What is Fluctuations: Definition and 149 Discussions

In quantum physics, a quantum fluctuation (or vacuum state fluctuation or vacuum fluctuation) is the temporary random change in the amount of energy in a point in space, as prescribed by Werner Heisenberg's uncertainty principle. They are tiny random fluctuations in the values of the fields which represent elementary particles, such as electric and magnetic fields which represent the electromagnetic force carried by photons, W and Z fields which carry the weak force, and gluon fields which carry the strong force. Vacuum fluctuations appear as virtual particles, which are always created in particle-antiparticle pairs. Since they are created spontaneously without a source of energy, vacuum fluctuations and virtual particles are said to violate the conservation of energy. This is theoretically allowable because the particles annihilate each other within a time limit determined by the uncertainty principle so they are not directly observable. The uncertainty principle states the uncertainty in energy and time can be related by



Δ
E

Δ
t




1
2







{\displaystyle \Delta E\,\Delta t\geq {\tfrac {1}{2}}\hbar ~}
, where 1/2ħ ≈ 5,27286×10−35 Js. This means that pairs of virtual particles with energy



Δ
E


{\displaystyle \Delta E}
and lifetime shorter than



Δ
t


{\displaystyle \Delta t}
are continually created and annihilated in empty space. Although the particles are not directly detectable, the cumulative effects of these particles are measurable. For example, without quantum fluctuations the "bare" mass and charge of elementary particles would be infinite; from renormalization theory the shielding effect of the cloud of virtual particles is responsible for the finite mass and charge of elementary particles. Another consequence is the Casimir effect. One of the first observations which was evidence for vacuum fluctuations was the Lamb shift in hydrogen. In July 2020 scientists report that they, for the first time, measured that quantum vacuum fluctuations can influence the motion of macroscopic, human-scale objects by measuring correlations below the standard quantum limit between the position/momentum uncertainty of the mirrors of LIGO and the photon number/phase uncertainty of light that they reflect.

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  1. S

    Power Fluctuations in our AC Mains Power Generation Facility

    I am currently at a power plant here in Texas and the 480VAC system swings from 480 while equipment is on line and as high as 536VAC when equipment is off line. They tell me that this is prefectly normal but I have never seen swings like this at any power plant. So, is this normal???
  2. J

    I Quantum fluctuations & 'virtual particles'

    I've been reading about how language around virtual particle fluctuations is metaphorical. This is helpful: https://www.physicsforums.com/insights/vacuum-fluctuation-myth/ I'm just trying to understand a bit more from a layman's point of view. I found Matt Strassler's article 'Virtual...
  3. J

    I Field fluctuations in the vacuum

    How does relativistic qft predict quantum fluctuations in the vacuum? We see this in the experiment proving the Casimir Effect so we know it's physical, but why?
  4. C

    I Simple model of thermal shape fluctuations of liquid interface

    Consider a container filled with two essentially incompressible liquids with densities ##\rho > \rho'## and (respective) volumes ##V##, ##V'##, rotated by a centrifuge in some orbit-based space lab to maintain a roughly constant (co-moving) simulated "gravitational field" g. Let's suppose that...
  5. D

    I The Casimir effect and Quantum vacuum fluctuations

    The Casimir effect is a small attractive force that acts between two close parallel uncharged conducting plates. That force is caused by quantum vacuum fluctuations of the electromagnetic field. What is the cause of the fluctuations? Or, they are uncaused (random)? At least, what are the...
  6. T

    I What are thermal fluctuations?

    I often think thermal fluctuations as random changes in the temperature but when it is said in the context "thermally fluctuate over the energy barrier" does it mean to classically overcome the barrier?
  7. G

    I Theory of fluctuations in disordered systems

    I'm reading the https://www.phys.uniroma1.it/fisica/sites/default/files/DOTT_FISICA/MENU/03DOTTORANDI/TesiFin26/Urbani.pdf at paragrph 4.6.2 "The interaction term". They write a right hand side: < f(na,nb) f(nc,nd) f(ne,nf) > and they want to use a symmetry, for example they assume that...
  8. TheHeraclitus

    Particle ontology and quantum fluctuations

    I have been reading about ontologies in quantum physics recently and I came across Bohmian mechanics. If I understood it correctly BM endorses Particle ontology. Particle ontology claims that point-like particles that move continuously in time are the fundamental building blocks. I know some...
  9. R

    B Why exactly do Virtual Particles not violate Conservation of energy?

