What is gravitational time dilation?
Einstein's General Theory of Relativity predicts that gravity warps spacetime. The stronger the gravitational field, the slower time passes relative to a distant observer. This isn't science fiction — GPS satellites must correct for this effect daily, or navigation errors would accumulate at 10 km per day.
The Schwarzschild radius
Every massive object has a Schwarzschild radius (r_s = 2GM/c²) — the distance at which escape velocity equals the speed of light. For Earth, this is about 9mm. For the Sun, about 3km. At the event horizon (r = r_s), time dilation becomes infinite: an outside observer would never see you cross it.
Time dilation formula
The time dilation factor near a non-rotating black hole is: t_far / t_near = 1 / √(1 − r_s/r), where r is your distance from the center and r_s is the Schwarzschild radius. At r = 2r_s (twice the event horizon), time runs at 70.7% of the rate far away. At r = 1.01r_s, it runs at just 9.9%.
The Cosmic Dashboard black hole simulator
The Cosmic Dashboard Black Hole Simulator lets you spawn orbiting black holes with a click, drop planets with Space, and watch them spiral in under gravitational wave damping. A live HUD shows two clocks — Earth time and time near the black hole — diverging in real time as dilation takes hold.
Frequently Asked Questions
What happens if you fall into a black hole?+
From your own perspective, you would cross the event horizon in finite time and feel nothing unusual at that exact moment (for a large enough black hole). To an outside observer, however, you would appear to slow down and freeze at the horizon, gradually redshifting into invisibility — never seen to cross. Beyond the horizon, tidal forces (spaghettification) would eventually stretch and compress you as you approach the singularity.
Can black holes die?+
Yes — Stephen Hawking showed in 1974 that black holes slowly radiate energy (Hawking radiation) due to quantum effects near the event horizon. Over an astronomically long time, this causes them to lose mass and eventually evaporate completely. A stellar-mass black hole would take roughly 10⁶⁷ years to evaporate — far longer than the current age of the universe.
Does time stop inside a black hole?+
Time does not stop from the perspective of an infalling observer. From a distant observer's perspective, your clock appears to slow infinitely as you approach the event horizon — you are never seen to cross. But in your own reference frame, time continues normally as you fall through. The singularity is a boundary of spacetime, not a place where time stops.
How large is the biggest known black hole?+
The largest known black holes are ultramassive black holes in the centres of giant galaxies. TON 618, a quasar 10.4 billion light-years away, hosts a black hole of approximately 66 billion solar masses — with a Schwarzschild radius larger than the entire solar system out to Pluto.