You can try to treat gravitation as an aspect of electromagnetism, but that would just complicate electromagnetism, specifically by adding something which is indistinguishable from gravitation. Let's see why they must be different things by checking some observations.
We'll start out simply. Perhaps the simplest observation we can make is that certain materials can become "charged". For example, we can rub a plastic rod with some wool, and suddenly it gains this magical ability to attract things, like small bits of paper.
We can also see that this charge can be transferred. Touch the rod to a free-hanging metal sphere, and now the sphere is charged and exhibits the same behavior. Now do this exact same process for another metal sphere, and bring the two close together without touching. They repel! That's interesting. Apparently this "charge" stuff doesn't like itself.Ok, now let's do something a little different. We'll take another metal sphere, and while holding the charged rod close to (but not touching) it, touch the sphere with a wire connected to ground. Then remove the wire, and then the rod. The sphere is now charged, even though we never touched it with something charged! Furthermore, this sphere will also attract the other two spheres we prepared earlier, and attract small bits of paper.
What this shows is that there are two types of charge. Two objects with the same charge repel, and the "opposite" charges attract. This is well known to us of course, but it's instructive to think about how to show it, and then what it implies:
If we think gravitation is an aspect of electromagnetism, then it should seem odd that masses always attract, while charges can attract or repel. It should seem odd that we can give an object either charge and it always has the same attraction to Earth. Well, maybe "mass" is just another kind of charge, which attracts all the other kinds of charge? Sure, you could try to go with that. But like I claimed above, that's equivalent to adding something equivalent to gravitation to electricity at this point.
Let's investigate a little more deeply, and bring in magnetism:
We observe that a charged object moving through a magnetic field experiences a Lorentz force
. However, this is not true for massive but uncharged objects, or for objects (charged or otherwise) moving through a gravitational field. This really indicates that gravitation and electromagnetism must be different kinds of interactions associated with different kinds of physical properties.
Perhaps now you are thinking,"But no Lorentz force appears within a purely electric field. Maybe a gravitational field is just an electric field?"
But that still doesn't work, because of how electricity and magnetism are related:
A stationary charge produces an electric field. Electric currents (moving charges) also create magnetic field. But by relativity, an observer moving alongside a moving charge will say the charge is stationary and thus there is no magnetic field, while different observer may say that it is moving and is producing a magnetic field. So electricity and magnetism are related by relativity, and together form the electromagnetic field.This works differently for gravitation. A gravitational field doesn't split up into different types depending on your speed relative to the source. If gravitation is electric field in the rest frame and magnetic field in the moving frame, then you should still be able to demonstrate Lorentz forces on uncharged objects.We'll go one last step and examine electromagnetic vs. gravitational waves. Moving charge produces a magnetic field, and changing magnetic fields produce electric fields, and vice versa. If a charge should move in a particular way (in the technical jargon, a "changing dipole moment"), then these changing electric and magnetic fields propagate at the speed of light. That is, they make an electromagnetic wave. An example of a changing dipole moment is two particles oscillating back and forth, like two masses on a spring.A similar thing happens in gravitation, but the nature of the source required, and the behavior of the waves, is different. Instead of requiring a changing dipole moment, it requires a changing quadrupole moment. An example of this kind of motion is two objects orbiting each other, or a mountain on the equator of a rapidly spinning ball. This emits gravitational waves, which also propagate with the speed of light, but instead of affecting charges, they stretch and squeeze space.
In summary, I hope this was a good introduction or review of some of the physics of electromagnetism, and perhaps helps convince you that these really are two very different kinds of interactions.
Finally, not only do they have different sources and behaviors, they have *very*
different strengths. The electromagnetic interaction is about 1036 times stronger than gravity!