    Recently I've read more about virtual particles and at first I tought that there were only doubts that virtual particles are not interpretable with the help of uncertainty principle. Furthermore it can't be used an an "excuse" for the temporary violation of the conservation of energy. Can...
  10. D

    I Differentiated Sakharov Equation for Vacuum Fluctuations

    To a non-physicist, I know some papers can appear very abstract, and Sakharovs equation was one of them. You can follow his ideas from various articles, here's a few to chew on...
  11. R

    I Understanding the 'vacuum fluctuations'

    Hello! As you might know or not know I am wroting a paper about the vacuum etc. Now I am having trouble understanding the fluctuations in the vacuum. I've seen many tell me that the fluctuations are not correct etc., but why? And how can I phrase it so that someone in 11h grade would understand?
  12. D

    Can any object cause fluctuations in a magnetic field?

    Summary:: Can a moving object cause disruptions in a magnetic field that could be detectable? Hello, I was hoping someone could assist me on a query I have regarding disruptions in a magnetic field. For some context, I am creating a science fiction story which features a non-humanoid alien...
  13. hyksos

    A The most striking example of vacuum fluctuations affecting experiments

    This is a question for experimentalists working in Condensed Matter Physics. What do you think is the most striking example of QFT vacuum state fluctuations affecting the results of an experiment? I have vague memory of reviewing some abstracts about quantum criticality in cuprate...
  14. Q

    I Gerard 't Hooft's "Fast Vacuum Fluctuations"

    Gerard 't Hooft has been a renegade in Quantum Foundations for quite some time, insisting that there is natural order underlying the Quantum Mechanical mysteries. Essentially a local, deterministic hidden variable perspective. He has recently posted a new paper on arXiv where he lays out his...
  15. Vanilla Gorilla

    B Could Quantum Fluctuations exist W/out the presence of Spacetime?

    I want to know whether Quantum Fluctuations could exist without the presence of Spacetime. Would it be possible, in the event of a Big Rip scenario, and if Spacetime really would get ripped apart, that quantum fluctuations could still occur? And if Spacetime is ripped apart, does that mean the...
  16. nomadreid

    I Why is the term "fluctuations" objectionable?

    I have read in several places (e.g., https://physics.stackexchange.com/questions/257035/confusion-in-understanding-of-quantum-fluctuations-and-vacuum-energy) that "quantum fluctuations" is an expression to be consigned to the sixth or eighth Circle of Dante's Inferno. OK, I can sympathize with...
  17. TheQuestionGuy14

    B Do quantum fluctuations actually occur in De Sitter space?

    A little while back I asked a question about quantum fluctuations, and I got some great answers. Just recently, I stumbled upon a paper by Sean Carroll, which states that there isn't quantum fluctuations after all, in a De Sitter space in a vacuum state. He used this to argue against Boltzmann...
  18. L

    Engineering Multimeter values different and fluctuations

    I measured current through a parrallel circuit and my multimeter fluctuated massively and compared to theoretical values they are miles out. multimeter was changed over to ampmeter. I used duel power supply. Throughtout the measuring i kept getting short circuits. The circuit on the...
  19. D

    Quantum Quantum Fluctuations & Virtual Bosons: A Guide for Amateur Physicists

    I am searching for anything on quantum fluctuations and virtual bosons for someone who is a serious but amateur physicist ie. I have completed undergrad physics/math and some graduate level math at university. I am having a hard time finding anything that isn't beyond pop science. Not really...
  20. MJM

    I When exactly did 'quantum fluctuations' in the early universe occur?

    I came across this video today: Which summarizes this new paper from University of Tokyo: https://arxiv.org/pdf/1907.02273.pdf I get that the video is just an explainer for primordial black holes, but I was hoping to get a better explanation on exactly when conventional wisdom says density...
  21. Gbox

    Finding inveriance size, equilibrium and fluctuations

    So I answered 1 and 2, got: 1. ##\vec(r)(\theta,\phi)=l(sin \theta cos \phi, sin \theta sin \phi, -cos \theta)## 2. ##L=\frac{ml^2 (\dot{\theta}^2+\dot{\phi}^2 sin^2 \theta)}{2}+mglcos \theta## 3. a ##mlsin \theta -mgsin \theta =l^2 \ddot{\theta}## , b. ##ml^2 \ddot{\phi}=0## 4. I know...
  22. epotratz

    I Does light consist of oscillating vacuum fluctuations?

