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What causes gravity

  1. Nov 23, 2011 #1
    what is the source of gravitational force

    will gravity be same for objects with same mass but with different content


    I can float a needle in air defying gravity with the help of magnets same time oort clouds are orbiting sun a light year away how could gravity be so weak and strong
     
  2. jcsd
  3. Nov 23, 2011 #2
    According to einstein, Gravity is cuased by bending the fabric of space time around an object. The effect would be similar to having a bowling ball on a blanket. If you put a tennis ball on the blanket, it would roll towards the bowling ball.

    The point here is that space consists of an external field, when you put mass in that field, it causes gravity.

    They have tons of toys online that "defy" gravity with the help of mangetism, just base your project off one of those toys.
     
  4. Nov 24, 2011 #3
    Thanks dude , crystal clear example !! fabric of space= blanket & celestial objects =balls of different mass ...,

    I think that's why heavier planets orbit sun on a slightly lower plane/torus than smaller planets coz heavier planets have mass to sink in to fabric may be that's why moon is above earth or may be it just came out of nowhere and got stuck in there

    theorys do make sense but hard to believe

    RIP einstein newton dirac
     
  5. Nov 24, 2011 #4

    sophiecentaur

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    I think you have over-simlified this one. The Sun is soooo massive compared with everything else in the solar system that that the orbits of the planets are pretty much totally dominated by the Sun's mass (99% of the whole mass of the Solar System) and do not depend on their own masses. The dip in the blanket is the same for all of them. The ball in a blanket model would be different for different masses of stars. (Or, indeed, when you're discussing the orbits of small satellites around various different planets - then the planets are the balls in their own bits of blanket)
     
  6. Nov 24, 2011 #5
    The source of gravity is gravitons. These gravitons are sub atomic particles emitted by anything that has mass. The more mass an object has, the more gravitons it emits.
     
  7. Nov 24, 2011 #6
    That is a conjecture, but I do not think anyone has tied it into general relativity or the framework of space/time, let alone proving the existence of gravitons.
     
  8. Nov 25, 2011 #7

    Drakkith

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    Gravitons are an aspect of quantum mechanics, since it has particles as force carriers for the three other forces. Unfortunately quantum gravity has yet to be successful, so currently they are merely hypothesized.

    One thing to remember about the ball on a blanket is that analogy only let's you visualize gravity in a 2d way. The moon is not above the earth, it orbits around us in 3d space.
     
  9. Dec 21, 2011 #8
    This blows my mind.What causes the object to sink in the fabric of space time?
     
  10. Dec 21, 2011 #9
    Well, one way to think about this is:

    If you drop a ball and it hits the ground, you observe that it stops and doesn't go through.
    What causes the ball to fall? Gravity
    What essentially prevents the ball from going through? The Strong Force, Weak Force and Electromagnetic Force.

    By seeing that, we can conclude that Gravity is relatively the 'weakest' of all the fundamental forces.

    Also, the force of gravity is given by an equation, Fg = GMm/d^2. Where the force of gravity between two object is the product of their masses and the Universal Gravitation constant, divided by the distance between them squared.

    I digress:

    Well, gravity is essentially the warping and bending of space-time due to an objects mass. A really neat way to see this, is if you search up a picture of the "Hubble Deep Field". You can see that light from galaxies are 'warped'. This warping isn't a defect, but actually a massive object in front of the source of light bends space-time around it, warping the light.

    I know this is a mess of information, but hopefully you can see a bit more clearly.
     
  11. Dec 21, 2011 #10

    Drakkith

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    Spacetime is not like a trampoline or other fabric. Objects do not "sink" into it. Spacetime is affected by mass and energy, commonly called "curving" or "warping", and the effect manifests as gravity. The effects are explained entirely within the framework of General Relativity, which is at heart a mathematical model, so there is no way to accurately describe it without using this math. Because of that the way it is described to most people as a fabric is only a visual aid and is not exact.
     
  12. Dec 21, 2011 #11

    sophiecentaur

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    The legendary Mr Higgs has a view on this.
     
  13. Dec 21, 2011 #12

    cmb

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    Not sure Prof Higgs is 'a legend' quite yet, as there is no current doubt over the evidence of his existence!

    "The eponymous Mr Higgs", perhaps?
     
  14. Dec 21, 2011 #13

    sophiecentaur

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    Anyone with a particle named after them (even one we haven't seen) is a legend by my standards. But I could also say he is wicked or that he rocks. Language changes.

    I look forward to the cmb boson emerging over at CERN haha.
     
  15. Dec 21, 2011 #14
    Finally a voice of 'reality'.
    Sinking in the blanket or trampoline is caused by earth gravity. There is no gravity ('force') to put a dent on the blanket if a massive ball is placed on the blanket in deep space.
    But I wonder if anyone has tried this:
    Take a 3-D drawing of the dent on a trampoline, then superimpose all images as the dent is rotated 360o and obtain a single 3D drawing. Just the way MRI people create 3D images. The final image will have no 'sink' or 'dent'. But we can call the space surrounding the 'massive ball' a 'field'.

    The bottom line is 'we do not know yet what causes gravity'.
     
  16. Dec 21, 2011 #15

    Drakkith

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    That is arguable. We know that gravity comes from energy and mass yet we do not know everything about it.
     
  17. Dec 21, 2011 #16

    sophiecentaur

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    That means we don't "know". Like all the other things we don't "know" but have partial models for. And we could have got it all really really wrong for any other circumstances but our own.

    One really should remember that analogies like trampolines are only very superficial and should not be used to 'prove' anything or to draw conclusions from. That just misleads the uninformed and is unfair to them.
     
  18. Dec 21, 2011 #17

    cmb

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    Should that be 'the bottom 4-space'? :shy:
     
  19. Dec 21, 2011 #18

    Nabeshin

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    I think there's an unfortunate misconception about the original question of causing gravity in the first place. It's all fine and well to say that energy warps spacetime, which alters the geodesics which is how we observe the 'force' of gravity, but one can equally well ask why it is the case that energy should warp it in the first place. The answer here is that it just does. We could probably dig around in string theory of some equally complicated theory of quantum gravity and tell you about interactions between fields and bosons and other things, but ultimately you can still ask 'well why do they behave like that?'

    If you see where I'm going with this, it's that science isn't about asking 'why' questions, but rather we like to answer the 'how' questions. If you ask me how gravity works, I can describe it to you very accurately by simply writing down the Einstein equations. Why do they work? Not sure, but I know they do to a remarkable degree of accuracy. Unfortunately, at some point you simply have to accept axioms about the world or else you're going to be lost in the doldrums of philosophy. When your axioms lead to predictions which contradict experimental evidence, then we revisit them in order to find axioms which will more accurately describe reality -- this is the way theoretical physics progresses.
     
  20. Mar 4, 2012 #19
    The effects of mass and of charges are very similar. They are on a different scale and charges are internal to matter but they behave in a similar way. Both the electro-magnetic field (polarized space - charges) and the gravity field (curved space - mass) have two functions. The primary function is an inertia effect and the secondary function is a gravity effect. The electro-magnetic field is caused by moving charges and gravity field is caused by moving mass. Both fields are caused by motion and cause motion.
     
  21. Mar 4, 2012 #20
    This is spot on.
     
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