QED could precisely predict the magnetic moment of electron

In summary, QED can precisely predict the magnetic moment of an electron and muon because the strong force that holds the neutron together is described by QCD. However, QED is not able to predict the lifetime of a neutron with the same accuracy due to the complexity of the weak force involved. The decay of a muon is also mediated by the weak force, making electroweak theory more applicable in this case. While QED is simpler to calculate due to its small coupling constant, the larger Fermi coupling and technicalities in the weak sector make predicting the lifetime of a muon more challenging.
  • #1
vincentchan
609
0
I have a little question about QED..
How come QED could precisely predict the magnetic moment of electron and muon, but can't predict the lifetime of neutron with the same accuracy?
 
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  • #2
Because the strong force holds the neutron together, the strong force is described by QCD.
 
  • #3
how about the life time of muon, can QED predict the lifetime of muon with a high accuracy?
 
  • #4
vincentchan said:
how about the life time of muon, can QED predict the lifetime of muon with a high accuracy?
Actually the decay of the muon is mediated by weak force (this can be seen by the large lifetime of the muon). So electroweak theory would govern this decay, not plain QED.
Cheers,
Ryan
 
  • #5
Yes,both neutron & muon decay are weak processes.Incidentaly,they're both wonderfully treated in [1].And in the same chapter,i.e.chapter 10.

Daniel.

--------------------------------------------------------------
[1]David J.Griffiths,"Introduction to Elementary Particles",Harper & Row,1987.
 
  • #6
So, Do we fully understand the weak interection?
I mean, if we understand weak interaction, we should able to predict the lifetime of muon, right?
But it seems like weak interaction is not as good as QED... can anyone tell me why...?
 
  • #7
They're both good.It's just that the calculations involved in QED are much simpler.

Daniel.
 
  • #8
Fundamentally the weak interaction is harder to calculate (even with a computer), b/c the coupling constant for QED is so small it allows many orders of perturbation series to reliably be calculated, before asymptotic renormalon behaviour starts corrupting your data. The Fermi coupling being larger doesn't give you that reliability.

Of course there are other issues in the calculational difficulty, some of which are based on the accuracy of experiment, and some technicalities in the weak sector that are quite challenging. First of all the propagator is massive, which adds extra stuff to the calculation, second of all the process is now distinctively axial in nature. Essentially this makes drawing feynmann diagrams for V-A interactions an enormous chore, best left for grad students =)

(note I am pulling an all niter grading papers, so forgive the brevity and conceptual mistakes I am likely making)

(incidentally I hate the weak interaction. I find it remarkably unbeautiful compared to QED or QCD. I also hated attending conferences with the electro weak experamentalists, as invariably some bayesian statistics debate would rear its ugly head and everything would degenerate)
 
Last edited:
  • #9
Yes,both neutron & muon decay are weak processes.

Yes, of course. :redface: I never meant to imply anything else by my post.
 

Related to QED could precisely predict the magnetic moment of electron

1. What is QED and how does it relate to the magnetic moment of an electron?

QED stands for quantum electrodynamics, which is a theory in physics that explains the behavior of particles and their interactions with electromagnetic fields. In this theory, the magnetic moment of an electron is a fundamental property that can be precisely predicted using mathematical equations and experimental data.

2. How does QED calculate the magnetic moment of an electron?

QED uses a mathematical framework called quantum field theory to calculate the magnetic moment of an electron. This theory combines principles from quantum mechanics and special relativity to accurately describe the behavior of subatomic particles, including electrons.

3. Why is the magnetic moment of an electron important?

The magnetic moment of an electron is important because it is a fundamental property that helps us understand the behavior of electrons in magnetic fields. It also plays a crucial role in many technological applications, such as MRI machines, computer hard drives, and particle accelerators.

4. How accurate is QED in predicting the magnetic moment of an electron?

QED has been extensively tested and has been found to be extremely accurate in predicting the magnetic moment of an electron. The predictions made by QED have been verified by numerous experiments and have been shown to agree with experimental data to an astonishing degree of precision.

5. Are there any limitations to QED's ability to predict the magnetic moment of an electron?

While QED is a highly successful theory, it does have some limitations. One of these limitations is that it does not fully account for the effects of gravity, which becomes significant at very small scales. Additionally, QED is a purely theoretical framework and does not provide explanations for the underlying reasons behind the values it predicts.

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