The four fundamental force of universe are
3.strong nuclear force
4.weak nuclear force
these four forces are carried by their respective particles as listed below
gravitational force by gravitons
electromagnetic force by photons
strong nuclear force by gluons
weak nuclear force by bosons
out of the four forces gravitational force is considered the weakest, and the strong nuclear force which is carried by gluons is considered the strongest.
Gravitational force, the weakest of the four forces, is about 10-36 times the strength of the strong nuclear force.The messenger particle of gravitational force is the graviton. It has not been experimentally verified, mainly because it is extremely hard to find the smallest denomination of the weakest force. Recent calculations show that it will likely be massless.
Gravitational force is always attractive and that's what hold our universe together.
And somehow scientists are trying to include this in to a grand unified theory, where they successfully included the other three ..
Its strength is a bit less than strong nuclear force, and unlike gravitational force, it has both attractive and repulsive nature and is of infinite range--like gravity.
If gravitational force is what responsible for keeping up our universe together, EM is responsible for keeping up electrons around nucleus(attraction force between nucleus and electrons).
It is the force that causes the interaction between electrically charged particles; the areas in which this happens are called EM fields, also known as B fields in physics classes.
The particle that carry electromagnetism is the photon, a massless particle that travels at a speed of 299 792 458 m/s or 299 972 km/s .
The Weak Nuclear Force
The weak nuclear force is one of the less familiar fundamental forces. It operates only on the extremely short distance scales found in an atomic nucleus. The weak force is responsible for radioactive decay. In actuality, it is stronger than electromagnetism, but its messenger particles (W and Z bosons) are so massive and sluggish that they do not faithfully transmit its intrinsic strength.
The Strong Nuclear Force
Like the weak force, its range is limited to subatomic distances. quarks which forms the protons and neutrons stick together through this force. this fprce is carried by gluons and is a massless particle, as it glues the quarks together,its called a gluon.gluons also acts on other glons and that is why, as the distance increases the force increases at subatomic level .
Attempts have been going on to unify all these four fundamental forces to form a grand unified theory, and had successfully unified the other three, excluding gravity. Hope they will succeed soon.