He wasn't exaggerating. Even our nearest star Proxima Centauri is a staggering 4.2 light years away - more than 200,000 times the
distance from the Earth to the sun. Or, if you like, the equivalent of 50 million trips to the moon and back.
Such vast distances would seem to put the stars far beyond the reach of human explorers. Suppose we had been able to hitch a ride on NASA's Voyager 1 the fastest interstellar space probe built to date. Voyager 1 is now heading out of the solar system at about 17 kilometres per second. At this rate it would take 74,000 years to reach Proxima Centauri - safe to say we wouldn't be around to enjoy the view.
So what would it take for humans to reach the stars within a lifetime? For a start, we would need a spacecraft that can rush through the cosmos at close to the speed of light. There has been no shortage of proposals: vehicles propelled by repeated blasts from hydrogen bombs, or from the annihilation of matter and antimatter. Others resemble vast sailing ships with giant reflective sails, pushed along by laser beams.
All these ambitious schemes have their shortcomings and it is doubtful they could really go the distance. Now there are two radical new possibilities on the table that might just enable us - or rather our distant descendants - to reach the stars.
In August, physicist Jia Liu at New York University outlined his design for a spacecraft powered by dark matter (arxiv.org/abs/0908.1429v1). Soon afterwards, mathematicians Louis Crane and Shawn Westmoreland at Kansas State University in Manhattan proposed plans for a craft powered by an artificial black hole (arxiv.org/abs/0908.1803).
No one disputes that building a ship powered by black holes or dark matter would be a formidable task. Yet remarkably there seems to be nothing in our present understanding of physics to prevent us from making either of them. What's more, Crane believes that feasibility studies like his touch on questions in cosmology that other research hasn't considered.
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