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Severian

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Everything posted by Severian

  1. Yes it does. This is a weak decay. The neutron is made up of three quarks: one 'up' quark and two 'down' quarks. One of the down quarks decays to an up quark by emitting a 'W-boson' (which then decays to lepton and a neutrino). Since the proton is two up quarks and a down quarks, the neutron has decayed into a proton. The actual calculation is a bit beyond the scope of a web forum though....
  2. Very often people come to these fora with a belief that our current theories of physics, such as the Standard Model or relativity, are flawed and present some alternative of their own. On the whole, this is a fine attitude to take - we should always be skeptical, and it is good if people can think a little 'out of the box' and generate ideas which more standard thinkers may not have come up with. I have always thought that genius was not an ability to think 'better' than everyone else - it is an ability to think differently from everyone else. However, when coming up with a new theory it is important that it should be better than the old one. Therefore the first step of coming up with a new theory is a sufficient understanding of the old one. You have to make sure that your new theory does everything at least as well as the old theory, otherwise the old theory remains more attractive. This is very difficult mainly because our current theories are so spectacularly good in their predictions. Let me give an example: the magnetic moment of the electron. If we look at the energy (Hamiltonian) of an electron in an electromagnetic field, we find that there is a contribution from the interaction of the electron's angular momentum and the magnetic field. For an orbital angular momentum [math]L[/math], this is [math]\vec{\mu}_L \cdot \vec{B}[/math] with a magnetic moment [math]\vec{\mu}_L = - \frac{e \hbar}{2mc} \vec{L}[/math] (The charge of an electron is [math]-e[/math] and its mass is [math]m[/math].) However, if the particle has 'spin' (intrinsic angular momentum) [math]\vec{s}[/math], we also have a contribution to the magnetic moment of [math]\vec{\mu}_s = - g \frac{e \hbar}{2mc} \vec{s}[/math] [math]g[/math] is known as the gyromagnetic ratio, and its value depends on the theory. Since this can be measured in experiment very accurately, it is a good test of a theory to check if it predicts the correct gyromagnetic ratio. For example, simple QM (the Dirac equation in an em field) predicts a gyromagnetic ratio [math]g=2[/math]. Experiments shows that [math]g[/math] is very close to 2, so this is good news, but since experiment shows that it is not quite 2, the Dirac equation cannot be the whole answer. Quantum Field Theory, in the form of the Standard Model, predicts a deviation from 2. It is usual to write down the prediction for this deviation from 2 rather than the gyromagnetic ratio itself. For the SM this is: [math]\frac{g_{\rm th}-2}{2} = 1159652140(28) \times 10^{-12}[/math] The experimantal result is: [math]\frac{g_{\rm exp}-2}{2} = 1159652186.9(4.1) \times 10^{-12}[/math] (A note on errors: the numbers in brackets denote the error on the prediction/measurement at the same precision to which the value is specified. For example [math]1159652140(28)[/math] means [math]1159652140 \pm 28[/math] and [math]1159652186.9(4.1)[/math] means [math]1159652186.9 \pm 4.1[/math].) You can see that the theory predicts the correct experimental value to incredible precision (although the experimental error is still better than the theory one). If you want to persuade scientists that the Standard Model is wrong, then you have to explain why this is a coincidence or show that your new theory predicts [math]g-2[/math] to at least this accuracy.

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