Of Particular Significance

What is the “Strength” of a Force?

POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON 05/31/2013

Particle physicists, cataloging the fundamental forces of nature, have named two of them the strong nuclear force and the weak nuclear force. [A force is simply any phenomenon that pushes or pulls on objects.] More generally they talk about strong and weak forces, speaking of electromagnetism as rather weak and gravity as extremely weak.  What do the words “strong” and “weak” mean here?  Don’t electric forces become strong at short distances? Isn’t gravity a pretty strong force, given that it makes it hard to lift a bar of gold?

Well, these words don’t mean what you think.  Yes, the electric force between two electrons becomes stronger (in absolute terms) as you bring them closer together; the force grows as one over the square of the distance between them.  Yet physicists, when speaking their own language to each other, will view this behavior as what is expected of a typical force, and so will say that “electromagnetism’s strength is unchanging with distance — and it is rather weak at all distances.

And the strength of gravity between the Earth and a bar of gold isn’t relevant either; physicists are interested in the strength of forces between individual elementary (or at least small) particles, not between large objects containing enormous numbers of particles.

Clearly there is a language difference here… as is often the case with words in English and words in Physics-ese.  It requires translation.  So I have now written an article explaining the language of “strong” and “weak” forces used by particle physicists, describing how it works, why it is useful, and what it teaches us about the known forces: gravity, electromagnetism, the strong nuclear force, the weak nuclear force, and the (still unobserved but surely present) Higgs force.  Physicists needed a deep understanding of quantum mechanics, special relativity, and their marriage in quantum field theory, developed over many decades, to understand that this way of talking about the strengths of forces is the best one to use.  It’s not the most natural one in daily life, but daily life reveals nothing of quantum field theory, so it isn’t surprising (or unusual) that what makes sense to us in our ordinary experience gives us a manner of speaking that isn’t useful in the world of particles and fields, and vice versa.

I hope this article will give you some interesting insights into how our world works, and clarify some things that may have been mysterious: why the weak nuclear force is weak; where the idea of “Grand Unification” initially comes from; why the proton’s size is what it is and why it is so much more complicated than an atom; why we observe gravity even though it is so much weaker than the other forces; and why the Higgs force hasn’t yet been observed, even though the Higgs force bears some passing (though misleading) resemblance to gravity, and even though we already know that there’s at least one Higgs field and one Higgs particle.

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13 Responses

  1. Yes Mr Russ Abbott,
    inhalation of the apeiron (field) by the peiron (ripple) – separated by “void” between them – is also what makes the world mathematical, not just possible to describe using maths, but truly mathematical since it shows numbers and reality to be upheld by the same principle.

    Why the number and reality is same ?

    There is connection , surpassing consciousness, making it a perpetual stairs ?

  2. Great article. I’m leaving this comment here since it’s less technical than the force article.

    What strikes me as amazing is that nature comes with built-in forces in the first place. The force article talks about how fields (and their ripples) interact with each other. But it doesn’t say what it is about fields (and ripples in them) that leads to those interaction effects.

      1. I do not like the idea of fields (gravitational field, electromagnetic field, Higgs field), because as I understand it they restrict the freedom of travel/movement in space.So I am somewhat distrustful as to where they come from.

  3. For an isolated system, Conservation of energy law means energy is localized and can change its location within the system, and it can change form within the system, for instance, chemical energy can become kinetic energy but it can be neither created nor destroyed.
    So the energy spent by angular momentum (localized field or ripple or force) is recycled in concrete (isolated) spacetime mechanism – which was encapsulated as quanta (mathematical) during Big bang temperature ?

      1. A quantum, though a ripple in a field, is like a particle in that…
        (*) it has a definite (and observer-independent) mass – observer independent means, agreed by mathematics ?
        Speed of the light is irrelevant at quantum level, unless otherwise, concrete 3D spacetime is proved ?

  4. James “Bond” 0.007.

    Penrose (stairs) or “Playing musical chairs”, where music is never stopped ?

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