Insights The Vacuum Fluctuation Myth - Comments

[RockyMarciano]

No, any physics theory has to establish correspondence with the experimental evidence we use to test it. What, if any, correspondence it has with "physical reality" is a question of philosophy or metaphysics, not physics.

I don't know about metaphysics but experimental(observational in general) evidence IS "physical reality" in physics by definition.

 

[clarkvangilder]

So...for the novice here...is it safe to say that the summary of all of this wrangling is that quantum fluctuations are a useful fiction? Useful in the sense that its metaphorical import is useful in describing some process or set of processes? Could the same be said of the probability waves that come with the overall game in QM?

NOTE: I freely admit that I may have missed what some are saying in this thread. Just trying to glean as much as I can with some direct questions. Feel free, however, to recommend further reading. I am not opposed to doing homework. ;-)

 

[PeterDonis]

.is it safe to say that the summary of all of this wrangling is that quantum fluctuations are a useful fiction? Useful in the sense that its metaphorical import is useful in describing some process or set of processes? Could the same be said of the probability waves that come with the overall game in QM?

I would say that it is important to keep in mind that terms like "quantum fluctuations", "probability waves", etc. are not the actual theory. They are attempts to describe some aspect of the actual theory in ordinary language. But ordinary language is vague and imprecise, and often there is no way to describe the theory in ordinary language without distortion. So you have to be very, very, very careful in trying to reason about the theory using ordinary language descriptions. That is why physicists themselves don't use these descriptions in their work; they use math. The mathematical description of the theory, and the concrete predictions derived from the math, are the actual theory, and to be sure you are reasoning correctly about what the theory says, the math is what you need to use.

 

[ftr]

NOTE: I freely admit that I may have missed what some are saying in this thread. Just trying to glean as much as I can with some direct questions. Feel free, however, to recommend further reading. I am not opposed to doing homework. ;-)

The best reference I could find for you with reasonable explanation in English is this

http://math.ucr.edu/home/baez/physics/Quantum/virtual_particles.html

 

[clarkvangilder]

The best reference I could find for you with reasonable explanation in English is this

http://math.ucr.edu/home/baez/physics/Quantum/virtual_particles.html

Perhaps a quick comparison of these virtual particles to the point-particle model in classical mechanics? It seems that virtual particles are much much more than just a model? (Not that you or anyone else said otherwise). The title of this article below sort of captures the spirit of misconception relative to this topic. Scientific American is not a great journal of physics; but the person who wrote it ought to be an expert.

https://www.scientificamerican.com/article/are-virtual-particles-rea/

 

[ftr]

Perhaps a quick comparison of these virtual particles to the point-particle model in classical mechanics? It seems that virtual particles are much much more than just a model? (Not that you or anyone else said otherwise). The title of this article below sort of captures the spirit of misconception relative to this topic. Scientific American is not a great journal of physics; but the person who wrote it ought to be an expert.

https://www.scientificamerican.com/article/are-virtual-particles-rea/

I don't have a scientific survey but I would say(10 years of watching) the majority here and elsewhere do not agree with that point of view.

 

[clarkvangilder]

I don't have a scientific survey but I would say(10 years of watching) the majority here and elsewhere do not agree with that point of view.

Thanks for that insight ... I was hoping/thinking that must be true.

 

[vanhees71]

Perhaps a quick comparison of these virtual particles to the point-particle model in classical mechanics? It seems that virtual particles are much much more than just a model? (Not that you or anyone else said otherwise). The title of this article below sort of captures the spirit of misconception relative to this topic. Scientific American is not a great journal of physics; but the person who wrote it ought to be an expert.

https://www.scientificamerican.com/article/are-virtual-particles-rea/

Hm, I'm a bit puzzled how an expert in particle physics can write such an article :-(. As an practicioner of QFT, I'm sure he knows very well that a particle interpretation of relativistic QFT is possible in clear terms only for asymptotic free states, and for vacuum QFT (i.e., the theory describing scattering events) the only observable outcomes are S-matrix elements, i.e., transition rates for going from an asymptotic free in state (usually two particles) to an asymptotic free out state (which can be any many-particle state, that is only restricted by the conservation laws like energy-momentum, angular momentum conservation and the conservation of various charges like electric charge etc.) or, equivalently, cross sections. All this is discussed already at length in this thread!

 

[tzimie]

I have a question.

