? also busts a lot of historical myths along the way, such as the true nature of Einstein’s qualms about quantum physics (it had little to do with indeterminism and more to do with locality), the real meaning of Bell’s theorem (realism is irrelevant to the theorem, and Bell hated Copenhagen), and more.
I understand that this may be controversial and that not everyone will agree with me. That’s fine. I’m happy to debate people on this subject—if you’d like me to do that at your university, drop me a line.
What was the inspiration and goal for writing “What is Real?”
Back when I was first learning about physics in all those popular science books I read when I was a kid, I noticed that explanations always got annoyingly vague whenever quantum physics came up. I figured that this would make more sense when I actually learned quantum physics. Once I did learn quantum physics in college, I was surprised to find that the vagueness got worse, not better—it was maddeningly unclear what a measurement was, or what part of the world obeyed the Schrödinger equation at all. And when I asked questions about this, some professors just shrugged, while others were sarcastic and dismissive of my questions. One professor made his disdain for my questions very clear, telling me in a witheringly haughty tone of voice that “if that’s the kind of questions you’re interested in, why don’t you go to the Philosophy Department!” I knew he meant it as an insult, but I did go over to the Philosophy Department, and ended up doing a double major in philosophy and physics at Cornell. At Cornell, and later at Michigan (where I went for my PhD in physics), I found that the philosophers actually cared about these questions, and had been thinking about them for a good long while and had developed some good ideas and arguments that most of the physicists didn’t know about. I also met some physicists (like David Mermin at Cornell) who didn’t think questions about the meaning of quantum physics were silly at all.
As a physicist, it’s nice to be able to explain asymmetries. And this asymmetry I’d found was a doozy: the philosophers of physics were, in general, quite well informed about physics, but the physicists were, by and large, wholly ignorant of philosophy, despite the fact that they were making philosophical claims when they dismissed questions about quantum foundations. As a result, the physicists were generally relying upon faulty philosophy when they answered such questions. (For example, say you ask “hey, what’s the electron doing when we’re not looking?” and you get the answer “that’s unobservable in principle, and it’s meaningless to talk about unobservable things.” That answer is dependent on an outdated and erroneous philosophy of science called “logical positivism,” and the flaws in that kind of reasoning are very well known to philosophers of science.) Where did this asymmetry come from? The answer had to be the history of quantum foundations. So I started digging into this field as a side project while I was in graduate school, and what I found there was this totally astonishing story about the history of physics in the 20th century. The story wasn’t exactly hidden—it’s easy to find out what happened by piecing together various papers and books on the history of physics, and by reading what John Bell and others actually said—but it was scattered, and most physicists didn’t seem to know the story. And it was an interesting story, one that physicists, philosophers, and the scientifically-minded public might find compelling reading. Hence the book.
In “What is Real?“, how do you balance the technicality of physics with the required accessibility for the general public?
That balancing act is hard, and it’s the central struggle of all science writing. (I’m not totally sure I pulled it off successfully, though I hope I did.) When I was writing What Is Real?, I had two basic rules that I kept in mind to try to keep things accessible.
First, people generally care more about other people than they do about ideas. That doesn’t mean people don’t care about ideas! It just means that people will care more about ideas if you can tie those ideas to a person, and use the story of that person to explain the ideas. So when I was writing the book, I generally tried to use personal stories from the history of quantum foundations to explain ideas that were new to the reader. This was also the animating principle behind the structure of the book as a whole: it’s structured as a history, so I can talk about the people in the story as a way into explanations of the ideas that we grapple with in quantum foundations. And focusing on the people also makes it easier for me to quote those people, and good quotations have a way of bringing a story to life.
Second, only explain the new concepts and jargon that are absolutely essential for telling the story. For example, despite the fact that quantum wave functions live in configuration space (when using the position basis), I don’t introduce the concept of configuration space in my book. That’s not because I think the average reader couldn’t understand the idea; I’m confident that they could, given a clear explanation. But there are already many other unfamiliar concepts that I’m throwing at readers in this book (wave functions and their collapse, entanglement, the measurement problem, decoherence, etc.) and I didn’t want to burden them with one more, especially if it wasn’t truly essential for explaining other things.
Should schools be trying to teach every kid physics or should they instead divert resources into the few that might have the potential to contribute?
I think that this question is based on a faulty premise: we don’t teach kids physics because we think they’re all going to become physicists, any more than we teach kids history because we think everyone’s going to become a historian. Instead, we teach kids history because a knowledge of history is vital to being an informed citizen of a democracy, and makes it possible to have a deeper understanding of other people, other cultures, and current events. We teach kids physics for exactly the same reasons. A basic understanding of physics gives a new and important perspective on the world, one that students will hopefully carry with them for the rest of their lives, whether or not they become physicists.
I’ll also add that any attempt to identify “the few that might have the potential to contribute” would run into insurmountable problems. There’s no good way to tell what a person’s future potential is in physics or in almost any other field. And if we tried to do it anyway, not only would we fail, but we’d most likely fail in ways that reinforce existing societal biases that favor white men, especially in the sciences. So yes, we should be teaching every kid at least some physics. We can’t know in advance where the next Einstein will be found, and finding the next Einstein isn’t the sole purpose of physics education anyhow.
What’s your opinion of still using ‘Apparent Magnitude’ in astronomy
I don’t feel strongly about this, but then again my background is in statistical cosmology, not observational astronomy.
What is considered an inertial frame in astronomy/cosmology and can you point one out?
I’m not sure what this question is driving at. The rest frame of the CMB is an inertial frame. And the rest frame of the sun is pretty close to an inertial frame; the acceleration it feels due to its orbit around the center of the Milky Way is very small. But the idea of “inertial frame” is an idealization; even if it turns out that it’s hard to define the rest frame of the CMB, it doesn’t mean there’s anything wrong with talking about inertial frames.
Is there anything you found particularly interesting about the evolution of the structure of the universe while working on your thesis? What about your thesis’ topic did you find particularly challenging?
One of the things I really liked best about my thesis was that I was trying to understand the inflationary epoch, a period so far back in the history of the universe that there’s no material of any kind left over from it—no atoms, no quarks or electrons, not even any photons. All that we have left from that time in history are the patterns in the distribution of stuff in the universe, and so our only hope of better understanding that period is to tease out statistical features of the cosmic microwave background radiation and large-scale structure. That kind of statistical work is where cosmological theory and observation and simulations all intersect, and that’s a great place to be when you’re doing science.
Do you have an explanation for the Cosmic Axis of Evil and the Spin of Galaxies?
No. It’s unclear what’s going on with the “axis of evil.” To the best of my knowledge, it’s an open problem.
As a science historian, can you generalize your insights about the lines of inquiry that have enjoyed traditional success in approaching big questions tackled by astrophysicists, and how these compare or may apply to big questions surrounding dark matter and dark energy?
From a historical perspective, the modern idea of dark matter is in pretty good company. There are other kinds of “dark matter” that have been suggested in the past to explain different phenomena, and they have often met with success. When astronomers in the early 1800s noticed an anomaly in the motion of Uranus, they invoked “dark matter” in the form of another as-yet-unseen planet, and they were right—that’s how Neptune was discovered. And when beta decay seemed to violate the conservation of energy, Wolfgang Pauli suggested “dark matter” in the form of neutrinos, which weren’t seen for another quarter-century. Of course, this kind of strategy doesn’t always work. In the mid-19th century, “dark matter,” in the form of an unseen planet or asteroids, was suggested as an explanation for the extra precession of the perihelion of the orbit of Mercury. That turned out to be false—that extra precession is a result of general relativity, as Einstein found in 1915. But dark matter is certainly a reasonable idea from a historical perspective. And from a scientific perspective, I don’t really think we can reasonably doubt that dark matter is there. The evidence is truly overwhelming.
