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Free Will & Absolute Motion

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  • Registered Users Posts: 10,558 ✭✭✭✭Fourier


    roosh wrote: »
    Not absolute velocity then?
    "Motion" is a vague pre-physical term.

    The models have absolute velocity. From now on I'd ask you to only use velocity and acceleration to clearly distinguish which you mean when you say "motion".
    Let's say that you and I are standing face to face, at rest relative to each other. What would be required for relative motion to occur between us? [inert joke here]. It would take for one of us to move. As soon as one of us moves, we are both moving relative to each other. But one of us has to move
    Has to accelerate. Try phrasing all of this using only physical terms not everyday ones.

    One of us has to accelerate. And since acceleration is an absolute notion every frame would agree that there is some change in our relative velocities.

    However this is not absolute velocity, but absolute acceleration.
    I'm familiar with the idea that our current theories say there is no such thing as absolute motion but my reasoning makes me inclined to believe that there must be.
    My point is that all your ideas have the same format:
    (a) Never learn the actual theories
    (b) Never use precise language, but a vague mix of everyday and philosophical language
    (c) Try to conclude old intuitive notions that have not been part of physics for over 400 years are still true


  • Registered Users Posts: 2,553 ✭✭✭roosh


    Fourier wrote: »
    "Motion" is a vague pre-physical term.
    The idea that you or I can move our hands or our bodies doesn't seem that vague or pre-physical. This is the idea that the hand is in "motion". The question of absolute motion then would be, is my hand really moving?
    Fourier wrote: »
    The models have absolute velocity. From now on I'd ask you to only use velocity and acceleration to clearly distinguish which you mean when you say "motion".
    I'm not necessarily referring to either velocity or acceleration. I'm trying to get at something even more fundamental. The idea of movement that isn't relative to something. It's a question of whether or not things are actually moving.

    Fourier wrote: »
    Has to accelerate. Try phrasing all of this using only physical terms not everyday ones.
    I know this isn't strictly the case, but rather than write the long form for the point, covering both sides, I'll make an affirmative statement that takes one side of it.

    In order to accelerate, a body has to actually move, without actually moving there would be no accelaration. Or we might say that a body which undergoes acceleration must actually move.

    Fourier wrote: »
    One of us has to accelerate. And since acceleration is an absolute notion every frame would agree that there is some change in our relative velocities.

    However this is not absolute velocity, but absolute acceleration.
    It is the notion of absolute velocity which I'm suggesting is a contradiction in terms because it seeks to define absolute velocity as velocity relative to something - that would be relative velocity.

    Absolute motion is a question of which of the two things moving relative to one another is actually moving. If one of the bodies must undergo acceleration, then would we not deduce that the body that undergoes acceleration absolutely moves*?

    *I expect the equivalence principle is relevant here.

    Fourier wrote: »
    My point is that all your ideas have the same format:
    (a) Never learn the actual theories
    (b) Never use precise language, but a vague mix of everyday and philosophical language
    (c) Try to conclude old intuitive notions that have not been part of physics for over 400 years are still true
    I know that the theories say that absolute motion does not exist and why. It's just that the reasoning that's usually given doesn't seem to address certain very basic facts.

    When I move my hand, that is neither vague nor pre-physical. It's a very clear, obvious and basic observation of the physical world.

    The question "is my hand actually moving" is another pretty basic question which makes sense to all but those who seem to have rejected the idea based on [apparent] philosophical or scientific reasoning.

    The reasoning appears to be, we cannot determine which body is actually moving, therefore absolute motion doesn't exist. That is a non-sequitir, however because we can deduce that where two bodies are in relative motion one of the bodies must be moving, in an absolute sense.


  • Registered Users Posts: 10,558 ✭✭✭✭Fourier


    The idea that you or I can move our hands or our bodies doesn't seem that vague or pre-physical.
    Yes but physics divides motion into several different aspects and makes distinct claims about each aspect. Thus in just saying "motion" you are eliding all these differences and getting confused as to what physics is specifically saying.

    This is what's leading you down this rabbit hole as you seem to believe physics says there is no such thing as absolute motion, where as current physical theories say no such thing. They say there is no absolute velocity.

    Thus if we take the motion of some body described by some function x(t) then knowledge of each of the derivatives of this function determine the function. Each derivative has been given a name:

    First: Velocity
    Second: Acceleration
    Third: Jerk
    Fourth: Jounce
    etc

    Physics makes different claims about each.

    It says velocity has no absolute meaning. The rest do.
    It says fundamental Forces only directly couple to acceleration
    Recoil effects are proportional to Jerk
    Physical stress limits are related to Jerk and Jounce...etc

    Because we are dealing with a precise science, one has to deal with precise terms. You think you are being more "fundamental", you are actually just being more vague. No theory says motion in your vague sense is relative. Every derivative above velocity has an absolute sense. Relativity concerns velocity alone.

    Thus this entire discussion is only a result of you not knowing physical terminology.
    It is the notion of absolute velocity which I'm suggesting is a contradiction in terms because it seeks to define absolute velocity as velocity relative to something - that would be relative velocity
    For the fourth time now. It is not a contradiction in terms because you can construct models in which absolute velocity exists and is well defined. I have given you their name. They are bundle models of Aristotelian physics. Please stop constantly repeating this, I have dealt with it four times now

    The point of physical models is that we have ruled out this model experimentally. Absolute velocity is not a part of our world. This was one of the advances of Newtonian-Galilean physics over previous ideas.

