Quantum Mechanics and the Uncertainty Principle

Quantum physicists use special instruments and equations to measure and predict their properties, such as their position, momentum, spin, and charge. These properties are not fixed, but change randomly according to the laws of quantum mechanics. Quantum mechanics is the branch of physics that describes how these particles behave. It is very different from the classical physics that applies to larger objects, like cars or planets. For example, in quantum mechanics, an electron can be in two places at once, or have both positive and negative charge at the same time. This is called superposition.

How can something be in two places at once?

Well, it's not really in two places at once, but rather in a state of uncertainty until we observe it. When we measure it, we collapse the superposition and find out where it is or what charge it has. But until then, we can only describe it by a wave function, which gives us the probability of finding it in any given state.

A wave function? Like a wave in the ocean?

Kind of, yes. A wave function is a mathematical function that describes how the particle behaves as a wave. It has peaks and troughs that indicate the likelihood of finding the particle in a certain position or with a certain momentum. The higher the peak, the more likely it is to be there. The lower the trough, the less likely it is to be there.

So you can't tell exactly where the particle is or how fast it is going?

No, we can't. There is a fundamental limit to how precisely we can know both the position and momentum of a particle at the same time. This is called the Heisenberg uncertainty principle. It says that the product of the uncertainties in position and momentum is always greater than or equal to a constant value.

Well, one way to think about it is that when we try to measure one property of a particle, we disturb another property. For example, if we use light to measure the position of an electron, we also impart some momentum to it by hitting it with photons. This changes its speed and direction. The more accurately we measure its position, the more we disturb its momentum, and vice versa.

So you can never know both exactly?

No, we can't. There is always some uncertainty involved in any measurement. This is not due to our lack of skill or technology, but rather to the nature of reality itself. Quantum mechanics tells us that reality is probabilistic, not deterministic.

Probabilistic? Deterministic? What do those words mean?

Probabilistic means that things happen by chance, not by necessity. Deterministic means that things happen by cause and effect, not by randomness. For example, if I flip a coin, the outcome is probabilistic. It could be either heads or tails, with equal probability. But if I push a ball down a slope, the outcome is deterministic. It will roll down with a certain speed and direction, depending on the force I applied and the angle of the slope.

So quantum mechanics is probabilistic and classical physics is deterministic?

Yes, that's right. Quantum mechanics deals with probabilities and uncertainties, while classical physics deals with certainties and determinations.