Dark energy is a little bit weirder, historically speaking—it’s hard to know what a good analogy is. Certainly there are many historical examples of a postulated thing permeating all of space, some of which we still accept (electromagnetic field) and some of which we don’t (luminiferous aether). As for the idea of dark energy itself, it’s got a long history, longer than dark matter. Einstein famously considered a cosmological constant and then dismissed it once Hubble discovered the distance-redshift relation, implying that the universe was expanding. And Einstein’s usage of a cosmological constant to keep the universe static wouldn’t have worked anyhow—it was an unstable equilibrium. So Einstein’s idea was abandoned for most of the 20th century. But although the first good evidence for dark energy showed up on the scene in the very late 1990s, it had been anticipated well before that. If you look in cosmology textbooks from the early 1980s, they’re already talking about the possibility of a cosmological constant quite seriously. And again, the cosmological evidence for dark energy is very good.
Do you think a consistent Bohmian formulation of QFT is possible?
That’s an open research question, and it’s not my area of expertise. I have heard that part of the difficulty people have encountered with developing a consistent Bohmian formulation of QFT comes from the fact that our best QFTs are questionably consistent, due to weirdness like Haag’s theorem and renormalization. But take that with a grain of salt—it’s really not my area.
Concerning the different interpretations of quantum mechanics... could one determine if one interpretation is more fundamental or more encompassing than another? An experimental test? A successful quantum theory of gravity or of unified fields?
Fundamentally, I don’t think we’re going to be able to determine which interpretation is closest to the mark until we have a theory that goes beyond quantum mechanics, like a theory of quantum gravity. But there’s a catch-22: I don’t think we’re going to be able to come up with such a theory if we’re stuck thinking about quantum mechanics in a fundamentally misguided way. So, since there’s no way to know which interpretation will lead to the insights that will yield a theory of quantum gravity, I think it’s important for researchers to be familiar with several different interpretations, even if they have a strong feeling about which interpretation is right.
Do you have a view on the ‘reality’ of the wave function?
I think that there must be something in nature that approximately resembles the wave function, or that directly gives rise to something like a wave function. That’s an intentionally broad statement. It could be that there really is a big wave function of the universe out there, constantly splitting in the way that the many-worlds interpretation posits. It could be that there’s something out there like a wave function, but it’s not the whole story, as pilot-wave theory (aka de Broglie-Bohm) posits. Or there’s any number of other possibilities: there’s something out there like the wave function but it doesn’t quite behave the way quantum mechanics dictates (spontaneous collapse); there’s something real out there that that isn’t much like the wave function, but it behaves in such a way that our information about it obeys the Schrödinger equation, and thus that information can be modeled with a wave function (information-theoretic interpretations); etc. But in all of these cases, there’s a real thing, out in the world, that guarantees that the Schrödinger equation will hold and that the Born rule applies in the usual way.
Why do I think this? Because quantum physics works phenomenally well. It explains a huge diversity of phenomena to a breathtaking degree of accuracy. How could quantum physics possibly work so well if there weren’t something out in the world that it was accurately describing? Why would the theory be so accurate if it bore no resemblance to nature at all? Remember, this is a theory that was initially developed to explain atomic spectra—that’s all. Now we use it to understand why the sun shines and how to build lasers. A theory that can do that has got to be latching on to some true fact about nature, even if it’s just in an indirect or approximate way.
Say we have a piece of matter with some temperature T, regarding it for now as a classical system. If we view it as a quantum system, does it still have a temperature?
Sure. The statistical mechanics definition of temperature still applies perfectly well to composite quantum systems.
Thanks so much for your time Adam! Now readers go out and buy his book!
Read the next interview with physicist Niels Tuning
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I just finished chapter 11 where Adam defends the various many-worlds views (string theory’s landscapes, inflation’s multiverse, and Everett’s Many-Worlds Interpretation, MWI). He admits MWI has a problem with the meaning of probability, but dismisses it as something to be solved in the future. I’m less optimistic, since the idea has been in vogue (in FoP anyway) for many years and yet the problem persists. For example, it can’t be simply that the branches split with a “frequentist interpretation of probability,” as Adam illustrates with the Schrodinger Cat in a 25% dead — 75% alive probability when there are only two possible outcomes. Another problem with a frequentist-splitting interpretation would be that many branches would not in fact obtain empirical evidence for the correct splitting probabilities (as seen from a global perspective “outside” all the branches), as Adrian Kent pointed out years ago. So, how do we know we’re in a branch where our experiments actually reflect the correct probabilities? Finally, Adam defends these many-worlds views against accusations that they’re unscientific because they’re unverifiable. He properly points out that all scientific theories are unverifiable in the sense of Popper, e.g., deviations in Uranus’s predicted orbit led to the discovery of Neptune, not the overthrow of Newtonian gravity. Later, deviations in the orbit of Mercury did lead to Newtonian gravity being “falsified,” i.e., replaced by a more accurate theory (GR). Here I think Adam’s defense is strained at best. There is a huge difference b/w Newtonian gravity not being falsified by a single apparently discordant measurement (Uranus’s orbit) and the fact that EVERY POSSIBLE measurement outcome is compatible with a theory. To claim the former case is equivalent to the latter is an egregious misrepresentation of the objection of unfalsifiability. To paraphrase one opponent of such views, “Does a theory that predicts everything explain anything?” On to chapter 12!
some of the history has surprised meI was surprised to find out how Wheeler treated Everett.
I'm reading Part III and some of the history has surprised me. I got into the game (1994) after the situation in foundations of physics had started to improve, but Aharonov warned me at the time there were perils associated with working in foundations. The hostility of the physics community towards physicists working in foundations was appallingly anti-intellectual. Albert had publications in Phys Rev with Aharonov yet his university would not let him do this work for his PhD thesis. He was told flat out that if he didn't do the problem in QFT they had given him, then he would be dismissed from their program. Work by Bell and even Clauser's experimental work were deemed "junk science." Another thing I didn't know was that Holt had repeated Clauser's experiment and found the Bell inequality was not violated. At that time, there were just the two contradictory results, so it wasn't clear whether QM was right or not. The guys doing these experiments had to beg for lab space and had to borrow or scrounge for equipment. It took Aspect six years to build, conduct and publish his first experiment. When he ask Bell about doing the experiment, Bell refused to talk to him until Aspect assured Bell that he had tenure. Zeh has similar horror stories. I already respected the pioneers in this field for their discoveries, now I respect them as well for their perseverance in the face of such adversity.
I cannot tell whether this post is tongue-in-cheek or serious.
I didn't know that Niels Bohr developed any wise dogmas. Dogmas, yes.- but don't forget, Bohr had Einstein to discuss things with; – and nowadays you only have guys whose Most Sacred Hope is just to attain unto perfect non-existence in the end; – so, to you, Bohr's ideas are of no use of course.