    Newtonian-Galilean physics said velocity was relative but space and time were absolutely distinguished and simultaneity was absolute. This is where Special Relativity disagreed.

    Thus modern theories say velocity and simultaneity are relative. No theory however has said that motion in general is not absolute.
    It's just that the reasoning that's usually given doesn't seem to address certain very basic facts
    No it's that you never take the time to actually learn the theories or the relevant terminology and thus have a massively incorrect notion of what is being said. I've counted at least eight physicists you've referenced in discussions I've seen where you've fundamentally misunderstood what they were saying since you don't the meaning of the precise words they use.


  • Registered Users Posts: 2,553 ✭✭✭roosh


    Fourier wrote: »
    Yes but physics divides motion into several different aspects and makes distinct claims about each aspect. Thus in just saying "motion" you are eliding all these differences and getting confused as to what physics is specifically saying.

    This is what's leading you down this rabbit hole as you seem to believe physics says there is no such thing as absolute motion, where as current physical theories say no such thing. They say there is no absolute velocity.
    OK, so this is contrary to discussions I have had previously on here, where it was stated that absolute motion, specifically, is ruled out.

    I have no issues with the idea of absolute velocity being ruled out.

    Fourier wrote: »
    Thus if we take the motion of some body described by some function x(t) then knowledge of each of the derivatives of this function determine the function. Each derivative has been given a name:

    First: Velocity
    Second: Acceleration
    Third: Jerk
    Fourth: Jounce
    etc

    Physics makes different claims about each.


    It says velocity has no absolute meaning. The rest do.
    It says fundamental Forces only directly couple to acceleration
    Recoil effects are proportional to Jerk
    Physical stress limits are related to Jerk and Jounce...etc
    Thanks Fourier, I am familiar with the first and second derivatives but not the subsequent ones.


    Fourier wrote: »
    Because we are dealing with a precise science, one has to deal with precise terms. You think you are being more "fundamental", you are actually just being more vague. No theory says motion in your vague sense is relative. Every derivative above velocity has an absolute sense. Relativity concerns velocity alone.
    I see. Thank you. This does appear to be contrary to what I've encountered in other discussion where I have made the same distinction between absolute velocity and absolute motion.


    Fourier wrote: »
    For the fourth time now. It is not a contradiction in terms because you can construct models in which absolute velocity exists and is well defined. I have given you their name. They are bundle models of Aristotelian physics. Please stop constantly repeating this, I have dealt with it four times now
    Apologies, I must be misinterpreting your previous statements. Here are the comments in order:
    roosh wrote: »
    The contradiction in terms is in the definition of something absolute as being relative to something. To define absolute velocity as velocity relative to an absolute reference frame is to define absolute velocity as relative velocity.
    Fourier wrote: »
    That's not what these models do though nor is it what I am discussing. They just have absolute motion.
    roosh wrote: »
    Not absolute velocity then?
    Fourier wrote: »
    "Motion" is a vague pre-physical term.

    The models have absolute velocity.

    These models have absolute velocity but the velocity is not measured relative to something, is that correct?

    To clarify the point I was making, defining absolute velocity as velocity relative to an absolute reference frame would be a contradiction in terms because it defines absolute velocity as relative velocity.

    If there are theories that define absolute velocity in another way i.e. not relative to something else, then this would not be a contradiction in terms.


    Fourier wrote: »
    The point of physical models is that we have ruled out this model experimentally. Absolute velocity is not a part of our world. This was one of the advances of Newtonian-Galilean physics over previous ideas.
    There is some confusion here because I never stated that it was.
    Fourier wrote: »
    Newtonian-Galilean physics said velocity was relative but space and time were absolutely distinguished and simultaneity was absolute. This is where Relativity disagreed.

    Thus modern theories say velocity and simultaneity are relative. No theory however has said that motion in general is not absolute.
    In presentist interpretations of relativity, wouldn't simultaneity be absolute; with the "relativity of simultaneity" being akin to local time in the Lorentzian interpretation?

    Fourier wrote: »
    No it's that you never take the time to actually learn the theories or the relevant terminology and thus have a massively incorrect notion of what is being said. I've counted at least eight physicists you've referenced in discussions I've seen where you've fundamentally misunderstood what they were saying since you don't the meaning of the precise words they use.
    I appreciate your correcting me along the way. As with here, where I was under the misapprehension that it was absolute motion that was ruled out of physical theories when in fact it was absolute velocity.


    I'm not sure why my example caused such an issue though, if we can say that [at least] one of the trains is in absolute motion.


