Dirac's sea is a theoretical concept introduced by physicist Paul Dirac to explain the behavior of electrons in the framework of quantum field theory, specifically in the context of the Dirac equation. In Dirac's formulation, the negative energy states in the Dirac sea are filled with electrons, and the absence of a negative energy electron is interpreted as a positive energy electron. This formulation was later refined by the development of quantum electrodynamics (QED), which provided a more accurate description of electron behavior.
It's important to note that the concept of negative energy states in the Dirac sea is a theoretical construct and should not be interpreted as observable physical particles with negative energy. These negative energy states serve as a mathematical tool to describe the behavior of particles in certain relativistic quantum theories.
In quantum field theory, the energy of a particle is measured relative to the vacuum state. The vacuum state is assigned an energy of zero for convenience and as a reference point. When an electron is present, its energy is measured relative to the vacuum state, and the positive energy of the electron corresponds to the energy above the vacuum energy.
In the context of the Dirac equation, the positive energy states represent observable electrons. The energy of an electron is given by the positive eigenvalues of the Dirac equation, which are not doubled or modified due to the presence of negative energy states in the Dirac sea. The negative energy states in the Dirac sea do not contribute directly to the observable properties of electrons.
Therefore, the positive energy state of an electron, as measured relative to the vacuum state, is not doubled or modified by the existence of negative energy states in the Dirac sea. The energy of an electron is determined by its positive energy eigenvalue, and that is the value that is observed and measured in experiments.