On causality

Cause and effectCausality is one strange concept. It is absolutely essential to our understanding of the so-called “manifest image” of the world, i.e., the world as perceived and navigated by human beings. (The distinction between the manifest and the scientific image was introduced by philosopher Wilfred Sellars.) It is crucial for us to distinguish between events that happen because (i.e., are caused by) other events, vs things that appear to be the result of chains of cause-effect but really aren’t. We think smoking, statistically speaking, causes cancer, meaning that there are physical events that make it more likely that if you are a smoker you will get cancer. But when a few years ago someone showed a statistically significant correlation between number of births in London and frequency of storks flying overhead, nobody cried out for a revision of human biology textbooks…

When it comes to the “scientific image,” i.e., how science tells us the world is, things are more complicated. Talk of causality is all over the place in the so-called “special sciences,” i.e., everything other than fundamental physics (up to and including much of the rest of physics). In the latter field, seems to me that people just can’t make up their minds. I’ve read articles by physicists, and talked to a number of them, and they seem to divide in two camps: those who argue that of course causality is still crucial even at the fundamental level, including in quantum mechanics. And those who say that because quantum mechanical as well as relativistic equations are time symmetric, and the very idea of causality requires time asymmetry (as in the causes preceding the effects), then causality “plays no role” at that level.

Both camps have some good reasons on their side. It is true that the most basic equations in physics are time symmetric, so that causality doesn’t enter into them. But it is also unquestionably true that we have to somehow explain the arrow of time and the fact that things do very much appear to happen one after the other. While we move freely back and forth the three spatial dimensions, we definitely don’t do that along the fourth, temporal, dimension.

Three possible solutions to this conundrum are: I) to say that causality is an “illusion,” part and parcel of the manifest image, but not really a scientifically viable concept; or II) to claim that causality somehow emerges from basic physics (whatever “emergence,” a philosophically controversial concept, means); or III) to argue that causality is fundamental and that there is something incomplete about quantum mechanics and general relativity, and that’s why it needs to be “added by hand,” so to speak, in order to describe how the world actually works.

This, in turns, depends on how one conceives time — the element that, after all, is needed for causality. For instance, Brad Skow adopts the “block universe” concept arising from Special Relativity and concludes that time doesn’t “pass” in the sense of flowing; rather, “time is part of the uniform larger fabric of the universe, not something moving around inside it.” If this is correct, than “events do not sail past us and vanish forever; they just exist in different parts of spacetime … the only experiences I’m having are the ones I’m having now in this room. The experiences you had a year ago or 10 years ago are still just as real [Skow asserts], they’re just ‘inaccessible’ because you are now in a different part of spacetime.

It isn’t entirely clear what this view does with respect to causality, and it doesn’t seem to explain why we feel like time is something very different from space. Moreover, it doesn’t explain, say, the manifest image-level difference between causation and correlation. None of this means that the block universe concept of time/causality is wrong, but it does mean that there are serious pieces of the puzzle still missing.

Lee Smolin has a very different idea of time, and therefore of causality, as I have explained in detailed in the past. For him quantum mechanics and relativity are indeed incomplete (on this everyone seems to agree, including string theorists, who vehemently reject Smolin’s approach), time is fundamental, and so is causality. Indeed, he goes as far as saying that the laws of nature emerge from the specifics of causal interactions at the fundamental level, not the other way around.

In philosophy too, causality has always been a messy business. Famously, according to David Hume, it is something we add onto our perception of the fabric of the universe, and that may not be inherent in it. As the excellent Internet Encyclopedia of Philosophy article on Hume and causality puts it: “Whenever we find A, we also find B, and we have a certainty that this conjunction will continue to happen. Once we realize that ‘A must bring about B’ is tantamount merely to ‘Due to their constant conjunction, we are psychologically certain that B will follow A,’ then we are left with a very weak notion of necessity. This tenuous grasp on causal efficacy helps give rise to the Problem of Induction — that we are not reasonably justified in making any inductive inference about the world.”

