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Mass = gravity?

  1. Sep 14, 2003 #1


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    Eddington was not the only skeptic. Many physicists thought the waves predicted by the theory were simply a mathematical artifact. Yet others continued to further develop and test the concept. By the 1960s, theorists had showed that if an object emits gravitational waves, its mass should decrease. Then, in the mid 1970s, American researchers observed a binary pulsar system (named PSR1913+16) that was thought to consist of two neutron stars orbiting each other closely and rapidly. Radio pulses from one of the stars showed that its orbital period decreases by 75 microseconds per year. In other words, the stars are spiralling in towards each other -- and by just the amount predicted if the system were losing energy by radiating gravity waves.
    my understandig is that gravity is a curvature of spacetime
    so how does spacetime "radiate" away?
    quote,if object EMITS gravitational WAVES its MASS should decrease?
    so mass converted to gravity??
    Last edited: Sep 14, 2003
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  3. Sep 14, 2003 #2


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    Sure, as the quote says, gravity waves carry away energy. And if there is no other energy to carry away, mass energy will have to be depleted (a big if there). That is a completely classical computation of course: non-quantum.

    The answer to "what is waving" is, "whatever is curving". If youi don't like to think of a space time fabric, you can have variation of geometry: angles of triangles add up to 180.001o over here, but 179.999o over there.
  4. Sep 14, 2003 #3
    Re: Re: mass = gravity?

    Quantum Gravity predicts Quantum foam, at this link (within PF) there is a reference (9th & 10th posts) to a reading that tells of the recent evidential proof, concerning the latest discoveries, relative to "Quantum Foam".

    (It isn't there, so that theoretical aspect of Quantum theory appears "Now" as invalid)
  5. Sep 14, 2003 #4


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    Wolram your headline asks a question "mass = gravity?"

    It seems to me that is the wrong way to put it. May be better to say that mass is one of the things that CAUSES spacetime curvature or that causes gravity.

    Sometimes it can help to be confronted with a totally unintuitive fact. If you put a cannonball in the oven and heat it up, the cannonball acquires some additional mass and becomes slightly more attractive gravitationally.

    Any way you can pump energy into a system will increase its mass.

    The changes are mostly unmeasurably small but folks are very confident about this because the theory is so well established (goes back to a 1905 paper of Einstein and has been well and truly tested over the years)

    A system of two stars circling each other has some potential energy you can calculate from how far apart they are----if you could twirl them a bit faster so they swung wider apart this would pump energy into the system.

    as they orbit they send out a changing pull-signal---a wave--that could drive something else in their neighborhood and even run a delicate little machine---so this signal carries energy away from them

    so they have to spiral in closer together because energy is being bled out of the system

    and also the mass of the system gets less (like the mass of a cooling cannonball gets less as it cools)

    it would be difficult to measure the mass of two dense stars tightly orbiting each other except as a combined system

    (it would be tough to yank them completely away from each other and measure their masses separately-----everything would be disrupted and the numbers would not even work out very well----mass depends on situation to some extent---it is a property of the whole system and you have to be careful about "assigning" it to separate parts which arent in reality separate)

    in the combined system of the two stars, the energy of their interaction, their orbit, is actually a part of the combined system's mass!

    and as orbit energy is bled off by causing ripples in the grav field,
    the system's mass decreases

    mass does not equal gravity, but mass is one of the things that causes curvature and causes gravity

    there is a major equation that says

    curvature = (some constant times) density of energy and also pressure

    and the pressure part of that is usually negligible and
    the energy-density part includes mass

    so if one casually throws away stuff that is usuall neglible the
    major (Einst. 1915) equation says

    curvature = (some constant times) mass

    but remember that is a simplification you got by throwing away stuff that usually is comparatively small

    so mass, and more generally the concentration of energy in a region, causes gravity but is not quite the same as gravity

    I'm responding here as best I can to these 3 comments of yours
    hope these thoughts useful and not too disorderly
  6. Sep 14, 2003 #5


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    Re: Re: Re: mass = gravity?

    Mr. RP could you please post the names of the authors
    of that article you referenced

    You said:
    "What I read was in the Aug 29 issue of the Journal "Science", (The A.A.A.S.) Vol 301 #5637 on Pg; 1169"

    But my subscription ran out and I dont have a copy handy.

