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the [possible] fallacy of Lorentz contractions

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  • Registered Users Posts: 2,552 ✭✭✭roosh


    Morbert wrote: »
    Absolute space. Hence, we are not compelled to assume absolute space even exists. Similarly, we cannot determine by experiment whether or not we are in the Matrix, hence we are not compelled to assume the Matrix exists.
    The point about the matrix is somewhat of a misnomer; because assuming one way or the other makes no difference to the question in hand, while assuming motion or rest does materially affect the conclusions we draw about which theory best describes the universe (or the matrix's projection of the universe). The question of "motion" or "rest" is equally applicable inside the matrix as it is outside it.

    I think the point of the stated consequence, of the different principles of relativity, is being missed, however; the point clearly distinguishes between two possible "states', that of being "in motion" and that of being "at rest"; such that no experiment can distinguish between them. This means that the observer is either "in motion" or "at rest" [relative to something], but can't tell the difference; but it is one or the other.

    You've stated above that the reference frame, relative to which the motion cannot be determined, is the absolute rest frame (or absolute space). This means that either the observer is "in motion" relative to absolute space, or he is "at rest" in absolute space. Either way, the "absolute space" is tacitly assumed. If the observer is "at rest" in absolute space, then Einsteinian relativity treats reference frames as being at "absolute rest"; if the observer is in motion relative to the undetectable, absolute rest frame, then the conclusions are Lorentzian not Einsteinian.


    Morbert wrote: »
    Again, if by "absolute motion" you mean that there is no reference frame which labels both observers as "at rest", then you are right. But this definition means we still don't have to tacitly assume absolute rest, or absolute space exists, and hence we don't have to assume one reference frame is more correct than another.
    I'm not sure how you are drawing the conclusion that that was what was meant by "absolute motion".

    "Absolute motion" is a simple "yes" or "no" answer to the question: is there motion?

    This can be extended to specific objects and observers i.e. is Albert in motion; yes, or no?


    Absolute space is not required for either of the above. The concept of absolute space would be required to measure absolute motion, but measurement, by its very nature, is relative, so absolute motion cannot be measured; but its "existence" can be deduced.

    Again, if we take our two observers - in empty space for simplicity sake; they start off at rest relative to each other (with no assumption of absolute space). In order for there to be relative motion, between them, at least one of them has to move; if neither one of them moves, then they will remain at rest relative to each other; and both reference frames will label both observers as "at rest".


    If relative motion occurs and both observers maintain that they remained at rest, then one of them must be wrong. We can personalise it a bit for the sake of intuition. If you and I are at rest relative to each other and then relative motion occurs, if you and I both maintain that we didn't move, then one of us has to be wrong. We might not be able to determine which one is wrong - as per the principle of relativity - but we can most certainly reason that one of us must be wrong. Because if we are both right, and we both remained at rest, then no relative motion would have occurred.

    Morbert wrote: »
    You are tacitly assuming absolute space here by switching definitions of "absolute motion". We have established that there is no reference frame which labels both observers as at rest. This in no way implies one observer must be wrong, unless you tacitly assume absolute space exists.
    There is no switching of definitions; we can reason all of the above from relative motion alone, without assuming absolute space.

    The point about no reference frame labeling both observers as "at rest" is just an extension of the issue that neither can determine which one is in motion. We can still reason that at least one of them, absolutely, must be in motion - otherwise they would remain at rest, relative to each other.

    Morbert wrote: »
    Which is indistinguishable from what we would conclude if all observers assumed absolute rest did not exist. Hence, absolute space and absolute rest are entirely superfluous concepts.
    I think we can say that all observers assume that absolute rest does not exist, but that the co-ordinate labeling convention tacitly assumes it - which would be fairly representative of the situation as is.

    Are we agreed so, that the treatment of reference frames, under Einsteinian co-ordinate labels, is indistinguishable i.e. is the same as, treating specific reference frames as being at absolute rest?


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


    roosh wrote: »
    The point about the matrix is somewhat of a misnomer; because assuming one way or the other makes no difference to the question in hand, while assuming motion or rest does materially affect the conclusions we draw about which theory best describes the universe (or the matrix's projection of the universe). The question of "motion" or "rest" is equally applicable inside the matrix as it is outside it.

    You are jumping back and forth between points. Your point was that, because asbolute space is referenced in the statement "There is no way to physically distinguish absolute space/rest", it must be assumed. This is false, for the same reason we do not have to assume the Matrix is real even if we say "There is no way to physically determine if we are in the Matrix".
    I think the point of the stated consequence, of the different principles of relativity, is being missed, however; the point clearly distinguishes between two possible "states', that of being "in motion" and that of being "at rest"; such that no experiment can distinguish between them. This means that the observer is either "in motion" or "at rest" [relative to something], but can't tell the difference; but it is one or the other.

    It does not have to be one or the other. You can adopt a third option: space is relative.
    You've stated above that the reference frame, relative to which the motion cannot be determined, is the absolute rest frame (or absolute space). This means that either the observer is "in motion" relative to absolute space, or he is "at rest" in absolute space. Either way, the "absolute space" is tacitly assumed. If the observer is "at rest" in absolute space, then Einsteinian relativity treats reference frames as being at "absolute rest"; if the observer is in motion relative to the undetectable, absolute rest frame, then the conclusions are Lorentzian not Einsteinian.

    It means absolute space is not implied by the physics. We are therefore not compelled to believe it exists. Absolute space is not a consequence of relativity. "In motion", in this case simply means no reference frame labels both observers as at rest. The observers are in motion relative to each other. It in no way implies one reference frame is more correct than another.
    I'm not sure how you are drawing the conclusion that that was what was meant by "absolute motion".

    "Absolute motion" is a simple "yes" or "no" answer to the question: is there motion?

    This can be extended to specific objects and observers i.e. is Albert in motion; yes, or no?

    It cannot be extended to specific objects. Again, it is your misuse of language, and apparent refusal to use rigorous terminology, that is causing the problem.

    Here is what relativity says in the case of two observers moving relative to one another: There is no coordinate system which labels both observers as "at rest". From this, you cannot conclude that therefore there must be an absolute space for one observer to be in motion with respect to.
    Absolute space is not required for either of the above. The concept of absolute space would be required to measure absolute motion, but measurement, by its very nature, is relative, so absolute motion cannot be measured; but its "existence" can be deduced.

    I.e. Absolute space can be deduced. That is incorrect. Absolute space cannot be deduced from the statement "There is no coordinate system which labels both observers as at rest".
    Again, if we take our two observers - in empty space for simplicity sake; they start off at rest relative to each other (with no assumption of absolute space). In order for there to be relative motion, between them, at least one of them has to move; if neither one of them moves, then they will remain at rest relative to each other; and both reference frames will label both observers as "at rest".

    If relative motion occurs and both observers maintain that they remained at rest, then one of them must be wrong. We can personalise it a bit for the sake of intuition. If you and I are at rest relative to each other and then relative motion occurs, if you and I both maintain that we didn't move, then one of us has to be wrong. We might not be able to determine which one is wrong - as per the principle of relativity - but we can most certainly reason that one of us must be wrong. Because if we are both right, and we both remained at rest, then no relative motion would have occurred.

    There is no switching of definitions; we can reason all of the above from relative motion alone, without assuming absolute space.

    The point about no reference frame labeling both observers as "at rest" is just an extension of the issue that neither can determine which one is in motion. We can still reason that at least one of them, absolutely, must be in motion - otherwise they would remain at rest, relative to each other.

    All that physically matters is they move relative to one another. That is what is implied by the statement "There is no coordinate system which labels both observers as at rest". Absolute space cannot therefore be deduced.
    I think we can say that all observers assume that absolute rest does not exist, but that the co-ordinate labeling convention tacitly assumes it - which would be fairly representative of the situation as is.

    We cannot say that the use of coordinate systems is a tacit assumption of absolute rest. Coordinate systems are perfectly consistent with the assumption that no absolute rest exists.
    Are we agreed so, that the treatment of reference frames, under Einsteinian co-ordinate labels, is indistinguishable i.e. is the same as, treating specific reference frames as being at absolute rest?

    We agree that we can metaphysically suppose an absolute space, and it will be consistent with the physics. We also should agree that we can suppose there is no absolute space, and it will be consistent with the physics.


  • Registered Users Posts: 2,552 ✭✭✭roosh


    Morbert wrote: »
    You are jumping back and forth between points. Your point was that, because asbolute space is referenced in the statement "There is no way to physically distinguish absolute space/rest", it must be assumed. This is false, for the same reason we do not have to assume the Matrix is real even if we say "There is no way to physically determine if we are in the Matrix".
    The point wasn't that "absolute rest" must be assumed because it is referenced through the PoR, that particular point was simply that absolute rest is referenced through the PoR.

    The point about the tacit assumption of absolute rest is that we can deduce that it must be a tacit assumption from the Einsteinian treatment of reference frames, the constancy of c, and the fact that light inherits the horizontal velocity of a moving emitter (mirror).


    Morbert wrote: »
    It does not have to be one or the other. You can adopt a third option: space is relative.
    That is the conclusion that we draw when we treat specific reference frames as being at absolute rest.

    Morbert wrote: »
    It means absolute space is not implied by the physics. We are therefore not compelled to believe it exists. Absolute space is not a consequence of relativity. "In motion", in this case simply means no reference frame labels both observers as at rest. The observers are in motion relative to each other. It in no way implies one reference frame is more correct than another.
    Your re-statement of the consequence above - "There is no way to physically distinguish absolute space/rest" -is not entirely complete; more accurately it should be "there is no way to physically distingusih absolute rest from absolute motion", with the implication that bodies are in one or the other state.

    While we are not compelled to believe that an absolute rest state exists, we cannot rule it out, because we cannot determine whether or not we are actually "at absolute rest"; for all we can determine, we could be. That being said, we can actually assume that no reference frame is at absolute rest, however, we can still use the concept to make a number deductions.

