On vacuum fluctuations

image credit: Pete Linforth (pixabay)

In my post titled “How do we know vacuum fluctuations exist?” [1] I was careful to add the terminology “zero-point fluctuations in quantum fields” in parenthesis right after “vacuum fluctuations“.

According to Arnold Neumeier [2] the terminology of “vacuum fluctuation” is problematic.

“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.” – Arnold Neumeier [2]

I understand the “virtual particle” terminology is controversial but I don’t understand the objection to the “vacuum fluctuation” terminology.

I assume no physicist objects to “zero-point fluctuations in quantum fields“. We have experimental evidence [1] that quantum fields fluctuate. We also know that quantum fields are embedded in space-time. Quantum fields are fluctuating in space-time. Is there any controversy about this?

I was aware of Matt Strassler’s clarifications [3] on “virtual particles”. But, I don’t think he particularly objects to the “vacuum fluctuation” terminology.

“Quantum fields are constantly fluctuating, and the unstable disturbances that we call ‘virtual particles’ are always there. It is just something that quantum fields do, and the mathematics known as “quantum field theory”, which I teach to first and second year graduate students and which is very well established both theoretically and experimentally, does a great job of predicting the details of these fluctuations/disturbances/virtual particles. No lingering mysteries here, not for many decades.” – Matt Strassler [3] (comments section)

Alternative approaches to calculations

There is another aspect of this subject that goes beyond terminology.

Consider electron. Dirac equation is the most accurate equation to model the behavior of the electron but there are observations such as the Lamb-shift and g-2 that show that we need corrections to the Dirac equation. These corrections can either be modeled as the interaction of the electron with vacuum fluctuations (zero-point fluctuations in quantum fields), or as the interaction of the electron with its own field.

My understanding is that these two approaches provide complementary interpretations for the complicated terms of the Quantum Field Theory (QFT) calculations.

Here’s two alternative explanations of the Lamb shift:

“The ‘self-interaction’ of the electron when it is near the proton causes the effective ‘smearing’ of the electron charge so that its attraction to the proton is slightly weaker than it otherwise would have been. This means it has encountered an interaction which makes it slightly less tightly bound than a 2p electron, hence higher in energy.” – Hyperphysics

“The fluctuation in the electric and magnetic fields associated with the QED vacuum perturbs the electric potential due to the atomic nucleus. This perturbation causes a fluctuation in the position of the electron, which explains the energy shift.” – Wikipedia

Direct observation of vacuum fluctuations

Experimental evidence for zero-point fluctuations in quantum fields come from indirect observations (Lamb shift, Casimir effect, g-2). There are attempts to measure vacuum fluctuations directly. The results are inconclusive but keep these experiments [4] in mind.


[1] How do we know vacuum fluctuations exist?

[2] Explore The Vacuum Fluctuation Myth in Quantum Theory (physicsforums.com)

[3] Virtual Particles: What are they? | Of Particular Significance (profmattstrassler.com)

[4] Physicists observe weird quantum fluctuations of empty space—maybe | Science | AAAS (sciencemag.org)

This entry was posted in physics and tagged , , . Bookmark the permalink.