• Andrew M
    664
    So what Carroll means is that fields are fundamental and particles (and everyday things generally) emerge from the interaction of those underlying fields.

    Or, as Wikipedia puts it, "QFT treats particles as excited states (also called quanta) of their underlying fields, which are—in a sense—more fundamental than the basic particles."
    — Andrew M

    ‘in a sense’ ;-)

    When it comes to this matter, that phrase carries a lot of weight.
    Wayfarer

    I would have thought that one sense was enough. How many senses are you requiring? ;-)

    Right, we are talking about the temporal ordering of two events, when the light reaches the front of the traincar, and when the light reaches the back. Special relativity allows for contradiction in the ordering of these events.Metaphysician Undercover

    No, the relative ordering of events necessarily follows from the invariant speed of light in different reference frames. Since the traincar is moving away from the train platform then the light emitted from the middle of the traincar, travelling at velocity c in the train-platform observer's reference frame, will take longer to reach the front of the traincar that is moving away from it than the back of the traincar that is moving toward it.

    I simply meant that without the selection postulate, it seems that RQM implies the splitting.

    Anyway, I agree with you. RQM seems simply silent on this point.
    boundless

    I think splitting might be implied only because Copenhagen and Consistent Histories don't specify any physical mechanism, whereas MWI does. But since some other unknown physical mechanism can't be ruled out at this point, then being silent seems a reasonable option (and treating interference as unactualized potential).
  • Pattern-chaser
    1.4k
    I consider it something discovered, not invented.noAxioms

    Can you "discover" something that is non-physical? Mathematics is not part of the scientific space-time universe, except trivially. How could you "discover" maths when there's nothing to come upon, and say "Oo look, that seems handy!" Maths is a collection of ideas; I think its emergence into our awareness has surely to be our invention.

    As for pi, as soon as you invent numbers, and all the stuff that goes with them, you notice pi as soon as you start considering circles. Bearing in mind that circles - not just things that are roughly circular - occur rarely if at all in the real world....
  • boundless
    154
    I think splitting might be implied only because Copenhagen and Consistent Histories don't specify any physical mechanism, whereas MWI does. But since some other unknown physical mechanism can't be ruled out at this point, then being silent seems a reasonable option (and treating interference as unactualized potential).Andrew M

    Well, yeah, this would explain the silence :smile:

    Another curiosity: what do you think about the problem of interfering branches in MWI (and maybe in RQM if no selection mechanism is accepted)? As 'I aM' (see here) noted it is true that due to the decoherence the interference term becomes very small. Yet, rigorously, it is not exactly 'zero'. Given the fact that decoherence occurs a lot of times, it seems possible that - sooner or later - interference will be observed. In other words, it seems that decoherence gives (multiple but) definite outcomes only 'for all practical purposes' (I remember to have read that decoherence is said to solve the measurement problem 'only for all practical purposes' but I am not sure that this the reason why it is said so...).
  • Metaphysician Undercover
    5.8k
    No, the relative ordering of events necessarily follows from the invariant speed of light in different reference frames.Andrew M

    Right, that's the point. The assumption that the speed of light is invariant (which is essential to special relativity), is what produces these contradictions.


    It's not a cop out. You can't just through phrases like "heat death" at me, and ask me a complex question concerning the event referred to, without providing me with some description as to what these terms refer to. I personally have no belief in "heat death", I think it's a misguided speculation. So your question is like asking an atheist a complex question about the nature of God. It's pointless.

    I assume that there will be no human beings in existence at the "heat death". So if you interpret "the capacity to do work" as "the capacity to do work for human beings" (which is how you seem to interpret it, but not how the definition is intended to be interpreted in physics), then there would be no such energy at the time of the heat death, because there would be no human beings.
  • Janus
    7.7k
    I nowhere qualified capacity to do work (that was your definition of potential energy that you claimed defined energy per se) with the adjective 'useful'. The heat death is the theoretical culmination of the process of increasing entropy (defined as the ongoing reduction of energy with the capacity to do (any not merely "useful') work).
  • Metaphysician Undercover
    5.8k

    You don't seem to understand, all energy is "the capacity to do work" whether it's potential energy or kinetic energy.

