The Weakest Force
- by Anton Skorucak and ScienceIQ.com
Did you know that gravity is the weakest force in the universe? It's true! Physicists know of four fundamental forces: the strong nuclear force, the electromagnetic force, the weak nuclear force and gravity. Every push and pull in nature comes down to one of these four.
| Force | Relative strength | Range | What it does |
|---|---|---|---|
| Strong nuclear | 1 | About the size of a nucleus | Holds atomic nuclei together |
| Electromagnetic | about 1/137 | Unlimited | Light, electricity, magnetism, chemistry |
| Weak nuclear | about 10−6 | Smaller than a proton | Radioactive decay; powers the Sun |
| Gravity | about 10−38 | Unlimited | Holds planets, stars and galaxies together |
(Comparing forces this way is rough: their relative strengths depend on the particles involved and the distance between them. But the ranking never changes.)
The strong force holds the protons and neutrons of an atomic nucleus together, overpowering the electric repulsion between the protons. The electromagnetic force is the strongest force we experience in daily life. Whenever you touch something, it is the electrons in your skin pushing against the electrons in that object; it's the reason you don't fall through the floor. The weak force is responsible for some kinds of radioactive decay, and it is also essential to the nuclear fusion that makes the Sun shine.
And gravity? Between two protons, the electric force is about 1036 times stronger than their gravitational pull. You can see how feeble gravity is with a simple fridge magnet: a tiny magnet easily lifts a paper clip off the table, beating the gravitational pull of the entire Earth.
So why does gravity rule the cosmos? Because it always attracts. Electric charges come in positive and negative and usually cancel each other out, but every bit of mass adds to gravity, so it builds up over planets, stars and galaxies. Why gravity is so much weaker than the other forces remains one of the big unsolved questions in physics, known as the "hierarchy problem."
