UFO / Relativistic Space Travel Calculator
How long would it take to travel to Alpha Centauri at 10% of the speed of light? And how much would you age along the way? Pick a destination (or enter any distance in light-years), set your speed as a percentage of c, and get both the Earth-frame travel time and the shorter proper time experienced aboard the ship thanks to special-relativistic time dilation.
Destination
% of c
How much slower ship clocks tick relative to Earth clocks at this speed
- 1
Speed ratio β = v ÷ c
10 ÷ 100 = 0.1 - 2
β²
0.1² = 0.01 - 3
1 − β²
1 − 0.01 = 0.99 - 4
Lorentz factor γ = 1 ÷ √(1 − β²)
1 ÷ √0.99 = 1.0050γ = 1 at rest; approaches infinity as speed approaches c.
How does this calculator work?
At speed β·c over distance d, Earth-frame travel time is t = d/(β·c) years (for d in light-years). Time dilation shrinks the crew's experienced time to t/γ, where γ = 1/√(1−β²) grows rapidly near c. At 10% c it takes 43.7 years to reach Alpha Centauri by Earth time; the crew ages only 43.5 years.
Formula
How this is calculated
At non-relativistic speeds the travel time is simply distance ÷ speed. As you approach the speed of light, Einstein's special relativity becomes important: clocks aboard the spacecraft run slower than clocks on Earth by the Lorentz factor γ = 1/√(1−β²), where β = v/c. The time measured by Earth observers is t_Earth = d/(β·c), while the crew ages only by t_ship = t_Earth/γ — always less than t_Earth.
For example, at 99.9% of c, γ ≈ 22.4, so a 22-year Earth journey corresponds to only about one year of ageing for the crew. This is not science fiction — particle accelerators routinely produce muons whose decay is slowed by precisely this factor. The round-trip paradox (twin paradox) is real but requires accounting for the acceleration phases; this calculator assumes constant-velocity travel.
Distances to solar-system bodies are given as average values (not current positions, which vary) and distances to stars are the best modern measurements. The speed of light is exactly c = 299,792,458 m/s; 1 light-year ≈ 9.461 × 10¹² km.
Frequently asked questions
Yes — the crew ages by t_ship = d/(γ·β·c) while people on Earth age by the longer t_Earth = d/(β·c). At very high γ the difference is dramatic: a round trip to Andromeda at 99.999% c would take ~5 million years by Earth clocks but only about ~23,000 years of ageing for the crew.
The kinetic energy of an object at speed v is (γ−1)·m·c². At 99% c, γ ≈ 7.1, so you'd need about 6.1·m·c² — roughly 6× the rest-mass energy of the spacecraft in propellant energy. No known propulsion system can remotely approach this for a crewed vehicle; it's ~10¹⁷ J per kilogram.
Planets orbit the Sun, so the distance from Earth to Mars, for example, ranges from ~56 million km (opposition) to ~401 million km (conjunction). The values shown here are average (mean) distances used as a useful reference — actual travel would depend on the launch window.
Also known as
TG we-Calculate Editorial Team. (2026). UFO / Relativistic Space Travel Calculator [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/ufo-travel-calculator
TG we-Calculate Editorial Team. "UFO / Relativistic Space Travel Calculator." TG we-Calculate. 2026. https://we-calculate.com/calculator/ufo-travel-calculator.
TG we-Calculate Editorial Team, "UFO / Relativistic Space Travel Calculator," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/ufo-travel-calculator
@misc{wecalculate_ufo_travel_calculator, title = {UFO / Relativistic Space Travel Calculator}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/ufo-travel-calculator}}, year = {2026}, note = {TG we-Calculate} }
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