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Politics : Formerly About Advanced Micro Devices -- Ignore unavailable to you. Want to Upgrade?

To: combjelly who wrote (776251)	3/23/2014 6:25:41 PM
From: Bilow	Read Replies (1) \| Respond to of 1573902

Hi combjelly; Re: "There you go again. In QM, the concept of "forbidden areas" just means it that it cannot be traversed in a conventional manner. It doesn't mean it cannot happen at all because particles don't necessarily travel ballistic trajectories. Good example, tunnel diodes. Classically speaking, they should not be able to conduct. Yet they do under the right circumstances."; Nice that you're willing to debate the issue with a guy who's employed in it, LOL. Of course I should point out that the post you're responding to does not have the phrase "forbidden areas" in it so your comment does not apply. The article I'm quoting is not about classical physics in any way. This is purely quantum mechanics. Let me define the terms for you so you can more intelligently argue your incorrect side. Now your position is apparently in support of koan who argues that "For you to put it at 0.00000 (no probability) shows your ignorance right there. There is a probability for anything (the HUP!)." Message 29444285 If your position is different from koan, please specify, LOL. Quantum mechanics is a theory of probabilities. The usual calculation begins with a given initial state and finds the probability that it evolves (in time) into a given final state. If you calculate the probability and you get zero, then the transition cannot happen. And anyone who's done any amount of QM calculations at all knows that transition probabilities give zero all the time in QM. This often happens when doing computations that are simplified (for example electronic transitions that are forbidden by not having angular momentum change by the angular momentum of a single photon, these happen, but slower, by more complicated processes). But it's a general feature of the structure of QM. For any given state vector, there are an infinite number of state vectors that are orthogonal to it, and therefore give zero transition probabilities. So even when you allow transitions by including rare processes, the result is that there are some other transitions that were allowed in the simplified version but now are impossible. By contrast, superselection rules say that some transition probabilities are completely impossible. Thus the statement: In contrast, a SSR[superselection rule] is usually thought of as making a more rigorous statement. It not only forbids certain transitions through particular modes, but altogether as a matter of some deeper lying principle; hence the “Super”. In other words, transitions are not only inhibited for the particular dynamical evolution at hand, generated by the given Hamiltonian operator, but for all conceivable dynamical evolutions. This is not about where an electron travels temporarily. It's about things that absolutely cannot happen. Ever. By any "conceivable dynamical evolution". Can't get there from here. An example of something that is forbidden by a superselection rule is the decay of an electron (under the assumptions of the Standard Model of elementary particles which is the currently accepted model of elementary particles like the electron). They never decay. Never. Things forbidden by superselection rules are the easiest to prove examples of processes that are forbidden in quantum mechanics. But like I said above, given any particular Hamiltonian, there are infinitely many processes that are forbidden. Most of them are just more difficult to specify than the ones that violate superselection rules. So you think an electron can decay??? And do you agree with koan that the Heisenberg Uncertainty Principle supports your position??? Here, let me quote the HUP to you: In quantum mechanics, the uncertainty principle is any of a variety of mathematical inequalities asserting a fundamental limit to the precision with which certain pairs of physical properties of a particle known as complementary variables, such as position x and momentum p, can be known simultaneously. en.wikipedia.org Since this is way above your pay grade, let me simply point out that the HUP applies only to "pairs of physical properties of a particle known as complementary variables". Do you really think that "anything" can be written in terms of "pairs of physical properties"? If that were true, then I can conclude that you think that any and all properties are complementary. Nope. So do you think the HUP applies to measurements of the momentum of a particle in the x direction as compared to the y direction? Come on, let's hear you explain the HUP. To help get you started, let me explain how the HUP applies to electron trajectories in classically forbidden regions. In this case, the complementary variables are time and energy. The electron is energetically forbidden in these regions but so long as the time it spends there is sufficiently small, it is allowed by the HUP. Now it's your turn. Go ahead and explain how the HUP allows the decay of an electron into photons. -- Carl P.S. I'm still waiting....