Explore The Vacuum Fluctuation Myth in Quantum Theory
This Insight Article is a sequel of the Insight Articles ”The Physics of Virtual Particles” and “Misconceptions about Virtual Particles“ which make precise what a virtual particle is and what being real means, document some of the liberties taken in physics textbooks in the use of this concept, and mention the most prominent misuses. A further Insight Article, ”Vacuum Fluctuations in Experimental Practice”, shows the example of a recent article in the scientific literature how some authors claim the observation of vacuum fluctuations, justified only by superficial, invalid reasoning.
In short, the concept of virtual particles is well-defined and useful when restricted to its use in Feynman diagrams and associated technical discussions. But it is highly misleading when used to argue about vacuum fluctuations as if these were processes happening in space and time. The latter is a frequent misunderstanding, a myth that has not the slightest basis in particle physics. (The proper meaning of some terms related to the vacuum is explained at the end of ”The Physics of Virtual Particles”.)
The two articles mentioned do not, however, explain how it is possible that this misunderstanding is so widespread, and even serious experts resort to misleading imagery when explaining the subject to the general public. This is answered here at the example of Steve Carlip’s page on Hawkings radiation, where Steve Carlip, a well-known theoretical physicist working on quantum gravity, gave a lucid but completely mythical narrative about how vacuum fluctuations create Hawking radiation. This vacuum fluctuation myth comes from taking pieces of intuition and connecting them with a plausible narrative. The following is a reconstruction of the sort of thoughts that combine to justify the myth in the eyes of those who use this language. (For those interested, a non-mythical description of Hawking radiation is given by Sabine Hossenfelder here.)
The starting point is the sound knowledge that there are technical notions of vacuum fluctuations (= nonzero vacuum expectation values), virtual particles (=internal lines in a Feynman diagram), and that in bare quantum field theory with a cutoff, the vacuum is a complicated multiparticle state depending on the cutoff – though in a way that it diverges when the cutoff is removed, so that nothing physical remains. Then the question arises: Is is possible to convey a bit of this to ordinary people? It is highly unsatisfactory not to be able to talk about what one is doing in one’s research…
So one goes for analogies and images. Already calling internal lines ”virtual particles” is a step in this direction. Allow yourself a little more liberty and combine it with Feynman’s classical absorber theory of radiation; after all, Feynman also invented the diagrams bearing his name, possibly even inspired by this analogy. The lines defining the virtual particles look like world lines in a classical process, so why not interpret them (in one’s imagination) as the quantum remnants of the classical world lines of Feynman’s earlier (later abandoned) theory? This happy accident makes the story possible. It is not completely accurate but plausible (in the absence of the correction of the intuition by mathematical formulas) because both classical particles and virtual particles are represented pictorially by lines, and it is something that ordinary people can imagine. This is the beginning of the myth. An extra reassurance that you are on a good path is that the arrows that physicists draw on their diagrams (to indicate the sign of conserved quantum numbers) happen to match Feynman’s classical (later abandoned) idea that antiparticles are just particles moving backward in time.
To bring in more physics one has to be able to interpret complete Feynman diagrams. Tree diagrams are easy but bring in a new aspect. They talk about real and virtual particles. On an electron line containing two external vertices, the electron changes its status from being real (external) to being virtual (internal) and back (external) again. We learn from it a new fact – a virtual particle can become real, and conversely. The interpretation as world lines teaches us other things: A single Feynman diagram should in fact be considered just as a tiny snapshot of an extended web containing all particles in the universe; after all, world lines do not begin and end nowhere. Thus ”in reality” (meaning in the simplified virtual reality painted for the general public) all particles should be viewed as virtual until they are observed (where they obviously are real). This matches a version of the highly respected Copenhagen interpretation: Unobserved particles have a sort of ghost existence since properties emerge only when they are subjected to quantum measurement. You are pleased by this coincidence – it seems to say that there is a coherent story to be told. Also, since most of the lines in the Feynman diagram end, you have a layman’s picture for decaying particles: What you see in a bubble chamber is just a Feynman diagram made visible! This is the first serious manifestation of the myth. In spite of lacking any grounding in real physics (being grounded instead in the visual analogy), you feel entitled to make this identification – it serves your final goal to make some of the intricacies of microphysics accessible to the general public. No one there will ever ask how it can be that two virtual particles can bend as in a Feynman diagram with a loop – so that they find each other exactly at the right place and with exactly the right momentum to annihilate. Therefore such impossibilities – that would spoil the goal of giving a simplified picture of what happens – are silently swept under the carpet.
The next thing is to interpret the bare multiparticle state. It is obviously a complex superposition of bare particles. Make the next move to identify bare particles with virtual particles; after all, both are unobservable but appear in some version of the formalism. Now you have the picture of the vacuum as teeming with particles. From the form of Feynman diagrams with one or more loops, you can read off that in order to make sense of the narrative these particles have to pop in and out of existence. This is the birth of the next item in the myth. That in a superposition nothing dynamical happens is a small nuisance that you happily sacrifice in order to be understandable to your intended audience. After all, you can now give an illusion of having conveyed something of the complexities of the naive perturbative approach without having to talk about perturbation theory. In addition, without asking for it, you have found an unexpected visual interpretation of the notion of a vacuum fluctuation: A teeming vacuum where particles constantly pop in and out of existence clearly fluctuates, and every single act of popping may rightfully be regarded as a fluctuation of the vacuum. Another piece of the myth has found its place. Never mind that there is not the slightest way of justifying this analogy on the level of mathematical formulas. What counts is how the picture appeals to the general public, and it is obvious that drastic simplifications are needed to achieve this goal.
