Science Fiction Writer
ROBERT J. SAWYER
Hugo and Nebula Winner

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A hundred years ago we didn't even have airplanes — and now we have space shuttles and interplanetary probes. Suppose it takes an additional hundred years — until A.D. 2100 — to develop starflight. And another hundred years — until A.D. 2200 — before we begin sending out colonists who have no intention of ever returning to Earth.

By this time, we will likely have defeated aging (see my speculations on the future of the human body, so that humans can easily endure centuries-long space voyages. Alternatively, travel could be done in suspended animation. Or we may simply send our genetic blueprints, and have shipboard computers reassemble humans once the destination world is reached.

Regardless of how we choose to travel, we will probably never go faster than the speed of light — the laws of physics seem unlikely to allow that. But even if we don't, we can still voyage widely. At just a tenth of lightspeed, a one-way 800-year journey (from A.D. 2200 to A.D. 3000) can take you 80 light-years away. We will certainly establish colonies around nearby sunlike stars, including Alpha Centauri A (4.4 light-years away), Epsilon Indi (11.8 light-years away), and Tau Ceti (11.9 light-years away). Radio communication — albeit with lags of up to 24 years between sending a message and receiving a reply — will keep these colonies in touch with each other and the home world. But for most travelers such journeys will be one-way trips; interstellar commerce is unlikely to ever develop.

The sole barrier to traveling even faster — and going even farther — is energy production. Thanks to relativity, as you approach lightspeed, your mass increases, requiring even more energy to continue to accelerate. Just one year of acceleration at 1 g (9.8 meters per second per second) should bring you very close to the speed of light (while at the same time simulating normal gravity aboard the starship) — if you can find the power to keep accelerating as your mass increases.

Matter-antimatter annihilation — the old Star Trek standby — will provide enough power to do just that, making speeds in excess of 99.9999% of light possible. At such speeds, profound relativistic time dilation occurs. A starship launched in A.D. 2500 would by the time the calendars on Earth read A.D. 3000 have made it almost 500 light-years out, to the neighborhood of the supergiant red star Betelgeuse (where we may decide to undertake steps to prevent that star, a prime candidate to go supernova, from ever doing so, since such an explosion might be harmful to Earth).

But according to relativity, the calendars aboard a starship are just as valid as those on Earth — and, with five hundred years of travel at just below the speed of light, by the time the shipboard calendars read A.D. 3000, a starship could have traveled as far as the Andromeda galaxy — two million light-years away.

The defining moment of the second millennium — happening within one third of one percent of the millennium's end — occurred in December 1968, when humans aboard Apollo 8 finally got far enough away from Earth that they could cup the entire planet in an outstretched hand, seeing it as one fragile whole.

The defining moment of the third millennium will be similar, but on a grander scale: the passengers aboard a starship heading to Andromeda will be able to look back, through optical sensors that adjust for the profound redshift, and cup the entire Milky Way galaxy in their hands. And just as the Apollo 8 astronauts could not discern any cities from that far away, even with powerful telescopes the starship passengers will be unable to resolve the average yellow star, one of a hundred billion in the galaxy they are leaving behind, that had long ago been the ancestral home of humanity.

More Good Reading

Rob's speculations on the future of:

• Artificial Intelligence
• The Human Body
• The Solar System
• Daily Life

Rob's essay on life in the future: "The Age of Miracle and Wonder"

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