# Insights Vacuum Fluctuations in Experimental Practice - Comments

Related Quantum Physics News on Phys.org

#### sanman

Sir, you write:
"what fluctuates in the experiment is the electro-optical signal detected, not the vacuum."

Sir, by what experimental/observational means can we discern that the fluctuations are not part of the Vacuum?

It's one thing to say that "vacuum fluctuations" are an unsupported assertion, but it's another thing to be able tor rule them out, particularly by experimental means. How can this "unsupported assertion" be ruled out, experimentally?

#### A. Neumaier

It's one thing to say that "vacuum fluctuations" are an unsupported assertion, but it's another thing to be able tor rule them out, particularly by experimental means. How can this "unsupported assertion" be ruled out, experimentally?
Claims require proof, otherwise they can be ignored. That's the rule in science. Nothing is ruled out in science; the demarcation line between science and speculation is the proof, not the disproof.

The electro-optical signal is the only thing measured, and it exhibits fluctuations. Thus they are fluctuations of the signal, not of the vacuum.
To understand what this means consider fluctuations of a visual signal seen on an oscilloscope in an ordinary experiment, and someone claims that these are a visual proof of fluctuations of the vacuum. Nobody would take such a claim serious without a proof.

To argue that fluctuations of the vacuum are measured one would have to give theoretical evidence that the signal fluctuates in the same way as the vacuum. Lack of this evidence is enough to reveal the claim as pure speculation.

Thanks Arnold!

#### mfb

Mentor
Nice article!
Compared to QED, QCD has the advantage that it is asymptotically free at large energies, with the consequence that – unlike QED – it can be studied in a lattice approximation, with enormous numerical effort ultimately rewarded by reasonable (few digit) accuracy.
Sometimes we would be happy to have a 10% accuracy...

#### A. Neumaier

Nice article!Sometimes we would be happy to have a 10% accuracy...
I know. I was thinking of optimistic figures (low lying baryon spectrum to $1-9$%), and deliberately used the vague expression ''few''.

As you probably know (I write this for @atyy who thinks no continuum limit is needed), a lot needs to be done to get values that can be compared with experiment, not just calculations on a fixed lattice. From the paper just cited:
Fodor and Hoelbling said:
p.29: What one would ideally like to do then is to fix the N_f + 1 dimensionless bare parameters of the lattice theory, the bare quark masses and the gauge coupling, such that the N_f dimensionless observables on the lattice assume their physical values exactly and the lattice spacing a is of the desired size. One could then measure any observable on the lattice for a range of lattice spacings a and, with the appropriate functional form that is given by the discretization effects of the specific action used, extrapolate them into the continuum a = 0. [...]
p.31: The removal of the cutoff, also known as continuum extrapolation, is an unavoidable part of any lattice calculation that wants to make a statement about the underlying fundamental continuum theory. The severity of the continuum extrapolation however depends very strongly on both the action used and the combination of scale setting observable and measured observable. [...]
p.46: While ground state non-singlet hadron masses can be computed to a few percent accuracy today, reaching the same level of precision for excited states or singlet hadrons is still a challenging task.
The final results for the baryon masses in the infinite volume limit, together with their error margins, are given in Table 1 on p.38.

#### Mordred

I've been reading up on QFT itself and I am beginning to see where Neumaiur is coming from. Still not sure I have everything straight though. Actually positive that I don't lol, the majority of the math itself isn't the issue though. I'm currently on the Ultraviolet cutoffs and the imaginary i. Though I still need to work on the LSZ reduction formula.

Point being is from what I've gotten so far I can see the validity behind this article. I've gotten far enough to realize what I thought of as vacuum isn't what I thought

Last edited:

#### PeterDonis

Mentor
Moderator's note: some off topic posts and responses have been deleted.

#### Daniel Kellis

I think virtual particles are OK in diagrams if they help solve the problem. But it is not OK to let virtual particles break the fourth wall, as is done with Hawking radiation. One virtual particle has positive energy and the other has negative energy. Hawking radiation relies on Maxwell's demon to ensure that the negative energy virtual particle always goes into the black hole and the positive energy virtual particle always escapes.

#### mfb

Mentor
The derivation of Hawking radiation does not use virtual particles at all. That is just a pop-science description that leads to misconceptions.

Mentor

#### Jeronimus

Sir, you write:
"what fluctuates in the experiment is the electro-optical signal detected, not the vacuum."

Sir, by what experimental/observational means can we discern that the fluctuations are not part of the Vacuum?

It's one thing to say that "vacuum fluctuations" are an unsupported assertion, but it's another thing to be able tor rule them out, particularly by experimental means. How can this "unsupported assertion" be ruled out, experimentally?
I don't think that this question has been answered fully.

Can you give us an example of an experiment(thought experiment) as YOU would imagine it, such that it would provide sufficient proof for vacuum fluctuations being "real" and being "directly" detected according to your standards? (You are allowed to use futuristic devices which do not exist yet, but may in the future)

edit: In particular. What kind of experiment would you propose/imagine for -> "...one would have to give theoretical evidence that the signal fluctuates in the same way as the vacuum. "

As far as i am concerned, real and direct is quite a mouth full. Special relativity for example is a nice and elegant theory which is capable of predicting some of our experiences of the world quite accurately as long as there is no gravity involved.
In the end however, it is just a method to predict experiences. There are other theories/methodologies which have the equivalent predictive power to SR. We simply cannot know if spacetime out there is as we imagine it to be. Nor can we know _directly_ if particles or fields are "real" as we imagine them to be.
All we CAN know is that by following the methodologies of the according/more successful theories, we can predict our experiences more accurately than following less successful theories.

