Question

describe Quantum field theory?

Answer 1

QFT treats particles as excited states of the underlying field, so these are called fieldquanta. In quantum field theory, quantum mechanical interactions among particles aredescribed by interaction terms among the corresponding underlying quantum fields.

Answer 2

Hello i hope you understand dear,
Remember the wave-particle duality? Mind-blowing, right..? Well, you might as well forget about it. In fact, there are no particles and no waves; just fields. Both "particles" and "waves" are merely two ways in which we naively interpret quantum fields.

There's one field for each type of particle. So one field for all photons in the universe, one field for all electrons, and so on. And these fields exist everywhere.

To "extract" a particle from a field, you need to give the field energy. If you give it enough energy, the field will go to a higher energy state. These states are what we interpret as particles.

The point in the field where you gave it energy will look like a particle, and as the energy propagates through the field, it will look like the particle is moving.

Some fields require more energy than others in order to create a particle. The amount of energy is proportional to the mass of the associated particle.

For example, a Higgs boson is much more massive than an electron. So electrons are very easy to create, but Higgs bosons are very hard to create.

This is why it took us so long to discover the Higgs boson. We had to build a huge machine, the Large Hadron Collider, that was capable of giving the Higgs field enough energy to create Higgs bosons from it.

The Candy Machine Analogy

Here's an analogy I like to use. Think of fields as candy machines. You put enough money in, you get a piece of candy. You put more money in, you get another candy.

The money in this analogy is energy, and the candies are particles. So if you have enough energy you can get as many particles that you want.

Note that the money (energy) is always conserved: if you have 10 coins and you put 5 in the machine, then now you have 5 coins and the machine has another 5, but the total number of coins is still 10!

However, the number of candies (particles) is not conserved: you can eat them and they disappear, or the factory makes new ones (and the maintenance guy comes and restocks the machine).

There are 18 such machines (that we know of). You can go, for example, to the electron machine, pay some money, and get an electron. And then you can go to the photon machine, pay some other amount of money, and get a photon.

Crucially, the fields also interact and exchange energy with each other. Think of an intricate network of tubes between the different machines, that can transfer coins from one machine to another.

However, these exchanges all happen within the tubes, hidden from sight. No actual candies are exchanged in the process. The same thing happens with fields: they interact "behind the scenes", not by exchanging particles, but by exchanging energy between them.

(Of course, it's actually much more complicated than that, but this is as far as the analogy can go
:-)