## Does a field ever finish? (physics)?

Question

I have been thinking about gravity and magnetic force, and seeing that these two forces have a field, does their field ever finish. For example, the Earth’s gravity field weakens the further you go from the Earth, but does it ever finish?

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General Physics
4 years
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## Answer ( 1 )

This is one of those tricky questions that depends on whether you consider the field from a classical perspective or a quantum perspective.

From a classical perspective, it is pretty obvious since fields fall of inversely to the distance away from the source. So, as the distance r approaches infinity, the field approaches zero.

From a quantum mechanical perspective, the value of a field depends on the mass of the particle that mediates the field. In quantum mechanics, as the distance approaches infinity, the field approaches zero IF the field quanta has zero mass. This would include photons as well as the hypothetical graviton which would need to be massless for a field with infinite range.

The reason is actually quite interesting. Static force fields are believed to be mediated by virtual particles. The range of a virtual particle depends on its mass because the existence of the virtual particle depends on the energy-time version of the Uncertainty principle. Therefore, the distance the virtual particle can travel depends on the time it can exist which in turn depends on the energy of the virtual particle. A photon which has zero mass can also have an infinitely long wavelength allowing effectively a zero energy photon. Based on the uncertainty principle, it can exist for an infinite amount of time and therefore be able to travel an infinite distance (within the bounds of the universe obviously if it is finite).

Quantum mechanics is the way we should interpret fundamental behavior.