Image: A Bussard ramjet in flight, as imagined for ESA’s Innovative Technologies
from Science Fiction project. Credit: ESA/Manchu.

The Velocity of Thought


How fast we go affects how we perceive time. That lesson was implicit in the mathematics of Special Relativity, but at the speed most of us live our lives, easily describable in Newtonian terms, we could hardly recognize it. Get going at a substantial percentage of the speed of light, though, and everything changes. The occupants of a starship moving at close to 90 percent of the speed of light age at half the rate of their counterparts back on Earth. Push them up to 99.999 percent of c and 223 years go by on Earth for every year they experience.

Thus the ‘twin paradox,’ where the starfaring member of the family returns considerably younger than the sibling left behind. Carl Sagan played around with the numbers in the 1960s to show that a spacecraft moving at an acceleration of one g would be able to reach the center of the galaxy in 21 years (ship-time), while tens of thousands of years passed on Earth. Indeed, keep the acceleration constant and our crew can reach the Andromeda galaxy in 28 years, a notion Poul Anderson dealt with memorably in the novel Tau Zero.

Read more: The Velocity of Thought — Centauri Dreams.

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