The thing is, everyone naturally has his own wishful thinking! To avoid offending someone's sacred hopes (like materialism or many worlds or Divine Choice), it's necessary to keep certain wise dogmas developed by Niels Bohr and company .I cannot tell whether this post is tongue-in-cheek or serious.
I didn't know that Niels Bohr developed any wise dogmas. Dogmas, yes.
The thing is, everyone naturally has his own wishful thinking! To avoid offending someone's sacred wishes (like materialism or many worlds), it's necessary to keep certain wise dogmas developed by Niels Bohr.
He’s advocating for dBB and MWI, not because he necessarily believes those are “right,” but simply because they offer counterexamples to Copenhagen. I didn’t realize Copenhagen was so dogmatic, I thought it was merely instrumentalist, which I have always considered “agnostic.”It depends on whose Copenhagen. I go to both churches without any sense of conflict.
Just finished Part II. Chapter 8 is what the Copenhagenists, instrumentalists, operationalists, and positivists among you should read.
He’s advocating for dBB and MWI, not because he necessarily believes those are “right,” but simply because they offer counterexamples to Copenhagen. I didn’t realize Copenhagen was so dogmatic, I thought it was merely instrumentalist, which I have always considered “agnostic.” Adam’s take on instrumentalism is a la positivism and operationalism, both of which strike me as more dogmatic. Physicists who are just not interested in analyzing various interpretations aren’t impeding progress, since their lack of interest means they wouldn’t likely contribute anything meaningful anyway. It’s those who naively believe they don’t even possess an interpretation themselves and actively dissuade younger physicists from asking those questions. Part II presents an interesting history explaining how the attitudes of Copenhagen, instrumentalism, positivism, and operationalism became so popular among physicists when philosophers have long since dismissed them on intellectual grounds.
The experiment instantiates a QM violation of a Bell inequality. There is nothing more needed to experimentally confirm the mystery a la Adam's roulette wheels or Mermin's device, unless you believe there is something wrong with QM (Adam's third option). Is that what you're implying? It's the theoretical gloss in the paper that I find lacking. I'm confident the experiment as given, using off the shelf components, violates Bell inequalities, and I'm reading you to be saying that your students have done the experiment dozens of times over the years? I asked for Gregor Weihs' raw data at one time and analyzed it in a way that showed him a new feature, though it's not earth-shattering (arXiv:1207.5775, also on my very irregularly maintained blog, https://quantumclassical.blogspot.com/2010/03/modulation-of-random-signal.html — astonishing, for me, to see that that is 8 years ago).
So I don't doubt the weirdness.
I'm by no means saying that others can't tackle classical chaos in sophisticated ways in an attempt to model quantum level systems deterministically, it'd be great if someone could give us a toe-hold on that, but I'm certain I'm not a good enough mathematician to tackle that head on. My only hope would be to notice something serendipitously as a result of being so immersed in the relationship between quantum and random fields, although I think that's probably already given in to the urge to address chaos with probability.
Quantum theory, being probabilistic, only makes predictions about statistics associated with recorded measurements. As a probabilistic theory, it has nothing to say about individual recorded events, only about their statistics. As a statistical theory, it includes the notion of microcausality, that measurements associated with space-like separated regions commute, but this is consistent with us being able to prepare states in which there are correlations at space-like separation.Thnx for intervening, hopefully this exchange will educate those who are likewise confused :-) The issue isn't with the formalism and it isn't with the data (I hope that isn't what you're implying). The formalism maps beautifully onto the data, as you can see in the paper. The issue is what you appear to brush aside. The statistical data is collected one event (coincidence) at a time (within the 25-ns coincidence window), just like the roulette balls in Adam's analogy. Therefore, any explanation for the correlation in the statistical data should be based on the nature of reality as it pertains to each trial (and it's not accidental coincidences as you can see from the last column of Table 1).
I think we have no honest choice but to say "hypotheses non fingo").Bring your explanation supra to bear on Adam's roulette wheel analogy and you'll see where it's lacking. That is, you'd be attempting to resolve the mystery by saying, "I have a statistical mathematical formalism that maps onto the statistical data." That answer in no way tells me what is causing the two balls to land in the same color every time the two experimentalists choose the same wheel number, but land in the same color only 25% of the time that the two experimentalists choose a different wheel number. [This is exactly the Mermin analogy, see my QLE explanation, where we expect at least 33% agreement for different wheel numbers in order to account for 100% agreement for same wheel numbers.] Giving up on finding the underlying cause for the experimental correlations is your choice, but that in no way resolves the issue for those of us who haven't given up.
I can see some merits to the paper you attach, but, of course, I'd like something better.The experiment instantiates a QM violation of a Bell inequality. There is nothing more needed to experimentally confirm the mystery a la Adam's roulette wheels or Mermin's device, unless you believe there is something wrong with QM (Adam's third option). Is that what you're implying?
how QFT micro-causality is supposed to solve the EPR macro stochastic causality behaviors ?QFT "micro-causality" means that spacelike separated measurements must commute (i.e., the results must not depend on the order in which they are performed). Bell-inequality violating experiments meet this condition. So I don't see what there is to "solve".
That is a nice refresher for those who think that quantum theory is a description of reality, instead of just a description of what would happens to "equally prepared state", that is "in a laboratory"What I said, that QM/QFT is a probabilistic theory —which can be understood to model, and hence in appropriate circumstances to predict, statistics of recorded experimental events—, seems to me not inconsistent with quantum theory being "a description of reality". I think of QM/QFT, admittedly loosely, as being as much as we can say about "reality" because to predict individual events in a chaotic world would require more information than I think we can plausibly have access to, perhaps even might require infinite information.
As a layman, do you know of any resource that will explains how QFT micro-causality is supposed to solve the EPR macro stochastic causality behaviors ? I have a terrible memory, I'm afraid. I retain concepts more-or-less, once I've grokked them, but I too often forget where I learned about them and where the good references are. That said, I don't think of microcausality as solving EPR. Microcausality —that measurements are compatible with and don't change the statistics of other measurements that are at space-like separation— is apparently consistent with experiment, whereas in fact we can set up states in which there are correlations and Bell inequality violations between space-like separated measurements.
On this topic of timing, isn't Bohmian's mechanic supposed to have more predictive power over classical QM ? I think of Bohmian mechanics more as retrodicting a trajectory, given an individual actual event, if we know (or think we know) the quantum dynamics. That is, if the event is caused by a particle, that particle must have come from somewhere, because that's what particles do. We can massage the quantum dynamics to give us an equation that determines a trajectory when it's given just a single point on that trajectory (it's sometimes cited as a conceptual difficulty for Bohmian mechanics that we don't need to know the velocity as well as the position to determine the trajectory —differently from the case for classical mechanics, that is). BUT, at least in those cases where we do not observe more than one point (not high energy physics, and not a football or anything else large, in other words, but for most low energy experiments, because then the particle is absorbed and doesn't carry on along the same trajectory), that's not a prediction. To claim that de Broglie-Bohm is empirically equivalent to QM, one has to say that de Broglie-Bohm is a probabilistic theory.
Personally, I'm OK with de Broglie-Bohm trajectories for the non-relativistic case, except that, crucially, the math is a mess compared to just using Hilbert spaces. When we use QFT, however, I've not seen de Broglie-Bohm work out well enough. Most physicists just cite the QFT case as a one-line dismissal.
