A Quantum Summary of Physics
Introduction
Beyond Newton’s theory of gravity, founded by the visible drop of an apple, quantum physics exists at a more atomic level. It attempts to explain the behaviour of molecules and atoms in nature based on mathematical and energetic principles derived primarily through calculation. Despite the fundamental laws of physics, it is interesting to note the philosophical juxtaposition between mathematics and logic and their resultant interference in the evolution of quantum mechanics. Take Schrödinger's cat: based on quantum theory, if a cat has a 50:50 chance of survival, as you open the box, the cat is in equal parts both alive and dead- only upon observation can it be seen in a single state. Impossible, right? Without this psychologically disturbing concept, the evolution of our understanding of everyday matter would’ve come to a grinding halt.
Quantum principles
To generate a basic understanding of quantum mechanics, I will first highlight some of its key concepts. Three of its main principles are superposition, entanglement and measurement. Of these, I will first outline the former.
Superposition
Superposition is the ability of a physical system to simultaneously exist in multiple states until it is measured, akin to Erwin Schrödinger's famous cat thought experiment. There are many other ways to observe superposition, and it is often demonstrated through the behaviour of waves. Here’s an example: if you shine beams of light through a horizontally polarised filter followed by another horizontal filter, all of the light travels through the second filter. However, if you then pass light through a horizontal filter and then a vertical one, none of the light will pass through. But, add a 45-degree polarised filter between the horizontal and vertical ones, and you’ll see that around 50% of the light passes through. This shows how the light exists in a superposition of states until measured. The second filter resets the polarisation of the light, making it more likely to pass through in a new state.
Quantum Entanglement
Quantum entanglement relies on the principle that multiple wave functions can have a relationship between different systems that violates the conventional rules of space and time. At the time, this clashed with Einstein’s principle of local realism, which stated that for photons (or particles) to influence each other, they must be in close proximity. Entangled particles, however, appear to instantaneously affect each other regardless of distance- something Einstein famously referred to as “spooky action at a distance.”
Measurement
Because quantum theory relies on probabilism until a single measurement is taken, there remains an issue of definite outcomes. Quantum systems can exist in superpositions, but measurements reveal them in a single, definite state. The act of measurement collapses the wave function into one observable reality. This process- where observing or interacting with a system forces it into a fixed state- is fundamental to quantum mechanics and is what gives us usable data.
Quantum Biology
The application of quantum mechanics can also be applied to facilitate our understanding of biological systems which can't solely be answered through the laws of physics. One such example of quantum biology can be seen through bird migration. Birds are able to travel across the same seascape for thousands of miles without misdirection, but how? Interestingly, the earth's magnetic field gives rise to directionality which is believed to stem from quantum entanglement. Located on their retina, birds have a protein called cryptochrome 4 which is sensitive to magnetic fields and are thought to be quantum entangled to assist with directionality.
Physics of disease
Quantum tunnelling is another feature biologically associated in relation to DNA and consequent disease through mutation. During cell replication, quantum tunnelling can allow particles to pass through energy barriers, potentially leading to mutations that could trigger diseases like cancer. This suggests that quantum behaviour may be fundamental not just to physics but to the origin of life and disease itself.
Conclusion
From atoms to avian navigation and the architecture of thought, quantum mechanics delves far beyond what it is traditionally seen as. It challenges the foundations of how we perceive reality, reminding us that uncertainty isn't just a glitch in our understanding but it in fact may be a fundamental feature of the universe. As we continue to explore its weird and wonderful consequences, we’re not just redefining science, we’re redefining what it means to be human.