lighttravel

Lighttravel is a term used to describe travel concepts that rely on or are constrained by the properties of light. In physics, light travel time is the time required for light to traverse a given distance. In science fiction and speculative science, lighttravel often refers to propulsion methods that use light or light pressure to move spacecraft.

The speed of light in vacuum is approximately 299,792 kilometers per second, a universal speed limit. Distances can be expressed as light-travel time; for example, the Moon is about 1.3 light-seconds away, while Proxima Centauri is about 4.24 light-years away, meaning light takes 4.24 years to reach Earth.

Propulsion approaches associated with lighttravel include photonic propulsion, which uses light to push a sail via radiation pressure; solar sails rely on sunlight, and laser sails use high-power ground-based lasers to push a sail. Projects such as Breakthrough Starshot have proposed gram-scale probes accelerated to up to about 0.2c with Earth-based lasers.

Relativistic effects and challenges are central to lighttravel discussions. As speeds approach the speed of light, time dilation and length contraction become significant. Engineering challenges include immense energy requirements, material durability, deceleration after acceleration, navigation, and protection from micrometeoroids and radiation.

Practically, lighttravel denotes the ongoing exploration of light-based transport concepts. While current technology achieves limited, near-term demonstrations, true relativistic interstellar travel remains speculative and faces substantial scientific and engineering hurdles.

See also: speed of light, photonics, solar sail, laser propulsion, time dilation.