Wednesday, September 03, 2014

Myth Physics: Gravity Is Much Weaker Than Electromagnetism

In this article, Vic Stenger tries to debunk the "myth" that gravity is much weaker than electromagnetisim.

I don't see this as a myth, but rather, an explanation on what we mean when we say that gravity is weaker than EM. Stenger explains it here:

The gravitational force between two particles is given by Newton's law of gravity, which says that the force between two point masses is proportional to the product of the masses and inversely proportional to the square of the distance between them.

The electric and gravitational force laws are both inverse square laws, so if one computes the ratio of the forces between two bodies, the distances cancel. For the electron and proton, the gravitational force is 39 orders of magnitude weaker than the electrical force. This is the source of the myth that gravity is a much weaker force than electromagnetism.

The absolute strength of the electromagnetic force is specified by a dimensionless parameter alpha called, for historical reasons, the fine structure constant. It is actually not a constant but varies with energy. However that variation is very gradual and for most practical purposes alpha can be taken to have a value of 1/137

Conventionally a dimensionless parameter alpha-G is defined to represent the gravitational force strength. It is proportional to the square of the proton mass and has a value 23 orders of magnitude less than alpha. So "officially," gravity is this much weaker than electromagnetism.

So there you have it. This is another lesson on why one must understand a bit of the physics behind the phrases and expressions that we all often hear out of science. You cannot just take something at face value, the way pseudoscientists such as Deepak Chopra often do all the time.


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