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- Thread starter d-wat
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"Why does July taste like the color purple?"

It's not said to be rude or mean but to bring humor in asking a non-question.

your question contains asking why things are the size they are, is that your question?

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Boundary conditions..

The blackbody radiation experiment had boundary conditions.

QM equations have boundary conditions, even if we have to make the length between boundaries go to infinity.

Let's remove boundaries then.

Take the free particle hamiltonian energy eignvalue equation. The energy eigenvalues are p^2/2m where p is continuous. No more quantum levels.

The blackbody radiation experiment had boundary conditions.

QM equations have boundary conditions, even if we have to make the length between boundaries go to infinity.

Let's remove boundaries then.

Take the free particle hamiltonian energy eignvalue equation. The energy eigenvalues are p^2/2m where p is continuous. No more quantum levels.

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Okay but that's not the cause for that scale, it's the equations to work in those scales. And unless I misunderstand your hamiltonian Eq, your setting the energy level of the plane wave high enough so that the eigenvalues becomes close enough to be free particles?, that really doesn't do away with the quantum level but removes that upper boundry. do correct me if I'm off on that.Boundary conditions..

The blackbody radiation experiment had boundary conditions.

QM equations have boundary conditions, even if we have to make the length between boundaries go to infinity.

Let's remove boundaries then.

Take the free particle hamiltonian energy eignvalue equation. The energy eigenvalues are p^2/2m where p is continuous. No more quantum levels.

To me the question from the OP is the equivalent of asking what is the cause for finer resolution? which really isn't a question at all.

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i don't think it is a non-question at all, i may just be referring to reality as to what might be a physical or at least a theory that may explain its physical cause, but just to make my self clearer, i will rephrase my question: what i'm asking is what causes the existence of the the thing that keeps electrons in place?

"Why does July taste like the color purple?"

It's not said to be rude or mean but to bring humor in asking a non-question.

your question contains asking why things are the size they are, is that your question?

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The Uncertainty Principle. As the electron becomes more isolated in space (closer to the nucleus) the electron's probability for a higher and higher momentum increases. This is another example of the wave like properties of an electron, uncertainty has always been a factor in even classical wave mechanics.what i'm asking is what causes the existence of the the thing that keeps electrons in place?

The boundary conditions of the central potential determine exactly what the lowest state can be.

Funny how uncertainty gives us certainty in so many things, in the end its uncertainly certain.

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stop miss using the uncertainty principle! it has to do with observations not energy levelsThe Uncertainty Principle. As the electron becomes more isolated in space (closer to the nucleus) the electron's probability for a higher and higher momentum increases. This is another example of the wave like properties of an electron, uncertainty has always been a factor in even classical wave mechanics.

The boundary conditions of the central potential determine exactly what the lowest state can be.

Funny how uncertainty gives us certainty in so many things, in the end its uncertainly certain.

Have you done your QM class boy??...

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Huh?stop miss using the uncertainty principle! it has to do with observations not energy levels

Have you done your QM class boy??...

http://www.physics.sfsu.edu/~greensit/book.pdf [Broken]

Page 90 "Why the hydrogen atom is stable"

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SpectraCat

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You might want to watch your tone ... especially since you are wrong. The HUP has to do with whether or not observable quantities can be simultaneously well-defined ... it is completely independent of measurement or observation. The HUP sets a lower limit on the width of distributions from which non-commuting observables are sampled, so it is often explained in terms of observed distributions for repeated measurements. However it is far more fundamental than that, and actually is directly derivable from the postulate that quantum states are representable as vectors in a Hilbert space.stop miss using the uncertainty principle! it has to do with observations not energy levels

Have you done your QM class boy??...

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those derivations are just heuristic pseudo arguments found in introductory booksHuh?

http://www.physics.sfsu.edu/~greensit/book.pdf [Broken]

Page 90 "Why the hydrogen atom is stable"

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are you cute?You might want to watch your tone ... especially since you are wrong. The HUP has to do with whether or not observable quantities can be simultaneously well-defined ... it is completely independent of measurement or observation. The HUP sets a lower limit on the width of distributions from which non-commuting observables are sampled, so it is often explained in terms of observed distributions for repeated measurements. However it is far more fundamental than that, and actually is directly derivable from the postulate that quantum states are representable as vectors in a Hilbert space.

I said that HUP has to do with measurements and not energy levels, I had no time to give a full derivation of HUP

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Enlighten us ansgar.

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Yes, but if you questioned them seriously, you would be aware that those derivations can be carried over quite far in full QFT, and although they must certainly be taken with a grain of salt, still they remain quite suggestive.those derivations are just heuristic pseudo arguments found in introductory books

In "The quantum vacuum, introduction to QED" Milonni discusses in section 2.6 how the momentum-position commutator for a charged particle would be damped exponentially to zero without fluctuations of the electromagnetic field to which it couples. That is because we can couple a charged particle to its own field.