Quantum theory, being probabilistic, only makes predictions about statistics associated with recorded measurements. As a probabilistic theory, it has nothing to say about individual recorded events, only about their statistics.That is a nice refresher for those who think that quantum theory is a description of reality, instead of just a description of what would happens to "equally prepared state", that is "in a laboratory"
As a statistical theory, it includes the notion of microcausality, that measurements associated with space-like separated regions commute, but this is consistent with us being able to prepare states in which there are correlations at space-like separation.As a layman, do you know of any resource that will explains how QFT micro-causality is supposed to solve the EPR macro stochastic causality behaviors ?
Also Ruta's point on block -universe "interpretation" seems quite interesting, I'll try to dig into that also…
I see this as resolving the difference between vanhees71 and yourself, that quantum theory is microcausal as a probabilistic theory, whereas a theory that non-stochastically predicts the precise timings of individual recorded events would appear to have to be either nonlocal or superdeterministic (or some combination thereof: any such model might require infinite information to be predictive if there's any chaos, so I can't see how we could determine what a non-stochastic theory would be, I think we have no honest choice but to say "hypotheses non fingo").Aouch .. Latin hurts more than math :wink: On this topic of timing, isn't Bohmian's mechanic supposed to have more predictive power over classical QM ? If some spin value is observed to be X by Alice, isn't the (entangled?) pilot wave time dependency suppose to make more accurate prediction over the entangled value over time (and space) at Bob's end ?
I just finished Part I of Adam's book. Did you read it? It speaks precisely against this attitude.As I haven't read the book yet, I don't know Adam Becker's attitude.
That's not true, the formalism maps beautifully onto the experimental set-ups and data. There are many analyses, but one for undergrads that I use in my QM course is attached. There's nothing in the formalism that resolves this issue.Quantum theory, being probabilistic, only makes predictions about statistics associated with recorded measurements. As a probabilistic theory, it has nothing to say about individual recorded events, only about their statistics. As a statistical theory, it includes the notion of microcausality, that measurements associated with space-like separated regions commute, but this is consistent with us being able to prepare states in which there are correlations at space-like separation.
I see this as resolving the difference between vanhees71 and yourself, that quantum theory is microcausal as a probabilistic theory, whereas a theory that non-stochastically predicts the precise timings of individual recorded events would appear to have to be either nonlocal or superdeterministic (or some combination thereof: any such model might require infinite information to be predictive if there's any chaos, so I can't see how we could determine what a non-stochastic theory would be, I think we have no honest choice but to say "hypotheses non fingo").
I can see some merits to the paper you attach, but, of course, I'd like something better. In particular, IMO the role played by the incompatibility of the pairs of measurements at each end should be emphasized: if we were to perform only compatible measurements at each end separately, there would be no violation of any Bell inequalities. That there are incompatibilities means that there are time-like dependencies, but between the two measurements at A and between the two measurements at B, not between the ends (that is, if we have two measurements at A and two measurements at B, ##[A_i,B_j]=0, [A_1,A_2]not=0, [B_1,B_2]not=0##.) And I'd prefer "particles" not to be mentioned at all (instead of the word appearing 34 times): to be trite, for the quantized EM field there's just a wave/field duality. But that's a different paper altogether.
He forgot the third, which is the contemporary solution of this apparent problem, which is local microcausal relativistic QFT. It's local (i.e., fulfilling the linked-cluster principle) and allows for the long-range correlations described by entanglement of parts of quantum systems that are observed at far-distant points. Of course, you have to give up naive collapse interpretations, which introduce an artificial action at a distance, which is in clear contradiction to the very foundations the Standard Model rests upon, namely locality and microcausality. Of course QM is only a non-relativistic approximation of the relativstic QFT and thus becomes wrong when applied to situations where the approximation is invalid.That's not true, the formalism maps beautifully onto the experimental set-ups and data. There are many analyses, but one for undergrads that I use in my QM course is attached. There's nothing in the formalism that resolves this issue.
I just finished Adam's analysis of the Bell inequality via a roulette wheel. I've heard this before in a different context, but it's a very nice way to introduce the Bell inequality to laymen. His claim afterwards is that only one of three logical possibilities exists: nonlocality, superdeterminism, or QM is wrong.He forgot the third, which is the contemporary solution of this apparent problem, which is local microcausal relativistic QFT. It's local (i.e., fulfilling the linked-cluster principle) and allows for the long-range correlations described by entanglement of parts of quantum systems that are observed at far-distant points. Of course, you have to give up naive collapse interpretations, which introduce an artificial action at a distance, which is in clear contradiction to the very foundations the Standard Model rests upon, namely locality and microcausality. Of course QM is only a non-relativistic approximation of the relativstic QFT and thus becomes wrong when applied to situations where the approximation is invalid.
vanhees71, I can't see which comment you're referring to here. I understand if you might not want to use QUOTE, but it would help a lot if you would cite a comment number. TBH, I'm saying this because I've been unsure what or who you've been referring to a number of times, not just because of this one comment. Sorry!:sorry: I won't say this again until I forget that I said it.I only quote if I refer to a posting not immediately before the posting I'm answering to.
I just finished Adam's analysis of the Bell inequality via a roulette wheel. I've heard this before in a different context, but it's a very nice way to introduce the Bell inequality to laymen. His claim afterwards is that only one of three logical possibilities exists: nonlocality, superdeterminism, or QM is wrong. Most people accept the experimental results vindicating QM, so few if any argue for the third option anymore (it was more common when I started working on this in 1994). I'm assuming he believes retrocausality falls into the SD camp? It's semantics, but I'd disagree with that since the "common cause" resides in both the future and past. I wouldn't say that any of the three options applies to the ontology of Relational Blockworld (RBW) where explanation is adynamical and QM is certainly correct. Therein, the fundamental ontological element is 4-dim and QM provides a distribution function for these 4D "spacetimesource elements" in the context of a classical block universe. So, we do have "realism" and there are no superluminal signals required in the explanation of the distribution of these real 4D objects in spacetime. I'm not even sure that the concept of nonlocality is relevant when discussing 4D objects (careful, this nonlocality has to do with superluminal signaling, not the locality assumed in differentiable manifolds). Silberstein and I are giving a talk to the foundations group at the Univ of MD next Wed, so I'll solicit their opinions. But, he and I agree that the standard analyses of Bell inequalities tacitly assume dynamism and are meaningless for adynamical explanation. Continuing, there is certainly no SD in RBW because there is no dynamical causation in adynamical explanation. In other words, when Adam claims to have exhausted all logical possibilities for the implications of Bell's inequality, he has failed to consider adynamical explanation.
Foundations of physics (FoP) doesn't spend much time on this subject. FoP's attitude is that the weird/fun stuff is in QM, the only mysteries about QFT are technical, e.g., Haag's theorem, so FoP deals almost exclusively with QM. In my 24 years of attending FoP conferences and talks, I don't remember even one presentation on QFT issues. I'm very interested in your interpretation of QFT, as you know, because it looks to fill in technical gaps with my interpretation of QFT.Different circles! I think you're right, although I haven't been to a Foundations of physics conference, ##lo##, the last ten years. Perhaps it's more the philosophers who have taken up the philosophy of QFT, and there are several mathematicians who have tried to make sense of the mathematics of renormalization/interacting QFT with what seem almost philosophical motivations. I filter out a majority of non-QFT foundations these days, so it seems quite the opposite way round. QFT changes the game totally, IMO, makes everything much easier, partly because there are already fields, so it's fields/waves duality, which I think is easier to live with, but of course I have to convince anyone of that.