    We can start with Albert, who cannot determine if he is at absolute rest, or in motion. We can consider the scenario where he is at absolute rest and see that it resembles, exactly, the treatment of the reference frame under Einsteinian relativity.

    We can then consider the scenario where he is not at absolute rest, but in motion; knowing that the photon in his clock will be imparted with the horizontal velocity of his train carriage (or platform). Under Galilean relativity we would expect Albert to measure a speed of less than c, due to the vertical velocity component being less than c. Einsteinian relativity states that he will measure the speed to be c. In order for this to happen, Albert's instruments must contract by an amount unknown to himself due to his motion relative to the absolute rest frame - this however, is the Lorentzian interpretation.

    Only the scenario where Albert is at absolute rest matches the Einsteinian interpretation.

    Morbert wrote: »
    It cannot be extended to specific objects. Again, it is your misuse of language, and apparent refusal to use rigorous terminology, that is causing the problem.

    Here is what relativity says in the case of two observers moving relative to one another: There is no coordinate system which labels both observers as "at rest". From this, you cannot conclude that therefore there must be an absolute space for one observer to be in motion with respect to.
    Again, the question of absolute motion is a yes or no question; absolute space is not necessary.

    That "there is no coordinate system which labels both observers as "at rest" is just a the consequence of the PoR in a different guise; it simply demonstrates the point that neither observer can determine which one is actually in motion.

    Again, if we consider two observers and only their relative motion, we can deduce absolute motion.

    If the two observers start off at rest relative to each other, then, unless one of them actually moves, they will remain at rest relative to each other. In order for relative motion to occur between them, one of them absolutely has to actually move. Again, if they didn't, they would remain at rest relative to each other.


    This can be extended to specific objects (or indeed observers) simply by asking the question is X moving?
    Morbert wrote: »
    I.e. Absolute space can be deduced. That is incorrect. Absolute space cannot be deduced from the statement "There is no coordinate system which labels both observers as at rest".
    ...
    All that physically matters is they move relative to one another. That is what is implied by the statement "There is no coordinate system which labels both observers as at rest". Absolute space cannot therefore be deduced.
    As mentioned, I don't think absolute space is necessary to answer the question is there motion? We can deduce that there must be motion from relative motion. The above statement simply demonstrates that we cannot actually determine which one is in motion and which (if any) are at rest; hence we cannot, knowingly at least, measure absolute velocity - but we can deduce that there is absolute motion.

    Morbert wrote: »
    We cannot say that the use of coordinate systems is a tacit assumption of absolute rest. Coordinate systems are perfectly consistent with the assumption that no absolute rest exists.
    It's not necessarily the co-ordinate systems alone, as outlined above.

    Morbert wrote: »
    We agree that we can metaphysically suppose an absolute space, and it will be consistent with the physics. We also should agree that we can suppose there is no absolute space, and it will be consistent with the physics.
    But, as above, we can deduce that Einsteinian relativity tacitly assumes absolute rest.


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


    mangaroosh, you are consistently making the same mistakes over and over again. And when I correct mistakes, you revert to earlier examples that had been previously resolved.

    Here is an abbreviation of your logic.

    Suppose two observers are in motion relative to each other.
    Therefore at least one of them has to be in motion with respect to a state of absolute rest.
    Therefore absolute rest exists.

    The argument is wrong because you cannot jump from "Two observers are in motion relative to each other" to "At least one has to be in motion with respect to a state of absolute rest". All you can say is one of them has to be in motion with respect to the other. You cannot tacitly assume a state of absolute rest, define motion as "motion with respect to absolute rest", and then assert that therefore relativity tacitly assumes absolute rest exists. Yes, you can say it doesn't rule it out. That is not in dispute. Just as the laws of physics do not rule out the Matrix. The reference frame formalism of Einstein's relativity is perfectly consistent with the notion that no absolute rest, or absolute space exists.

    Now, if you want to define absolute motion as something other than "motion with respect to absolute rest", then that's fine. But then you cannot use it to infer absolute rest in the presentist, neo-Lorentzian sense (which I am assuming is your goal). For example, if you define absolute motion as non-geodesic spacetime paths, then absolute rest becomes geodesic spacetime paths. Both observers would be considered at absolute rest, even if reference frames describe relative motion between them.


  • Registered Users Posts: 2,552 ✭✭✭roosh


    Morbert wrote: »
    mangaroosh, you are consistently making the same mistakes over and over again. And when I correct mistakes, you revert to earlier examples that had been previously resolved.

    Here is an abbreviation of your logic.

    Suppose two observers are in motion relative to each other.
    Therefore at least one of them has to be in motion with respect to a state of absolute rest.
    Therefore absolute rest exists.

    The argument is wrong because you cannot jump from "Two observers are in motion relative to each other" to "At least one has to be in motion with respect to a state of absolute rest". All you can say is one of them has to be in motion with respect to the other. You cannot tacitly assume a state of absolute rest, define motion as "motion with respect to absolute rest", and then assert that therefore relativity tacitly assumes absolute rest exists. Yes, you can say it doesn't rule it out. That is not in dispute. Just as the laws of physics do not rule out the Matrix. The reference frame formalism of Einstein's relativity is perfectly consistent with the notion that no absolute rest, or absolute space exists.

    Now, if you want to define absolute motion as something other than "motion with respect to absolute rest", then that's fine. But then you cannot use it to infer absolute rest in the presentist, neo-Lorentzian sense (which I am assuming is your goal). For example, if you define absolute motion as non-geodesic spacetime paths, then absolute rest becomes geodesic spacetime paths. Both observers would be considered at absolute rest, even if reference frames describe relative motion between them.
    The abbreviation provided above, demonstrates that there is some confusion about the points that are being made; I have to accept partial responsibility for, perhaps, not distinguishing between the points more clearly, but hopefully we can clarify them.

    Two observers in motion
    Firstly, the point about the two observers in motion, relative to each other, being verification of absolute motion, is separate from the point of absolute rest in Einsteinian relativity. It is a stand-alone point; it isn't being used to infer the existence of absolute space or rest.

    In general it is a riposte to the recurring statement that "it makes no sense to talk about something being actually in motion"; the point demonstrates that it does make sense, even if it can't be determined which one is actually in motion. It is based a definition of absolute motion that doesn't necessarily require the existence of absolute space.

    Absolute rest in ER
    The inference of the absolute rest state in Einsteinian relativity is not based on the above. The deduction, that ER treats specific reference frames as being at absolute rest, is inferred from the treatment of reference frames in ER, the Principle of Relativity - which implies absolute rest, as you mentioned - the measurement of c by an observer (Albert), and the fact about the photon incurring the horizontal momentum of the moving clock/train.


    The conclusions which can be drawn, as outlined above, are either; a) Albert, and his reference frame, are at absolute rest; or b) Albert's instruments are contracted by an amount unknown to himself, due to his motion relative to an undetectable reference frame.


    Principle of Relativity
    The stated consequence of the PoR, as mentioned, effectively says that a state of absolute motion cannot be distinguished from a state of absolute rest; implying that an observer is in one state or the other.

    If an observer is in absolute motion (but can't determine it) and he measures the speed of light in his light clock to be c, then his instruments must be contracted by an amount unknown to himself, due to his absolute motion.

    Alternatively, he is at absolute rest.


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


    roosh wrote: »
    The abbreviation provided above, demonstrates that there is some confusion about the points that are being made; I have to accept partial responsibility for, perhaps, not distinguishing between the points more clearly, but hopefully we can clarify them.

    Two observers in motion
    Firstly, the point about the two observers in motion, relative to each other, being verification of absolute motion, is separate from the point of absolute rest in Einsteinian relativity. It is a stand-alone point; it isn't being used to infer the existence of absolute space or rest.

    In general it is a riposte to the recurring statement that "it makes no sense to talk about something being actually in motion"; the point demonstrates that it does make sense, even if it can't be determined which one is actually in motion. It is based a definition of absolute motion that doesn't necessarily require the existence of absolute space.

    And I agree that it does make sense, provided in motion does not mean in motion with respect to some absolute space, or state of absolute rest. It is perfectly valid to say the observers are actually in motion with respect to each other.
    Absolute rest in ER
    The inference of the absolute rest state in Einsteinian relativity is not based on the above. The deduction, that ER treats specific reference frames as being at absolute rest, is inferred from the treatment of reference frames in ER, the Principle of Relativity - which implies absolute rest, as you mentioned - the measurement of c by an observer (Albert), and the fact about the photon incurring the horizontal momentum of the moving clock/train.

    The conclusions which can be drawn, as outlined above, are either; a) Albert, and his reference frame, are at absolute rest; or b) Albert's instruments are contracted by an amount unknown to himself, due to his motion relative to an undetectable reference frame.

    Or c) There is no state of absolute rest, no undetectable absolute reference frame, and hence Albert is neither at absolute rest, nor in motion with respect to absolute rest. He measures the speed of light to be c because of the Minkowski geometry relating all events to one another.

    Principle of Relativity
    The stated consequence of the PoR, as mentioned, effectively says that a state of absolute motion cannot be distinguished from a state of absolute rest; implying that an observer is in one state or the other.

    If an observer is in absolute motion (but can't determine it) and he measures the speed of light in his light clock to be c, then his instruments must be contracted by an amount unknown to himself, due to his absolute motion.

    Alternatively, he is at absolute rest.

    It implies no such thing. It implies an absolute rest, and motion with respect to absolute rest, are physically meaningless. Again, you are tendering the false dichotomy: If you are not at absolute rest, then you must be in motion with respect to absolute rest. I have shown that relativity is perfectly consistent with the postulate that absolute rest, and hence motion with respect to absolute rest, does not exist. You say it is implicitly assumed. If this were true, you would be able to show a contradiction between relativity, and the postulate that no absolute rest exists.