  • Registered Users Posts: 10,558 ✭✭✭✭Fourier


    OK, so this is contrary to discussions I have had previously on here
    If this refers to discussions with Morbert I think he took your "motion" to mean velocity. He was just trying to disambiguate the term and made a guess.
    If there are theories that define absolute velocity in another way i.e. not relative to something else, then this would not be a contradiction in terms.
    They have absolute velocity not relative to anything.
    There is some confusion here because I never stated that it was.
    I'm just explaining Newtonian-Galilean physics to make it clear how it advanced over previous notions so you can see the progression of ideas. It's not meant to be a counterpoint to anything you said.
    In presentist interpretations of relativity, wouldn't simultaneity be absolute
    No absolutely not.
    I'm not sure why my example caused such an issue though
    The issue was one of confusion since you weren't being precise.

    I said a few times the acceleration was absolute but the velocity wasn't. From your posts it was hard to tell if by motion you meant velocity or something more general. You then introduced further confusion (reference frames are artefacts, absolute velocity is a contradiction in terms).

    My taking of "motion" to mean velocity is exactly what happened with Morbert, since from our perspective if you meant motion in general it wouldn't even be worth pointing out. Since you were presenting it as contrary to usual physics the natural assumption is that by motion mean you mean velocity. Confusing two people because you try to discuss subjects without ever bothering to learn them and their terminology and then describing that as them confusingly "having an issue" is lazy.

    "I will constantly argue against scientific theories and never learn them. Please recognise my own imprecisions as quickly as possible while educating me for free. Any misunderstandings resulting from my odd stance are issues on your end"


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  • Registered Users Posts: 2,553 ✭✭✭roosh


    Fourier wrote: »
    If this refers to discussions with Morbert I think he took your "motion" to mean velocity. He was just trying to disambiguate the term and made a guess.
    I'm pretty sure that isn't the case. He was arguing against the idea that one of two bodies actually moves, with the term actually being the point of contention.
    Fourier wrote: »
    They have absolute velocity not relative to anything.
    I see, thank you.

    Fourier wrote: »
    I'm just explaining Newtonian-Galilean physics to make it clear how it advanced over previous notions so you can see the progression of ideas. It's not meant to be a counterpoint to anything you said.
    Thanks. I'm familiar with that from my discussions with Morbert. It seems as though the confusion is arising from the idea of absolute velocity. I outlined the interpretation of absolute velocity I was referring to.

    Fourier wrote: »
    No absolutely not.
    This is my understanding, based on discussions with Morbert.

    If there is a universal now, which is true for all observers, then, as a matter of necessity simultaneity must be absolute.

    The relativity of simultaneity contradicts this idea, saying that there is no universal now for all observers.

    A consequence of RoS is that the past and future of every observer is as equally real as their present - if only their present were real, then we would have absolute simultaneity, as above.


    The following is from more recent discussions:

    If an observer's future is as real as their present it means that their choices are pre-determined/deterministic. This would contradict the principle of free will.


    Fourier wrote: »
    The issue was one of confusion since you weren't being precise.
    I think a contributory factor was that you were assuming I meant something other than what I had said.

    Fourier wrote: »
    I said a few times the acceleration was absolute but the velocity wasn't. From your posts it was hard to tell if by motion you meant velocity or something more general. You then introduced further confusion (reference frames are artefacts, absolute velocity is a contradiction in terms).
    And I clarified that defining absolute velocity relative to an absolute reference frame is a contradiction in terms because it defines relative velocity as absolute velocity.

    The question of reference frames as mathematical artefacts stems from the statement that there is always a frame in which Train A is at rest. This begged the question, relative to what is Train A at rest, given that it was specified from the beginning that we were talking about an otherwise empty universe, save for the two trains.

    If the answer to the question, relative to what is train A at rest, is "its reference frame", this implies, in an otherwise empty universe, that the train is at rest relative to a set of mathematical coodrindates.

    If by "reference frame" we mean introducing measuring rods and synchronised clocks which are always at rest relative to the train, then we are simply modifying the problem. The scenario is no longer that of two trains moving relative to each other but two trains and their associated rods and clocks moving relative to each other.

    This means that the statement about the train being at rest in a given frame doesn't make the point that you think it is making - or perhaps that addresses the question - bcos the frame can be treated as an extension of the train - given that they are always at rest relative to each other.

    Fourier wrote: »
    My taking of "motion" to mean velocity is exactly what happened with Morbert, since from our perspective if you meant motion in general it wouldn't even be worth pointing out. Since you were presenting it as contrary to usual physics the natural assumption is that by motion mean you mean velocity. Confusing two people because you try to discuss subjects without ever bothering to learn them and their terminology and then describing that as them confusingly "having an issue" is lazy.
    That wasn't the nature of my discussion with Morbert.

    Fourier wrote: »
    "I will constantly argue against scientific theories and never learn them. Please recognise my own imprecisions as quickly as possible while educating me for free. Any misunderstandings resulting from my odd stance are issues on your end"
    The question at hand can be illustrated using a very simple and easy to grasp example.


    Two students sitting in a classroom. The teacher has to leave the room and tells them not to move. Whoever moves will be punished. The teacher leaves and returns and notices that there is a bigger distance between the two students than when he left.

    The teacher deduces that there are only two possible scenarios:
    1) One of the students moved.
    2) Both of the students moved.


    Note, we're not talking about acceleration or velocity here, we're talking about something more basic or fundamental. Acceleration and velocity are not necessary in this question - they may indeed have occurred, but they are not necessary for the teachers conclusion.

