Questions tagged [virtual-particles]

Use for computational-device notional particles which are not observable in the lab, such as "off-the-mass-shell" particles, "spurions", renormalons, merons. Do *not* use for unobserved hypothetical particles such as the graviton, or Goldstone bosons which could have been observable, but got rearranged into other particles through QFT mechanisms.

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Force carrier exchange = attraction. How? [duplicate]

Edit: Mod who closed the question as duplicate: direct me to the answer I get one could explain repulsion between particles using the "2 men on frozen lake throwing a ball between each other" analogy,...
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Why aren't all particles virtual? [duplicate]

It is my understanding that virtual particles are those that are internal to a particular interaction. They do not fulfill the requirements of a freely-travelling particle (ie a plane wave) and as ...
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Are force carrying particles always virtual particles?

Of course we have real (i.e. non-virtual) photons, but when photons play the role of "force carrier" are they virtual? Same thing for gluons. Real gluons have been detected, but when playing the role ...
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How does one calculate branching ratio of Higgs particle decaying into virtual particle?

Very often when people talk about decay they use branching ratio to describe a particular decay channel, for example: $$Z\rightarrow e^{+}+e^{-}$$ If both Z and the electron and positon are one-...
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Propagation of mechanical waves in vacuum

It is known that, while electromagnetic waves can propagate in vacuum as they do not need a medium, mechanical waves (e.g. sound waves) cannot. However, vacuum has vacuum fluctuations, where (virtual)...
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How can there be an exchange of virtual photons between delocalized particles?

Basically talking about Coulomb interactions here, and how they could happen without definite particle positions since Coulomb repulsion or attraction depends on distance which depends itself on ...
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What parameters determine the probability of virtual photon emission/absorption?

Suppose an electron is producing an electric field by emission of virtual photons and interacting with other particles. What parameters determine the probability that it will emit at least one virtual ...
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Why is Cosmic Microwave Background Radiation attributed to the Big Bang? [duplicate]

When searching for CMBR all articles start by stating as a fact that it is a remnant of the Big Bang. Why? Why is it well understood and accepted? Why sure that it's not an effect of something else ...
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Casimir effect: where did the pressure come from?

From my understanding of Casimir effect, there exists a difference in energy between plates and that of the outside environment. How did this translate to a pressure difference and eventually where ...
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Are there anti virtual particles (mediator bosons)?

I have read these questions: Can bosons have anti-particles? Is there a possibility for discovery of anti-graviton, i.e. the graviton antiparticle? Antiparticle for Higgs boson? According to ...
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Masssive mediator boson, a game changer, so is the weak force fundamentally different from the other forces?

I have read this question: How it is possible to mediate a weak interactions by very heavy particle such as Boson? How can a pion have a mass, given it's a "field mediator" and ...
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Quantum mechanical photon exchange [duplicate]

Background: While trying to understand the Standard Model I stumbled on a paper that explained it in very simple terms. I recognized that I don't even understand the quantum mechanical way of the ...
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Virtual pair of particle-antiparticles trajectory [duplicate]

Is it possible to do heuristic calculations on virtual pair of particle-antiparticle trajectories that appear in a vacuum? For example, what is the maximum distance between them during virtual process?...
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How can one of the particles on a pair of virtual particles created by vacuum fluctuations have negative energy? How does it lower black hole mass?

Assuming Stephen Hawking’s 1975 “Particle Creation by Black Holes” : “One might picture this negative energy flux in the following way. Just outside the event horizon there will be virtual pairs of ...
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Why can't a particle interaction $A + B \rightarrow C$ conserve energy and momentum at the same time?

I learned that in the Feynman diagram for electron photon scattering, the intermediate particle represented by the middle solid line must be a virtual particle because it violates energy-momentum ...
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Why accelerating observer can see Unruh radiation?

I read that uncertainty principle allows a pair of virtual particles to spawn in a vacuum as long as time is $h/E$ and nature forbid negative energy to exist, a accelerating person will see the photon ...
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Can particles popped into existence from the vacuum have electromagnetic effects on other particles?

I know my question might have problems, but I am curious about it. In quantum field theory, particle-antiparticle pairs continuously pop in and out of existence from vacuum. These particles have a ...
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If lamb shift is really due to the effect caused by virtual particles how come it only affect 1 orbital?

I was watching a video explaining virtual particle can be drawn to the positively charged necleus which explain why there is a tiny step between the higher energy level and ground state, but I'm not ...
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What are the similarities/differences between the behaviors of Quantum particles and bouncing droplets? [duplicate]

Bouncing droplets on a fluid surface show many weird behaviors of the quantum world. Look at this for example: https://arxiv.org/abs/1307.6920 They can show tunneling, double-slit interference ...
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Are vacuum-fluctuations a consequence of causality?

I'n new to QFT, and recently lerned about the propagator of a free scalar field theory in Minkowski-space, which according to our lecture notes looks like $$G(p, q) = \frac{1}{q^\mu q_\mu + M^2} \...
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If electromagnetic wave travels in a straight line how do you explain magnetic line of forces? [closed]

Imagine a piece of bar magnet and the presence of magnetic line of forces indicated by iron filings around the magnet, this magnetic line of force is compose of virtual photon right? and since ...
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Virtual particles

I use Wikipedia to learn physics. In a recent search I found an ample description of virtual particles in terms of a discontinuous (in the present) and asymptotic distribution of these particles from -...
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Hawking said virtual particles can almost become real particles, following closed trajectories. What does that mean?

Here's hawking quote from his latest book. Brief Answers to the Big Questions "When space-time gets warped almost enough to allow travel into the past, virtual particles can almost become real ...
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Particles, fluctuations and the quantum vacuum: is this right?