  • Registered Users Posts: 2,552 ✭✭✭roosh


    Morbert wrote: »
    And I agree that it does make sense, provided in motion does not mean in motion with respect to some absolute space, or state of absolute rest. It is perfectly valid to say the observers are actually in motion with respect to each other.
    OK, so you would agree that it demonstrates absolute motion; not necessarily motion with respect to absolute space?

    Morbert wrote: »
    Or c) There is no state of absolute rest, no undetectable absolute reference frame, and hence Albert is neither at absolute rest, nor in motion with respect to absolute rest. He measures the speed of light to be c because of the Minkowski geometry relating all events to one another.
    When reference frames are treated as being at absolute rest, then the conclusion of something like Minkowskian geometry is inevitable. I dare say, this is partly the reason why the notion of absoluteness remains in Einsteinian relativity.


    Regardless of the Minkowskian geometry, however, if Albert's clock is in motion, it will be imparted with the horizontal velocity of the train. In order for him to measure the speed of light to be c, his instruments will have to contract by an amount unknown to himself.


    This, I would imagine, is where the notion of absolute spacetime measurements will probably come in.

    Morbert wrote: »
    It implies no such thing. It implies an absolute rest, and motion with respect to absolute rest, are physically meaningless. Again, you are tendering the false dichotomy: If you are not at absolute rest, then you must be in motion with respect to absolute rest. I have shown that relativity is perfectly consistent with the postulate that absolute rest, and hence motion with respect to absolute rest, does not exist. You say it is implicitly assumed. If this were true, you would be able to show a contradiction between relativity, and the postulate that no absolute rest exists.
    The implication of the PoR is not so much that both are physically meaningless, rather that both are physically undetectable; this is an entirely different proposition.

    That we cannot detect absolute rest or motion, doesn't mean that they don't exist, it simply means we cannot tell if we are in either state. They are physically meaningful because we can use both to draw conclusions about the physical world. We can ask the question, are we at absolute rest? The answer is, we don't actually know. We could be, or we might not be. We cannot, therefore, conclude that it doesn't exist.

    Also, there would only be a contradiction between relativity and the postulate that no absolute rest exists, if absolute velocity and relative velocity were contradictory notions; there not, so no contradiction arises.


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


    roosh wrote: »
    OK, so you would agree that it demonstrates absolute motion; not necessarily motion with respect to absolute space?

    Yes, they are absolutely in motion with respect to each other.
    When reference frames are treated as being at absolute rest, then the conclusion of something like Minkowskian geometry is inevitable. I dare say, this is partly the reason why the notion of absoluteness remains in Einsteinian relativity.

    Or when reference frames are treated as arbitrary coordinate labels, making no implicit or explicit statement about absolute rest.
    Regardless of the Minkowskian geometry, however, if Albert's clock is in motion, it will be imparted with the horizontal velocity of the train.

    Yes, if Albert's clock is in motion, with respect to an observer, they will see the photon inherit the horizontal velocity of the train.
    In order for him to measure the speed of light to be c, his instruments will have to contract by an amount unknown to himself.

    This does not follow from the above premises. Albert's clock is absolutely at rest with respect to himself. It is absolutely in motion with respect to the other observer. Since the two observers' perspectives can be transformed into each other via the Lorentz transformation, there is no need to postulate some unknown mysterious set of dynamics unknown to Albert.
    The implication of the PoR is not so much that both are physically meaningless, rather that both are physically undetectable; this is an entirely different proposition.

    That we cannot detect absolute rest or motion, doesn't mean that they don't exist, it simply means we cannot tell if we are in either state. They are physically meaningful because we can use both to draw conclusions about the physical world. We can ask the question, are we at absolute rest? The answer is, we don't actually know. We could be, or we might not be. We cannot, therefore, conclude that it doesn't exist.

    Also, there would only be a contradiction between relativity and the postulate that no absolute rest exists, if absolute velocity and relative velocity were contradictory notions; there not, so no contradiction arises.

    If no contradiction arises, then absolute rest, and hence motion with respect to absolute rest, are not implicitly assumed. So not only are we unable to detect absolute rest/motion with respect to absolute rest, we are not logically compelled to assume it exists, as relativity is perfectly consistent with the assumption that no absolute rest exists.


  • Registered Users Posts: 2,552 ✭✭✭roosh


    Morbert wrote: »
    Yes, they are absolutely in motion with respect to each other.
    And also in absolute motion.

    Morbert wrote: »
    Or when reference frames are treated as arbitrary coordinate labels, making no implicit or explicit statement about absolute rest.
    We seem to be agreed on the fact that the two are at least indistinguishable from each other; but we disagree on the implicit assumptions. The implicit assumption can be deduced however, primarily on the basis of the fact that the photon will inherit the horizontal velocity of the moving train.

    Morbert wrote: »
    Yes, if Albert's clock is in motion, with respect to an observer, they will see the photon inherit the horizontal velocity of the train.
    It is not necessarily the perceived motion that causes the photon to be imbued with the horizontal velocity, it is the actual motion of the train.

    Morbert wrote: »
    This does not follow from the above premises. Albert's clock is absolutely at rest with respect to himself. It is absolutely in motion with respect to the other observer. Since the two observers' perspectives can be transformed into each other via the Lorentz transformation, there is no need to postulate some unknown mysterious set of dynamics unknown to Albert.
    It doesn't matter if Albert's clock is absolutely at rest relative to Albert, because, unless Albert is also at absolute rest [full stop], then the photon will be imbued with a horizontal velocity; that is, if Albert is in motion at all, then the photon in the clock will be imbued with a horizontal velocity. If there is relative motion between Albert and Henry then, at least, one of them has to be in motion, in an absolute sense.

    This means that, at least, one of their photons will be imbued with a horizontal velocity; if they both measure the speed of light to be c, then it means that the instruments belonging to one of them, must be contracted by an amount unknown to themselves.

    This true even if Minkowskian geometry is correct - Minkowskian geometry simply offers the explanation as to why this happens.

    Morbert wrote: »
    If no contradiction arises, then absolute rest, and hence motion with respect to absolute rest, are not implicitly assumed. So not only are we unable to detect absolute rest/motion with respect to absolute rest, we are not logically compelled to assume it exists, as relativity is perfectly consistent with the assumption that no absolute rest exists.
    It is also perfectly consistent with the assumption that reference frames are treated as being at absolute rest.

    No contradiction arises, because relative motion and absolute motion are not contradictory ideas. We can deduce a number of things based on the fact that a photon will be imbued with the horizontal momentum of a clock in motion.Unless the clock is not in motion whatsoever i.e. at absolute rest, then it will be imbued with the horizontal momentum of the clock. If an observer, at rest relative to the clock, measures the speed of the light to be c, then their instruments must contract by an amount unknown to themselves. Minkowskian geometry offers a constructive explanation as to how this can be, but it still implies that it must happen.


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


    roosh wrote: »
    And also in absolute motion.

    We seem to be agreed on the fact that the two are at least indistinguishable from each other; but we disagree on the implicit assumptions. The implicit assumption can be deduced however, primarily on the basis of the fact that the photon will inherit the horizontal velocity of the moving train.

    It is not necessarily the perceived motion that causes the photon to be imbued with the horizontal velocity, it is the actual motion of the train.

    It doesn't matter if Albert's clock is absolutely at rest relative to Albert, because, unless Albert is also at absolute rest [full stop], then the photon will be imbued with a horizontal velocity that is, if Albert is in motion at all, then the photon in the clock will be imbued with a horizontal velocity. If there is relative motion between Albert and Henry then, at least, one of them has to be in motion, in an absolute sense.
    <snip>

    Again, you implicitly assume the thing you are trying to deduce. You are saying, if Albert is not at absolute rest, then he is in motion with respect to an absolute rest. I.e. You are saying absolute rest exists. You are just using different words each time.

    It is also perfectly consistent with the assumption that reference frames are treated as being at absolute rest.

    And that is entirely irrelevant to what you are trying to argue. I have said numerous times before that relativity is consistent with the metaphysical position that absolute rest exists. This is what allows us to make connections between Einsteinian and neo-Lorentzian relativity. But relativity is also consistent with the position that no absolute rest exists. This is what you disagree with. This is what you must address.
    No contradiction arises, because relative motion and absolute motion are not contradictory ideas. We can deduce a number of things based on the fact that a photon will be imbued with the horizontal momentum of a clock in motion.Unless the clock is not in motion whatsoever i.e. at absolute rest, then it will be imbued with the horizontal momentum of the clock. If an observer, at rest relative to the clock, measures the speed of the light to be c, then their instruments must contract by an amount unknown to themselves. Minkowskian geometry offers a constructive explanation as to how this can be, but it still implies that it must happen.

    Here, you repeat your implicit assumption. If it is not assumed that absolute rest exist, then the statement "Unless the clock is not in motion whatsoever i.e. at absolute rest, then it will be imbued with the horizontal momentum of the clock." does not follow. I.e. If absolute rest does not exist, then we are not compelled to say "if the clock is not at absolute rest, then it must have a horizontal velocity with respect to absolute rest".

    Also, if what you say was true, there must be a contradiction between the statement "There is no state of absolute rest." and Einstein's relativity. Otherwise, you cannot say relativity implicitly assumes a state of absolute rest exists.


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  • Registered Users Posts: 2,552 ✭✭✭roosh


    Morbert wrote: »
    Again, you implicitly assume the thing you are trying to deduce. You are saying, if Albert is not at absolute rest, then he is in motion with respect to an absolute rest. I.e. You are saying absolute rest exists. You are just using different words each time.
    Firstly, we can establish absolute motion by considering the example the two observers at rest relative to each other who then move relative to one another. This requires absolute motion, otherwise there would be no relative motion; with absolute motion not being dependent on an absolute reference frame; it is a simple yes or no answer to the question, is something moving or not. We can deduce that yes one of the observers has to be moving; that motion can only be measured relatively is immaterial, because we can still deduce that absolute motion exists.