How that usual claim (virtual particles are not real, they are just math) can be interpreted in a framework of MUH (Mathematical Universe Hypotesis) - as obviously in MUH there is no distinction between "actually happening" and "being just math".

 

[vanhees71]

How does Bohmian mechanics solve "the measurement problem" (I assume you mean the question, why you find sharp values when measuring an observable on a system at a state which is not an eigenstate of the observable)? It assumes unobservable, i.e., ficticious, trajectories, but it doesn't claim that all observables are determined before the measurment, right?

 

[Demystifier]

I have a question.

How that usual claim (virtual particles are not real, they are just math) can be interpreted in a framework of MUH (Mathematical Universe Hypotesis) - as obviously in MUH there is no distinction between "actually happening" and "being just math".

According to MUH, any self-consistent mathematical theory, even a theory which directly contradicts observations, is true.

 

[tzimie]

According to MUH, any self-consistent mathematical theory, even a theory which directly contradicts observations, is true.

1. It is not "true", it "exists" in some methaphysical way.
2. And only some of these universes are "observed"

Anyway, I think the "insights" are not interpretation-neutral (actually they are Copenhagen-biased) hence not universally valid. (Am I wrong?)

 

[vanhees71]

Hm, if you call the minimal interpretation Copenhagen, then of course the Insights are biased towards these, since this is a science and not a philosophy forum!

 

[tzimie]

Hm, if you call the minimal interpretation Copenhagen, then of course the Insights are biased towards these, since this is a science and not a philosophy forum!

It is perfectly fine to say that you don't want to talk about interpretation wars because it is philosophy, not physics.
If there is a big period after that claim.
But after the point you added that Copenhagen is the best/minimal/etc - then your position is inconsistent.

I don't want to start Interpretation Wars. It is science forum and not a philosophy one. Ah, and BTW, Copenhagen doesn't make any sense and MWI is the best )))
Happy New Year! )))

 

[vanhees71]

Well, it should be Copenhagen without collapse, i.e., the minimal statistical interpretation. Some people think that's alreayd MWI, but I don't need unobservable branches of the universe where something else happens than what's observed in the branch I'm living in ;-)). Happy New Year!

 

[OmCheeto]

I still don't know what "the myth" is, and I read the article 3 times.
Perhaps, some of us were not meant to know.

 

[haushofer]

Hm, I'm a bit puzzled how an expert in particle physics can write such an article :-(. As an practicioner of QFT, I'm sure he knows very well that a particle interpretation of relativistic QFT is possible in clear terms only for asymptotic free states, and for vacuum QFT (i.e., the theory describing scattering events) the only observable outcomes are S-matrix elements, i.e., transition rates for going from an asymptotic free in state (usually two particles) to an asymptotic free out state (which can be any many-particle state, that is only restricted by the conservation laws like energy-momentum, angular momentum conservation and the conservation of various charges like electric charge etc.) or, equivalently, cross sections. All this is discussed already at length in this thread!

I''m also puzzeled. I can't make anything of that article.

 

[mattt]

Perhaps a quick comparison of these virtual particles to the point-particle model in classical mechanics? It seems that virtual particles are much much more than just a model? (Not that you or anyone else said otherwise). The title of this article below sort of captures the spirit of misconception relative to this topic. Scientific American is not a great journal of physics; but the person who wrote it ought to be an expert.

https://www.scientificamerican.com/article/are-virtual-particles-rea/

I am more than puzzled, I am seriously dissapointed.

 

[mikeyork]

I am curious as to how those who say that virtual particles are a myth would describe "resonances" such as the $\Delta(1232)$ that appears in pion-nucleon scattering. This is usually called a particle as its sits in the baryon decouplet of SU(3). Yet it seems to have all the characteristics of a "virtual particle" in that it is extremely shortlived and because it is seen as a peak in the scattering cross-section and can be viewed as having uncertain mass -- suggesting temporary violation of energy conservation over an interval inversely proportional to the width of the bump. (In order to allocate a precise mass, one has to allow the mass to be complex, the imaginary part given by the width of the bump and representing the uncertainty in real energy.)

 

[mfb]

See the previous pages, we discussed this (mainly with the Z as example) in detail. It depends on your point of view.

 

[mikeyork]

See the previous pages, we discussed this (mainly with the Z as example) in detail. It depends on your point of view.

I looked through (fairly quickly through the whole thread) but couldn't find what you were referring to. Do you have a post number?

 

[weirdoguy]

I think it's in the thread about virtual particles.

