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Newtonian relativity

  1. Apr 18, 2012 #1
    The following discussion emerged under the topic "at rest" in Einsteinian relativity, and while out of place there it may be worth a little elaboration:
    Yes indeed. Newton developed a mechanics that uses Galilean relativity as a logical consequence of his model of the world that was based on such observations.

    Thus, to demand Newton to disprove Galilean relativity in order to support his model is a demand for self contradiction. Isn't that obvious?
     
    Last edited: Apr 18, 2012
  2. jcsd
  3. Apr 18, 2012 #2

    Dale

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    Yes. He should contradict/correct himself.

    Scientific assumptions should either be empirically justified or logically required from things that are empirically justified. The assumption of absolute time and space is neither, so it should be removed. That was Galileo's (correct) point, and would require that Newton contradict himself.

    Alternatively, he should find experimental evidence supporting the idea. Such evidence would necessarily refute his 3 laws, and would again require that he correct himself.
     
    Last edited: Apr 18, 2012
  4. Apr 19, 2012 #3
    I don't recall to have ever seen anyone claim that Newton's theory is self contradictory. I think that it's generally accepted that the theory is self consistent, and to me it always looked very logical, based on observations - even critics such as Mach did not state otherwise. Please present the apparent contradiction.
     
  5. Apr 19, 2012 #4
    Interestingly in the thread on Einsteinian relativity now another comment was added that to me sounds like an attack on Newton:
    Newton's scientific argument can be found here:
    http://gravitee.tripod.com/definitions.htm
    Press "cancel" and scroll to halfway in his Scholium.
     
  6. Apr 19, 2012 #5

    Dale

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    That is an excellent straw-man.

    Why don't you start with my premise, that scientific assumptions should be experimentally justified or logically implied, and attack my actual argument.
     
  7. Apr 19, 2012 #6
    I commented on your claim that Newton should have found an experimental violation of his theory of mechanics to justify his absolute space postulate. Perhaps my reply wasn't clear or incomplete; or perhaps we misunderstood each other. I'll try again. As his theory of mechanics is based on his postulates and relies on them, your demand for Newton to contradict himself doesn't make any sense to me. It suggests that Newton's theory as he developed it is illogical, inconsistent or not based on experiments.

    D_H and I referred earlier to Newton's explanation of his logic as based on experimental evidence, and I next provided a link to that section in which he set out the experimental basis for his mechanics, in disagreement with Leibniz. The therefrom following theory of mechanics is presented on the following pages. It establishes what we nowadays call Galilean relativity. In order to judge the argument that you have against this logical presentation, you should first present it.
     
    Last edited: Apr 19, 2012
  8. Apr 19, 2012 #7

    Dale

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    The point is that the absolute velocity postulate is superfluous, and it is not correct to say that his theory of mechanics relies on the idea of absolute velocity. It is a part of the theory that is unnecessary, as pointed out by Galileo and recognized by most everyone from Galileo on.

    Do you agree with my premise?
    (P) Scientific assumptions should be experimentally justified or logically implied

    Then my argument is as follows:
    (1) Absolute velocity is not experimentally justified
    (2) Absolute velocity is not logically implied
    (3) Therefore, absolute velocity should not be a scientific assumption

    (3) follows logically from (1) and (2) given (P). So if you disagree with (3) then please identify what you disagree with: (P), (1), or (2).
     
  9. Apr 19, 2012 #8
    The issue was between the model of Leibniz and the model of Newton, as elaborated for example here:
    http://www-groups.dcs.st-and.ac.uk/~history/HistTopics/Newton_bucket.html
    Quite, but not in absolute way: postulates and models should be allowed as basis of a theory. Else it's not really a theory - and it's just not how science works. Instead, one invents physical or mathematical models that could explain observations, preferably in a simple way. And if one has two models with different predictions, then if one of the two fits the observations, that's what one uses for the further theoretical development.
    The only alternative model of the time was the relative velocity model of Leibniz - and it didn't work. Newton's absolute velocity model did work, just as he explained. That is sufficient experimental justification for any theory of physics.
     
  10. Apr 19, 2012 #9

    russ_watters

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    I'm not sure I need/want to participate in this thread since Dale is doing great as always, but since my post was copied into it (which is fine), I'll give a quick $.02:

    1. I'm a big fan of Newton. Inventing calculus as a tool to help him figure out gravity is a genius two-fer. Einstein may have had 3 ideas worthy of Nobel prizes, but they were all basically separate. Newton, on the other hand, created one masterpiece as a mere stepping stone to a second. He may have been the all-time champ.

    2. I didn't intentionally challenge him with that post, but after reading the descriptions of Newton's position on the issue, it does indeed read like a direct challenge.

    3. The history is interesting to me too and it is now my understanding (just from reading here) that Newton's contemporaries noticed the superfluous nature of the assumption and pointed it out at the time, resulting in some controversy. That's fascinating to me.

    4. Learning about this mistake of his way invalidates #1 for me: Invention/discovery is an inherrently error-prone process.

    5. This is a little more than just an error due to insufficient information and incomplete development (as opposed to, say, Newton's gravity's conflict with GR). I agree with Dale that this error was Newton not adhering to the scientific method/process/way of thinking. But I'll cut him some slack on that: That had just been invented too!