However, it is not at all clear whether Hume thought that this is all there is to causality, or rather simply all that an empiricist approach to causality allows us to say, and Hume scholars disagree on this point.

Modern philosophers have developed a number of different theories of causation (and of time), that attempt to take into account what we have learned from science, and particularly physics, and make sense of it. It’s not an easy task, to put it mildly.

One of my favorite modern ways of thinking about causality (though, of course, it has its critics and drawbacks) is the co-called conserved quantity theory of causation. Here are the two major versions, according to the Stanford Encyclopedia of Philosophy (if you keep reading that article, you will also see a number of standard objections raised against it, the proposed responses, etc.):

P. Dowe’s version (1995, p. 323):

CQ1. A causal interaction is an intersection of world lines which involves exchange of a conserved quantity.

CQ2. A causal process is a world line of an object which possesses a conserved quantity.

W. Salmon’s version:

Definition 1. A causal interaction is an intersection of world-lines that involves exchange of a conserved quantity.

Definition 2. A causal process is a world-line of an object that transmits a nonzero amount of a conserved quantity at each moment of its history (each spacetime point of its trajectory).

Definition 3. A process transmits a conserved quantity between A and B (A ? B) if it possesses [a fixed amount of] this quantity at A and at B and at every stage of the process between A and B without any interactions in the open interval (A, B) that involve an exchange of that particular conserved quantity.

Here is a list of universally conserved properties in interactions between elementary particles:

  • energy
  • linear momentum
  • angular momentum
  • electric charge
  • baryon number
  • electron-muon-tauon number
  • lepton number

All of this, of course, has profound implications for both science and philosophy, but also for the way we should think about the world, i.e., these considerations affect both our scientific and our manifest images of the world.

Recently, I’ve began to think of causality as somewhat similar, in its manifestations, to physical forces, such as gravity. While gravity is universal, meaning that it acts in every point of the universe, so that in theory we are subject to the gravitational pull of every body in the cosmos that has mass, in practice we only need to be concerned with the gravitational effects induced by sufficiently massive bodies laying close enough to us. Our everyday life is affected by the gravity of Earth, the Moon, and the Sun, and little else. You need not worry about the gravitational pull of, say, the Andromeda galaxy because, even though it’s huge, the thing is so far from us that its orbital period is billions of years, so that it has no measurable effect on your existence. You also don’t need to concern yourself with the gravitational influence of people around you, because while they are nearby, their mass is just too small to do anything of consequence to you.

Perhaps causality is like that: while it makes sense to think of cause and effect as a universal phenomenon, with everything connected to everything else, for any practical purpose we are free to take into account only local causal interactions, all the other ones being dampened or overridden so to become irrelevant. It remains to be seen what such view would do to radical metaphysical notions like universal determinism (and consequent reductionism), or to controversial ones such as top-down causation (and consequent anti-reductionism).

You would think that this is an obvious area of inquiry where scientists and philosophers should come together. It isn’t, in my opinion, simply a matter of letting science tells us how things really stand. For one thing, because I’m confident that a fundamental physicist, a non-fundamental one, a biologist, and a social scientist would have very different views of what “science tells us” (indeed, as I mentioned above, even fundamental physicists vehemently disagree among themselves, so…).

Nor, of course, is it a question of calling the philosophical cavalry to explain to the naive scientists how they ought to think about the matter. That would be presumptuous to the level of silliness.

But why isn’t the question of time, or that of causality, a straightforward scientific issue? Why do we need philosophers to begin with?

One answer would be because philosophers have spent literally centuries thinking about these issues, much more so than scientists, and so there is likely something to learn from the best proposals they have put forward so far.

