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Lunar Recession

  1. Mar 25, 2007 #1
    Right. Even well-documented observations that do not fit easily into a
    preconceived notion of how the world should work, may be rationalized away
    or just neglected. One example of this is the observed mean acceleration
    [tex] {\dot n} [/tex] of the Moon; from lunar laser ranging experiments this has the value of about -13.8 arcseconds/(century)^2. Furthermore, the
    mean motion of the Moon [tex] n [/tex] is about .549 arcseconds/s.
    Now the interesting part is that to within one standard deviation,
    [tex]{\dot n}=-Hn[/tex], where H is the Hubble parameter.

    How should a real skeptic react to this fact?
     
  2. jcsd
  3. Mar 26, 2007 #2

    Pythagorean

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    I haven't done any astronomy (currently studying Lagrangian and Hamiltonian in classical mechanics) so I'm a little shaky, but I'm interpreting what you're saying is that the velocity of the moon depends only on it's location about its center of orbit.

    Until I understand what you're saying though, I can't see your point.
     
  4. Mar 26, 2007 #3

    Hurkyl

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    One appriate response is "So what?"
     
  5. Mar 26, 2007 #4
    I think he's stating a coincidence.

    A skeptic would probably say that looking in an enormous sea of facts and figures, you are bound to find some meaningless coincidences.

    Humans are VERY good at naturally finding patterns in nature. After all, that's what intelligence really is, at its core. Humans are not so good at separating meaningful patterns from coincident ones (correlation vs causation). Hence, superstition.
     
  6. Mar 26, 2007 #5

    Aether

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    This equation implies that the fundamental physical constants vary over cosmological time scales: e.g., the SI base units of time (the second), of length (the meter), and Newton's gravitational constant. That is an interesting proposition that deserves to be carefully examined. If it is presented in that way (e.g., as a proposal for further investigation), then a "real skeptic" (e.g., a scientist) should react positively. If however this is presented as a claim/conclusion, then a "real skeptic" should react by pointing out (directly or indirectly) that it is premature to be making claims/conclusions at this stage of your investigation.

    In this particular case for example, all spinning and orbiting bodies in the universe should also obey this equation if it is really true (e.g., not just a coincidence) for the earth's moon. Therefore, a claim/conclusion like this should at least be accompanied by a thorough analysis of the orbits of all planets and moons in our solar system, and of the observed spin-down rates of all known millisecond binary pulsars (this data is readily available in several online catalogs) before it is presented as a claim/conclusion.

    A good starting point for such an investigation would be to review this article: J.P. Uzan, The fundamental constants and their variation: observational and theoretical status, Reviews of Modern Physics, Vol. 75, April 2003, pp. 403-455.
     
  7. Mar 26, 2007 #6
    Taken in isolation, the equation just describes an observational fact. Attempting to implement the equation into a wider setting or theory is a different cup of tea.
    The question is if this equation represents something potentially significant or if it
    represents only a coincidence.
    The equation was presented as representing an observational fact, nothing more.
    The "real skeptic" would be asked for an assesment of the significance of this
    observation as basis for further investigation.
    Of course the equation should be significant for orbits of other bodies than the Moon,
    if it represents something more than just a coincidence. However, spin-down rates
    of millisecond pulsars is another matter, since by extrapolation, the equation should apply only to orbits. For spinning bodies, extrapolation of the equation would be more risky. Overgeneralizing is not a good thing.
    Yes, I am aware of this paper. For LLR data and their interpretation, see

    J. Chapront, M. Chapront-Touze and G. Francou, Astron. & Astrophys. 387, 700 (2002).
     
  8. Mar 27, 2007 #7

    Hurkyl

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    Contrary to popular belief, facts do not speak for themselves. Your post provided absolutely no reason why one would be interested in this fact, or what its implications might be. You never even raised the issue of whether the fact is interesting or significant. Asking, "so what?" cannot deny anything -- you haven't said anything that can be confirmed or denied!* "So what?" is exactly the question that prompts you to supply that missing information.


    *: except for the veracity of the fact, which I will assume for the sake of argument and because I'm too lazy to check it myself)
     
  9. Mar 27, 2007 #8

    Aether

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    Assuming that these numbers accurately reflect well-documented observations of LLR (Lunar Laser Ranging) measurements, and that you don't mean to suggest that they "do not fit easily into a preconceived notion of how the world should work" or that anyone has "rationalized away or just neglected" them; then it must be this statement of yours that you are saying does "not fit easily into a preconceived notion of how the world should work", and it must be this statement of yours that you are saying has been "rationalized away or just neglected":
    Right?

