The Gravitational Field

by Albert Einstein Icon

3 minutes • 531 words

An action at a distance must have some intermediary medium.

According to Faraday, a magnet attracts a piece of iron not through the medium of empty space, but through the medium of a magnetic field*.

This magnetic field is always around the magnet. It operates on the piece of iron, so that the iron moves towards the magnet.

Superphysics Note

In Cartesian Physics, the magentic field is a combined effect of Electromagnetism, Matter, and Spacetime, with Spacetime being the true medium. A magnet attract the iron really eliminates the spacetime between them. A magnet that repels another magnet really creates space between them.

This idea is arbitrary. Nevertheless, it represents electromagnetic phenomena and is applied to the transmission of electromagnetic waves.

The effects of gravitation is analogous to the effects of magnetism.

The action of the earth on a falling stone happens indirectly.

The earth produces a gravitational field around itself which acts on the stone and causes it to fall.
The intensity of this diminishes according to a definite law as we move farther away from the earth.

From our point of view this means that the law governing the gravitational field in space must be perfectly definite.

The earth produces a field in its immediate neighbourhood directly. The field’s intensity and direction at farther areas are thence determined by the law which governs the properties of the space of the gravitational fields themselves.

Einstein Con-man

In contrast to electric and magnetic fields, the gravitational field makes bodies accelerate. This is of fundamental importance.

This acceleration does not depend at all on that body’s material or its physical state. A piece of lead and a piece of wood fall in exactly the same way*.

Superphysics Note

It only depends on their Nature as Matter (as opposed to Electromagnetic Nature like light or electrons)

According to Newton’s 2nd law of motion, this is:

Force = inertial mass × acceleration

The “inertial mass” is a characteristic constant [g] of the accelerated body.

If gravity caused the acceleration, we then have:

Force = gravitational mass × intensity of the gravitational field

The “gravitational mass”* is also a characteristic constant [G] for the body.

Superphysics Note

Here, Einstein subtly hacks Newton by converting his ‘mass’ into ‘gravitational mass’. This is in order to make room for his new idea which he calls ‘inertial mass’ which in Superphysics is ’electromagnetic potential’

From these, 2 relations follows:

acceleration = (gravitational mass / inertial mass) × intensity of the gravitational field

The ratio of the gravitational to the inertial mass is likewise the same for all bodies if there is no acceleration.

Through a common unit, this ratio becomes equal.

This leads to the following law:

Einstein

The gravitational mass of a body is equal to its inertial mass.

This important law is already in mechanics. But it had not been interpreted*.

Superphysics Note

Inertia in rest mass is gravity. It had not been interpreted because no one would be crazy to assign the cause of gravity to electromagnetism. Even in Cartesian Physics, the cause of gravity is Spacetime and not Matter.

I interpret it as: The inertia of body is its weight.

This is connected to General Relativity.