About the concept of particle: an introduction
2015
Abstract
In this paper we consider important aspects characterizing the physical concept of particle. Starting by a possible definition, we deal with classical and quantum aspects of particles, reality and dimensionality. We considering then theoretical developments related to the gravitational interaction about the notion of particle in quantum field theories (QFT) and how the concept of "point-like particle" changes in consideration to the recent theories of unification of forces in physics, in particular in relation to superstring theories and quantum gravity.
FAQs
AI
What challenges arise in defining particle stability in quantum physics?
The paper reveals that even long-lived unstable nuclei, like free neutrons, challenge the clarity of particle stability. Stability manifests variably across different conditions, complicating definitive categorization.
How do quantum field theories change the understanding of particle states?
The study indicates that particle states are difficult to define in curved space-times and suggest that quantum field theories should be viewed as eigenstates of local operators. This shift highlights the complexity of distinguishing between global and local particle states.
What role do virtual particles play in quantum field theory?
The concept of virtual particles emerges from perturbation series, where individual terms can contain infinities addressed through renormalization. They facilitate interactions, such as electron exchanges via virtual photons, despite not adhering to standard energy conservation laws.
How do string theories alter the traditional notion of particles?
String theories propose that particles are not point-like but rather different vibrational modes of one-dimensional strings with a size near the Planck length. This conceptual shift addresses inconsistencies between quantum mechanics and general relativity while introducing higher-dimensional geometries.
What is the importance of excited states in characterizing particles?
Excited states, revealed as resonances during diffusion processes, reflect the underlying energy levels of particles as seen in sharp peaks of efficiency curves. These resonances challenge the definition of particles, indicating a complex hierarchy of 'elementary' constituents.
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