Now one needs to worry about the basic principles of physics in all this. After all, one doesn’t want to talk about particles alone but conveys some general physics as well. Let us bring in conservation laws. Everyone knows that energy is conserved in Nature. But wait, doesn’t the creation of particles require some energy? Never mind, quantum mechanics comes to the rescue. People will have heard of the Heisenberg uncertainty relation, and if they haven’t this is an opportunity to make your audience acquainted with it. It states the intrinsic uncertainty of position and momentum in nonrelativistic mechanics. What does it tell about energy conservation? Nothing at all, but analogy comes to the rescue. In relativistic physics, time is the 4th coordinate of position, and energy the 4th coordinate of momentum. Thus we don’t make a big blunder if we consider a time-energy uncertainty relation. (Though in mainstream quantum physics, time is not an observable – it has a completely different status.) Uncertain energy can be liberally interpreted as a slightly inaccurate conservation law. After all, one can derive from quantum mechanics only that the expectation of the energy operator is conserved. Expectation brings to mind that whatever you measure inaccurately must be measured many times for getting an improved accuracy. Thus only the average energy needs to be conserved. Reinterpret the physical ensemble average (in the service of simplifying the physics to give your audience a coherent story) as an average in time.
Thus you found the solution: Energy can be borrowed for a short period of time if it is returned on average. The next item of the myth arrived. Now you are quite confident that you’ll be able to get a full and rich story (for laymen only, so all the small and big blunders made can be excused) and continue to turn it into something you’ll tell in public (or write in a book). You hope that the attentive audience will not ask where the energy is borrowed from, but unfortunately, you told the story first to a colleague with an unbiased mind and he insisted on that this should be clarified first. You need to look at some more pieces of information to get the next input. Fortunately, you soon find it: The zero-point energy of a harmonic oscillator had in the past always been ignored by saying that only energy differences are observable. Maybe it is the bank from which the virtual particles lining up for popping into existence can borrow their energy. And yes – it turns out that the bare quantum field has a huge amount of zero-point energy – an infinite amount if you take the physical limit. Clearly, this must be the source – and no ordinary person will be interested to question it. Thus the final piece of the myth arrived. You are happy – it will be a really good story conveying a lot of physics while still being understandable to ordinary people.
That there is no physical mechanism for how the borrowing works is a small nuisance that (for the layman) can be ignored – after all, they want a simple story that they can believe, not a technical discussion of all the problems involved – they know that quantum mechanics is full of unresolved problems. At this point, your story is already so convincing that you don’t mind that all observable quantities also become infinite in the limit considered and that when you instead do a proper renormalization (needed to get the high accuracy predictions quantum field theory is famous for) the whole capital of the vacuum energy bank shrinks to zero!
Now the particle philosophy for the laymen is essentially complete. Only a few – to laymen imperceptible – jumps of the imagination were needed in the service of understandability. Like in a cinema, where the pictures jump in discrete steps but provide a sufficient illusion for the audience to see a continuous story. To make sure that the audience, captured by the imaginative illusion, will not take it for physical reality, and to ensure that your status as a respected scientist is preserved, you begin with a caveat (like Steve Carlip did on his page on Hawkings radiation, in the inconspicuous first line after the heading ”An Incomplete Glossary” – long forgotten at the time the reader enters the mythical narrative linked to above): ”Be warned – the explanations here are, for the most part, drastic oversimplifications, and shouldn’t be taken too literally.” But in spite of this, you can instead be sure that most of your audience will ignore this sentence said in the first few seconds in favor of the nice mental pictures that you took a whole hour to explain and make intelligible.
When Hawking discovered what was later called Hawking radiation this picture for the general public was already well entrenched. So he only had to figure out how his discovery would fit in – and it fitted well. Instead of talking about gravitational energy (not visible, hence a sort of vacuum) creating a particle-antiparticle pair one partner of which escapes there is only a small step to saying what the educated general public expects. Since the particles are not (yet) observable by the faraway observer seeing only the radiation, they must be sold according to the philosophy developed above as virtual particles created (hence vacuum fluctuations in action). Years later, when one of the particles is finally observed by the faraway observer, it becomes real as a piece of the observable Hawking radiation.
Thus if you want to summarize to lay people the Hawking effect in a single phrase, what is more, natural than to say that ”vacuum fluctuations cause the Hawking radiation” without repeating the warning that this ”shouldn’t be taken too literally”?
Full Professor (Chair for Computational Mathematics) at the University of Vienna, Austria
If vacuum fluctuations are fictitious, then what is the proper explanation of the Casimir effect?https://www.physicsforums.com/threads/vacuum-fluctions-and-the-casimir-effect.828475/
If vacuum fluctuations are fictitious, then what is the proper explanation of the Casimir effect?
I used to know a bit about the "toy model" ##phi^4_2## QFT in 1+1 dimensions (Glimm & Jaffe). They rigorously construct interacting particle states with bound states and scattering. AFAIK there is nothing corresponding to vacuum fluctuations in this mathematically well defined theory. I can't think how you could even rigorously ask "are there vacuum fluctuations?" in this context.
"Vacuum fluctuations" seem to be an artifice of trying to apply perturbation theory when you don't know that the perturbed theory is mathematically well defined.Vacuum fluctuations refer to the fact that smeared field operators have in the vacuum state a nonzero variance. This is captured by the Wightman distribution functions, hence a fact even in ##phi^4_2## QFT in 1+1 dimensions.
On the other hand, interpreting (as in most popular accounts of quantum phenomena) these vacuum fluctuations as happenings in time is completely fictitious.
I used to know a bit about the "toy model" ##phi^4_2## QFT in 1+1 dimensions (Glimm & Jaffe). They rigorously construct interacting particle states with bound states and scattering. AFAIK there is nothing corresponding to vacuum fluctuations in this mathematically well defined theory. I can't think how you could even rigorously ask "are there vacuum fluctuations?" in this context.
"Vacuum fluctuations" seem to be an artifice of trying to apply perturbation theory when you don't know that the perturbed theory is mathematically well defined.
This is a different context of happening than deterministically evolving which applies to the wf as a whole. For something to happen, you need measurement.No. In more complicated contexts, a lot may happen, and this is expressed in the evolution of the state. Indeed, ''the moment of measurement'' is itself a gross simplification of a very complicated interaction that happens between the electron and the measurement device, described not by the state of the electron alone but by the state of the combined system electron+device+environment. The apparent randomness in the fate of the electron state alone is due to this additional complexity.
