Einstein would have loved this because it's an attempt to achieve constant velocity. Buster Keaton saves the day by virtue of simply being in a better movie than everyone around him: a faster one, a more determined one, one that knows how to get the obstacles out of its path like that. Everyone else is stuck in the mud or pissing about on horseback. But when Keaton's on that train there's just no stopping him. I wish filmmakers these days understood the power of forward motion like he did. Paul Greengrass maybe?