# Why can't gravity be just a form of magnetic attraction?

• B
• mamba76

#### mamba76

Based on the photo electric effect. Maybe its perception that is the problem? Charge doesn't travel through a vaccuum. Electro magntic waves alway carry photons. Photons can make charge. Charge creates magnetism? Would explain why Coulumbs equation is the same as the one for gravity but on a much, much bigger scale.

• PeroK

Based on the photo electric effect. Maybe its perception that is the problem? Charge doesn't travel through a vaccuum. Electro magntic waves alway carry photons. Photons can make charge. Charge creates magnetism? Would explain why Coulumbs equation is the same as the one for gravity but on a much, much bigger scale.
Although they both obey a similar-looking inverse square law in one particular case (nothing is moving) there are many differences:
- gravitational forces are always attractive and independent of the electric charge present.
- gravitational fields change differently than electromagnetic fields when the source is moving (Google for “retarded potential”).
- gravitational waves are mathematically different than electromagnetic waves (Google for “gravitational wave quadrupole moment”)
- gravity doesn’t really follow an inverse square law; the Newtonian ##1/r^2## is an approximation that breaks down in strong gravitational fields (Google for “Mercury anomalous precession”)

Probably some more, but this will do for a start

• • jsgruszynski, ohwilleke, Nik_2213 and 5 others
In addition to the correct points mentioned by @Nugatory one huge difference that is specific to magnetic fields instead of electric fields is that magnetic fields have no monopole solution, only a dipole solution at lowest order. The gravitational sources we observe around us are all approximately monopolar sources. A monopole source has a ##1/r^2## field, but a dipole source has a ##1/r^3## field. There is no way to get Kepler's law from dipoles.

Gravity is not a magnetic interaction. It has nothing to do with perception or the photo electric effect or anything else you mentioned.

• ohwilleke, Nik_2213 and PeroK
Although they both obey a similar-looking inverse square law in one particular case (nothing is moving) there are many differences:
- gravitational forces are always attractive and independent of the electric charge present.
- gravitational fields change differently than electromagnetic fields when the source is moving (Google for “retarded potential”).
- gravitational waves are mathematically different than electromagnetic waves (Google for “gravitational wave quadrupole moment”)
- gravity doesn’t really follow an inverse square law; the Newtonian ##1/r^2## is an approximation that breaks down in strong gravitational fields (Google for “Mercury anomalous precession”)

Probably some more, but this will do for a start
Would the 1/r^2 thing never breakdown with point like sources? Is the distribution of matter what confounds it?

Would the 1/r^2 thing never breakdown with point like sources? Is the distribution of matter what confounds it?
The ##1/r^2## rule for electrical fields is exact as long as ##r## is non-zero, although we will have to use the integral form of that rule for the most charge distributions. In the special case of a spherically symmetric charge distribution (which includes point sources) the integral form reduces to the familiar Coulomb’s law.

The infinity that appears when we set ##r=0## is just telling us that that case is unphysical - the idealization of a point charge with a definite position breaks down at small distances so ##r## is no longer meaningful.

• mamba76
Update -- after a bit of cleanup this thread will remain closed. LOL

• sophiecentaur and mamba76