 

[mfb]

Oh right, wrong thread. See the virtual particle thread.

 

[mikeyork]

Thanks. An interesting read.

 

[ftr]

I have a question.

How that usual claim (virtual particles are not real, they are just math) can be interpreted in a framework of MUH (Mathematical Universe Hypotesis) - as obviously in MUH there is no distinction between "actually happening" and "being just math".

I think MUH does not claim to have the exact mathematical structure, it just conjectures from all the present physics that reality is a mathematical structure. So, since there is no acceptable quantum gravity theory yet , none of the math that is being done in physics today can be taken as the actual math, only that they are approximate models. Hence no ontology is involved.

 

[A. Neumaier]

See the previous pages, we discussed this (mainly with the Z as example) in detail. It depends on your point of view.

actually it was discussed in the pages commenting on the
Misconceptions about Virtual Particles.

 

[Mordred]

Good article but I do have issues with this whole which excitation is more real.
Particles themselves are excitations, so is virtual excitations. Which is more real comes down to simply conventional rational. That's the real myth. Physics doesn't define real. We simply describe aspects of what we can describe as reality.

In some aspects I like prof Strasslers description "virtual particles are wavefunctions that aren't quite nice" Not very detailed but certainly more accurate than "on shell"/ "off shell".

Quite frankly there is no way one can define real. At least not with 100% accuracy. We can measure relations/interactions but these are all under specific treatments.

Fields themselves are mathematical treatments. By definition a field is simply a collection of objects. Those objects can be mathematical constructs such as a vector/scalar field or a collection of events.
Wave/particle duality itself is simply aspects of these field excitations neither defines the excitation as they are both aspects/properties of that excitation.
When you think about it different particle species are simply excitations that display certain characteristics that can be classified under various particle names with specific wavefunction characteristics.

This is what I feel should be stressed. Not real particles vs virtual particles.

Just my take on the subject

Now the question I have is how can an excitation not fluctuate to a certain degree? Is that not what an excitation is in the first place?

Here is a decent arxiv article. "There are no particles only fields"

http://www.google.ca/url?sa=t&sourc...G2ax22sA9BakBSaTQ&sig2=OLrYE7fyEIHsA3zMw400rQ

 

[A. Neumaier]

In some aspects I like prof Strasslers description "virtual particles are wavefunctions that aren't quite nice"

This is meaningless gibberish. Virtual particles have no associated wave functions at all. Wave functions are obtained by creation operators from the vacuum state, and this is possible only for on-shell particles. You should read the other Insight Article ”The Physics of Virtual Particles”, which contains an exposition of definitions that are physically justified, and in particular makes precise what a virtual particle is and what being real means.

how can an excitation not fluctuate to a certain degree? Is that not what an excitation is in the first place?

Take a violin string. The fundamental excitation is harmonic and oscillates very regularly. Unlike noise, a harmonic excitation does not fluctuate in any meaningful sense. The same holds for excitations of other physical systems, including the quantum field vacuum.

 

[Mordred]

did you even bother to read the arxiv article?

 

[Mordred]

maybe you should read Strasslers site itself

https://profmattstrassler.com/artic...ysics-basics/virtual-particles-what-are-they/

as you obviously didn't read the arxiv article I posted. I'm more than familiar with your violin string.
Your article seems to feel that simply because virtual particles are not directly observable they are not as real. I disagree with this. It can be equally be argued that particles themselves are not real. Quite frankly though what is real or not real is a philosophy argument. In all honesty does this make sense. Particularly since a particle is an excitation.

"all particles should be viewed as virtual until they are observed (where they obviously are real)" That is like saying forget the term virtual. Its simply a real unobservable particle by what I read here. Doesn't define any distinction except observation. Now if you included that it must have all the defining qualities that define a particular particle I would agree.

Reference https://www.physicsforums.com/insights/vacuum-fluctuation-myth/

 

[Mordred]

I guess my point is whether or not a particle is observable or not isn't the same thing as whether its real or not.

 

[A. Neumaier]

I guess my point is whether or not a particle is observable or not isn't the same thing as whether its real or not.

In my first insight article about virtual particles, I defined real as having a state. This is objective, very natural and consistent with the use in most of physics. In this sense, virtual particles are not real. That's why they are called virtual.