The smooth evolution of the wave function is dynamically happening while it passes a magnet. It is not the wave function but the intuitive semiclassical picture of an electron as a moving point that ''causes'' the apparent jumps.Got it. To me, to say that the electron ia fluctuating in its position is roughly to say that it is jumping between one position and another when not measured which is clearly related to the semiclassical picture you (and vanhees) described. And which is of course false.
When I said nothing happens in the wf, I meant that. Electron isn't jumping between the spots, it literally is in a state of variance which may change over time. But it is still only a variance – nothing happens 'inside' the wf. This is a different context of happening than deterministically evolving which applies to the wf as a whole. For something to happen, you need measurement. Would you agree with this line of reasoning?
But would you still say that nothing dynamical happens inside the wavefunction before the measurementThe smooth evolution of the wave function is dynamically happening while it passes a magnet. It is not the wave function but the intuitive semiclassical picture of an electron as a moving point that ''causes'' the apparent jumps.
To say that the electron has no definite position just means that one cannot think of it as being a point. The position of an electron is as well-defined as that of a cloud – it is located in a well-defined region but not in a well-defined point. Only the latter would have a definite position. Thus if one wants a more valid intuitive picture one needs to consider an electron as a smoothly changing cloud distributed over all electron rays with a non-negligible mass density, and contracting to a small spot upon measuring.
The wave functions evolve according to Schrödinger's equation (i.e., unitary time evolution). I don't know what you mean by "nothing happens inside the wave function". The Schrödinger equation is describing the dynamics of the system.
According to quantum theory nothing is jumping at all. It's another bad idea from "old quantum theory" that should not be used in any modern physics curriculum anymore. Indeed an electron has never a definite position (although in principle it can be quite localized, because it's a massive particle and thus admits the definition of position as an observable). Within non-relatistic quantum theory the position-probability distribution is given by ##|psi(t,vec{x})|^2##.
In this case the wave function changes deterministically. The wave function of the spin of an electron changes very smoothly with time, except at the moment of measurement, where it changes randomly. But this randomness has nothing to do with vacuum fluctuations.But would you still say that nothing dynamical happens inside the wavefunction before the measurement, even if we take into account the deterministic evolution you mentioned?
It's not like the electron is jumping from one spot to anothee. It literally is in a state without a definite position, right?
if the wave function is time dependent, for instance an electron in the double slit experiment, do fluctuations in the quantum state happen then?In this case the wave function changes deterministically. The wave function of the spin of an electron changes very smoothly with time, except at the moment of measurement, where it changes randomly. But this randomness has nothing to do with vacuum fluctuations.
I have a closely related question. In the insight it is mentioned that generally, inside a superposition nothing dynamical happens. But what if the wave function is time dependent, for instance an electron in the double slit experiment, do fluctuations in the quantum state happen then?
I don't see where the second quote would imply vacuum fluctuations. We cannot really predict a cosmological constant from QFT, but if it is non-zero, the natural scale would be the Planck density.
Yes, it's very hard to get wrong ideas from popular-science books (sometimes even textbooks!) out of the minds of people. Some famous guy (Feynman?) said, that for any problem there's a simple solution, which is wrong.
Some people still seem to think vacuum fluctuations are a real thing.
• Theoretical estimates of various contributions to the vacuum energy density in QFT exceed the observational bound by at least 40 orders of magnitude. This large discrepancy constitutes the cosmological constant problem. One can distinguish at least two different meanings to the notion of a cosmological constant problem:
1. Calculations of Λ = 8 π G ρvac from assuming real QFT vacuum fluctuations, lead to a huge fine-tuning problem.
…
John MoffatThe value of the cosmological constant is infamously the worst prediction ever made using quantum field theory; the math says it should be 120 orders of magnitude larger than what we observe.
Sabine Hossenfelder
How would one rebut these statements:
[1] Vacuum fluctuations have observable consequences, like the Casimir force between two plates in vacuum.
[2] The Casimir effect is a small attractive force which acts between two closed parallel uncharged conducting plates. It is due to quantum vacuum fluctuation of the electromagnetic field.
They are from this publication:
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0ahUKEwjh0OKKv_XSAhUMu48KHbcMD6gQFgggMAA&url=http%3A%2F%2Fwww.hep.caltech.edu%2F~phys199%2Flectures%2Flect5_6_cas.pdf&usg=AFQjCNECAPGduk4ABGP6lQ3y0UixN-pg6g&cad=rja
Please forgive me if you have already addressed this in one of your earlier insight articles, but I did search for “Casimir” in those articles and concluded that they probably don’t address this point.
Wait, let me try to answer my own question, and then please tell me if I’m on the right track. Can we say that the observed Casimir force is not necessarily caused by something “real”, just as the different random outcomes of a quantum measurement are not directed by anything real (unless one goes with hidden variables).
Can we also say that there is an interference of probabilities in the Casimir configuration, so that there is more amplitude for the plates to move together than to move apart?
I will also add a philosophical note:
The existence of a "vacuum" (ie a region where all fields are in their ground state) is an unscientific postulate, in that it cannot be observed, as observation requires interaction, interaction requires the existence of non-zero expectation values, and if there is no interaction, then there is no observation.
It's like an anti-singularity; The hypothesized singularity at the center of a black hole cannot be observed, as no signal can exit from it, and to come into contact with it implies total destruction of the observational apparatus, so its existence too is an unscientific postulate.
Unruh radiation.
It seems to me that the author is saying "A totally empty vacuum has no quantum fluctuations, but when you introduce real particles, it behaves as if there are quantum fluctuations." Lamb shift, vacuum polarization, Unruh effect, Hawking radiation, etc. The ψ at each point in space has an uncertain H for each field.
So, when no observer is present to observe nothing, nothing happens.
https://en.m.wikipedia.org/wiki/QuantumIn physics, a quantum (plural: quanta) is the minimum amount of any physical entity involved in an interaction. The fundamental notion that a physical property may be "quantized," referred to as "the hypothesis of quantization".[1] This means that the magnitude of the physical property can take on only certain discrete valuesHow can you possibly apply the above to a VP ?
