In quantum mechanics, the difference between a particle and a wave is not absolute, but rather about how the same entity can behave under different conditions. Here’s the key idea:
1. Particle-like behavior
- A particle is something localized in space — it has a well-defined position (like a small dot).
- In experiments, particles show up as discrete “clicks” on detectors. For example, photons hitting a screen arrive as individual points.
- Properties: mass, charge, momentum, and sometimes spin are thought of in a “particle” sense.
2. Wave-like behavior
- A wave is spread out in space — it has wavelength, frequency, and can interfere or diffract.
- In quantum experiments (like the double-slit experiment), electrons, photons, and even atoms show interference patterns, which are characteristic of waves.
- A quantum “wave” is described mathematically by a wavefunction, which encodes probabilities of finding the particle in different places.
3. Wave–particle duality
- Quantum objects are neither purely particles nor purely waves. They can display either property depending on how you observe them.
- Example:
- Fire electrons one by one at a double slit → each electron lands like a particle.
- After many electrons → they form an interference pattern, showing wave behavior.
4. Modern interpretation
- Instead of thinking of them as switching between “particle” and “wave,” physicists usually describe quantum objects as quantum states.
- The wavefunction spreads like a wave, but when you measure it, you get a localized outcome like a particle.
So, the difference is in how they manifest:
- Particles = localized, discrete detections.
- Waves = extended, interference and diffraction.
- Quantum reality = both aspects coexist, unified by the wavefunction.