    To say that there is always a frame in which each student was at rest makes no difference. We conclude that [at least] one of the students actually moved [in an absolute sense].


    In my discussions with Morbert, he would have argued that we cannot conclude that one of the students actually moved for the same reason you have given previously - because there is a frame in which each student is always at rest.


  • Registered Users Posts: 3,457 ✭✭✭Morbert


    [edit] - posted before seeing the other pages of this thread. Deleting


  • Registered Users Posts: 3,457 ✭✭✭Morbert


    roosh wrote: »
    I'm pretty sure that isn't the case. He was arguing against the idea that one of two bodies actually moves, with the term actually being the point of contention.

    I don't remember all the details of the convo but
    Fourier wrote: »
    Just because they are in relative motion with respect to each other does not mean one is absolutely moving. You've never described the experimental protocol that shows one is absolutely moving. What quantity can I measure to conclude this?

    I would echo this. We can reject absolute velocity as a physical property without also rejecting assertions about relative velocity. I can't remember if I made distinction between actual and absolute in the context of a previous convo but if I did feel free to show it to me.
    If the answer to the question, relative to what is train A at rest, is "its reference frame", this implies, in an otherwise empty universe, that the train is at rest relative to a set of mathematical coodrindates.

    Yes. There is no sense of the train being at absolute rest.


  • Registered Users Posts: 2,553 ✭✭✭roosh


    Morbert wrote: »
    I don't remember all the details of the convo but
    Just having a quick read back over this thread and I think I've misremembered some details myself - not all, but some.

    Just in case I am misremembering details of our other discussions - although this one I'm pretty sure I'm not - am I right in saying that the Relativity of Simultaneity is contradictory to presentism; and as such, implies that past and future exist ala the Block Universe?

    Morbert wrote: »
    I would echo this. We can reject absolute velocity as a physical property without also rejecting assertions about relative velocity. I can't remember if I made distinction between actual and absolute in the context of a previous convo but if I did feel free to show it to me.
    I was misremembering that you did initially emphasise the point about absolute velocity. I'm not sure if we talked past each other somewhat on that because I was trying to emphasise that I wasn't talking about absolute velocity. We did move on from that, somewhat, to the idea of "intrinsic" motion.
    Morbert wrote:
    This does not establish any form of "intrinsic" motion independent of reference frames.
    Post

    In general this was the discussion about which of two relatively moving bodies is actually moving. Or in the example above, with the Garda and the criminal, who is it that does the moving.

    Morbert wrote: »
    Yes. There is no sense of the train being at absolute rest.
    This was an issue that arose in the previous discussion also. We can forget about the idea of absolute rest altogether bcos that isn't my contention.

    To my mind, there is an issue with saying "there is a frame in which train A is always at rest". The reason being, we can specify from the outset that the Universe is empty other than for the two trains.

    This then begs the question, relative to what is train A at rest? It isn't train B, since train A and B are moving relative to each other.

    If the answer to this is "the co-ordinate reference frame", the issue is that co-ordinate reference frames are mathematical artefacts relative to which bodies do not move, in the [physical] Universe.

    We can of course theoretically construct the physical analog of the co-ordinate frame, using synchronised clocks and measuring rods but:
    a) we have specified at the outset that the Universe is empty other than for the two trains.

    b) if we do "construct" the physical analog of the co-ordinate reference frame, then we have only slightly changed the scenario. The physical analog of the co-ordinate reference frame can be viewed as an extension of the train - since they are always at rest relative to each other. We are still left with the question of relative to what is train A at rest (given the rods and clocks can be affixed to the train without an consequence).

    Alternatively, our scenario simply becomes one where train A and its clocks and rods are moving relative to train B and its clocks and rods.


  • Registered Users Posts: 3,457 ✭✭✭Morbert


    roosh wrote: »
    If the answer to this is "the co-ordinate reference frame", the issue is that co-ordinate reference frames are mathematical artefacts relative to which bodies do not move, in the [physical] Universe.

    This wouldn't be an issue. Relative velocity can be understood as a choice of description. It might be better in this context to call it a co-ordinate velocity. So e.g. "The co-ordinate velocity of train A is 0" can be understood as "Upon application of this co-ordinate system, the quantity dx/dt of the train is 0"


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  • Registered Users Posts: 2,553 ✭✭✭roosh


    Morbert wrote: »
    This wouldn't be an issue. Relative velocity can be understood as a choice of description. It might be better in this context to call it a co-ordinate velocity. So e.g. "The co-ordinate velocity of train A is 0" can be understood as "Upon application of this co-ordinate system, the quantity dx/dt of the train is 0"
    This would remain true for train A if it were in a state of absolute motion*.

    *Note, I'm not talking about absolute velocity here.


    Is your position still the same with regard to presentism and relativity? Am I remembering the following conclusion correctly?
    roosh wrote:
    the Relativity of Simultaneity is contradictory to presentism; and as such, implies that past and future exist ala the Block Universe?


  • Registered Users Posts: 3,457 ✭✭✭Morbert


    roosh wrote: »
    This would remain true for train A if it were in a state of absolute motion*.

