# Gravititonal fields compared to electromagnetic fields - are they infinite in range?

me and my friend has a discussion last night, and he argued that both an electromagnetic field and gravititonal field are infinite in their area of effect, but with diminishing effects as you get farther away from the object.

I argued that only gravity field is infinite in range.

So which one of us is correct, and please explain in laymen's terms, as we're not physicists :)

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## 2 Answers

Actually, your friend is right! The electromagnetic field has an infinite range, for example for a charged point particle the electric field is proportional to $\frac 1{r^2}$, where $r$ is the distance to the particle. However in very special circumstances, like inside a superconductor, the electromagnetic field will be short-range because the photons will effectively be massive.

See this table, where you can see both the electromagnetic and gravitational fields have infinite range of interaction, but the Weak doesn't. It's the famous Higgs boson which renders the weak field short range (by making the corresponding gauge bosons massive), very similar to what happens inside a superconductor.

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You've got a typo here: the electric field is proportional to $1/r^2$, not to $1/r$. Alternatively, the electric potential is proportional to $1/r$. –  Ted Bunn Jul 3 '11 at 15:45
Also, it's kind of misleading to say that the Higgs boson makes the weak force short-range. It's really due to the mass of the W and Z bosons. Plus, the strong force is kind of strange since it actually increases with distance; you could say that means its range is infinite, but not in the same way as gravity and the EM force. –  David Z Jul 3 '11 at 17:29
@Ted, thanks for the correction. @David Yes, but the masses of the W and Z bosons are generated through interaction with the Higgs field. Regarding the strong force, I agree. It's more subtle than I made it appear. –  Heidar Jul 4 '11 at 11:53

The key difference is that there are positive and negative electric charges and the universe is basically neutral. The opposite effects of the charges cancel out so on large scales, ie astronomical, the net electrical forces are much less than the gravitational forces, which are all one sign and hence never "cancel out."

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