Ground State Vs Excited State: Fill & Download for Free

The unexcited field is simply the ground (lowest energy) state of the field.Take electromagnetism. Excitations of the quantized electromagnetic field are what we know as photons. The electromagnetic field is always present, even in the absence of photons. The absence of photons simply means that the field is in its lowest energy state.To see what this means, consider a pair of electrons that repel each other in otherwise empty space. They repel each other because of the way they interact with the ever present electromagnetic field. This interaction is said to take place by the exchange of “virtual photons”, but that’s just a fancy, visually appealing way of thinking about what really is a mathematical expression describing the interaction of two fields: the “electron field” with its two localized excitations vs. the electromagnetic field in its ground state. The resulting nasty integral can be expanded into a sum of terms of increasing complexity, and these terms can then be represented by those nice Feynman diagrams that show the exchange of one photon, the exchange of two photons, etc.I thank my generous supporters on Patreon. If you like my answers, please consider joining them.

There are many different ways atoms can emit radiation.When an electron of an atom is in an excited state, as it returns to the ground state, it emits a photon of a very definite energy (frequency).However, when atoms just wiggle about due to heat... although atoms at large are electrically neutral, the distribution of electric charge in an atom is not spherically symmetric. So when an atom accelerates (e.g., by bouncing into another atom, its positive and negative charges exert slightly different influences on the electromagnetic field, and the difference appears as radiation. This can have any frequency; in fact, the emitted frequency will be related to temperature according to Planck's radiation law. And of course in very hot stuff (e.g., in a star) the temperature is so high, electrons are not bound to atoms at all, so once again as atoms and electrons bounce about and accelerate, they will emit radiation at arbitrary frequencies.The short version is that you must distinguish between radiation that happens when electrons bound to an atom drop to lower energy levels vs. radiation that happens when a charge accelerates.

With due respect to Viktor Toth who answers here, he is not a physicist and he tends to misunderstand several fundamental concepts such as this one. His answer to this question is incorrect.Yes e=mc^2 means that things with mass have potential energy, but with possible exceptions …If some of the mass in question can be converted into kinetic energy, then it’s correct to say the validity of e=mc^2 proves that mass has potential energy. This is a question about the structure of the mass, and is crucial to the subject of particle decay. Protons and neutrons, for instance, are thought to have internal structure to them. In each case there is a probability of decaying (i.e. converting energy) into other particles while imparting kinetic energy to some or all of those particles. In the case of a free proton, physicists are unable to explain why they have never observed decay. In the case of the free neutron however, the process of mass conversion to kinetic energy is easily confirmed: Free neutron decay - WikipediaIn the case of the electron we don’t see decay, but it’s theorized to be possible. Here’s an example of a theory that claims the electron may have some structure to it. Electron Decay Quoting …“The simplest theoretical model which would give rise to such a decay is one where the electron is regarded as the first excited state and neutrino as the ground state of a fundamental spin 1/2 particle bound to a scalar particle by a super strong force and the photon is considered as a bound state of a fundamental spin 1/2 fermion-antifermion pair.”Again just theoretical, but the idea follows directly from e=mc^2 and yes, this means that electron mass has potential energy, ie the potential for some of its mass to be converted to kinetic energy.More fundamental is the difference in mass of an atom in an excited state vs its ground state. For instance, the Hydrogen atom in its ground state has less mass than it does after absorbing a photon that changes the atomic state. Energy Added = More Total Energy = More MassNow when the atom decays to its ground state again kinetic energy is created/released. This is exactly the definition of potential energy of mass converted to kinetic. E=mc^2 is how we know the mass of the atom is partly due to Potential Energy.