    6. Though I just gave a genius a pass for an error I considered unforgivable by laypeople in another thread, there is no contradiction in my position there: The difference is 500 years, during which time the scientific process proved its mettle and the knowledge that was originally only accessable to all-time giants came down into high schools. But to clarify just a little:

    7. I'm fine with people being religious (if that's the origin of this error). But people should be self-aware enough to recognize when they are making a conscious choice to accept a non-scientific belief. But that isn't happening in the other thread. We're still discussing the issue precisely because one user refuses to accept that the error is, in fact, an error -- at least in a scientific context. Once again, Newton may have been guilty of the same thing (not being self-aware about his belief), since his statement about the rotating bucket implies to me that he believed the PoR wasn't really valid and that absolute time and space did exist and was identifiable experimentally. But also again, he didn't have anything anywhere close to the mountain of evidence and theoretical backing to climb out of in order to maintain that belief that today's crackpot does.
     
  11. Apr 19, 2012 #10

    russ_watters

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    Also, in reading the link, it appears to me that he recognized the contradiction and was looking for a way out, possibly involving rotation. He says at the end, essentially, that if rotation is absolute, then a rotating or orbiting object must be in absolute motion. It just seems like he doesn't get that that doesn't privide the bridge he is looking for.
     
  12. Apr 19, 2012 #11

    D H

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    No. Change the "or logically implied" to "and logically consistent" and I agree. To me, an axiom that is not testable is metaphysics, religion, or flubnubitz.


    Newton needed time to be absolute for religious rather than physical reasons. His absolute state and time are not testable; they are not a good starting point from the point of view of physics. His bucket argument does not require velocity to be absolute. What Newtonian mechanics does require is that rotation and acceleration are absolute, and that displacement and duration are invariant.
     
  13. Apr 19, 2012 #12
    Actually I agree with much of what you say; and as usual, I'll merely comment on where we strongly disagree:
    It's unclear to me if we completely disagree about the scientific method, or if you agree with me on the scientific method but, for some reason that escapes me, you think that Newton did not follow it.

    Best regards,
    Harald
     
  14. Apr 19, 2012 #13
    What do you mean with "testable"? For example, quarks and EM fields can not directly be tested; instead we measure effects that fit with the models. And do you disagree with the scientific method of model testing?
     
  15. Apr 19, 2012 #14
    I have the impression that this again questions the scientific method... Leibniz had a model of relative motion and Newton showed that it didn't work; while his model based on absolute motion did work. That's how model testing is done in physics. The resulting theory was a big success and it survived so long as no clear deviations were observed.
     
  16. Apr 19, 2012 #15

    russ_watters

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    I belive Newton did not follow the scientific method.
     
  17. Apr 19, 2012 #16

    Dale

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    Since you don't completely agree with the premise of my argument then there is no point in proceeding until we have resolved that. However, it sounds like my premise is not too far from something you would agree to completely, so perhaps I can agree to your version instead. Please write a premise that you would agree with "in absolute way" of the form:

    Scientific assumptions should ...
     
  18. Apr 19, 2012 #17

    russ_watters

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    There is no "directly" here. Quarks and em fields are testable.

    You are about to fall into the "true nature" trap. That is the philosophical belief that there is a "true nature" to things independent of our scientific models. This enables a non-religious justification of the absolute reference frame issue, for example. That is completely unscientific. In science, a phenomena or object is nothing more or less than the sum of its properties and behaviors. Quarks have testable properties and those properties is what they is.
     
  19. Apr 19, 2012 #18

    Dale

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    I agree 100%.
     
  20. Apr 19, 2012 #19

    A.T.

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    In what sense was Newton's model "based on" absolute motion? Is absolute (linear) motion a requirement for his model to work (give correct quantitative predictions)? Or is it just an irrelevant assumption that doesn't change the quantitative predictions of his model?
     
  21. Apr 19, 2012 #20

    rbj

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    regarding String Theory or M-Theory, are they metaphysics, religion, or flubnubitz? is it experimentally testable (i think the right word might be "falsifiable")?

    for (relative) speeds that are slow (w.r.t. c), isn't absolute time a reasonable axiom to draw from everyday experience? since Newton was a few centuries before Einstein or even Maxwell, he might consider a particle property of light traveling at a finite speed, but since this speed was sooo far faster than anything else he witnesses, i can totally understand why the absoluteness of time would be taken as axiomatic for that time. in fact, it continues to work for 99% of the mechanics we do today, including that of planetary and spacecraft motion.

    so i don't get either yours or Dale's critique of Newton's axiomatic insights of the day. they sure seem reasonable to me, but given them we would expect an absolute frame of reference for Maxwell's equations and we always seemed to put that in our own frames, as observers. eventually physicists started to think about testable consequences of that notion and hence the Michaelson-Morley experiment was conceived. even though Einstein must have known about M-M, he did not use it in his SR thought experiment. it was more of this insight that, if all constant-velocity observers have equal claim to being "at rest" (and they are at rest from the POV of their own frame-of-reference), then their laws of nature must be equal and they both should measure and observe c to be the same. that is sorta a logical consequence of Galilean relativity, but it's subtle, at least for the 17th century. he came to that insight without drawing explicitly on the negative result of M-M, but i imagine that he used that to reinforce his thinking.

    i wonder what Einstein would have done if there was some systemic mistake made in M-M and repeated experiments that caused them to conclude we were moving through the aether. he might have ignored it as non-sensical and proceeded with his development of SR.

    still, i don't see how Newton would have been expected to use any other axiom for time than he did, given the physical world he observed. and this lesson should apply to us today regarding SR and GR, QM, Standard Model, ΛCDM, etc. what we take now as axioms might be refuted by our descendants. for instance, the accelerating expansion of the universe surely left me slack-jawed in the 90s. i did not believe it at first, but unlike superluminal neutrinos (which i also didn't believe), the accelerated expansion of the universe is an observation that is standing the test of time and repeatability.
     
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