IF THERE IS INTELLIGENT LIFE out there, why haven’t we been visited by aliens yet? It’s a question that every child, and most adults, will ask at some point or other.

Think of it this way. How fast could the fastest supercharged alien rocket travel? A thousand miles an hour? A hundred thousand? OK, let’s assume the rocket can travel at a million miles an hour. (According to the Guinness Book of Records, the fastest earth-made rocket travelled at just under 50,000 miles an hour.) So these aliens would have mighty fast rockets.

The trouble is, the nearest star to us, Proxima Centauri, is 4.2 light years away. That’s over 24 trillion miles. Even if our aliens travelled at a million miles an hour, it would still take them nearly three thousand years to get here. And that’s a very long journey, just on the off-chance that we happened to be in when they called.