[QUOTE="PeterDonis, post: 5665661, member: 197831"]No, it isn't. The scalar field is the fundamental object. "Virtual particles" is just a shorthand way of describing particular things that arise in a particular approximation.You are making the common mistake of equating "quantized" with "discrete". That's not what quantization means.From the standpoint of quantum field theory, quantum fields (of which the scalar field is one) are the fundamental objects. "Particles" and "waves" are just names for particular kinds of quantum field states, and there are quantum field states that are not aptly described by either of those names.”http://wikidiff.com/quantum/discrete[quote]As adjectives the difference between discrete and quantum is that discrete is separate; distinct; individual; non-continuous while quantum is of a change, sudden or discrete, without intermediate stages.[/quote]I think I used quantum/quantized in the appropriate way.Discrete things do not have to be of the same size. But quantum things (quanta) are supposed to be of the same size, like fundamental units or fundamental blocks. Because of that, they are like fundamental deltas or units of change.
[QUOTE="Mordred, post: 5666093, member: 351508"]Yes he is absolutely correct fluctuations are intrinsic to the field. Fluctuations however do not form nor define a field. Fluctuations is a property of a field much like volume is intrinsic to a 3d object. It isn't seperate but an aspect of a field.”He's saying there's no reason to look for a cause for those fluctuations – ie. we should just accept them "as is".Why shouldn't we attribute a cause to the fluctuations? It's like saying there's no need to talk about energy separately from matter, because all matter is endowed with energy in some form or other.The field may have fluctuations, but we may wish to ask why. He's saying we shouldn't ask why. To me, that's ridiculous – why can't I look for the reason why?
Yes he is absolutely correct fluctuations are intrinsic to the field. Fluctuations however do not form nor define a field. Fluctuations is a property of a field much like volume is intrinsic to a 3d object. It isn't seperate but an aspect of a field.
[QUOTE="Mordred, post: 5665872, member: 351508"]To just add a caveat to Peterdonis excellent reply. There is alway a field even without fluctuations/particles etc. Just to stress the field is fundamental.”But Mr Neumaier said that the fluctuations are intrinsic to the field. I'm saying they should be discerned from the field.
Arnold, I found this paper(researching a different subject) by Jaynes which you mention his name in context of entropy issues in FAQ. But This paper has some relevance to the discussion, what do you think(I kind like what he is saying, but I need to study it more)http://bayes.wustl.edu/etj/articles/prob.in.qm.pdf
To just add a caveat to Peterdonis excellent reply. There is alway a field even without fluctuations/particles etc.
[QUOTE="sanman, post: 5665654, member: 65959"]Whether you want to describe the fluctuations as fluctuations in the Scalar Field, or whether you want to describe them as Virtual Particles, is just a matter of perspective.”No, it isn't. The scalar field is the fundamental object. "Virtual particles" is just a shorthand way of describing particular things that arise in a particular approximation.[QUOTE="sanman, post: 5665654, member: 65959"]I would argue that quantization tends to push you towards particles, since there's no inherent need for waves to be quantized.”You are making the common mistake of equating "quantized" with "discrete". That's not what quantization means.From the standpoint of quantum field theory, quantum fields (of which the scalar field is one) are the fundamental objects. "Particles" and "waves" are just names for particular kinds of quantum field states, and there are quantum field states that are not aptly described by either of those names.
[QUOTE="PeterDonis, post: 5664512, member: 197831"]You are assuming that these are two different possibilities–two different ways the universe could be, and we have to figure out which.What Arnold is saying is that they are just two different ways of trying to describe, heuristically, in ordinary language, the same single way the universe is. There is no actual difference in the physics; the only difference is in the words.”But that's actually what I said, and not him. I pointed out that applying a particle model is just a way of describing something. He said that there can only be a Scalar Field.Whether you want to describe the fluctuations as fluctuations in the Scalar Field, or whether you want to describe them as Virtual Particles, is just a matter of perspective.But I would argue that quantization tends to push you towards particles, since there's no inherent need for waves to be quantized.
[QUOTE="ftr, post: 5664629, member: 465682"]The fact that there is a variance does indicate that there is fluctuation, doesn't it”In principle it could be interpreted as a fluctuation of the measurement results in repeatedly prepared copies of the system in identical states. But this is a sensible interpretation only for tiny systems of which one can prepare many copies in the same state. One cannot copy a quantum field. It exists only once at each point in spacetime. What is measured is always a (smeared) field expectation value. If something fluctuates there then due to turbulence, which indeed is a random field phenomenon happening in space and time. But turbulence is absent in a vacuum. [QUOTE="ftr, post: 5664629, member: 465682"]do you mean the electron field and the EM field together "added", but the electron field does not "generate" EM.”No. I mean the mathematical sum (no quotation marks) of the two pieces of the electromagnetic field mentioned in Wikipedia in the context of your quote, denoted ##A_mu## and ##B_mu##. The electron field is ##psi## and is a separate entity that cannot be added to the e/m field as it has a completely different transformation behavior.[QUOTE="ftr, post: 5664629, member: 465682"]the issues you raised in your insight are very well known and debated endlessly but you have put them in a nice prospective story to highlight several interconnected concepts”The purpose of these insight articles is to put an end to this seemingly endless debate. Debates are always signs of using a language so imprecise that people continuously misunderstand each other. Once a clear and sufficiently authoritative language becomes widespread, misunderstanding begin to cease and debate becomes as pointless as debating irrational or imaginary numbers. The language exists already but is diluted so much by current informal practice that attempting to make sense of the whole mess is immensely confusing. It took me many years of wading through this confusion before I learnt to understand things in such a way that I can point to the sources of misunderstanding in a consistent and hopefully convincing way.
D'oh I feel like an idiot I completely forgot the creation/annihilation operators add/subtract a quanta of energy. How embarrassing.Ok I fully understand where you are coming from Neumaiur with regards to virtual particles.
