Sunday, January 05, 2014

Earth probably has no dark matter ring

Three days ago, Nude Socialist was probably the first source that mentioned a provocative suggestion.



In the article GPS satellites suggest Earth is heavy with dark matter, Anil Ananthaswamy mentions an unpublished proposal voiced by Ben Harris at a recent meeting of the American Geophysical Union.




Harris determined the Earth's mass from the trajectories of the satellites and his result was between 0.005 and 0.008 percent higher than a figure of the International Astronomical Union. So he decided that the extra mass is due to a 190-kilometer-thick ring of dark matter surrounding the equator because it was the coolest explanation he was thinking about even before he was trying to quantify the mass.




Call me a big skeptic. Harris hasn't incorporated relativistic effects – an omission that produces 10 miles of a new error in the GPS location every day. He has even failed to include the Sun's and Moon's gravitational effect on the satellites' trajectories. He's probably not terribly experienced and even if he were, the discrepancy doesn't seem too statistically significant – at most a few sigma.

Moreover, I have serious problems with his would-be explanation, too. I don't believe that dark matter would create rings above the equator. The Earth's spin is probably a negligible effect for particles such as dark matter. A static spherical halo or rings oriented in random directions would seem more likely to me (the direction of the galactic plane could be preferred).

Even more seriously, I don't understand why this dark matter should reveal itself as a difference between two measurement of the Earth's mass. For example, the Earth's gravitational field affecting the motion of the Moon has always included all "terrestrial dark matter components" as well, didn't it? It's not clear to me why his calculation should "see" the dark matter contribution while the others "shouldn't see" it.

So while I would find some dark matter concentrated around us exciting, I think that this particular line of argument isn't even half-baked. It is almost completely unbaked. An average particle physicist or cosmologist has several such crazy ideas every week – that's millions of similar ideas from the particle physics community every year. The procedure that allowed this particular one to generate a whole article in Nude Socialist seems incomprehensible to me. More precisely, I think that the primary factor is the lack of any quality standards.

15 comments:

  1. I'm not sure I understand all this, so let me get something straight, Luboš — you don't have any confidence in Harris's ring? Is that right?

    Good. But I hope you don't have anything else in there either, you big sceptic — even if scepticism is legal in Czechia.

    And this dark matter stuff? It sounds suspiciously like chocolate to me. It wouldn't be Harris's big chocolate 'starburst' ring you're really talking about here, would it?

    I do hope not. I think that kind of innuendo is highly offensive and most inappropriate on a serious blog and I think you ought to stick to physics.

    Of course, if it's God's big chocolate ring then that's OK. I never thought about it before but I suppose He must have one too.

    It does make me wonder about His mode of creation though and what He thinks of us, given our position in it.

    What a depressing thought.

    I think I'll stick to beer.

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  2. kashyap vasavadaJan 5, 2014, 2:06:00 PM

    I think at this point science does not have a solution to these questions. If you believe, religion , metaphysics or philosophy, whatever you may want to call it, has some ideas. So let us return to theoretical physics!!!

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  3. kashyap vasavadaJan 5, 2014, 2:13:00 PM

    Let me add something. Question of free will is connected to the deeper question of consciousness. That is not really subject to scientific method as defined today.

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  4. I saw this yesterday, and read that Harris didn't include relativistic effects. Then I noticed the very small discrepancy between his calculated mass and others, and pretty much immediately dismissed the idea.

    I think Harris was looking for attention or, perhaps, some silly "journalist" seized upon a chance remark he had made.

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  5. Stephan Adler, of Princeton's IAS, perhaps at the behest of one of the DAMA scientists, briefly looked at a dual dark matter rings or shells with regard to resolving the flyby anomaly. The hypothesis made no distinctions whether the orbit was hyperbolic or not. Hence, when confronted with data from closed orbit craft, predictions were wrong by orders of magnitude except for the craft suffering the anomaly. The inconsistency was sufficient for Adler to claim the hypothesis falsified. All the same, he awaits the results from the JUNO flyby.

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  6. 1) http://arxiv.org/abs/1306.5534
    2) http://relativity.livingreviews.org/open?pubNo=lrr-2006-3&page=articlesu9.html
    http://en.wikipedia.org/wiki/Apache_Point_Observatory_Lunar_Laser-ranging_Operation
    3) GPS corrections, precision geoid orbital measurements like GRACE (gravity recovery and climate experiment); LARES (Laser Relativity Satellite,
    4) bullshit

    If dark matter can be gravitationally bound into a tight belt orbit, then the entire Tully-Fisher curve fit rationalizing spiral galaxies' persistence disappears. Why would the Earth have such a belt, but not Jupiter (correlation of moons' orbits) and Saturn (rings' orbits)?