    I was specifically addressing the issue "co-ordinate reference frames are mathematical artefacts relative to which bodies do not move, in the [physical] Universe." re/ describing train A as at rest. We can apply a co-ordinate frame and describe train A as at rest without needing to worry about conjuring up some ancillary system that justifies this description.

    Re/ Presentism etc. It has been a while since I have thought about the issues. I do not think relativity is a priori incompatible with presentism as a metaphysical property of the world, but I have also seen little motivation/success re/ introducing it to physical models.
    *Note, I'm not talking about absolute velocity here.

    I don't know what you mean by this. I also don't know what you mean when you describe the co-ordinate system as an artefact.


  • Registered Users Posts: 2,553 ✭✭✭roosh


    Morbert wrote: »
    I was specifically addressing the issue "co-ordinate reference frames are mathematical artefacts relative to which bodies do not move, in the [physical] Universe." re/ describing train A as at rest. We can apply a co-ordinate frame and describe train A as at rest without needing to worry about conjuring up some ancillary system that justifies this description.
    Thanks Morbert, I understand that. I'm saying we could do this also if train A were in a state of absolute motion.

    In the example of our empty universe with the two trains, at rest relative to each other. When the trains start moving relative to each other, the observer in the train has that split second question of, is it my train that is moving, or is it the other train? They obviously know that their train is moving relative to the other train, but the question points to a more fundamental, absolute aspect of motion.

    Morbert wrote: »
    Re/ Presentism etc. It has been a while since I have thought about the issues. I do not think relativity is a priori incompatible with presentism as a metaphysical property of the world, but I have also seen little motivation/success re/ introducing it to physical models.
    As far as I am aware, the mathematics of relativity are not incompatible with presentism. I believe Lorentz's competing Ether Theory was predicated on the notion of absolute simultaneity. From what I can gather, neo-Lorentzian relativtiy is a more modern interpretation that has removed any vestiges of the ether and is empirically equivalent to Special Relativity. The last I had read though, there had been no successful attempt to generalize neo-Lorentzian relativity. But it does, I believe, demonstrate that the mathematics of relativity is compatible with absolute simultaneity.

    Absolute simultaneity would be a particular signature of presentism in that presentism is the position that only the present moment exists, which is the same for all observers. In my best attempt to use the appropriate terms, it is the position that there exists only a single foliation* of spacetime, a single simultaneity hypersurface* or "slice".

    Relativity of Simultaneity (RoS) then, would be contradictory to the notion of absolute simultaneity. A consequence of RoS, as you were patient enough to explain to me, is that past and future states of the Universe are equally as real as present states - a model colloquially known as "the Block Universe".

    This would appear to make RoS incompatible with free will, if I'm not mistaken.


    *I've butchered those terms haven't I?


  • Registered Users Posts: 3,457 ✭✭✭Morbert


    roosh wrote: »
    Thanks Morbert, I understand that. I'm saying we could do this also if train A were in a state of absolute motion.

    In the example of our empty universe with the two trains, at rest relative to each other. When the trains start moving relative to each other, the observer in the train has that split second question of, is it my train that is moving, or is it the other train? They obviously know that their train is moving relative to the other train, but the question points to a more fundamental, absolute aspect of motion.

    I don't know what you mean by motion here, absolute or otherwise. On the same note, the observer in the train should ask a more precise question. One like "What is the co-ordinate velocity of my train?" Or "Is my train undergoing proper acceleration?"


  • Registered Users Posts: 2,553 ✭✭✭roosh


    Morbert wrote: »
    I don't know what you mean by motion here, absolute or otherwise. On the same note, the observer in the train should ask a more precise question. One like "What is the co-ordinate velocity of my train?" Or "Is my train undergoing proper acceleration?"
    I suppose I mean it in the same sense that, when you move your arm, your arm is in motion i.e. it is your arm that is moving and not your body.


  • Registered Users Posts: 3,457 ✭✭✭Morbert


    roosh wrote: »
    I suppose I mean it in the same sense that, when you move your arm, your arm is in motion i.e. it is your arm that is moving and not your body.

    We could e.g. construct a co-ordinate frame that labels your body as at rest and your arm with a co-ordinate velocity v or co-ordinate acceleration a such that ||v(t)|| > 0, ||a(t)|| > 0.

    Or if we wanted some invariant quantity like proper acceleration we could compute that easily enough.

    "Motion" could be ascribed to any of these quantities. We could in a sense call the latter absolute but not I suspect in a sense suitable for your purposes re/ establishing presentism.


  • Registered Users Posts: 2,553 ✭✭✭roosh


    Morbert wrote: »
    We could e.g. construct a co-ordinate frame that labels your body as at rest and your arm with a co-ordinate velocity v or co-ordinate acceleration a such that ||v(t)|| > 0, ||a(t)|| > 0.
    I understand this and I'm not questioning it. But here, as with the train example, you are making the statement that the train is labelled as "at rest". This simply begs the question, relative to what is the train labelled as "at rest"?

    The answer appears to be "relative to the co-ordinate frame". But the co-ordinate frame does not exist in nature and so the train cannot be at rest relative to it, in any physical sense.

