|MadSci Network: Physics|
Frankly, I hesitate in answering this question because it is a fundamental question and its answering needs knowledge of quantum physics, which I am not familiar with. Therefore, I can only give some general idea. Hope that may help. According to the Standard Model (the theory currently accepted by most physicists), there are four fundamental forces and there are force carrier particles associated with each force. Gravity is one of the four fundamental forces and its force carrier particle is called graviton. The properties of graviton have been predicted by the theory but it has not been observed until now. Magnetic force, or Lorentz force, is the force exerted on moving charged particles in magnetic field. It can not be isolated from electric force exerted on charged particles in electric field. According to special relativity they can transform into each other in different reference frames. Therefore it is more suitable to regard it as part of an integrate electromagnetic force, which is also one of the four fundamental forces and its force carrier particle is photon. There is a very good page answering your questions: The Particle Adventure. Please see "The Standard Model/What Holds It Together" part.
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