Question

why gravity is the weakest fundamental force among the four fources of nature

Answer 1

Gravity is weaker, by thirty-nine or forty muliples of ten.

For example if you took a gram of table salt and separated the negative and positive bits, and put the protons at the south pole and the electrons at the north pole, they'd be pulling on each other with an electrostatic attraction of MANY TONS.

Do the same thing with a gram of dirt, and the gravitational attraction is forty zeroes less than that.

We don't notice this huge difference because most everything is electrically balanced or very close to it, so we don't notice the tremendous forces in play there.

But with gravity the forces are very small, but they all add up, so the combined force of the planet pulls us down, but not so hard that we can't stand up. That should give you a clue-- the whole planet is pulling down, but the very weak electrical forces in your muscles are enough to beat out a whole planet of pulling!

So gravity can be said to be really weak, in comparison to electromagnetism. But if you get enough mass together, interesting things happen, like planets and stars.

Another explanation is that it *has* to be this weak, because if it was any stronger, then stars would burn up in a few years, not giving life a chance to evolve. So maybe there are a trillion trillion other universes with gravity at levels more equal to the other forces, but those universes just don't work, at least not the way ours works. They might be all made up of neutron stars or black holes.

It takes a really weak gravity to get stars with the lifetimes needed to develop life. As far as we know. Perhaps if gravity was a million times stronger there could be some other star-like objects that put out energy for eons. We won't be able to simulate such a universe except thru math and computers.

Answer 2

Hey friend
Here is your answer

Gravity is the weakest force as it coupling constant is small in value.Gravity cannot felt by us in our life because universe is surrounding us. 

If you determine the coupling constants of all different forces, you discover that, in decreasing order, strong, electromagnetic and weak forces are much, much stronger than gravity.

You need around 10321032 (that is 100,000,000,000,000,000,000,000,000,000,000) times more "stuff interacting" to get around the same energy scale with gravity if you compare it with the weak force. Moreover, the difference between strong, weak and electromagnetic forces among themselves isn't nearly as extreme as the difference between gravity and the other forces.