- “Arthur let out a low groan. He was horrified to discover that the kick through hyperspace hadn't killed him.”
- —from The Hitchhiker's Guide to the Galaxy[src]
Hyperspace is the void or alternate dimension between light speed and 0.97c (light speed). It is used as a method of travelling, offering a faster-than-light mode of travel through space. One of the species in the galaxy to have harnessed this power are the Vogons. Prostetnic Vogon Jeltz, of the Galactic Hyperspace Planning Council, followed orders to destroy the planet Earth to make way for a hyperspace bypass in that region of space at the beginning of the story.
Not long after the Earth was destroyed, the Vogon Fleet planned to jump into hyperspace for the journey to Barnard's Star, which was six light years away. Ford Prefect, who had hitched a lift on board one of the Vogon ships, "curled himself up into a foetal ball" to prepare himself for the jump. Arthur Dent, also on board the ship, did not react well to the hyperspace jump; he felt as though his eyes had "turned inside out", his feet had begun "to leak out of the top of his head", and "the room folded flat about him, spun around, shifted out of existence and left him sliding into his own navel." Ford reacted better, however he still found the travelling-through-space part of space travel "rather trying."
Hyperspace is the closest velocity to reaching the speed of light judging based on the object's size and, of course, its mass. To travel in this speed-void, one must have thrust capabilities of (π x 30,428,697)/(Mass in kg) Watts of power. In the case of transporting a 2cm fly at 0.97 x light speed would require energy somewhere in the region of 1 billion years' energy output of the sun.
If a carbon-based life-form was to reach hyperspace without adequate protection, the eyes of such species would be fried and the body melted into an unrecognisable mess. Travelling through hyperspace even with protection feels, as Ford said, "unpleasantly like being drunk."