But that’s not actually it, or at the least, it isn’t the whole story. I think time and causality are a perfect example of the power of “sciphi,” if you will, because the issue isn’t just one of discovering facts about time and causality, it is to develop an understanding of these concepts that allow us to keep pursuing Sellars’ overarching objective: “to formulate a scientifically oriented, naturalistic realism which would ‘save the appearances'” [1]. The more I think about it, the more it seems to me that the (or at the least a major) goal of philosophy is precisely to articulate a mapping function that connects the scientific image — which only science can provide us — with the manifest image, which we simply cannot do without as cognitively limited biological creatures of a certain kind (and that includes scientists, obviously).


[1]  “Autobiographical Reflections (February 1973),” p. 289 in Action, Knowledge, and Reality: Studies in Honor of Wilfrid Sellars, H-N. Castañeda (ed.), Indianapolis: Bobbs-Merrill, 1975: 277-93.

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125 thoughts on “On causality

  1. Hi Massimo,

    … as far as I understand … the principle [2nd law] doesn’t emerge naturally from QM, which means that the arrow of time has to be added after the fact, so to speak, to the fundamental equations.

    Let’s take synred’s scenario of gas molecules in a box, starting with them all in one corner. The fundamental equations of QM are deterministic and time-symmetric. Compute them forward, and the molecules spread out. That is 2nd-law behaviour.

    Now, if we kept the deterministic equations, reversed the direction of time, and started from the exact ending points from above, then the molecules would all gather in the corner again. That is anti-2nd-law behaviour and is contrary to how the universe works.

    But, now add in some indeterminacy, some dice throwing associated with the “collapse of the wavefunction” or whatever is actually going on. That dice throwing scrambles the effect of the initial conditions, and the gas molecules will again demonstrate 2nd-law behaviour regardless of starting points (since, by definition, dice-throwing indeterminacy is probabilistic, and the 2nd law is probabilistic).

    So, to summarise, QM without any indeterminacy does not give rise to the 2nd law; but QM with added dice-throwing indeterminacy does. That’s why I argued in my first comment above that the arrow-of-time behaviour comes from indeterminacy associated with the “collapse of the wavefunction”. The problem is, of course, that this aspect of QM is simply not understood.

    Thus physicists such as Sean Carroll will argue for a completely deterministic version of QM, as given by Everettian Many Worlds, and thus land themselves with an arrow-of-time problem.

    Now, obviously, when it comes to fundamental physics people should listen to Sean Carroll far more than myself, but I’m still sticking to my version (and Everettian Many Worlds is a minority taste among physicists, though espoused by some big names). I also tried to persuade (the sadly missed) vmarko of this several times, though failed.

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  2. Hello Massimo:

    “I’m aware of that, but as far as I understand (please correct me if I’m wrong, oh physicists!) the principle doesn’t emerge naturally from QM, which means that the arrow of time has to be added after the fact, so to speak, to the fundamental equations. So the problem does exist”

    Thermodynamics is my favorite example of ’emergence’. Conceptually it emerges from the statistics of large numbers. Thinking in terms of simulation, if you set up QM problem with a large number of particles/states and run it thermodynamic behavior will happen. To understand why it happens you have to add the concepts of the statistics of large numbers. It is the one case where we can understand ’emergence’ in detail.

    Storing a memory whether in chip or brain involves an ‘irreversible’ change (so many interactions you have to change and so many momenta flipped to reverse them that it’s for all practical purposes impossible). Hence, one very rarely remembers he future.

    It’s like my particles in the corner example. If I watch them through time they will spread out and fill the box. If I reverse time (which just is reversing all their momenta) they will also spread out and fill the box. This is just because there are a lot more ways to fill the box than to be in a corner. The chances that they will reassemble in a corner are nil, if the number of particles is large. You can’t derive this from staring at the equations — you have to count the states in the specified situation. The equations are time symmetric, the solutions are not.

    Time is not emergent (it’s there in field theory or classical mechanics), but it’s direction is.

