Quantum field theory

[PB666]

https://en.wikipedia.org/wiki/Quantum_field_theory

Sorry about posting this, its not new material I just wanted to correct some misinformation being thrown about the group.

I suspect that most of the participants of this group already know this, some may even have points of contention or correction of this but

as far as I know the understanding appears largely correct.

Albert Einstein in 1905, attributed "particle-like" and discrete exchanges of momenta and energy, characteristic of "field quanta", to the electromagnetic field. Originally, his principal motivation was to explain the thermodynamics of radiation. Although the photoelectric effect and Compton scattering strongly suggest the existence of the photon, it might alternately be explained by a mere quantization of emission; more definitive evidence of the quantum nature of radiation is now taken up into modern quantum optics as in the antibunching effect.

-WP

subatomic particles in particle physics and quasiparticles in condensed matter physics. A QFT treats particles as excited states of an underlying physical field, so these are called field quanta. In quantum field theory, quantum mechanical interactions between particles are described by interaction terms between the corresponding underlying fields.-WP

Ordinary quantum mechanical systems have a fixed number of particles, with each particle having a finite number of degrees of freedom. In contrast, the excited states of a QFT can represent any number of particles. This makes quantum field theories especially useful for describing systems where the particle count/number may change over time, a crucial feature of relativistic dynamics.

The key point of this approach is that when fields (pl) appropriate parameters superpose, a particle can be observed, the fields propagate whether or not a particle is observed. For example two sufficiently powerful EM fields can superpose and result in a matter-antimatter pair. It does not have to be EM, it could be fields found within plasma, or even unknown field. Waves and particles are a manifestation or propagation of the field.

Most theories in standard particle physics are formulated as relativistic quantum field theories, such as QED, QCD, and the Standard Model. QED, the quantum field-theoretic description of the electromagnetic field, approximately reproduces Maxwell's theory of electrodynamics in the low-energy limit, with small non-linear corrections to the Maxwell equations required due to virtual electron–positron pairs.

The wave-function of the field is given by simple wave functions Psi(x,t) in the above Schrodinger equation to derive the below for interactions.

Again there will always be some uncertainty at the smallest scales because of quantum uncertainty and Monte Carlo effects. Particles and waves are manifestations of the field.

The Feynman lectures are now on line as mentioned in the other post, the parameters such and vector field and intensity are defined there rather completely, as completely as one can describe them.

Instead of arguments with folks that might have their facts awry or are using observations from the 1930s to 1950s that were not mainstream, it might be better to compare the facts with a current accepted set of baselines. QFT in my mind is not perfect, that is because it lacks a fundamental basis in itself (although not for lack of trying as in string theory), not a fault of QFT but a fault in our ability to observe that basis. When we look at Newtonian or relativistic physics, they appear complete until we observe things on very large or small scales, and quantum mechanics has the same limitiations, but in fact we cannot see anywhere near Planck's scale, so resolving more basal level of physics is difficult.

But even at that, at least the way i see things the inconsistencies between particle and wave theories can be explained with QFT.

Edited October 14, 2015 by PB666

[K^2]

I'm not sure what you're trying to say here.

Yeah, in QFT, there are no problems with particle/wave duality, because there isn't really a duality. Everything is a field, and "particle" representation is nothing more than mathematical trick to represent the same field in a different basis. It still, ultimately,describes the same field.

Also, as a small correction, EM wave cannot constructively interfere in vacuum to produce a particle-antiparticle pair because that does not conserve momentum. It must scatter from matter that's already there. Now, if you happen to have at least an electron, and you hit it with a powerful enough beam of EM radiation, sure, you can produce a bunch more particles. But something has to be there. Just EM and vacuum won't cut it.

[PB666]

I'm not sure what you're trying to say here.

Yeah, in QFT, there are no problems with particle/wave duality, because there isn't really a duality. Everything is a field, and "particle" representation is nothing more than mathematical trick to represent the same field in a different basis. It still, ultimately,describes the same field.

It involves something tacitly approved in another thread that at least the way I read it, was inconsistent with QFT in any form that I have read. As you know when have had discussions in the past to specify feild when it could be replaced by particle or wave. We know that field propagation is a consistent feature of the universe, we cannot be clear, for instance, that gravity has a particle duality. Nor is it clear that any new feild that might be discovered will show a duality, so discussing a duality; although it is unlikely that it will not show aspects of a wavefunction. Thats why I gave the equations.

Also, as a small correction, EM wave cannot constructively interfere in vacuum to produce a particle-antiparticle pair because that does not conserve momentum. It must scatter from matter that's already there. Now, if you happen to have at least an electron, and you hit it with a powerful enough beam of EM radiation, sure, you can produce a bunch more particles. But something has to be there. Just EM and vacuum won't cut it.

that was my effort to be inclusive, there could be circumstances when E(photon) exceed PeV that might have existed in the very early universe where charge is not a manifestation of the electron or proton (proper), and actually one could argue it could have technically preceeded quark-gluon plasma. vacuum depends on how you define it, prolly best not to during inflation.

https://en.m.wikipedia.org/wiki/Inflationary_epoch