Hydrogen is the simplest of all the atoms, containing just an electron and a proton. It normally takes 13.6 eV of energy to separate the electron and proton when the atom is in the ground state. Similarly, if an electron and proton combine to form a hydrogen atom in the ground state, 13.6 eV of energy is released in the process. However, if there is a new energy state below the ground state it could be possible to release even more energy.

The ground state of hydrogen is stable in the sense that it cannot emit photons. However, Mills argues that it can undergo a non-radiative transition to a lower state with the help of a catalyst, releasing the additional energy in the process. "In layman's terms, a catalytic process causes the latent energy stored in the hydrogen atom to be released by allowing the electron that is otherwise in a stable orbit to move closer to the nucleus to generate power as heat, light and the formation of a plasma," Mills told PhysicsWeb. Similar non-radiative transitions occur in fluorescent lights and in the formation of chemical bonds in cases where the excess energy is carried away by a third particle.

Mills, who has a medical degree from Harvard, started working on the electronic structure of hydrogen in the late 1980s and has published more than 60 papers on the hydrino state since then. "This research represents a new primary energy source and a new field of hydrogen chemistry," he says. "It may also explain or lead to explanations to many important scientific questions such as the identity of dark matter and a physical rather than mathematical theory of atomic physics."

Earlier this year, however, Andreas Rathke of the European Space Agency published a paper in which he argued that the theory for the hydrino state put forward by Mills was "the result of a mathematical mistake" (New J. Phys. 7 127).

Now another theorist has joined the debate with a different point of view. Jan Naudts of the University of Antwerp in Belgium argues that the Klein-Gordon equation of relativistic quantum mechanics does indeed permit the existence of a low-lying hydrino state, although he stops short of claiming that hydrino states really exist (physics/0507193). "In physics the experiment decides," says Naudts. "Either the hydrino exists, in which case we have to accept a small correction to the textbooks on quantum mechanics, or it does not exist, in which case we have to find better arguments to explain why it does not exist." Naudts says that results of Mills and co-workers have recently been confirmed by a group at the Technical University of Eindhoven. "Nothing is decided yet, but I think it is time to fill the holes in our theoretical understanding of the hydrogen atom."

However, Rathke remains sceptical, claiming that the solution found by Naudts "is known in the literature and had previously been discarded as unphysical." He also says that Naudts has found evidence for just one new state, whereas Mills claims to have found 137, and that the binding energy calculated by Naudts does not correspond to any of these states.

Mills, not surprisingly, welcomes the results of Naudts: "It is a very good sign that he has initiated the work in the quantum physics community to reconcile quantum theory with the enormous amount of data that confirms the existence of new states of hydrogen."