I'm in Adam's chapter 6 on Bohm and Everett. I haven't seen anything about QFT mentioned in the other reviews and he has made no mention of it so far in his book, so I doubt he talks about interpretations of QFT. We offer an interpretation of QFT in chapter 5 of our book and that chapter opens with the following:
As for progress in this area, Healey notes, “no consensus has yet emerged, even on how to interpret the theory of a free, quantized, real scalar field” [Healey,
2007, p. 203]. And, “There is no agreement as to what object or objects a quantum field theory purports to describe, let alone what their basic properties would
be” [Healey, 2007, p. 221].
Foundations of physics (FoP) doesn't spend much time on this subject. FoP's attitude is that the weird/fun stuff is in QM, the only mysteries about QFT are technical, e.g., Haag's theorem, so FoP deals almost exclusively with QM. In my 24 years of attending FoP conferences and talks, I don't remember even one presentation on QFT issues. I'm very interested in your interpretation of QFT, as you know, because it looks to fill in technical gaps with my interpretation of QFT. With your help, I'll figure it out :-)
In the first 5 chapters, Adam has focused on the history of the Copenhagen interpretation (in its many variations) and why we're stuck with it now. His coverage of interpretational issues of QM has been sparse to this point. Based on reviews I've read, I'm assuming he'll plug those holes in part 3 of the book.
Did you read Adam's book?I look forward to reading a review from you, RUTA. Having been to the talk Adam gave last night in New York, I'm not very enthusiastic. The last time I remember someone landing hard on a conversation at a foundations of physics conference with "Copenhagen says X, so everything you're saying is nonsense", was in the early 90's, and my sense is that physicists now more often fall back on decoherence (notwithstanding that the last mile from a mixed state to actual events is glossed), an interpretation which Adam didn't mention in his talk (I suppose because many philosophers would be loath to call decoherence an interpretation at all). Furthermore, I just read that Feyerabend in 1962 said (cited in arXiv:1509.09278, page 43) . . . many physicists are very practical people and not very fond of philosophy. This being the case, they will take for granted and not further investigate those philosophical ideas which they have learned in their youth and which by now seem to them, and indeed to the whole community of practicing scientists, to be the expression of physical common sense. In most cases these ideas are part of the Copenhagen Interpretation.
A second reason for the persistence of the creed of complementarity in the face of decisive objections is to be found in the vagueness of the main principles of this creed. This vagueness allows the defendants to take care of objections by development rather than a reformulation, a procedure which will of course create the impression that the correct answer has been there all the time and that it was overlooked by the critic. Bohr's followers, and also Bohr himself, have made full use of this possibility even in cases where the necessity of a reformulation was clearly indicated. Their attitude has very often been one of people who have the task to clear up the misunderstandings of their opponents rather than to admit their own mistakes. which seems a clear statement, 56 years ago, of what seemed to be a large part of Adam's argument for why Copenhagen is still given lip service today.
Adam at one point said that he hopes to give his talk to physics departments, but TBH with nothing at all said about QFT (is there anything about QFT in the book?), and decoherence unmentioned, I can't see physicists taking him seriously. One high point of going to Adam's talk was that I talked to several Masters and PhD students and postdocs, all of whom seemed quite knowledgeable about and willing to talk about the interpretation of QFT.
Sir Arthur Stanley Eddington in "The Nature of the Physical World“:
"Scientific instincts warn me that any attempt to answer the question “What is real?” in a broader sense than that adopted for domestic purposes in science, is likely to lead to a floundering among vain words and high-sounding epithets."Did you read Adam's book?
Indeed. Even the most appealing creative thought has to be confronted with observations and accurate measurements. If you cannot make contact to observables, it's a nice mathematical idea at best or just philosophical gibberish at worst. If your predictions are clearly countered by observation, it's a physical theory that's wrong and needs to be modified (at best) or abandoned (at worst)! As all natural sciences physics after all is an empirical science.vanhees71, I can't see which comment you're referring to here. I understand if you might not want to use QUOTE, but it would help a lot if you would cite a comment number. TBH, I'm saying this because I've been unsure what or who you've been referring to a number of times, not just because of this one comment. Sorry!:sorry: I won't say this again until I forget that I said it.
I just finished Part I of Adam's book. Did you read it? It speaks precisely against this attitude.Sir Arthur Stanley Eddington in "The Nature of the Physical World“:
"Scientific instincts warn me that any attempt to answer the question “What is real?” in a broader sense than that adopted for domestic purposes in science, is likely to lead to a floundering among vain words and high-sounding epithets."
Indeed. Even the most appealing creative thought has to be confronted with observations and accurate measurements. If you cannot make contact to observables, it's a nice mathematical idea at best or just philosophical gibberish at worst. If your predictions are clearly countered by observation, it's a physical theory that's wrong and needs to be modified (at best) or abandoned (at worst)! As all natural sciences physics after all is an empirical science.
You have to find an answer for yourself to such a question. To my mind, it’s beyond the scope of "Physics" to answer this question or questions like “What is real?”.Sure
You can conceive that in course of experiments photographic plates have been blackened or that cloud droplets have been formed, without the intrusion of a conscious observer, but how should "Physics" prove your idea.Why should physics prove anything?
Nevertheless, "Modern physics" now indicates that one cannot arbitrarily cut “NATURE” into – so to speak – subjective or objective parts or – let’s say – into Descartes’ mind and matter. Here I follow Bohr who said: I consider those developments in physics during the last decades which have shown how problematical such concepts as "objective" and "subjective" are, a great liberation of thought.Science requires two things to do it. First, you have to have creative thinking to come up with possible explanations of phenomena. And second, you have to have critical thinking to throw away useless explanations.
"Great liberation of thought" is good for creative thinking, but if you loose the critical thinking part as a result of this liberation … well, it's just not going to work.
You have to find an answer for yourself to such a question. To my mind, it’s beyond the scope of "Physics" to answer this question or questions like “What is real?”. You can conceive that in course of experiments photographic plates have been blackened or that cloud droplets have been formed, without the intrusion of a conscious observer, but how should "Physics" prove your idea.
From an instrumentalist' point of view, such questions are idle ones. "In science we study the linkage of pointer readings with pointer readings." (Arthur Stanley Eddington). That’s all. The confusion begins when one tries on base of a schedule of pointer readings to draw conclusions as to the nature of “NATURE”.
Nevertheless, "Modern physics" now indicates that one cannot arbitrarily cut “NATURE” into – so to speak – subjective or objective parts or – let’s say – into Descartes’ mind and matter. Here I follow Bohr who said: I consider those developments in physics during the last decades which have shown how problematical such concepts as "objective" and "subjective" are, a great liberation of thought.I just finished Part I of Adam's book. Did you read it? It speaks precisely against this attitude.
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So do the records of experimental data and setup details have mind independent existence?You have to find an answer for yourself to such a question. To my mind, it’s beyond the scope of "Physics" to answer this question or questions like “What is real?”. You can conceive that in course of experiments photographic plates have been blackened or that cloud droplets have been formed, without the intrusion of a conscious observer, but how should "Physics" prove your idea.