After answering a question on quantum fluctuations Could quantum fluctuations spawn real matter?, I got into conversation with E. D. Kramer (to whom thanks) and in the end it may be that we had a ...
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Could quantum fluctuations spawn real matter?

Would it be plausible for fluctuations in the QED vacuum to spawn actual matter (such as quarks, electrons the constituents of a hydrgen atom) given enough time and space?
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Lamb Shift and virtual particles [closed]

Can someone explain about the Lamb Shift?
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If the electric force is the exchange of virtual photons, how can free electrons be accelerated by it?

I know that free electrons can't absorb photons. It is, however, known that electric forces can accelerate electrons. But if electric interactions are merely an exchange of virtual photons, how can ...
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Why do nearby charges increase the probability of virtual particles?

I'm a layperson currently reading through Matt Strassler and on his website, he states, in relation to using positronium as an example of vacuum fluctuation effects: The stronger force between the ...
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Is the term “quantum fluctuation” an aide to understanding? [closed]

I would like to ask if anyone has found a tight enough way to define the term "quantum fluctuation" so that it can become a useful rather than a misleading piece of physics terminology. Terminology ...
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Heisenberg energy uncertainty [duplicate]

I am biologist and just new to the field of quantum mechanics and trying to understand the subject by reading. It is said that virtual particles are created due to the uncertainty of energy when ...
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In terms of energy, are virtual particles an intermeidiate state between real particles and a vacuum?

What exactly is the difference between real and virtual particles? Are virtual particles just fluctuations in their quantum field? If so, how is that different to real particles?
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Feynman diagrams

Feynman diagrams are drawn on Space-time graphs. So is it possible for any particle path in that diagram to have a slope smaller than 45° or greater than 135°, i.e. can they travel faster than light? ...
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Why isn't energy conserved in time-ordered diagrams?

I'm new to particle physics, and I'm reading chapter 5 of Prof. Mark A. Thompson's "Modern Particle Physics", which talks about Time-ordered perturbation theory vs QED. However, in page 119 he wrote: ...
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Can Virtual particles be knocked on shell (become real)?

I have read these questions: Can virtual particles be 'boosted' into becoming real particles by fields other than gravity? where dmckee specifically mentions J/Ψ meson production as a clear ...
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Interaction of charges [duplicate]

As it is known in Physics, two point-size charges (say two electrons) interact with each other through em forces. How this is happening? do they exchange photons? And if so, then do they exchange ...
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How much virtual photons does an rest electron emits instantly, per time?

I've asked this question How much electrons can absorb a single photon? , but guys contradicted each-other, in the question about how much virtual photons does rest electron emits. One of them said ...
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Can/do Virtual Particles have mass/energy?

Apologies, as you can tell I am not an expert... My question arose during a thought experiment regarding that elusive Dark Matter/Energy and the rate at which the universe should be expanding. It ...
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Virtual photon does not changes energy, but changes momentum. How it could be, if energy depends on momentum?

You say virtual photon caries only momentum and changes only momentum of the particle. Momentum $p$ of electron is $v*m$. Energy of moving electron is $E=\dfrac{mc^2}{\sqrt{1-v^2/c^2}}$, which means, ...
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Free (unbound, so not bound to a nucleus) accelerated electron cannot emit/absorb a real photon?

I have read these questions: Can a free electron absorb a virtual photon even though it cannot absorb an ordinary photon? Where Michael Seifert says: It is entirely possible for a real electron ...
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How much electrons can absorb a single photon?

In the one hand, energy can be emitted\absorbed only by a discrete portions. In the other hand - according to Coulomb law the higher distance - the lower force, because count of force lines per area ...
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1answer
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Where do “virtual” particles come from? [duplicate]

Quantum physics tells us that even a perfect vacuum be populated by "virtual" pairs of subatomic particles. I have read that these particles are allowed to violate the Conservation of Matter and ...
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How to interpret the Feymann diagram of two photons scattering off each other?

I've attached a Feynmann diagram of two photons scattering with the nuclear reaction: γ + γ --> γ + γ May I ask how would one interpret this diagram? My attempt in interpreting is that the photon ...
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1answer
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Why can there be only 3-particle vertices in Feynman diagrams? [closed]

Why can there be only 3-particle vertices in Feynman diagrams? For example, when a particle and its anti-particle annihilate to form two photons, why is its Feynmann drawn the way it is in diagram 2 (...
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According to Coulomb law, why do fixed charges interact, if they don't emit the photons?

Why does it happens, if fixed charges don't oscillate the em field?
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Why there is a distance dependence in Coulomb's law if photons can travel to infinity?

Why there is a distance dependence in coulombs law if photons can travel to infinity? Why there is distance dependence at all?
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1answer
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Hawking Radiation specific clarification [duplicate]

If virtual particles on the edge of a black hole pop into existence randomly, wouldnt the likelyhood of a antiparticle generating on the inside of the black hole equal to a particle doing the same? So ...
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4answers
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Is the magnetic field/force just a relativistic electric field/force or is there a fundamental difference?

I have read these questions: Difference between electric and magnetic field (relating to EEG & MEG) Can someone please explain magnetic vs electric fields? Explain the origin of magnetic fields ...
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Are EM fields made of photons or are they fundamental?

I have read these questions: Virtual photon description of B and E fields How do virtual photon cloud produce discrete magnetic field lines in bar magnet? How virtual photons give rise to electric ...
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Virtual photon exchange instantaneously

I have read these questions: Virtual Photon transmission speed of a Static Electric Field? where John Rennie's comments say: Virtual photons can travel faster than light Is there a "...
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Why aren’t photons re-absorbed into the electromagnetic field?

I understand that the quanta of electromagnetic field is a photon. Anyway, the electron field quanta is the electron. And the process of electron-positron annihilation releases two photons when the ...