Fluctuations Definition and 149 Threads

Hello everyone, I know this is a very basic question but I was wondering, in the context of inflation, what does it mean to have gaussian or non-gaussian fluctuations. First of all, are we talking about the fluctuations of the inflation? Second of all, how is the nature of the fluctuations...

hello, I was wondering what caused quantum fluctuations within an electromagnetic field as i recently accepted that there are no virtual particles what causes the energy to fluctuate. here the quantum fluctuations are said to be caused by virtual particles. essentially I'm asking for an...

The general logic of Inflation is that some field popped into existence just long enough to flatten out the universe, then disappeared again. Before the field, the universe had tiny fluctuations in the plasma. Inflation blew these up from the size of an atom to the size of a grapefruit (If I...

Hi everyone, I had a related, more complicated post in another thread - I hope it's ok to post a simplified and slightly different question here (posting as a layman): Let's say I have an electron traveling alone in the vacuum, when a vacuum disturbance (fluctuation) occurs nearby. If the...

I want to ask a question about the Quantum Vacuum, but I want to make a few statements about my understanding of the Classical concept of a vacuum to act as a background. 1.)As I understand it, the classical vacuum is a place where there is nothing. 2.)Two attributes of the classical vacuum are...

Is there a good explanation for how we can explain an ordered universe arising from an inherently uncertain quantum world? I'm aware of the conflict between special relativity and quantum vacuum fluctuations, but is this the only issue? The correspondence principle would seem to imply that...

According to wikipedia: "As for a classical second order transition, a quantum second order transition has a quantum critical point (QCP) where the quantum fluctuations driving the transition diverge and become scale invariant in space and time." I am confused about what this means. Why do the...

Hi. I'd like to learn how to calculate the probability of a photon being emitted from a radio antenna where the energy per wavelength is below the threshold to emit photons. Let's assume the electrical thermal noise is insignificant. The antenna temperature could be sufficient low or the...

Homework Statement Consider a system of fixed volume in thermal contact with a reservoir. Show that the mean square fluctuation in the energy is < e-U >^2= t^2*(∂U/∂t) where U=<e> Hint: use the partition function to relate (∂U/∂t) to the mean square flucuation. Also, mulitply out the (...)^2...

Electron can scatter off virtual photon of Coulomb field (or even emit real photon). But why it cannot do the same off virtual photons of vacuum fluctuations without external field?

I am interested specifically in the rate of formation of particle-antiparticle pairs in the empty void of vacuum space according to Quantum Theory? For example: for any given cubic centimeter of empty vacuum space, the rate of formation of electron-positrons is X pairs per second; the rate of...

Homework Statement The figure below shows the path of a particle governed by the Lorenz equations with r = 28, σ = 10, b = 8/3. The x'es and boxes show points where the path crosses the plane z = r − 2σ > 0. (a) Which indicator shows a decreasing z and which shows an increasing z? (b) Show...

The force in the Casimir effect can be "explained" by two causes, see, http://en.wikipedia.org/wiki/Casimir_effect#Possible_causes In some optics experiments we must account for the fluctuations of the quantum vacuum to get the right experimental results. See, Vacuum noise...

So, from what I understand, quantum uncertainty means these vacuum fluctuations occur, and out of them come virtual particle and antiparticle pairs. How does this not create a preferred frame of reference? A particular particle pair must have a certain amount of energy, and in one frame where...

Homework Statement Statistical Mechanics by Pathria. Problem 3.1 Homework Equations (1) <(△nr)2>=<nr2>-<nr>2=(wrd/dwr)(wrd/dwr)lnΓ, for all wr=1 How to derive above equation from these equations? <nr>=wrd/dwr(lnΓ), for all wr=1 <nr2>=(1/Γ)(wrd/dwr)(wrd/dwr)Γ, for all wr=1 (2) Also, if you...

I was lately interested in learning how the human body weight changes through out the day. Like, how much weight (may be in just 10s of grams) is lost during sleeping, after bathing, after workout and like that. For that I would require a highly precise scale. But most commercially available...

Please, can anyone help to analyse fluctuations of density in De Sitter Space in case of long waves? Formulas and Solutions are welcome.

How do quantum fluctuations originate?

Hi, I have read that quantum fluctuations have created our universe through the Big Bang. The issue that I didn't understand is that as far as I know quantum fluctuations are properties of space. How could these fluctuations exist before the Big Bang while there was no space before the Big...

Hi all, I know how if a statistical partition function is written as a path integral in imaginary time (Wick's rotation) the fluctuations around the mean-field represent thermal fluctuations. If the path integral is instead done in real time then fluctuations from the...

Hi, I wondered if it is theoretically possible that the vacuum energy produces an electron/positron pair which then bonds into positronium instead of directly annihilating again. And if it is theoretically possible has this ever been observed ? Thanks and cheers.

Consider any of the latest maps of the temperature fluctuations of the CMB. Such a map can be considered a 2 dimensional topographical map of the surface of a sphere, high points hotter, low points cooler. Consider the contours that divide such a map into the two regions, fluctuations hotter...

In chapter 10 of Robert D. Klauber's excellent QFT book, there's a nice overview of different concepts occurring in the context of vacuum fluctuations. Inspired by that chapter I ask: If one would state that there is no such thing as vacuum fluctuations, what counter arguments are there? In...

Why is it stated that a fluctuation could occur and spontaneously gather all the molecules of air onto the corner of the room, or that a brain can spontaneously form in empty space if given enough time. Personally I don't agree with this because these events would contradict the laws of...