The fact that there is a variance does indicate that there is fluctuation, doesn't it[QUOTE="A. Neumaier, post: 5664609, member: 293806"]There is no way to separate the two parts of the field and only their sum has a measurable, hence physical meaning”do you mean the electron field and the EM field together "added", but the electron field does not "generate" EM.Arnold, I think people appreciate very much what you have been trying to do, even though the issues you raised in your insight is very well known and debated endlessly but you have put them in a nice prospective story to highlight several interconnected concepts mainly regarding Feynman diagrams which were suppose to make things easier.I also understand that it might become tiring for you, but an elaborated response might actually shorten to back and forth responses. Thank you again.
[QUOTE="ftr, post: 5664575, member: 465682"]vacuum fluctuations (= nonzero vacuum expectation values)”I never equated the two. Note that a nonzero variance ##sigma(X)## is a special case ##langle(X-bar X)^2rangle## of a nonzero vacuum expectation value.''The covariant four-potential of the electromagnetic field generated by the electron itself'' is sloppiness on the part of Wikipedia. The term is used solely to distinguish it from the external field mentioned in the same sentence. There is no way to separate the two parts of the field and only their sum has a measurable, hence physical meaning.
[QUOTE="PeterDonis, post: 5664512, member: 197831"]You are assuming that these are two different possibilities–two different ways the universe could be, and we have to figure out which.What Arnold is saying is that they are just two different ways of trying to describe, heuristically, in ordinary language, the same single way the universe is. There is no actual difference in the physics; the only difference is in the words.”Oh how true this is unfortunately often trying to describe things heuristically can cause greater confusion. I've been quilty of that on more than one occasion.At Neumaiur now that I have a better handle on what you trying to express to me. I rectract my concerns.
[QUOTE="A. Neumaier, post: 5664227, member: 293806"]In QED there is just a single electromagnetic field and a single electron-positron field.”Ok, this is from wiki QED
A_mu is the covariant four-potential of the electromagnetic field generated by the electron itself; do you agree with that?Also you sayvacuum fluctuations (= nonzero vacuum expectation values)Reference https://www.physicsforums.com/insights/vacuum-fluctuation-myth/But I think people mean VF by the variance not the EV.
[QUOTE="sanman, post: 5664159, member: 65959"]That assumes they are just mere fluctuations, and not manifestations of something deeper (eg.virtual particles)”You are assuming that these are two different possibilities–two different ways the universe could be, and we have to figure out which.What Arnold is saying is that they are just two different ways of trying to describe, heuristically, in ordinary language, the same single way the universe is. There is no actual difference in the physics; the only difference is in the words.
[QUOTE="ftr, post: 5664190, member: 465682"]in your FAQ there is nothing about vacuum polarization”I just added at the end of my insight article The Physics of Virtual Particles relevant definitions of this and related items.
[QUOTE="sanman, post: 5664159, member: 65959"]manifestations of something deeper (eg.virtual particles), which could be the basis for the Field.”Fields are deeper than both fluctuations or virtual particles, hence the latter cannot be the basis for the former.
[QUOTE="ftr, post: 5664190, member: 465682"]1. in your FAQ there is nothing about vacuum polarization, can you explain it from your point of view.”Vacuum polarization is the name for the radiation corrections to the photon self-energy. If computed in perturbation theory, it is given by the sum of all Feynman diagrams with two external photon lines. It is a physical effect caused by the interaction with the electron field, not by the virtual particles in the diagrams, which are pure mnemonic for the integrals used for the computation and play no causal role.The tale told by the wikipedia page linked to is just a fairy tale, of the same kind as the myth about Hawking radiation that I discussed in the Insight article.[QUOTE="ftr, post: 5664190, member: 465682"]2. in QED we assume an "associated" EM field for the electron. It seems this field is a kind of pseudo-field because no real photon but a VP as its quanta, am I right.”I never heard about associated e/m fields for the electron. In QED there is just a single electromagnetic field and a single electron-positron field.[QUOTE="ftr, post: 5664190, member: 465682"]3. do you agree that VP if they do not exist but some kind of a disturbance is generated”The hypothesis ''they do not exist'' is false, hence there is nothing to agree to.
Neumaier, I have few questions.1. in your FAQ there is nothing about vacuum polarization, can you explain it from your point of view.2. in QED we assume an "associated" EM field for the electron. It seems this field is a kind of pseudo-field because no real photon but a VP as its quanta, am I right.3. do you agree that VP if they do not exist but some kind of a disturbance is generated which could be due to above field or equivalently to "vacuum fluctuation". this a view of Matt Strassler I think.
[QUOTE="A. Neumaier, post: 5664151, member: 293806"]No chicken or egg. Fluctuations are definable only after one has already defined fields. Without fields the notion of fluctuations wouldn't make scientific sense.”That assumes they are just mere fluctuations, and not manifestations of something deeper (eg.virtual particles), which could be the basis for the Field.We have already seen that light is quantized as photons – which is the reason that particle model has been accepted.When the background fluctuations in the field are also quantized, why should we imagine such quantization is an intrinsic property of the field, without being open to accepting a particle model to explain the quantization?
[QUOTE="sanman, post: 5664146, member: 65959"]It seems like a Chicken-and-Egg argument: Is the Field the basis for the fluctuations, or are the fluctuations the basis for the Field?”No chicken or egg. Fluctuations are definable only after one has already defined fields. Without fields the notion of fluctuations wouldn't make scientific sense.
[QUOTE="A. Neumaier, post: 5664130, member: 293806"]If you remove all matter from spacetime there will still be the electromagnetic and the gravitational field. But no one to observe it, so no physics.Absolute zero is a fiction like the vacuum itself. One cannot reach it, only approach it.This has nothing to do with vacuum fluctuations, which are not things happening.”Alright, to use your parlance – would the "minimal background fluctuations in the field" cease to exist under any circumstances?It seems like a Chicken-and-Egg argument: Is the Field the basis for the fluctuations, or are the fluctuations the basis for the Field?It's like arguing over whether Light is "a particle with wave-like characteristics" versus Light being "a wave with particle characteristics"
[QUOTE="sanman, post: 5664135, member: 65959"]I'm not as immediately concerned with a cause for the field as I am with why it fluctuates “Fields fluctuate because this is a general property of fields. Asking about their causes is as meaningless as asking about why sine waves oscillate. It is because they are defined that way.
