Basic Concepts

1In the first quarter of the 20th century, the established classical paradigm of physics was increasingly being challenged because it had started to fail to explain a number of new phenomena:

Each of these topics will be discussed separately in the following pages, as they provide an important insight for anybody wishing to understand how scientists were compelled to abandon the determinism of classical physics for the probability that became known as the ‘quantum weirdness’ . By way of a historical backdrop, in the first decade of the 20th century, a picture of the internal structure of atoms was beginning to emerge. This picture largely comprised of empty space; in which each atom consisted of a small positively charged nucleus ‘orbited’ by one or more negatively charged electrons, analogous to planets orbiting a star.  However, it was known that such an arrangement was problematic, as a rotating negative electron would radiate energy and collapse into the nucleus. Shortly after, in 1913, Bohr proposed that Planck's constant could be applied to electrons orbiting within the atoms. According to the Bohr model, the electron was constrained to certain orbits by the quantization of angular momentum. However, this was just the beginning of a paradigm shift towards a quantum theory that would take place over the next 20-30 years. However, while a model of the quantum universe would ultimately emerge, it was a model that even science itself would struggle to accept. For it seemed that this model of the micro-universe contradicted all human perception and intuitive understanding of the universe, as well as challenging the very foundations of accepted science. In this context, the following discussions will only attempt to summarise some of the key issues that led to the branch of physics known as quantum mechanics. From a historical perspective, it might be suggested that the breakdown of classical physics started with Planck’s outline of the quantization of energy, which then found application in Einstein’s examination of the photoelectric effect and Bohr’s atomic model, which required the quantization of electron momentum. In combination, these ideas would profoundly affect the way in which the emerging science of the 20th century would come to consider the underlying nature of matter.

  • In classical or Newtonian mechanics, a particle can acquire energy or speed over a continuous range. In quantum mechanics, a particle can only have discrete or quantum values of energy and momentum.

  • Classical physics allows the exact location and velocity of a particle to be determined. In contrast, one of the central axioms of quantum mechanics is known as 'Heisenberg's Uncertainty Principle', which would deny access to classical determinism within the quantum universe.

However, it should be noted that the level at which Heisenberg’s uncertainty principle applies is so microscopically small, its effects are normally only apparent within the quantum universe. For this reason, the effects of quantum uncertainty are far from obvious within the realm of human experience. So, step by step, fundamental principles of classical science were being subject to radical revision, as the study of the universe began to extend ever further beyond all previous human and intuitive experience. As such, it might be argued that scientific verification became, and has remained, increasingly dependent on mathematical proof rather than empirical verification. So while most of us can follow the logic of Newton's laws of motion, and some may follow the convolutions of Einstein's space-time, it is said that there are few who truly understand quantum mechanics. In 1965, Richard Feynman, considered by many as the greatest physicist of his generation, wrote something along the following lines:

"There was a time when the newspapers said that only twelve men understood the theory of relativity. I do not believe that there ever was such a time. On the other hand I think I can safely say that nobody understands quantum mechanics."

One implication of Feynman’s statement is that the full scope of the universe is becoming increasingly complex and non-intuitive in respect to human experience. Of course, whether we have reached the point where even the brightest individuals of our society now struggle to fully comprehend the extent of this complexity may still be debated. From this perspective, it may be presumptuous to assume that we have reached the stage where science can say it fully understands the true nature of matter even here on Earth, let alone within the complexity of the Universe as a whole. If this point is accepted, it would seem that science should remain open-minded to new ideas, while still demanding the highest level of empirical  verification possible.