Physics Help Forum Widespread misinterpretation of quantum mechanics

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Feb 21st 2018, 01:57 AM   #11
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 Originally Posted by THERMO Spoken Here If you have trouble sleeping, no booze needed. A few pages of Microscopic Thermodynamics @ THERMO Spoken Here! will do the trick. Check out Table IIIA-1 (Unit IIIA page 10). Exhaustive computer run determines microstates among energy-levels, degeneracies to show "migration to equilibrium."
I guess this happens a lot here...

 Feb 21st 2018, 06:40 AM #12 Senior Member     Join Date: Feb 2017 Posts: 203 My try. Usually I dont much answer others questions. But I will try. If this is stupid just mention so in your new post OP. It would be helpful to state Heisenberg Uncertainty Principle. You might say electrons are negatively charged and protons are positively charged. So as per classical mechanics they should fall into each other. But the above principle states that when the electron is closer to the nucleus the position is best determined but not the velocity. But velocity will be large enough so that the electron just flies off the atom. So I am assuming that the electron is far away from the nucleus so its velocity will be determined accurately which will be lower than when the electron is near the nucleus. That being said the position will not be accurate. Replace the electron cloud concept with this principle. Does this help?
Feb 22nd 2018, 04:35 AM   #13
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 Originally Posted by avito009 Usually I dont much answer others questions. But I will try. If this is stupid just mention so in your new post OP. It would be helpful to state Heisenberg Uncertainty Principle. You might say electrons are negatively charged and protons are positively charged. So as per classical mechanics they should fall into each other. But the above principle states that when the electron is closer to the nucleus the position is best determined but not the velocity. But velocity will be large enough so that the electron just flies off the atom. So I am assuming that the electron is far away from the nucleus so its velocity will be determined accurately which will be lower than when the electron is near the nucleus. That being said the position will not be accurate. Replace the electron cloud concept with this principle. Does this help?
No, I don't think it does. The "electron cloud" is a reasonable, if not good, qualitative descriptor because the reality is that the position of the electron in space is best described as a probability density function that describes how likely it is that the position of an electron is at a particular point in space with respect to its environment.

Feb 22nd 2018, 05:30 AM   #14

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 Originally Posted by avito009 Usually I dont much answer others questions. But I will try. If this is stupid just mention so in your new post OP. It would be helpful to state Heisenberg Uncertainty Principle. You might say electrons are negatively charged and protons are positively charged. So as per classical mechanics they should fall into each other. But the above principle states that when the electron is closer to the nucleus the position is best determined but not the velocity. But velocity will be large enough so that the electron just flies off the atom. So I am assuming that the electron is far away from the nucleus so its velocity will be determined accurately which will be lower than when the electron is near the nucleus. That being said the position will not be accurate. Replace the electron cloud concept with this principle. Does this help?
No, actually.

First, velocity in QM is a very difficult property to work with. Momentum works much better. (Though see here.) Yes, we're back to the Math.

Second, it is a bit chancy to talk about electron states in terms of a cloud. As benit13 mentioned the Schrodinger wave equation deals with a "probability cloud" rather than something more physical. Electrons do not exist in a cloud about the nucleus but the probability of finding an electron in a particular state does. (Actually it's more like a weighted sum over probability states but let's not be picky.) Here, too, we are back to the Math.

-Dan
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Last edited by topsquark; Feb 22nd 2018 at 05:33 AM.

 Feb 22nd 2018, 07:39 AM #15 Physics Team   Join Date: Apr 2009 Location: Boston's North Shore Posts: 1,573 It is my opinion that one doesn't need most of the QM math to understand what QM is about. The math allows one to make quantitative predictions. However the fundamental item needed to grasp QM is the notion of a quantum state. This is represented by the quantity |Psi> which is known as a ket and in mathematical terms its known as a vector (in a Hilbert Space). Its sufficient for the non-mathematically inclined to merely think of it as representing a quantum state (whatever that means). Feynman describes QM in terms of amplitudes. All of this is how QM is conveyed in QM books for the general public. What is often poorly, if ever explained/defined is what constitutes a measurement. A measurement consists of the interaction of a quantum system with a macroscopic system which yields information. about the quantum system. topsquark likes this. Last edited by Pmb; Feb 22nd 2018 at 08:38 AM.

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