    Again, not relative to an absolute reference frame, which would be necessary for measuring absolute velocity; absolute velocity, although inextricably linked to the notion of absolute motion, is a distinct concept.

    Where there is relative motion we can reasonably and logically ask the question, are the objects moving. We might not be able to discern which one is moving, but we can deduce that one must be moving, in an actual and absolute sense; again, no reference to an absolute reference frame; although we can hypothesise a theoretical one for the purpose of explanation.

    From this we can deduce that the photon in Albert's clock will be imparted with the horizontal momentum of the actual motion of the train - again, no reference to motion relative to absolute rest, just the deduction that absolute motion must occur for there to be relative motion.


    Morbert wrote: »
    And that is entirely irrelevant to what you are trying to argue. I have said numerous times before that relativity is consistent with the metaphysical position that absolute rest exists. This is what allows us to make connections between Einsteinian and neo-Lorentzian relativity. But relativity is also consistent with the position that no absolute rest exists. This is what you disagree with. This is what you must address.
    The point being made is that it is consistent with the metaphysical position of absolute rest, and that absolute rest is tacitly assumed. We can do this by considering the position of absolute rest, that is compatible with relativity and then seeing what deductions can be made.

    Absolute rest exists, and absolute rest doesn't exist are contradictory statements, so that relativity is compatible with both seems to make it contradictory.

    Morbert wrote: »
    Here, you repeat your implicit assumption. If it is not assumed that absolute rest exist, then the statement "Unless the clock is not in motion whatsoever i.e. at absolute rest, then it will be imbued with the horizontal momentum of the clock." does not follow. I.e. If absolute rest does not exist, then we are not compelled to say "if the clock is not at absolute rest, then it must have a horizontal velocity with respect to absolute rest".
    The clock will be imbued with horizontal momentum regardless of whether or not absolute rest exists, even assuming Minkowskian geometry. If Albert's train is in motion at all, then it will be imparted with a horizontal velocity; only if his train isn't moving will it not.

    We can apply this to all other observers such that, the only way that no photon will be imbued with horizontal momentum, is if no clock, train, or observer is moving. If no observer, train, or clock is moving then there would be no relative motion. That there is relative motion allows us to conclude that some obesrvers instruments must be contracted unknown to themselves.
    Morbert wrote: »
    Also, if what you say was true, there must be a contradiction between the statement "There is no state of absolute rest." and Einstein's relativity. Otherwise, you cannot say relativity implicitly assumes a state of absolute rest exists.
    The contradiction lies in what you say above, that relativity is compatible with two contradictory ideas.

    No contradiction exists between the notion of absolute velocity/motion and relative velocity/motion; hence no contradiction would exist between the idea that no state of absolute rest exists and ER.

    Again, the contradiction lies in the fact that it is compatible with two contradictory ideas.


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


    roosh wrote: »
    Firstly, we can establish absolute motion by considering the example the two observers at rest relative to each other who then move relative to one another. This requires absolute motion, otherwise there would be no relative motion; with absolute motion not being dependent on an absolute reference frame; it is a simple yes or no answer to the question, is something moving or not. We can deduce that yes one of the observers has to be moving; that motion can only be measured relatively is immaterial, because we can still deduce that absolute motion exists.

    Again, not relative to an absolute reference frame, which would be necessary for measuring absolute velocity; absolute velocity, although inextricably linked to the notion of absolute motion, is a distinct concept.

    Where there is relative motion we can reasonably and logically ask the question, are the objects moving. We might not be able to discern which one is moving, but we can deduce that one must be moving, in an actual and absolute sense; again, no reference to an absolute reference frame; although we can hypothesise a theoretical one for the purpose of explanation.

    From this we can deduce that the photon in Albert's clock will be imparted with the horizontal momentum of the actual motion of the train - again, no reference to motion relative to absolute rest, just the deduction that absolute motion must occur for there to be relative motion.

    ---

    The clock will be imbued with horizontal momentum regardless of whether or not absolute rest exists, even assuming Minkowskian geometry. If Albert's train is in motion at all, then it will be imparted with a horizontal velocity; only if his train isn't moving will it not.

    We can apply this to all other observers such that, the only way that no photon will be imbued with horizontal momentum, is if no clock, train, or observer is moving. If no observer, train, or clock is moving then there would be no relative motion. That there is relative motion allows us to conclude that some obesrvers instruments must be contracted unknown to themselves.

    Again, you implicitly assume absolute rest. Here is your line of reasoning:

    Assume Absolute rest exists.
    Consider two observers in motion with respect to each other.
    Therefore at least one observer must be in motion with respect to absolute rest.
    Therefore absolute rest exists.

    We can just as easily consider two observers in motion with respect to each other, while assuming no absolute rest exists. The absolute motion in this case, is absolute motion between the two observers (I.e. If any observer is labelled at rest, the other will be labelled as in motion), and not absolute motion with respect to some state of absolute rest. Therefore, both reference frames, both labelling systems, are equally valid, and length contraction/time dilation emerges from the geometry relating the two arbitrary reference frames.
    The point being made is that it is consistent with the metaphysical position of absolute rest, and that absolute rest is tacitly assumed. We can do this by considering the position of absolute rest, that is compatible with relativity and then seeing what deductions can be made.

    No we can not. I have explained this before. By assuming absolute rest exists, we can show that relativity is consistent with the assumption. But to show that relativity implicitly assumes absolute rest, you must show a contradiction between "No absolute rest" and relativity.
    Absolute rest exists, and absolute rest doesn't exist are contradictory statements, so that relativity is compatible with both seems to make it contradictory.

    The contradiction lies in what you say above, that relativity is compatible with two contradictory ideas.

    Again, the contradiction lies in the fact that it is compatible with two contradictory ideas.

    They are not contradictions. Basic logic shows that two contradictory statements can both be consistent with a third statement. Consider the following three statements:

    1) P → Q
    2) R
    3) ¬R

    2) and 3) are contradictory, but both are consistent with 1), since 1) says nothing about 2) or 3). Similarly, since relativity assumes nothing about absolute rest, it is consistent with absolute rest, and no absolute rest.
    No contradiction exists between the notion of absolute velocity/motion and relative velocity/motion; hence no contradiction would exist between the idea that no state of absolute rest exists and ER.

    Leaving aside problems with the derivation, the conclusion "no contradiction would exist between the idea that no state of absolute rest exists and ER", means ER does not implicitly assume absolute rest.


  • Registered Users Posts: 2,552 ✭✭✭roosh


    Morbert wrote: »
    Again, you implicitly assume absolute rest. Here is your line of reasoning:

    Assume Absolute rest exists.
    Consider two observers in motion with respect to each other.
    Therefore at least one observer must be in motion with respect to absolute rest.
    Therefore absolute rest exists.
    But we don't start off by assuming that absolute rest exists.

    We start by considering only the relative motion between two observers. If we take the example of a door and a door frame, where the door starts off at rest relative to the frame, in the closed position. Subsequently, the door changes to the open position. Here we have only considered relative motion.

    The question is, how can the door go from being closed to open, without either the door, the frame, or both, actually moving i.e. without absolute motion - here we are not assuming absolute motion, we are deducing it.

    Of course, we can define a reference frame where the door is "at rest" and the frame is "in motion", and vice versa, but that just reiterates the idea that we cannot determine the absolute nature of motion i.e. we can't tell if it was the door that actually moved, or if it was the frame; we can, however, deduce that one of them, absolutely must have moved. How else could the door go from being closed to open?
    Morbert wrote: »
    We can just as easily consider two observers in motion with respect to each other, while assuming no absolute rest exists. The absolute motion in this case, is absolute motion between the two observers (I.e. If any observer is labelled at rest, the other will be labelled as in motion), and not absolute motion with respect to some state of absolute rest. Therefore, both reference frames, both labelling systems, are equally valid, and length contraction/time dilation emerges from the geometry relating the two arbitrary reference frames.
    Here you are saying that absolute motion is relative motion; absolute motion in this case, is absolute motion between the two observers; but that is a contradiction in terms.

    Again, it is easier to discern absolute motion by considering the scenario where two observers/objects start off at rest relative to each other and then start moving relative to each other. In order for relative motion to occur, one of them has to start moving in an absolute sense; this will inevitably manifest as relative motion, but still, one of the observers has to actually move in order for there to be relative motion.

    Morbert wrote: »
    No we can not. I have explained this before. By assuming absolute rest exists, we can show that relativity is consistent with the assumption. But to show that relativity implicitly assumes absolute rest, you must show a contradiction between "No absolute rest" and relativity.
    If relativity is consistent with the assumption of absolute rest, then we are perfectly entitled to start with that assumption and see what we can deduce.


    Again, the contradiction lies in the fact that relativity is compatible with two mutually exclusive assumptions.


    Morbert wrote: »
    They are not contradictions. Basic logic shows that two contradictory statements can both be consistent with a third statement. Consider the following three statements:

    1) P → Q
    2) R
    3) ¬R

    2) and 3) are contradictory, but both are consistent with 1), since 1) says nothing about 2) or 3). Similarly, since relativity assumes nothing about absolute rest, it is consistent with absolute rest, and no absolute rest.

    Leaving aside problems with the derivation, the conclusion "no contradiction would exist between the idea that no state of absolute rest exists and ER", means ER does not implicitly assume absolute rest.
    Absolute rest exists is a metaphysical assumption, which is incompatible with the other metaphysical assumption that absolute rest does not exist.

    Absolute rest exists + relativity is contradictory to Absolute rest does not exist + relativity.

    Regardless, however, we can still start off with the assumption of absolute rest and see what we can conclude, if relativity is consistent with that assumption.


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


    roosh wrote: »
    But we don't start off by assuming that absolute rest exists.

    We start by considering only the relative motion between two observers. If we take the example of a door and a door frame, where the door starts off at rest relative to the frame, in the closed position. Subsequently, the door changes to the open position. Here we have only considered relative motion.