    So, as I said already, and as indicated in the quote I brought from your referenced article, at the so-called heat death there would still be energy, as the capacity to do work.
  • Metaphysician Undercover
    5.8k

    I told you, I don't believe in heat death. And I also told you that I think your description of it, as energy (which is by definition the capacity to do work), that is not available to do work, is contradictory. Why would I want to read up on this? It's like you're telling an atheist to go read some theology. What's the point?
  • Andrew M
    664
    Another curiosity: what do you think about the problem of interfering branches in MWI (and maybe in RQM if no selection mechanism is accepted)? As 'I aM' (see here) noted it is true that due to the decoherence the interference term becomes very small. Yet, rigorously, it is not exactly 'zero'. Given the fact that decoherence occurs a lot of times, it seems possible that - sooner or later - interference will be observed. In other words, it seems that decoherence gives (multiple but) definite outcomes only 'for all practical purposes' (I remember to have read that decoherence is said to solve the measurement problem 'only for all practical purposes' but I am not sure that this the reason why it is said so...).boundless

    David Wallace has a good discussion of this in his paper Decoherence and Ontology, or: How I Learned To Stop Worrying And Love FAPP.

    As he puts it, decoherence gives us quasi-classical worlds (branches) but not actual classical worlds. Which means that decoherence can be treated as irreversible and the worlds as classical for all practical purposes. Nonetheless interference between branches continues to happen in accordance with quantum mechanics.

    So the Wigner's friend thought experiment is a good example of this. For the friend, decoherence has occurred (i.e., the friend, measurement and lab have become entangled), but not for Wigner, who continues to detect interference and can, at least in principle, reverse the friend's measurement.

    Whereas in the actual experiment of the OP, decoherence hasn't occurred since the photons involved haven't become entangled with their surrounding environment. Sean Carroll discusses this in his DailyNous essay on the experiment.

    Right, that's the point. The assumption that the speed of light is invariant (which is essential to special relativity), is what produces these contradictions.Metaphysician Undercover

    OK. So do you claim that the light emitted from the middle of the moving traincar towards the front is travelling at c + v (where v is the velocity of the traincar) from the train-platform observer's reference frame?
  • Metaphysician Undercover
    5.8k
    OK. So do you claim that the light emitted from the middle of the moving traincar towards the front is travelling at c + v (where v is the velocity of the traincar) from the train-platform observer's reference frame?Andrew M

    I don't think that the movement of objects can be satisfactorily related to the movement of light, in the manner suggested by special relativity, because the relationship between the objects and the medium within which the light waves exist, has not been properly established.
  • Andrew M
    664
    OK. So do you claim that the light emitted from the middle of the moving traincar towards the front is travelling at c + v (where v is the velocity of the traincar) from the train-platform observer's reference frame?
    — Andrew M

    I don't think that the movement of objects can be satisfactorily related to the movement of light, in the manner suggested by special relativity, because the relationship between the objects and the medium within which the light waves exist, has not been properly established.
    Metaphysician Undercover

    So apart from rejecting Lorentz invariance (in favor of Galilean invariance?), I'm not clear on what your model is. When the light is emitted from the middle of the traincar, what do you think the observers on the traincar and train platform see?
  • Metaphysician Undercover
    5.8k

    I don't understand the question. They see the thing which is emitting the light, as emitting light.
  • noAxioms
    745
    Ok, I agree. But my point was another. If you say that 'your' present exist (the 't=0' 3D hypersurface), then the Andromeda Paradox is unavoidable.
    — boundless

    This hypersurface exists. So does this different hypersurface. That's just two different things, not a paradox.
    — noAxioms

    Well, I think I see where you are getting at but I am not sure you can really avoid the paradox if you say that all events in the hyper surface are in a definite state. I am not saying you are wrong, I just do not know.
    boundless
    The Andromeda Paradox is about the ambiguity of what time it is elsewhere, not about the state being definite. The former is a frame dependent thing and the latter is a statement of superposition of something unmeasured. I think you meant the former but your wording suggested the latter.

