How It Works

As an object's speed approaches the speed of light, time passes more slowly for it relative to a stationary observer. The Lorentz factor (γ) quantifies this effect — at everyday speeds it's essentially 1 (no noticeable dilation), but it grows rapidly as velocity approaches c.

Δt = Δτ ÷ √(1 − v²/c²), where Δτ is proper time, v is velocity, and c is the speed of light. The Lorentz factor is γ = 1 ÷ √(1 − v²/c²), so Δt = γ × Δτ.

Example

At 0.8c, the Lorentz factor is about 1.6667, so 1 year of proper time corresponds to about 1.6667 years for a stationary observer.

Frequently Asked Questions

What happens at very low speeds?

At everyday speeds, the Lorentz factor is extremely close to 1, so time dilation is imperceptible — it only becomes significant at a substantial fraction of the speed of light.

Why can't velocity equal or exceed the speed of light?

The time dilation formula involves dividing by √(1 − v²/c²), which becomes zero (or imaginary) at or beyond the speed of light — special relativity treats c as an unreachable limit for objects with mass.