Theories of the Universe: Chunks of Uncertainty

Chunks of Uncertainty

All quantum physicists will agree that they can't explain quantum theory and that it doesn't make sense. So why would they use something to define the fundamental structure of the universe if they don't understand what it is? Well, physicists who work in the field use the straightforward formulas handed down to them by the brilliant minds that developed them, but often don't understand why they work or even what they mean. But what is known about it has produced remarkably accurate results. And that's why it's used. Some even feel that quantum mechanics offers some of the most accurate numerical predictions that science has ever developed. And until something else comes along, the mathematical system used to define the quantum world is all that is available. For now, let's pick up where we left off in the last section and follow the unfolding of quantum cosmology.

Waves of Matter

Neils Bohr came up with a description of how light was radiated from inside an atom. He also has shown why an atom was stable. His explanation of what the structure of the atom was like was close to but not quite like the one envisioned by Rutherford that we touched upon earlier. Remember that he theorized that the atom's structure was very much like a planetary system with the electrons orbiting the nucleus the way planets orbit the Sun. Bohr adopted this basic configuration, but couldn't imagine the electrons orbiting the nucleus as some cosmic cloud that was indefinable. So he had arranged the orbiting electrons into layers or shells. Have you seen Russian nesting dolls or Chinese stacking boxes? In those you have one complete doll or box contained within another. Every time you open up one there's a smaller one inside. The shells Bohr described were just like that, except that each shell had a specific number of electrons.

Bohr was able to calculate mathematically the diameter of each electron orbit along with the maximum number of electrons in each shell. The angular momentum of the electron in orbit was counteracted by the attraction of the nucleus. In other words, since unlike electrical charges attract each other, the positive charge inside the nucleus attracted the negative charge of the electron. This theory explained the structure of the atom and why it remained stable.

A French Prince Discovers Matter Waves

In 1923, a graduate student at the Sorbonne in Paris, Prince Louis de Broglie (1892-1987), introduced the remarkable idea that particles may exhibit wave properties. He had been strongly influenced by Einstein's arguments that light had a dual nature. He was also deeply impressed by Einstein's particles of light that could cause the photoelectric effect (knock electrons out of metal) while also producing the interference patterns caused by waves as in the double slit experiment. He proposed one of the great unifying principles in quantum physics. He was convinced that the wave/particle duality discovered by Einstein in his theory of light quanta was a general principle that extended to all forms of matter. In other words, the propagation of a wave is associated with the motion of a particle of any kind—photon, electron, proton, or any other.

De Broglie wished to develop a mechanical explanation for the wave/particle duality of light and to extend this to all forms of matter. He needed to find a mechanical reason for the photons in the wave to have an energy that was determined by the frequency of that wave.

De Broglie noticed a connection between the angular momentum of the electron in a Bohr orbit and the number of nodes in a standing wave pattern (remember you created those with the jump rope in the last section). The orbiting electrons could only have one unit of h (Planck's constant) or two units, etc. Could these discontinuous changes in the electron's angular momentum, these changes in the amount of h allowed, be due somehow to a similar change in standing wave patterns?

De Broglie realized that the Bohr orbit could be seen as a circular violin string, like a snake swallowing its own tail. Would the orbit size predicted by his standing matter waves correspond to Bohr's calculated electron shells? What would his wave do if confined to a circle? Well, what he discovered was that his matter waves fit Bohr's orbits exactly. And when he calculated the wavelength of the lowest orbit, he discovered another astonishing mathematical connection between the wave and the particle. The momentum of the orbiting electron equaled Planck's constant divided by the wavelength.