    Totally agree. Two observers at the same place but different frames might disagree about what is going on at Andromeda, but they'll agree entirely about what has been measured. The light cone from that location is a frame independent thing.
    — noAxioms

    Yes! In Relativity the ordering of events in every light cone is an invariant (unless one accepts tachyons or any FTL influence).
    I didn't say that. I said the set of events in a given light cone is frame independent. The ordering of those events is still quite frame dependent.

    Interesting corollary for a presentist, who by definition cannot observe any existing thing. In 8 minutes, the thing I observe will not be the present state of the sun. It will be an observation of something nonexistent.
    — noAxioms

    Yep! Presentism is somewhat problematic in Relativity. I would say that 'global presentism' is simply incompatible with relativity of simultaneity. Maybe a form of 'local presentism' can be saved but it is surely counter-intuitive (I personally lean towards some form of presentism and I admit that I am troubled by this).
    I have done an advocatus diaboli thread defending the compatibility of relativity and presentism, so I maintain that they're not incompatible. SR says that the preferred frame cannot be determined given the special case after which it is named. But inability to detect such a frame does not mean that there isn't a special one. Presentism doesn't even require it to be a inertial frame, and no presentist that knows their physics seems to assert that it corresponds to such a frame. The foliation is always bent, which has the interesting paradoxical implication that no two stationary observers are simultaneous in each other's inertial frames. I find that hilarious, but not paradoxical.
  • Andrew M
    664
    I don't understand the question. They see the thing which is emitting the light, as emitting light.Metaphysician Undercover

    Do you think light reaches the front and the back of the traincars simultaneously for both observers? If so, then what is the speed of the light? Is it c for the traincar observer, but c + v for the train-platform observer? Or is it c for both of them? Or something else?
  • Metaphysician Undercover
    5.8k

    As I said, I don't think we have the principles required to precisely measure the various motions of objects in relation to the motions of light because we have not yet determined the relationship between objects and the medium in which the light waves exist.
  • noAxioms
    745
    I simply meant that without the selection postulate, it seems that RQM implies the splitting.

    Anyway, I agree with you. RQM seems simply silent on this point.
    — boundless

    Maybe it's embarrassed. :yikes:
    — Wayfarer

    Well, possibly! :razz:
    boundless
    This is why I resist describing RQM under presentist terms. If time is external to the structure that is the universe, then such selection is an objective act relative to this realm under which time exists, and it isn't really RQM anymore if such an objective action takes place.

    With time being part of the structure, no event/state (something to which a relation can be made) 'flows' to a different event, necessitating such a selection. Thus there is no selection postulate.
    This isn't an embarrassment, just an implication of a relative interpretation.
  • Janus
    7.7k
    The argument was over the scientific definition of energy, which cannot be understood separately from the Second Law of Thermodynamics, but if now you just want to insist on your own definitions, then further discussion will be pointless.
  • noAxioms
    745
    Can you "discover" something that is non-physical?Pattern-chaser
    Obviously yes, your topic being a prime example.
    Mathematics is not part of the scientific space-time universe, except trivially.
    I choose to interpret it otherwise.

    How could you "discover" maths when there's nothing to come upon, and say "Oo look, that seems handy!"
    Yet that is exactly how mathematical progress was always made. Nobody found it under a rock or through a telescope. Not even talking about mathematical models of the universe here. I'm just talking about pure mathematics like Calculus, imaginary numbers, 14 dimensional space, and octonions and such. These are not 'come upon', yet are discovered.

