Transit Times
Why Relativity Shortens the Trip
How can a ship arrive at its destination faster than light? A fast interstellar ship never outruns light. Instead, relativity changes the journey itself: the distance from Earth stays the same, but the ship travels a shorter distance in its own frame.
1.0 g
Acceleration presets
Trip Distance at Relativistic Speeds
Destination distance from Earth
Distance measured from Earth
Distance traveled by the ship
Earth time
13.70 years
Elapsed time for observers who stay home.
Ship time
5.14 years
Elapsed time experienced onboard.
Distance from Earth
11.90 ly
The route length measured from Earth's frame.
Onboard distance crossed
3.81 ly
The distance accumulated in the ship's changing frame during acceleration, flip, and deceleration.
Peak speed
0.990c
Top speed reached at the midpoint before the flip.
Light travel time
11.90 years
How long a beam of light takes in Earth's frame.
At relativistic speeds, two things happen at once:
- Time passes more slowly on the ship; this is known as time dilation.
- Distances ahead are compressed in the ship's frame; this is called length contraction.
A ship traveling to Tau Ceti at relativistic speeds never exceeds the speed of light. Less time passes onboard because the ship crosses a shorter version of the journey.