Quantum Mechanics And The Uncertainty Principle
Quantum mechanics is one of the two pillars of modern physics. As explained elsewhere, general relativity reshaped our understanding of gravity. Quantum mechanics has had an even weirder effect on how we view the world.
The field mainly deals with the behaviour of the universe's smallest particles. These include the particles that make up atoms. Under our current understanding, they don't even have size. We treat them like dimensionless dots. Let's see how their behaviour differs from our experience.
Classical vs. Quantum Mechanics
Quantum mechanics shows us that things get bizarre on this tiny scale. We used to assume that everything in the universe obeyed classical mechanics. This is the model of motion and behaviour for everything from molecules to tennis balls to planets. These things behave predictably. They move only when acted on by forces. They stay still when left alone. We can predict where they will be from their location and momentum.
These seem like universal truths. Quantum mechanics bends our minds because it refutes these ideas. The theory has three primary features:
Particles behave like both particles and waves, or matter and energy
Their energy and momentum are restricted to certain levels, or quanta
The more we know about a particle's momentum, the less we know about its position, and vice versa
We are only going to look into #3. There are many fascinating explanations on #1 (particle-wave duality) and #2 (energy quantization). Give those a look if you're in for a trip. #3 is known as the Uncertainty Principle. It is the most accessible of the three. It may also be most foreign to our everyday experiences.
Unpacking The Uncertainty Principle
Werner Heisenberg put forth this unusual idea in 1927. He found an inverse relationship between the accuracy of quantum momentum and position measurements. Let's untangle this a little.
We know a particle is located within a certain area. We want to double the accuracy of this measurement. This halves the area where the particle can be located. According to the Uncertainty Principle, this accuracy isn't free. The cost is a loss of accuracy in measuring the particle's momentum. We know more about where the particle is located. But we know less about where it's moving, and how fast. The increase and decrease happen in exact proportion to one another. Overall, our understanding of the particle stays the same. It's just distributed differently.
We must remember that the Uncertainty Principle only affects quantum objects. Quantum uncertainty is irrelevant for everyday objects. We have no problem finding the location and momentum of a ball at any instant along its path. Our mainly stable everyday world emerges from an uncertain sub-atomic one. This is a great example of science revealing unusual truth when we extend our natural senses. Nobody sane would suspect uncertainty lurking below our surface reality. Yet frontier research has shown it to be as real as any rock.
The Consequences of the Uncertainty Principle
What does all of this mean? In the extremes, it means that if we know exactly where a particle is, we have no idea about its movement. That's fairly shocking. It shows that there is a limit on what we can know. Reality's foundation has uncertainty built into it.
This goes against the pre-quantum mechanics view of science. It was initially assumed that we could discover every aspect of every object in the universe. We could know every fact about every situation. Theoretically, we had the capacity to plot the location and path of every particle. This would enable us to know the history and future of the universe.
Heisenberg's Uncertainty Principle scrapped this assumption. He revealed that there are some things that we absolutely cannot know. It doesn't matter how advanced our technology gets. A 100% accurate measurement of both the momentum and location of a quantum particle is impossible. This isn't a reason to despair, or to doubt the scientific method. It's a leap in our intellectual maturity. There is equal value in understanding what you can't know and what you don't know.
Is Quantum Mechanics A Scam?
No it isn't. In the beginning of any Uncertainty Principle conversation, it's fair to be skeptical. These wild revelations can be mistaken for speculation. These particles are far too small to interact with without million dollar equipment. They're also notoriously uncooperative. We matter even less to them than the New York Stock Exchange matters to a pigeon.
So what's our basis for considering this science rather than science fiction? Technology. The shrinking of modern electronics means our devices function at quantum scales. This means we can harness quantum effects. We see this in everything from smartphones to the atomic clocks in a GPS. There's no shame in feeling a thankful the next time you have a clear phone call or your GPS cuts ten minutes off your trip. It's all thanks to our decoding of the quantum mysteries.