Question about Quanta

[LogicBear]

I don't fully understand "force particles."

In "The Elegant Universe," Brain Greene says that "...all of these interactions between various objects and materials, as well as any of the millions upon millions of others encountered daily, can be reduced to combinations of four fundamental forces" (pg. 10). He then goes on to name them (gravity, electromagnetism, strong and weak).

He says that each of those four forces have a corresponding "force particle" (graviton, photon, gluon, and weak gauge boson). However, when I asked my physics teacher about these, she said that those fundamental forces are "field forces," and implied that "contact forces" would not involve force particles.

If that is the case, then what causes the transfer of energy when an object experiences a contact force? And if that is not correct, and force particles are involved in contact forces, then what particles are involved in a simple push or pull, such as the kicking of a ball?

 

[Salv]

http://en.wikipedia.org/wiki/Electromagnetism

The electromagnetic force is the one responsible for practically all the phenomena encountered in daily life, with the exception of gravity. All the forces involved in interactions between atoms can be traced to the electromagnetic force acting on the electrically charged protons and electrons inside the atoms. This includes the forces we experience in "pushing" or "pulling" ordinary material objects, which come from the intermolecular forces between the individual molecules in our bodies and those in the objects. It also includes all forms of chemical phenomena, which arise from interactions between electron orbitals.

So which particles are involved? Probably the electrons repelling each other? When you're touching an object, you're not really touching it. What you're feeling, if I recall correctly, are the EM forces acting on each other. Although, it's probably best to read up a bit, because I could be speaking complete BS ofc. You'll probably want to check out some QED and some Feynman diagrams to see some of the subatomic interactions. It's been ages since I've delved into some physics. :/

The best place to ask these sort of questions is over at physics forums.

You can also check out some of Brian Greenes vids on youtube.

 

[aeroeng314]

He says that each of those four forces have a corresponding "force particle" (graviton, photon, gluon, and weak gauge boson). However, when I asked my physics teacher about these, she said that those fundamental forces are "field forces," and implied that "contact forces" would not involve force particles.

He's wrong. Contact forces are a particular manifestation of the electromagnetic force. Mostly what's called Van der Waals forces which is an umbrella term for interactions between dipoles and induced dipoles (a non-polar molecule that temporarily becomes polar due to the presence of a nearby dipole causing the charges within the non-polar molecule to move and create a dipole) and induced dipole-induced dipole interactions (more specifically known as London dispersion forces). To be technical, there's really no such thing as contact since atomic and subatomic particles don't have well-defined boundaries.

If that is the case, then what causes the transfer of energy when an object experiences a contact force? And if that is not correct, and force particles are involved in contact forces, then what particles are involved in a simple push or pull, such as the kicking of a ball?

It's all electromagnetism. When the molecules in the tip of your foot get near the molecules on the face of the ball, the electron clouds get close enough to interact and start to repel each other. The electron clouds distort to the opposite side of the nucleus (on average) which makes the molecules start acting like little magnets (dipoles). The dipoles are oriented in opposite directions, so there's a quite strong repulsion force.