    The question is, how can the door go from being closed to open, without either the door, the frame, or both, actually moving i.e. without absolute motion - here we are not assuming absolute motion, we are deducing it.

    Of course, we can define a reference frame where the door is "at rest" and the frame is "in motion", and vice versa, but that just reiterates the idea that we cannot determine the absolute nature of motion i.e. we can't tell if it was the door that actually moved, or if it was the frame; we can, however, deduce that one of them, absolutely must have moved. How else could the door go from being closed to open?

    Here you are saying that absolute motion is relative motion; absolute motion in this case, is absolute motion between the two observers; but that is a contradiction in terms.

    Again, it is easier to discern absolute motion by considering the scenario where two observers/objects start off at rest relative to each other and then start moving relative to each other. In order for relative motion to occur, one of them has to start moving in an absolute sense; this will inevitably manifest as relative motion, but still, one of the observers has to actually move in order for there to be relative motion.

    Your deduction implicitly assumes absolute rest. Your reasoning, which I have pointed out in the previous post, and which you have reiterated above, contains the following:

    1)Consider two observers in motion with respect to each other.
    2)Therefore at least one observer must be in motion with respect to absolute rest.

    2) does not follow from 1) unless you assume absolute rest exists.

    If relativity is consistent with the assumption of absolute rest, then we are perfectly entitled to start with that assumption and see what we can deduce.

    Again, the contradiction lies in the fact that relativity is compatible with two mutually exclusive assumptions.

    Absolute rest exists is a metaphysical assumption, which is incompatible with the other metaphysical assumption that absolute rest does not exist.

    Absolute rest exists + relativity is contradictory to Absolute rest does not exist + relativity.

    Regardless, however, we can still start off with the assumption of absolute rest and see what we can conclude, if relativity is consistent with that assumption.

    I don't think you are following what you are saying. We have the following propositions:

    P: Einstein's Relativity
    Q:Absolute rest

    It is, of course, true that (P ∧ Q) ∧ (P ∧ ¬Q) leads to a contradiction. This, however, has nothing to do with what either of us is saying. I am saying, if Einstein's relativity implies absolute rest, then Einstein's relativity and "no absolute rest", must lead to a contradiction. I.e.

    (P → Q) → ¬(P ∧ ¬Q)

    The contrapositive of this is

    (P ∧ ¬Q) → ¬(P → Q)

    I.e. If Relativity and "No absolute rest" are consistent, then it is not true that relativity implies absolute rest. And this is the case. I can, for example, assume relativity is true, and that there is no absolute rest, and they will be perfectly consistent with each other.

    In short, the fact that relativity is perfectly consistent with the assumption that there is no absolute rest means relativity does not imply absolute rest.


  • Registered Users Posts: 2,552 ✭✭✭roosh


    Morbert wrote: »
    Your deduction implicitly assumes absolute rest. Your reasoning, which I have pointed out in the previous post, and which you have reiterated above, contains the following:

    1)Consider two observers in motion with respect to each other.
    2)Therefore at least one observer must be in motion with respect to absolute rest.

    2) does not follow from 1) unless you assume absolute rest exists.
    I think the problem might lie in the assumptions being made about absolute motion.

    A common representation of absolute motion appears to say that absolute motion is relative to an absolute reference frame; this effectively says that absolute motion is relative, which, of course, would be a contradiction in terms.

    If we think of absolute motion as a simple "yes or no", or "either, or" question, then there is no need to assume an absolute reference frame. Indeed, this would be more in keeping with the idea of the all important, qualifying adjective "absolute".

    We can simply ask the questions "is X moving?" or "is Y moving?"


    This is something which most people take to be common sense; when driving down the road in a car most people would come to the conclusion that it is the car that is actually moving.

    Of course, the earth could be moving too, and the car along with it; but it is possible for the car to subsequently move again. Here, there is no need for an absolute reference frame, it is a simple question of whether or not something is actually moving. Something most people take to be common sense.


    Morbert wrote: »
    I don't think you are following what you are saying. We have the following propositions:

    P: Einstein's Relativity
    Q:Absolute rest

    It is, of course, true that (P ∧ Q) ∧ (P ∧ ¬Q) leads to a contradiction. This, however, has nothing to do with what either of us is saying. I am saying, if Einstein's relativity implies absolute rest, then Einstein's relativity and "no absolute rest", must lead to a contradiction. I.e.

    (P → Q) → ¬(P ∧ ¬Q)

    The contrapositive of this is

    (P ∧ ¬Q) → ¬(P → Q)

    I.e. If Relativity and "No absolute rest" are consistent, then it is not true that relativity implies absolute rest. And this is the case. I can, for example, assume relativity is true, and that there is no absolute rest, and they will be perfectly consistent with each other.

    In short, the fact that relativity is perfectly consistent with the assumption that there is no absolute rest means relativity does not imply absolute rest.

    Relativity is effectively a description of the universe; to say that a description of the universe where absolute rest exists is compatible with a description of the universe where absolute rest does not exist, is contradictory.

    But to say that there should be a contradiction between relativity and "no absolute rest" is an empty statement, particularly when the consequences of "no absolute rest" are functionally equivalent to treating specific reference frames as being at absolute rest.

    To say that relativity is compatible with "no absolute rest" is an equally empty statement if "absolute rest" is tacitly assumed; what needs to be demonstrated is the difference between the two, and how relativity is compatible with both. Simply stating that absolute rest isn't assumed isn't sufficient, when the issue is to demonstrate that it isn't tacitly assumed.


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


    roosh wrote: »
    I think the problem might lie in the assumptions being made about absolute motion.

    A common representation of absolute motion appears to say that absolute motion is relative to an absolute reference frame; this effectively says that absolute motion is relative, which, of course, would be a contradiction in terms.

    If we think of absolute motion as a simple "yes or no", or "either, or" question, then there is no need to assume an absolute reference frame. Indeed, this would be more in keeping with the idea of the all important, qualifying adjective "absolute".

    We can simply ask the questions "is X moving?" or "is Y moving?"

    "Moving", using the concept of notion in relativity, is a coordinate statement. I.e. It implies you are making a statement in the context of a coordinate system. So if you ask "Is X moving?", you are asking "Is X moving, according to an arbitrary coordinate system?". Hence, if you don't also supply the coordinate system, the question is meaningless. So "X is moving and Y is still." implies an arbitrary coordinate system, as does "Y is moving and X is still". They are both equally true statements.
    This is something which most people take to be common sense; when driving down the road in a car most people would come to the conclusion that it is the car that is actually moving.

    Science has repeatedly shown that intuition and common sense is not a reliable litmus test for what is and isn't physical. Just look at Quantum Mechanics for a variety of examples.
    Of course, the earth could be moving too, and the car along with it; but it is possible for the car to subsequently move again. Here, there is no need for an absolute reference frame, it is a simple question of whether or not something is actually moving. Something most people take to be common sense.

    To reiterate my above paragraph. You cannot use the word "moving" without some reference to a coordinate system. "Moving" does not exist independently from coordinate systems.
    Relativity is effectively a description of the universe; to say that a description of the universe where absolute rest exists is compatible with a description of the universe where absolute rest does not exist, is contradictory.

    But to say that there should be a contradiction between relativity and "no absolute rest" is an empty statement, particularly when the consequences of "no absolute rest" are functionally equivalent to treating specific reference frames as being at absolute rest.

    To say that relativity is compatible with "no absolute rest" is an equally empty statement if "absolute rest" is tacitly assumed; what needs to be demonstrated is the difference between the two, and how relativity is compatible with both. Simply stating that absolute rest isn't assumed isn't sufficient, when the issue is to demonstrate that it isn't tacitly assumed.

    This bit in red is the important bit. You are absolutely correct. "No absolute rest" is physically equivalent to the assumption that there is absolute rest. Hence, you cannot say relativity assumes absolute rest, since we can equivalently say relativity assumes no absolute rest. So instead, what we say is statements about absolute rest are not a part of relativity.


  • Registered Users Posts: 2,552 ✭✭✭roosh


    Morbert wrote: »
    "Moving", using the concept of notion in relativity, is a coordinate statement. I.e. It implies you are making a statement in the context of a coordinate system. So if you ask "Is X moving?", you are asking "Is X moving, according to an arbitrary coordinate system?". Hence, if you don't also supply the coordinate system, the question is meaningless. So "X is moving and Y is still." implies an arbitrary coordinate system, as does "Y is moving and X is still". They are both equally true statements.
    Fair enough, but that doesn't mean that an absolute reference frame has to be assumed for the purpose of absolute motion, because to suggest that absolute motion is relative would be a contradiction in terms.

    Morbert wrote: »
    Science has repeatedly shown that intuition and common sense is not a reliable litmus test for what is and isn't physical. Just look at Quantum Mechanics for a variety of examples.
    That's fair enough, but we're talking about what can be deduced from relative motion, and absolute motion is one such thing that can be deduced.

    Morbert wrote: »
    To reiterate my above paragraph. You cannot use the word "moving" without some reference to a coordinate system. "Moving" does not exist independently from coordinate systems.
    You can, we do it everyday of our lives; we talk about the earth orbiting the sun and the earth rotating, as opposed to the sun orbiting the earth; we talk about us moving as we walk down the street, as opposed to us walking on the spot while the world moves past us as though on a giant conveyor belt; we talk about an escalator moving up or down, as opposed to the entire universe shifting in such a way to give the same effect.

    All of these use the word "moving" without reference to a co-ordinate system; that the movement manifests as relative motion is secondary.

    That we cannot determine which is the true case does not mean that both are equally true, it simply means we cannot determine which is the true case; but we can deduce that one of them must be i.e. one of them must actually be moving, in an absolute sense.