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  3. Coel:

    I don’t think ‘many worlds’ has a serous arrow of time problem. To get the particles back in the corner you have to revere time in all the worlds not just yours. It’s hard enough to do that in one world, so even classical mechanics has no practical arrow of time problem. In many worlds it would seem unlikely that somebody would decide to reverse time in all of ’em at the same time . It would be difficult for them to synchronizes there watches. Should I decide to reverse time at a certain time by my watch in whatever world I find myself in, since everything that can happens would find myself unable to in at least some worlds (my finder tunneled into the key board as I wrote up the experimental protocol in some worlds and in others while I searched google for ideas on how to do the time reversal), so it’s not going to work. I need to reverse all the worlds to get back in the corner.

    LOL )=

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  4. Hi synred,

    Well I don’t claim to understand Everettian many-worlds QM, but:

    I don’t think ‘many worlds’ has a serous arrow of time problem. To get the particles back in the corner you have to revere time in all the worlds not just yours.

    I gather (though am open to correction) that in EQM reversing the arrow of time would reverse time in all the worlds. Afterall, the whole point of EQM is that it’s all one big wave function (with terms decohered and thus added with “+” rather then being entangled), is it not?

    Thus, reversing the arrow of time would cause the worlds to “merge” (opposite of “split”), and thus the gas molecules would indeed all end up back in the corner. Therefore you do have a 2nd-law problem. Carroll then solves that by appealing to special initial conditions (i.e. the 2nd-law is then a peculiarity of our universe, resulting from the initial conditions, whereas another universe with different initial conditions could exhibit anti-2nd-law behaviour).

    Personally I much prefer an indeterministic account of QM, which then exhibits the 2nd law always and naturally.

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  5. Hi Massimo,

    To [m]e mathematics describes really, it is not reality.

    Right. And we agree that mathematics can describe reality, by modelling aspects of reality as mathematical objects and using the tools and syntax of mathematics to describe those objects. In other words, we pretend that reality is a mathematical object because this is useful. But just because this is assumed to be a useful fiction doesn’t rule out the possibility that reality actually is a mathematical object. Some mathematical objects do not correspond very closely to anything in reality. This doesn’t stop mathematicians describing those objects too. We shouldn’t confuse the syntax mathematicians use to describe mathematics (a language) with what is described

    I’m aware of that, but as far as I understand (please correct me if I’m wrong, oh physicists!) the principle doesn’t emerge naturally from QM,

    It emerges naturally from almost any rule based system where state changes bit by bit over time. Let’s take a simple example. Suppose you have a million coins, and the rule of the system is that every clock tick you flip an arbitrary coin. The coin doesn’t have to be chosen truly randomly — you could use a deterministic pseudorandom sequence like the digits of Pi to guide your selection. All that matters really is that the rules governing the choice be neutral with respect to entropy — you’re not deliberately trying to maximise or minimise entropy.

    Low entropy would be a remarkable state we would be very unlikely to reach by chance, e.g. where all coins are heads or all coins are tails. High entropy would be the state we would expect to see after the laws have been at work for a long time, e.g. where the coins are split about 50/50. If you start with all coins showing heads, we will observe a tendency for entropy to increase with each clock tick. This will continue until you reach equilibrium and we reach a state where the coins are split approximately 50/50. The initial state of all heads corresponds to the Big Bang and equilibrium corresponds to the heat death of the universe.

    The 2nd law of thermodynamics is an inevitable consequence of the fact that the Big Bang was a moment of low entropy, and then the laws of physics proceeded to mess it up (flipping coins). There’s nothing particular to QM to explain this or in need of reconciliation with this. The same would hold in a world without QM, and the same would hold in most worlds with even radically different laws of physics. All you need is an initial low entropy state and then a set of laws which can mess this state about. Almost any laws will do.