From an instrumentalist' point of view, such questions are idle ones. "In science we study the linkage of pointer readings with pointer readings." (Arthur Stanley Eddington). That’s all. The confusion begins when one tries on base of a schedule of pointer readings to draw conclusions as to the nature of “NATURE”.
Nevertheless, "Modern physics" now indicates that one cannot arbitrarily cut “NATURE” into – so to speak – subjective or objective parts or – let’s say – into Descartes’ mind and matter. Here I follow Bohr who said: I consider those developments in physics during the last decades which have shown how problematical such concepts as "objective" and "subjective" are, a great liberation of thought.
So do the records of experimental data and setup details have mind independent existence?I'll mostly defer to vanhees71's account, comment #70. I think of triggers as a definite lossy data compression, but how the data is compressed is presumably decided by some committee, which hopefully has some minds. One could perhaps say that once an experiment has been constructed as an automated object, the data collected can be automated and be mostly independent of mind. Indeed, if human intervention is required to keep an experiment on track because of an error condition that lies outside the automation specified, one would expect that any data during the period during which human intervention was required ought to be discarded (unless, perhaps the human intervention can be formally modeled).
I'll paste in an account I wrote last night to a correspondent, which seems to be a propos:
Consider an Avalanche PhotoDiode, an APD: we set up an exotic state of matter so that the output signal is almost always near zero current, but occasionally it is some obviously non-zero value. Hardware is usually set up to record the time at which a transition from zero to non-zero current happens (we could instead record the current as a 14-bit output from an Analog-to-Digital Converter, an ADC, every nanosecond, say, but the record of current transition times is essentially a very compressed, very lossy record of the same information.) Also of interest in experiments is the dead time, the time it takes the hardware to restore the current to near zero so that another transition can be noticed and the time recorded.
Suppose we have this device. When it's set up in a dark room, there is a low rate of current transitions, called the dark rate; when we enter the room and turn on a dim light, the rate of current transitions changes; when we move around the room, the rate of current transitions changes; when we change the intensity of the light or introduce new lights, the rate of current transitions changes. If we set up some barriers, again the rate of current transitions changes, and again when we move the barriers around. If we set up two or more APDs, we can calculate more elaborate statistics, cross-correlations at the same or at different times.
If we ask what could be causing these events, one answer is that we've set up a ridiculously exotic state of matter, so of course weird stuff will happen. More than that, however, we notice that as we continuously change the conditions of the experiment, the current transition statistics change more-or-less continuously, if we collect enough data. Even though the events are discrete, the statistics change continuously. Historically, elementary physics has said that each current transition is caused by a particle, but more sophisticated physics works with a quantum field, which can be understood to make no claims about what happens outside the APD, nor about details of the APD current, but does discuss the statistics one would observe for a given theoretical model of an APD, and how those statistics would change continuously as we move the lights or the barriers or the APDs around.
For what it's worth, my YouTube video from last February, Quantum Mechanics: Event Thinking, deliberately short at 4'26", presents more-or-less this story.One additional note, keying in to vanhees71's account, is that triggers for large experiments are usually much more elaborate (and can slip into dangerously ad-hoc territory) than just whether one electrical signal transitions from zero to non-zero.
I think it's best not to get too hung up on the Bishop Berkeley problem. Ultimately I can't see that it helps much to be solipsist about the world. Go to the world of extreme positivism for a visit if you like, which I've found occasionally useful as a way to get out of the box, but best to come back. I've been peppering everything I've written on PF with links to my arXiv:1709.06711 (comment #30 has a more up to date version attached) because that's how I think about QM/QFT (for which sorry, I guess) and it's not yet well-known, but for this specific question, I think its mathematical derivation of a random field as a subalgebra of a free quantum field algebra more reconciles a classical perspective and a quantum field perspective than any other math I've seen in the literature (there's a parallel with the de Broglie-Bohm approach, deriving trajectory probabilities from the wave function, but there are also fundamental differences, that I keep to the mathematics of operators acting on Hilbert space as a model for signal analysis, manifest Poincaré invariance is maintained, and I keep to an operational interpretation of the math as far as possible). One significant point, however, is that the philosophy of classical probability has become significantly less settled than it used to be. I'm happy with an instrumental, construct-an-ensemble-and-compute-statistics approach, which I think is what physicists do, but philosophers have worries that I find significant about that approach, and physicists who want to construct a model for the whole observable universe obviously can't construct an ensemble (also, if we take away the background Minkowski space, constructing an ensemble becomes quite fraught, AFAICT —amongst other worries, of course).
I'd say, if anything is free of prejudices it's a "machine read" record of experimental results. Of course, these records are of no value, if one doesn't know, how the measurement devices and DAQ (i.e., both hard and software) has been constructed. E.g., at the LHC even the best DAQ technology cannot produce "raw data", i.e., there are hardware triggers already in the detectors before anything is stored to electronic storage. These triggers are to a certain extent constructed using models. It's not so clear to me, whether one really could perhaps through away interesting signals by such cuts. Recently there was an interesting article concerning the still mute search for particles beyond the Standard Model concerning possible long-lived candidates in the Quanta Magazine:
https://www.quantamagazine.org/how-the-hidden-higgs-could-reveal-our-universes-dark-sector-20170926/
So one should be aware that there is indeed a subjective element in objective observations, that cannot be eliminated, namely the "arbitrary choice" of the observational apparati. I you'd say, e.g., only the direct human senses are valid, you'd miss a lot of stuff, which objectively exists: e.g., of the electromagnetic spectrum, restricting yourself what can be seen by the human eye, you'd exclude all em. waves at wavelenths outside the one octave from about 400 too 800 nm that can be seen directly by the human eye.
Nevertheless there's some objective reality in observations (particularly those not related to direct involvement of the human senses), because they are reproducible everywhere and at any time independently from each other, given a precise enough description of what is observed in terms of possible setups for measuring the concerning quantities. That becomse, of course, the more convincing if two or more such setups are also using different technology to measure the very same observable.
In modern experiments, it will usually mean a record in a computer, not any direct experience, microsecond by microsecond. For experimental data to be really out there, it should be in "Supplementary Material", or at least available to other physicists on application. Where things get edgy is in the instrumental details of how the experimental apparatus was constructed, including how whatever exotic materials were used were exotically processed, where apparatus was sourced, what sources of noise were shielded and corrected for, et cetera, whchi all in all should be as much as is needed to reproduce the results.So do the records of experimental data and setup details have mind independent existence?
I'm not sure what do you mean with "pointer readings". Do you mean either:
1) direct experience of expermentalist;
2) any type of record from which one can learn about certain measurement result?In modern experiments, it will usually mean a record in a computer, not any direct experience, microsecond by microsecond. For experimental data to be really out there, it should be in "Supplementary Material", or at least available to other physicists on application. Where things get edgy is in the instrumental details of how the experimental apparatus was constructed, including how whatever exotic materials were used were exotically processed, where apparatus was sourced, what sources of noise were shielded and corrected for, et cetera, whchi all in all should be as much as is needed to reproduce the results.
The scope of physics and its operational formalism is limited to pointer readings (the experience of what is called “observations”), which physics can study and connect to other pointer readings. There is no need for any assumption of realism or anti-realism or anything else. All these assumption belong to the realm of beliefs, personal “hypotheses” about yourself and about your experiences of “observations”.I would use a slightly different wording but….yes, that is exactly correct.
