The tiny world
What rules do the tiniest things in the universe follow?
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Explain
At the tiniest scale, things behave very strangely. Energy isn't smooth, but comes in tiny packets, called quanta.
A packet of light is a photon. Blue light has photons with more energy than red light.
Tiny particles can act like waves too. Scientists predict them with chances, not certainties.
Planck's equation: E = h × f, where h = 6.63 × 10⁻³⁴ J s.
Electrons in atoms can only have certain energies. When one drops to a lower level, it emits a photon of exactly that energy.
Worked example: light at f = 5 × 10¹⁴ Hz has E = 6.63 × 10⁻³⁴ × 5 × 10¹⁴ ≈ 3.3 × 10⁻¹⁹ J.
- Energy comes in packets
- Light is a wave and a particle
- Tiny things follow chance
Want the full story?
Quantum physics is very well tested, though it can be hard to picture. The uncertainty principle says that you can't know a particle's position and momentum exactly at the same time. Nobody fully agrees on what is "really" happening, but its predictions are extremely accurate.
The Formula
energy of a packet of light = Planck's constant × frequency
- the photon energy, measured in joules (J)
- Planck's constant, 6.63 × 10⁻³⁴, measured in joule seconds (J s)
- the frequency of the light, measured in hertz (Hz)
Try the numbers
Photon energy: 3.32 × 10⁻¹⁹ J
Try it at home
You need a coin.
You need: a coin.
- Flip a coin 20 times, and count the heads.
- You can't predict one flip.
- But you can predict about 10 heads overall.
What's happening: quantum physics works a bit like this. Single events are chance, while the overall pattern is predictable.
Physics is life
Your body
Your eyes catch single photons of light.
Daily life
Phones and LEDs use quantum physics.
Nature
Plants may use quantum effects.
Space
Quantum physics makes stars shine.
Quick check
Question 1 of 3
Words to know
Photon: A tiny packet of light energy.