I have six unanswered questions which I believe are fundamental to an understanding of the universe. They all relate to the structure of the hydrogen atom for which the current models are woefully inadequate.
The first of these was formulated most succinctly by Richard Feynman when he asked every physicist to write the value of the Fine Structure Constant on his blackboard and ponder its significance:
1 What is the physical significance of the Fine Structure Constant ?
What Feynman was asking, and I am reiterating, is not how to calculate its value, that is well understood, it is much more fundamental than that. What he is looking for is an explanation as to the fundamental nature of the Fine Structure Constant. What mechanisms or physical processes lie behind its existence and thereby behind its value?
2 Why does the hydrogen atom have energy levels which are quantised?
When Bohr first formulated his model for the hydrogen atom he took the idea from another physicist, John Nicholson, that the angular momentum of the electron orbiting the hydrogen atom could only take on certain discrete values which were integer multiples of Planck’s constant. He never sought to explain why this should be the case and no one since has bothered to ask the question. Subsequent theories all rest on this same assumption. De Broglie, for example, suggested that the electron could be regarded as a wave as well as a particle. He calculated the wavelength as Planck’s constant divided by the linear momentum of the electron. The energy levels all then corresponded to harmonics each of some fundamental frequency and a harmonic is an integer multiple of some fundamental frequency. In effect this is making the same assumption as Bohr, simply restated in terms of a wavelength rather than in terms of angular momentum. Schrödinger developed his wave function, but in doing so he used de Broglie’s formula for calculating the wavelength. So in effect he was making the same basic assumption. No one has since bothered to even ask the question and nowhere is there an explanation of why the orbits of the electron can only take on characteristics which are discrete.
3 The third question is in a similar vein and concerns another of Bohr’s assumptions which remains unanswered by subsequent theories.
According to classical mechanics, the electron orbiting the atomic nucleus is subject to continuous centripetal acceleration and should therefore emit synchrotron radiation. This in turn should cause the orbit of the electron to decay and eventually the electron to fall into the atomic nucleus or spin off into space. It does not, there is no synchrotron radiation from the hydrogen atom, why?
Bohr chose to overlook this rather inconvenient fact and nobody since has thought to provide an explanation as to why the electron does not emit synchrotron radiation.
4 While the Bohr model is no longer considered an accurate description of the hydrogen atom, it does nevertheless describe the essential geometry of the atom. The orbits of the Bohr model correspond to the orbitals of the current model.
The size of the orbits in the Bohr model increase as the square of the energy level, so an atom with an energy level of 10 is 100 times the diameter of one in the base energy state, and one with an energy level of 100 is 10,000 times larger. Since the physical and chemical properties of the atom must ultimately be determined by its shape and size:
How is it possible for an atom to retain the same physical and chemical properties while its size varies over such a large dynamic range?
5 The actual energy of the electron orbiting the nucleus of the Bohr model decreases with increasing energy level. This is obfuscated in the descriptions of the atomic energy levels by talking about energy potential rather than absolute energy level. Nevertheless the energy of a supposedly higher energy state is less than that of a lower energy state.
How can this be and what has happened to the missing energy?
6 Finally and perhaps the most difficult question of all to answer is:
What is the nature of the wave particle duality? What is its physical nature, in other words precisely what is it that is waving?