    Morbert wrote: »
    This bit in red is the important bit. You are absolutely correct. "No absolute rest" is physically equivalent to the assumption that there is absolute rest. Hence, you cannot say relativity assumes absolute rest, since we can equivalently say relativity assumes no absolute rest. So instead, what we say is statements about absolute rest are not a part of relativity.
    To say that relativity assumes no absolute rest is an empty statement, because the assumption of absolute rest is implicit. That the two are functionally equivalent demonstrates the point, it doesn't invalidate it.


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


    roosh wrote: »
    Fair enough, but that doesn't mean that an absolute reference frame has to be assumed for the purpose of absolute motion, because to suggest that absolute motion is relative would be a contradiction in terms.

    That's fair enough, but we're talking about what can be deduced from relative motion, and absolute motion is one such thing that can be deduced.

    You can, we do it everyday of our lives; we talk about the earth orbiting the sun and the earth rotating, as opposed to the sun orbiting the earth; we talk about us moving as we walk down the street, as opposed to us walking on the spot while the world moves past us as though on a giant conveyor belt; we talk about an escalator moving up or down, as opposed to the entire universe shifting in such a way to give the same effect.

    All of these use the word "moving" without reference to a co-ordinate system; that the movement manifests as relative motion is secondary.

    All of those statements make implicit reference to a coordinate system. Walking down the street is moving "with respect to the street". Orbiting the sun is moving "with respect to the sun". Since all statements of moving make reference to a coordinate system, we cannot therefore infer an "absolute" reference frame where objects are "truly" moving, without the added assumption that absolute rest exists.
    That we cannot determine which is the true case does not mean that both are equally true, it simply means we cannot determine which is the true case; but we can deduce that one of them must be i.e. one of them must actually be moving, in an absolute sense.

    You cannot even deduce that one of them must be a "truer" case, because physics itself, not just experimental apparatus, is invariant in either case. I.e. To speak of a "correct" reference frame is physically meaningless.
    To say that relativity assumes no absolute rest is an empty statement, because the assumption of absolute rest is implicit. That the two are functionally equivalent demonstrates the point, it doesn't invalidate it.

    That the two are physically equivalent completely invalidates your point, as I showed earlier. If you cannot show a logical contradiction between relativity and "no absolute rest", then you cannot say relativity implicitly assumes absolute rest. This is why I have repeatedly asked you for a contradiction between relativity and "no absolute rest".


  • Registered Users Posts: 2,552 ✭✭✭roosh


    Morbert wrote: »
    All of those statements make implicit reference to a coordinate system. Walking down the street is moving "with respect to the street". Orbiting the sun is moving "with respect to the sun". Since all statements of moving make reference to a coordinate system, we cannot therefore infer an "absolute" reference frame where objects are "truly" moving, without the added assumption that absolute rest exists.
    We make plenty of unqualified statements such as "I am moving"; "I didn't move, you moved"; [on a train] "we're moving"; [in traffic] "we're not moving"; and many, many more.

    None of which refer to a reference frame; and none of which assume that absolute rest exists. Indeed, the idea of absolute rest isn't necessary for the concept of absolute motion. To say that absolute motion is motion relative to absolute rest is to say that absolute motion is relative motion, which is a contradiction in terms.

    Absolute motion is the idea of motion that isn't qualified as being relative to anything; it is a "yes or no", "either, or" question.


    While we don't need to assume that any object is in a state of absolute rest, we can use the concept as a purely hypothetical, mathematical construct for the purpose of deduction; we can't measure velocities relative to it, but we can make certain deductions about the physical world by considering it. Something you mention is entirely compatible with Einsteinian relativity.

    Morbert wrote: »
    You cannot even deduce that one of them must be a "truer" case, because physics itself, not just experimental apparatus, is invariant in either case. I.e. To speak of a "correct" reference frame is physically meaningless.
    The issue might lie in stating that we cannot say that one reference frame is more true than any other, and I wouldn't necessarily disagree with that; what we can deduce however, is that, at least one object must absolutely be in motion. This would have certain deductive consequences that would not, necessarily, be revealed by the mathematical reference frames.


    Morbert wrote: »
    That the two are physically equivalent completely invalidates your point, as I showed earlier. If you cannot show a logical contradiction between relativity and "no absolute rest", then you cannot say relativity implicitly assumes absolute rest. This is why I have repeatedly asked you for a contradiction between relativity and "no absolute rest".
    The statement that "relativity doesn't implicitly assume absolute rest" is a bare assertion fallacy; it's an empty statement.

    What you need to demonstrate is the difference between "no absolute rest" and "absolute rest" and how relativity includes one but not the other; because if there is no difference between them, then they are the same thing i.e. what you are asserting isn't absolute rest, is actually absolute rest.

    Bear in mind that the difference between inertial motion [that isn't absolute rest] and absolute rest pertains to the path length of a photon in a light clock.


  • Registered Users Posts: 170 ✭✭antiselfdual


    roosh wrote: »
    We make plenty of unqualified statements such as "I am moving"; "I didn't move, you moved"; [on a train] "we're moving"; [in traffic] "we're not moving"; and many, many more.

    Come on, that's the English language, not physics.

    Can you write down a single physical formula for motion which is equivalent to the statement that something is "absolutely moving"?
    roosh wrote: »
    None of which refer to a reference frame; and none of which assume that absolute rest exists. Indeed, the idea of absolute rest isn't necessary for the concept of absolute motion. To say that absolute motion is motion relative to absolute rest is to say that absolute motion is relative motion, which is a contradiction in terms.

    Motion by definition is something like "change in position with respect to time." Change in position is inherently relative because "position" is a physical property that depends on where you choose to measure from.

    Absolute motion would be motion with respect to an absolutely defined (valid everywhere in the universe) set of position measurements. The motion is relative to those measurements which can be used by anybody anywhere to see if an object is absolutely moving or not absolutely moving.

    For instance, if somebody is "moving" down a street then by that motion we mean that if we measure from the start of the street, or from one metre from the start of the street, that their distance from that point changes.

    If on the other hand we were walking beside this person at the exact same pace in the same direction then they have no motion away from us, so then they are not moving if we choose to measure all motion as motion with respect to our own position.

    There is no physical reason to say "motion with respect to the start of the street" is more fundamental than "motion with respect to my own position." However if there was a notion of absolute motion, ie if there was an absolute set of coordinates that someone walking down the street could use to measure the motion of somebody walking beside them, then they could try to say things like "this person is really moving, absolutely."

    Notice that when I say things like "someone walking down the street" that is not saying "someone is absolutely moving down the street." Someone walking down the street is an English sentence that in proper physical terms means just that another person placed at the start of the street measures the distance between them and the someone as changing.


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  • Registered Users Posts: 2,552 ✭✭✭roosh


    Come on, that's the English language, not physics.

    Can you write down a single physical formula for motion which is equivalent to the statement that something is "absolutely moving"?
    The english language, like language in general, evolved to allow us to communicate about our experience of the universe; Physics is just an extension of that, and where it uses the english language in its formulation, it isn't completely divorced from it.

    As for writing down an equation, I don't see why it is necessary; we only need to be able to make certain deductions, that don't necessarily involve any measurements or calculations.

    Motion by definition is something like "change in position with respect to time." Change in position is inherently relative because "position" is a physical property that depends on where you choose to measure from.
    Motion is also a state, the absolute nature of which cannot be determined by experiment.

    Absolute means
    Philosophy
    • a value or principle which is regarded as universally valid or which may be viewed without relation to other things
    So absolute motion would be the state of motion that may be viewed without relation to other things.

    Absolute motion would be motion with respect to an absolutely defined (valid everywhere in the universe) set of position measurements. The motion is relative to those measurements which can be used by anybody anywhere to see if an object is absolutely moving or not absolutely moving.
    This is saying that absolute motion is relative motion, just motion relative to an absolute reference frame. Absolute motion ins't relative motion, not least because it is possible to experimentally determine relative motion. It would also be a contradiction in terms.
    For instance, if somebody is "moving" down a street then by that motion we mean that if we measure from the start of the street, or from one metre from the start of the street, that their distance from that point changes.

    If on the other hand we were walking beside this person at the exact same pace in the same direction then they have no motion away from us, so then they are not moving if we choose to measure all motion as motion with respect to our own position.
    If someone is "moving" down the street then we mean that we can measure the change in distance from a given point, but also, we mean that the person is actively "doing the moving", while the street is passive.

    We don't say, as the univers shifted around the person, and the road behaved like a treadmill, so as to cause a change in distance between the person and the point of reference, as they pumped their legs; this is because we attribute the movement to the person walking

    Even if we cannot determine which scenario actually happened, we know that it must have been one or the other, otherwise there would have been no relative motion to measure; the person would have remained at rest relative to the street.

    Yes we can define a frame of reference which labels either as moving, but unless one actually moves, then there would be no relative motion to warrant those labels.

    There is no physical reason to say "motion with respect to the start of the street" is more fundamental than "motion with respect to my own position." However if there was a notion of absolute motion, ie if there was an absolute set of coordinates that someone walking down the street could use to measure the motion of somebody walking beside them, then they could try to say things like "this person is really moving, absolutely."
    We cannot say that "motion with respect to the start of the street" than "motion with respect to my own position" - let's call that A, and the reverse B - because we cannot determine if that is the case; what we can say, however, is that either A is mor fundamental than B, or B is more fundamental than A i.e. one is more fundamental than the other, we just cannot determine which one.

    Of course, both A and B could be true, but that would just further compound the idea of absolute motion.

    Notice that when I say things like "someone walking down the street" that is not saying "someone is absolutely moving down the street." Someone walking down the street is an English sentence that in proper physical terms means just that another person placed at the start of the street measures the distance between them and the someone as changing.
    It is an english sentence that attempts to characterise our experience of the physical world; it ascribes the act of motion to the person walking; notice that you don't say that the road is moving [like a treadmill], this is because we view the road as being passive in the scenario where relative motion occurs between us and the road.

    Of course, the road can be moving, as indeed it is, if the earth is in orbit or rotating; but being in motion with it, we can subsequently move again, along the surface of the earth.