The scope of physics and its operational formalism is limited to pointer readings (the experience of what is called “observations”), which physics can study and connect to other pointer readings.I'm not sure what do you mean with "pointer readings". Do you mean either:
1) direct experience of expermentalist;
2) any type of record from which one can learn about certain measurement result?
Scientific approach is based on assumption of realism…..The scope of physics and its operational formalism is limited to pointer readings (the experience of what is called “observations”), which physics can study and connect to other pointer readings. There is no need for any assumption of realism or anti-realism or anything else. All these assumption belong to the realm of beliefs, personal “hypotheses” about yourself and about your experiences of “observations”.
Einstein believed “that the notions of physics would refer to a real external world and that these ideas would be set by things that claim a "real existence" independent of the perceiving subjects.” And then he tried to force quantum physics into the corset of his conceptions. Everybody knows how successful he was. “Physics” cannot establish that such beliefs are true, but it can establish that such beliefs are not true. But, instead of learning from Einstein’s convoluted and ultimately entirely unsuccessful attempts, some are still on the quest to find some good elements of “objective reality” in quantum theory. And the “interpretative game” goes on. It’s not the word "reality" that has almost lost its usability, it’s the concept of a physical reality that has lost all its usability.Scientific approach is based on assumption of realism (defined as "there is mind independent reality" or as opposite of solipsism). So the realism is common basis for any meaningful scientific discussion (this applies to positivists too). If you reject realism there can be no meaningful discussion with you about any science topic.
Again, one of Einstein’s fallacies, merely based on his psychological predispositions and his desire to return to the ontology of materialism.
In his book “Chemistry, Quantum Mechanics and Reductionism: Perspectives in Theoretical Chemistry“ Hans Primas cites Fock:
“The deeper reason for the circumstance that the wave function cannot correspond to any statistical collective lies in the fact that the concept of the wave function belongs to the potentially possible (to experiments not yet performed), while the concept of the statistical collective belongs to the accomplished (to the results of experiments already carried out) (Fock 1952, 1957).”It's well known, why Fock wrote quite "interesting" philosophical articles concerning QT in Soviet times! I don't know, whether it's also in the English edition of Blokhintsev's famous QM textbook, but in the (then Eastern!) German edition there was also a "philosophical appendix"…
atyy's comment,
is perhaps too much a cute fussing about words, but I'll further note that there are no “objective reproducible quantitative observations in nature” insofar as events never repeat perfectly. Of course pragmatically a given experimenter makes their choice of what is close enough (perhaps quantitatively, a formal choice of a distance between events, but even in the most meticulous experiments there are also judgement calls), there are "good" experimenters who serve as exemplars of best practice, and there are social conventions that have been honed over centuries that make intersubjective seem objective to those who have been trained in those social conventions, but there is a gap. Research is arguably about getting "out of the box" —or, for some, the straightjacket— that we find ourselves trained into, and creating a new and beautiful box for students to have to get out of in their turn. All of us have some groups of outsiders, people who have been trained into different social conventions than those we have been trained into, to whom we pay some attention. We can and should make our own choices, and perhaps it's OK even to disdain some other groups, but, I suggest, philosophers of physics are too diverse a group, at least as I find them, for physicists to dismiss all of them.
I'll also add that there's no such thing as “pure qualitative "philosophical" thought”, except as a straw man. Most of the philosophers I pay attention to engage in quantitative mathematics of one kind or another.Well, particularly due to quantum mechanics we have some things that are really reproducible exactly. E.g., any electron is precisely as any other, they are even indistinguishable in a very strict sense. Thus to the best of our knowledge each electron has precisely the same mass, magnetic moment, and charges of the standard model as any other. Of course, these quantities can be measured only with some finite accuracy, but so far even by getting this accuracy down to up to 12 significant digits (for the magnetic moment), there's no deviation from the assumption of indistinguishability. In this sense we have objective reproducible quantitative observations in nature in much better approximation than within classical physics.
That natural sciences are not sheer convention within a science community can be seen that indepedent researchers find the same result, measuring, e.g., the properties of elementary particles.
Mathematics is not philosophy. The mathematicians for already some time like to group mathematics into the category of "structural sciences" rather than "philosophy". Of course, mathematical physics (like axiomatic QFT) is not philosophy but an important part of physics (maybe also mathematics, but that the mathematicians have to judge). If I was a mathematical physicist I'd consider it an insult to be named a philosopher of science!
How come it's not ok to talk about "reality", but it is ok to talk about "Nature"?
Is Nature different from reality?It's ok to talk about reality with physicists, but with philosophers you never know what they mean!
His view is concisely expressed as follows [Einstein (1949), quoted here without the supporting argument]:
“The attempt to conceive the quantum-theoretical description as the complete description of the individual systems leads to unnatural theoretical interpretations, which become immediately unnecessary if one accepts the interpretation that the description refers to ensembles of systems and not to individual systems.”Again, one of Einstein’s fallacies, merely based on his psychological predispositions and his desire to return to the ontology of materialism.
In his book “Chemistry, Quantum Mechanics and Reductionism: Perspectives in Theoretical Chemistry“ Hans Primas cites Fock:
“The deeper reason for the circumstance that the wave function cannot correspond to any statistical collective lies in the fact that the concept of the wave function belongs to the potentially possible (to experiments not yet performed), while the concept of the statistical collective belongs to the accomplished (to the results of experiments already carried out) (Fock 1952, 1957).”
Physics is about objective reproducible quantitative observations in nature, and theoretical physics aims at a mathematical description and the derivation of the observable phenomena from as little assumptions (fundamental Laws of Nature, themselves finally always based on empirical evidence) as possible. This implies also the aim to adapt our intuitive sense for whatever ideas we have about nature. Locality and causality have a very clear and well-defined meaning in local microcausal relativistic QFT, which is the mathematical basis for the Standard Model of elementary particles. It in my opinion and open question, how to incorporate self-consistently gravitation and spacetime structure, i.e., some theory of "quantum gravity", but that's not a philosophical but purely scientific problem, which I doubt very much to be solvable by pure qualitative "philosophical" thought.atyy's comment,
How come it's not ok to talk about "reality", but it is ok to talk about "Nature"?is perhaps too much a cute fussing about words, but I'll further note that there are no “objective reproducible quantitative observations in nature” insofar as events never repeat perfectly. Of course pragmatically a given experimenter makes their choice of what is close enough (perhaps quantitatively, a formal choice of a distance between events, but even in the most meticulous experiments there are also judgement calls), there are "good" experimenters who serve as exemplars of best practice, and there are social conventions that have been honed over centuries that make intersubjective seem objective to those who have been trained in those social conventions, but there is a gap. Research is arguably about getting "out of the box" —or, for some, the straightjacket— that we find ourselves trained into, and creating a new and beautiful box for students to have to get out of in their turn. All of us have some groups of outsiders, people who have been trained into different social conventions than those we have been trained into, to whom we pay some attention. We can and should make our own choices, and perhaps it's OK even to disdain some other groups, but, I suggest, philosophers of physics are too diverse a group, at least as I find them, for physicists to dismiss all of them.
I'll also add that there's no such thing as “pure qualitative "philosophical" thought”, except as a straw man. Most of the philosophers I pay attention to engage in quantitative mathematics of one kind or another.
