Meet little Molly Modern. Her family seems to always be on the move.

Molly's mother takes her to school in the morning and then takes the train to work. Molly's father, who works nights and also rides the train, usually gets in somewhat after Mrs. Modern leaves.

Sometimes it happens that Mr. Modern's train passes Mrs. Modern's train just as they both pass little Molly's school. Whenever this happens, the Moderns always try to wave at each other as the trains pass.

But this day, something unusual happens. Lightning strikes the middle cars of the trains where Mr. and Mrs. Modern are standing, each going in different directions.

Fortunately, no one is hurt. It's a good thing that charge resides on the outside of a conductor, and the trains are made of good conductive steel. The lightning passes through the trains leaving burn marks where the wheels touch the rails.

Over dinner, the Modern family have much to talk about.

All three agree on the facts, but they interpret the facts from different perspectives of time and space. Their measurements of time and space are relative to each of their frames of reference according to the structure of space and time first understood by Albert Einstein a hundred years ago.

Before Einstein, certain features of what the Modern family must observe and measure were understood in terms of the old aether theory of light. It was understood that moving clocks must run slow and that moving measuring sticks must be short in the direction in which they are going. People had even figured out by precisely how much clocks must run slow and by how much measuring sticks must be short.

What Einstein explained in his miracle year of 1905 was that time itself runs slow and space itself is foreshortened in moving frames of reference. He not only did away with the cumbersome old aether theory, but he was then able to see how the laws of motion were affected by this improved understanding of space and time. This led him to predict his famous relationship between energy and mass, E = mc² , the equation of the twentieth century.

To understand Einstein's approach to space and time, we should start by examining the facts observed by the Modern family from each of their points of view. We will see that each of them have a profoundly different understanding of what is meant by "at the same time."