    We could of course have two observers on the train each using a different co-ordinate frame, where one labels the train as "at rest" while the other labels it with a co-ordinate velocity. Both perfectly valid and useful. Again however, these co-ordinate frames do not exist in nature and so the train cannot be at rest or in motion relative to it, in any physical sense.


    When the trains start off at rest relative to each other and then start moving relative to another, they move relative to each other in a physical sense. When relative motion occurs between two bodies previously at rest, it must be because at least one of them was moving in a physical sense and not just in the sense of relative to the co-ordinate frame.

    The principle of relativity together with the equivalence principle says that we cannot determine which of the two is actually moving, but we don't need to be able to determine which is actually moving to conclude that, at least, one of them must be.


    Morbert wrote: »
    "Motion" could be ascribed to any of these quantities. We could in a sense call the latter absolute but not I suspect in a sense suitable for your purposes re/ establishing presentism.
    The question of presentism is separate to the question of absolute motion, although they may be related, I'm not actually sure.

    To my mind, and I am certainly open to correction on this, the necessity of free will in quantum mechanics effectively (re)establishes presentism because the alternative is not compatible with free will.

    If past and future states co-exist with present states, in a "block-like" structure, it means that there are no free choices for experimenters because the "choosing event" (and its outcomes) co-exists with the birth of the experimenter in the "block universe". It is set in stone even as the experimenter is born.

    This appears to be the necessary consequence of the relativity of simultaneity meaning it would be incompatible with free will, which appears to be a necessity of quantum mechanics.


  • Registered Users Posts: 3,457 ✭✭✭Morbert


    roosh wrote: »
    I understand this and I'm not questioning it. But here, as with the train example, you are making the statement that the train is labelled as "at rest". This simply begs the question, relative to what is the train labelled as "at rest"?

    The answer appears to be "relative to the co-ordinate frame". But the co-ordinate frame does not exist in nature and so the train cannot be at rest relative to it, in any physical sense.

    As I mentioned before, this wouldn't be an issue. Relative velocity can be understood as a choice of description. It might be better in this context to call it a co-ordinate velocity. So e.g. "The co-ordinate velocity of train A is 0" can be understood as "Upon application of this co-ordinate system, the quantity dx/dt of the train is 0".

    Therefore, no question is begged.


  • Registered Users Posts: 2,553 ✭✭✭roosh


    Morbert wrote: »
    As I mentioned before, this wouldn't be an issue. Relative velocity can be understood as a choice of description. It might be better in this context to call it a co-ordinate velocity. So e.g. "The co-ordinate velocity of train A is 0" can be understood as "Upon application of this co-ordinate system, the quantity dx/dt of the train is 0".

    Therefore, no question is begged.
    If we plug this back in as the response to the statement about moving an arm, where it was said that, when I move my arm, it is my arm that is actually moving and not my body:

    we can indeed apply a co-ordinate system which labels the dx/dt of the arm as 0, or we can apply one which labels it as >0. This is just a way of measuring the relative velocity between the two "bodies" and the tautological value for the relative velocity of an object to itself.

    This doesn't mean that the arm isn't actually moving. When I move my arm, it is still the arm that is still actually moving and not the body.

    The same is true for the trains. An observer on a train, which is at rest relative to another train, can employ a co-ordinate system which labels the dx/dt of both trains as 0. Then, something happens, and the dx/dt of both trains is no longer 0. That observer can apply a frame which labels his dx/dt = 0 and the other train as >0; or even vice versa.

    For the relative velocity between both trains to go from 0 to >0, something has to happen. That something is that at least one of the trains has moved or is moving - both are moving relative to each other, but one of them had to move for there to be relative velocity between them in the first place.


  • Registered Users Posts: 2,553 ✭✭✭roosh


    Fourier wrote: »
    Since you were presenting it as contrary to usual physics the natural assumption is that by motion mean you mean velocity. Confusing two people because you try to discuss subjects without ever bothering to learn them and their terminology and then describing that as them confusingly "having an issue" is lazy.

    I was reading back over a few posts and this point struck me. Now, I know you may have been moving relative to Morbert and I at a sizeable fraction of the speed of light and so the order of events may have been different :pac:, but it was actually the case that usual physics was presented as contrary to what I had been saying.


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  • Registered Users Posts: 3,457 ✭✭✭Morbert


    roosh wrote: »
    If we plug this back in as the response to the statement about moving an arm, where it was said that, when I move my arm, it is my arm that is actually moving and not my body:

    we can indeed apply a co-ordinate system which labels the dx/dt of the arm as 0, or we can apply one which labels it as >0. This is just a way of measuring the relative velocity between the two "bodies" and the tautological value for the relative velocity of an object to itself.

    This doesn't mean that the arm isn't actually moving. When I move my arm, it is still the arm that is still actually moving and not the body.

    The same is true for the trains. An observer on a train, which is at rest relative to another train, can employ a co-ordinate system which labels the dx/dt of both trains as 0. Then, something happens, and the dx/dt of both trains is no longer 0. That observer can apply a frame which labels his dx/dt = 0 and the other train as >0; or even vice versa.

    For the relative velocity between both trains to go from 0 to >0, something has to happen. That something is that at least one of the trains has moved or is moving - both are moving relative to each other, but one of them had to move for there to be relative velocity between them in the first place.