    I have disagreed with Coel on this stuff. Coel thinks that the irreducible randomness of QM is necessary to explain the second law of thermodynamics, but I think he’s dead wrong on this. I don’t think randomness or QM has much to do with it.

    None of which, even though likely true, sounds to me like even the beginning of an explanation for why we perceive time so qualitatively different from space.

    Physics does not treat time as interchangeable with space. Time and space have different properties so it is not surprising that we perceive them differently.

    What is actually happening when we move in space and time passes?

    Strictly speaking, nothing is “happening”. Everything is static. But there are points in spacetime where we think we’re in one place and then “later” points in space time where we think we are somewhere else. We perceive this as having moved from one place to another. It’s like a video. The video is just a thing. It isn’t changing. But the video is made up of an ordered series of events. If we deem some events to be “later” than other events, we can interpret things as moving, even though there isn’t really any motion if we consider the video holistically as a single artifact.

    What does it mean for something physical to be mathematically necessary?

    Suppose the laws of physics are such and such and suppose that the state of the world at time t is such and such. Given this state and these laws of physics, we can do mathematics to show that the state of the world at time t+1 is determined. It is mathematically necessary.

    But only given these laws and this initial state. Neither of these are mathematically necessary, so nothing physical is ultimately mathematically necessary. Necessity only applies given the givens!

    Why is it that QM, contra its Newtonian counterpart, doesn’t say that one billiard ball hitting another is necessary at all, but just highly probable?

    Because the laws are different. So we don’t have absolute necessity, but merely very high probability. I gave a mathematical example of this too with how 90% of numbers divide by ten the same number of times as their successors.

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  6. Hi DM,

    I have disagreed with Coel on this stuff. Coel thinks that the irreducible randomness of QM is necessary to explain the second law of thermodynamics, but I think he’s dead wrong on this.

    I think that non-deterministic dice-throwing is necessary to guarantee 2nd-law behaviour. You could indeed get 2nd-law behaviour with deterministic laws by specifying your initial conditions to get that result. Equally, you could specify initial conditions to get anti-2nd-law behaviour.

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  7. I prefer indeterministic QM too. Indeed Everett can be reversed formally. Not likely to happen though, so observing an arrow of time doesn’t rule it out (which I would like to do).

    I also recently learned that ‘many worlds’ can not derive the Born rule, so they have to add it as an additional assumption just like ‘Copenhagen’. That reduces it appeal even more too me. It doesn’t even has even a vague ‘Occam’ edge. In my ‘many worlds’ simulation I have to add ‘worlds’ rather than ‘collapse’ them (or actually never make ’em) to get the Born rule to come out.

    Decoherence is nice work inspired by ‘many worlds’ but it applies equally to ‘Copenhagen-like’ interpretations.

    I was trying something pretty crazy. Using a two-time theory (Mueller from Duke) to try to collapse the wave function (or more like cancel it out). I couldn’t figure out how to make it work (which doesn’t mean much one way or the other). I even managed to write down an solve the Dirac eqn. in two times formalism, but couldn’t figure out what to do with it. The idea was that measurement doesn’t ’cause’ collapse, but collapse causes measurement. I didn’t get anywhere.
    Though it does bring up the issue of what cause means in QM measurement theory. While we typically say measurement causes the collapse, since it’s non-local the time-order is not defined and it’s not clear what that means (though it gets the right answer).

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  8. Coel:

    You don’t need to have non-determinant dice throwing to explain our observations. Over very long periods of time entropy may occasionally (very occasionally) go down even with in determinant dice. The second law is not absolute though very nearly so…

    The only thing indeterminism buys you is that you can’t reverse all the particles and get them to go back in the corner reliably. It could still happen (if you could pull off the reversal — lots of Maxwell/s demons pushing particles in sync [a]), it just makes it less likely to work.

    Which is not to say I don’t think QM is indeterminate, it’s just in determinism is not needed to explain arrow-of-time observation. It is needed to compute the probability of Schrödinger’s cat dying in a given interval. [b].

