Scientists think that a few hundred million years or so after the big bang, space cooled off enough for matter to form. this matter spread out around the universe with no structure. but each little bit of matter exerted the force of on each other little bit.

Gravity

Explanation:  The force that is generated by matter is the gravitational force, is the force that attracts the bits of matter to each other, and is described by the equation:

F = G*(m₁*m₂)/r^2

Where G is the gravitational constant, m₁ and m₂ are the masses of the bits of matter, and r is the distance between them.

The complete paragraph is:

Scientists think that a few hundred million years or so after the Big Bang, space cooled off enough for matter to form. This matter spread out around the universe with no structure. But each little bit of matter exerted the force of gravity on each other a little bit.

the closer the planet is to the sun, the larger the gravity