    Here the same imprecision is creeping back in. What do we mean if we say "both are moving relative to each other, but one of them had to move". The second use of the word "move" is unqualified and therefore needs to be unpacked.

    Do you mean, for example, that there is no reference frame that labels both both trains as having 0 magnitude co-ordinate velocity or co-ordinate acceleration? Do you mean at least one of them must have experienced proper acceleration? Do you mean there is some underlying ontic property "motion" that some reference frames capture better than others?

    When I previously asked you what you meant by motion, you answered with motion in the sense that when I wave my hand, my hand moves but not my body. But as we have seen, this sense is satisfied by co-ordinate velocity or acceleration, which is precisely the sense you are trying to distinguish "motion" from.


  • Registered Users Posts: 2,553 ✭✭✭roosh


    Morbert wrote: »
    Here the same imprecision is creeping back in. What do we mean if we say "both are moving relative to each other, but one of them had to move". The second use of the word "move" is unqualified and therefore needs to be unpacked.
    That is somewhat the point, that it is unqualified i.e. it is absolute.

    Morbert wrote: »
    Do you mean, for example, that there is no reference frame that labels both both trains as having 0 magnitude co-ordinate velocity or co-ordinate acceleration? Do you mean at least one of them must have experienced proper acceleration? Do you mean there is some underlying ontic property "motion" that some reference frames capture better than others?

    When I previously asked you what you meant by motion, you answered with motion in the sense that when I wave my hand, my hand moves but not my body. But as we have seen, this sense is satisfied by co-ordinate velocity or acceleration, which is precisely the sense you are trying to distinguish "motion" from.
    I'm not certain what the correct terminology would be. Ontic property sounds closest, but it wouldn't be the case that there is a reference frame which captures it better than others. It would be more the case that co-ordinate reference frames cannot capture it at all because it is not a relational property.

    The best I can do is try to give examples that hopefully speak to the point in such a way as to illustrate it.


    Imagine you and I are standing opposite each other, at rest relative to each other, and we want to test this question. The conversation goes like this:

    roosh: You move, so that we can test this idea.
    Morbert: I'm not moving, you move.
    roosh: well, one of us has to move in order to test this idea.

    Then, to end the deadlock, you make the free choice to move. When you make the move, we both start moving relative to each other. But, you are the one who moved, in that situation, not me - but we both move relative to each other, regardless.


    Does this make sense on some level?


  • Registered Users Posts: 3,457 ✭✭✭Morbert


    roosh wrote: »
    That is somewhat the point, that it is unqualified i.e. it is absolute.

    "Absolute" is typically invoked in contrast to "relational". E.g. Metaphysically speaking, if all motion is a relational concept, then there is no absolute motion even if there is motion.
    Imagine you and I are standing opposite each other, at rest relative to each other, and we want to test this question. The conversation goes like this:

    roosh: You move, so that we can test this idea.
    Morbert: I'm not moving, you move.
    roosh: well, one of us has to move in order to test this idea.

    Then, to end the deadlock, you make the free choice to move. When you make the move, we both start moving relative to each other. But, you are the one who moved, in that situation, not me - but we both move relative to each other, regardless.

    We can't conclude the bit in bold a priori*. You and I are at rest relative to each other. I then choose to induce a relative velocity between us. This means we can conclude that we are now moving relative to each other. But there needs to be some additional reasoning or stipulation to conclude that I have moved in some other absolute sense. What if, metaphysically, motion is all relational? Then we could not conclude that I have moved in some intrinsic/absolute sense.

    *I say a priori because normally philosophers would at this point discuss empirical findings and the theory of general relativity, proper acceleration, Mach etc etc. I'm willing to go down this route but first we must agree that absolution motion is not an implication of relative motion, in the sense that if we start moving relative to one another, we do not need to therefore conclude that one of us must have moved inherently/instrinsically/absolutely. Without further input from e.g. GR, it is sufficient to conclude a relation between us characterised as motion.


  • Registered Users Posts: 2,553 ✭✭✭roosh


    Morbert wrote: »
    "Absolute" is typically invoked in contrast to "relational". E.g. Metaphysically speaking, if all motion is a relational concept, then there is no absolute motion even if there is motion.
    That is how I am attempting to use the term. It is motion, not relative to something else. In the example where you and I are at rest relative to each other and you move. It is you that moves and not me, even though I am moving relative to you, as you are to me.

    This is where I was thinking free will would enter the equation. You're free choice to move means that it is you who moves, and not me. Not in a relational sense because in a relational sense we both move relative to each other.

    Morbert wrote: »
    We can't conclude the bit in bold a priori*. You and I are at rest relative to each other. I then choose to induce a relative velocity between us. This means we can conclude that we are now moving relative to each other. But there needs to be some additional reasoning or stipulation to conclude that I have moved in some other absolute sense. What if, metaphysically, motion is all relational? Then we could not conclude that I have moved in some intrinsic/absolute sense.

