[Leejohnston]

## Hubble’s Law — Why the Universe Expands

### 1. The Equation

v = H₀d

---

### 2. What Each Symbol Means

- v = recessional velocity
- H₀ = Hubble constant
- d = distance

---

### 3. What the Equation Is Telling Us

The farther away a galaxy is:
- the faster it moves away from us

Space itself is expanding.

---

### 4. Where It Comes From (Intuition)

Expansion is not motion through space.

It is space itself stretching.

---

### 5. Real-World Applications

- Cosmology
- Universe age estimates
- Dark energy studies

---

### 6. Common Misconceptions

- Galaxies fly through space → false
- Earth is the centre → false
- Expansion breaks relativity → false

---

### Try It Yourself

Why don’t atoms and galaxies expand?