Why are anti-particles defined as particles having negative energy and propagating backward in time in solutions for the Dirac equation?
Do they really have negative energy and if so, what is it?
Paul Camp, Ph. D. in theoretical physics wrote:
There exist negative energy solutions of the Dirac equation. Mathematically, this is because the relativistic energy - momentum relation is quadratic so it has both positive and negative roots.
Viktor T. Toth, wrote:
Particles (or antiparticles) really do have negative energy… if they are moving backward in time. But they aren’t. Or rather, quantum physics works the same either way.
https://www.quora.com/Why-are-anti-particles-defined-as-particles-having-negative-energy-and-propagating-backward-in-time-in-solutions-for-the-Dirac-equation
The real answer to this question is hidden in the left side of relation , for this reason, CPH Theory has a new and different approach to this question. In CPH Theory, instead of thinking to negative energy, we must focus on Dirac Sea and extend the Dirac equation. This approach suggests that the photon has been structure.
https://www.researchgate.net/publication/312471904_Why_are_anti-particles_defined_as_particles_having_negative_energy?ev=prf_pub
Article Why are anti-particles defined as particles having negative energy?
Hossein> Why are anti-particles defined as particles having negative energy and propagating backward in time in solutions for the Dirac equation?
All that is mostly poetry, which makes it more enjoyable to carry out nitty-gritty quantum field theory calculations. And, if interpreted properly, may help you to arrive at correct results.
Roughly, when you have a linear, homogeneous, time translation invariant, field equation, you may expand its general solution into positive and negative frequency eigen-modes, with arbitrary coefficients. For canonical quantisation you promote the coefficients of positive frequency modes to annihilation operators of particles, and the negative frequency modes to creation operators of anti-particles.
The propagating backward metaphor is related to a particular kind of path integral formulation.
Dear Kåre
According to quantum field theory and Feynman's diagram, you are right and I agree with you. But they have not describe how a charged particle such as electron absorbs a photon. Scattering of light by matter has been studied extensively in the past. Yet, the most fundamental process, the scattering of a single photon by a single atom, is largely unexplored. One prominent prediction of quantum optics is the deterministic absorption of a travelling photon by a single atom, provided the photon waveform matches spatially and temporally the time-reversed version of a spontaneously emitted photon.
Here we experimentally address this prediction and investigate the influence of the photon’s temporal profile on the scattering dynamics using a single trapped atom and heralded single photons. We don't often think of photons as being spread out in time and space and thus having a shape, but the ones in this experiment were some four meters long. Christian Kurtsiefer, Principal Investigator at CQT, and his team have learned to shape these photons with extreme precision.
This experiment is incompatible with point-like and unstructured photon.
https://www.researchgate.net/publication/311511253_Review_the_time-resolved_scattering_of_a_single_photon_by_a_single_atom?ev=prf_pub
Article Review the time-resolved scattering of a single photon by a ...
While, historically, that may have been the case, it turns out that this statement is misleading. The more useful statement is in all the textbooks on relativistic quantum field theory and is expressed by the CPT theorem. Antiparticles are just as ordinary as particles and are described by applying charge conjugation to particles.
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