Comparing Gravity and Electromagnetism

In summary, both gravity and electromagnetism are infinite-range interactions and can be described by an inverse-square force law in the case of a static monopole source. They are also both mediated by massless particles, with the graviton being the mediator for gravity. However, electromagnetic waves have 90-degree polarization and are generated by a changing dipole moment, while gravitational waves have 45-degree polarization and are generated by a changing quadrupole moment. Both waves travel at the speed of light. In the weak-field linearized approximation, the gravitational field can be broken down into gravitoelectric and gravitomagnetic fields, similar to Maxwell's equations. However, the gravitomagnetic force has a different magnitude and sign compared
  • #1
imi
5
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Am interested in comparing gravity with electromagnetism. What are the differences in properties between the forces and how are they alike?
 
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  • #2
They're both infinite-range interactions that, in the case of a static monopole source, can be described at least approximately by an inverse-square force law. (Exactly in the case of the electric force; for gravity, you get inverse-square only in the limit of large distances.)

In the quantum theory, both are mediated by massless particles (although for gravity, the mediator particle -- the graviton -- probably isn't fundamental).

Electromagnetic waves have 90-degree polarization, and are generated by a changing dipole moment; gravitational waves have 45-degree polarization, and are generated by a changing quadrupole moment. (Spin 1 vector photon vs. spin 2 tensor graviton.) Both waves propagate at the speed of light.

In the weak-field linearized approximation (neglecting gravitational self-interaction), the gravitational field can be decomposed into gravitoelectric and gravitomagnetic fields obeying something analogous to (but not the same as) Maxwell's equations. There is an analog of the Lorentz force law, but the gravitomagnetic force part has a different magnitude and sign. In full GR, this force-based description of gravity breaks down.

Electromagnetic sources have two signs (positive and negative) and the interaction can be attractive or repulsive; gravitational sources have just one (positive) and is always attractive (unless you introduce a cosmological constant or something). Actually, the source of electromagnetism is a vector (4-current) and the source of gravity is a tensor (stress-energy).
 
  • #3
And the Gravitational force is about 10^42 times weaker than electromagnetism!
 
  • #4
Thanks for your replies.
 

1. How are gravity and electromagnetism different?

Gravity is a force that attracts objects with mass towards each other, while electromagnetism is a force that acts between electrically charged particles. Gravity is a long-range force, while electromagnetism can act over both long and short distances.

2. What is the relationship between gravity and electromagnetism?

While both gravity and electromagnetism are fundamental forces in the universe, they have very different properties and do not directly interact with each other. However, both forces play important roles in the behavior of matter and energy in the universe.

3. Which force is stronger, gravity or electromagnetism?

Gravity is the weaker force compared to electromagnetism. While gravity has an infinite range, its strength decreases with distance. Electromagnetism, on the other hand, has a limited range but is much stronger, with a force that decreases much slower with distance.

4. How do gravity and electromagnetism affect the behavior of matter and energy?

Gravity is responsible for the formation of large-scale structures in the universe, such as galaxies and clusters of galaxies. Electromagnetism is responsible for the formation of chemical bonds between atoms, as well as the behavior of light and electricity. Both forces play a crucial role in the interactions between matter and energy in the universe.

5. Can gravity and electromagnetism be unified into one theory?

Scientists have been trying to unify gravity and electromagnetism into one theory, known as the theory of everything or the grand unified theory. However, this has not yet been achieved, and it remains one of the biggest challenges in modern physics.

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