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A. Neumaier submitted a new PF Insights post
The Vacuum Fluctuation Myth
Continue reading the Original PF Insights Post.
The Vacuum Fluctuation Myth
Continue reading the Original PF Insights Post.
Only if you're willing to put Hawking's derivation (the real thing, not the heuristic upon which Professor Neumaier is heaping scorn) in the category of "myth".Collin237 said:But Hawking radiation itself is a myth. A
Collin237 said:All we know about black holes is that there are things that match the description as deduced from billions of miles away.
Those are taken seriously as objects. If a physicist has a new idea about them, it's explored, refined, etc., and goes through an ordinary Kuhnian trial. Ideas about black holes, however, are argued on merely theoretical merit.Drakkith said:The same is true of stars, nebulas, exoplanets, galaxies, etc.
What else would you call it? Already in just the abstract, the remarks about "entropy" are a huge red flag.Nugatory said:Only if you're willing to put Hawking's derivation (the real thing,
Collin237 said:Ideas about black holes, however, are argued on merely theoretical merit.
HyperStrings said:Quantum fluctuations are also observed through the lamb shift [4].
The paper [4] states: ''It arises because zero-point fluctuations of the electromagnetic field in vacuum perturb the position of the hydrogen atom’s single bound electron.'' The truth - shown by all sources that actually do the calculations - is that the electromagnetic field interacting with the hydrogen atom’s single bound electron introduces radiative corrections into the corresponding Dirac equation. According to standard quantum mechanical perturbation theory, these corrections result in the Lamb shift. Nothing with vacuum fluctuations or ''virtual photons popping in and out of existence'' as your source claims.HyperStrings said:Quantum fluctuations are also observed through the lamb shift [4].
bhobba said:Its a total myth that quantum fluctuations, virtual particles yada, yada, yada exist. Its part of the pictorial language that has grown up with Feynman diagrams - but are really just terms in a Dyson series:
https://en.wikipedia.org/wiki/Dyson_series
One of the intriguing consequences of inflation is that quantum fluctuations in the early universe can be stretched to astronomical proportions, providing the seeds for the large scale structure of the universe. The predicted spectrum of these fluctuations was calculated by Guth and others in 1982. These fluctuations can be seen today as ripples in the cosmic background radiation, but the amplitude of these faint ripples is only about one part in 100,000. Nonetheless, these ripples were detected by the COBE satellite in 1992, and they have now been measured to much higher precision by the WMAP satellite and other experiments. The properties of the radiation are found to be in excellent agreement with the predictions of the simplest models of inflation.
It is a very useful (and historically sanctioned) tool to capture the imagination of an audience without presenting any formula, although it does not resemble at all what happens. The latter is discovered only if one wants to see what the talk means - and one discovers that it means nothing. ''vacuum fluctuations'' are just a buzzword for ''field theoretic effects'', nothing more.stevendaryl said:Of course you (and A. Neumaier) are right. However, it is interesting that respectable physicists (most recently, I saw a video lecture by Alan Guth where this happens) very often present their informal reasoning in terms of vacuum fluctuations. It seems like it's a useful heuristic for reasoning about what's possible, even though the mathematical details, when you actually try to calculate things, don't actually resemble the "fluctuation" reasoning much at all.
Quantum fluctuations are everywhere, but calling an unexcited crystal a quantum vacuum, as the authors of your source [4] do, is quite a misnomer. Analogies don't create truth.HyperStrings said:I don't see how your retort disproves acoustic quantum fluctuations.
A. Neumaier said:It is a very useful (and historically sanctioned) tool to capture the imagination of an audience without presenting any formula, although it does not resemble at all what happens. The latter is discovered only if one wants to see what the talk means - and one discovers that it means nothing. ''vacuum fluctuations'' are just a buzzword for ''field theoretic effects'', nothing more.
That's the problem. It is nowhere meaningfully defined, but used a lot in informal talk.Haelfix said:whether its just a matter of terminology. I'm fine with saying the quantum vacuum is a subtle creature, and it's a little hard to define what a 'fluctuation' actually means
This isn't about vacuum fluctuations, but about the proper definition of what the vacuum state means in QCD.Haelfix said:one can show that instantons can contribute to the QCD vacuum.
A nonzero vacuum expectation value doesn't mean in any sense that the vacuum is fluctuating. Otherwise the ground state of a single harmonic oscillator would also be fluctuating...Haelfix said:we can actually demonstrate that the vacuum is nonzero in certain cases.
There is a good physics lecture on 'The Dangers of Analogies' and I agree with you, we should be very discerning of analogy. Though, in the lecture/paper he gives rules to how to properly use analogies safely when discussing/teaching physics and admits that sometimes there is no other way to explain something. Just as all Gaileleo had to prove his theory was an analogy. Its a double edged sword, as we must also be aware, we are heading into a time of where experiments will need to be able to represent complex Planckian scale effects, so we may very well have to bite the bullet and start to understand analogous experiments. As it is very possible for them to be useful. With that being said, I will try to be more discreet and specific as I can respect your position.A. Neumaier said:Analogies don't create truth
A. Neumaier said:Quantum fluctuations are everywhere,
Which brings me to another point that, we are using normalization because of Planck scale discrepencies, and 'science' is okay with that, but if you try to isolate those discrepencies with a mathematical application of a 'mistake fixing, re-normalization', science is not okay with that? The very process of normalization is in essence, 'blurring the clarity of the image'. Then a proper re-normalization can result with 'sharpening of the image'.Haelfix said:(and then there are all the complicated renormalization scheme caveats associated with what we mean by this
A. Neumaier said:A nonzero vacuum expectation value doesn't mean in any sense that the vacuum is fluctuating. Otherwise the ground state of a single harmonic oscillator would also be fluctuating...