So to me, the question on if virtual particles are real or can be directly observed is nonsensical. What matters to me is, if the theory which is based on virtual particles and their fluctuations is capable of predicting what i will experience in the future more accurately or equally accurate as other competing theories.

Last edited:

#### vanhees71

Gold Member
Since vacuum fluctuations are not existing (at least not accoring to standard relativistic QFT), you cannot even define an experiment to measure them. For the conception of measurements you need at least some model!

#### Karolus

I did not understand exactly, I'm sorry, but the topic is very interesting. For all I knew, the Casimir experiment would prove the existence of "a quantum vacuum." In addition, other authors, such as Feynman and Hawking argue explicitly a state of vacuum in which particles and anti-particles "virtual" is created and destroyed. In the second quantization are introduced proper operators of "creation" and "destruction. "
Now the article casts doubt this description? How are and things?

Thank you very much

#### weirdoguy

In addition, other authors, such as Feynman and Hawking argue explicitly a state of vacuum in which particles and anti-particles "virtual" is created and destroyed.
Can you show any textbook/peer reviewed article on QFT where they say that?

#### Karolus

Particle Creation by Black Holes
S. W. Hawking
Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge, England Received April 12, 1975

https://www.brainmaster.com/software/pubs/physics/Hawking Particle Creation.pdf

At page 202 :
Just outside the event horizon there will be virtual pairs of particles, one with negative
energy and one with positive energy

but there are many other, very technical, and not simply informative, for example on the vacuum polarization, or the effect Lamb-shift etc.

#### mfb

Mentor
It should be emphasized that these pictures of the mechanism responsible for the thermal emission and area decrease are heuristic only and should not be taken too literally.
You can make up those things to describe something in English, but the actual calculations don't have any virtual particles or vacuum fluctuations.

Same for vacuum polarization, Casimir effect, Lamb shift and everything else. Sometimes virtual particles are a nice (but not necessary) tool in calculations, but that is different from vacuum fluctuations.

#### weirdoguy

but there are many other, very technical, and not simply informative, for example on the vacuum polarization, or the effect Lamb-shift etc.
And all of them treat virtual particles as a mathematical tool, not physical 'reality' (whatever that means). And that is the whole point A. Neumaier is bringing up.

#### Karolus

And all of them treat virtual particles as a mathematical tool, not physical 'reality' (whatever that means). And that is the whole point A. Neumaier is bringing up.
does not convince me. So whatever it is nothing more than a mathematical tool. Even quarks have no physical reality, are only mathematical tricks, but then whatever. Even the light, we have only the equations of Maxwell there is no other reality than the Maxwell equations. Has anyone ever seen a "photon"? or a "quark"? What is the reality of a photon? Only mathematical tool...

#### PeterDonis

Mentor
Has anyone ever seen a "photon"? or a "quark"?
Yes. We have detectors that can detect single photons (they're called photomultipliers). We ran experiments called deep inelastic scattering experiments in the 1960s where we shot high energy electrons into nuclei and watched them bounce off quarks; that's how the quark model was developed.

But now ask the question: are photons and quarks "particles"? I would answer no: "particle" is just a mathematical tool we use to construct our models. Photons and quarks are photons and quarks. They are not little billiard balls or pointlike masses. But there are real things there that we see in experiments like the ones I mentioned above, and "photon" and "quark" are the names we give to those real things.

So if you want to say that "virtual particles" are the name you will give to "whatever real thing it is that explains the Casimir effect, Hawking radiation, Lamb shift, etc.", sure, you can do that. But then you are using the term "virtual particles" to describe something that isn't a particle any more than photons or quarks are particles. The term "vacuum fluctuations" is really no better in that regard, because it invites the inference that whatever it is is fluctuating, like a wave--but it isn't a wave any more than it is a particle. It is something for which we have no intuitive analogy at all; it's not like anything we have an ordinary language word for.

This is a major reason why many (like myself) keep emphasizing that to really understand physics, you have to use math, not ordinary language. There is no dispute about the math: we know how to construct mathematical models that make accurate predictions about all of the experiments I referred to above. The only disputes are about which ordinary language words are the "right" ones to use to refer to the physics; but that dispute is ultimately pointless because no ordinary language words are "right".

#### weirdoguy

does not convince me
So just take QFT textbook and learn it properly by yourself. Then you'll see what everyone here is talking about, because:

to really understand physics, you have to use math, not ordinary language.

#### Karolus

:to really understand physics, you have to use math, not ordinary language.
ok, then teach me the first law of Newton, or any other physical argument, without using a single word of "ordinary language", ie using only the language of mathematics. There is no discussion in physics, (and even math!) no matter how advanced, you do not use ordinary language, because, after all, mathematics, I think, is just a language

#### Karolus

Yes. We have detectors that can detect single photons (they're called photomultipliers).
not entirely true. The photomultiplier detects only the intensity of the current ... where is the "photon"?

#### PeterDonis

Mentor
There is no discussion in physics, (and even math!) no matter how advanced, you do not use ordinary language
You might be using words like "energy", "work", "force", etc., but those words do not refer to ordinary language concepts. They refer to particular parts of the math.

mathematics, I think, is just a language
But not the same kind of language as ordinary language, because mathematical terms have precise referents.

The photomultiplier detects only the intensity of the current
The intensity of the current is the output of the photomultiplier, not the input. "Photon" is the name we give to whatever-it-is that goes into the photomultiplier and causes the current to be output.

"Vacuum Fluctuations in Experimental Practice - Comments"

### Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving