A few doubts about quantum field theory and high energy physics.

In summary: The electrical interaction being attractive repulsive is determined by the charge of the charged particle, not photon.This is correct. The interaction is attractive because the charge on the two particles makes the photon act like a middleman, transferring energy from one particle to the other. The interaction is repulsive because the opposite charge on the particles pushes the photons away from each other.1. I read that the picture of gauge bosons as mediators of interaction originates in and is valid in perturbation theory. But how do we know that picture is correct? We do perturbation theory only because we do not know how to study a system in a fully non-perturbative way. If someday we discover a non-pert
  • #1
arroy_0205
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1. I read that the picture of gauge bosons as mediators of interaction originates in and is valid in perturbation theory. But how do we know that picture is correct? We do perturbation theory only because we do not know how to study a system in a fully non-perturbative way. If someday we discover a non-perturbative way of doing all such calculations what will happen to this picture?


2. In quantum electrodynamics a chargeless and massless particle called photon mediates interaction between two electrically charged particles. Then how can such a photon give rise to attraction between oppositely charged particles and repulsion between particles of same charge. I mean how does a chargeless particle cause different effects?

3. Why do we consider 1TeV to be very high energy and difficult to produce while energy of the order of Joule commonplace in daily life?

I hope experts here will bear with my elementary doubts in such difficult subjects.
 
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  • #2
arroy_0205 said:
1. I read that the picture of gauge bosons as mediators of interaction originates in and is valid in perturbation theory. But how do we know that picture is correct? We do perturbation theory only because we do not know how to study a system in a fully non-perturbative way. If someday we discover a non-perturbative way of doing all such calculations what will happen to this picture?


2. In quantum electrodynamics a chargeless and massless particle called photon mediates interaction between two electrically charged particles. Then how can such a photon give rise to attraction between oppositely charged particles and repulsion between particles of same charge. I mean how does a chargeless particle cause different effects?

3. Why do we consider 1TeV to be very high energy and difficult to produce while energy of the order of Joule commonplace in daily life?

I hope experts here will bear with my elementary doubts in such difficult subjects.

1) Actually, we do have non-perturbative method, e.g. lattice QCD
2) The electrical interaction being attractive repulsive is determined by the charge of the charged particle, not photon.
3) Accelerating a proton to 1 TeV means the single proton carried 1TeV energy, whereas 1 Joule energy in a macroscopical object, say a cup of tea, is shared by zillions of proton and electrons, then one particle carried little energy.
 
  • #3
arroy_0205 said:
1. I read that the picture of gauge bosons as mediators of interaction originates in and is valid in perturbation theory. But how do we know that picture is correct?

We test theories by comparing their predictions with experimental results. In the case of QED for the electromagnetic interaction, I don't know of any experiment that disagrees unambiguously with the theory, outside of experimental uncertainties. Of course, next week someone might make a measurement that goes a few decimal places beyond what has been done before, and thereby uncovers a discrepancy that eventually forces us to modify the theory.

We don't know that QED is "absolutely correct," but I don't see how we can know that any theory is "absolutely correct," given that we can do only a finite number of experiments to test it.
 
  • #4
arroy_0205 said:
1. I read that the picture of gauge bosons as mediators of interaction originates in and is valid in perturbation theory. But how do we know that picture is correct? We do perturbation theory only because we do not know how to study a system in a fully non-perturbative way. If someday we discover a non-perturbative way of doing all such calculations what will happen to this picture?
In order to do that you need some theory (= a collection of mathematical expressions and rules how to use them). Then you can start to test perturbative and non-perturbative approaches. For QCD we have both (applicable in different regimes) and it seems that it works quite well.

As long as we start to write down a Lagrangian which contains gauge bosons we will never find sonmething else and the final theory will always contain gauge bosons; the question whether we do perturbative or non-perturbative calculations is only a technical one.

So the picture with gauge bosons will not break down when we do non-perturbative calculations using gauge bosons; it will break down when we write down something which does not contain gauge bosons ;-)
 
  • #5
It would be interesting to see if there is an example where a problem can be solved both perturbatively and non-perturbatively and to check if these give same results. Also in case of perturbative calc we should see upto what order the results are same. Perhaps for harmonic oscillator we can do both upto lower order of perturbation but are there more complicated examples?
 
  • #6
arroy_0205 said:
It would be interesting to see if there is an example where a problem can be solved both perturbatively and non-perturbatively and to check if these give same results. Also in case of perturbative calc we should see up to what order the results are same. Perhaps for harmonic oscillator we can do both up to lower order of perturbation but are there more complicated examples?
Perturbative calculations are notoriously tricky.

Even in classical dynamics, an approach to the quartic anharmonic oscillator by naive perturbation from the harmonic oscillator gives unphysical runaway solutions even at low order. More sophisticated methods are possible, however, in which the various physical parameters (mass, stiffness, etc) are also expanded perturbatively.

Another example is the Morse potential
http://en.wikipedia.org/wiki/Morse_potential
which is useful to describe 2-atom molecules, and for which we have exact nonperturbative solutions. At low energy, the atoms are bound and their relative motion is approximately that of a harmonic oscillator. But as the energy rises, the motion becomes more and more anharmonic until, at a so-called "dissocation threshold" energy, the atoms separate and fly off to infinity. The latter behaviour obviously cannot be accommodated within the sinusoidal solutions of a harmonic oscillator, so here is an example where perturbation breaks down totally for high enough energy, even though it's reasonable for low energy.
 

FAQ: A few doubts about quantum field theory and high energy physics.

1. What is quantum field theory?

Quantum field theory is a theoretical framework that combines the principles of quantum mechanics and special relativity to describe the behavior of subatomic particles and their interactions. It is a fundamental theory in the field of high energy physics.

2. How does quantum field theory differ from classical field theory?

In classical field theory, particles are described as localized objects with definite positions and momenta. In quantum field theory, particles are represented as excitations in a quantum field, which can exist in multiple states simultaneously and have uncertain positions and momenta. This is due to the principles of quantum mechanics, which govern the behavior of particles at the subatomic level.

3. What is the role of symmetry in quantum field theory?

Symmetry plays a crucial role in quantum field theory, as it allows for the prediction and understanding of particle interactions. The fundamental symmetries of the universe, such as conservation of energy and momentum, are incorporated into the mathematical equations of quantum field theory, allowing for the calculation of probabilities for particle interactions.

4. How is high energy physics related to quantum field theory?

High energy physics is the study of particles and their interactions at very high energies, typically in particle colliders. Quantum field theory is the theoretical framework used to understand and predict these interactions. By studying high energy phenomena, scientists can test the predictions of quantum field theory and further our understanding of the fundamental building blocks of the universe.

5. What are some of the current challenges in quantum field theory and high energy physics?

One of the major challenges in quantum field theory and high energy physics is the reconciliation of this theory with general relativity, which describes gravity. Another challenge is the development of a unified theory that can explain all fundamental forces of nature. Additionally, there is ongoing research to better understand the properties of dark matter and dark energy, which make up a significant portion of the universe but are not yet fully understood within the framework of quantum field theory.

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