From 2100 to the End of Time by Frank J. Tipler:

(Professor of Mathematical Physics at Tulane University, Tipler is the co-author of The Anthropic Cosmological Principle (Oxford University Press, 1986), about the significance of intelligent life in the universe, and the author of The Physics of Immortality (Doubleday, 1994) about the ultimate limits of computers, and the role computers will play in the universe. Professor Tipler was the post-doc of a post-doc of John von Neumann, the mathematician who made the first American digital computer. Tipler was also the post-doc of a post-doc of a post-doc of Albert Einstein. Finally, Tipler was the post-doc of John Wheeler, the man who named the black hole, and Wheeler was in turn the post-doc of Niels Bohr, one of the founders of quantum mechanics. Not surprisingly, Tipler’s research is on discovering the mutual implications of computer theory, relativity, and quantum mechanics.)

The year is 2100. AI’s and human downloads have begun to explore and colonize interstellar space. The spaceships carrying the AI’s and human downloads are tiny, massing no more than a kilogram. Quantum computers, which can code more bytes of information in 400 atoms than there are atoms in the entire visible universe, do not require much mass. An entire simulated city with thousands of humans and AI’s can be coded in a few grams. And a tiny spaceship has a huge advantage over the ponderous rockets of today. Powered by matter- antimatter annihilation, such tiny spaceships can reach 90% of lightspeed with only a few kilograms of fuel. At such a speed, the nearest star, some four and one-half light years away, will be reached in only five years. Acceleration to 90% of lightspeed will be very fast, because the downloads and AI’s will be impervious to acceleration. Humans not living in computers can take only a few gravities of acceleration, and can take that small acceleration only for a short time. Simulated humans will experience only the usual one gravity acceleration in their simulated environment. Human downloads have such a natural advantage over present-day humans in the environment of space, that it is exceedingly unlikely non-downloaded humans will ever engage in interstellar travel. The stars are to be the inheritance of our downloaded descendants, of the children of our minds rather than our bodies.