    Hello, I've been studying electromagnetics, electromagnetic radiation, and bit of quantum electrodynamics for about 12 months, but I'm stumped on an issue.. This is what I understand so far: Charge consists of countless "vacuum fluctuations" (i.e., virtual particles). Accelerated charges...
  23. S

    A Measuring Quantum Vacuum Fluctuations

    I have been reviewing potential methods for measuring Quantum Vacuum Fluctuations that I might be able to implement in a home hobbyist environment. Must be room temperature devices. I have seen that there are only a couple of possibilities: The Tunnel FET and the Single Electron Transistor. I...
  24. J

    A Cosmological fluctuations (Weinberg's cosmology, p. 284)

    Hi everyone, I'm unable to understand how to derive Formula (6.3.11) in Weinberg's cosmology book. It's a relation between time-related derivation (d/dt) and RW-scale-factor-related derivation (d/dy, where y = a(t)/aEQ, a(t) is the RW scale factor in the metric and the EQ subscript denotes the...
  25. Cerenkov

    B The Spectral Gap and Quantum Vacuum Fluctuations

    Hello. Recently Scientific American magazine carried an article about the work of the authors of this paper. https://arxiv.org/abs/1502.04573 The Undecidability of the Spectral Gap. The SciAm article is linked to here -...
  26. ForgeJB

    I How can there be fluctuations in the inflaton field value?

    http://www.counterbalance.org/cq-turok/etern-body.html https://ned.ipac.caltech.edu/level5/Kolb/Kolb3_1.html) http://www.astronomy.ohio-state.edu/~dhw/A873/notes7.pdf) According to QFT, if you make repeated measurements of some property of the field then you will in general measure a...
  27. F

    I Variations in the speed of sound in a star

    I try to understand the following graphics with x-axis being the radius of a typical star : I would like to knwo if ##\delta c/c## (y-axis) represents the relative error between theoretical and experimental values or if it represents the fluctuations of speed of sound inside. If these are...
  28. mastrofoffi

    Weird fluctuations in Ising model

    Not 100% sure this thread belongs in this section, sorry if it's out of place. I was trying to run a simulation of a 2D Ising model; i thought everything was going fine until I started to look at the numerical results and I noticed that I get some wild fluctuations in my results; as an example...
  29. J

    I Are the energy fluctuations in space real or virtual?

    Heisenberg's uncertainty relation says: $$\Delta x \Delta p \ge \hbar$$ If we assume a massless quantum object then we have the relationship ##\Delta E = c\Delta p## so that the above uncertainty relationship becomes $$\Delta E \ge \frac{\hbar c}{\Delta x}.\tag{1}$$ I understand that if we have...
  30. davidge

    I So, do vacuum fluctuations exist?

    I'd like to know the reasons many physicists support the existence of quantum vacuum fluctuations. It seems that QED doesn't predict such phenomenum, nor any experiment has undoubtedly confirmed it, at least on the grounds of QED.
  31. T

    B So Quantum Fluctuations don't exist?

    Is it true that when we dig deep into the math, we realize that Quantum Fluctuations and virtual particles are just a heuristic way of explaining certain phenomena to lay public?
  32. M

    A Quantum fluctuations of the metastable false vacuum

    I have been trying so hard to get some answers to a few questions I have in regard to this paper: https://arxiv.org/abs/1404.1207 I think those questions can best be summarized this way: 1) A metastable false vacuum is a field and fields are just the changing value of a parameter in...
  33. nomadreid

    I Do quantum fluctuations mean metric fluctuations?

    I suspect the following reasoning is faulty, but I am not sure why. Hence I would appreciate someone pointing out the errors. That is, which, if any, of the following statements are incorrect, and why? 1) Theoretically, albeit not practically due to the large numbers involved, the laws of...
  34. R

    How can thermal fluctuations decrease entropy?

    https://en.wikipedia.org/wiki/Future_of_an_expanding_universe "Over an infinite time there could be a spontaneous entropy decrease, by a Poincaré recurrence or through thermal fluctuations (see also fluctuation theorem)"
  35. C

    I Scale invariant thermal fluctuations

    There's something that has been bugging me for over a year now and I seem to be unable to find the answer. I would appreciate it very much if somebody could help me out. The thing is that I don't understand how it is possible that in second order phase transitions the correlation legth becomes...
  36. L

