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At quantum scale, gravity is the weakest force. Its even negligible in front of weak force, electromagnetic force, strong force.

At macroscopic scale, we see gravity everywhere. Its actually ruling the universe. Electromagnetic force is also everywhere, but its at rank 2 when it comes to controlling motion of macroscopic bodies. And, there's no luck finding strong force and weak force.

How can that be? Is that because gravity only adds up but others cancelled out too? I am unable to understand how resultant of weakest force can be so big. Can you please show it with calculation?

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Earth is a Spoon
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2 Answers2

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For EM, macroscopic bodies are generally electrically neutral so there is no net electric force between them. For gravity, macroscopic bodies are gravitationally "charged"; I can't think of any that are gravitationally neutral.

Alfred Centauri
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  • And, magnet is also electrically neutral. Talk in electromagnetic, man. Plus, you've ignored quantum gravity, Strong force and Weak force. – Earth is a Spoon Jul 07 '12 at 12:14
  • You're harming only yourself with the tone of your comments. – Alfred Centauri Jul 07 '12 at 12:26
  • Sorry.. My intentions weren't to hurt you. Its just casual. – Earth is a Spoon Jul 07 '12 at 12:38
  • It's not possible for your comments to hurt me. It's not within your power to do that. Casual comments are fine but always keep the context in mind. This isn't a private conversation. – Alfred Centauri Jul 07 '12 at 13:21
  • Okay, I don't have power to hurt that. Buddy, you've taken it seriously.. – Earth is a Spoon Jul 07 '12 at 14:05
  • @SachinShekhar: The electromagnetic force is not what prevents you from falling through the floor, it's the Pauli exclusion principle. This was discussed here ad nauseum. The electron exclusion gives a macroscopic contact force independent of the fundamental forces. – Ron Maimon Jul 07 '12 at 21:04
  • +1, this is fine, but you should say that it is impossible to make a zero gravitational source, because gravity is sourced by energy, and energy is always positive. This is also true in GR, where you have a positive mass theorem. – Ron Maimon Jul 07 '12 at 21:05
  • @Ron Macroscopic contact force is independent of fundamental forces? Interesting!!! Can you please link me to that discussion? – Earth is a Spoon Jul 07 '12 at 21:27
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Of the four forces in the quantum field theory framework:

  1. the strong is mediated by the gluon and the effective potential this creates is of the order of the size of nuclei, because it is very short range at the current size of the universe . Very short range.

  2. The Z and W bosons are mediators of the weak interaction, and are much heavier than protons or neutrons and it is the heaviness that accounts for the very short range of the weak interaction

  3. As @AlfredCentauri said, the electromagnetic, though being long range and with a similar classical potential as the gravitational one ( and at present times when we are talking of gravitation the classical view suffices for the overall forces displayed) is always created in pairs of positive and negative values and long range becomes neutralized. The charges cannot build up without at some point discharging and turning neutral.

  4. The mediator of gravity is the graviton, a spin two zero charge particle if one talks of a quantum field theory model . But in General Relativity gravity cannot be neutralized as there is no antigravity. Everything has mass and distorts the four dimensional space time according to that mass. The wedding of the quantum field theories of the three previous forces with General Relativity is a current field of research, and the popular theoretical models are based on string theories.

So gravity wins long range by default and patience :).The story is different at the very early universe after the Big Bang, when the other three forces could dominate and did.

anna v
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  • Gravity is very weak which is more dangerous than short ranges of weak and strong forces. I think, range is increased when you add forces to increase magnitude. – Earth is a Spoon Jul 07 '12 at 17:16
  • It'd be great if you include how we get to the current gravity dominant world from Big Bang. That'd make the answer complete. – Earth is a Spoon Jul 07 '12 at 17:26
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    The link says it. It needs a lot of background in Big Bang theory, which after all is a theory to reach the point of saying how the three stronger forces become irrelevant as the expansion continues. – anna v Jul 08 '12 at 04:03