An introduction to the mystery of quantum physics

Lent 2019: Day 3

Until physicists started to understand what was going in within the atom in the first decades of the 20th century, the scientific model of the university was based on measurable certainties. When it was first posited that within the shell of an atom, electrons can move from one energy state to another without any external cause, Einstein was shocked. He retorted famously that "God does not play dice". For there to be effect, there must be cause - thus spake Newton.

Several quantum effects outraged Einstein, including the communication between entangled pairs of electrons, where the spin of one affected the spin of another instantaneously, despite the two particles being a long way apart (therefore faster than the speed of sound). This Einstein called "spooky action at a distance".

The first decades of the 20th century saw rapid advances in mankind's understanding of the subatomic world, leading to the invention of the atom bomb and the nuclear power station. Yet for most of us, who do not probe the atom's inner workings, the model taught in schools during physics classes is the nearest we ever get to grasping it. This model is out of date and over-simplified. Reality is so counter-intuitive that it's hard to find everyday metaphors that can help us understand. Even those who do probe deeply have difficulties in making philosophical sense of it all.

The hydrogen atom - as simple as it gets. One proton in the nucleus, one electron whizzing around it in what is a shell of probability. To scale, imagine the dome of St Paul's Cathedral with a pea in the middle of it representing the proton, and a grain of sand - the electron, somewhere on the periphery. That grain of sand is in perpetual motion around that proton. Imagine a guitar string vibrating. Now imagine it not only vibrating up and down, but also side to side - and indeed in all directions. And then bend that stretched string until its ends meet, forming a circle around that proton.

So is an electron a wave then?

Consider the famous double-slit experiment. (Google this; there are many fine YouTube videos just several minutes long that do it justice with explanatory graphics). An effect first found by Thomas Young in 1801, it took on greater significance more than a century later when physicists were trying to determine whether light was formed of particles or waves. Turns out it's both - but only until the moment you check - and then it turns out to be purely particular in nature. How can this be?

Consider light passing through two parallel slits in a thin sheet of metal. The light - made up of photons - that passes through to the other side falls onto a dark screen beyond, where it forms a series of parallel lines, caused by the ripples of waves interfering with one another, the light bands where two waves peak together, the dark bands in between where the waves cancel each other out. OK, so light is waves.

Now repeat, firing one photon at a time. It will pass through either slit. Photon after photon, a pattern emerges - yes, it's the parallel bands associated with wave interference. Now here's the weird part: place a photon detector by each slit, to measure definitively through which slit each photon has passed. Monitor and observe, consciously. Will it be slit A or slit B?

We watch, we measure. Now what happens on the screen that records all the photons on it? No - it's not parallel bands. It's just two single lines. Now that we are watching, consciously observing, the photons behave differently. Not as waves this time, but as particles. No interference, no ripples, no waves. Particles travelling in straight lines. Again, this freaked Einstein out. He believed that light was particles, not waves. And proponents of light as waves were also proved wrong. Light - photons - is both waves and particles, until one observes them close-up. Then they behave like particles. The act of observation that causes light to alter its behaviour leads to what is called the collapse of the wave function.

Now here's the most interesting part of this experiment - conducted many thousands of times around the world over the decades - if you leave the photon detectors in place by the two slits, but this time you don't bother recording or observing the outcome - guess what - the resulting pattern is once again parallel bands. In other words, the lack of a conscious observer in the experiment results in there being no collapse of the wave function.

This discovery literally changed everything. No longer was Man a passive object in a preordained universe that majestically sweeps along its destined path. Now, human consciousness has a part in how this universe is perceived - and how it unfolds.

This discovery delivered more questions than answers, questions to which we don't have answers. Will we ever have answers? In the heady days of the 1920s, nuclear physicists believed that mankind was just a few years - months maybe - from solving all the essential questions of the universe.

Perhaps we never will.

This time last year:
Right and wrong in science and philosophy

This time three years ago:

Free thinking at the Second Vatican Council

This time five years ago:
Getting ul. Karczunkowska ready for Biedronka opening

This time six years ago: 

God's own risk

This time seven years ago:
A third of the way through Lent

This time eight years ago:
Balancing surfeit and shortage

This time nine years ago:
Congruent consciousness