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Newton's law of gravitation.

  1. Oct 27, 2009 #1

    PrincePhoenix

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    What are the problems in Newton's law of universal gravitation? Please explain using simple physics if possible.
     
  2. jcsd
  3. Oct 27, 2009 #2

    arildno

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    1. First off, it is an "action-at-a-distance" force, meaning that any change happening at one locality generates immediately an effect at other places.
    That is, INFORMATION is spread at infinite speed throughout the universe.
    Newton himself was deeply dissatisfied with this, and regarded his universal law of gravitation as an ad-hoc formula, that probably wasn't entirely right.

    With Einstein's special relativity, physicists understood that information transmission speed CANNOT exceed the speed of light (a FINITE speed!!), and thus, that in this crucial respect, Newton's law had to be false.

    2. With Einstein's general theory of relativity, the interconnections of mass and space made for a fascinating solution:

    Space is NOT like the rectangular box Newton envisaged it to be, within which matter resided without changing the box itself.

    Rather, the presence of mass warps space(-time) itself, somewhat similar to that if you put a heavy ball on a linen sheet, you deform the linen sheet itself in that process.

    3. Thus, if you are to calculate CORRECTLY the orbit for, say, a planet very close to a sun, the envisaged box structure of space, as Newton's theory presupposes, distorts your calculations because you neglect the spatial warping due to the presence of the sun.
    This was, back in the 19th century, known as the anomaly of Mercury's orbit; the calculations simply didn't match the observations.

    Einstein's theory of general relativity rectified that flaw.

    4. Einstein's theory is entirely LOCAL, in the sense that a heavy object warps its local spatial region, and sends out information about its position&warp&mass at light speed (by means of yet unobserved gravitational waves).

    5. In some sense, you could say that gravitation is no longer a force that acts directly upon an object; rather, gravitation acts upon space, and objects close to that warped region moves FREELY (i.e, without being influenced by a force), but in curved paths, rather than "straight lines".

    Remember from Newton's first law that if an object is not under the influence of any force, it will move in a "straight line"; within general relativity, this holds as well, but because the space is warped/curved close to a massive object, that "straight line" (shortest distance between two points) will be a curved path instead (called a "geodesic")
     
  4. Oct 27, 2009 #3

    PrincePhoenix

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    Thank you. That helped a lot.
     
  5. Oct 27, 2009 #4
    What is wrong with explanation that small particles bombarding Earth, Sun and Moon from all directions and from directions which they can't bombard (space between earth and sun) apears smaller pressure than from those side from which they can bombard? Feynman was saying it's wrong because soon earth or whatever planet should soon stop, but if those particles fast enough and enough small (like atom size) then realy not nessasary some over explanation than that which was assumed by old civilisation which meaned Feynman. At least this theory which mentioned feynman shouldn't be such easy pushed away and at least mentioned in physical books in high school or 5-10 classes. How they can hide such things anyway?
    edit: also inductiom of this small particles by sun the earth, erth inducting moon, and sun rotation about galaxy is inducted by rotation of this galaxy and so on.
     
    Last edited: Oct 27, 2009
  6. Oct 27, 2009 #5

    ZapperZ

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    Because it is quackery.

    Would you prefer we teach everything that hasn't shown to be valid in high school classes? Do you know how quickly we have to keep changing those books once we figure out they don't work? Do you know how many of such theories have been shown to be FALSE?

    This "shadow" gravity effect has been discussed before, and it is off-topic to this thread. If you think there is a valid formalism for such a model, please use the IR forum, not here.

    Zz.
     
  7. Oct 27, 2009 #6
    But from philosophycal or whatever point of view it's still very small probability that enshtein theory of gravity can be right even do not taking in count that it is not finished.
     
  8. Oct 27, 2009 #7

    ZapperZ

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    Er... you are arguing physics based on PHILOSOPHY?

    Since WHEN is physics done this way, and since when is physics ever thrown by philosophy? Is it because you lack the empirical verification?

    Gravity may not be finished, but it certainly doesn't mean you are correct! That's the same tactic as that used by Intelligent Design folks. They have no evidence, so all they do is point to the apparent "holes" in Evolution.

    Don't try this at home, or in this forum. You're just making your argument looks even more foolish.

    Zz.
     
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