    Again, we can define reference frames that label either the road or ourselves as moving, but unless one of us us actually moving, then there would be no relative velocity to cause us to label either as moving. We can't determine which it is, but we can determine it must be one or the other.

    Example
    Just to try and highlight the example again; you start off at rest relative to the road; in order for relative motion to occur either your walking must propel you forward, or you walk as though on a treadmill; those two scenarios account for the relative motion that is measured, but both are two different examples which entail relative motion.

    I don't doubt that you understand the difference.


  • Registered Users Posts: 147 ✭✭citrus burst


    I've been following this thread for a while now and have gotten a little lost. Roosh what do you mean by absolute motion? I saw the definition you wrote earlier, but it doesn't really make the idea clear. Its one thing to define something, its another thing to explain something and show that you fully understand it.

    For me the English word absolute, means in a physical sense, something that is observed to agree with all observers no matter how, when, where or what the measurement is taken or the theory is described . There are few instances in science where it is actually used, the only one I can think of is absolute zero.

    Any way from what I can see from what you say by absolute motion, this is an agreed upon reference frame, that the entire universe has decided is moving. No matter where the observer is or what they are doing they will all say it is moving, even if they are moving along with the absolute frame.

    My understanding could be wrong, but to me that seems a little unintuitive.


    As regard to relative motion
    roosh wrote: »
    If someone is "moving" down the street then we mean that we can measure the change in distance from a given point, but also, we mean that the person is actively "doing the moving", while the street is passive.

    We don't say, as the univers shifted around the person, and the road behaved like a treadmill, so as to cause a change in distance between the person and the point of reference, as they pumped their legs; this is because we attribute the movement to the person walking

    This is true, however in a relativistic sense. Although we know that we are doing the moving down the street, both scenarios are equal. Its just a matter of how you set up your initial coordinate system.
    roosh wrote: »
    Even if we cannot determine which scenario actually happened, we know that it must have been one or the other, otherwise there would have been no relative motion to measure; the person would have remained at rest relative to the street.

    This is not entirely true. We could set up a coordinate system where both the street and the person is moving, with the exact same consequences. Although it would be pointless and greatly increase the difficulty of the problem it can still be done.
    roosh wrote: »
    Yes we can define a frame of reference which labels either as moving

    True
    roosh wrote: »
    but unless one actually moves, then there would be no relative motion to warrant those labels.

    Also true, but it would be a terribly very boring universe, in an already boring universe with only a man and a street.:)
    roosh wrote: »

    We cannot say that "motion with respect to the start of the street" than "motion with respect to my own position"

    Again true, they are two different scenarios.
    roosh wrote: »
    - let's call that A, and the reverse B - because we cannot determine if that is the case; what we can say, however, is that either A is mor fundamental than B, or B is more fundamental than A i.e. one is more fundamental than the other, we just cannot determine which one.

    Again true, but not in the sense that you think. Neither is "fundamental," that is a bad choice of words. Both are scenarios that we arbitrarily set up to determine the outcome of the same event. Both are correct, both are equivalent and both are equal. Just a different way of looking at the same thing.

    roosh wrote: »
    Of course, both A and B could be true

    In fact both are true.
    roosh wrote: »
    but that would just further compound the idea of absolute motion.

    Again I need further clarification of what you mean.*
    roosh wrote: »
    It is an english sentence that attempts to characterise our experience of the physical world; it ascribes the act of motion to the person walking; notice that you don't say that the road is moving [like a treadmill], this is because we view the road as being passive in the scenario where relative motion occurs between us and the road.

    English has no place in science :pac:
    roosh wrote: »
    Of course, the road can be moving, as indeed it is, if the earth is in orbit or rotating; but being in motion with it, we can subsequently move again, along the surface of the earth.

    Think of a car and a tree. The tree sees a car coming straight at it at an alarming speed. The car sees a tree coming at it at an alarming speed. We know that the car is doing the "actual" moving ( I think this is what you mean by "absolute motion" ) however both are right. The tree didn't uproot and run at the car.

    Introducing the earth is an unnecessary complication, but we can still use it if we want.
    roosh wrote: »
    Again, we can define reference frames that label either the road or ourselves as moving, but unless one of us us actually moving, then there would be no relative velocity to cause us to label either as moving. We can't determine which it is, but we can determine it must be one or the other.

    This further increases my belief that you mean the "thing" doing the motion when you say "absolute motion." We are lucky (and unlucky) to have a stable reference frame that we call the earth, from which we can make all of our measurements. Most day to day measurements wrt to motion are made relative to this stable frame. As a result humans have a fundamental built in intuition about what moves wrt it. This is not to say that its correct. Essentially everything not moving (trees, buildings, mountains etc) is in the same reference frame as the earth, everything else is in a different frame. Its how we compare these reference frames that matters.

    We use the earth like the street in the earlier argument. For most its a good approximation of a flat infinite plane.

    Hope this all makes sense

    *Just had an idea, by absolute motion, do you mean the thing that is actually doing the motion?


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


    Instead of repeating what citrusburst and antiselfdual have said, I will ask you these question:

    If you believe there is a state of absolute motion, do you believe it is possible to not be in a state of absolute motion? What would you call this state?

    Hopefully these questions should illustrate why you are (perhaps unknowingly) presupposing a state of absolute rest in your understanding of motion.


  • Registered Users Posts: 2,552 ✭✭✭roosh


    Cheers Citrus, it's refreshing to not just get the usual reply that "actually moving" doesn't make sense. I will reply to individual points in your post, but just to say that you are correct in your interpretation, by "absolute motion" I mean "the thing that is actually doing the motion"
    I've been following this thread for a while now and have gotten a little lost. Roosh what do you mean by absolute motion? I saw the definition you wrote earlier, but it doesn't really make the idea clear. Its one thing to define something, its another thing to explain something and show that you fully understand it.

    For me the English word absolute, means in a physical sense, something that is observed to agree with all observers no matter how, when, where or what the measurement is taken or the theory is described . There are few instances in science where it is actually used, the only one I can think of is absolute zero.

    Any way from what I can see from what you say by absolute motion, this is an agreed upon reference frame, that the entire universe has decided is moving. No matter where the observer is or what they are doing they will all say it is moving, even if they are moving along with the absolute frame.

    My understanding could be wrong, but to me that seems a little unintuitive.
    I'm not sure if what you say later in the post supercedes this, but I will address it for the sake of clarity.

    By "absolute motion" I am not suggesting that there is an agreed upon reference frame, that the entire universe has decided is moving.

    My understanding of the term absolute is
    Philosophy
    • a value or principle which is regarded as universally valid or which may be viewed without relation to other things
    That is, the concept of a reference frame doesn't necessarily come into it. It is a statement about the absolute nature of motion, as opposed to the measurement of what that motion is relative to.

    The experimental test of the principle of relativity states that
    Any uniformly moving observer in an inertial frame cannot determine his "absolute" state of motion by a co-moving experimental arrangement.
    Tests of SR

    The term "absolute motion" I take to refer to a "state of motion", without necessarily qualifying it as being relative to something.


    Contextual understanding
    For some reason the idea seems to cause some confusion, but I think some contextual examples should help clarify the meaning.

    I see "absolute motion" as being a "yes or no" question, or an "either, or" question e.g.:
    "Is X moving?"
    "Is Y moving?"
    "Is X or Y moving?"

    None of these make reference to a reference frame, they don't qualify the statement with "relative to Z"; they are questions about the absolute nature of motion i.e. which one is doing the moving.


    Everyday examples
    An everyday example would be driving down the road; we can ask the question "is my car moving?" or "is the road moving?". Yes, the car is moving relative to the road, and the road is moving relative to the car - that is relative motion; but the question of which is actively "doing the moving", without qualifying the statement by adding "relative to X", is a question of "absolute motion".


    Even if we cannot determine which one is actively "doing the moving", we can deduce that, at least one of them has to be.

    As regard to relative motion


    This is true, however in a relativistic sense. Although we know that we are doing the moving down the street, both scenarios are equal. Its just a matter of how you set up your initial coordinate system.
    While we can define different co-ordinate labeling systems which label us as moving relative to the road, and the road as moving relative to us, and both those are perfectly equal; the question of "which one is doing the moving" introduces a disparity, which has logical consequences.

    They represent two different scenarios which result in the same, observed, relative motion, but we can make deductions about the physical consequences, that aren't necessarily revealed by co-ordinate labeling systems,

    This is not entirely true. We could set up a coordinate system where both the street and the person is moving, with the exact same consequences. Although it would be pointless and greatly increase the difficulty of the problem it can still be done.
    Apologies, I should have included that third possibility, but I find that it can, sometimes, help to deal with just the two contrasting possibilities and say that "at least" one of them has to be the case.

    The point is, essentially, wherever there is relative motion, at least one of the relatively moving bodies has to, actually, be doing the moving.

    Also true, but it would be a terribly very boring universe, in an already boring universe with only a man and a street.:)
    Very true; but it would narrow the number of possible answers to the question, "how many roads must a man walk down, before you can call him a man?
    :D

    Again true, they are two different scenarios.
    With different deductive consequences.

    Again true, but not in the sense that you think. Neither is "fundamental," that is a bad choice of words. Both are scenarios that we arbitrarily set up to determine the outcome of the same event. Both are correct, both are equivalent and both are equal. Just a different way of looking at the same thing.
    Again, apologies, I was trying to stick with the terminology that antiselfdual had used, for the purpose of explanation.

    While both scenarios are potentially two different ways of looking at the same thing, I wouldn't necessarily say that they are equal or equivalent; they each have different deductive consequences.

    The mathematical reference frames may be equivalent, or equally valid, but the mathematical reference frames don't allow us to make certain deductions, that considering the two physically different scenarios does.

    In fact both are true.
    I would say that both mathematical reference frames, which label each as moving relative to the other, are true; however, we cannot determine which physical scenario is the true one, or even if both are true; these physical scenarios are independent of the co-ordinate referencing system, despite the fact that the co-ordinate labeling system is entirely dependent on the physical scenario.

