Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Cause of Gravity?

  1. May 18, 2009 #1
    Now this is something that just came to mind. As an undergrad Physics major, I have already taken a few introductory Physics courses. We have studied gravity, electromagnetic forces, etc. All of the work we have done involved measuring these forces and understanding how a body will react while under the influence of said forces. Anyway, have scientists been able to figure out why these forces exist? For example, we know that the gravitational force explains why the Earth orbits the Sun the way it does. But what causes this attractive force? The same applies to the electromagnetic force.

    Have I missed something really important, or is there no explanation for this as of yet?
     
  2. jcsd
  3. May 19, 2009 #2
    To my understanding [I'm no physicist, just a hobbist nerd], the leading theory for gravity is General Relativity. In a nutshell: GR states that space-time bends in the presence of mass. Things just follow the natural path of this curved space (light included).

    Imagine a straight line drawn on a sheet of paper (a really big one). Now, find a spot of your preference [on the line] and press down with your finger: your line will bend, depending on how much force you apply. Mass is the equivalent of your finger in the real world. Objects passing by this curvature will tend to fall into it, depending on how big they are and how fast they're moving.

    The sun bends space-time around it; and the Earth just follows what "it thinks" is a straight line on this curved space.

    As for EM.. I have a vague idea (flow/exchange of electrons) but I'll let the EM-versed people speak up.
     
  4. May 19, 2009 #3
    That's pretty much it. Going further down into particle physics we have this theory of the graviton:

    http://en.wikipedia.org/wiki/Graviton

    Here is another analogy for the what JRPB described:

    Imagine a bunch of people holding a circular tarp and pulling on it as hard as they can. Then someone puts a bowling ball in the centre. The centre of the tarp sags down, no matter how hard the people pull. If you were to put a ball on this tarp it would roll into the centre.

    It's pretty much that, but in three dimensions.
     
  5. May 19, 2009 #4
    mass or energy bends space-time
     
  6. May 19, 2009 #5
    Aye, good ol' [tex] E = mc^2[/tex]
     
  7. May 19, 2009 #6
    Hi there,

    Remember that these theories are terribly far, and some of them, like for the graviton, have not yet been measured experimentally.

    The graviton is a particle imagined by the theorist to explain gravity. Many experiments are underway to try to detect and isolate this graviton, but (to my knowledge) without success, yet.

    Cheers
     
  8. May 19, 2009 #7
    Ah yes. The Large Hadron Collider. So big they can't even get it to stay on.

    I wonder though, if matter moves toward the centre of a gravitational field, then would anitmatter move away?
     
  9. May 20, 2009 #8
    Hi Lancelot59,

    Anti-matter is matter of another type. In a gravitational field, anti-matter would react the same way as matter, by being attracted by it.

    Anti-matter is a name given by scientist to try to understand and come up with a symetric Universe. Since its discovery, our view of the Universe has made a leap forward. Therefore, nowadays, you should understand matter/anti-matter as two particles that are created from energy. From many different conversation principles, in Earthly labs, when a particle of matter is created, its anti-matter counter part is also created in the process. There is not much difference between an electron and a positron, except for the fact that the positron has a positive charge +1e. Otherwise, they are identical in every way.

    Cheers
     
  10. May 20, 2009 #9
    anti-matter would not move away , beacuse the graviton is its own anti particle .
     
  11. May 20, 2009 #10
    this might be a dumb question but i was just wondering could the photon be the particle of gravity .?
     
  12. May 20, 2009 #11
    Hi there,

    I would bet my kids study fund into it. Photons are particles carrying energy through an electro-magnetic field.

    Cheers
     
  13. May 20, 2009 #12
    so ur saying it is possible .
     
  14. May 20, 2009 #13

    Pengwuino

    User Avatar
    Gold Member

    That doesn't really connect mass/energy to gravity.

    This is definitely not the case. General Relativity has predicted various empirical observations that had previously gone unexplained so at least in GR's case, theories aren't necessarily untested.
     
  15. May 20, 2009 #14
    Hi there,

    Being from the experimental field, I still believe that theories are great, but without further experimental results, they stay at a theory level.

    On top, I never said that graviton don't exist, just that there existence have not yet been proven experimentally.

    On the other, history tought us, that even though a theory exist and is well anchored into people's mind, does mean that it is reality. Therefore, I a firm believer in confirming these theories with experimental results.

    Cheers
     
  16. May 20, 2009 #15
     
  17. May 20, 2009 #16
    Firstly, İ' m sorry for my english grammatical mistakes and word of which i use in this text.may be it isnt true.

    İn QM we need a space,it is called hilbert space.Features of hilbert space are ortogonal,has n dimension...
    QM need hilbert space because We use operators for dynamic variables.
    same the QM,General Relativity needs a space for to work.But different from classical mechanics,General relativity use 4 dimension for space-time coordinats.
    The mass curved the space-time in its vicinity.so there arent any forces for moving around the sun or any mass.There are geodesics where the mass moving.These are orbits of mases.
    There arent any forces,there is only curved space-time,so Gravity is a geometry.
    we know that in QM we solve schrıdinger equation for positions or energies of particles.Schrodinger equation not same Newton's equation; F=m.a;
    Schrodinger Equation is provided the conversations of energy not force law.however we use geodesics equation for positions of bodies.

    sorry for many mistakes thet i do.
     
  18. May 20, 2009 #17

    ShawnD

    User Avatar
    Science Advisor

    This is one thing about physics I don't get. We say gravity is basically a fourth physical dimension called "space time" which we can't see, but we just assume it's true because the math fits and it's a fairly good working model. Without skipping a beat, the same physicists who accept space time will reject gravitons and string theory because we can't detect gravitons. My holy book says trampoline (space time) while your holy book says messenger particle (graviton).

    spacetime (accepted model)
    graviton (untested, proposed by string theory)
    field carrier particles (why someone might think gravitons are real)
     
  19. Jan 10, 2010 #18
    In QM we need a space,it is called hilbert space.Features of hilbert space are ortogonal,has n dimension...
    QM need hilbert space because We use operators for dynamic variables.
    same the QM,General Relativity needs a space for to work.But different from classical mechanics,General relativity use 4 dimension for space-time coordinats.
    The mass curved the space-time in its vicinity.so there arent any forces for moving around the sun or any mass.There are geodesics where the mass moving.These are orbits of mases.
    There arent any forces,there is only curved space-time,so Gravity is a geometry.
    we know that in QM we solve schrıdinger equation for positions or energies of particles.Schrodinger equation not same Newton's equation; F=m.a;
    Schrodinger Equation is provided the conversations of energy not force law.however we use geodesics equation for positions of bodies.
     
  20. Jan 11, 2010 #19
    Personally, I don't know of physicists who reject the validity of a new model simply because it has yet to be tested (as opposed to it being fundamentally untestable). Things like string theory get a lot of flack, in my humble opinion, simply because people become so enraptured with the possibility of unifying forces that they end up modifying fundamental equations in arbitrary ways to get them to fit with new observations. To some, this sounds a lot like Ptolemy's epicycles. That said, Murray Gell-Mann himself has said that there's something very interesting about a theory that gets rid of the infinities that plague GR.

    In the end, whether it's space-time or the graviton, it's all about which makes more sense for particular experiments and observations. That's okay, though; this is not uncharted territory for modern physics (after all, is an electron a wave or a particle?).
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Cause of Gravity?
  1. What causes gravity? (Replies: 0)

  2. What causes gravity? (Replies: 3)

  3. What causes gravity (Replies: 19)

Loading...