Then in section 3.3 he goes on to atomic stability. He applies the same ideas, balancing how much the electron absorbs energy from the vacuum to how much it gives away, and obtains... Bohr quantization conditionWhat we have here is an example of a "fluctuation-dissipation relation." Generally speaking, if a system is coupled to a "bath" that can take energy from the system in an effectively irreversible way, then the bath must also cause fluctuations. The fluctuations and the dissipation go hand in hand; we cannot have one without the other. In the present example the coupling of a dipole oscillator to the electromagnetic field has a dissipative component, in the form of radiation reaction, and a fluctuation component, in the form of the zero-point (vacuum) field; given the existence of radiation reaction, the vacuum field must also exist in order to preserve the canonical commutation rule and all it entails.

This "derivation" of the Bohr quantization condition obviously should not be taken very seriously. It suggests only how Bohr's quantization condition, at least for n = 1, might have been interpreted by physicists in 1913. We now know that the vacuum field is in fact formally necessary for the stability of atoms in quantum theory: as we saw in Section 2.6, radiation reaction will cause canonical commutators like [x,p] to decay to zero unless the fluctuating vacuum field is included, in which case commutators are consistently preserved.

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"Uncertainty" is quite a badly chosen name. The inequality is nothing but the Cauchy-Schwarz inequality. This is so well-known, it is in the introduction of a wikipedia article. Seriously, this is elementary Hilbert space theory.Enlighten us ansgar.

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There is no "uncertainty"

Second, there is no "principle"

Otherwise, yes, the inequality is best understood geometrically, thinking of functions as vectors.The reason why the uncertainty theorem shouldn't be called a "principle" is that a principle is an idea, usually stated in non-mathematical terms, that you can use to find an appropriate mathematical structure for a new theory that you're trying to find. The "principle" restricts the number of mathematical structures you can use, because you're only looking for theories in which a mathematical statement that resembles the principle can be derived as a theorem.

The "HUP", or rather the statement thatshouldbe called the HUP, is a statement that predates QM. It was used tofindQM. The inequality that people insist on calling "the HUP" is a theorem derived from the axioms of QM.

Other examples of "principles" in physics are "Einstein's postulates" (which are even more inappropriately named than "the HUP", because "postulate" is a synonym for "axiom", and these aren't even mathematical statements) and "the equivalence principle". The former can help you guess that Minkowski spacetime is an appropriate model of space and time, and the latter can help you guess that some other 4-dimensional smooth manifold with a Lorentzian metric determined by a bunch of fields on that manifold, might be an even better choice.

It bugs me a bit every time I see someone refer to the HUP, Einstein's postulates or the equivalence principle when they want to prove something. It sounds like they're referring to the ideas that led to the discovery of the theories, when they could andshouldbe usingthe actual theories. But most of the time, what they have in mindarethe actual mathematical statements that appear in the theories, and not the loosely stated ideas that predate the theories. So the arguments are usually not wrong. They just use annoyingly inappropriate terminology.

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Please note that I am not lobbying for any interpretation. I only point out that Heisenberg's inequality does not mathematically imply fundamental uncertainty.I have heard mixed opinions about hidden variables.

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so you don't know how to derive it but still uses it as if you know what it is?Enlighten us ansgar.

there are library items here on the forum which is really good, have a look at them.

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SpectraCat

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Yes, and I said that you were wrong, and pointed out why I think so. Do you have a rebuttal?are you cute?

I said that HUP has to do with measurements and not energy levels, I had no time to give a full derivation of HUP

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I can derive the existence of discrete energy levels without the HUP if that is what you mean by rebuttal?Yes, and I said that you were wrong, and pointed out why I think so. Do you have a rebuttal?

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I thought we were using HUP to prove how atoms can be stable. The OP question changed after a couple posts.I can derive the existence of discrete energy levels without the HUP if that is what you mean by rebuttal?

I was saying that boundary conditions are the reason for discrete energy levels.

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HUP is an integral (maybe the most fundamental) part of quantum theory, so much so that without it Quantum Mechanics becomes "Classical Mechanics"... And needless to say, you don't have any discrete levels in classical mechanics. So, no, without HUP you cannot "derive" anything..I can derive the existence of discrete energy levels without the HUP if that is what you mean by rebuttal?

(Solving a wave equation in 1D with the simplest boundary condition does not qualify for a theory, if that's your secret derivation!..)

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Atoms are stable without hupI thought we were using HUP to prove how atoms can be stable. The OP question changed after a couple posts.

I was saying that boundary conditions are the reason for discrete energy levels.

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yes it as an important thing, but people are miss using it since they don't really know where it comes from, can YOU derive it?HUP is an integral (maybe the most fundamental) part of quantum theory, so much so that without it Quantum Mechanics becomes "Classical Mechanics"... And needless to say, you don't have any discrete levels in classical mechanics. So, no, without HUP you cannot "derive" anything..

(Solving a wave equation in 1D with the simplest boundary condition does not qualify for a theory, if that's your secret derivation!..)

you do have quantization in CM, nodes in a flute, string or whatever!

you don't need and should not use HUP to derive energy levels in an atom and why it is stable! HUP is the standard deviation of measurment of momentum times the standard deviation of position is greater than hbar/2.

all we can say about the hydrogen atom is about standard deviations of it's energy levels etc, NOT absolute values!

Do you want me to call ZapperZ to step in here and judge who of you and I are correct?

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