However—and here’s the thing—people on the train would have no sense of these distortions.
To them, everything on the train would seem quite normal.
It would be we on the platform who looked weirdly compressed and slowed down.
It is all to do, you see, with your position relative to the moving object.
This effect actually happens every time you move.
Fly across the United States, and you will step from the plane a quinzillionth of a second, or something, younger than those you left behind.
Even in walking across the room you will very slightly alter your own experience of time and space.
It has been calculated that a baseball thrown at a hundred miles an hour will pick up 0.000,000,000,002 grams of mass on its way to home plate.
So the effects of relativity are real and have been measured.
The problem is that such changes are much too small to make the tiniest detectable difference to us.
But for other things in the universe—light, gravity, the universe itself—these are matters of consequence.
So if the ideas of relativity seem weird, it is only because we don’t experience these sorts of interactions in normal life.
However, to turn to Bodanis again, we all commonly encounter other kinds of relativity—for instance with regard to sound.
If you are in a park and someone is playing annoying music, you know that if you move to a more distant spot the music will seem quieter.
That’s not because the musicis quieter, of course, but simply that your position relative to it has changed.
To something too small or sluggish to duplicate this experience—a snail, say,
the idea that a boom box could seem to two observers to produce two different volumes of music simultaneously might seem incredible.