[QUOTE="A. Neumaier, post: 5664118, member: 293806"]Black body radiation is caused by the electromagnetic field. Hawking radiation is real particles created by the gravitational field. Nothing is created by either the vacuum or by virtual; particles.That's the scientific part.[/quote]Sir, I feel your assertion is no less metaphysical than mine. You want to assert that fluctuations are intrinsic to the field, and cannot be conceptually distinguished from it. By the same token, you could also say that energy is an intrinsic property of all matter, and doesn't deserve to be discerned or distinguished from matter. At that point, it does feel like arguing a religious debate.[quote]But you wanted a cause for the field itself, which is metaphysics.”Sir, I'm not as immediately concerned with a cause for the field as I am with why it fluctuates and doesn't remain at a mathematical zero.Your assertion that it's the presence/influence of other things in the universe that cause the fluctuations, doesn't explain the consistency between the various experimental measurements that have been made over time on these fluctuations, nor does it explain the anisotropic characteristics observed, in spite of matter not being homogenously distributed across the universe.
If you remove all matter from spacetime there will still be the electromagnetic and the gravitational field. But no one to observe it, so no physics. Absolute zero is a fiction like the vacuum itself. One cannot reach it, only approach it. This has nothing to do with vacuum fluctuations, which are not things happening.
[QUOTE="A. Neumaier, post: 5664110, member: 293806"]It says that the bottle has an exterior which is not empty, from which the radiation comes. This means that a real bottle is not really empty. The bottle I was talking about was an abstraction, just like the vacuum of quantum field theory.So, the effects in an apparent piece of vacuum (apparent since there are invisible fields in any vacuum that can be created experimentally) between pieces of matter are caused by the matter and fields surrounding the vacuum,.”What if all matter in the universe is reduced to absolute zero in temperature – will Vacuum Fluctuations cease?What if all matter in the universe is removed from spacetime – will spacetime cease to exist, or at least its Vacuum Fluctuations?
[QUOTE="sanman, post: 5664116, member: 65959"]Blackbody radiation can be measured reliably”Black body radiation is caused by the electromagnetic field. Hawking radiation is real particles created by the gravitational field. Nothing is created by either the vacuum or by virtual; particles.That's the scientific part.But you wanted a cause for the field itself, which is metaphysics.
[QUOTE="A. Neumaier, post: 5664109, member: 293806"]The fields are there, all the time. The vacuum state is just the special state of the system where the state is Poincare invariant – timeless, spaceless, due to the symmetry. This is like an empty, infinitely extended container – an abstraction.Real spacetime is nowhere a vacuum. it is filled everywhere with fields – gravity, radiation, and traces of matter – with big lumps here and there. These fields are not in a pure vacuum state, however, not even locally, far away from stars and planets.If you ask for a cause of that, you need to ask God. The answer is outside the realm of physics.”Sir, I don't wish to invoke a metaphysical explanation, I feel that physics and the scientific method can probe everything usefully.Blackbody radiation can be measured reliably, and isn't overly dependent on whatever combination of cosmic events (radiating suns, exploding stars, black holes) may be happening around the rest of the cosmos at the time.Casimir force can be measured reliably, and experimental observation of it doesn't give radically different results when done with appropriate experimental rigor.Furthermore, the very ideas of waves or particles or fields are themselves concepts we apply onto reality. If I choose to call an automobile a particle, then that's my choice, and as long as I maintain a logical consistency, then I can describe the universe that way.Saying that it's wrong to choose to describe Vacuum fluctuations with particles, is like saying it's wrong to describe light using photon particles.If the fluctuations of the Scalar Field exist, then there's no reason why the idea of particles can't be adopted to describe it.
[QUOTE="sanman, post: 5664107, member: 65959"]a bottle doesn't need to have black body radiation – the fact that it does says there is something more than the bottle which is there.”It says that the bottle has an exterior which is not empty, from which the radiation comes. This means that a real bottle is not really empty. The bottle I was talking about was an abstraction, just like the vacuum of quantum field theory.So, the effects in an apparent piece of vacuum (apparent since there are invisible fields in any vacuum that can be created experimentally) between pieces of matter are caused by the matter and fields surrounding the vacuum,.
[QUOTE="sanman, post: 5664103, member: 65959"]Okay, but what is causing/producing the scalar field?”The fields are there, all the time. The vacuum state is just the special state of the system where the state is Poincare invariant – timeless, spaceless, due to the symmetry. This is like an empty, infinitely extended container – an abstraction. Real spacetime is nowhere a vacuum. it is filled everywhere with fields – gravity, radiation, and traces of matter – with big lumps here and there. These fields are not in a pure vacuum state, however, not even locally, far away from stars and planets. If you ask for a cause of that, you need to ask God. The answer is outside the realm of physics.
[QUOTE="A. Neumaier, post: 5664098, member: 293806"]It is made of nothing, it is just a container for real stuff. You could as well ask what the interior of an empty bottle contains.”But conceptually, a bottle doesn't need to have black body radiation – the fact that it does says there is something more than the bottle which is there.Conceptually, a bottle doesn't need to have a Casimir force inside it – the fact that it does says there is something more than bottle which is there.I feel as if you've just told me to ignore that photons have wave characteristics – ie. "just ignore it, this is a mere artifact of observation, and doesn't signify anything"I cannot ignore it, I cannot pretend it isn't there – I want to know what's causing it. I want to know if whatever's causing it has its own deeper properties, which perhaps I can't immediately/easily see.
[QUOTE="Mordred, post: 5664058, member: 351508"]removing all matter a scalar field would be my answer”Okay, but what is causing/producing the scalar field? There seem to be fluctuations happening in the Vacuum – Black Body radiation indicates this. DeBroglie wavelength of objects also seems to indicate this. So what is that stuff? What is causing these fluctuations/disturbances in the Scalar Field?