    *I say a priori because normally philosophers would at this point discuss empirical findings and the theory of general relativity, proper acceleration, Mach etc etc. I'm willing to go down this route but first we must agree that absolution motion is not an implication of relative motion, in the sense that if we start moving relative to one another, we do not need to therefore conclude that one of us must have moved inherently/instrinsically/absolutely. Without further input from e.g. GR, it is sufficient to conclude a relation between us characterised as motion.
    I'm not sure we need to conclude it a priori. In the example above we can conclude it on the basis of your free choice.

    Your choice to move your arms and legs to walk, contrasted with my free choice to not move a muscle, means that it was you that moved and not me. Your movement is not solely in a relational sense, because we are both moving relative to each other. It's your free choice which means that there is something unaccounted for in the relational picture.


  • Registered Users Posts: 3,457 ✭✭✭Morbert


    roosh wrote: »
    Your movement is not solely in a relational sense, because we are both moving relative to each other. It's your free choice which means that there is something unaccounted for in the relational picture.

    I don't understand this step. Sepcifically, why does "we are both moving relative to each other" imply "my movement is not solely in a relational sense"?

    A relativist (as in someone who rejects absolute motion) would say "It was my free choice to induce my motion relative to you, and equivalently it was my free choice to induce your motion relative to me".


  • Registered Users Posts: 2,553 ✭✭✭roosh


    Morbert wrote: »
    I don't understand this step. Sepcifically, why does "we are both moving relative to each other" imply "my movement is not solely in a relational sense"?

    A relativist (as in someone who rejects absolute motion) would say "It was my free choice to induce my motion relative to you, and equivalently it was my free choice to induce your motion relative to me".

    And the absolutist would agree that yes, it was your free choice to induce your motion relative to me, and equivalently it was your free choice to induce my motion relative to you. The question is, how did you induce the relative motion between us? You made a free choice to move your arms and your legs in a process we call walking. This caused you to move, not me. You were the one doing the moving.


  • Registered Users Posts: 3,457 ✭✭✭Morbert


    roosh wrote: »
    And the absolutist would agree that yes, it was your free choice to induce your motion relative to me, and equivalently it was your free choice to induce my motion relative to you. The question is, how did you induce the relative motion between us? You made a free choice to move your arms and your legs in a process we call walking. This caused you to move, not me. You were the one doing the moving.

    But a relativist would reject that. I.e. Your explanatory chain of events seems to be

    I apply a force -> I move absolutely -> We move relative to each other

    A relativist would instead use the chain

    I apply a force -> We move relative to each other


  • Registered Users Posts: 2,553 ✭✭✭roosh


    Morbert wrote: »
    But a relativist would reject that. I.e. Your explanatory chain of events seems to be

    I apply a force -> I move absolutely -> We move relative to each other

    A relativist would instead use the chain

    I apply a force -> We move relative to each other

    The question is, why does your application of a force result in relative motion between us? Why does you moving your feet in a process we call walking, result in relative motion between us? To my mind, it makes sense to say that it causes you to move but not me. Alternatively, I could make the decision to walk and that would cause me to move, but not you. Another alternative would be that both of us choose to walk, and therefore both you and I move.

    To me there appears to be 3 possible scenarios to explain "we move relative to each other".



    We could take the scenario where we remain at rest relative to each other but just move our arms e.g. wave at each other.

    In this case, you make a choice to raise your arm and move it side to side. It is your arm that is doing the moving. Would the corresponding neural activity not evidence this?


  • Registered Users Posts: 3,457 ✭✭✭Morbert


    roosh wrote: »
    The question is, why does your application of a force result in relative motion between us? Why does you moving your feet in a process we call walking, result in relative motion between us? To my mind, it makes sense to say that it causes you to move but not me. Alternatively, I could make the decision to walk and that would cause me to move, but not you. Another alternative would be that both of us choose to walk, and therefore both you and I move.

    What is the explanatory gap you are referring to? A relationalist and the substantivalist (a more precise notion of absolutist common in literature discussing motion and space) have different ontological commitments regarding motion, but both would explain the presence of motion with my choices.

    As an aside, if we swap the explananation and explanandum, we get close-ish to a common question in the relationalist debate: Instead of asking why does force induce relative motion. People ask why relative motion would result in me experiencing a force.


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  • Registered Users Posts: 2,553 ✭✭✭roosh


    Morbert wrote: »
    What is the explanatory gap you are referring to? A relationalist and the substantivalist (a more precise notion of absolutist common in literature discussing motion and space) have different ontological commitments regarding motion, but both would explain the presence of motion with my choices.

    As an aside, if we swap the explananation and explanandum, we get close-ish to a common question in the relationalist debate: Instead of asking why does force induce relative motion. People ask why relative motion would result in me experiencing a force.

    In the first instance we would explain the presence of motion with your choices. In the second instance we would explain them with my choices. In the third, it would be both of our choices. So I see three different scenarios here, all of which result in relative motion.

    What are those choices though? In the first case you make a decision which has a causal effect on you i.e. you choose to move. In the second, I make a decision which has a causal effect on me i.e. I choose to move, and in the third we both choose to move.

    Am I right in saying that, in each of these cases our individual decisions results in our experiencing acceleration? This acceleration tells us which one of us changes our state of motion. Acceleration itself is absolute, so presumably this would tell us which one of us, or which body, moves in an absolute sense?


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