    [a] I’m guessing the demons entropy would go up quite a bit in order to carry out this feat.

    [b] “Schrodinger’s Cat and the Law” here: https://skepticalsciencereviews.wordpress.com/story-land/

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  9. Coel,

    I think that non-deterministic dice-throwing is necessary to guarantee 2nd-law behaviour.

    But the Schrödinger equation is perfectly deterministic. It’s only when we observe a system that there’s a non-deterministic aspect.
    (There’s also a statistical aspect when we describe a system about which we have incomplete information with a density operator, but that’s not the same as the non-deterministic behaviour of a system when it’s observed. The evolution of the density operator is governed by a deterministic law.)

    How do observations cause or explain the second law?

    Another point: even in special relativity time has a special status. The whole idea of SR is more or less that physical laws should be invariant under transformations that keep the expression

    (ct)^2 – x^2 – y^2 – z^2

    invariant. Exchanging x and y (the spatial coordinates) keeps this expression invariant, but exchanging t and a spatial coordinate not. The Lorentz transformations mix time with the spatial coordinates, but time always keeps its distinct status.

    (This is because the “light cone” – which is important to define causality, at least in the context of SR – must stay invariant under transformations, The light cone basically is the geometric figure defined by the expression above, if I remember correctly).

    I think it’s physically dubious to treat the “time coordinate” as if it’s equivalent to a “spatial coordinate”. That’s one of the reason I’m suspicious of a block universe.

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  10. Calling the a universe static when time is only define with in it seems like an oxymoron. W/o time there is no static.

    Having said that you certainly think about the universe as laid out in time. Whether that has ‘ontological’ status or not you can argue with disagreeable (and Tegmark about),

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  11. Causality is conservation of energy, not sequence/time.

    Kicking a ball is a transfer of the energy from your foot and so that action ceases to exist, once the energy is transferred to the ball. So no block time, because the energy is conserved and doesn’t continue to exist as the sequence of events, only the one being manifest by the energy.

    Time, on the other hand, is sequence and there might be little effective transfer of energy from one event in a sequence, to the next. For instance, yesterday doesn’t directly cause today, because the energy isn’t directly transferred. Though the energy radiated into the atmosphere yesterday would be causing some weather patterns of today. The sun shining on a spinning planet causes this effect we experience as a sequence of days.

    While we experience time a a sequence of events and so think of it as the point of the present moving along this “fourth dimension,” the reality is that change is creating and dissolving those events, transferring the energy through various relationships, as the energy coming together to form one event will then radiate away in multiple directions, becoming input into myriad other events. Thus no single trail of temporal causality.

    It is just that our mental processes function narratively and so we have to make sense of these flashes of perception, even though the primary relationship between one and the next may be just in our mental processing. Thus we tend to equate time with motion in space, as it is our point of view in space, that is the primary organizing principle of the relationships between these events we experience.

    While the block time model is described in terms of a movie, or book, if you think how they are consumed, it is these events flowing past the observer, from future to past, as the observer is tantamount to the present. So the observer goes from past to future events, while the events themselves, go from future to past.

    We could take this out to any scale. For instance, our individual lives, as events, go from being in the future, when we are born, to being in the past, when we die. While the species, as the present manifestation, moves onto the next generation, shedding the old.

    So time is asymmetric due to the inherent inertia of energy. It is only that physics treats it as some underlaying dimension, of which the measure of duration supposedly exposes. So the duration of a cup falling from a table would be the same as it jumping back up on the table, under the assumption of time as that foundational dimension. Yet duration is entirely the state of the present, as these events occur and not external to it.

    If we think of time as an effect of action, i.e. frequency, then it is more like temperature, which is an effect of frequency and amplitude, than space.

    This would make thermodynamic circularity more elemental than temporal linearity. High pressure pushes, just like the causal transfer of energy, while low pressure directs where this energy goes.