    As for pi, as soon as you invent numbers, and all the stuff that goes with them, you notice pi as soon as you start considering circles. Bearing in mind that circles - not just things that are roughly circular - occur rarely if at all in the real world....
    Exactly. We notice pi despite the complete absence of any actual circles in nature to measure. Figuring out pi to a lot of precision doesn't involve hunting down an ever closer physical approximation to a circle.
  • Metaphysician Undercover
    5.8k
    The argument was over the scientific definition of energy, which cannot be understood separately from the Second Law of Thermodynamics, but if now you just want to insist on your own definitions, then further discussion will be pointless.Janus

    My definition is the same as the one on your referred site. The laws of thermodynamics came into existence following the defining of energy. So you're wrong, energy was understood prior to the second law, and therefore separately from the second law. You really just blabber on, demonstrating that you have absolutely no understanding of this subject
  • Metaphysician Undercover
    5.8k
    Figuring out pi to a lot of precision doesn't involve hunting down an ever closer physical approximation to a circle.noAxioms

    How does one approach the figuring out of pi?
  • Janus
    7.7k
    Of course I am referring to current scientific understanding of energy. Before the idea of entropy obviously energy was understood "separately form the second law"; unfortunately that doesn't support your incoherent position, since it is irrelevant.

    What you are saying is like saying that oxidation is irrelevant to understanding fire, since fire was originally understood separately from oxidation. The annoying blabbering sound is emanating from you, not from me.
  • Andrew M
    664
    As I said, I don't think we have the principles required to precisely measure the various motions of objects in relation to the motions of light because we have not yet determined the relationship between objects and the medium in which the light waves exist.Metaphysician Undercover

    Then you don't have a model. Whereas special relativity is a self-consistent model that makes predictions that have been experimentally confirmed in numerous ways. See https://en.wikipedia.org/wiki/Tests_of_special_relativity
  • Wayfarer
    7.7k
    So what Carroll means is that fields are fundamental and particles (and everyday things generally) emerge from the interaction of those underlying fields.

    Or, as Wikipedia puts it, "QFT treats particles as excited states (also called quanta) of their underlying fields, which are—in a sense—more fundamental than the basic particles."
    — Andrew M

    ‘in a sense’ ;-)

    When it comes to this matter, that phrase carries a lot of weight.
    — Wayfarer

    I would have thought that one sense was enough. How many senses are you requiring? ;-)
    Andrew M

    Well, consider the context. The idea of the atom was that it was a discrete indivisible point-particle - posited as the ultimate constituent of matter. I mean, ask the person in the street what the Universe is made of, and s/he will probably say 'atoms'. But as we have been discussing, it turns out the nature of the atom is actually rather ambiguous - particles that 'interfere with themselves' or that can appear as waves rather than particles at all. So it seems to me that substituting 'fields' for particles as a kind of ontological basis is a bit of a pea and thimble trick or sleight-of-hand. Which is not to question the efficacy of field theory as it obviously works. But we ought to remember that the same guy who won a Nobel for work in that very field is also famous for saying that 'ultimately nobody understands quantum mechanics.'
  • Janus
    7.7k
    Quantum physics is just counterintuitive; which shouldn't be such a surprise. General relativity is also counterintuitive, as is the fact (if it is a fact) that the Universe is expanding at an ever greater rate. Why, since we live in a middling world, in Middle Earth, so to speak, should we be surprised when study of the very large and the very small present us with counter-intuitive results?
  • Metaphysician Undercover
    5.8k
    Of course I am referring to current scientific understanding of energy. Before the idea of entropy obviously energy was understood "separately form the second law"; unfortunately that doesn't support your incoherent position, since it is irrelevant.Janus

    It seems like you did not read the quote I posted from your referred site:

    "Recall that the simple definition of energy is the ability to do work. Entropy is a measure of how much energy is not available to do work. Although all forms of energy are interconvertible, and all can be used to do work, it is not always possible, even in principle, to convert the entire available energy into work. That unavailable energy is of interest in thermodynamics, because the field of thermodynamics arose from efforts to convert heat to work."

    That is from the site you referenced on "heat death". Notice, "the ability to do work" is the definition of energy, even today. Also, at the proposed "heat death" there is still energy, therefore the ability to do work. Speculators have simply taken some principles from thermodynamics, and have concluded in an extremely dubious way, that this capacity to do work (energy) becomes unavailable to do work through entropy, until the "proposed heat death" when all energy is unavailable. It is extremely dubious because that conclusion requires some completely unsubstantiated, and improbable premises, concerning the nature of time, human capacities to create systems, and the universe.