    If you tell me the authors (and title would help but is less important) then I can very likely find the preprint online.
  7. Sep 14, 2003 #6


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    thankyou MARCUS the penny has droped, i find it enjoyable
    when one can VISULISE a system, the vertical hold slips
    on mine sometimes but it is stabalizeing.
  8. Sep 14, 2003 #7


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    LOL, really like the analogy

    better to have VH problems than screen full of snow

    you and me both, like to keep adjusting screen to get better picture
  9. Sep 15, 2003 #8
    Re: Re: Re: Re: mass = gravity?

    God willing I will make the effort to aquire all of the relevant names of all of the relevant Authors.....TBC.......
  10. Sep 15, 2003 #9


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    Re: Re: Re: Re: Re: mass = gravity?

    If you dont have the information handy (dont want to put you to a lot of trouble) wait a bit. I might be able to find it online
    even without an authorname or title

    feeling guilty thinking of you riding your bicycle to the library
    on some dark night pursued by wolves and so on----sit tight
    and I or someone will get the reference
  11. Sep 15, 2003 #10
    Re: Re: Re: Re: Re: Re: mass = gravity?

    Thanks for the concern, the reward? here's ya goes....

    So Marcus it's "Adrian Cho" who was the writer of the article, that I read, citing works either published, (by now) or To be Published, (TBP) as comming from #1) Floyd Stecker Of NASA Goddard in Md relating to Observational evidence (TBP) in The Journal of Astroparticle Physics and the second #2) A Ted Jacobsen of the U of M Pub in Nature and coorelated to the expressed opinion of one Lee Smolin of the Perimeter Inst. For Theoretical Physics who makes the 'case' of Hypotheis V Experimental Evidence hence the clear Victor in that one being "Observational Evidence" thus resulting in an expressed 'Validation' of Einstein's understandings of "Universal workings".

  12. Sep 15, 2003 #11


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    Re: Re: Re: Re: Re: Re: Re: mass = gravity?

    Very much ok, thanks

    With Adrian Cho's name I can almost surely find a preprint in the arxiv!
  13. Sep 16, 2003 #12
    There is one more person whom I have neglected to mention, sadly, as that is the person who formulated the postulate that was followed as to seek the verification of the theory.

    God Willing I will go, and find that name, and post it, as well, as clearly that person deserves Accreditation for the work that they clearly did. They have/had demonstrated a depth of understanding of the current knowledge, and the pathway of testing from available obsevation, as to understand how to extract from the "Universal Flashlight" the needed reading.
  14. Sep 16, 2003 #13
    If I am reading it properly, then One Giovanni Amelino-Camelia, a Theoretical Physicist @ "The University of Rome, La Sapienza", was the postulator of the method of search. (what I have previously called "The Precept"....no, I am not the first to do that!)

    As per the Article, This is the person who suggested in 1998 that "Scutinizing Gamma Ray Burts" would be a method of revealling if Lorentz Invariance Held, or was Violated.
  15. Sep 16, 2003 #14


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    Thanks RP for your efforts and good offices here
    In fact I know a little of Giovanni A-C's work which
    has been referred to by several PF posters over the past few
    months. I did a search and came up with Tom and Thermonuclear
    though I seem to remember other references (maybe in attachments or pages linked-to) He seems to be a very prominent guy and might even be worth going to Rome to chat with.
    As it happens yesterday I was reading an article of Giovanni A-C,
    called "Quantum Symmetry, the Cosmological Constant and Planck Scale Phenomenology"
    This paper argues that if the cosmo constant Lambda is not zero (astronomers suggest it may be positive based on their observations) then the energy-momentum relation of special relativity is not quite right---but must be modified very slightly
    in a non-linear way.

    The observational evidence (which has now seemingly become famous frontpage stuff) is still very far from being conclusive so
    people are loudly arguing this way and that about observations
    of "gammaray bursts" and "crabnebula synchrotronradiation". It certainly has attracted a lot of attention and real interest on the part of astronomers! And old Roman Giovanni at "La Sapienza" is at the root of all this ruckus.

    I guess you may know some Italian (with a name like Parsons you are bound to:wink:) and Sapienza is their word for Wisdom which given the state of the scientific endeavor could strike you as ironical.
    Last edited: Sep 16, 2003
  16. Sep 16, 2003 #15
    So Sorry, but I am adopted, so my last name reflects little. But, I had known that Spaienza should have meaning like wisdom, from "Homos Sapiens"/"Wise man".

    But "Thanks!", just the same.
  17. Sep 17, 2003 #16
    I dont know why, but I've never thought about this before.
    Does this mean that any existing object with mass is losing its mass to gravity?
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