Gravity's mechanism

Discussion in 'Physics & Math' started by quantum_wave, Feb 4, 2013.

  1. Lakon Valued Senior Member

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    1,117
    Still doesn't answer the simple question. What CAUSES an object to move along the supposed curved space in the first place ? Geometric theory represents motion - it doesn't cause it, any more that the French language causes the Eiffel Tower
     
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  3. Motor Daddy Valued Senior Member

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    The cause of an object following a curved space around an axis is clear, the greater the distance away from the axis the greater the rotational velocity about that axis. In order to maintain a rotational velocity about an axis there must be an outward force maintaining that acceleration. Yes, I said that correctly, acceleration, because along the radius in a straight line, each point has a different rotational velocity. In order to keep different velocities along the same radius there must be an acceleration between every point. Nature is purely geometrical, and these things are not trivial matters. This is why the universe works the way it works, because of geometry.
     
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  5. Q-reeus Banned Valued Senior Member

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    Quite sure about that last bit?

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    Anyway, as to first point, get used to the formalism in SR/GR that assigns an (locally) invariant 4-momentum to every material particle. In this formalism, even in a frame where one is nominally at rest, there is still 'movement' at velocity c in spacetime - which is not just space. The animations linked to in #20 try and show this in the spacetime diagrams there - note the free falling apple automatically is moving through a straight line in spacetime. And it just so happens in that setting it also falls in a radial straight line through space. To repeat, continual motion through spacetime is an unavoidable mathematical feature in SR/GR. If you want more formal and precise mathematical explanation just try Googling spacetime, or maybe wait till a fully qualified boffin steps in here with heavy math. Sorry if this still doesn't help. But then I'm a bit sorry to find so little feedback here at SF, appreciative or not.
     
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  7. A.T. Registered Member

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    It's not curved space, but curved space-time. The advance in space-time is simply a postulate of the theory. Even if you are rest in space, you still advance in space-time, along the time dimension.

    Not "motion" in the common sense, but rather advancing in space-time.

    Physics in general doesn't cause anything. It just says how things behave.
     
  8. Lakon Valued Senior Member

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    1,117
    I still suspect that spacetime is a fairytale - a mathematical abstraction at best.

    http://www.sciforums.com/showthread.php?122827-Spacetime-Is-a-Fairytale&

    Thank you for trying, but you haven't answered my simple question in terms I can understand. Much of the above is beyond me. You should be able to tell me what compels an object to move in space, along the so called curvature of it.

    Edit grammar last paragraph
     
    Last edited: Feb 16, 2013
  9. Lakon Valued Senior Member

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    1,117
    Geometry is a measurement (metry) of earth (geo), but OK, leave out the 'geo' as we've superceded it - still, geometry is measure.

    How can measurement be(the)cause of the workings of the universe ?

    I measured a pint of milk being poured into a jug. Did my measurement cause the milk, flow, etc ?
     
  10. Lakon Valued Senior Member

    Messages:
    1,117
    Ah, but that is another thing. We advance in time, while we're in space, of course.

    How does an object at rest relative to the earth move along some curvature of space as a substitute to Newtonian gravity ? What force motivates it to so move ?
     
  11. Lakon Valued Senior Member

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    1,117
    PS, MD - I find your explanation of gravity, above, odd and confusing. I drop a ball. It doesn't seem to me to move around any radial path .. or whatever. It just seems to be moving straight down in a path toward the earths centre. Some VERY sensitive measuring instruments rely on that fact too.
     
  12. Motor Daddy Valued Senior Member

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    So what you are saying is that basically there is a straight line from the object to axis perpendicular to the axis, and the object will travel towards the axis along that line when it "falls," correct? So am I correct to assume that you also believe that the earth is rotating about that axis continuously? So if I look at that line from the axis to the object from atop the north pole of the earth, which direction would the object be falling along that line, in a spiral fashion, or a straight on that line at all times direction?
     
  13. Lakon Valued Senior Member

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    1,117
    Why not just go the full hog then, and look at it from a galaxy far far away ? Then you will observe it moving in all manner of spirals, trajectories, etc, and probably at close to the speed of light !
     
  14. A.T. Registered Member

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    73
    Again, not space but space-time.

    No force is acting if something advances in space-time on a straight path. But when space-time is distorted, then advancing on a straight path in space-time means that you will deviate from the purely temporal advance, and start advancing along the spatial dimensions too. That's exactly what the video shows:

    [video=youtube;DdC0QN6f3G4]http://www.youtube.com/watch?v=DdC0QN6f3G4[/video]
     
  15. Motor Daddy Valued Senior Member

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    5,425
    You mean like this? Do you see the mass moving away from the center or moving towards the center?

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  16. Lakon Valued Senior Member

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    1,117
    Saw the video .. sigh ..

    We curve all of space and time just to keep an apple falling striaght .. and without force ..
     
  17. Lakon Valued Senior Member

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    1,117
    Away .. but my apple is still falling in a straight line toward the centre of the earth relative to it.
     
  18. Motor Daddy Valued Senior Member

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    You skirted my questions in an attempt to avoid the task at hand here. Please answer the questions I asked you to answer in #29. Spiral or straight? Rotation or not?
     
  19. A.T. Registered Member

    Messages:
    73
    Correct.

    And there are good reasons for it:
    - An accelerometer in free fall on Earth measures zero, just like an accelerometer in space with no force on it.
    - The distortion of the time dimension explains why clocks run at different rates, when placed at different heights.
    - The distortion of the space dimension explains light bending at the sun and orbit precession more accurately.

    See also:
    http://www.physics.ucla.edu/demoweb..._and_general_relativity/curved_spacetime.html

    Of course everyone still uses Newton when possible, because the math is much simpler.
     
  20. OnlyMe Valued Senior Member

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    3,914
    This much is accurate.

    Not so much in the above.

    Both are descriptions of what happens not how or why it happens. They describe rather than explain.
     
  21. Motor Daddy Valued Senior Member

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    No, the cause of the milk flow is directly related to the second law of thermodynamics.

    So, thermodynamically in your brain (through the process of increasing entropy) you created what is commonly referred to as an "idea." That idea of yours caused the milk to flow.
     
  22. A.T. Registered Member

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    73
    That's true for all physics. Newton didn't explain why there is a gravitational force either.
     
  23. Motor Daddy Valued Senior Member

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    I have an alternative explanation, and that is that the "explanation" for all things is that mass evolves to space. All things exist through the evolution of entropy increasing.
     

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