# Thread: The 4 forces and a question

1. Hi all not sure if this is a question that can be answered but it is certainly one of those things that got me thinking.

I was watching a 3 part documentary "the elegant universe" on the 4 forces in the universe that we are aware of and string theory. Namely gravity, electromagnetic forces, weak nuclear forces, strong nuclear forces.

they then went on to say that a unified field theory has yet to be put together because gravity is billions of times weaker than the other forces.

What is this statement based on and is it correct?

They demonstrate this by showing a guy jump off a building and landing safely on a pavement saying that the electromagnetic forces under your feet and on the pavement have stopped u from falling all the way to the center of the earth.

My problem with those claims is that (and correct me if I am wrong) I would of thought that its all the atoms between the center of the earth and the top of your head working together that stops u from falling to the center of the earth.

From what I can think the electronic force keeping all these atoms from compressing into each other is what would stop u from the inevitable fall if just the pavement was there.

Any thoughts would be helpful to explain why it is that gravity is so much weaker than all the other forces.

2.

3. I don't know if this will help, but imagine two atoms placed a metre apart in a total vacuum, billions of light years from any other matter. The two atoms will be attracted to each other gravitationally. Now imagine that these are oppositely charged ions. They will now be attracted to each other both gravitationally and eletrically. The electrical attraction is as many times greater than the gravitational attraction as you have noted.

I may simply have restated what you were questioning, but I'm not sure of any other way of putting it other than we can measure the forces of attraction and they are as different as described in the documentary. Why that is, is another matter. (Pun intended.)

4. Originally Posted by Ophiolite
I don't know if this will help, but imagine two atoms placed a metre apart in a total vacuum, billions of light years from any other matter. The two atoms will be attracted to each other gravitationally. Now imagine that these are oppositely charged ions. They will now be attracted to each other both gravitationally and eletrically. The electrical attraction is as many times greater than the gravitational attraction as you have noted.

I may simply have restated what you were questioning, but I'm not sure of any other way of putting it other than we can measure the forces of attraction and they are as different as described in the documentary. Why that is, is another matter. (Pun intended.)
Thanks for the reply that makes it a bit clearer.

I want to try take that situation a further step, if there were only those 2 atoms in the entire universe, and the forces were opposite(one repulsive and one attractive)

gravity attracting and the other electrically repulsing

how far would the 2 atoms need to be from each other to make the gravity and the electric force balance each other out.

I know gravity has the inverse square law on distance but there would have to be a point in space where the forces balanced as measured by distance between them, I don't know how the electric force works in terms of the distance between the 2 bodies.

might take some maths, but I don't know how to do it. Hoping someone will know how to work it out

5. http://en.wikipedia.org/wiki/Electri...cs_and_gravity

This specific point in the wiki page gives you both relations. As you can see, both are proportional to the inverse square of distance.

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