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  7. "For those not familiar with type theory, the “axiom” of choice is in fact a theorem..." http://existentialtype.wordpress.com/2012/08/09/churchs-law/
    Type theory is not set theory.

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  8. Dear Lubos



    I am a little surprised with not finding the Computable Universe
    hypothesis' in yours and Sabine's blogs memos about free will. There is ample discussion currently about it
    (see http://www.mathrix.org/experimentalAIT/ComputationNature.htm) and with it
    there is a lot of discussion about free
    will. I am not a qualified expert on
    this subject but It happens that I just finished a police thriller novel in
    Spanish (Asesino de Dios, God's
    Killer) to be published soon. I did some reading on the Computable Universe
    theory which supposes that our universe is composed of Cellular Automaton in
    which the evolution of each cell is deterministically governed by (i) a rule or key (which could be
    equivalent to the Theory of Everything, ToE, written in 1's and 0,s), and (ii)
    the initial conditions of the Automaton. This hypothesis is central to my story,
    and my main character (and I think myself too) arrived to the conclusion that
    given the same initial conditions and same rule for ToE, the universe will
    evolve exactly the same each time it is
    reproduced. True, there will be at times
    locations in the universe evolving in complexity conditions, making it
    impossible to determine a priori any
    outcome, situation that some scientists have taken as a proof that free will
    exists (v.g. Wolfram, see
    http://www.philosophytogo.org/wordpress/?p=1880). But being the final outcome determined from
    the start of times, How can one have any free choice?



    This comment is just to call the attention on this subject. Forgive me for any misinterpretation I have
    made to the Computational Universe hypothesis, but as I explained above, I am
    not a qualified expert on this subject.



    Regards

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  9. Venus doesn't have a ring around it either, be it dark matter or comet dust, but that doesn't make this planet any less beautiful than Saturn.

    Counting stars by candlelight, all are dim but one is bright;
    The spiral light of Venus, rising first and shining best,
    On, from the northwest corner, of a brand new crescent moon,
    While crickets and cicadas sing, a rare and different tune,
    Terrapin Station

    http://www.youtube.com/watch?v=GAIvo6QkOgc

    I'm not much of a Grateful Dead fan, never have been nor will I ever be, but Terrapin Station 1977 has got to be, despite what the critics say, one of the finest rock songs ever written. It is sixteen and a half minutes of pure brilliance, both in terms of music and lyrics.

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  10. Mark Twain got the preprint. That explains his comment: "...Science. One gets such wholesale returns of conjecture out of such a trifling investment of fact."

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  11. Well, for how long analysing the data takes? Flyby happened approx. three months ago :-) God damn!

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  12. "It seems much wiser to me to define the free will of a human or an object as"

    Yes, you can define it to fit your view, but we must take what philosophers and theologian consider to be: causal decoupling of human decisions by God's will (or God's laws). So, I think Sabine's definition is the right one.

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  13. Hi Lubos, sorry to bring this point to the discussion a bit late, but you're wrong about the moon's orbit not 'seeing' any discrepancy.

    You say "I don't understand why this dark matter should reveal itself as a difference between two measurement of the Earth's mass. For example, the Earth's gravitational field affecting the motion of the Moon has always included all "terrestrial dark matter components" as well, didn't it? It's not clear to me why his [Ben Harris's] calculation should "see" the dark matter contribution while the others "shouldn't see" it."

    Before Adler's flyby anomaly paper, he found a similar kind of discrepancy by calculating the Earth's mass in two different ways, one via the moon's orbit, the other via Lageos.
    http://iopscience.iop.org/1751-8121/41/41/412002/fulltext
    He set a limit of no more than 4e-9 Earth masses for the amount of DM that might be between the two orbits.

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  14. Thanks, but I don't understand the comment. Moon's orbit follows - at a huge accuracy - Newton's equations or Kepler's laws with the total mass being the whole mass in the ball of radius 380,000 km centered at the Earth. Everything that is this close enough to the Earth - less than the Moon - and that is perhaps spherically symmetrically bound to the Earth contributes to the gravitational field.


    Another speculation would be that the field is significantly spherically asymmetric. Some asymmetry or anisotropy is caused by the Earth's being an approximate ellipsoid. The other effects are almost certainly much weaker.

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  15. Well, I expect Adler's figures are nearer the mark than Harris's, but until we get numbers that are the same from all calculations the question remains, particularly in the light of the flyby anomaly.

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