I learned a new reason why the number 42 is so cool today.
Imagine a straight tunnel directly through the center of the Earth. Now imagine an unpowered vehicle attached to rails in this tunnel. You get in this vehicle and to start your journey you release the clamps and begin to fall by the power of gravity alone. As you fall toward the Earth's core, you accelerate. Then as you pass the Earth's core, you start to decelerate. It works out (if you ignore wind resistance) that when you reach the surface of the Earth on the other side of the tunnel, you will come to a stop (and engage the clamps to prevent falling back in).
How long would that complete journey take? 42 minutes.
Now imagine a straight tunnel from Los Angeles to New York. This tunnel would cut through the mantle at a shallow angle. A journey through this tunnel would also take 42 minutes in a vehicle powered by gravity alone.
It turns out that a tunnel between any two points on the globe would take 42 minutes to traverse.
So, yeah.
42 (youtube video about this phenomenon)
