Science fiction movies and books have given the general public the impression that interstellar travel is possible, inevitable, and perhaps even relatively easy. And recent tentative steps to explore the moon, Mars and other nearby celestial objects has reinforced that impression. But in fact interstellar travel involves some immense problems, and may well be unattainable unless we have badly misunderstood the physics of the universe (always a possibility).
In this short series of “Interstellar” posts I will explore the major problems that would face such an endeavor.
The first problem is the immense distances involved. Our nearest star (actually three stars orbiting each other) is Alpha Centauri, about 4.4 light years away from us. Now 4.4 is a smallish number, easily graspable by the human mind, but a light year is an immense number, 5.88 TRILLION miles (9.46 TRILLION kilometers). We humans have trouble getting a “gut feeling” for how far 100 miles is, let alone a TRILLION miles. In fact, we really can’t grasp a trillion of anything except as an abstract number (like the immense US national debt at about $30 trillion dollars).
The fastest spacecraft the world has managed to launch thus far are the two Helios Solar Probes, which were sent near the sun. At closest approach, accelerated by the immense gravitational pull of the sun, the fastest reached a speed of about 250,000 km per hour. Even at that speed, it would take 18,000 years – longer than recorded human history – to reach our nearest star system, Alpha Centauri.
Clearly any project that took 18,000 years to reach completion would have long since been forgotten or relegated to the realm of myth. So for practical purposes one would need to reach Alpha Centauri in much less time, say in a century or less, and even that would stretch political and public support, and memory, pretty far.
But to reach even our nearest star system in a century would require traveling an average of at least 10% the speed of light, about 30,000 km/sec. (108,000,000 km/hour), or over 430 times faster than any spacecraft we have ever launched thus far, and that one cheated by using the sun’s immense pull to speed it up. The fasted spacecraft we ourselves have accelerated (without a gravitational assist from the sun) to date is the Voyager 1, headed out to interstellar space about 1/18,000 the speed of light.
So the immense distances involved are our first major problem.
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