    Wrong. This equation describes a line extending from a time several billion years in the past when the Moon was first formed to a time several billion years in the future when the Sun will burn out. The LLR observations that you have presented so far might represent, at most, one single point on this line. If you are claiming that this line is a plausible one, then please show a plot of this line over the life-span of the Moon vs. the mainstream scientific estimate of what this line should actually be (e.g., where the total angular momentum of the Earth-Moon system is conserved over the time period).
     
  10. Mar 27, 2007 #9
    Sure, noone is disputing the numbers. However, the numbers (represented by the equation) also suggest that cosmology may be relevant to the Solar system, since the Hubble parameter pops up for no apparent reason. If cosmology is indeed relevant to the Solar system, that would be contrary to predictions coming from standard theory "how the world works".
    I agree that the equation should be shown to be consistent with paleo-geological data.
    However, these data involve the spin-down of the Earth (sedimentary tidal rhythmities)
    and usually a theory-dependent assumption (that the length of the year is constant).
    To compare the equation to these data, one would need a prediction of the spin-down
    of the Earth and a knowledge of the cosmic time variation of the Hubble parameter. To predict that, having a general theory yielding these predictions would be necessary. (One
    must also correct the data for any theory-dependent assumptions inconsistent with the
    theory one is going to test.)

    And by the way, the "mainstream scientific estimate" contains a free parameter (the paleo-geological tidal friction) which may be tweaked to give consistency with the data.

    In short, you ask too much since a general theory is needed to compare the equation
    to paleo-geological data.
     
  11. Mar 27, 2007 #10
    Well, according to standard theory, the Hubble parameter should have no
    relevance for the Solar system. Yet H pops up in the LLR data, and very close
    to the value found from cosmic observations. I would say that this is an
    incredible "coincidence". A second, independent Solar system observation is
    the infamous Pioneer anomaly, where the "anomalous acceleration" is close to cH.
    Another "coincidence", suggesting cosmic relevance where none should be.
     
  12. Mar 27, 2007 #11
    If you look through enough data, you'll probably find my birthdate, also. This just doesn't seem very convincing.
     
  13. Mar 27, 2007 #12
    OK, I have a challenge for you. Please show how the (inverse) time scale 10H (.1H or 100H or whatever) pops out naturally from the LLR data, or the Pioneer data. When you fail this challenge, maybe you will learn that some facts are not arbitrary and cannot be dismissed
    as such.

    And, since I am interested in how people assess inconvenient facts; what would it take
    to convince you that such a fact should be taken seriously?
     
  14. Mar 27, 2007 #13

    Ivan Seeking

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    It is okay to point out an interesting "coincidence", but without a mathematical model to support your assertion, we can't argue that a significant relation is found. And even if you did it would be inappropriate for the S&D Forum. If you have such a model that meets the specified criteria, you may post it in the Independent Research Forum
     
  15. Mar 27, 2007 #14

    Hurkyl

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    Does the standard theory predict the wrong value for the ratio of the mean acceleration and the mean motion of the moon? If not, then your premise is patently false. If so, then it's the disagreement with observation that's inconvenient; not that you can express it in terms of the Hubble parameter.

    This is part of why I strongly dislike implied arguments -- I don't know what you're trying to argue, and I don't know what you are assuming to make that argument. If it's not worth your time to say what you mean, then it's certainly not worth my time to guess at it!
     
    Last edited: Mar 27, 2007
  16. Mar 27, 2007 #15
    The standard theory does not "predict" any specific value for this ratio. Rather, the tidal
    friction term is a free parameter determined from the data, i.e., representing the
    difference between the calculated effects of the planetary perturbations and the LLR observations. This means that standard theory is consistent with a wide range of this
    ratio - yet the ratio that emerges from the data is the Hubble parameter. That's what
    makes it inconvenient - from a large set of possible values, a very special one is observed. But it seems that I'm the only person here who thinks that this is an incredible "coincidence".
    The only thing that I'm trying to argue is the incredibility and inconvenience of this "coincidence". Moreover I wanted to know how others assessed it. Ivan Seeking gave a clear opinion, you, however, seem reluctant to give an opinion.
     
  17. Mar 27, 2007 #16

    Ivan Seeking

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    I moved this GD and leave it up to Hurkyl to move or close it.
     
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