    While we cannot determine which of A, B, or C is correct, we can deduce that either A, B, or C has to be correct.

    And each one has different deductive consequences.

    Again I need further clarification of what you mean.*
    You are pretty much spot on with the "addendum"; I am referring to "the thing that is actively, or actually, doing the motion"

    Hopefully the above also helps to clarify it.

    English has no place in science :pac:
    Apparently so!
    :p

    Think of a car and a tree. The tree sees a car coming straight at it at an alarming speed. The car sees a tree coming at it at an alarming speed. We know that the car is doing the "actual" moving ( I think this is what you mean by "absolute motion" ) however both are right. The tree didn't uproot and run at the car.
    I would agree that we can define a reference frame which says the car is moving relative to the tree and a different reference frame which says the tree is moving relative to the car; I would also agree that it is the car that is doing the "actual" moving.

    However, we apparently cannot determine if the car is doing the "actual" moving; for all we know, the earth could be doing the "actual" moving and the cars wheels could just be rotating in the opposite direction to a giant conveyor belt, at the exact speed to offset the speed of the conveyor belt moving in the opposite direction.

    It think, however, that we can deduce that it is, at the very least, one or the other which is true; of course, the cars wheels could be turning at a faster pace than the conveyor belt and both could be true.


    All three scenarios would have different deductive consequences though, which is probably easier to determine if we introduce a light clock for each observer.

    Introducing the earth is an unnecessary complication, but we can still use it if we want.
    I would agree with that, that is why I generally tend to avoid it; we can equally consider just the relative motion between the earth and the sun, but the deductions would be the same.


    This further increases my belief that you mean the "thing" doing the motion when you say "absolute motion." We are lucky (and unlucky) to have a stable reference frame that we call the earth, from which we can make all of our measurements. Most day to day measurements wrt to motion are made relative to this stable frame. As a result humans have a fundamental built in intuition about what moves wrt it. This is not to say that its correct. Essentially everything not moving (trees, buildings, mountains etc) is in the same reference frame as the earth, everything else is in a different frame. Its how we compare these reference frames that matters.

    We use the earth like the street in the earlier argument. For most its a good approximation of a flat infinite plane.
    That is pretty much exactly what I mean, "the 'thing' doing the motion".

    My understanding though, is that everything in the universe is in every reference frame, it just depends on what the motion is measured relative to. That is, the sun is in the reference frame that labels the earth as "at rest", but the sun is labeled as "in motion relative to the Earth", and vice versa.

    The Lorentz transform then allows us to determine the co-ordinates of a different refrence frame, using the co-ordinates of any given reference frame,

    Hope this all makes sense
    Cheers Citrus, it did make perfect sense; I hope that what I said also made sense.

    *Just had an idea, by absolute motion, do you mean the thing that is actually doing the motion?
    Pretty much.


  • Registered Users Posts: 2,552 ✭✭✭roosh


    Morbert wrote: »
    Instead of repeating what citrusburst and antiselfdual have said, I will ask you these question:

    If you believe there is a state of absolute motion, do you believe it is possible to not be in a state of absolute motion? What would you call this state?

    Hopefully these questions should illustrate why you are (perhaps unknowingly) presupposing a state of absolute rest in your understanding of motion.

    If I can just turn the question around: if we can deduce that at least one observer, of two relatively moving observers, has to actually be moving i.e. has to be in a state of absolute motion, is it possible to be in a state of non-absolute motion; what would you call this state of non-absolute motion?

    This should hopefully demonstrate that it is a deduction, not an assumption.


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


    roosh wrote: »
    If I can just turn the question around: if we can deduce that at least one observer, of two relatively moving observers, has to actually be moving i.e. has to be in a state of absolute motion, is it possible to be in a state of non-absolute motion; what would you call this state of non-absolute motion?

    This should hopefully demonstrate that it is a deduction, not an assumption.

    The problem is we can't deduce such a thing. "Motion", in this case, means any coordinate system we use has to label at least one of the observers as in motion. That is all it means. You cannot deduce absolute motion, in the sense of an absolute velocity, from this.

    What is happening is you are deducing a specific concept of motion (The idea that no reference frame labels both observers as at rest), and then unknowingly switching your definition of motion to mean an absolute velocity.


  • Registered Users Posts: 170 ✭✭antiselfdual


    So after thinking about this my own explanation of this argument is the following:

    What you're saying is basically that if X perceives Y to be moving, and itself fixed, and we could also switch to the Y reference frame in which Y is fixed and X is moving, then it must be true that one of X or Y is "actually" moving, which you call "absolute" motion.

    The first point here is that your definition of "absolute motion" is not the same as the standard physics definition of absolute motion (as you yourself have said and which I did not realise at first). So I will therefore term what you are describing as "intrinsic motion." You argue that if both X and Y observe the other to be moving then one of them must have an "intrinsic motion" as otherwise no motion could have occurred.

    The problem is that this notion is completely unphysical, because even if we suppose that object X in some situation has an intrinsic motion we are always able to find a reference frame in which X is not moving (actually we can find an infinite number of reference frames in which X is not moving as well as an infinite number of reference frames in which X is moving). In fact we can describe all of the laws of physics in the reference frame in which X is not moving, and they will be as valid there as in a reference frame in which X is moving. Therefore it makes absolutely no physical difference if we regard X as to have "intrinsic motion" or not.

    As a result I think your argument that "something must actually be moving" is in some sense pure semantics, because there is no way you can draw a physical distinction between X having intrinsic motion or Y having intrinsic motion.


  • Registered Users Posts: 2,552 ✭✭✭roosh


    Morbert wrote: »
    The problem is we can't deduce such a thing. "Motion", in this case, means any coordinate system we use has to label at least one of the observers as in motion. That is all it means. You cannot deduce absolute motion, in the sense of an absolute velocity, from this.

    What is happening is you are deducing a specific concept of motion (The idea that no reference frame labels both observers as at rest), and then unknowingly switching your definition of motion to mean an absolute velocity.

    I think that is where the confusion lies; the purpose isn't to deduce the existence of an absolute velocity, it is to deduce something about absolute motion; that is, to deduce something about the nature of motion as opposed to its measurement.

    When we talk about motion with respect to a reference frame, we are necessarily talking about relative motion, not absolute motion. Absolute motion doesn't necessarily require a reference frame because it pertains to the nature, or state of motion.

    In general, where there is relative motion between two bodies we can determine three physically distinct scenarios which account for the relative motion, all of which make different statements pertaining to the nature of motion of the bodies involved. We can't deduce which scenario is the true one, but we can deduce that one of them must be, and with it that one of the bodies must absolutely be in motion.


  • Registered Users Posts: 2,552 ✭✭✭roosh


    So after thinking about this my own explanation of this argument is the following:

    What you're saying is basically that if X perceives Y to be moving, and itself fixed, and we could also switch to the Y reference frame in which Y is fixed and X is moving, then it must be true that one of X or Y is "actually" moving, which you call "absolute" motion.

    The first point here is that your definition of "absolute motion" is not the same as the standard physics definition of absolute motion (as you yourself have said and which I did not realise at first). So I will therefore term what you are describing as "intrinsic motion." You argue that if both X and Y observe the other to be moving then one of them must have an "intrinsic motion" as otherwise no motion could have occurred.

    The problem is that this notion is completely unphysical, because even if we suppose that object X in some situation has an intrinsic motion we are always able to find a reference frame in which X is not moving (actually we can find an infinite number of reference frames in which X is not moving as well as an infinite number of reference frames in which X is moving). In fact we can describe all of the laws of physics in the reference frame in which X is not moving, and they will be as valid there as in a reference frame in which X is moving. Therefore it makes absolutely no physical difference if we regard X as to have "intrinsic motion" or not.

    As a result I think your argument that "something must actually be moving" is in some sense pure semantics, because there is no way you can draw a physical distinction between X having intrinsic motion or Y having intrinsic motion.
    The argument only seems like semantics because there appears to be some dispute over what the concept of absolute motion means; I'm trying to use a more rigorous definition that accurately reflects the idea of "absolute" and pertains to the nature of motion. The standard scientific definition, which attempts to define absolute motion as being relative [to an absolute referece frame], is self-contradictory, and only relates to the measurement of motion. The term "intrinsic" is probably helpful in this regard.

    It's interesting that you should say that the intrinsic motion of a body is completely unphysical and then qualify it by saying that we will always be able to find a reference frame in which the body is not moving; when it is, of course, the abstract, mathematical reference frames which have no intrinsic physicality. The intrinsic motion of an object is entirely phyiscal, and is not dependent on mathematical reference frames.

    Indeed, once we establish the idea of intrinsic motion we can then proceed to see what deductive consequences that it has; which, of course, will be entirely phyiscal.


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


    roosh wrote:
    I think that is where the confusion lies; the purpose isn't to deduce the existence of an absolute velocity, it is to deduce something about absolute motion; that is, to deduce something about the nature of motion as opposed to its measurement.

    When we talk about motion with respect to a reference frame, we are necessarily talking about relative motion, not absolute motion. Absolute motion doesn't necessarily require a reference frame because it pertains to the nature, or state of motion.

    In general, where there is relative motion between two bodies we can determine three physically distinct scenarios which account for the relative motion, all of which make different statements pertaining to the nature of motion of the bodies involved. We can't deduce which scenario is the true one, but we can deduce that one of them must be, and with it that one of the bodies must absolutely be in motion.

    ---

    Indeed, once we establish the idea of intrinsic motion we can then proceed to see what deductive consequences that it has; which, of course, will be entirely phyiscal.

    That is the problem. You have not established the idea of intrinsic motion. We know that the motion of a body is reference-frame dependent, and we know that there are scenarios where no reference frame will label two objects as at rest. This in no way establishes intrinsic motion.


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