[QUOTE="sanman, post: 5664022, member: 65959"]what the Vacuum is actually made out of, if it's not made out of "virtual particles".”It is made of nothing, it is just a container for real stuff. You could as well ask what the interior of an empty bottle contains.
removing all matter a scalar field would be my answer
[QUOTE="A. Neumaier, post: 5614588, member: 293806"]A. Neumaier submitted a new PF Insights post”Hi Arnold, I really want to thank you for this article, as I find the topic of the Vacuum (or spacetime) to be truly interesting.It was physicist Andrei Sakharov who said "the mysteries of the vacuum will be the great challenge for 21st-century physics"But after having read you tell me what I shouldn't believe, I then really want to know what I should believe.You've just told me why it's wrong to believe that 6 x 7 = 45 and I hear you on that. But now I want to know what the actual answer is.And as far as I can see, you're not explicitly saying "the answer isn't 45" – you're instead saying "we as yet have no reason to believe it's 45"So I'm looking for someone to tell me what the Vacuum is actually made out of, if it's not made out of "virtual particles".
[QUOTE="A. Neumaier, post: 5663504, member: 293806"]You chase me through the whole physics literature… But this is the last time I answer. My context was your comment ''There are numerous professional researches ongoing on the aspects of the Higgs field I just mentioned.'' (and the aspects you had mentioned were ''the non zero VeV of the Higg's field'' and ''that due to the non zero VeV we may be in a false vacuum state.'' I see none of these in the formula you just displayed. Note that a ''false vacuum state'' does not belong to the set of physical states of a field theory since it is incompatible with causality. Hence we cannot be in such a state.” Where are you getting incompatible with causality from? Are you ignoring multiparticle system states?
So Neumaiur are you going to address the issue that although an individual virtual particle doesn't cause action a group of virtual particles can ? This is precisely what I have been trying to get you to answer.
[QUOTE="OmCheeto, post: 5663605, member: 103343"]…I can assure you, that I have no "theories" of my own….”Ok. That was kind of a lie.My theory is, that virtual particles exist in hyper-dimensional space.And beings that they have to obey the rules of the universe, they have to stay there.For the most part.Kind of like my bank account:Monthly Maintenance Fee________ $6.95a planck time passes andMonthly Maintenance Fee Waived $6.95………..as always: ok to delete, infract, and ban. :frown:
[QUOTE="Mordred, post: 5663478, member: 351508"]Um you quoted someone else that isn't my quote lol”That was me he was quoting.[QUOTE="vanhees71, post: 5663473, member: 260864"]Well, Griffiths may be busy with his research and teaching at the university, and from my own experience I can say that if somebody comes by my office, whom I've never seen in my live before, saying he "wants just to discuss about Einstein/relativity, quantum theory, etc." I always pretent to have no clue about these subjects. Then they leave my office quickly. Once, when I was still a diploma student, I was uncareful enough to answer an email of this type. The guy claimed (first indication of a dangerous person) that he had "disproven Einstein", and that he wanted to present his theory to me. I read the rest of the long e-mail, and it was garbage. Then I answered him, explaining what's garbage. That wasn't a good idea, because I got swamped with e-mails of the guy, which at one point I simply ignored. One day, he appeared in person, and it took the whole afternoon to get finally rid of him. Understandably that's why physicists tend to ignore such attempts to disproved established science. So Griffiths's "silence" is everything else than mysterious, it's shear self-defence against unnecessary distruction from work ;-).”I can assure you, that I have no "theories" of my own. I would describe my thoughts as; "hmmmmmm….. Perhaps these quantum physicists can visualize extra dimensions, which we mere mortals, can not".Have you ever seen this video?[MEDIA=youtube]Eu1klHizoDM[/MEDIA]Things don't make sense, when seen in two dimensions, when they are three dimensional.I imagine that Quantum Mechanics, being hyper-dimensional, IMHO, is kind of like that.ps. The ":rolleyes:" at the end of my comment should have clued you in that his "actions, were totally understandable. :smile:
Oh really
[QUOTE="Mordred, post: 5663518, member: 351508"]I'm chasing you through these branches of physics because your inplying they are all wrong.”Well, so almost every textbook on QFT imply "they are all wrong"… Have you taken any course in quantum field theory? Because as far as I can see, only people who haven't have issues with what A. Neumaier wrote in his insights. All those who really learnt QFT during their studies agree with what he wrote. That's weird, isn't it?
[QUOTE="Mordred, post: 5663540, member: 351508"]then how do explain spinfoam action below a quanta of energy? How do you account for any energy/density below a quanta? You certainly cannot state energy exists on its own as energy is a property.[/quote]None of these questions make sense.[quote]https://arxiv.org/abs/1201.4598"This means that, although individual terms in the perturbation expansion of a physical amplitude may diverge due to radiative corrections involving closed loops of virtual particles, "”Please don't just type "virtual particle" into the search field of your PDF viewer and randomly quote sentences. If you had read Abhay's article, you would have seen that he is talking about a completely different theory and not about LQG. And he explains that this different theory was not successful. Moreover, even if it was, the Arnold's comments would still apply to it.
then how do explain spinfoam action below a quanta of energy? How do you account for any energy/density below a quanta? You certainly cannot state energy exists on its own as energy is a property. https://arxiv.org/abs/1201.4598
[QUOTE="Mordred, post: 5663518, member: 351508"]I'm chasing you through these branches of physics because your inplying they are all wrong. As they do not consider virtual particles as just internal lines on a feyman diagram. That individual virtual particles do not have sufficient momentum to cause action. Collectively in a finite volume they can”LQG has neither Feynman diagrams nor virtual particles.
I'm chasing you through these branches of physics because your inplying they are all wrong. As they do not consider virtual particles as just internal lines on a feyman diagram.