While you have only a vague and informal view of what should be real, with which one cannot argue because it is up to everyone to fill it with meaning. The arxiv article (which I knew already for a long time) doesn't improve the situation. Strassler's page (which I also knew before) is for the lay person, not for those who want to gain a deeper understanding. It also dabbles in words without giving them a precise meaning. At the end Strassler admits: ''particles are just not simple objects, and although I often naively describe them as simple ripples in a single field, that’s not exactly true.''

 

[Mordred]

no problem it is after all your insight article. Just making my take on the subject. I recognize the need to keep it as simple as possible for the average layperson. Just for the record though I do have a far greater knowledge on the topic than I presented in this thread. Knowledgable enough to fully understand everything you have stated at the very least. The insight articles certainly don't provide me any understandings I didn't already have. I also recognize many physicisists share your views but at the same time there are valid counter arguments. One of those views is virtual particles has real measurable influences. Therefore should be considered just as real.

Lol I recall a lengthy 30 plus page argument on this very forum several years back on this very topic. Myself I simply consider the very term real more of a metaphysics argument than a physics one. Opinions certainly seem to vary depending on individual viewpoints. Doesn't particularly help distinquish the differences between the virtual gauge vector bosons as opposed to the on shell boson particle itself.

 

[ftr]

It seems the discussion is becoming an entanglement of many situations. First, the discussion here is about "Vacuum fluctuation". Second, these fluctuation are considered under interaction and non interaction. Then with interaction I don't know if we can look at it as if vacuum had already "virtual particles" in it or started appearing once interaction started? The discussion here seem to be veering towards "particles" in the vacuum. It is becoming like the old joke "who is on the first base", I think we need to be clear what we are talking about and not assume the reader can figure it out, I certainly can't.

 

[PeterDonis]

It seems the discussion is becoming an entanglement of many situations.

No, it is demonstrating that what looks to you like "an entanglement of many situations" is really a mixture of approximations, heuristics, and misstatements from pop science sources, and only very rarely actually describes our best current model of the fundamental physics.

the discussion here is about "Vacuum fluctuation".

The Insights article is about how the term "vacuum fluctuation" is a myth--it's not a very useful concept even as a heuristic or approximation, and it certainly is not part of our best current model of the fundamental physics.

these fluctuation are considered under interaction and non interaction

I'm not sure quite what this is referring to, but as far as our best current model of the fundamental physics is concerned, there is no such thing as a "non-interacting" quantum field (quantum fields are the fundamental concept here). Sometimes we can consider particular quantum systems to be "non-interacting" as a reasonable heuristic or approximation, but that's all. Fundamentally all quantum fields are interacting fields.

with interaction I don't know if we can look at it as if vacuum had already "virtual particles" in it or started appearing once interaction started?

Neither of these ideas have anything to do with our best current model of the fundamental physics. Your comment illustrates that "virtual particles" is not even a very good heuristic, since it is hindering your understanding rather than helping it.

The discussion here seem to be veering towards "particles" in the vacuum.

I'm not sure what you are basing that on, but I seriously doubt that the article's author would agree with it. Of course he can correct me if I'm wrong.

I think we need to be clear what we are talking about and not assume the reader can figure it out

It's unfortunate that we can't put level labels on Insights thread discussions. If we could, this thread would be firmly labeled "A". It's hard to even understand the reasons why the Insights article was written without a graduate level background in quantum field theory, or the equivalent.

If you want a good brief summary of the lesson to be learned from the article and this discussion, I would say it is that you should not even try to use the concept of virtual particles; it causes more problems than it solves. QFT says the fundamental concept is quantum fields, not particles; even "real" particles are not fundamental entities in QFT. There are ways in which experts can use the concept of "virtual particles" that can be useful, but those experts already know who they are; if you have to ask whether you are one of those experts, the answer is no.

 

[Mordred]

Well in QFT treatments every point in space is a field of creation/annihilation operators. In essence a sea of Virtual particles. In some texts this is an overlapping field sometimes referred to as virtual space. Normal particles being in observational space.

There is some debate that as this is a mathematical treatment that isn't reflective under other treatments its not considered real with the counter argument that a field or energy/density vacuum of value zero is simply a global average. Locally at the quantum levels their is always inherent quantum fluctuations.

One commonly known example being zero-point energy. Which essentially prevents absololute zero from being possible.
edit noticed cross posted with Peter. The only thing I'd like to add to his post is that the complex nature of particles is oftentimes oversimplified. This includes their interactions.

