Monday | 24 October 1927 | Brussels
While the official title of the 5th Solvay conference was “on Electrons and Photons”, it was abundantly clear amongst the guests that the presentations would center on the new theory of quantum mechanics. [Planck], [Einstein], [Bohr], [de Broglie], [Schrodinger], [Heisenberg] and many other giants of the time would be in attendance. Just a month earlier, [Niels Bohr] had revealed his idea of complementarity to fellow physicists at the Instituto Carducci, which lay just off the shores of Lake Como in Italy.
The theory suggested that subatomic particles and waves are actually two sides of a single ‘quantum’ coin. Whichever properties it would take on, be it wave or particle, would be dependent upon what the curious scientist was looking for. And asking what that “wave/particle” object is while not looking for it is meaningless. Not surprisingly, the theory was greeted with mixed reception by those who were there, but most were distracted by the bigwig who was not there – [Albert Einstein]. He couldn’t make it due to illness, but all were eager to hear his thoughts on [Bohr’s] somewhat radical theory. After all, it was he who introduced the particle nature of light in his 1905 paper on the photoelectric effect, revealing light could be thought of as particles called photons. [Bohr’s] theory reconciled [Einstein’s] photoelectric effect theory with the classical understanding of the wave nature of light. One would think he would be thrilled with it. [Einstein], however, would have no part of [Bohr’s] theory, and would spend the rest of his life trying to disprove it.
Complementarity – Wave , Particle or both?
For more than a century it was thought that light was a wave. In 1801, [Thomas Young] had discovered interference patterns when shining a light through two very close slits. Interference is a well known property of waves. This combined with [Maxwell’s] equations, which predicted the existence of electromagnetic radiation put little doubt into anyone’s mind that light was nothing more, or less, than a wave. There was a very odd issue, however, that puzzled physicists during the 18th century. When shining light upon a metallic surface, electrons would be ejected from that surface. Increasing the intensity of the light did not translate to an increase in speed of the expelled electrons, like classical mechanics says it should. Increasing the frequency of the light did increase the speed. The explanation of this phenomenon could not be had until 1900, when [Max Planck] realized that physical action could not be continuous, but must be a multiple of some small quantity. This quantity would lead to the “quantum of action”, which is now called [Planck’s] constant and birthed quantum physics. It would have been impossible for him to know that this simple idea, in less than two decades, would lead to a change in understanding of the nature of reality. It only took Einstein, however, a few years to use [Planck’s] quantum of action to explain that mind-boggling issue of electrons releasing from metal via light and not following classical law with the incredibly complex equation:
E = hv
Where E is the energy of the light quanta, h is Planck’s constant and v is the frequency of the light. The most important item to consider here is this light quanta, later to be called a photon. It is treated as a particle. Now, if you’re not scratching your head in confusion right about now, you haven’t been paying attention. How can light be a wave and a particle? Join me after the jump and we’ll travel further down this physics rabbit hole.
The Other Side of the Quantum Coin
While the wave – particle duality of light was busy mystifying the world’s smartest physicists, Prince [Louis de
Broglie] of France had an odd idea. If an electromagnetic wave can have a particle nature, could particles have a wave nature? In 1923 [de Broglie] introduced academia to his hypothesis with his PhD thesis. He would be awarded the Nobel Prize in Physics in 1929, two years after his thesis was verified by an English physicist by the name of G.P. Thompson. Thompson fired X-rays and electrons, two entities whose wave and particle nature were obvious, at a thin sheet of aluminum foil with a teeny tiny hole in it. The results of the X-rays emanating from the tiny hole showed what classical physics would predict what a wave would show – a diffraction pattern. The stream of electrons showed the same diffraction pattern, proving the wave-like nature of the electron in accordance with [de Broglie’s] hypothesis. The fact that a particle can display wave-like properties puts into question the ability to know precisely where it is in space and time.
The End of Determinism
So how does one go about trying to locate an electron anyway? According to [de Broglie’s] hypothesis, the smaller the dimensions of the particle, the more wave-like it becomes. Electrons are so small, that saying one is at a particular point in space at a particular point in time is not really possible. It’s too wave-like to make this type of observation. There are numerous ways to illustrate this idea, better known as [Heisenberg’s] uncertainty principle. My favorite, and I think the easiest, way to understand this is mathematically. Consider the following super advanced complex quantum physics equation:
xy = z
Let 'x' equal momentum
Let 'y' equal position
Let 'z' equal the constant of h/4pi. Where 'h' is [Planck's] constant.
It should be easy to see that x and y are inversely proportional. As one goes up, the other goes down. In other words, as you increase the value of the momentum of a particle (x), the accuracy of the position of that particle (y) decreases. And vice versa. This is the heart of [Heisenberg’s] uncertainty principle. You can’t know both the location and momentum of a particle at the same time. The more accurate you make one, the less accurate you make the other.
The Copenhagen Interpretation
[Niels Bohr’s] complementarity theory together with [Heisenberg’s] uncertainty principle makes up what is known as the Copenhagen Interpretation of quantum mechanics. This theory, while still contested to an extent, is the most widely held view of the nature of reality to date. To put it in the most simplified terminology – It’s not possible to know if our subject of investigation is a particle or wave, just like it’s not possible to know its location and momentum. You can know one, but not the other. Neither can be known at the same time. There is an inherent uncertainty, an inherent randomness to our universe. It is ingrained in our very existence, and to deny it is futile.
Now that our little history lesson in quantum theory is done, we can get to the fun part of applying our new found knowledge to hacking! We now know that the electrons zooming around in our microprocessor have a wave like property. What does this mean? Where can we go with this? This will be the subject of next week’s installment of Quantum Mechanics in your Processor. Stay tuned!