    Energy fluctuations in canonical ensemble

    Homework Statement Consider an ensamble of particles that can be only in two states with the difference ##\delta## in energy, and take the ground state energy to be zero. Is it possible to find the particle in the excited state if ##k_BT=\delta/2##, i.e. if the thermal energy is lower than the...
  37. Kara386

    Temperature fluctuations in helium

    I'm about to do an experiment on second sound in superfluid helium. Reading the lab manual it says we will generate it by putting a heater into the fluid and then passed an AC current through it. What we are going to measure is apparently the 'normal fluid fraction', which I guess under the two...
  38. A. Neumaier

    Insights Vacuum Fluctuations in Experimental Practice - Comments

    A. Neumaier submitted a new PF Insights post Vacuum Fluctuations in Experimental Practice Continue reading the Original PF Insights Post.
  39. FallenApple

    I Gluon Field Fluctuations

    So below is an animation of a quantum field's energy density fluctuating. Specifically, a gluon field. So the empty spots are not truly empty but where the field is at the lowest energy. I saw a video from veritasium stating that the quarks are likely to live on top of those lumps. Why...
  40. A

    I 'Localization,' particle motion, and quantum fluctuations....

    Hi all, Some time ago I was reading about Anderson localization (posted a question about it was well) - this got me thinking about vacuum fluctuations. I think I have the wrong idea in my mind - so wanted to ask the great community here about it: Quantum (vacuum) fluctuations must have an...
  41. T

    I Vacuum fluctuations - possible stupid question

    My background is in Health Physics and as such, I have had only rudimentary instruction in quantum mechanics, so my understanding (such as it is) is largely conceptual. With that in mind, this may be a very ignorant question, so I apologize in advance. I understand the theoretical basis for...
  42. Doctor Strange

    A How do quantum fluctuations become gravity wells?

    How do quantum fluctuations become gravity wells? I thought the whole idea of the fluctuation was that it had to happen so quickly that the universe didn't notice. I see how a field could have a random, but non-zero value, but I don't see how that momentary variation in the field can stick...
  43. Paul Colby

    I Light fluctuations and finding exoplanets

    All light sources fluctuate and I've wondered if auto correlation of the natural fluctuation of a star's output might be used to range it's planets? The concept is to stare at a star (like Kepler does) and record high frequency intensity fluctuations say at a sample rate of 10 times per second...
  44. S

    A Quantum fluctuations in early universe

    Why do quantum fluctuations of fields arise at high energies and temperatures? What is the mathematical formulation of these quantum fluctuations? Why are the sizes of these quantum fluctuations approximately the Planck size?
  45. F

    Velocity fluctuations, variance and moment in turbulence

    I'm studying CFD and I'm on turbulence. It states that the fluctuating part of velocity squared and time averaged is the variance but variance in statistical terms is the deviation from the mean squared and averaged. So what is variance in turbulent fluctuating velocity? This variance is also...
  46. usED

    H2SO4 and pH fluctuations

    Homework Statement pH fluctuations need to be determined at a maximum dosage of 50mg/L of 93% sulphuric acid . Homework Equations If the start pH of the water sample is 8, how much will pH be lowered by adding of 50mg/L of 93% sulphuric acid, and what is the correlation between the different...
  47. L

    Can power supplies cause temperature fluctuations....

    can power supplies cause temperature fluctuations in a circuit? Or, instead, are they sensitive to temperature fluctuations in the environment, which can cause temperature fluctuations in a circuit?
  48. F

    I Relation between quantum fluctuations and vacuum energy?

    As far as I understand it, the non-zero vacuum energy attributed to a quantum field (at each point in space-time) is precisely due to the Heisenberg uncertainty principle (and the fact that the energy of the quantum field at each space-time point is quantised). Accordingly (in order to satisfy...
  49. M

    I Some questions regarding quantum fluctuations

    First of all, would I be correct in using the following explanation? Quantum fluctuations are not actually events but properties of the quantum vacuum, they don't have a physical cause but they are not an example of creation ex nihilo, they are created from other things. I think of it like a...
  50. bbbl67

    I Can Dark Matter just be vacuum fluctuations?

    Has there been any theories proposed that model Dark Matter as just the pressure from vacuum fluctuations? It would be just a big cosmological-scale version of the Casimir Effect, where instead of using a couple of plates separated by microns, we're using the gravity wells of galaxies to create...
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