[QUOTE="Mordred, post: 5663490, member: 351508"]Oh and what about field of quantum geometrodynamics? Or the following equation from a LQC article. [tex] stackrel{Action}{overbrace{mathcal{L}}} sim stackrel{relativity}{overbrace{mathbb{R}}}- stackrel{Maxwell}{overbrace{1/4F_{munu}F^{munu}}}+stackrel{Dirac}{overbrace{i overline{psi}gamma_mupsi}}+stackrel{Higg's}{overbrace{mid D_mu hmid-Vmid hmid}} +stackrel{Yugawa-coupling}{overbrace{hoverline{psi}psi}} [/tex]”You chase me through the whole physics literature… But this is the last time I answer. My context was your comment ''There are numerous professional researches ongoing on the aspects of the Higgs field I just mentioned.'' (and the aspects you had mentioned were ''the non zero VeV of the Higg's field'' and ''that due to the non zero VeV we may be in a false vacuum state.'' I see none of these in the formula you just displayed. Note that a ''false vacuum state'' does not belong to the set of physical states of a field theory since it is incompatible with causality. Hence we cannot be in such a state.
[QUOTE="mfb, post: 5663324, member: 405866"]It is challenging to answer "how does a neutron decay" or "how does the study of rare decays helps with new physics searches" without the concept of virtual particles.”I don't see why it should be. For example, I learned about neutron decay in my nuclear physics classes in college without anyone ever mentioning virtual particles.[QUOTE="mfb, post: 5663324, member: 405866"]the experts you mention later are using the concept of virtual particles exactly in those cases.”As I said, they're experts. My post was directed at non-experts.
Oh and what about field of quantum geometrodynamics? Or the following equation from a LQC article. [tex] stackrel{Action}{overbrace{mathcal{L}}} sim stackrel{relativity}{overbrace{mathbb{R}}}- stackrel{Maxwell}{overbrace{1/4F_{munu}F^{munu}}}+stackrel{Dirac}{overbrace{i overline{psi}gamma_mupsi}}+stackrel{Higg's}{overbrace{mid D_mu hmid-Vmid hmid}} +stackrel{Yugawa-coupling}{overbrace{hoverline{psi}psi}} [/tex] I suppose next your going to claim that The entire findings of a virtual particle cloud in a proton shown by LQCD is wrong too
[QUOTE="Mordred, post: 5663464, member: 351508"] Not all models in cosmology are semiclassical Loop quantum gravity certainly isn"t”My statement was made in context. Loop quantum gravity makes no assertion about Higgs.
Um you quoted someone else that isn't my quote lol
[QUOTE="Mordred, post: 5662178, member: 351508"]So would you like to hear my theory on what virtual particles are? I offered to explain this to D. J. Griffiths, as he is a neighbor of mine, but he has mysteriously remained silent. :rolleyes:”Well, Griffiths may be busy with his research and teaching at the university, and from my own experience I can say that if somebody comes by my office, whom I've never seen in my live before, saying he "wants just to discuss about Einstein/relativity, quantum theory, etc." I always pretent to have no clue about these subjects. Then they leave my office quickly. Once, when I was still a diploma student, I was uncareful enough to answer an email of this type. The guy claimed (first indication of a dangerous person) that he had "disproven Einstein", and that he wanted to present his theory to me. I read the rest of the long e-mail, and it was garbage. Then I answered him, explaining what's garbage. That wasn't a good idea, because I got swamped with e-mails of the guy, which at one point I simply ignored. One day, he appeared in person, and it took the whole afternoon to get finally rid of him. Understandably that's why physicists tend to ignore such attempts to disproved established science. So Griffiths's "silence" is everything else than mysterious, it's shear self-defence against unnecessary distruction from work ;-).
[QUOTE="A. Neumaier, post: 5663328, member: 293806"]The concept of virtual particles is well-defined and useful when restricted to its use in Feynman diagrams and associated technical discussions. But it is highly misleading when used to argue about vacuum fluctuations, as if these were processes happening in space and time.”I agree. Peter's post looked much more general, however, including Feynman diagrams.
Are you really saying these professional cosmologicists don't know how to properly use QFT? That they don't know how to properly renormalize their equations?You can't be saying that Not all models in cosmology are semiclassical Lop quantum gravity certainly isn"t
[QUOTE="Mordred, post: 5663449, member: 351508"]There are numerous professional researches ongoing on the aspects of the Higgs field I just mentioned. ” None of these are based on a thorough understanding of quantum field theory. Most cosmology is semiclassical with only superficial use of quantum mechanics, diluted by speculations that something special must happen when gravity is quantized.[QUOTE="A. Neumaier, post: 5663448, member: 293806"]A nonzero VEV just means that the field to be quantized is not the original field but the field obtained from it by subtracting the VEV.”This holds for every field, not only in the muddy waters of Higgs in a cosmological context, where things may be obscure because of unsolved issues in quantum gravity.For example, in QED, nobody ever tried to quantize the Coulomb field, since it is just an expectation value. Quantized are only the oscillations around the expectation value, and this restriction leads to QED.
You really believe this is just me ? There are numerous professional researches ongoing on the aspects of the Higgs field I just mentioned. These aren't my ideas but published researches. If you like I can get you several of these paper's
[QUOTE="Mordred, post: 5663441, member: 351508"]1) the non zero VeV of the Higg's field2) the false vacuum vs true vacuum condition in that were not sure if we are in a true vacuum condition. There is some hypotheses that due to the non zero VeV we may be in a false vacuum state.”A nonzero VEV just means that the field to be quantized is not the original field but the field obtained from it by subtracting the VEV. This is the very simplest of all renormalization operations! Without that one just obtains meaningless formulas. Just as you need to renormalize Higg's by subtracting the apostrophe, before your statement makes sense.
Then how do you define two key aspects of research in Cosmology? 1) the non zero VeV of the Higg's field2) the false vacuum vs true vacuum condition in that were not sure if we are in a true vacuum condition. There is some hypotheses that due to the non zero VeV we may be in a false vacuum state.I won't worry about the cosmological constant itself. Nor the 70+ still viable Inflationary models. Many of which uses some form of virtual particle production such as the inflaton.