How Does Gravity Work?
Gravity is the force that pulls objects with mass toward each other. It keeps you on Earth, Earth orbiting the Sun, and galaxies from flying apart.
But what causes gravity? Two revolutionary thinkers gave different answers.
Newton's View: A Force
Isaac Newton (1687) described gravity as a force acting at a distance.
The equation: F = G(m₁m₂)/r²
- Every mass attracts every other mass
- Force increases with mass
- Force decreases with distance squared
- Works instantaneously across space
This explained falling apples and planetary orbits with one elegant formula. For over 200 years, it was considered the final word.
But Newton couldn't explain how gravity works across empty space. He called this "action at a distance" and found it philosophically troubling.
Einstein's View: Curved Spacetime
Albert Einstein (1915) reimagined gravity entirely with general relativity.
The insight: Mass doesn't pull objects — it bends space and time around it.
Imagine a bowling ball on a stretched rubber sheet. It creates a dip. Roll a marble nearby, and it curves toward the bowling ball — not because of a force, but because the surface is curved.
Spacetime works similarly. The Sun curves spacetime around it. Earth follows the straightest possible path through that curved space — which happens to be an orbit.
Key Differences
| Newton | Einstein |
|--------|----------|
| Force pulls objects | Curved geometry guides objects |
| Instantaneous | Travels at light speed |
| Time is absolute | Time slows near mass |
| Approximate | More accurate |
Where Einstein Matters
Newton works perfectly for everyday situations. Einstein becomes necessary for:
- GPS satellites (must account for time dilation)
- Black holes (extreme curvature)
- Gravitational waves (ripples in spacetime)
- Mercury's orbit (Newton's prediction was slightly wrong)
Gravity and Quantum Mechanics
Neither Newton nor Einstein is the final answer. Gravity doesn't fit with quantum mechanics — the physics of tiny particles.
Finding a "quantum theory of gravity" remains physics' greatest unsolved problem.
Related Reading
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