Okay, we have now identified all known forces, but particle physicists don't stop here. They ask questions that we normally take it for grant:
How do the forces work? Why do we sense forces - pushing and pulling? In fact the basic forces between particles of matter all act through a
'force carrier', which is exchanged between the interacting particles. These exchange carriers are also known as field particles,
or gauge boson.
An analogy to this is like exchange of messages between two persons maintains a conversation. In this case the conversation is the 'force' that 'binds' two persons while the 'carrier' of the
conversation is the message or language ('catching' the message, hence the attractive force). Ever feel that you wish to say good bye to your boring yet talkative friend that you meet on a street? In this case the conversation may be one way and you are not 'catching' it by not responding.
Eventually your friend may notice it, stop the conversation and walk away (thus the repulsion). This analogy must not be taken in the literal sense. The force carriers are not the actual particle. They must be viewed as some kind of entity that exist in order to regulate the force
Each basic force has a different type of carrier. They are listed below:
1. The Strong Force Carrier: Gluons (g)
Gluons have no mass and no electric charge. They carry a special 'charge-like' property that hold quarks (constituents
of protons and neutrons) together. The theoretical treatment of this carrier is described in the theory of quantum chromodynamics (QCD).
2. The electromagnetic force Carrier: Photons (g)
Photons is responsible to 'carry' electromagnetic forces. It is also known as the particle of 'light' as they also 'carry' light as what we
see. They have no mass, and no charge and can exchange between two particles over infinite distance. This is also the reason
why light can travel to infinite distance and we can see stars that are far away. Detailed theoretical description of photons is given in quantum electrodynamics (QED).
3. The weak force Carrier: W and Z (W+, W-, Z0)
The carrier W can be either positively charged (W+) or negatively charged (W-), while Z is neutral
(Z0). The reason why the force is weak is because these carriers are massive, about 100 times that of the weight of a
4. The gravitaional force Carrier: Graviton (?)
The existence of this carrier is yet to confirm. If it exists it should have zero mass and zero charge. It may will be the discovery of the century if its presence is ever detected.