The Lightway Express boasts half the speed of light. According to the advertisements, this relativistic speed literally shortens long trips. This is true. At one point, the train goes through a tunnel of about 111.8 km, but from the train's point of view, it is exactly 100 km long.

As a curious tourist, I resolved to experience relativistic speeds, and furthermore, bring home memories in photo form. So while I was riding the Lightway Express, I pointed my camera out a window, and took a picture of the entire 100 km tunnel. Later, when I examined my excellently timed photo, I was disappointed to find that the picture showed a tunnel that was much longer than 100 km.

How long is the tunnel in my photo, and why is it longer than I expected? Was I looking out the front or the back window of the train?

Well, my calculations were okay, but I did make another mistake.  I was considering the tunnel to be at rest (based on the premise that the Theory of Relativity is not required, so it didn't matter which frame of ref I used...wrong!).  But it is required if you choose the wrong frame.  You'll get the wrong answer unless you use Special Relativity...  

So let's choose the right frame of reference...the one that avoids the need to use Relativity:  Consider the photographer to be at rest so that the tunnel is moving toward him.  Now, consider a photon leaving the far end of the tunnel and moving at speed c toward the camera, while the tunnel also moves toward the camera at c/2.  Both the front of the tunnel and this photon reach the camera at the same time (when the camera clicks), so where was the rear of the tunnel when the photon left?  Because it's traveling twice as fast as the tunnel, it traveled twice as far.  This means it was 200km away. Therefore the tunnel appears to be 200km long.

Third time's a charm, right?  (shees! I sure hope so.)