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A. Neumaier submitted a new PF Insights post
The Physics of Virtual Particles
Continue reading the Original PF Insights Post.
The Physics of Virtual Particles
Continue reading the Original PF Insights Post.
Particles generated by the Unruh effect are indeed virtual only - of the same kind as the virtual photons in the Coulomb interaction. Since the bath is hot, one needs a quasiparticle picture to get something resembling actual particles.naima said:If an accelerated observer tells you that she is in a hot bath of particles that you do not feel, will you call them virtual?
It is the ##K_i## in the standard notation for the generators. https://en.wikipedia.org/wiki/Poincaré_groupanorlunda said:Help please, "another 3-vector describing infinitesimal boosts"
I was careful in my language, not talking about a harmonic oscillator but about an oscillator in general. The Hamiltonian tells which kind of oscillator one has - harmonic or anharmonic. The form of the Hamiltonian depends on the way the system is embedded into its surrounding.dextercioby said:Hi Arnold, nice and thorough writing, bravo! Now, there's a tiny, but relevant, addendum. The fundamental observables of the quantum harmonic oscillator are coordinates, momenta and the Hamiltonian. There's no way you can leave out the Hamiltonian from the algebra: if you do, there's no way to tell a system from another and there's no dynamics.
In technical terms, the Unruh effect produces from the vacuum state (in the rest frame) a coherent state (in the accelerated frame), more specifically a so-called Hadamard state. When phrased in finite terms, the accelerated observer sees no physical particles but a heat bath modeled by the coherent state. The virtual particles are an artifact of forcing upon the coherent state (in a non-Fock space) a particle picture (that makes sense only in a Fock space).naima said:You say that virtual particles "are" internal lines in Feynman diagrams. Is it the case with the virtual particles of the Unruh effect?
Ben Wilson said:"If your audience can understand this definition, then you are preaching to the converted.
To avoid confusion, it would be useful to give a precise difference between virtual particle and quasiparticle, and also between quasiparticle and real particle. It is probably only a matter of definition, but from your statement above it seems that my definition differs from yours.A. Neumaier said:Particles generated by the Unruh effect are indeed virtual only - of the same kind as the virtual photons in the Coulomb interaction. Since the bath is hot, one needs a quasiparticle picture to get something resembling actual particles.
Demystifier said:it would be useful to give a precise difference between virtual particle and quasiparticle, and also between quasiparticle and real particle.
naima said:do we need quasiparticles or virtual particles to cook the food?
Real particles are the elementary excitations of the vacuum state.vanhees71 said:In a microwave oven we have coherent states that cook the food :-).
See post #9.naima said:coherent states here. How do they appear in the context of an accelerated observer?
I added the following paragraph to the Insight text:Demystifier said:To avoid confusion, it would be useful to give a precise difference between virtual particle and quasiparticle, and also between quasiparticle and real particle. It is probably only a matter of definition, but from your statement above it seems that my definition differs from yours.
The Bogoliubov transformation is the unitary transformation that turns the vacuum state (in an approximation with cutoff) into a coherent or squeezed state, or their fermionic analogue. In the physically relevant cases, it becomes, however, ill-defined in the limit where the cutoff is removed, reflecting the fact that quasiparticles states belong to a different representation (superselection sector) of the observable algebra than the vacuum state and ordinary particle states.naima said:I found here a link between accelerated observer and coherent states thru Bogoliubov transformation.
Free particles.naima said:So give me something that is not virtual and not observed.
(if virtuality is strictly included in non observability)
The present insight article is intended to be preaching to the converters.Ben Wilson said:If your audience can understand this definition, then you are preaching to the converted.
I would writeAccording to the Born rule, the distribution of a quantum observable gives the probabilities for measuring values for the observable in independent, identical preparations of the system in identical states. Thus the presence of a Gaussian distribution means that the attempt to measure the electromagnetic field in the vacuum state cannot be done with arbitrary precision but has an inherent uncertainty.
Yes, that's an improvement. I updated the page.vanhees71 said:According to the Born rule, the distribution of a quantum observable gives the probabilities for measuring values for the observable in independent, identical preparations of the system in identical states. Thus the presence of a Gaussian distribution means that the value of the electromagnetic field in the vacuum state is not determined with arbitrary precision but has an inherent uncertainty.
Virtual particles are particles that spontaneously appear and disappear in a vacuum. They are not observable directly, but their effects can be measured through various physical phenomena.
According to quantum field theory, virtual particles arise from fluctuations in the quantum vacuum. These fluctuations create temporary imbalances in energy, resulting in the appearance of virtual particles.
No, virtual particles do not violate the law of conservation of energy. They are simply a manifestation of the uncertainty principle and do not have a net effect on the total energy of the system.
Yes, virtual particles can become real particles under certain circumstances. For example, in particle accelerators, virtual particles can gain enough energy to become real particles that can be detected.
Virtual particles play a crucial role in our understanding of the fundamental forces and interactions in the universe. They are an essential component of quantum field theory and have been confirmed through various experiments and observations.