 

[PeterDonis]

in QFT treatments every point in space is a field

More precisely, there is a field at every point in spacetime.

of creation/annihilation operators

This is one way of describing the field, but not the only one.

In essence a sea of Virtual particles

And this is just picturesque language that doesn't help (and often hinders) understanding the physics. So is most of the rest of your post.

One commonly known example being zero-point energy. Which essentially prevents absololute zero from being possible.

Um, what? Zero point energy is the energy a system has at absolute zero.

 

[ftr]

if you have to ask whether you are one of those experts, the answer is no.

Will never have the nerve to claim that, even if I was. I have many books(ZEE for example) that do talk about VP, so if only in the know know, then what is the purpose of PF if not to clarify thing satisfactorily.

 

[Mordred]

Umm on the first quote why didn't you completely quote the entire sentence? I didn't complete the sentence to indicate any meaning beyond that which is contained in the full sentence. I'm positive you at least know what I mean by creation/annihilator operators.

I agree using the terminology virtual particles is quite frankly not helpful. It is a oversimplification

 

[PeterDonis]

on the first quote why didn't you completely quote the entire sentence?

Because my responses to the first part and the second part of the sentence were different, so I quoted each part separately.

 

[OmCheeto]

...
It's unfortunate that we can't put level labels on Insights thread discussions. If we could, this thread would be firmly labeled "A". It's hard to even understand the reasons why the Insights article was written without a graduate level background in quantum field theory, or the equivalent.

If you want a good brief summary of the lesson to be learned from the article and this discussion, I would say it is that you should not even try to use the concept of virtual particles; it causes more problems than it solves. QFT says the fundamental concept is quantum fields, not particles; even "real" particles are not fundamental entities in QFT. There are ways in which experts can use the concept of "virtual particles" that can be useful, but those experts already know who they are; if you have to ask whether you are one of those experts, the answer is no.

THANK YOU!

I was getting the feeling that I was the only person in the world that couldn't comprehend what the article was about.

I still don't know what "the myth" is, and I read the article 3 times.
Perhaps, some of us were not meant to know.

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.

 

[Mordred]

Your right my last post is an oversimplification but I would have thought you would recognize the relations of the creation/annihilator operators in terms of the zero-point energy.

http://www.google.ca/url?sa=t&source=web&cd=2&ved=0ahUKEwii3KySg7nRAhWEilQKHdikDqUQFggcMAE&url=http://www.damtp.cam.ac.uk/user/tong/qft/two.pdf&usg=AFQjCNGAHbSIOpMVp8w6m9gF4DjnD70Kbg&sig2=TEYpS-0cDfRPwaE4EOumEw

Or its relation to the following.
" In fact, however, kinetic energy is retained by particles even at the lowest possible temperature. The random motion corresponding to this zero-point energy never vanishes as a consequence of the uncertainty principle of quantum mechanics."

https://en.m.wikipedia.org/wiki/Zero-point_energy

Though you are correct my post above is poorly worded. I was trying to avoid going into too much detail as its a little off topic to the insight article itself. Though related on several aspects with regards to the HUP and its relations to virtual particles. Yes I am aware of the 120 orders of magnitude too much energy problem.

@OmCheeto quite frankly I'm a little hesitant to answer what the author of that article is suggesting in regards to myths. I've read several of his articles even posts on other sites. Some of them several months ago. I've seen similar arguments made by others both for and against virtual photons being not truly real as they are not observable.

Though I did have to review the more common arguments lol. Had to sit down for a couple of hours poring over numerous articles on the debate. Myself I'm still sitting one the fence on this one lol

 

[A. Neumaier]

virtual particles has real measurable influences

But not a causal influence. It is an influence like the influence of the spectral theorem on results of measurements since the latter measure eigenvalues predicted by the spectral theorem.

 

[mfb]

If you want a good brief summary of the lesson to be learned from the article and this discussion, I would say it is that you should not even try to use the concept of virtual particles; it causes more problems than it solves.

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.

And the experts you mention later are using the concept of virtual particles exactly in those cases.

 

[A. Neumaier]

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.
And the experts you mention later are using the concept of virtual particles exactly in those cases.

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.

 

[Mordred]

Then how do you define two key aspects of research in Cosmology?
1) the non zero VeV of the Higg's field
2) 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.

 

[A. Neumaier]

1) the non zero VeV of the Higg's field
2) 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.

 

[Mordred]

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

 

[A. Neumaier]

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.

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.

 

[Mordred]

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