    The past is where the energy comes from, while the future is where the energy goes.

    As for those billiard balls, what about gravity? Doesn’t that pull them into the center, where they break down and radiate the energy back out?

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  12. Massimo–

    Very good post, but at a bad time when I can’t devote much effort to run through all the comments. I’m interested because I’m under contract to write about determinism for an anthology. So to cut to the chase: do you think that the complementarity between energy and time is at all revealing to the basis of causality? I do tend to agree about Salmon’s account(s) of causality BTW.

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  13. One thing that has not been picked up on is ‘the collapse of the wave function’ which in standard QM interpretation is thought of as being ‘caused’ by a measurement. However, as it’s a non-local effect the time order is ill defined.

    So how does Philosophy deal with that? Physics doesn’t do well unless you go for ‘many worlds’ which dodges the issue but has its own problems. Or you can take the ‘shut up and calculate’ approach and just not think about it though the non-local effects have been established experimentally by Alain Aspect and others with Bell inequality violations.

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  14. I think you are making this too complicated. Prior to quantum physics, causes equalled forces. That’s it. Newton’s laws. If something changes its trajectory, it is because a force is applied. The force is the “cause” of change. All changes are due to forces. Or am I missing something? I don’t think you need to deal with conservation of energy, etc. Quantum mechanics changes all this, as you note, and some physicists don’t believe forces, as we think about them, exist, they are only there to get equations to work. (it’s all fields, etc). ( a book I found very helpful is Max Jammer’s “Concepts of Force”). (apologies for they typing. Hunt and peck on my ipad).

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  15. Arthur,

    ‘So how does Philosophy deal with that?”

    Isn’t the “map” the measurement?

    “Well Field Theory is just a theory, but then so is evolution by natural selection. FF is a way reality might be. We’ll likely never know the ‘ding am sich’.”

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  16. Jkubie, for physicists, maybe, but not for philosophers since Hume.

    Re QM, as I’ve said here before, I support the ensemble interpretation precisely because it is minimalist:
    Or, perhaps more accurately, some halfway point between it and objective-collapse theories.

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  17. If you mean by ensemble interpretation what I understand as an ensemble probability it doesn’t work. Bell would not be violated (I think).

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  18. Massimo, the Stanford bio on Sellars talks about how he dealt with various Humean ideas, including somewhat the problem of induction. But — and I know they were very much contemporaries — it doesn’t discuss at all how he dealt with Goodman’s new problem of induction, or if he even considered it something that needed dealing with. More info?

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  19. Yeah, I found the Wiki. I don’t buy it. It seems to be implicitly a hidden variables theory with out specifying the variables. I’d ask Dieter Zeh (Mr. decoherence), but I already pestered him about ‘many worlds’ and Born [a] rule this week and don’t want to wear out my welcome. Non local effects have been measured and are even being used in quantum encryption (if Bell isn’t violated your being spied on or at least could be).

    [a] It’s my opinion that ‘many worlds’ does not naturally yield the Born probability rule and, thus, has the same problem as ‘Copenhagen’ in that they have to assume it. Maybe worse as the simplest ‘world counting’ in many worlds contradicts the Born rule. If you just count ‘worlds’ ‘worlds’ in which my finger tunnels into the key board are no more uncommon than normal worlds (though any particular world is uncommon as there are so many of hem). Awful things would be happening all the time. Having a small amplitude/wave function norm does not mean that world does not exist. So far tunneling hasn’t happened to me or anyone I’ve heard of. I think we would notice.

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  20. Hi synred,

    Maybe worse as the simplest ‘world counting’ in many worlds contradicts the Born rule. If you just count ‘worlds’ ‘worlds’ in which my finger tunnels into the key board are no more uncommon than normal worlds (though any particular world is uncommon as there are so many of hem). Awful things would be happening all the time. Having a small amplitude/wave function norm does not mean that world does not exist. So far tunneling hasn’t happened to me or anyone I’ve heard of. I think we would notice.