Do quantum fluctuations come from "nothing"? Hello, I have two questions regarding quantum fluctuations. Do the particle (and its' anti-particle) appear from nothing? I know it happens in a Quantum vacuum. But do the particles themselves appear from nothing? Where do they get their energy...

Hi, Similar to the position-momentum uncertainty principle, there is a time-energy uncertainty of the form $$\Delta E \Delta t \geq\frac{\hbar}{2}\enspace .$$ However, since time is not an observable, the derivation and interpretation of this inequality is somehow different compared to...

Hello! I was hoping somebody may be able to help me understand something much beyond the physics I have learned so far. I need to complete an assignment that I believe is asking me to find the Higgs potential function? 1. My professor mentioned the following: minimization at the origin...

Hello Physics Forums, This is my first time posting so apologies for any mistakes or misunderstand of forum etiquette here. I am having difficulty understanding a phenomenon known as "dark current" I've tried for a few hours to research it but most of what i find is very vague on the...

What is meant by "being driven by quantum fluctuations" in QPTs Hello all, I'm reading a bit about quantum phase transitions, and in almost every description out there one will find the following mysterious phrase: "quantum phase transitions are driven by quantum fluctuations rather than...

How do pressure fluctuations in a fluid flowing through a complicated pipe system (such as an engine lubrication system) affect its temperature? Does the net fluid temperature increase with increase in the magnitude of pressure fluctuations? Or does it decrease? Thanks in advance.

Contrary to a classical vacuum, particles tend to pop into and out of existence in a quantum vacuum. When analyzing a Feynman diagram (such as Moller scattering), is the virtual photon that mediates the electromagnetic interaction considered to be a quantum fluctuation? (Any feedback will be...

Hello, I am trying to build a SIMULINK model in Matlab in order to determine the RPM of a wind turbine. Can someone please tell me how I can obtain the RPM of a wind turbine from the voltage fluctuations of a generator? Any good sites in the subject are also welcome. Thanks in advance.

I notice that many physicists say that virtual particle fluctuations occur in space "because Heisenberg's Uncertainty Principle allows them" Is this really the best form of reasoning? Isn't it actually the other way around - that because virtual particle fluctuations happen, then there is a...

Hey all, I'm reading Chaikin's Principles of Condensed matter, and he's talking about the effect fluctuations have in various systems. He says: So I get why order is destroyed in 1D, and not in 2D. But I don't see why they destroy the phase transitions. Can anyone tell me? Thanks!

Characteristic energy "units" of primordial fluctuations if gaussian Correct me if wrong, but I think a purely gaussian distribution of the primordial fluctuations could be characterized by a certain unit of energy (which I'll express as mass). If so, then the observed fluctuations are...

I work in the Aggregate industry and we use ceramic magnets to pull ferrous materials out of the feed of Aggregate materials passing by on a conveyor belt. So i have a basic knowledge about how they work, but my technical knowledge about magents is extremely lacking. Wondering if anyone...

How does a transformer react to a changing frequency Obviously the inductive reactance of the primary changes, which causes a decrease in the current for an increase in reactance, then so too shouldn't the output voltage be less? This seems to contradict Vs/Vp = Ns/Np What I am saying is...

I'm working on a board that takes measurements of voltage off a thermistor through an arduino and amplified by an opamp (really an instrumentation amp AD623), also there are two potentiometers (picture of schematic attached). I've been receiving some very strange voltage fluctuations that I...

This is from Krauss' A Universe from Nothing How could Guth know what density fluctuations arise after inflation? More context to better help a potential answerer:

How Does Lightning cause Voltage fluctuations in house's power supplies?

What are quantum "fluctuations"? We get to know that vacuum is not really empty but that its energy ground state is non zero. Is this what is represented by quantum "fluctuations"? As far as I understand QM this seems to me a very misleading representation of things. If we believe that...

Hi, I was trying to measure DC link current on a switched mode power supply when I came across a quirk of my circuit. I'm using an LEM HX 03-p SP2 hall effect current transducer to measure current. I couple the output node of my current transducer to ground via a 2KΩ resistor. The device's...

Say you have a giant mercury barometer. Let's suppose that the area exposed to atmospheric pressure is 1 square meter Normal pressure at sea level is 101325 Pa Lets say the variation in 24 hours in atmospheric pressure goes from a low of 100,000 Pa to a high of 102,000 Pa Using...

The Lamb shift showed that quantum fluctuations could have a real, measurable effect on the orbits of electrons. Since these fluctuations can impact the momentum of mass, is it possible that quantum fluctuations could impact electro-magnetic momentum, such as the momentum of photons...

Hi there. I am a layman, and I have a question. As far as I have gathered, the prevalent view in cosmology is that the universe appeared as a result of the Big Bang, which in turn occurred due to expansion of singularity. Ok. Some go further and propose that singularity appeared through...

How are internal lines with no free ends of Feynman diagrams of the perturbative expansion of QFT related to the quantum tunnelling barrier's negative kinetic energy and the HUP of QM? (if they are related at all)

has quantum fluctuations and the Wand der walls force that they produce been measured at different heights? Are there any results? Would there/ should there, according to accepted theories, be any difference?

Usually when studying thermodynamics and statistical mechanics of a macroscopic body one uses a "heat bath model" to define a temperature. In quantum mechanics one can assume that the heat bath has arbitrary low temperature. When studying quantum electrodynamics one has vacuum fluctuations...

weight is more at night than day. is this right? if not why?

Recent searching of the light from the quasars indicate lack of the quantum fluctuation of the spacetime. http://arxiv.org/PS_cache/arxiv/pdf/1108/1108.6005v1.pdf Does it mean the lack of quantum foam rules out the discretness of the spacetime too ? How to explain Casimir effect and...