My criticism against philosophy in QT is not that it doesn't solve any problems, but that they pretend that there are problems, where there are none and then confusing the subject by unclear definitions of prime notions like "reality". Thanks to philosophy (starting with the unfortunate EPR paper, which according to Einstein has not brought out his main concerns with QT which was more about inseparability due to entanglement, as he wrote in his Dialectica article of 1948 [*]) the word "reality" has almost lost its usability, because it is not clear anymore what exactly an author using it wants to say ;-)).
[*] A. Einstein, Quanten-Mechanik und Wirklichkeit, Dialectica 2, 320 (1948)Einstein believed “that the notions of physics would refer to a real external world and that these ideas would be set by things that claim a "real existence" independent of the perceiving subjects.” And then he tried to force quantum physics into the corset of his conceptions. Everybody knows how successful he was. “Physics” cannot establish that such beliefs are true, but it can establish that such beliefs are not true. But, instead of learning from Einstein’s convoluted and ultimately entirely unsuccessful attempts, some are still on the quest to find some good elements of “objective reality” in quantum theory. And the “interpretative game” goes on. It’s not the word "reality" that has almost lost its usability, it’s the concept of a physical reality that has lost all its usability.
Physics is about objective reproducible quantitative observations in nature, and theoretical physics aims at a mathematical description and the derivation of the observable phenomena from as little assumptions (fundamental Laws of Nature, themselves finally always based on empirical evidence) as possible. This implies also the aim to adapt our intuitive sense for whatever ideas we have about nature. Locality and causality have a very clear and well-defined meaning in local microcausal relativistic QFT, which is the mathematical basis for the Standard Model of elementary particles. It in my opinion and open question, how to incorporate self-consistently gravitation and spacetime structure, i.e., some theory of "quantum gravity", but that's not a philosophical but purely scientific problem, which I doubt very much to be solvable by pure qualitative "philosophical" thought.How come it's not ok to talk about "reality", but it is ok to talk about "Nature"?
Is Nature different from reality?
My criticism against philosophy in QT is not that it doesn't solve any problems, but that they pretend that there are problems, where there are none and then confusing the subject by unclear definitions of prime notions like "reality".Philosophy, per se, is not confusing. It’s merely the person itself which gets confused when philosophy questions his/hers implicit assumptions.
Finally, you're right about the first Hegerfeldt paper I cited; in future I will cite only the second paper, which I think enough applies to the relativistic case as well as to the nonrelativistic case to be at least of historical interest to anyone who wishes to understand nonlocality/locality in QFT.By QFT I mean what's used in practice. Of course, I'm aware that QFT is not strictly defined in the mathematical sense, but renormalized perturbative QFT is well defined and obeys all the fundamental properties you expect, including locality of interactions and causality (in the sense of the linked-cluster theorem). In Hegerfeldt's paper it's not clear to me, how he defines his observables. You cannot define particles in transient states in the Heisenberg picture at all. A particle interpretation is only possible for asymptotic free states, which makes it pretty clear that relativistic particles are even less localizable as "little billard balls" than non-relativistic particles. This is all well known since Bohr and Rosenfeld and no contradiction to causality.
Author is Ballentine. The book is Quantum Mechanics A Modern Development (1998). p47:
In classical mechanics the word “state” is used to refer to the coordinates and momenta of an individual system, and so early on it was supposed that the quantum state description would also refer to attributes of an individual system. … However, such assumptions lead to contradictions (see Ch. 9), and must be abandoned.
The quantum state description may be taken to refer to an ensemble of similarly prepared systems. One of the earliest, and surely the most prominent advocate of the ensemble interpretation, was A. Einstein. His view is concisely expressed as follows [Einstein (1949), quoted here without the supporting argument]:
“The attempt to conceive the quantum-theoretical description as the complete description of the individual systems leads to unnatural theoretical interpretations, which become immediately unnecessary if one accepts the interpretation that the description refers to ensembles of systems and not to individual systems.”
and look at chapter 9.3. The Interpretation of a State VectorYes sure, that's the minimal interpretation, advocated by Ballentine in his famous RMP article and also in his excellent textbook. For me the probabilistic interpretation taking Born's rule as a fundamental postulate (the only logical way, because attempts to derive Born's rule from the other postulates failed so far; see Weinberg, Lectures on Quantum Mechanics, Cambridge University Press) implies that the predictions of QT can only be experimentally tested on ensembles. Formally, a state is defined as an equivalence class of preparation procedures and as such of course refers to individual systems, because in order to create ensembles the state has to refer to a preparation procedure on a single system, since each ensemble consists of many realizations of the same state (in the sense of a preparation procedure). E.g., at the LHC you have well-defined bunches of protons which in a well defined way collide at specified interaction points, where the detectors are located.
The way I read philosophers on this is that they are not so much questioning the precise quantitative descriptions as physics, as questioning whether they properly capture our intuitive sense of the ordinary language terms "locality", "causality", etc.Physics is about objective reproducible quantitative observations in nature, and theoretical physics aims at a mathematical description and the derivation of the observable phenomena from as little assumptions (fundamental Laws of Nature, themselves finally always based on empirical evidence) as possible. This implies also the aim to adapt our intuitive sense for whatever ideas we have about nature. Locality and causality have a very clear and well-defined meaning in local microcausal relativistic QFT, which is the mathematical basis for the Standard Model of elementary particles. It in my opinion and open question, how to incorporate self-consistently gravitation and spacetime structure, i.e., some theory of "quantum gravity", but that's not a philosophical but purely scientific problem, which I doubt very much to be solvable by pure qualitative "philosophical" thought.
I agree with you that the latter quest is, in the end, a fool's errand, because if our ordinary language intuitions conflict with the precise quantitative physics that has been confirmed to umpteen decimal places by experiment, then what needs to change is our ordinary language intuitions, not the physics. But philosophers don't seem to like that very much, which is not surprising, since our ordinary language intuitions are the basis of their entire discipline.Ordinary language is inadequate for any kind of physics in the natural sense. Already Galileo new that "the book of nature is written in terms of geometry…". This is still true today, even in a much narrower sense. Of course you have to use a modern idea of geometry, which reaches back to Klein's Erlanger program, but that's another story.
I'm very interested in foundations of physics, but I don't think that philosophy helps to formulate the foundations clearly. To the contrary, philosophy tends to obscure clearly-defined notions (as "locality", "causality", etc) which have a very clear meaning and quantitative description in physics in terms of the most fundamental theories (relativistic local and microcausal QFT and GR).You’re missing the point, quantum nonlocality and delayed choice experiments are analyzed within experimental limits using non-relativistic QM. So, obviously, Lorentz invariance does nothing to abate these mysteries. Now let’s look at some problems in physics that can actually be resolved with philosophy, i.e., the problematic initial conditions of big bang cosmology known as the low entropy problem, the horizon problem, and the flatness problem.
These are indeed problems in physics, as evidenced by the creation of inflationary cosmology whose practitioners are physics professors at highly regarded institutions. How could mere philosophy resolve these problems? We explain that at length in chapter 3 of our book, but the short answer is that all we have to do as physicists is move from dynamical explanation per the Newtonian Schema Univese to block universe explanation per the Lagrangian Schema Universe. Those problems are created by physicists’ dynamical bias, as pointed out by … philosophy of physics. You may not like the answer, but it is an answer from philosophy for a problem in physics. If you want to argue about it, we’ll have to take that to another thread. Let’s try to keep this thread on topic, i.e., Adam’s book.