    The same thought has occurred to me.

    I also have a problem with the idea that you can derive the Born Rule from epistemic probability, but that is a little more difficult to put.

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  21. I think ensemble interpretation is inconsistent with Field Theory. In field theory there are no particles in the usual sense. There are quantized excitations off the fields.
    That’s what we call particles. There is no wave-particle duality — all is waves/excitations. That wave goes through both slits. The waves tend to clump in ‘packets’ — this is what looks like particles to us.

    If you just turn the crank on the FT will clump and decoher and you get many worlds very naturally, but you don’t get the born rule.

    The there’s no mystery of why a ‘particle’ can be two places at once in FT. The excitation just happens to have a large amplitude at two well separated places. The mystery is how a spread out excitation comes to be in only once place. Decoherence can mae it clump in a few or many places, but how does only one surive and how does the energy in the field spread out all oer or in a couple of spots suddenly concentrate in one when a measurement occurs. ‘Many worlds’ explains this, but not the Born probability rule which is the key to the experimental success of QM. My opinon is that ‘many worlds’ advocates sweep this under the rug.

    Field theory explains the profound identy of ‘particles’, i.e., they are waves and even the Pauli exclusion rule (spin 1/2 Dirac field can only have one excitation in each state). Without Pauli we would not be here, but we don’t need weak anthropic princlple (WAP) to explain it. It isl almost a geometrical property of a spin 1/2 field. So while WAP might be needed to ‘explain’ some detailed constant choice, FT provides the basic structure of states and forces from first principle, just as albert would have liked.

    A lovely book and relatively easy to understand, e.g.,, that mattress analogy.

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  22. I have a little program which is just dots moving around the screen and bumping into each other. It would be a stretch even to call it a simple model of ideal gas but it is quite good for thinking about some of these issues.

    So if I have a box with faster moving particles and another box with slower moving particles and a gap between them then the average speed of the dots in the slower moving box will increase and the average speed of the dots in the faster moving dots will decrease until they are about the same.

    This is at least basic 2nd law behaviour without any randomness.

    There are arrangements from which the average speed of the faster moving box increases and the average speed of the slower moving box decreases. But if I had the one of these arrangements and then I changed just one dimension of just one vector the smallest amount that I could possibly change it, then I would just get a system which goes to equilibrium. That gives a feel for just how rare those arrangements are in which entropy decreases without any outside influence and why we never find them.

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  23. It’d be easy enough to write a little ideal gas simulation. Putting in just random directions would result in them spreading out through out the box even w/o any interactions or coming to thermal equilibrium. Of course if you make ’em all go the same direction you’ll get some pretty odd behavior.

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  24. But if you have interactions then you can start with them all in the same direction, apart from one and you get them spreading out. And you get an equilibrium when one box has faster moving particles and the other has slower moving particles and there is a hole in the barrier between them.

    You can write a little differential equation to describe the rate at which the box “cools”.

    Interestingly if you decide to try and get reverse 2LT behaviour by reversing time just as they are half way towards equilibrium it doesn’t work – just carries onto equilibrium without a blip. I suppose that is the error of using a “double” type value.

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  25. Hi jkubie,

    Newton’s laws. If something changes its trajectory, it is because a force is applied. The force is the “cause” of change. All changes are due to forces. Or am I missing something?

    Even in classical mechanics “forces” are not things, they are not ontological entities, they are more of an accounting device. Thus they don’t answer the basic question of causality in the sense of event/thing A causing event/thing B.

    While Newton’s gravity law prescribes a force between two masses, it doesn’t answer any questions along the lines of what actually is a “force”, what’s it made of, how does it work, how does one mass know about the existence of the other, and what, if anything, is traveling between the two masses?

    Quantum field theory does answer those questions, but then you get into the whole issue of causality within quantum mechanics.

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