    Then you don't have a model. Whereas special relativity is a self-consistent model that makes predictions that have been experimentally confirmed in numerous ways. SeeAndrew M

    Right, we went through this already, in this very thread. The Michelson-Morley experiments failed to determine the relationship between the wave medium and physical objects, and special relativity gave what appeared to be a simple and satisfactory way around this problem. However, the problems of QM, and wave-particle duality ought to indicate to you that special relativity really is not satisfactory. Without understanding the relationship between objects and the wave medium, we cannot establish the relationship between the wave and the particle in wave-particle duality.

    Notice, that to produce the conclusion that there is no wave medium, from the Michelson-Morley experiment, requires the premise that the medium is independent from physical objects. But the conclusions from QM indicate that the particles (physical objects) are a feature of the wave function. So QM actually disproves the premise required to say that the Michelson-Morley experiment demonstrates the non-existence of the medium. Now we need to go back and determine the relationship between the particle (object) and the wave medium, to understand wave-particle duality. But this will never happen if physicists adhere to special relativity and deny that there is a medium.
  • i aM
    23

    You're mixing up "medium" with the QM wavefunction. That's a linguistic mistake, which is understandable because the word "wave" is in there.

    You also confuse the physical property of "energy", which can really only be defined in mathematical terms in specific contexts with what you say is its linguistic definition, "the ability to do work".

    But even linguistically, that is still not quite right. Here is the first sentence from the Wikipedia article on "energy":

    "In physics, energy is the quantitative property that must be transferred to an object in order to perform work on, or to heat, the object."

    So if you get to a state like "heat death", energy can no longer be transferred. "the quantitative property that must be transferred in order to perform work" is still there, but no such transfer is possible and there is no longer any "ability to do work".
  • Janus
    7.7k
    "Recall that the simple definition of energy is the ability to do work. Entropy is a measure of how much energy is not available to do work. Although all forms of energy are interconvertible, and all can be used to do work, it is not always possible, even in principle, to convert the entire available energy into work. That unavailable energy is of interest in thermodynamics, because the field of thermodynamics arose from efforts to convert heat to work."

    Energy is the ability to do work. If at maximum entropy there is no energy available to do work, then effectively there is no energy on that definition.

    Firstly the "ability to do work" is only known about at all insofar as the the activity of energy; that is work being done, is constantly observed.

    Secondly, if no energy is any longer available to do work, then there is only the "in principle" inherent potential energy "locked up" in "dead" matter itself, and no energetic activity (heat exchange) at all remaining.

    Also, whether or not the "heat death" is a realistic scenario is irrelevant because we have been discussing the current scientific understanding of energy and its implications.
  • Metaphysician Undercover
    5.8k
    You're mixing up "medium" with the QM wavefunction. That's a linguistic mistake, which is understandable because the word "wave" is in there.

    You also confuse the physical property of "energy", which can really only be defined in mathematical terms in specific contexts with what you say is its linguistic definition, "the ability to do work".
    i aM


    It seems like you have an aversion to discussing things "linguistically".

    But even linguistically, that is still not quite right. Here is the first sentence from the Wikipedia article on "energy":

    "In physics, energy is the quantitative property that must be transferred to an object in order to perform work on, or to heat, the object."
    i aM

    That's interesting, because Wikipedia doesn't even have an entry for "quantitative property". So by defining "energy" as a quantitative property, and not defining "quantitative property", the author of this quote has led me on a wild goose chase. Did you happen to read the footnote to that quote you produced? Some author of self-help books for high school students, Robert L Lehman, arguing that energy is not the capacity to do work. So much for your appeal to authority.

    Sorry, you can count me out of your discussion because I discuss things linguistically.
  • i aM
    23

    I tried to help you. You think you know alot more than you actually do know.
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