I have seen the word used only in the context of (relativistic or nonrelativistic) quantum field theory. It doesn't make sense for a harmonic oscillator or a particle in a box. The quantum mechanical ground state is dynamically completely inert under the quadratic Hamiltonian that defines the oscillator. Nothing fluctuates. There is an uncertainty about the values of observables not commuting with the energy, but this is because it is impossible to measure them more accurately, not because these would fluctuate in time. The traditional interpretations refrain from saying what happens in between measurememt; none of them claims that these observables have all the time exact but fluctuating values.Haelfix said:if the origin of the word in textbooks is precisely when discussing simple harmonic oscillators, particles in a box, and other simple nonrelativistic quantum mechanics. There it would presumably mean a fluctuation relative to a classical zero.
Well, the interaction with the crystal, or if you wish, the field defined by it cause these effects. Switch the interaction or the mean field off and the effect is gone. This proves that these are the responsible agents. Not mystical quantum fluctuations.HyperStrings said:, what is causing the ''field theoretic effects'' that oscillate the atom
A. Neumaier said:. The quantum mechanical ground state is dynamically completely inert under the quadratic Hamiltonian that defines the oscillator. Nothing fluctuates.
The Heisenberg uncertainty relation is not about quantum fluctuations but about the intrinsic uncertainty in measuring noncommuting observables. Nothing fluctuates there.RockyMarciano said:To me quantum fluctuations are defined by the fact that the ground state in qm must also obey the Heisenberg principle
Though this is somewhat unrelated to the present topic, let me mention that quantum tunneling is a misnomer. It is motion over the barrier and not through the barrier. For the ''tunneling'' probability tends to zero as the barrier gets higher, and is zero when the barrier is infinitely high. No matter how long a tunnel through the barrier would have to be! Thus it is like the motion of a classical particle with a random kinetic energy - it has a small probability of being kicked over the barrier and ending up outside the well it was in originally.Haelfix said:I have heard the word used more when discussing things like barrier penetration in nrqm. So an author will write something like "classically you will never measure a particle here, but b/c of 'quantum fluctuations' or 'quantum jitters' you will see a tunneling phenomenon on the other side and the nonzero possibility for the detection of a particle".
This is purely semantic but both the insight and thread are about semantics so why not get it right?. Fluctuation is a word that is synonim both of oscillation and of indeterminacy or uncertainty. All it means in the quantum context is the Heisenberg indeterminacy of the ground state, and what fluctuates(vacillates i.e. it is intrinsically uncertain) is precisely the noncommuting observables. Of course many people by extension thinks about something moving or oscillating, that I guess it is what you understand if you disregard the meaning of fluctuation as vacillation/indeterminacy. Since Heisenberg indeterminacy lies at the heart of the quantum departure from classical physics, quantum fluctuations by extension are also referred by many as this departure from classicality.A. Neumaier said:The Heisenberg uncertainty relation is not about quantum fluctuations but about the intrinsic uncertainty in measuring noncommuting observables. Nothing fluctuates there.
RockyMarciano said:This is purely semantic but both the insight and thread are about semantics so why not get it right?. Fluctuation is a word that is synonim both of oscillation and of indeterminacy or uncertainty. All it means in the quantum context is the Heisenberg indeterminacy of the ground state, and what fluctuates(vacillates i.e. it is intrinsically uncertain) is precisely the noncommuting observables. Of course many people by extension thinks about something moving or oscillating, that I guess it is what you understand if you disregard the meaning of fluctuation as vacillation/indeterminacy. Since Heisenberg indeterminacy lies at the heart of the quantum departure from classical physics, quantum fluctuations by extension are also referred by many as this departure from classicality.
On the other hand if one is strict with the math not even the fields or the waves actually oscillate, since the math always describes a rigid picture, a shortcoming of analysis. But this should show just how ridiculous can blind strictness get.
No. Fluctuation in today's usage always means change, not just being uncertain! All the major dictionaries agree on that:RockyMarciano said:Fluctuation is a word that is synonim both of oscillation and of indeterminacy or uncertainty.
This is only your private interpretation of the term. Never before I heard of someone talk about quantum vaccilations! And even that word means not just uncertainty but wafering uncertainty - a process in time!RockyMarciano said:what fluctuates(vacillates i.e. it is intrinsically uncertain) is precisely the noncommuting observables.
As stated, it is meaningless since ##\Phi(x)## is not an operator, hence not an observable. As remarked in your quote, one has to use a smeared version (averaging over a small open region in space-time) to produce an operator. Even with this amendment, the statement is misleading. The ''vacuum value'' is not a commonly used expression. The nearest expression with a formal meaning is the vacuum expectation value, but this is completely determined and hence certain. What is probably meant is that if one could measure the local value of a smeared field in the vacuum state (don't ask how this ever can be done, as the vacuum contains no particles, hence no observer), the result would have a significant uncertainty, i.e., there is a nonzero probability of getting a result significantly different from the vacuum expectation value. This is formally true if one assumes (as is commonly done) that the Born interpretation holds in this (counterfactual) case.ftr said:What do you think this statement is saying